1. PHOTON EFFECTS IN DAMAGE OF POROUS LOW-k SIOCH DURING PLASMA CLEANING * Juline Shoeb a) and Mark J. Kushner b) a) Department of Electrical and Computer Engineering Iowa State University, Ames, IA 50011 jshoeb@eecs.umich.edu b) Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor, Ann Arbor, MI 48109 mjkush@umich.edu http://uigelz.eecs.umich.edu Nov. 2011 * Work supported by Semiconductor Research Corporation

2.  Low-k Dielectrics  Modeling Platforms  Low-k Damage During Ar/O 2 And He/H 2 Plasma Clean  Damage Reduction Using He/H 2 Plasmas  Photon and Interconnectivity Influence On Low-k Damage  H 2 O Uptake and Low-k Degradation AGENDA University of Michigan Institute for Plasma Science & Engr. AVS_02

3. 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 SiO 2 (CH n lining pores) reduce the RC delay.  Porosity  0.5, Interconnectivity  0.5.  Plasmas may remove hydrophobic -CH 3 groups. Free radical sites adsorb H 2 O and increase k.  Desire to maintain low-k value by minimizing -CH 3 damage. AVS_03

4. LOW-k PLASMA DAMAGE University of Michigan Institute for Plasma Science & Engr. Mask Si Porous Low-k SiCOH  Typical porous SiO 2 has CH 3 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 H 2 O uptake of SiOCH is modeled as multistep process  Etch Ar/C 4 F 8 /O 2 CCP  Damage/Clean Ar/O 2 or He/H 2 ICP  Low-k H 2 O Uptake  Sealing To Prevent H 2 O Uptake AVS_04 Ref: http://www.betasights.net/wordpress/wp-ontent/uploads/2011/01/renesas_edram_mims.jpg

5. LOW-k DAMAGE: O 2 AND H 2 PLASMAS University of Michigan Institute for Plasma Science & Engr.  O atoms can abstract H from –CH 3 groups and remove -CH 3 : O + Si-CH 3 (s)  Si-CH 2 (s) + OH(g) O + Si-CH 2 (s)  Si(s) + CH 2 O(s) O + CH 2 O(s)  CO(g) + H 2 O(g).  O atoms can cause Si-C bond scission and remove –CH 3 groups: O + Si-CH 3 (s)  -CH 3 (s) + Si(s) + O(g) O + -CH 3 (s)  -CH 2 O(s) + H(g) O + CH 2 O(s)  CO(g) + H 2 O(g).  H removes -CH 3 as CH 4 (g) and abstracts H forming Si-CH x-1 groups: H + Si-CH 3 (s)  -Si(s) + CH 4 (g) H + Si-CH x (s)  Si-CH x-1 (s) + H 2 (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

6. PHOTON GENERATION AND DAMAGE: Ar/O 2, He/H 2 ICP  Photons penetrate into the porous SiCOH, are adsorbed by SiO 2 and break Si-CH 3 bonds producing adsorbed CH 3 (ads) which enhances demethylation rate (-CH 3 removal): hv + Si-CH 3 (s)  -Si(s) + CH 3 (ads) hv + SiO 2 (s)  SiO 2 * (s).  Ar/O 2 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/H 2 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

7. LOW-k DEGRADATION: WATER VOLUME University of Michigan Institute for Plasma Science & Engr. Ref: T. Kikkawa, S. Kuroki, S. Sakamoto, K. Kohmura, H. Tanaka, and N. Hata, Journal of The Electrochemical Society, 152(7), G560-G566 (2005).  Since H 2 O has a high k (~80), water adsorption can seriously degrade k of porous SiCOH.  Even a small percentage of H 2 O addition degrades the low-k.  Only 2.5% of water volume makes the k as high as solid SiO 2 (~3.9).  Degradation of k and adsorbed water volume are related: AVS_07

8. LOW-k DAMAGE BY H 2 O UPTAKE AND SEALING  O 2 Plasma :  O 2 plasmas remove CH 3 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 NH 3 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 Physics AVS_08

9. University of Michigan Institute for Plasma Science & Engr.  N/NH x species are adsorbed by activated sites (generated by He treatment) forming Si-N and C-N bonds to seal pores.  Further Bond Breaking M + + SiO 2 (s)  SiO(s) + O(s) + M M + + SiO(s)  Si(s) + O(s) + M  N/NH x Adsorption NH x + SiO n (s)  SiO n NH x (s) NH x + Si(s)  SiNH x (s) NH x + CH n-1 (s)  CH n-1 NH x (s)  SiNH x -NH y /CNH x -NH y compounds seal the pores where end N are bonded to Si or C by C-N/Si-N NH y + SiNH x (s)  SiNH x -NH y (s) NH y + CH n-1 NH x (s)  CH n-1 NH x -NH y (s) SEALING MECHANISM IN Ar/NH 3 PLASMA AVS_09

10. 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/H 2 or Ar/O 2 PLASMA DAMAGE Porous Low-k Coils Wafer Substrate Metal Plasma HUMID AIR (H 2 O) University of Michigan Institute for Plasma Science & Engr. AVS_10

