AN ABSTRACT OF THE THESIS OF Wimol Lertwiwattrakul for the degree of Master of Science in Chemical Engineering
presented on December 6,2000. Title: Fabrication of Ultrathin SiC Film Using Grafted
Poly(methylsilane).
Redacted for Privacy
____
Abstract approved: ___
Shoichi Kimura
~-SiC
is a semiconductor for high temperature devices, which exhibits several
outstanding properties such as high thermal stability, good chemical stability and wide
band gap. There is a possibility of fabricating a crack-free ultrathin SiC film on silicon
wafers by pyrolysis of polymethylsilane (PMS) film.
This study looks into the possibility, as the first phase, to modify the surface of
silicon and graft PMS onto the surface. A new technique reported in this thesis consists
of a surface modification with trimethoxysilylpropene (TSP) followed by the surface
attachment of dichloromethylsilane (DMS) in the presence of a platinum catalyst, which
acts as the first unit for grafting PMS molecules by the sodium polycondensation of
additional DMS monomers. The grafted PMS polymers would serve as the pyrolytic
precursor to be converted into thin layers of SiC.
Surface analysis of these films on silicon wafers by X-ray photoelectron
spectroscopy (XPS) indicated that the silicon surface was successfully modified with
TSP, attached with DMS, and finally grafted with PMS. It was also confirmed by
powder X-ray diffraction (XRD) that PMS formed simultaneously in the bulk solution
was converted into SiC by pyrolysis at temperatures above 1100°C under Ar atmosphere.
Extended studies showed that the PMS-derived coatings, formed in an Ar stream
containing 1% H2 at 400°C, were significantly oxidized, and further heating to 700°C
yielded a Si0 2 layer with graphitic carbon. The intensity of the graphite peak decreased
with an increase in the pyrolysis temperature. Based on these preliminary studies
towards the second phase, i.e. the pyrolysis of PMS to SiC, the need for further research
to eliminate the oxidation source(s) is strongly suggested.
Fabrication of Ultrathin SiC Film Using Grafted Poly(methylsilane)
by
Wimol Lertwiwattrakul
A THESIS submitted to Oregon State University in partial fulfillment of
the requirements for the
degree of
Master of Science
Presented December 6, 2000 Commencement June, 2001 Master of Science thesis of Wimol Lertwiwattrakul presented on December 6, 2000
APPROVED: Redacted for Privacy
Major Professor, representing Chemical Engineering
Redacted for Privacy
Head or Chair of Department of Chemical Engineering
Redacted for Privacy
I understand that my thesis will become part of the permanent collection of Oregon State
University libraries. My signature below authorizes release of my thesis to any reader
upon request.
Redacted for Privacy
Wimol Lertwiwattrakul, Author
ACKNOWLEDGMENTS Many people have made significant contributions to this thesis. They have given
continuous support and encouragement that have been a tremendous help to me.
Therefore, I would like to express my sincere appreciation to the following people:
• Dr. Shoichi Kimura, my major professor, for his advice and guidance throughout this
research without his support this study could never been successful.
• Dr. Moon Il-Shik, Department of Chemical Engineering at Sunchon National
University, from whom the idea of the research originates.
• My committee members: Dr. Phillip R. Watson, Dr. Chih-Hung Chang, and Dr.
Bernd R.T. Simoneit for taking the valuable time to evaluate my thesis.
• Dr. D. Keszler in Chemistry Department at O.S.U., for his permission to use the
powder X-ray diffraction equipment.
• Dale Govier from Albany research center, OR, for his assistance on X-ray
photoelectron spectrometer.
• Tsai-Chen Wang, Wafertech LLC., for providing silicon single-crystal wafers.
• Nick Wannenmacher, not only for his technical assistance on the experimental set-up,
but also for his help with the computers.
• Barry William, who corrected my writing.
• Everyone in Dr. Kimura's lab: Varong Pavarajarn, and Panut Vongpayabal for their
suggestion and help.
• My family in Thailand: Mr. Taweesak, my father, Mrs. Uraiwan, my mother, and my
brothers for their encouragement and financial support.
•
My entire dear friends, especially Thanat Kriausakul, for their friendship,
understanding, and patience during difficult times.
TABLE OF CONTENTS 1. INTRODUCTION, LITERATURE REVIEW AND OBJECTIVES
1.1 Introduction 1
1.2 Literature Review 2
1.2.1 Preparation of SiC Ceramics from Organosilicon Polymeric
Precursors 1.2.1.1 Bulk SiC and SiC Fibers 1.2.1.2 SiC Coatings on Planar Substrates 1.2.2 Surface Modification 1.3 Objectives 2. EXPERIMENTAL APPARATUS AND PROCEDURES 3
3
5
7
8
10 2.1 General Comments 10 2.2 Materials 10 2.3 Coating Apparatus and Procedures 11 2.3.1 Pretreatment of the Silicon Wafer Substrates
2.3.2 Surface Modification 11 12 2.3.2.1 Anhydrous Silylation 2.3.2.2 Hydrolysis and Condensation 12 13 2.3.3 Attaching DMS Through Hydrosilylation
2.3.4 Graft Polymerization 15 18 2.4 Pyrolysis of PMS Formed in the Bulk Solution 18 2.5 Characterization 19 3. RESULTS AND DISCUSSION 3.1 X-Ray Photoelectron Spectra of the Films on Silicon Wafers
20 20 TABLE OF CONTENTS (Continued) 3.1.1 TSP-Modified Silicon Wafer
3.1.2 DMS-Attached Silicon Wafer 3.1.3 PMS-Grafted Silicon Wafer 3.2 Powder X-Ray Diffraction Studies of Pyrolysis Residues 21 23 24 28 4. CONCLUSIONS 32 5. PRELIMINARY STUDIES FOR SECOND PHASE 33 5.1 Results and Discussion 34 5.1.1 Pyrolysis of Bulk PMS under 1% H2 in Ar Atmosphere
5.1.2 PMS-Derived Coatings Formed at 400°-1 300°C on Silicon Wafers 34 36 5.1.2.1 Pyrolysis at 1200° and 1300°C with and without H2
Addition 5.1.2.2 Pyrolysis at Temperatures in the range of 400°1000°C with 1% H2 Addition
36 37
5.2 Conclusions 47 5.3 Recommendations for Future Study 48 5.3.1 Avoidance of the Presence of Oxygen on PMS Film
5.3.2 Other Recommendations
48 49 BIBLIOGRAPHY
50 APPENDICES
53 LIST OF FIGURES Figure Page
1.1 Schematic of the thin SiC film of the new method and spin coated
method 9
2.1 Silylation reaction apparatus
14 2.2 Schematic of silylation reaction
15 2.3 Schematic of silane hydrolysis and condensation
15 2.4 Schematic for hydrosilylation of DMS with TSP modified surface
16 2.5 Attaching DMS reaction apparatus
17 2.6 Schematic of graft polymerization
19 3.1 XPS spectra of TSP on silicon wafer: (a) broad scan spectrum, (b)
narrow region spectrum of Cis, (c) Si 2p binding energy regions 22 3.2 The wetting characteristics of the substrates: (a) before, and (b) after
modification reaction 23 3.3 XPS survey scan spectrum of DMS anchored on TSP-modified
silicon wafer 25 3.4 XPS spectra of PMS grafted on DMS-attached silicon wafer: (a)
broad scan spectrum, (b) narrow region spectrum of N a 1s 26 3.5 N arrow scan profiles over the CIs region of the XPS spectrum of
(a) DMS-attached silicon wafer, and (b) PMS-grafted silicon wafer
27 3.6 The heating program for pyrolysis of bulk PMS
30 3.7 XRD patterns of pyrolyzed PMS annealed at different temperatures
under argon: (a) 1100°C, (b) 1200°C, (c) l300°C, (d) 1400°C, and 1500°C 31 5.1 Schematic of pyrolysis of the PMS grafted wafer
33 5.2 XRD patterns of PMS heat treated in Ar at: (a) 1300°C, (b) 1200°C,
(c) 1100°C and in 1% H2 in Ar at: (d) 1300°C, (e) 1200°C, (f) 1100°C
35 LIST OF FIGURES (Continued)
Figure Page
5.3 XPS survey scan spectrum of PMS-derived films on silicon wafers:
(a) 1200°C in 1% H2, and (b) 1300°C in 1% H2
38 5.4 Temperature effect on atomic ratio of C:Si
41 5.5 Bandfitted narrow scan profile over the 0 1s region of the XPS
spectra of PMS films heated to selected temperatures: (a) room temperature, (b) 400°C, (c) 600°C, and (d) 700°C in 1% H2 42 5.6 Bandfitted narrow scan profile over the C Is region of XPS
spectra of PMS films heated to selected temperatures: (a) room temperature, (b) 400°C, (c) 600°C, and (d) 700°C in 1% H2 43 5.7 Bandfitted narrow scan profile over the Si 2p region of the XPS
spectra of PMS films heated to selected temperatures: (a) 600°C, and (b) 700°C in 1% H2 44 5.8 The heating program for pyrolysis of PMS films
47 LIST OF TABLES Table
3.1 The relative atomic percent and atomic ratio of TSP, DMS, and
PMS films on the silicon wafers 20 5.1 XPS data of samples coated at 1200° and 13000e
36 5.2 The maximum peak of 0 1s, e 1s, Si 2p, el 2P3/2 and Na 1score
signal of films formed at temperatures of 400°-1 ooooe in 1% H2 39 5.3 The relative atomic percent of unheated PMS films and heated
PMS-derived films at temperatures of 4000-10000e in 1% H2 40 5.4 Integrated areas of the Si-H and Si-O stretch curves during the
room-temperature oxidation of PMS deposited on silicon wafers [scarlete et al., 1994] 46 LIST OF APPENDICES Appendix A: XPS Spectra of TSP, DMS, and PMS Films
54 Appendix B: XPS Spectra of Pyrolysis PMS Films in Argon
Atmosphere Using Heating Program in Figure 3.6 59 Appendix C: XPS Spectra of Pyrolysis PMS Films in 1% H2/Ar
