photon effects in damage of porous low-k sioch during plasma cleaning * juline shoeb a) and mark j....
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PHOTON EFFECTS IN DAMAGE OF POROUS LOW-k SIOCH DURING PLASMA CLEANING*
Juline Shoeba) and Mark J. Kushnerb)
a) Department of Electrical and Computer EngineeringIowa State University, Ames, IA 50011
b) Department of Electrical Engineering and Computer ScienceUniversity of Michigan Ann Arbor, Ann Arbor, MI 48109
http://uigelz.eecs.umich.edu
Nov. 2011
* Work supported by Semiconductor Research Corporation
Low-k Dielectrics
Modeling Platforms
Low-k Damage During Ar/O2 And He/H2 Plasma Clean
Damage Reduction Using He/H2 Plasmas
Photon and Interconnectivity Influence On Low-k Damage
H2O Uptake and Low-k Degradation
AGENDA
University of MichiganInstitute for Plasma Science & Engr.AVS_02
POROUS LOW-k DIELECTRICS
Ref: http://www.betasights.net/wordpress/wp-ontent/uploads/2011/01/renesas_edram_mims.jpg
The capacitance of the insulator contributes to RC delays in interconnect wiring.
Low-k porous oxides, such as C doped SiO2 (CHn lining pores) reduce the RC delay.
Porosity 0.5, Interconnectivity 0.5.
Plasmas may remove hydrophobic -CH3 groups. Free radical sites adsorb H2O and increase k.
Desire to maintain low-k value by minimizing -CH3
damage.AVS_03
LOW-k PLASMA DAMAGE
University of MichiganInstitute for Plasma Science & Engr.
Mask
Si
Porous Low-kSiCOH
Typical porous SiO2 has CH3 lining pores with Si-C bonding – referred to as SiOCH.
Ave pore radius: 0.8-1.1 nm
Porosity: up to 50%
Etching, damage, cleaning, sealing and H2O uptake of SiOCH is modeled as multistep process
Etch Ar/C4F8/O2 CCP Damage/Clean Ar/O2 or He/H2 ICP Low-k H2O Uptake Sealing To Prevent H2O Uptake
AVS_04Ref: http://www.betasights.net/wordpress/wp-ontent/uploads/2011/01/renesas_edram_mims.jpg
LOW-k DAMAGE: O2 AND H2 PLASMAS
University of MichiganInstitute for Plasma Science & Engr.
O atoms can abstract H from –CH3 groups and remove -CH3:
O + Si-CH3 (s) Si-CH2(s) + OH(g)
O + Si-CH2(s) Si(s) + CH2O(s) O + CH2O(s) CO(g) + H2O(g).
O atoms can cause Si-C bond scission and remove –CH3 groups:
O + Si-CH3 (s) -CH3(s) + Si(s) + O(g)
O + -CH3 (s) -CH2O(s) + H(g)
O + CH2O(s) CO(g) + H2O(g).
H removes -CH3 as CH4(g) and abstracts H forming Si-CHx-1 groups:
H + Si-CH3 (s) -Si(s) + CH4 (g)
H + Si-CHx(s) Si-CHx-1(s) + H2(g).Ref: M.F.A.M. van Hest et al., Thin Solid Films 449 40 (2004) O. V. Braginsky et al., Journal of Aplied Physics 108 073303 (2010) A. M. Urbanowicz et al., Journal of The Electrochemical Society, 157 5 H565-H573 (2010).
AVS_05
PHOTON GENERATION AND DAMAGE: Ar/O2, He/H2 ICP Photons penetrate into the porous SiCOH, are adsorbed by SiO2 and
break Si-CH3 bonds producing adsorbed •CH3(ads) which enhances demethylation rate (-CH3 removal):
hv + Si-CH3(s) -Si•(s) + •CH3(ads)
hv + SiO2(s) SiO2*(s).
Ar/O2 Plasmas:
e + O O(1D), O(3s), O(5s), O(5p) + e O(3s) O + hν (130 nm) O(3s) O(1D) + hν (164 nm) O(5p) O(5s) + hν (777 nm) O(5s) O + hν (136 nm)
He/H2 Plasmas:
e + He He* + e
e + He He** + e
e + He* He* + e
He** He + hν (~100 nm) University of Michigan
Institute for Plasma Science & Engr.Ref: J. Lee and D. B. Graves, J. Phys. D 43, 425201 (2010). AVS_06
LOW-k DEGRADATION: WATER VOLUME
University of MichiganInstitute for Plasma Science & Engr.