11. 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 rate And predicts etch profile University of Michigan Institute for Plasma Science & Engr. AVS_11

12. LOW-k DAMAGE : PLASMA REACTOR University of Michigan Institute for Plasma Science & Engr.  Ar/O 2 Plasmas:  Major fluxes to the substrate (cm -2 s -1 ): O 1.0 x 10 18 O 2 2.0 x 10 18 O + 2.0 x 10 15 O 2 + 4.0 x 10 15 Ar + 5.0 x 10 14  He/H 2 Plasmas:  Major fluxes to the substrate (cm -2 s -1 ): H 6.0 x 10 17 H 2 3.0 x 10 18 H 2 (v=1) 2.0 x 10 16 H 2 (v=2) 2.0 x 10 16 H + 2.0 x 10 15 H 2 + 8.0 x 10 13  Conditions: H 2 /He = 25/75, Ar/O 2 =5/95, 10 mTorr, 300 W ICP  H 2 /He Plasma AVS_12

13. PHOTON EFFECTS: O 2 PLASMAS  130 nm photons in Ar/O 2 plasmas deeply penetrate into the low-k (~100 nm), breaking Si- CH 3 bonds to enhance removal of -CH 3. University of Michigan Institute for Plasma Science & Engr. Photon 10 14 cm -2 s -1 Photon 10 15 cm -2 s -1 Animation Slide Without Photons AVS_13

14. DAMAGE: Ar/O 2 AND He/H 2 (PHOTON FLUX)  Photons form O 2 plasmas penetrate ~100 nm but for He/H 2 plasmas its ~20 nm.  Overall O 2 plasmas cause ~3 times more damage. University of Michigan Institute for Plasma Science & Engr. Ar/O 2 Clean Animation Slide He/H 2 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_14

15. DAMAGE: Ar/O 2 AND He/H 2 (INTERCONNECTIVITY)  A higher interconnectivity enables more damage. Interconnectivity 40% Interconnectivity 100% Animation Slide  Ar/O 2 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

16. LOW-k DAMAGE: DURING POLYMER CLEAN University of Michigan Institute for Plasma Science & Engr. Ar/O 2 Clean He/H 2 Clean CF x Depos -ition  A CF x polymer layer was deposited.  Polymer was then cleaned by Ar/O 2 and He/H 2 plasmas with a ~20s exposure.  During clean, some etching of -CH 3 radicals occurred.  Photons produce Si-C scission and CH 3 (ads) which is separated from Si. CH 3 (ads) can be etched by H 2 O present in humid air. AVS_16

17. LOW-k INTERACTIONS: H 2 O UPTAKE AFTER CLEAN University of Michigan Institute for Plasma Science & Engr.  Photons break Si-CH 3 bonds during clean. CH 3 (ads) is then etched by H 2 O in humid air: H 2 O + CH 3 (ads)  CH 4 (g) + OH.  Si  reacts with and adsorbs H 2 O through H bonding H 2 O + -Si  (s)  -SiOH(s) + H H 2 O + SiOH(s)  SiOH-H 2 O(s).  Pore sealing by forming hydrophobic Si-NH y or CH x - NH y 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/H 2 Plasma Clean  Humid Air Exposure After He/H 2 Plasma Clean Animation Slide AVS_17

18. LOW-k DEGRADATION: Si-OH AND SiOH-H 2 O University of Michigan Institute for Plasma Science & Engr.  Total k degradation is distributed between chemisorbed H 2 O (SiOH) and hydrogen bonded H 2 O (SiOH- H 2 O).  -OH from Si-OH requires T > 400C to thermally remove while hydrogen bonded H 2 O can be removed at T ~200C.  k degrades more for Ar/O 2 clean because more -CH 3 groups are etched. AVS_18

19. LOW-k INTEGRITY: NH 3 PLASMA SEALING University of Michigan Institute for Plasma Science & Engr.  Pore sealing by successive He and Ar/NH 3 plasmas produce a hydrophobic –NH x layer.  H 2 O uptake is reduced, thereby limiting low-k degradation.  NH 3 Plasma Sealing  Post-Sealing Humid Air Exposure Animation Slide AVS_19

20. WATER VOLUME, DIELECTRIC CONSTANT University of Michigan Institute for Plasma Science & Engr.  After critical amount of H 2 O adsorption (~10% volume), pore openings are blocked by Si-OH and H bonded H 2 O.  Water uptake following sealing Ar/NH 3 plasma is nominal as hydrophobic –NH x layer prevents H 2 O molecules from entering the network.  Increase in water volume directly correlates to increase in dielectric constant.  Saturated k-value exceeds that of SiO 2. AVS_20

21. CONCLUDING REMARKS  Ar/O 2 plasmas cause more damage to low-k SiOCH than He/H 2 plasmas.  Photons can break Si-CH 3 bonds and accelerate -CH 3 removal process, more so in Ar/O 2 plasmas than He/H 2 plasmas  High interconnectivity enables more damage by providing pathways for radicals and enabling deeper penetration of photons.  -CH 3 removal produces free radical sites that adsorb H 2 O 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 Michigan Institute for Plasma Science & Engr. AVS_21