UV PHOTON ASSISTED CVD OF SiO2 FOR
LOW-DRIFT InP MISFET’S
P. Dimitriou, G. Post, A. Scavennec
To cite this version:
P. Dimitriou, G. Post, A. Scavennec. UV PHOTON ASSISTED CVD OF SiO2 FOR LOWDRIFT InP MISFET’S. Journal de Physique Colloques, 1989, 50 (C5), pp.C5-675-C5-679.
<10.1051/jphyscol:1989579>. <jpa-00229612>
HAL Id: jpa-00229612
https://hal.archives-ouvertes.fr/jpa-00229612
Submitted on 1 Jan 1989
HAL is a multi-disciplinary open access
archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d’enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.
JOURNAL DE PHYSIQUE
Colloque C5, suppl6ment au n05, Tome 50, mai 1989
UV PHOTON ASSISTED CVD OF SiO, FOR LOW-DRIFT InP MISFET'S
P. DIMITRIOU, G. POST and A. SCAVENNEC
CNET, Laboratoire de Bagneux, 196, avenue Henri Ravera, F-92220
Bagneux, France
RESUME
Des couches de silice ont CtC dCposCes B basse tempCrature (100~200°C)sur des substrats de InP
par le procCdC CVD assist6 par photon UV avec photosensibilisation au mercure de melanges SiH,-N20.
Les propriCtCs Clectriques et physico-chimiques des couches isolantes et des interfaces isolantsemiconducteur ont ktk ktudikes. La rkduction de l'oxyde natif sur InP par l'hydrogkne atomique, produit
par photodtcomposition UV de l'ammoniac avant dCp6t de SiO,, permet de rCduire la dispersion de la
capacitC MIS en frCquence et conduit Zi une rkduction de la dCrive du courant drain-source des transistors
MIS InP.
Abstract
Silicon dioxide (SiO,) films were produced at low temperatures (100"-200°C) on InP substrates by
mercury-photosensitized CVD from SiH,-N20 mixtures. Electrical and physico-chemical properties of
the insulator films and insulator-semiconductor interfaces were investigated. Prior to the deposition of
SiO, films, the native oxide film on InP substrates was reduced by atomic hydrogen formed by UV
photon-assisted decomposition of ammonia. This preliminary step was found to be effective in reducing
the frequency dispersion of C-V characteristics and more importantly the drift in drain source current of
InP MISFET's.
1 - INTRODUCTION
InP and its alloys, are very promising materials for the fabrication of high speed active devices for
microwave and integrated optoelectronic applications.
Since native oxide of InP usually present very poor dielectric properties, realisation of InP
Metal-Oxyde-Semiconductor Field Effect Transistors (MOSFET's) has so far met little success. High
quality heteromorphic insulators such as silicon dioxide (SiO,) can be deposited by chemical vapor
deposition (CVD). However this has to be done only at low temperatures because InP electronic surface
properties degrade when temperature rises above 300°C. On the other hand as the substrate temperature
decreases, SiO, dielectric and physicochemical properties tend to become unsatisfactory due to the
inclusion of impurities.
As the InP Metal-Insulator FET's (MISFET's) performances depend critically on the control of
the semiconductor insulator interface and on the bulk dielectric properties of SiO,, a compromise between
deposition temperature and SiO, dielectric quality has to be found.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1989579
JOURNAL DE PHYSIQUE
C5-676
High quality SiO, films on InP can be chemically vapor deposited at low temperatures via UV
photodissociation of SiH,-N,Omixtures [ l ][2]. UVphoton assisted CVD is asoft and appropriate$echnique
as well as the SiHJO, pyrolysis techniques [3][4] in contrast to direct plasma CVD, in which damage due
to the presence of energetic particles degrade the InP surface and interface properties.
In this paper, we report the beneficial effect on electrical properties form NH, UV dissociation
before SiO, deposition on InP, and the influence of substrate temperature on the deposition rate.
2 - BACKGROUND ON SiH,/N,O UV DISSOCIATION PROCESS
As reported earlier [5][6], dissociation of reactant gases by UV photons (2537 A) for SiO, formation
is quite complex. For direct dissociation of reactant gases the main chemical reactions are :
hV
N,O
-+ N,+O
SiH,
+ SiH,
for
h <2115A
for
h < 1650A
hU
As the availableUV photon sources are emitting at h = 2537 W, the above reactions are characterised
by a very low yield. For that reason reactant gases are mixed with mercury atoms (Hg) in order to induce
electronic energy transfer during inelastic collisions between the active molecules and the Hg atoms
excited by resonant photoabsorption (photosensitized process). Moreover, surface reactions may
contribute to the formation of SiO, layers by lowering the energy of chemical bonds of the various radicals.
Typical deposition rate of 50 A/min at 170°Chave been reported elsewere [2].