Ref: T. Kikkawa, S. Kuroki, S. Sakamoto, K. Kohmura, H. Tanaka, andN. Hata, Journal of The Electrochemical Society, 152(7), G560-G566 (2005).
Since H2O has a high k (~80), water adsorption can seriously degrade k of porous SiCOH.
Even a small percentage of H2O addition degrades the low-k.
Only 2.5% of water volume makes the k as high as solid SiO2 (~3.9).
Degradation of k and adsorbed water volume are related:
AVS_07
LOW-k DAMAGE BY H2O UPTAKE AND SEALING
O2 Plasma :
O2 plasmas remove CH3 groups and increases the k (water adsorption from humid air).
He Plasma Power
Increase in power of He plasma improves surface activation.
A better activated surface seals the pores better (blocks water uptake) during NH3 plasma treatment.
Ref: K. Maex, M. Baklanov, D. Shamiryan, F. Iacopi, S. H. Brongersma, K. Maex, and Z. S. Ya novitskaya, J. Appl. Phys. 93, 8793 (2003).
Ref: A. M. Urbanowicz, D. Shamiryan, A. Zaka, P. Verdonck, S. De Gendt and M. R. Baklanov, J. Electrochem. Soc. 157, H565 (2010). Iowa State University
Optical and Discharge PhysicsAVS_08
University of MichiganInstitute for Plasma Science & Engr.
N/NHx species are adsorbed by activated sites (generated by He treatment) forming Si-N and C-N bonds to seal pores.
Further Bond Breaking M+ + SiO2(s) SiO(s) + O(s) + M
M+ + SiO(s) Si(s) + O(s) + M
N/NHx Adsorption NHx + SiOn(s) SiOnNHx(s)
NHx + Si(s) SiNHx(s)
NHx + CHn-1 (s) CHn-1NHx(s)
SiNHx-NHy/CNHx-NHy compounds seal the pores where end N are bonded to Si or C by C-N/Si-N
NHy + SiNHx(s) SiNHx-NHy(s)
NHy + CHn-1NHx(s) CHn-1NHx-NHy(s)
SEALING MECHANISM IN Ar/NH3 PLASMA
AVS_09
MODELING : PLASMA DAMAGE OF LOW-k
Hybrid Plasma Equipment Model (HPEM)
Plasma Chemistry Monte Carlo Module (PCMCM)
Monte Carlo Feature Profile Model (MCFPM)
Energy and angular
distributions for ions and
neutrals
He/H2 or Ar/O2
PLASMA DAMAGE
Porous Low-k
Coils
WaferSubstrate
Metal
Plasma
HUMID AIR(H2O)
University of MichiganInstitute for Plasma Science & Engr.AVS_10
MONTE CARLO FEATURE PROFILE MODEL (MCFPM) The MCFPM resolves the surface topology
on a 2D Cartesian mesh to predict etch profiles.
Each cell in the mesh has a material identity. (Cells are 4 x 4 A ).
Gas phase species are represented by Monte Carlo pseuodoparticles.
Pseuodoparticles are launched towards the wafer with energies and angles sampled from the distributions obtained from the PCMCM.
Adsorption of photons and photon-surface interactions considered.
Cells identities changed, removed, added for reactions, etching, and deposition.
PCMCM
Energy and angular distributions for ions
and neutrals
HPEM
MCFPM
Provides etch rateAnd predicts etch
profile
University of MichiganInstitute for Plasma Science & Engr.AVS_11
LOW-k DAMAGE :PLASMA REACTOR
University of MichiganInstitute for Plasma Science & Engr.
Ar/O2 Plasmas:
Major fluxes to the substrate (cm-2 s-1): O
1.0 x 1018 O2
2.0 x 1018 O+ 2.0 x 1015 O2
+ 4.0 x 1015 Ar+ 5.0 x 1014
He/H2 Plasmas:
Major fluxes to the substrate (cm-2 s-1): H
6.0 x 1017 H2
3.0 x 1018 H2(v=1)
2.0 x 1016 H2(v=2) 2.0 x 1016 H+
2.0 x
1015 H2+
8.0 x
1013
Conditions: H2/He = 25/75, Ar/O2 =5/95, 10 mTorr, 300 W ICP
H2/He Plasma
AVS_12
PHOTON EFFECTS: O2 PLASMAS
130 nm photons in Ar/O2 plasmas deeply penetrate into the low-k (~100 nm), breaking Si-CH3 bonds to enhance removal of -CH3.
University of MichiganInstitute for Plasma Science & Engr.