Atmosphere Using Heating Program in Figure 3.6 64 Appendix D: XPS Spectra of Pyrolysis PMS Films in 1% H2/Ar
Atmosphere Using Heating Program in Figure 5.8 80 LIST OF APPENDIX FIGURES
Figure Page
Al
XPS Spectrum of TSP Monolayer on Silicon Wafer
55 A2
XPS Spectra of DMS Anchored on TSP-Modified Silicon Wafer
56 A3
XPS Spectra of PMS Grafted on DMS-Attached Silicon Wafer
58 B.l XPS Spectra of the Film Pyrolyzed at 12000e on Silicon Wafer in
Ar Atmosphere 60 B.2 XPS Spectra of the Film Pyrolyzed at 13000e on Silicon Wafer in
Ar Atmosphere 62 e.l XPS Spectra of the Film Pyrolyzed at 400°C on Silicon Wafer in
1% H2/Ar Atmosphere 65 e.2 XPS Spectra of the Film Pyrolyzed at 600°C on Silicon Wafer in
1% H2/ Ar Atmosphere 67 e.3 XPS Spectra of the Film Pyrolyzed at 700°C on Silicon Wafer in
1% H2/Ar Atmosphere 69 e.4 XPS Spectra of the Film Pyrolyzed at 800°C on Silicon Wafer in
1% H2/ Ar Atmosphere 70 e.5 XPS Spectra of the Film Pyrolyzed at 900°C on Silicon Wafer in
1% H2/ Ar Atmosphere 72 e.6 XPS Spectra of the Film Pyrolyzed at 10000e on Silicon Wafer in
1% H2/Ar Atmosphere 74 e.7 XPS Spectra of the Film Pyrolyzed at 12000e on Silicon Wafer in
1% H2/Ar Atmosphere 76 e.8 XPS Spectra of the Film Pyrolyzed at l3000e on Silicon Wafer in
1% H2/ Ar Atmosphere 78 D.l XPS Spectra of the Film Pyrolyzed at 400°C on Silicon Wafer in
1% H2/ Ar Atmosphere 81 D.2 XPS Spectra of the Film Pyrolyzed at 600°C on Silicon Wafer in
1% H2/Ar Atmosphere 84 LIST OF APPENDIX FIGURES (Continued)
Figure
D.3
XPS Spectra of the Film Pyrolyzed at 700°C on Silicon Wafer in
1% H2/ Ar Atmosphere
87
D.4
XPS Spectra of the Film Pyrolyzed at 1200°C on Silicon Wafer in
1% H2/Ar Atmosphere
90
Fabrication of Ultrathin SiC Film Using Grafted Poly(methylsilane)
Chapter 1
Introduction, Literature Review and Objectives
1.1 Introduction
Many silicon carbide (SiC)-based electronic devices have been developed,
including smart sensors for hot engines, high-power and high frequency systems, metal­
oxide-semiconductor field effect transistor (MOSFET), hetero-emitter junction bipolar
transistors, photoreceptors and p-i-n solar cells. The utility of SiC is due to two intrinsic
properties that make it a particularly promising semiconductor material for electronics
applications. Firstly, SiC has a wider band gap than does silicon (Si), therefore the
electronic devices incorporating SiC technology can be operated at much higher
temperatures than is possible with those based on Si. Secondly, the superior chemical
stability of SiC films, even under such harsh conditions as highly oxidizing atmospheres
and high radiation fluxes, is important in their use in integrated circuits for smart sensors
[Scarlete et aI., 1994]. Therefore, economic interest in the production of SiC-based
electronic devices is being considered as a substitute to silicon technology in the
electronic industry.
Structured semiconductor-grade SiC layers are currently produced primarily by
chemical vapor deposition (CVD), the plasma process, and ion beam techniques. Still,
2
there is considerable interest in the development of new synthetic routes to thin films of
SiC. Routes that involve polymeric precursors are especially considered because of their
successful application in the formation of bulk SiC and SiC fibers [Scarlete et al., 1995].
The coating of substrates with organic precursors using simple techniques such as spin­
or dip-coating followed by pyrolysis offers a more controlled, versatile, and potentially
more economical route to ceramic coatings than would be afforded by using CVD,
plasma, and ion beam techniques [Mucalo et al., 1994]. However, spin- or dip-coating
methods render the thin SiC films susceptible to many cracks. Therefore, an efficient
method to fabricate ultra-thin, crack free SiC films is highly demanded for advanced
electronic applications.
1.2 Literature Review
Several researchers have prepared silicon carbide ceramics by the thermal
decomposition of organosilicon polymeric precursors. Such precursors offer potential
processing advantages over traditional solid-state methods due to their low
decomposition temperature, solubility, thermoplasticity, and potential for microstructural
control of the ceramic product [Schmidt et al., 1991]. The literature review is divided
into two main topics: preparation of SiC ceramics from organosilicon polymeric
precursors and surface modification. The first topic is also divided into two parts related
to the application of organosilicon polymeric precursors in preparation of SiC ceramics.
The second topic introduced is one part of our new method.
3
1.2.1 Preparation of SiC Ceramics from Organosilicon Polymeric Precursors
1.2.1.1 Bulk SiC and SiC Fibers
Most notably, Yajima et al. (1978), Hasegawa et al. (1980), and Hasegawa and
Okamura (1983) discovered polysilane polymers as the precursors for
~-silicon
carbide.
They have demonstrated a two-step pyrolytic conversion of polydimethylsilanes to
silicon carbide, with intermediate formation of polycarbosilanes (PCS). Their process for
making
~-silicon
carbide begins with the reaction between dimethyldichlorosilane and
sodium (Eg. 1.1).
(l.1 )
The polydimethylsilane is pyrolyzed above 400°C as shown in Eg. 1.2 to produce
polycarbosilane.
H
(MezSi)n
450",Ar)
fSi -CH2+n
(l.2)
I
Me
From the hexane-soluble, nonvolatile portion of the latter, polymer fibers can be meltspun. They are crosslinked by surface oxidation in air, then further pyrolyzed at 1300°C
for one hour in a nitrogen atmosphere to make
~-SiC
fibers with outstanding physical
properties and oxidative resistance as shown in Eg. 1.3.
4
H
I
~ Si -CH 2 Tn
I
1)air,350°C)
2)N 2 ,1300°C
~-SiC + CH4 + H2
0·3)
Me
However, pyrolysis of Yajima' s polycarbosilane precursor yields an excess of
elemental carbon (C) in addition to SiC ceramic fibers. Since the polymeric precursor is
(SiHCH 3CH2)n with a C:Si ratio of 2, the formation of some elemental C when the final
polycarbosilane is pyrolyzed in an inert atmosphere is unavoidable [Seyferth et aI., 1992].
Most of the current polymeric precursors do not have 1: 1 Si to C ratios. Recently,
polymethylsilane (PMS), [(CH3SiH)x-(CH 3Si)l-x]n has been studied as a promising
precursor for SiC with no excess carbon because its Si/C ratio is one. Schilling et aI.
[1983] synthesized the first PMS and obtained ceramic products in 15-60% yields [Iseki
et aI., 1999]. Several groups also prepared PMS by using dichloromethylsilane (DMS),
[CH 3SiHCb] as a starting material, and tried to improve the yield of SiC.
In 1992, Seyferth et aI. prepared pardy cross-linked PMS by the reaction of
CH3SiHCb with Na in tetrahydrofuran (THF), Eq. 1.4.
0.4)
Pyrolysis of these polysilanes in a stream of argon gives SiC and a substantial amount of
elemental silicon. Treatment of such polysilanes with catalytic quantities of group-IV­
metal-organometallic complexes, «11-CsHshZrH2)n, (11-CsHshZr(CH 3h, (11­
CsHs)2ZrHCI, and (11-CsHshTi(CH3)2, results in cross-linking processes such that
pyrolysis of these polysilanes gives close to stoichiometric SiC with 71 %-85% yields and
only very little elemental Si.
5
Gozzi and Yoshida (1995) obtained PMS from a mixture of CH 3SiHCh and
CH 3SiCh. PMS was thermally and photochemically cross-linked before its conversion to
SiC as a means of improving the ceramic yields. The increase in ceramic was stronger
when the polymer irradiation was performed in the presence of azobis(isobutyronitrile)
(AIBN). However, the ceramic powders obtained from thermal treatment of irradiated
PMS samples still showed a composition rich in silicon.
In 1998, Czubarow et ai. reported a synthesis of high molecular weight PMS of
composition [(CH 3SiH)x(CH 3Si)y(CH 3 SiH 2 )z]n by the sodium polycondensation reaction
of CH 3SiHCh in a solvent mixture of hexane or toluene and THF using ultrasonic
activation. This polymer pyrolyzed in argon gave higher yields of ceramic residue (up to
90%) than did the polymers obtained using reflux or room temperature conditions.
Moreover, ceramic fibers, films, and solid monoliths were prepared from this PMS
without requiring a curing step.
1.2.1.2 SiC Coatings on Planar Substrates
There are few detailed reports dealing with the preparation of ceramic coatings
from pyrolysis of organic precursors on planar substrates with most studies concerned
with the application of ceramic coating to fibers [Mucalo et aI., 1994].
Mucalo et ai. (1994) demonstrated that mostly crack-free ceramic coatings of
black amorphous SiC can be formed on silicon, silica, and alumina substrates by multiple
depositions and firings of polycarbosilane (PCS) layers in a nitrogen atmosphere at
1100°C applied by spin- or dip-coating methods. X -ray photoelectron spectroscopy
(XPS) studies revealed that the surface of SiC coatings consist of an Si0 2 layer. These
6
results are also generally supported by the Rutherford backscattering spectra, which also
indicates considerable phase mixing of silicon, carbon and oxygen within the bulk of the
SiC coatings on alumina.
