Processing and Characterization of PMSSQ Based Materials for
Nanoporous Low-K Dielectrics
J.J. Park1, Z. Lin1,, R.M. Briber1, G.W. Rubloff1, P. Lazzeri2, L. Vanzetti2, M. Bersani2, M. Anderle2, R.D. Miller3
1 University of Maryland, 2145 A.V. Williams Building College Park, MD, 2 ITC-irst, v. Sommarive 18, 38050 Povo, Trento, Italy, 3 IBM Almaden Research
Center, San Jose, CA
PMSSQ Finger Print Analysis
Device Shrinkage and Interconnect Delay
O
x10
O
O
Si
O
Si
O
Si
Porogen : Gas phase analysis
High –SiOH vs. Low –SiOH
SSIMS, negative SI
C H3
5
O
O
Si
O
Si
O
Si
O
O
Si
O
CH 3
C H3
C H3
C H3
C H3
O
8.0
O
O
Si
O
Si
Si
O
O
Si
O
O
Si
O
O
O
x600
O
Si
Si
O
Si
O
Si
O
n=0
cleavage of the parent ion
(i.e. by loss of SiO2)
Interconnect
CH 3
O
1.2
Si
1
O
O
Si
0.5
0.35 0.25 0.18 0.13
n=1
n
CH 3
n=2
n=1
3.0
0.1
C H3
n=2
Shrinking Progress
0.8
0.6
Low –SiOH
200
400
mass
CH3
Precursor Chemistry
0
.
8
O
Si
Si
Si
O
CH 3
CH 3
intensity
Matrix
Porogen
OH + HO
Si
x10
Si
Spin on
(Solution)
RT
Si
Si
O
O
Si
+ H 2O
Si
O
O
Si
O
O
Si
O
Si
Si
O
Si
O6
x10
Low –SiOH PMSSQ
High –SiOH PMSSQ
0
.
4
CH3
CH 3
1.98 amu
x700
CH 3
1.0
n
7.0
0.8
6.0
Thermal
Cycle
0
.
2
ƒ Characterizing surface and bulk
- ToF –SIMS
- XPS
Twin peaks
0.4
3.0
2.0
0
.
0
Fully cured
• Cross link
• Nanopores
0.2
1.0
2
0
0
C
o
m
p
r
e
s
s
io
n
F
a
c
to
r:5
2
0.0
450
400
200
600
mass
400
600
mass
Compression Factor : 52
• Mass spectrum of high –SiOH PMSSQ has a twin peak near the key species with mass difference
1.98 amu by replacing CH3 group with OH group.
• [SiOH]high ~ 2 * [SiOH]low
- Low –SiOH and high –SiOH PMSSQ
CH2
125
175
1.00E-09
0.00E+00
0.00E+00
Temperature [°C]
225
275
325
3.00E-09
CH3
0
50
4.00E-09
2.00E-09
N
H3C
5.00E-09
High –SiOH
As deposited
0% Porogen
C 1s
225°C – 325°C
Temperature [°C]
225°C – 325°C 350°C – 450°C
450
• Mass spectrometer detected fragment of DMAEMA (mass 58) and PMMA parent ion (mass 100).
• The decomposition temperature range for DMAEMA is 225°C ~ 325°C ,and PMMA 350°C ~ 450°C.
• Good agreement with ToF –SIMS result.
Thermal Behavior of Nanoporous PMSSQ
Fully cured
30% Porogen
Backbone
(C-OH)
DMAEMA
(C-N)
High -SiOH
0% Porogen
C 1s
30% Porogen
Porogen
backbone
Low –SiOH
292
290
288
286
284
282
292
280
290
288
286
284
282
280
PMMA
Binding Energy (eV)
Binding Energy (eV)
- TDMS (Thermal Desorption Mass Spectrometry)
ƒ Compare precursor recipe
H2C
1.00E-08
PMMA
MASS( 100 )
0.0
200
Compression Factor : 52
ƒ Compare surface to gas phase
450°C
0.6
4.0
ƒ Characterizing volatile product
Porogen
Volatilization
intensity
intensity
5.0
• Matrix
cross link,
• Nano phase
separation
Low –SiOH
0.4
O
1.50E-08
MASS( 85)
5.00E-09
O
High –SiOH
n
O
Large size
fragments
0.6
Porogen : Surface Analysis (XPS)
CH 3
CH 3
OH
SSIMS, negative SI
5
8.0
Si
325
Si8O13C7H21
C
2.00E-08
Backbone
CH
O
O
O
x700
O
Si
O
SSIMS, negative SI
Heat
Si
Si
CH 3
O
CH 3
O
O
0
.
6
Matrix cross linking
450
H3C
6.00E-09
O
O
CH 3
325
• High – SiOH PMSSQ crosslinks faster than low – SiOH PMSSQ.
• Reaction rate depends on the concentration and proximity of SiOH end groups.
