Technische Universität Chemnitz, Zentrum für Mikrotechnologien Mesoporous silica low-k dielectric...
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Technische Universität Chemnitz, Zentrum für Mikrotechnologien Mesoporous silica low-k dielectric films: Deposition, characterisation and integration Chris Murray Chemnitz University of Technology, Center of Microtechnologies, Germany
Technische Universität Chemnitz, Zentrum für Mikrotechnologien Mesoporous silica low-k dielectric films: Deposition, characterisation and integration Chris
Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Mesoporous silica low-k dielectric films: Deposition,
characterisation and integration Chris Murray Chemnitz University
of Technology, Center of Microtechnologies, Germany
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Contents Where is Chemnitz? Why low-k? Sol-gel route to mesoporous
silica Characterisation techniques Integration Conclusions
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Wheres Chemnitz?
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Why low k? The RC delay problem C LL C V =C LG WS P T Upper Metal
Layer Interconnect Lower Metal Layer R=2 L/PT C=2(C LL +C V ) = 2k
0 (2LT/P+LP/2T) RC=2 k 0 (4L 2 /P 2 +L 2 /T 2 ) M. Bohr, Tech.
Digest IEEE Int. Electron. Devices Meeting 1995 p. 241
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Why Low k?
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Metals Exchanging Cu for Al reduces delay by about 35% although
many problems exist for integration.
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Roadmap (1999 ITRS, International SEMATECH) Interconnect Technology
Requirements - Near Term
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Dielectrics A range of dielectrics are becoming commercially
available Morey & Asthana, Solid State Technology, Vol. 2, No.
6, June 1999 p.71,
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Introduction of pores to lower k By making SiO 2 porous, the
effective k value is reduced
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Sol Gel Processing Sol Gel Science, Brinker & Scherrer,
Academic Press, 1990, p. 1
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
General Sol-Gel Process Flow for Porous SiO 2
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Mesoporous xerogel low-k film production Precursor = TEOS, water,
solvent, catalyst hydrolysis / condensation reactions Spin on
Post-spin on gelation Drying / Annealing 450C Hydrophobisation with
HMDS Pre-spin on gelation Precursor & catalyst mixing n-type
150 mm Si wafers Si-O-Si porous network forms after spin-on Replace
hydrophylic surface -Si-OH groups with hydrophobic -Si-O-Si(CH 3 )
3 5 process variations = range of dielectric constants
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Film properties Nanoglass is a trademark of Allied Signal /
Honeywell
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Film Characterisation Atomic Force Microscopy TEM of Pt imprint of
xerogel film very smooth film surface maximum height R max < 8
nm mean roughness R a < 1 nm
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Mikrotechnologien
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Ellipsometric Porosimetry (EP) n porosity AND, toluene
absorption pore size and distribution, pore interconnectedness
pumpPC P adsorptive laser sample detector OP=55% FP=54% CSA=260 m 2
cm -3
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Laser Induced Surface Acoustic Waves (LSAW) Laser Pulse SAW
Piezoelectric pickup V film thickness, density, elastic modulus and
Poissons ratio Velocity (m s -1 ) Frequency (MHz)
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Nanoindentation Can measure elastic modulus hardness Cant measure
porosity !! Careful sample and substrate effects for films <
1m
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Porosity Results LSAW & RBS agree to within experimental error
EP up to 20% lower than RBS How realistic is the reference density?
* Film reference density used for LSAW and RBS porosity = 2.26 g cm
-3 RBS measured thermally grown dense SiO 2 = 2.24 0.1 g cm -3
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Skeletal Density Combine LSAW or RBS mean film density with EP open
porosity skeletal density skeleton = 1.4 - 1.7 g cm -3
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Surface Area & Pore size r (mean) increases and pore surface
area decreases as porosity increases i.e. fewer, larger pores
Elastic Modulus & Hardness Modulus and hardness correlate well
with porosity and each other Overestimation of nanoindentation
modulus by >20% due to substrate effects Refinements needed
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Patterning of xerogel thin films using PECVD SiO 2 cap layer Trench
etch: ICP using CF 4 / CHF 3 trench depth: 500 nm cap: 50 nm PECVD
SiO profile angles > 85 no undercut of cap layer bowing was
observed at large open areas Si xerogel cap MOCVD TiN Trench after
MOCVD TiN deposition Si Cu TiN SiO 2 Xerogel Si xerogel Etched 0.2
m trenches
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Outlook Porous silica materials posess lowest k values Many
integration issues remain to be resolved Davies & Corbett Solid
State Tech., Vol. 43, Issue 4, April, 2000
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
How do we define porosity? skeleton pore
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Can measure film thickness refractive index full and open porosity
pore size distribution pore connectivity cumulative surface area
Cant measure elastic modulus !! Careful full porosity calculated
using reference refractive index value of dense SiO 2 toluene
cannot penetrate pores of radius < 0.3 nm Ellipsometric
Porosimetry Non-destructive Simple vacuum equipment Non-hazardous
adsorptive
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Can measure average film density elastic modulus Cant measure Pore
size distribution surface area !! Careful Need a film skeletal
density value for porosity calculations e.g. dense SiO 2 Laser
Induced Surface Acoustic Waves Non-destructive / non-invasive No
patterned substrates or vacuum chamber required Only technique
which provides density/porosity and mechanical characteristics
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Measurement Capabilities Proven Possible Proven for dense
films
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Technische Universitt Chemnitz, Zentrum fr Mikrotechnologien
Conclusions Porosity depends on choice of reference values used in
calculations Cant use skeleton = SiO2 ? Can we still use n skeleton
= n SiO2 EP shows pores are interconnected LSAW mean film density
correlates with RBS LSAW or RBS mean film density combined with EP
open porosity gives film skeletal density skeleton = 1.4 -1.7 g cm
-3 Elastic modulus values low, hard to measure with accuracy
Techniques should refine themselves as the sample database
grows