Mucalo and Milestone (1994) decided to extend their study to include metal
substrates, which could benefit from any increased corrosion resistance that the
application of these coatings may offer. They explored the conditions necessary for
forming coherent PCS-derived SiC coatings on stainless steel and mild steel plates using
the same technique as in the previous study. The coatings on mild steel plates at firing
temperatures of 700°C are cracked. Uncracked coatings can be formed on stainless steel
substrates at 800°C. However, on the basis of the XPS studies, the surfaces coatings
formed at this temperature are covered with a layer of Si0 2 and contain graphitic carbon.
the coatings formed above 800°C cracked, and those formed at I 100°C became totally
disrupted. SiC or possible iron silicides, Si02, and iron oxides were found in the coating
on mild steel at I 100°C in N 2. A possible combination of both thermal expansion
mismatch and CrN formation, which causes the growth of chromium-rich nodules in the
stainless steel, results in coating failure by slowly emerging from the substrate, creating
fissures or breaking through weak spots in the SiC coating. Therefore, a sol-gel derived
Si0 2 coating, as a barrier, has been applied to mild steel and stainless steel plates prior to
PCS-application and 1100°C pyrolysis. Unfortunately, they do not function as effective
barrier coatings to prevent the disruption wreaked upon SiC coatings formed on the metal
substrates at a pyrolysis temperature of I 100°C. The XPS revealed that the coatings
formed on Si0 2pre-coated stainless steel plates at II OO°C in N2 ambient present the
phase mixing of SiC, SiCxO y , Si0 2, and metal oxides.
7
1.2.2 Surface Modification
Surface modification by grafting polymer chains to solid substrates is a useful
method for the creation of materials, which possess specific surface and structural
properties [Chaimberg et aI., 1989]. For several years, organosilanes were widely used to
alter the surface characteristics of inorganic oxides. In composite systems, organosilanes
serve as coupling agents to promote adhesion between the filler and polymer matrix.
Polymers may be chemically bonded to solid substrates by way of graft polymerization in
which reactive surface sites are generated by silylation of the surface with an appropriate
silane-coupling agent. The general formula of organosilanes is RnSiX4 _n , where X is a
hydrolyzable group (i.e., halogen, amine, alkoxy, acyloxy) and R represents a
nonhydrolyzable organic radical [Chaimberg and Cohen, 1990].
In 1989, Chaimberg et aI. demonstrated the graft polymerization of
polyvinylpyrrolidone (PVP) onto vinyltriethoxysilane-modified silica particles. Since
PVP is a nontoxic and biocompatible polymer, this system should be of interest in a
number of biomedical applications.
One year later, Chaimberg and Cohen obtained three different silylation
techniques for vinyltriethoxysilane onto silica substrates: the one-step aqueous, two-step
aqueous, and anhydrous silylation technique. The anhydrous silylation technique resulted
in silane surface concentrations that were much larger than those obtained by the aqueous
silylation methods because the polysilanes formed in the aqueous reaction solution
sterically hindered the silylation reaction and led to reduce surface coverage.
Browne and Cohen (1993) presented the adsorption of phenol, trichloroethene
(TCE), tetrachloroethene (PCE), and chloroform (CHCh) from water using novel resins
8
prepared by graft polymerizing vinylpyrrolidone and vinyl acetate onto a vinylsilylated
surface.
1.3 Objectives
It has been mentioned so far that the ceramic coating of SiC on planar substrate
by pyrolysis of organosilane precursor applied by spin- or dip-coating methods renders a
cracked, thin SiC film. Therefore, an efficient method to fabricate a crack free, thin SiC
film is highly demanded. This research looks into the possibility of fabricating a crack­
free ultrathin SiC film on silicon wafers using a new method, which combines the surface
modification technique and the preparation of SiC from a polysilane precursor.
Polymethylsilane (PMS) is selected as the polysilane precursor in this research which
consists of two phases. The first phase, the objective of this study, is to find methods to:
• Modify the surface of silicon for forming polymethylsilane.
• Anchor the first mono-layer of dichloromethylsilane (DMS) onto the modified
surface
• Graft PMS onto the DMS-anchored surface
For the first modification of silicon surface, trimethoxysilylpropene (TSP) is
selected based on the study by Chaimberg and Cohen (1990), the advantage of which will
be described in a later chapter.
The second phase, a future study, is to:
• Convert the grafted PMS into a thin, crack-free SiC film by pyrolysis.
The polyorganosilane grafted on the target surface may have some advantages
over simple spin-coated polyorganosilane on the target surface. Theoretically, the grafted
9
polyorganosilane will attain an ordered state due to the van der Waals interaction
between the grafted polymer molecules, and hence it is expected that they are
transformed into SiC with a high crystallinity at a lower temperature. Furthermore, the
polyorganosilane grafted on the surface will render a crack-free surface of the resulting
SiC because the first units of the grafted polyorganosilane molecules are chemically
anchored on the surface. The resulting SiC will show a highly oriented single-crystal like
structure, as illustrated in Fig. 1.1.
~
Grafted polyorganosilane
ified-surface
SiC
Pyrolysis
/n Spin coated
/'
polyorganosilane
SiC
Citi] Figure 1.1 Schematic of the thin SiC film of the new method and spin coated method
10
Chapter 2
Experimental Apparatus and Procedures
2.1 General Comments
For all the experiments, the glassware was oven-dried prior to use. All the
reactions were carried out in a nitrogen or argon atmosphere. Since most of the
chemicals and intermediate products are moisture- and air-sensitive, all processes must
avoid being exposed to the air as much as possible. All the intermediate products were
kept in a vacuum desiccator before use, except PMS products (both bulk and film forms),
which were stored under N2 prior to pyrolysis.
2.2 Materials
The silicon single-crystal wafers (8-inch in diameter, surface orientation [100],
polished on one side, provided by WaferTech LLC) were used as supports. A 37%
hydrochloric acid, used for cleaning silicon wafers, was ACS reagent grade. Surface
silylation was carried out with allyltrimethoxysilane (or trimethoxysilylpropene, TSP).
P-xylene, 99+% anhydrous grade, was used as the solvent in the silylation reaction. ACS
reagent grade acetone and acetonitrile were used for the silylated silicon wafer and the
attached DMS-silicon wafer washing, respectively. Dichloromethylsilane monomer
(DMS, CH 3SiHCb), 99%, was used in the DMS-attaching reaction and graft
polymerization. Tetrahydrofuran (THF), 99.9% anhydrous grade, was used as the solvent
11
in the DMS attaching reaction and solvent mixture in the graft polymerization. Hydrogen
hexachloroplatinate(lV), 8 wt% solution in water, was dried and dissolved in the distilled
THF prior to use. Toluene, 99.8% anhydrous grade, was used in the solvent mixture for
the graft polymerization and for washing the DMS-attached and PMS-grafted silicon
wafers. Lump sodium, 99%, was stored in kerosene. All chemicals were obtained from
Aldrich and used as supplied without further purification, except THF which was distilled
and toluene which was deoxygenated by bubbling N2 through it for 30 minutes to 1 hour
before use.
2.3 Coating Apparatus and Procedures
In the present work, four steps to graft PMS on the silicon wafers were explored:
(1) pretreatment of the silicon wafer substrates, (2) surface modification, (3) attaching
DMS through hydrosilylation, and (4) graft polymerization.
2.3.1 Pretreatment of the Silicon Wafer Substrates
The pretreatment procedure used in this study is based on the work by Chaimberg
and Cohen (1990). Firstly, the silicon wafers were cut into 1 x 2 cm pieces. Prior to
silylation, the silicon wafers were cleaned by soaking in a 6 M hydrochloric acid solution
for 12 hours to remove any possible contaminants. The substrates were then thoroughly
washed with deionized water. In addition to the cleaning of the substrates, prolonged
immersion of the silicon wafers in aqueous solution is expected to lead to hydrolysis of
12
surface siloxane groups to form silanol groups. Surface silanol groups are expected to
provide the necessary reactive sites for silane bonding.
2.3.2 Surface Modification
2.3.2.1 Anhydrous Silylation
Generally, there are two silylation techniques: aqueous and anhydrous phase
silylation techniques. In the aqueous silylation, polysilanes form while in the anhydrous
silylation the silane polymerization is eliminated. Steric hindrance of these large
polysilane molecules formed in the aqueous silylation may limit the surface coverage and
leads to nonuniform silylation. Therefore, it is generally assumed that silane forms a
monomeric "brush-like" coverage. It is important to note that multilayer coverage can be
obtained when adsorbed water remains on the substrate surface due to incomplete drying
of the substrate. The adsorbed water may react with the alkoxy groups of the surface­
bonded silane to form silanol groups. Silane molecules in solution may then react with
the silanol groups of the surface-bonded silane to form a multilayer coverage [Chaimberg
and Cohen, 1990]. Therefore, proper drying of substrates at elevated temperatures is
necessary to remove adsorbed water from the substrate surface, thus ensuring the desired
anhydrous reaction condition. However, extreme caution must be taken to ensure that the
drying step does not lead to the condensation of surface silanol groups to form siloxane
bonds. Drying temperatures between 100°C and 200°C are commonly employed [lier,
1979].
13
In this study the silicon wafers were dried at 110D C under nitrogen atmosphere
overnight to remove adsorbed water. The hydroxylated silicon wafers were kept in the
vacuum dessicator until the start of the silylation reaction.
The anhydrous silylation reaction was performed using the procedure described
by Chaimberg and Cohen (1990). The silicon wafers were placed in 70 mL of a solution
containing 0.19 M TSP in xylene. The silylation was carried out in a reflux condenser for
24 hours, under N 2 . The temperature of the condenser was kept at 80 D C to drive off the
methanol produced from the bonding of the TSP to the surface of silicon wafers. The
apparatus and silylation reaction are shown in Fig. 2.1 and Fig. 2.2, respectively.
The advantages of using TSP [C 3H sSi(OCH 3)3] are that an organofunctional
group (C3HS) provides the necessary surface active sites for hydrosilylation reaction with
DMS while a hydrolyzable group (OCH 3) is an intermediate for bonding to silicon
surface and most commercial coupling agents are supplied as methoxysilanes. [Leyden
and Collins, 1980].
2.3.2.2 Hydrolysis and Condensation
After the termination of the reaction, the stability of the surface-bonded silane
was ascertained by silane hydrolysis and condensation. The modified silicon wafers were
rinsed with acetone, an appropriate water carrier [Maoz et aI, 1996], in order to hydrolyze
the remaining methoxy groups, and then dried in a vacuum desiccator for 48 hours to
produce the siloxane bridges, as illustrated in Fig. 2.3.