Photon1014
cm-2s-1
Photon1015
cm-2s-1
Animation Slide
Without Photons
AVS_13
DAMAGE: Ar/O2 AND He/H2 (PHOTON FLUX) Photons form O2 plasmas
penetrate ~100 nm but for He/H2 plasmas its ~20 nm .
Overall O2 plasmas cause ~3 times more damage.
University of MichiganInstitute for Plasma Science & Engr.
Ar/O2 Clean
Animation Slide
He/H2 CleanModel
Experiment
Ref: M. A. Worsley, S. F. Bent, S. M. Gates, N. C. M. Fuller, W. Volksen, M. Steen and T. Dalton, J. Vac. Sci. Technol. B 23, 395 (2005).
AVS_14
DAMAGE: Ar/O2 AND He/H2 (INTERCONNECTIVITY)
A higher interconnectivity enables more damage.
Interconnectivity 40%
Interconnectivity 100%
Animation Slide
Ar/O2 Clean
Model
Experiment
Ref: M. A. Worsley, S. F. Bent, S. M. Gates, N. C. M. Fuller, W. Volksen, M. Steen and T. Dalton, J. Vac. Sci. Technol. B 23, 395 (2005).
AVS_15
LOW-k DAMAGE: DURING POLYMER CLEAN
University of MichiganInstitute for Plasma Science & Engr.
Ar/O2
Clean
He/H2
Clean
CFx Depos-ition
A CFx polymer layer was deposited.
Polymer was then cleaned by Ar/O2 and He/H2 plasmas with a ~20s exposure.
During clean, some etching of -CH3 radicals occurred.
Photons produce Si-C scission and •CH3(ads) which is separated from Si.
•CH3(ads) can be etched by H2O present in humid air.
AVS_16
LOW-k INTERACTIONS: H2O UPTAKE AFTER CLEAN
University of MichiganInstitute for Plasma Science & Engr.
Photons break Si-CH3 bonds during clean. •CH3(ads) is then etched by H2O in humid air:
H2O + •CH3(ads)CH4(g) + OH.
Si reacts with and adsorbs H2O through H bonding
H2O + -Si(s) -SiOH(s) + H
H2O + SiOH(s)SiOH-H2O(s).
Pore sealing by forming hydrophobic Si-NHy or CHx-NHy compounds can block such water uptake.
Ref: J. Proost, E. Kondoh, G. Vereecke, M. Heyns, and K. Maex, J. Vac. Sci. Technol. B 16, 2091(1998).
He/H2 Plasma Clean
Humid Air Exposure After He/H2 Plasma Clean
Animation SlideAVS_17
LOW-k DEGRADATION: Si-OH AND SiOH-H2O
University of MichiganInstitute for Plasma Science & Engr.
Total k degradation is distributed between chemisorbed H2O (SiOH) and hydrogen bonded H2O (SiOH-H2O).
-OH from Si-OH requires T > 400C to thermally remove while hydrogen bonded H2O can be removed at T ~200C.
k degrades more for Ar/O2 clean because more -CH3
groups are etched.
AVS_18
LOW-k INTEGRITY: NH3 PLASMA SEALING
University of MichiganInstitute for Plasma Science & Engr.
Pore sealing by successive He and Ar/NH3 plasmas produce a hydrophobic –NHx
layer.
H2O uptake is reduced, thereby limiting low-k degradation.
NH3 Plasma Sealing
Post-Sealing Humid Air Exposure
Animation SlideAVS_19
WATER VOLUME,DIELECTRIC CONSTANT
University of MichiganInstitute for Plasma Science & Engr.
After critical amount of H2O adsorption (~10% volume), pore openings are blocked by Si-OH and H bonded H2O.
Water uptake following sealing Ar/NH3 plasma is nominal as hydrophobic –NHx layer prevents H2O molecules from entering the network.
Increase in water volume directly correlates to increase in dielectric constant.
Saturated k-value exceeds that of SiO2.
AVS_20
CONCLUDING REMARKS
Ar/O2 plasmas cause more damage to low-k SiOCH than He/H2 plasmas.
Photons can break Si-CH3 bonds and accelerate -CH3 removal process, more so in Ar/O2 plasmas than He/H2 plasmas
High interconnectivity enables more damage by providing pathways for radicals and enabling deeper penetration of photons.
-CH3 removal produces free radical sites that adsorb H2O and degrade the k value.
Sealing of pore openings using –NHx hydrophobic layers can be an effective way to maintain low-k integrity.
CO plasmas are recently used to enhance PR ash rate and also to minimize C depletion.
University of MichiganInstitute for Plasma Science & Engr.AVS_21