3 - RESULTS AND DISCUSSION
Our experiments were carried out in a commercial PVD 1000 system with a square stainless steel
reactor covered by a thick quartz window (viton 0-ring). The susceptor was back heated up to 200°C by
infrared lamps placed inside the chamber. UV light (2537 A) was provided by a mercury lamp (Vilber
Lourmat TG 120) situated in the upper part of the reactor. Premixed reactant gases were flown over a
mercury cell before introduction in the chamber. Deposition rate of Si0,depends drastically on the UV
photon intensity and on the total pressure. But the quality of SiO, insulating layer depends mainly on
reactant gases ratio and substrate temperature. For that, the total pressure, deposition time and reactant
gas ratio of diluted SiH, (5 % in NZ)and N20, were kept constant. Silicon dioxide deposition was obtained
simultaneously on InP and Si substrates. SiO, thickness and refractive index measured by ellipsometry
(6328 A). The large influence of the substrate temperature on the Si0,film quality has been analysed in
more details : In figure 1 the SiO, deposition rate on InP is plotted versus substiate temperature. For each
point we considered the mean optical power received on the surface during the deposition time. The same
shape of the curve was observed on Si substrates. The deposition rate increases with increasing temperature
up to 180°Cand then tends to saturate. In the whole range of deposition temperature no noticeable change
in the dielectric constant was observed.
InP
5% SiH4
h
s
*s
W
z
0
8
W
0
160
170
180
190
200
210
Fig. 1: Deposition rate of SiO, on InP versus substrate temperature at constant total pressure
and reactant gas ratio of diluted SiH, and N,O
After evaporation of Ti-Au electrodes (160 pm in diameter) through a metal shadow mask, electrical
properties of MIS diodes were studied for as deposited SiOzlayers on InP. The breakdown strength was
usually 5 to 7 MV/cm and the resistivity in the range of 1014- 1015Qcm.
15
I
SiO, /
0287
-
I
I
InP
e = 920A
LL
P.
v
18-
5-
-1%
-5
0
5
I0
VOLTAGE I V )
Figure 2 : Capacitance versus applied voltage of SiO,/InP diodes at 1MHz, after Ti-Au electrodes annealing a t 250°C. The plot diameter was 160 pm, the sweep rate 0.5 Vls and SiO, thickness
920 A.
On the recorded curves measured for field strength up to I MV/cm giving the MIS capacitance
versus applied voltage, we can see a small hysteresis and a satisfactory capacitance modulation. The
interface state density evaluated following the Nicollian and Goetzberger method [7] is usually in the 10"
- 1012~ r neV-'
- ~ range.
In-situ cleaning with UV excited NH, before dielectric deposition has already been proposed as an
efficient step for improving the interfacial properties of MIS structures on GaAs [8].We applied the same
surface treatment on InP with different conditions for native oxide reduction.
JOURNAL DE PHYSIQUE
C5-678
In order to control the drain source current I, drift behaviour of InP MISFET's we carried out
additional electrical investigations on MIS diodes, with and without surface cleaning. The frequency
dispersion from 1 KHz to 100 KHz of capacitance in the full bias range is evaluated to about 2 % and is
displayed in figure 3. Without InP surface treatment C-V frequency dispersion is usually about 6 %. This
illustrates the benefitresulting from aphotochemical in situ treatment of InP surface before SiO,deposition,
which is attributed to the reduction of the InP native oxide.
15
1
OZILM
SiOl / InP
e = 920A
A C = 2%
Fig. 3 : Frequency dispersion of capacitance with applied voltage within 1 KHz and 100 KHz for
SiO,/InP diodes at 1 MVIcm
With these two methods, with and without surface cleaning, wecompared the output characteristics
of MISFET's realised on InP. The drift in drain current is a major drawback of the InP MISFET technology
and has so far hampered any development of this device. The drift in current, which can be associated
with a drift in threshold voltage due to carrier trapping, is quite often recorded for different bias conditions
which prevents direct comparison of the results from different teams.
Here we monitored the drain current in saturation at V, = 2V on depletion devices with a 2 pm
long channel after applying a voltage step on the gate (VG = OV to -2V or -2V to OV). We observed that
the I, drift was much lower for in situ UV NH, surface treated transistors that for untreated samples
(typically 10 % instead of 30 % after 105sec). This can be related to the corresponding observed frequency
dispersion of MIS diodes [9].
4
- CONCLUSION
Si0,deposition at low temperature by UV photodissociation of reactant gases is a very promising
method for the fabrication of InP MISFET's and the passivation of active components on InP or more
generally on 111-V compounds. We showed that under appropriate conditions (surface preparationldeposition), one can reduce the dispersion in capacitance of SiOJInP MIS diodes. This also lead to the
reduction of the drift in source drain current of InP MISFET's.
REFERENCES
[l]
[2]
Peters J.W.
Tech. Digest of 1981IEEE, IEDM, 240
Sharma V.
RCA
Review, v01 47, (1986), 551
a
[3]
[4]
[5]
[6]
[7]
[8]
[g]
Nissim Y.,,BensoussanM., Post G., Bensahel D. and Regolini J.L.
E-MRS Proc. Edit. de Physique, (1987), 213
Bennett B., Lorenzo J.P., Vaccozo K.
Electron. Letters, vol. 24, (1988), 172
Calvert J. and pias J.
"Photochemistry", Wiley, New York, 1966
Dimitriou P.
E-MRS Proc. Edit de Physique, v01 12, (1966), 349
Nicollian E. and Goetzberger A.
Bell Syst. Tech. J. v01 41, (1964), 803
Yoshida M. Mizuguchi K., Murotani T., and Fujiliawa K.
Proc. 18thInt. Conf. Solid State Dev. and Materials, Tokyo, (1986), 103
Post G., Dimitriou P., Falcou A., Duhamel M. and Mermant G.
Proc. ESSDERC 1988, J. de Physique, 64, vol. 49,223