The observation of the substrate wetting characteristics is the simplest method to
judge if the surface has been successfully modified. During the silylation reaction, the
Cooling water
Condenser
P-Xylene
+ TSP
Pump
Temp. = 149JC
Water Bath
Oil Bath
Figure 2.1 Silylation reaction apparatus
Silicon wafers
15
CH 2-CH=CH 2
I
MeO - Si - OMe
I
CH 2
CH 2
CH
CH
I
I
CH 2
CH 2
I
I
I
I
0
II
~
(Xylene)
0
Me
+
OH
OH
I
I
II
+
2MeOH
MeO-Si -OMeMeO-Si -OMe
Refluxing
I
0
I
Si-wafer
Figure 2.2 Schematic of silylation reaction
CH,
II
CH,
II
CH
CH
I
I
CH,
CH,
I
MeO-Si -OMe
Hydrolysis
CH,
CH,
II
II
CH
CH
I
I
CH,
CH,
I
MeO-Si -OMe
HO-Si -OH
I
0
I
0
0
~
I
+
I
c===::J
Water
I
I
I
4MeOH
>
Condensation
II
II
CH
CH
I
I
CH,
CH,
I
HO-Si -
I
0 -Si -OH
I
I
0
I
+
I
HO-Si -OH
CH,
CH,
0
0
J
I
I
+
H2O
Figure 2.3 Schematic of silane hydrolysis and condensation
surface of silicon wafer substrate changes from hydrophilic to hydrophobic [Arkles,
1977].
2.3.3 Attaching DMS Through Hydrosilylation
Dichloromethylsilane (DMS) was attached to TSP on the silicon wafer surface,
following the procedure for the hydrosilylation reaction proposed by Pesek et al. [1996].
16
They fabricated polysiloxanes bearing perfluoroether as side chains in addition to alkyl
disulfide anchoring groups onto gold surfaces since perfluoroether species is of particular
interest for lubrication technologies. These polymers were prepared by co­
hydrosilylation of linear poly(hydrogen methyl siloxane) (PHMS) with both
perfluoroether and alkyldisulfide side chains and chemisorbed to gold surfaces. In this
research, the hydrosilylation of DMS with TSP-modified surface was investigated instead
of the PHMS and perfluoroether combination.
The TSP modified silicon wafers were simply placed into 100 mL of THF
solution containing DMS (13.33 mmol, 1.39 mL). The mixture was slowly heated under
N2 until the solution reached the desired reaction temperature (80°C, above boiling point
of the solution). Four drops of hydrogen hexachloroplatinate(IV) catalyst complex (8%
in THF) were then added. The TSP modified silicon wafers were kept in the solution
mixture for about 18 hours to allow the reaction to proceed. The DMS-attached silicon
wafers were washed thoroughly with acetonitrile and toluene, and vacuum dried in the
desiccator. The reaction and apparatus of this step are shown in Fig. 2.4 and Fig. 2.5,
respectively.
CH 2
CH 2
CH
CH
II
II
I
I
CH 2
CH 2
I
I
-Si-O -Si-
I
o
I
I
o
I
TSP modified-Si wafer
THF
IPt(cat)
>
CH 2
I
CH 2 I
-Si-O-Si-
I
o
I
I
0
I
DMS attached -Si wafer
Figure 2.4 Schematic for hydrosilylation of DMS with TSP modified surface
Condenser
Cooling Probe
THF
+ OMS + catalyst
Pump
Sensor
Temp. = 80 0 C
Cooler
Iso-Propanol
Container
(Temp. = O°C)
Figure 2.5 Attaching DMS reaction apparatus
Water Bath
Silicon wafers
18
2.3.4 Graft Polymerization
According to the procedure, proposed by Czubarow et al. (1998), for the synthesis
of bulk PMS via the sodium polycondensation reaction of CH3SiHCh in a mixture of
hexane or toluene and THF using ultrasonic activation, a 125-mL flask equipped with a
funnel, containing 17.33 mL (166 mmol) of CH 3SiHCh, was charged with 7 mL of THF,
50 mL of toluene (-1:7 vol. of THF:toluene), the DMS modified silicon wafers and 9.66
g (0.42 mol) of Na metal, respectively in this order. The flask was placed in an ultrasonic
bath (operating at 60 Hz, 40 W), and the DMS was added in a dropwise fashion over a
period of 1.5 hours. The mixture was ultrasonicated at room temperature for 42 hours.
After termination of ultrasonication, the silicon wafers were removed from the solution
and washed with toluene and dried under N2 or Ar. The sample of bulk PMS was
decanted and concentrated under vacuum at 11 O°C. The schematic of graft
polymerization on the DMS attached wafer is shown in Fig. 2.6.
2.4 Pyrolysis of PMS Formed in the Bulk Solution
The pyrolysis of bulk PMS was conducted in a Lindberg two-zone programmed
alumina tube furnace, equipped with two temperature controllers, at temperatures in the
range of 11 00-1500°C with an accuracy of ± 2°C under flowing argon or 1% H2 in argon
(100 mUmin). In all cases of pyrolysis of PMS to SiC, samples were heated at 300°C for
2 hours on the way to pyrolysis temperature and held at the pyrolysis temperature for 3
hours before being allowed to cool using a cooling rate of SOC/min.
19
2.5 Characterization
Samples of bulk PMS precursor pyrolyzed at various temperatures were examined
by powder x-ray diffraction, acquired using a Norelco-12045 diffractometer with a CuKa
radiation. Layer coatings of each step: surface modification, attaching DMS, and graft
polymerization were determined by x-ray photoelectron spectroscopy, carried out using
an SSX-lOO ESCA spectrometer with a monochromatic Al Ka source.
+4nNaCI
CH 2
I
CH 2
I
--Si - - 0 --Si ­
I
o
I
0
I~
OMS attached -Si wafer
DMS grated Si wafer
Figure 2.6 Schematic of graft polymerization
20
Chapter 3
Results and Discussion
3.1 X-Ray Photoelectron Spectra of the Films on Silicon Wafers
X-ray photoelectron spectroscopy (XPS) was used to characterize the surface of
each layer formed on the silicon wafer. Spectra were referenced to the C Is peak (284.6
eV) due to the layer of adventitious hydrocarbons inherently present on samples.
The relative intensities of the 0 Is, CIs, Si 2p, Pt 4f7/2, Cl2p312 and Na Is peaks
for thin films of TSP, DMS and PMS on the surface of Si wafer are given in Table 3.1.
Table 3.1 The relative atomic percent and atomic ratio of TSP, DMS, and PMS films on
the silicon wafers
Atomic %
Elemental
Atomic ratio
Composition
TSP
PMS
TSP
DMS
PMS
o Is
47.2
31.64
3.69
3.16
1.41
C Is
25.74
33.75
2.01
2.18
1.51
Si 2p
12.79
22.41
1
Si 2p (substrate)
14.27
Pt 4f7/2
Cl2p3/2
5.7
Na Is
6.5
21
3.1.1 TSP-Modified Silicon Wafer
XPS spectra, collected for a monolayer of trimethoxysilypropene (TSP,
SiC 3H s(OCH 3)3) chemically bonded on the surface of the silicon wafer, indicate a broad
scan XPS spectrum as presented in Figure 3.1a, showing the spectra of 0 Is, C Is and Si
2p, corresponding to the TSP on the wafer. The narrow scan spectra of the CIs and Si
2p regions are shown in Figure 3.1b and 3.1c, respectively, in which the binding energy
positions are shifted downwards by 4.6 eV due to electron charging. In Fig 3.1 b, typical
high-resolution XPS carbon Is spectrum for this film on the wafer represents many
possible carbon species: peak centered at 280.0 eV-280.9 eV (CH 2 , CH 3 , C-Si, C=C, C­
C), and a shoulder at 282.1 eV (C-O). In the case of Si 2p spectrum (Figure 3.1c), there
are two peaks at 94.4 e V and 98.3 e V. The peak at 94.4 e V is characteristic of elemental
silicon from the silicon wafer. The fitted peak at 98.3 eV is associated with silicon of the
TSP monolayer itself and Si0 2 , which is a natural layer of oxidized silicon on the surface
of silicon wafer. Usually the thickness of this native oxide layer is about 20-30
A
[Jaeger, 1988].
The stoichiometric O:Si ratio of TSP monolayer is 2: 1 while the O:Si ratio by
XPS (which accounts for the TSP and Si0 2 layers) is 3.69: 1. Adsorbed water present on
the surface may be attributed to the excess oxygen, have come from several sources:
residual water due to incomplete drying or moisture in the atmosphere. The sample
specimen may have been damaged by irradiation with x-rays (XPS), which can alter the
chemical and physical film structure [Pesek and Leigh, 1994].
Another piece of evidence to ascertain the successful surface modification is the
wetting characteristics of the substrate surface. It is known that the surface of silicon is
22
20000
o 1S
(a)
C 1s
~O.\~.---------.~ LJ-,-X't
.
.~~~
i l l
1000.0
880.8
600.0
408.0
I
I
,
200.0
0.8
Binding energy, (eV)
5000
(b)
292.0
288.8
284.0
288.0
276.0
272.0
Binding energy, (eV)
2000
(c)
...... , ......... . 107.0 183.8
99.0
95.8
91.0
87.0
Binding energy, (eV)
Figure 3.1 XPS spectra ofTSP on silicon wafer: (a) broad scan spectrum, (b) narrow
region spectrum of CIs, (c) Si 2p binding energy regions (Binding energy positions are
shifted downwards by 4.6 eV due to charging.)
23
hydrophilic while the TSP-coated surface is hydrophobic [Leyden, 1986 and Arkles,
1977]. Before the surface modification reaction, the cleaned surface showed hydrophilic
behavior, as illustrated in Fig. 3.2a. In contrast, after modifying the surface with TSP, the
substrate displayed hydrophobic behavior (Contact angle = 49°), as shown in Fig. 3.2b.
(a)
(b)
Figure 3.2 The wetting characteristics of the substrates: (a) before, and (b) after
modification reaction
3.1.2 DMS-Attached Silicon Wafer
DMS monomer (CH3 SiHCh), as the first unit of grafted PMS, was chemically
anchored on the TSP-modified surface. A broad scan XPS spectrum ofDMS-attached
silicon wafer is shown in Figure 3.3. The XPS reveals that silicon, carbon, oxygen,
platinum and chlorine are present on the surface. Several interesting results are noted.