CH 3
C H3
O
275
275
7.00E-09
MASS( 58 )
TEMPERATURE [°C]
• Peak assignments are well matched to experimental results.
• Peaks are regularly spaced by a monomer unit.
• Fragmentation pattern depends on chemical structure and is sensitive to cross linking.
Strategy for Nanoporous Low – K
225
TEMPERATURE [°C]
600
Compression Factor : 52
PMSSQ
+ curing @ 50 °C x 3’
Low polarizability matrix (K ~ 2.7)
Nano porous low K (K ≤ 2.0)
Low water uptake (<1%), thermal stability,
mechanical strength.
175
225
0.8
0.2
125
175
TEMPERATURE [°C]
Si7O11C7H21
High –SiOH
50
125
1
0
Nanoporous PMSSQ
High –SiOH
1.2
0.4
Photoemission Intensity (a.u.)
Low k (k ~ 2.0)
Cu (ρ - 1.7 µΩ cm)
CH3
2.50E-08
0.4
50
0.0
SiO2 (K = 4.0)
Al (ρ − 3.0 µΩ cm)
Small size
fragments
0.6
PMMA and backbone
°
3.00E-08
Low –SiOH
0
1.0
Nano porous low K materials
DMAEMA ligand
0.8
0.2
0.2
(organic, silica based materials)
Al / SiO2 Æ Cu / Low K
Si6O10C5H15
2.0
Low K materials
Si4O7C3H9
Si4O7C3H9
1
Si5O8C5H15
O
Photoemission Intensity (a.u.)
0.65
C H3
C H3
O
C H3
n
O
4.0
0.8
C H3
5.0
10
1.0
Si
O
Gate
5
O
C H3
C H3
15
Si
6.0
Total
20
intensity
Delay (pS)
Interconnect delay dominates
overall circuit delay
1.2
C H3
C H3
O
Intensity [amp]
25
Increased line resistance
and capacitive coupling
Si
Intensity [amp]
O
RELATIVE INTENSITY
7.0
Si
RELATIVE INTENSITY
O
RELATIVE INTENSITY
30
Matrix
cross link
DMAEMA
• Porogen related components : Backbone and DMAEMA
• Porogen materials completely volatilized at T = 450°C
100
200
450
300
T [°C]
Polymerization of High –SiOH PMSSQ
Porogen materials
1.2
Cross linking reaction
Major crosslinking
100°C – 200°C
Backbone
Intensity
SiO1.5CH3
0.8
PMMA
DMAEMA unit:
contains N
Remaining
crosslinking
0.6
1.4
H2O desorption product
Si4O6C3H9
Si5O7C5H15
Si6O9C5H15
Si7O10C7H21
Si8O12C7H21
Si9O13C9H27
ToF-SIMS
1
Porogen : Surface Analysis
0.4
TDMS
ToF – SIMS
Mass spectrometer
PMMA (CH3O)
1.50E-08
MASS( 18 )
1.10E-08
7.00E-09
3.00E-09
50
150
250
350
450
• Polymerization kinetics of PMSSQ Matrix
0.8
Polymerization of PMSSQ was observed mainly at 100°C – 200°C, and
water was detected as a byproduct by mass spectrometry
DMAEMA (CN)
0.6
0.4
Rate of polymerization depends on the concentration of OH functional
groups: high –SiOH PMSSQ shows faster polymerization
0.2
Temperature [°C]
50
PMSSQ
Methyl group Æ Non-polar, hydrophobic and space-occupying
Hydroxyl group Æ Cross linking of matrix
PMMA-co-DMAEMA
Tertiary amino group Æ Hydrogen bonding with OH in Matrix
Miscibility between matrix and porogen
• Porogen behavior upon thermal processing
0
0
125
175
225
275
Temperatrure [°C]
325
50
450
Water signal from pure PMSSQ
• Major crosslinking ∼ 100°–200°C, completed at 450°C.
• Dehydration occurs as OH groups crosslinks.
• ToF–SIMS, XPS, and TDMS were used to analyze the
thermal behavior of porogen-containing PMSSQ
1
-1.00E-09
0.2
Conclusion
Porogen in High –SiOH matrix
1.2
RELATIVE INTENSITY
Matrix material
Intensity [amp]
Nanoporous PMSSQ Materials
125
175
225
275
325
450
TEMPERATURE [°C]
• DMAEMA ligand : Cleavage and evolution 225°C - 325°C (90%)
Remaining material desorbs by > 325 °C
• PMMA ligand : No apparent transformation until > 325 °C
• Backbone : Behavior follows that of PMMA ligand
• No porogen agglomeration observed in high –SiOH matrix.
Porogen materials decompose at higher temperatures than PMSSQ
polymerization temperatures ( > 225°C)
DMAEMA and PMMA thermally decompose at different temperatures
(225°C – 300°C , PMMA and backbone > 325°C)