photon effects in damage of porous low- k sioch during plasma cleaning *

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

[email protected]

b) Department of Electrical Engineering and Computer ScienceUniversity of Michigan Ann Arbor, Ann Arbor, MI 48109

[email protected]

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


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 MichiganInstitute for Plasma Science & Engr.Ref: J. Lee and D. B. Graves, J. Phys. D 43, 425201 (2010). AVS_06

LOW-k DEGRADATION: WATER VOLUME


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


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

Wafer Substrate

Metal

Plasma

HUMID AIR(H2O)


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


LOW-k DAMAGE :PLASMA REACTOR


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.


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.


Ar/O2 Clean

Animation Slide

He/H2 CleanModel

ExperimentRef: 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


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


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


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


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


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.


photon effects in damage of porous low- k sioch during plasma cleaning *

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