Firstly, the analysis indicates only a trace level of chlorine on the surface at - 200 eY.
Since only one expected monolayer ofDMS presents over the TSP-modified surface, it is
conceivable that the chlorine concentration on the surface dropped below the detection
level of the XPS [pesek et aI., 1996]. Secondly, the relative atomic percent ofC Is and
Si 2p for the DMS film slightly increased in comparison with those of TSP film, while
that of 0 Is decreased (see Table 3.1), approaching the theoretical DMS Si:C:O ratio of
24
1: 1:0. Additionally, a decrease in the base substrate Si 2p signal suggests that the film
had become thicker. Finally, the platinum remained on the surface due to the use of the
platinum complex as a catalyst. These results support the formation of a DMS layer on
the TSP-modified surface.
3.1.3 PMS-Grafted Silicon Wafer
The PMS film grafted on the modified-surface was investigated with XPS. The
spectra of elemental compositions, shifted downwards by 3.4 eV, are given in Figure 3.4a
and b. The XPS indicates the presence of oxygen, carbon, silicon, chlorine, and sodium
on the surface. The peaks of sodium (Na Is) and chlorine (CI2p3/2) core signals
appearing at 1068.9 eV and 195.9, respectively, are assigned to Na metal and NaCI, since
Na is a starting material and N aCI is a by-product of the polymerization reaction. As
shown in Table 3.1, the atomic percent of both C Is and Si 2p in PMS film increased
compared to those of the TSP and DMS films. The estimated atomic ratio of Si:C is not
in accord with the theoretical value of 1: 1. However, the observed Si:C ratio of PMS
film is closer to 1: I than that of DMS film. The narrow scan profiles over the CIs region
of two samples, before and after polymerization, are shown in Fig. 3.5a and b,
respectively. The C Is peak ofPMS film at 280.8 eV (C-H) has become the great
majority, as shown in Figure 3.5b, implying that the PMS film has many C-H groups as
PMS (CH3SiH)x(CH3SiMCH 3SiH2 )z]n has many CH3 groups. The disappearance of Si
2p (substrate) and Pt 4f3/2 suggests that a significantly thick film of several tens of
angstroms has formed on the DMS-modified surface. The Al x-rays, used to excite
sample atoms to emit photoelectrons, penetrate the sample to a depth of a few
25
micrometers. The photoelectrons, however, can only escape from the sample surface
from depths within tens of Angstroms or about 50 Angstroms [Moulder et aI., 1992].
These XPS results support that PMS was successfully grafted on the modified surface.
The presence of oxygen in this film at a significantly high level may be attributed to the
oxidation during the handling (e.g., cleaning, transferring, and storing samples) and
especially during the handling for the XPS analysis, because the PMS is a very air- and
moisture-sensitive polymer [Abu-Eid et aI. (1992), Scarlete et aI. (1994), Gozzi and
Yoshida (1995), and more recently Czubarow et aI. (1998) and Boury et aI. (1998)].
According to the study of Abu-Eid et.aI. (1992), even the PMS synthesized in
bulk solution is moisture sensitive. They indicated with FfIR that the transformation of
Si-H to Si-OH still occurred although carefully stored under N2 . Further exposure to
moisture enhanced the intensity of the Si-OH peak.
20000
1000.0
015
800.0
600.0
400.0
200.0
0.0
Binding energy. (eV)
Figure 3.3 XPS survey scan spectrum of DMS anchored on TSP-modified silicon wafer
26
20000 015
Naa
C 15
l C125~C12P
~-....--"_______-4,""","".J~_~_
Si25 Si2p
Na 25
,....'
1000.0
800.0
400.0
600.0
200.0
0.0
Binding energy, (eV)
(a)
5000
Na15
...... -...
1082.0
1078.0
1070.0
1074 .0
1056.8
1062. B
Binding energy, (eV)
(b)
Figure 3.4 XPS spectra ofPMS grafted on DMS-attached silicon wafer: (a) broad scan
spectrum, (b) narrow region spectrum ofNa Is (binding energies are shifted by -3.4 eV
due to charging.)
27
5000 292.0 288.8
288.0
284.0
276.0
272.0
276.0
272.0
Binding energy, (eV)
(a)
2000
. '.
292.0 .'
.
288.8
284.0
288.0
Binding energy, (eV)
(b)
Figure 3.5 Narrow scan profiles over the C Is region of the XPS spectrum of (a) DMS­
attached silicon wafer (binding energies are shifted by -4.3 eV.), and (b) PMS-grafted
silicon wafer (binding energies are shifted by -3.8 eV.)
28
Scarlete et al. (1994) also reported the oxidation of a PMS sample supported on a
silicon single-crystal wafer by spin-coating. Their investigation on the oxidation of PMS
revealed several interesting features in the IR spectra. However, the most evident change
is the increasing intensity of the Si-O-Si stretch accompanied by a corresponding
decrease in the intensity of the Si-H stretching band.
3.2 Powder X-Ray Diffraction Studies of Pyrolysis Residues
Samples of PMS formed in the bulk solution for the PMS grafting reaction were
pyrolyzed at various temperatures to ascertain the conversion of PMS into SiC after
pyrolysis. The heating program for the pyrolysis of bulk PMS, recommend by Czubarow
et al. (1998), was employed in this study. Special attention was paid on the temperature
in the range between 200°-450°C, in which a transition from polysilane to
polycarbosilane (PCS) takes place, (eq. 3.1). Therefore, during the pyrolysis ofPMS, a
2-hour hold was incorporated into the pyrolysis program at 300°C on the way to the
maximum temperature under argon atmosphere, as shown in Fig. 3.6.
-----( eq. 3.1)
The bulk PMS samples pyrolyzed at temperatures in the range of 1100-1500°C
under argon (100 mLimin) were examined by powder x-ray diffraction (XRD). The
XRD patterns of those bulk samples show the appearance of P-SiC (Fig. 3.7). Upon
heating from 1100° to 1400°C (Fig. 3.7a-d), the broad peaks are observed at 28
= 35.66°
and 59.99°, which correspond to the (111) and (220) plane of P-SiC, respectively.
However, when the bulk sample was pyrolyzed at 1500°C, the (200) diffraction line of P­
29
SiC at 28 = 41.4° appears (see Fig 3.7e). Similar to the work proposed by Zhang et al.
(1998) and Chew et al. (1999), very broad peaks appear in samples heated to 1100°C,
suggesting nanocrystalline material. Samples heated at 1200-1500°C undergo some grain
growth, as evidenced by peak sharpening and narrowing. Crystals thus grow with an
increase in heat-treatment temperature. However, the peaks remain broad, even at
1400°C, indicating that the material remains mostly nanocrystalline.
Several investigators have reported the synthesis of SiC by the pyrolysis of bulk
PMS. Czubarow et ai. (1998) and Riedel and Gabriel (1999), and Chew et aI., (1999)
reported that, based on their XRD studies, the P-SiC phase was obtained by the pyrolytic
conversion of PMS at 1000-1600°C, where the sharp and narrow P-SiC peaks appeared at
2:: 1500°C. Most recently, Kho et ai. (2000) demonstrated that PMS was converted to SiC
with excess Si, with peak sharpening and narrowing at 1400°C.
The pyrolysis temperature for converting bulk PMS to P-SiC is rather high, at
about 1500°C. It is still believed that thin SiC film can be formed at lower temperature as
evidenced by Mucalo and Milestone (1994). They pyrolyzed a PMS layer, applied by
dip-coating to stainless steel plates pre-coated with sol-gel derived Si02 , at 1 100°C in N2 ,
and demonstrated by XPS the presence of SiC on the surface. It is expected that a
grafted-PMS film can be converted into a thin, crack-free SiC film by the pyrolysis at
low-temperature.
30
Maximum temperature, 3 h
Room temperature
SOC/min
Figure 3.6 The heating program for pyrolysis of bulk PMS
1600,-----------------------------------------------------------------,
~-SiC
1400 20
24
28
32
36
40
44
48
52
56
60 two-theta Figure 3.7 XRD patterns of pyrolyzed PMS annealed at different temperatures under argon: (a) 1100°C, (b) 1200°C, (c) 1300°C, (d)
1400°C, and (e) 1500°C.
32
Chapter 4
Conclusions
The feasibility of forming a PMS film grafted on the surface of silicon single­
crystal wafer, which can be readily used as a direct pyrolytic precursor to the formation
of SiC layer, was studied. The silicon wafer surfaces were first modified with a TSP
monolayer by the anhydrous silylation, hydrolysis, and condensation reactions, DMS was
chemically anchored onto the modified-surface by the hydrosilylation reaction, and then
PMS was grafted to the DMS-attached surface of the silicon wafer. The presence of
these films on the silicon surface was confirmed by XPS. A high level of oxygen was
found in the PMS film, which is suspected to have resulted from the oxidation of PMS
during the sample preparation for the XPS analysis because of its high sensitivity to
oxygen and moisture in air. The XRD study evidenced that PMS formed in the bulk
solution for the grafting reaction was pyrolytically converted to SiC at temperatures
above 1100°C under an Ar atmosphere.
33
Chapter 5
Preliminary Studies for Second Phase
The pyrolysis of grafted-PMS film to an ultrathin, crack-free SiC film, was also
explored in this work as the preliminary studies to elucidate any difficulties associated
with the SiC film formation. It was demonstrated that bulk SiC could be formed
successfully at pyrolysis temperatures of llOOD-1500DC in an Ar stream. However, it is
expected that the PMS layers grafted on silicon wafers are converted to thin SiC films at
lower temperatures. To prove this, it was attempted to convert the grafted-PMS films
into SiC at temperatures below 1300D C using the heating program shown in Fig. 3.6. The
structure of thin SiC film expected after pyrolysis of the PMS grafted wafer is illustrated
in Fig. 5.1.
I
I
I
I
c-­
I
I
-- C -I
I
- - C --Si-­
--Si - -
Si-­
Pyrolysis
DMS grated Si wafer
'------------>
- - Si - - C
I
I
SiC on Si wafer
Figure 5.1 Schematic of pyrolysis of the PMS grafted wafer
34
Based on studies by Gozzi and Yoshida (1995), although this polymer was
carefully synthesized and handled under N 2, freshly prepared PMS was already oxidized.
It is known that Si0 2 layers can be formed by thermal oxidation of silicon in wet or dry
oxygen. The thickness of oxide layers depends on the temperature and oxidation time.
Therefore, in this study the small amount of hydrogen (H 2) was introduced along with Ar
during pyrolysis of PMS films. It is believed that H2 addition will reduce the amount of
oxygen on the PMS surface, which has two effects on the SiC synthesis: (1) the inhibition
of Si02 formation, and (2) the stimulation of the formation of SiC. Thus, the pyrolyses
were performed under different H2 contents: pure Ar, 1%, and 5% H2 in Ar.
5.1 Results and Discussion
5.1.1 Pyrolysis of Bulk PMS under 1 % H2 in Ar Atmosphere
The hydrogen (H 2) addition experiments were conducted to determine the
influence of H2 addition on the crystallization behavior of SiC. The experiments of SiC
synthesis through the pyrolysis of bulk PMS were performed in a 1% H2 addition
atmosphere balanced by Ar. Figure 5.2 shows the XRD analysis results for the products
heated at 11000 -1300°C under Ar atmosphere (5.2a-c) and 1% H2 in Ar atmosphere
(5.2d-f). The XRD patterns for the products obtained also show peak characteristics
of~­
SiC. The peaks of ~-SiC, that is, at 35.66°, and 59.99°, were observed as the dominant
peaks in all products. No significant changes were observed in the XRD patterns with or
without additional H 2. However, the effect of H2 addition on the probability of thin SiC
films formation was also investigated and is discussed in section 5.1.2.
600.-------------------------------~
500
C
:::J
..:
(a)
400
of
ns
-
~
.;;;
300
c
CD
.=
(b)
CD
>
ns
:0:;
~
100
(c)
25
30
35
40
45
2-theta
50
55
60
25
30
35
40
45
50
55
60
2-theta
Figure 5.2 XRD patterns ofPMS heat treated in Ar at: (a) 1300°C, (b) 1200°C, (c) 1100°C and in 1% H2 in Ar at: (d) 1300°C, (e)
1200°C, (f) 1100°C
36
5.1.2 PMS-Derived Coatings Formed at 400o-1300°C on Silicon Wafers
5.1.2.1 Pyrolysis at 1200° and 1300°C with and without H2 Addition
The examination of the coatings by XPS reveals silicon, carbon and oxygen to be
present on the surface in both the cases with and without H 2. The relative atomic
percentages of C, Si, and 0 on the films are summarized in Table 5.1. The broad scan
XPS spectra of the films pyrolyzed at 1200° and 1300°C in 1% H2 are shown in Figures
5.3a and b, respectively. For all films in Table 5.1, the 0 Is peak is particularly strong
and a quantitative analysis of the surface components showed that the Si:O ratio was ­
1:2 suggesting that Si02 is a major surface species on the coating. This was confirmed
from the binding energy position of the Si 2p peak (-103.5 eV), which is typical for Si02.
Table 5.1 XPS data of samples coated at 1200° and 1300°C
Elemental Composition
Conditions
%C
%Si
%0
C Is (B.E. 284.6 eV)
Si 2p (B.E. 103.5 eV)
1200°C in Ar
2.97
30.52
66.51
1200°C in 1%H2
6.21
28.81
64.98
1200°C in 5%H 2
3.55
29.84
66.61
1300°C in Ar
3.88
30.10
66.02
1300°C in 1%H 2
3.39
29.21
67.4
1300°C in 5%H 2
2.58
29.7
67.72
o
Is (B.E. 533 eV)
37
The binding energy position of the C Is peak was found to occur at 284.6 eV, which is
associated with adventitious hydrocarbon or graphite and not with carbide.
The elemental compositions of the films heated at 1200°C and 1300°C in Ar are
almost the same. Consequently, the atomic percent of carbon in those films is 3-4 %,
which seems to indicate adventitious hydrocarbon. The atomic percent of carbon in the
film with 1% H2 (1200°C) increased to 6.21 % in comparison with 2.97% in the film
without H2 (1200°C). On the other hand, when 5% H2 was introduced instead of 1% H2,
the relative concentration of carbon decreased to about 3.55 atomic percent. In the case
of 1300°C, the amount of carbon decreased with increasing H2 .
Therefore, the additional of 1% H2 showed a more enhanced effect on the relative
concentration of carbon in film pyrolyzed at 1200°C than did the addition of 5% H2 .
5.1.2.2 Pyrolysis at Temperatures in the range of4000-1000°C with 1% H2
Addition
PMS-derived films prepared with 1% H2 addition at a temperature range of 400°­
1000°C on silicon wafers were investigated with XPS. Also, the maximum peak position
and the relative atomic percent of the 0 1s, CIs, Si 2p, Cl 2P312 and N a 1s core signals
are given in Tables 5.2 and 5.3, respectively.
The relative atomic percentages of C and Si in the 400°C-PMS film have reduced
to about 113 of those in the unheated PMS film (see Table 5.3). This drastic decrease of
the relative atomic percent of C and Si is probably due to the escaping of some species in
the PMS films during pyrolysis. This observation was in close agreement with recent
results by Iseki and co-workers (1999) that based on thermogravimetric (TG) analysis,
38
50000
015
Si 25
C 15
~_~~-----,,-
1000.0
800.0
600.0
Si 2p
',t
. .......---J -----.JL. 200.0
400.0
025
0.0
Binding energy, (eV)
(a)
50000
015
~~~1000.0
Si 25
~~~--".-"---'\\
800.0
C 15
600.0
400.0
Si 2p
-----lLJ
200.0
025
0.0
Binding energy, (eV)
(b)
Figure 5.3 XPS survey scan spectrum of PMS-derived films on silicon wafers: (a)
1200°C in 1% H2, and (b) 1300°C in 1% H2
39
Table 5.2 The maximum peak of 0 Is, Cis, Si 2p, CI 2P312 and Na Is core signal of
films formed at temperatures of 400-1 OOO°C in 1% H2
Corrected Binding Energy (eV)
Temperature
(OC)
o Is
C Is
Si2p
Cl2p312
Na Is
400
530.4
284.6
102.6
198.2
1071.1
532.1
288.5
198.3
1071.1
535.6
530.6
282.8
100.6
532.0
284.6
102.6
535.8
288.4
700
532.9
284.6
103.3
800
533
284.6
103.5
900
533
284.6
103.5
1000
533
284.6
103.6
600
the low-molecular-weight volatile PMS oligomers escape from the system at 500-650 K
The temperature effect on C:Si atomic ratio of pyrolysis films is shown in
Figure 5.4. The narrow scan XPS spectra over regions of 0 Is and C Is on PMS films
and after heat treatment at 400°-700°C are shown in Figure 5.5 and 5.6, respectively.
When narrow scans were recorded over the 0 Is and C Is regions in the XPS spectra of
the 400 and 600°C films, the resultant profiles were very broad and distorted, indicating a
complex oxide mixture of carbon-containing species. In contrast, the profiles over the 0
40
Table 5.3 The relative atomic percent of unheated PMS films and heated PMS-derived
films at temperatures of 400°-1 OOO°C in 1% H2
Atomic %
Elemental
Composition
Unheated
400°C
600°C
700°C
800°C
900°C
1000°C
Is
31.64
36.61
40.74
69.10
68.77
70.01
70.10
C Is
33.75
11.05
14.29
10.82
10.38
7.28
6.88
Si 2p
22.41
6.81
9.51
20.08
20.85
22.71
23.02
C12p3/2
5.70
8.16
4.12
Na Is
6.50
37.37
31.34
o
1sand CIs regions of the 700°C film reveal somewhat narrower 0 1sand CIs profiles
where the binding energy peak of 0 Is (at 528.2 eV) is mostly due to Si0 2 while C Is (at
280.1 eV) is possibly due to graphite and hydrocarbon. Additionally, the C:Si ratio for
the 600° and 700°C PMS-derived films were 1.50: 1 and 0.54: 1, respectively (Fig 5.4).
Thus, for a pyrolysis temperature increase of 100°C, the level of graphitic carbon in the
coatings decreases by over 64.14%. Therefore, it is evident that carbon on PMS films is
oxidized by oxygen at 400°-600°C, but leaves as a gas at temperatures above 700°C.
Similarly, scans over the Si 2p region of the 600°C film also gave a distorted Si 2p
profile, which is shown in Fig 5.7a. However, above 700°C, the Si 2p profile was shifted
to a higher binding energy (99.0 eV) associated with Si02, and gave a symmetric profile
as well (Fig 5.7b). This indicates that the silicon species is oxidized at temperature
1.8
1.6 ­
•
•
1.4 ­
U5
•
1.2 ­
cj
......
0
0
;;:J
C1l
"-
u
0.8
'E
0
~
0.6
•
0.4
•
•
0.2
0
0
I
I
I
200
400
600
•
I
800
0
Temperature ( C)
Figure 5.4 Temperature effect on atomic ratio of C:Si
1000
1200
5000
540. (l
10000
536.0
532.0
528.0
524.0
520.0
540.0
536.0
Binding energy, (eV)
532.0
528.0
524.0
520.0
Binding energy, (eV)
(a)
(b)
20000
10000
\
-----------.---------:'~-==-,
540.0
536.0
532.0
528.0
Binding energy, (eV)
(c)
524.0
520.8
540.0
536.0
532.0
528.0
524.0
520.0
Binding energy, (eV)
(d)
Figure 5.5 Bandfitted narrow scan profile over the 0 Is region of the XPS spectra ofPMS films heated to selected temperatures: (a)
room temperature, (b) 400°C, (c) 600°C, and (d) 700°C in 1%H2
2000
2008
292.0
288.0
284.0
2813.0 276.0
272.13
292.0
288.8
Binding energy, (eV) 280.13
284.0
276.0
272.13
276.0
2;'2.8
Binding energy, (eV)
(a) (b)
1008
2000
(\
\
)
--/~ ~'
F-1.1-~~·-'~:':~""'-_"_"~4
292.0 288.13
284.0
280.13
Binding energy, (eV)
(c) 2;'6.0
272.8
292.0
288.8
284.0
288.0
Binding energy, (eV)
(d)
Figure 5.6 Bandfitted narrow scan profile over the C Is region ofXPS spectra ofPMS films heated to selected temperatures: (a)
room temperature, (b) 400°C, (c) 600°C, and (d) 700°C in 1% H2
44
200121 107. (]
103.0
95.0
99.0
91.0
87.8
91.0
87.8
Binding energy, (eV)
(a)
500121
/'\
/
.........
107.0
I
; \
\
\,
I
'\
./
\ ....
-<
.'-.
r-==:::::---------------------~':.~=,·
103.0
99.0
.... 95.0
Binding energy, (eV)
(b)
Figure 5.7 Bandfitted narrow scan profile over the Si 2p region of the XPS spectra of
PMS films heated to selected temperatures: (a) 600°C, and (b) 700°C in 1% H2
45
All of these results correspond to the studies by Mucalo et al. [1994]. They found
that the surfaces of PCS-derived coatings on stainless steel (applied by dip-coating),
formed at pyrolysis temperatures above 700°C in N 2 , contained Si02 , while the level of
graphitic carbon in the coatings decreased by over 50% for temperatures between 700
and 800°C. Finally, further pyrolysis to 1100°C in N2 resulted in the entire surface
containing a significantly thick Si0 2 layer.
The formation of the Si0 2 layer rather than a thin SiC film on pyrolyzed samples
as well as the presence of a small amount of carbon on those films might be attributed to
a high oxygen content in the PMS films, mostly resulting from its exposure to air.
In 1994, Scarlete and his co-workers studied the oxidation of PMS films applied by spin
coating on the surfaces of silicon single-crystal wafers. The integrated areas of the Si-O
and Si-H stretch curves in a series of IR spectra, recorded by them during the oxidation of
a PMS sample supported on a silicon wafer, are given in Table 5.4. The most evident
change is the increasing intensity of the Si-O stretch accompanied by a corresponding
decrease in the intensity of the Si-H stretching band. In addition, when PMS samples
were heated for 1 hour in an inert atmosphere (Ar or N 2 ) at different temperatures in the
150-450°C range, and subsequently exposed to air at room temperature, the IR spectra
results demonstrate that the higher the preheat temperature, the slower the rate of
oxidation at room temperature. However, even after pyrolysis for 1 hour at 450°C under
an inert atmosphere, the polymer does not totally lose its reactivity to oxygen. Finally,
the pyrolytically-induced transformation of PMS into PCS clearly takes place at
temperatures well below 400°C.
46
Table 5.4 Integrated areas of the Si-H and Si-O stretch curves during the room­
temperature oxidation of PMS deposited on silicon wafers [Scarlete et aI., 1994]
Stretch intensity
Oxidation time (min)
Si-H
Si-O
1
77.5
48.6
5
58.3
57.1
10
50.8
50.8
60
49.2
81.8
A typical pyrolysis cycle, which was modified based on Scarlete's studies,
consisted of two stages: (1) the heating rate set at 5°C/min up to 400°C, followed by
maintaining the sample for 2 hours before cooling in order to produce PCS and also to
retard oxidation of very air-sensitive PMS; (2) the heating rate set at 5°C/min up to a
desired temperature, and then maintaining the sample at this temperature for a further 3
hours prior to cooling. The pyrolysis were performed under 1% H2 in Ar. The heating
program is shown in Figure 5.8.
Again, 0 1s, Cis, and Si 2p were the principal components at the surface of the
coating formed at 1200°C in 1% H2 with the heating program shown in Figure 5.8, where
the relative atomic percentages of those atoms are similar to those in film formed in the
same conditions when the heating program shown in Figure 3.6 was used. However, the
coatings formed at 400°-700°C with the heating program shown in Fig. 5.8 behave
differently from the coatings formed at 400°-700°C with the heating program shown in
Fig. 3.6, in that the percent ratio of C:Si in the former film increased by about 22% in
47
Maximum temperature, 3 h
Room temperature
Figure 5.8 The heating program for pyrolysis of PMS films
comparison with that of the latter film. Yet, the heated films still contained a large
amount of oxygen. Finally, the 1200°C film was covered with Si0 2 , and contained a
small amount of carbon, with no SiC present.
5.2 Conclusions
The XPS studies of pyrolyzed PMS films revealed that the surface coatings
formed at temperature above 400°C under a gas stream of 1% H2 in Ar were extensively
oxidized. Consequently, when the pyrolysis temperature exceeded 700°C, the surface
coatings were found to be covered with Si02 and to contain graphite. Further increase in
temperature significantly enhances Si0 2 formation and reduces the amount of graphite.
Oxygen found in PMS films is probably originated from the PMS oxidation. Therefore,
avoiding the grafted-PMS films from being exposed to any oxidation environment is of
further interest.
48
5.3 Recommendations for Future Study
5.3.1 A voidance of the Presence of Oxygen on PMS Film
The presence of oxygen on PMS films seems to be attributed to the oxidation of
PMS during the handling and processing [Zhang et aI., 1991]. Since oxygen is a major
problem in pyrolytically converting PMS film to SiC thin film, the effective procedures
to eliminate the oxygen would be:
1. All air and moisture sensitive materials should be handled using standard Schlenk
techniques or in the argon atmosphere using a glove box [Zhang et aI., 1998].
2. Reagent grade sodium should be purified by melting it in stirred, refluxing xylene,
and allowing it to set in one large mass upon cooling. This process allows for
total exclusion of oxide impurities from the bulk of metal [Czubarow et aI., 1998].
3. All solvents should be distilled in Ar-N2 and deoxygenated by bubbling N2 or Ar
through them for about 30 minutes to 1 hour prior to use [Zhang et aI., 1998 and
Czubarow et aI., 1998].
4. DMS should be distilled from magnesium under argon prior to use [Czubarow et
aI., 1998].
5. Samples should be handled and transferred from the glove box to the furnace in
an Nrfilled bag to minimize exposure to air and moisture [Schmidt et aI., 1991].
49
5.3.2 Other Recommendations
l. Dissolving the PMS film in the oxygen-free water eliminates NaCl crystals, which
occlude unreacted sodium particles with encapsulated PMS. The polymer was not
hydrolyzed and, based on its far IR spectrum, remained free of Si-O-Si, which
would be the result of oxygen absorption [Czubarow et aI., 1998].
2. The appropriate amount of H2 may be added into the Ar stream during heating, to
reduce the surface oxidation. Thus, the optimum concentration of H2 in Ar should
be determined.
3. When the formation of the SiC thin film is successful, the mechanism for the
growth of SiC films may be considered by changing the size of grafted PMS by
varying both the reaction time and concentration.
50
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Kho, J.G., Min, D.S., and Kim, K.P., "Polymethylsilane Post-Treated with a
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Scarlete, M., Brienne, S., Butler, I.S., and Harrod, J.F., "Infrared Spectroscopic Study of
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53
APPENDICES 54
Appendix A
XPS Spectra of TSP, DMS, and PMS Films
55
A.1: XPS Spectrum of TSP Monolayer on Silicon Wafer
10000 /.
.' ~--------.,--:.;.::.-.~-=-, ..... 540.0
536.0
532.0
528.0
524.0
Figure A.1 Narrow scan profile over the 0 Is region
520.0
56
A.2: XPS Spectra of DMS Anchored on TSP-Modified Silicon Wafer
10000
<
......... ' .....
540.0
\
---.-/
;'-', ~
. .................. ~~"----- .. ....~:- ... -~ .. - ... --':.~~
.
536.0
532.13
-
528.0
524.0
520.0
Figure A.2 Narrow scan profile over 0 1s region
2000 .,'
\
~-·-·---.--,-------•.M:~:!..::.:_-_ ....._.. . ~ ......... . 107.13
103.0
99.0
95.0
91.0
Figure A.2 Narrow scan profile over Si 2p region
87.0
57
2000 82.0
78.0
74.0
70.0
65.0
Figure A.2 Narrow scan profile over Pt 4f7/2 region
62.0
58
A.3: XPS Spectra of PMS Grafted on DMS-Attached Silicon Wafer
1000
1
1
105.0
101.0
97.0
93.0
88.0
85.0
Figure A.3 Narrow scan profile over Si 2p region
2000
1 .
I··
203.0
199.0
195.0
191. 0
187.0
Figure A.3 Narrow scan profile over Cl 2P312 region
183.0
59
Appendix B
XPS Spectra of Pyrolysis PMS Films in Argon Atmosphere Using Heating Program in Figure 3.6 60
B.I: XPS Spectra of the Film Pyrolyzed at 1200°C on Silicon Wafer in Ar
Atmosphere
20000
015
C 15
Si25
Si2p
~---~jL._~~A___Jt_~5
1000.0
800.0
600.0
400.0
200.0
0.0
Figure B.I Survey scan spectrum
10000
..
540.0
536.0
532.0
528.0
524.0
Figure B.I Narrow scan profile over 0 Is region
1
520.0 61
1000
I
I
292.0
288.8
284.0
288.0
276.0
272.8
Figure B.1 Narrow scan profile over C Is region
2000
/\
jJ \\
/ .______.______._____"'
\" ::::-­
........ ... _. ___d ______
107.0
183.8
99.0
..............
95.8
91.0
Figure B.1 Narrow scan profile over Si 2pregion
87.8
62
B.2: XPS Spectra of the Film Pyrolyzed at 13000 e on Silicon Wafer in Ar
Atmosphere
50000
015
Si 25
1000.0
800.0
600.0
400.0
Si 2p
U~5
C 15
200.0
0.0
521 .0
517.0 Figure B.2 Survey scan spectrum
20000
I.
537.0
533.0
529.0
525.0
Figure B.2 Narrow scan profile over 0 Is region
63
500
I·
I
292.0
288.0
284.0
280.0
276.0
272.0
Figure B.2 Narrow scan profile over CIs region
2000
........ 105.0
101.0
97.0
......
93.0
'
.............. . 89.0
Figure B.2 Narrow scan profile over Si 2p region
I
85.0
64
Appendix C
XPS Spectra of Pyrolysis PMS Films in 1 % HJAr Atmosphere Using Heating Program in Figure 3.6 65
C.l: XPS Spectra of the Film Pyrolyzed at 400°C on Silicon Wafer in 1% H:JAr
Atmosphere
50000
Na1s
o 1s
1100. 0
660.0
880.0
440.0
220.0
0.0
91.0
87.0
Figure C.I Survey scan spectrum
1:\
1000
.
/
\
\
\
.
I
107.0
\
\
.~:'~:~------------------------->~ ....
/'
I
I
/
II
103.0
99.0
95.0
Figure C.I Narrow scan profile over Si 2p region
66
10000
I
I
1077.0
1073.0
1069.0
1065.0
105 1 .
(3
1057 . 0
Figure C.I Narrow scan profile over Na Is region
2000
I
I
205.0
201. 0
197.0
193.0
189.0
Figure C.I Narrow scan profile over CI 2P312 region
185.0
67
C.2: XPS Spectra of the Film Pyrolyzed at 600°C on Silicon Wafer in 1 % Hv'Ar
Atmosphere
50000 o
D
D
Z
0 0
1100.0
880.8
660.0
448.0
220.0
0.13
Figure C.2 Survey scan spectrum
10000
1080.0
10?6.0
10? 2 .0
1868.0
1064 . 0
Figure C.2 Narrow scan profile over Na Is region
106 0 . 8
68
2000
. ··1
208.[1
204.0
200.0
195.[1
192.0
Figure C.2 Narrow scan profile over Cl 2P312 region
188.0
69
C.3: XPS Spectra of the Film Pyrolyzed at 700°C on Silicon Wafer in 1 % Hv'Ar
Atmosphere
50000
01
o
...
C4
-
(\J
o
1000.0
Ul
800.0
600.0
400.0
Figure C.3 Survey scan spectrum
200.0
0.0
70
C.4: XPS Spectra of the Film Pyrolyzed at 800°C on Silicon Wafer in 1 % H2I'Ar
Atmosphere
50000
o
Ii,'
o
.­f\J
lJ)
1000.0
800.0
600.0
400.0
200.0
CL
ru
lJ)
0.0
Figure C.4 Survey scan spectrum
20000
II ..
................ ..... . I
S4D.D
536.0
532.0
528.0
524.0
Figure C.4 Narrow scan profile over 0 Is region
520.0
71
2000 292.0
284.0
288.0
280.0
276.0
272.0
Figure C.4 Narrow scan profile over C Is region
5000
~\
/
/\
\
\,.
..-'
.... ------ ....---- ..... -- ...... ---- ..'-'--"""­
-~""'-'..:
10?0
103.0
99.0
95.0
91.0
Figure C.4 Narrow scan profile over Si 2p region
87.0 72
C.S: XPS Spectra of the Film Pyrolyzed at 900°C on Silicon Wafer in 1 % Hz/Ar
Atmosphere
50000
o
'"
ru
o
CI..
(>,1
1Il
I-L
1000.0
800.0
600.0
400.0
200.0
0.121
Figure C.S Survey scan spectrum
20000 I
....... .......... . 54121.121
536.0
..
\
/'
'",-- .
". ~---------------------------==-, .
532.121
.'
528.0
524.121
Figure C.S Narrow scan profile over 0 Is region
52121.121 73
2000
1
..'1.
292.0
284.0
288.0
276.0
280.0
272.8
Figure C.S Narrow scan profile over C Is region
5000
i\
/
/
/ \
.
107.0
103.0
..'
\.
"­
,.
I .
I
\
~:':'--.------.------.----'-~ '.
99.0
95.0
.'
...... .
91.0
Figure C.S Narrow scan profile over Si 2p region
87.0 74
C.6: XPS Spectra of the Film Pyrolyzed at lOOO°C on Silicon Wafer in 1 % H~Ar
Atmosphere
50000
o
(b
1\1
o
-
1000.0
800.0
600.0
=+
Q..
1\1
+
400.0
200.0
0.0
Figure C.6 Survey scan spectrum
20000
...................
540.0
536.0
~.::.::.,.-L 532.0
528.0
524.0
Figure C.6 Narrow scan profile over 0 Is region
520.0
75
1000 292.0
288.8
284.0
280.0
276.0
272.8
Figure C.6 Narrow scan profile over C Is region
5000
1\
/
.... " .....
107.0
\
~---.------.------:~
183.8
99.0
........ . 95.8
91.0
Figure C.6 Narrow scan profile over Si 2p region
87.8
76
C.7: XPS Spectra of the Film Pyrolyzed at 1200°C on Silicon Wafer in 1 % H:JAr
Atmosphere
50000
o
..
.­
o
N
III
LJ)
IU
1000.0
800.0
600.0
400.0
Q.
I'\J
M
(\J
o
200.0
0.0
Figure C.7 Survey scan spectrum
20000
............I 540.0
536.0
532.0
528.0
524.0
Figure C.7 Narrow scan profile over 0 Is region
520.121 77
1000
I
I
292.0
288.0
284.0
280.0
276.0
272.0
Figure C.7 Narrow scan profile over C Is region
5000
1\
./ \
. . . ..
107.0
---/
.';,.
. .. ~--.------.,-----.--.----~~
103.0
99.0
-­
95.0
91.0
Figure C.7 Narrow scan profile over Si 2p region
87.0 78
C.S: XPS Spectra of the Film Pyrolyzed at 1300°C on Silicon Wafer in 1 % HiAr
Atmosphere
.. ......
o
n
0
~
1000.0
800.0
---J
600.0
..
-'
N
'"
.....0­
Ul
Ul
u
400.0
..
(\J
0
200.0
0.0
Figure C.S Survey scan spectrum
20000
540.0
536.8
532.0
528.0 524.0
Figure C.S Narrow scan profile over 0 Is region
520.0
79
1000
I .
I'" .
292.0
284.0
288.0
280.0
276.0
272.0
Figure C.S Narrow scan profile over C Is region
5000
(\
I \\
..l
107.0
./
/
103.0
-x
:\
99.0
95.8
91.0
Figure C.S Narrow scan profile over Si 2p region
87.0
80
Appendix D
XPS Spectra of Pyrolysis PMS Films in 1 % H:z/Ar Atmosphere Using Heating Program in Figure 5.8 81
D.I: XPS Spectra of the Film Pyrolyzed at 400°C on Silicon Wafer in 1% Hz/Ar
Atmosphere
50000
o 1s
Na1s
1100. 0
880.8
660.0
448.0
220.0
0.0
524.0
520.0 Figure D.I Survey scan spectrum
10000
I
I"
540.0
536.8
532.0
528.0
Figure D.I Narrow scan profile over 0 Is region
82
5000 2~3
2.0
288.0
284.0
280.0
276.0
272.0
Figure D.I Narrow scan profile over C Is region
2000
I .. · 107.0
103.8
99.0
95.0
91.0
Figure D.I Narrow scan profile over Si 2p region
87.0
83
10000
I
I
1077.0
1073.0
1069.0
106 1 . 0
1065.0
1057 . {3
Figure D.I Narrow scan profile over Na Is region
5000 .",
203.0
199.0
195.0
191. 0
..... .
187.0
Figure D.I Narrow scan profile over CI 2P312 region
183.0
84
D.2: XPS Spectra of the Film Pyrolyzed at 600°C on Silicon Wafer in 1 % Hv'Ar
Atmosphere
50000
Na1s
o 1s
~
'"
~ U
U
CI2p
~
1100.0
880.8
660.0
448.0
.
~i2S
SI2p
<...1"----'--
220.0
\
Na 2s
...~
0.0
Figure D.2 Survey scan spectrum
10000
540.0
536.8
532.0
528.0
524.0
Figure D.2 Narrow scan profile over 0 Is region
520.8 85
1000 I
I
292.0
288.0
284.0
280.0
276.0
272.0
Figure D.2 Narrow scan profile over C Is region
2000
(\
........... 107.0
..
\
/
r=L,--,--,------~
103.0
99.0
95.0
91.0
Figure D.2 Narrow scan profile over Si 2p region
87.0
86
20000
.. ... ..I
..........
1077.0
1073.0
1069.0
1065.0
106 1 . (3
1057 . 0
Figure D.2 Narrow scan profile over Na Is region
5000
.................I
....... 205.0
201.0
197.0
193.0
189.0
Figure D.2 Narrow scan profile over CI 2P312 region
185.0 87
D.3: XPS Spectra of the Film Pyrolyzed at 700°C on Silicon Wafer in 1 % Hv'Ar
Atmosphere
50000
015
Na 15
Na a
1100.0
880.0
660.0
440.0
220.0
0.13
Figure D.3 Survey scan spectrum
20000 ........
540.0
536.0
532.0
528.0
524.0
Figure D.3 Narrow scan profile over 0 Is region
520.13
88
2000
···1
292.0
288.0
284.0
280.0
276.0
272.0
Figure D.3 Narrow scan profile over C Is region
2000
..
107.0
~--.----.------.------.----~.::~ ...
103.0
99.0
95.0
.. I
I
91.0
Figure D.3 Narrow scan profile over Si 2p region
87.0 89
20000
·1
1077.0
1073.0
1069.0
1865.0
106 1 . 0
1057 . 0
Figure D.3 Narrow scan profile over Na Is region
2000
·1
205.0
201. 0
197.0
193.0
189.0
Figure D.3 Narrow scan profile over CI 2P312 region
185.0
90
D.4: XPS Spectra of the Film Pyrolyzed at 1200°C on Silicon Wafer in 1 % H:z/Ar
Atmosphere
50000
o
,,,
~
o
Q.
-
(\J
N
(I)
ill
Ul
("oJ
I J
1000.0
800.0
600.0
u
400.0
200.0
0.0
524.0
520.0 Figure D.4 Survey scan spectrum
20000
/\
I \
!I \\
I
540.0
)
\
~,~:::~.-~-------",------------:~~,..--536.8
532.0
528.0
Figure D.4 Narrow scan profile over 0 Is region
91
1000
()
I.· ..
I
292.0
.'
288.0
284.0
280.0
276.0
. .
272.0
Figure D.4 Narrow scan profile over C Is region
5000
j
/
.I
/\
\
\
\
-.-:.::-~.------.------.-~.:~ ..
..
110.0
106.0
102.0
98.0
94.0
Figure D.4 Narrow scan profile over Si 2p region
90.0