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SEALING OF POROUS LOW- k DIELECTRIC WITH H 2 /He PLASMA CLEANING

SEALING OF POROUS LOW- k DIELECTRIC WITH H 2 /He 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

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SEALING OF POROUS LOW- k DIELECTRIC WITH H 2 /He PLASMA CLEANING

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  1. SEALING OF POROUS LOW-k DIELECTRIC WITH H2/He PLASMA CLEANING Juline Shoeba) and Mark J. Kushnerb) 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 June 2010 *Work supported by Semiconductor Research Corporation ICOPS10_01

  2. University of Michigan Institute for Plasma Science & Engr. AGENDA • Sealing of Low-k Dielectrics • Modeling Platforms • Generation of Hot H • Polymer Removal and PR Stripping In He/H2 Mixtures • Sealing Mechanism Using Ar/NH3 Plasma Treatment • Sealing Efficiency • Pore Radius and Aspect Ratio • Concluding Remarks ICOPS10_02

  3. University of Michigan Institute for Plasma Science & Engr. POROUS LOW-k DIELECTRICS • 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. • Inter-connected pores open to plasma may degrade k-value by reactions with plasma species. • Desire to seal pores. Ref: http://www.necel.com/process/en/images/porous_low-k_e.gif ICOPS10_03

  4. University of Michigan Institute for Plasma Science & Engr. PORE PLASMA SEALING MECHANISM • Investigated 2-step process: • He/H2 plasma • He+ and photons break Si-O bonds • Hot H, He+ remove H from pore lining CHn groups, thereby activating sites. • Hot H strips off photo-resist. • NH3 plasma: Seals pores by forming C-N and Si-N bonds which bridges opening. • Reaction mechanisms and scaling laws for He/H2 and NH3 plasma sealing of porous SiCOH have been developed based on results from a computational investigation. Ref: A. M. Urbanowicz, M. R. Baklanov, J. Heijlen, Y. Travaly, and A. Cockburn, Electrochem. Solid-State Lett. 10, G76 (2007). ICOPS10_04

  5. University of Michigan Institute for Plasma Science & Engr. MODELING : LOW-k PORE SEALING He/H2 PLASMA Ar/NH3 PLASMAS Coils Energy and angular distributions for ions and neutrals Plasma Metal Porous Low-k Substrate Wafer • Plasma Chemistry Monte Carlo Module (PCMCM) • Hybrid Plasma Equipment Model (HPEM) • Monte Carlo Feature Profile Model (MCFPM) ICOPS10_05

  6. University of Michigan Institute for Plasma Science & Engr. 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 ). • 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. • Cells identities changed, removed, added for reactions, etching, and deposition. HPEM PCMCM Energy and angular distributions for ions and neutrals MCFPM Provides etch rate And predicts etch profile ICOPS10_06

  7. University of Michigan Institute for Plasma Science & Engr. INITIAL LOW-kPROCESS INTEGRATION • 80 nm thick porous SiCOH. • CH3 lines pores with Si-C bonding. • Ave pore radius: 0.8-1.1 nm • Process integration steps: • Ar/C4F8/O2 CCP: Etch 10:1 Trench • He/H2 ICP: Remove CFx polymer, PR; activate surface sites. • NH3 ICP: Seal Pores Hard Mask Porous Low-k SiCOH Si ICOPS10_07

  8. University of Michigan Institute for Plasma Science & Engr. SiOCH ETCHING IN Ar/C4F8/O2 PLASMAS • SiO2 Etching M+ + SiO2(s) SiO2*(s) + M CxFy+ SiO2*(s)  SiO2CxFy(s) M+ + SiO2CxFy(s)  SiFm + COn + M • CHn Group Etching M+ + CHn(s)  CHn-1(s) + H + M O + CHn(s)  CO + Hn • Polymer Deposition M+ + SiO2CxFy(s) SiO2CxFy*(s)+ M CxFy + SiO2CxFy*(s)  SiO2CxFy(s)+POLY(s) CxFy + CHn-1 CHn-1(s) + CxFy(s) M+ + CxFy(s)  CxFy*(s) + M CxFy* + CxFy (g)  CxFy(s) + POLY(s) ICOPS10_08

  9. He/H2 PLASMAS: POLYMER/PR ASHING AND SURFACE ACTIVATION University of Michigan Institute for Plasma Science & Engr. • Polymer Removal M++ POLY(s)  CF2 + M • H**+ POLY(s)  CHF2 • H**+ POLY(s)  CF + HF • H2**+ POLY(s)  CH2F2 • PR Etching M++ PR(s)  PR + M • H**+ PR(s)  CH4 • H2**+ PR(s)  CH4 • SiO2/CHn Activation M+ + CHn(s)  CHn-1(s) + H + M H** + CHn(s)  CHn-1(s) + H2 M+ + SiO2(s)  SiO(s) + O(s) + M hν+ SiO2(s)  SiO(s) + O(s) **Translationally hot ICOPS10_09

  10. University of Michigan Institute for Plasma Science & Engr. SEALING MECHANISM IN Ar/NH3 PLASMA • N/NHx species are adsorbed by activated sites 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) • NHx + P*(s)  P(s) + NHx(s) • SiNHx-NHy/CNHx-NHy compounds seal the pores where end N are bonded to Si or C by Si-C/Si-N NHy + SiNHx(s)  SiNHx-NHy(s) NHy + CHn-1NHx(s)  CHn-1NHx-NHy(s) ICOPS10_10

  11. University of Michigan Institute for Plasma Science & Engr. PORE-SEALING BY SUCCESSIVE He/H2 AND NH3/Ar TREATMENT • Surface pore sites are activated by 610s He/H2 plasma treatment. • Ar/NH3 plasma treatment seals the pores by forming bridging Si-N, N-N and Si-C bonds. • Initial Surface Pores • He/H2 Plasma Site Activation • Ar/NH3 Plasma Pore Sealing Animation Slide-GIF ICOPS10_11

  12. University of Michigan Institute for Plasma Science & Engr. TYPICAL PLASMA PROPERTIES: H2/He ICP • Total ion density (cm-3): 1.50 x 1011 • Neutral densities(cm-3): H9.0 x 1012 H27.0 x 1013 H2(v=1) 3.0 x 1011 H2(v=2)3.0 x 1011 H2(v=3)3.0 x 1011 H2(v=4)3.0 x 1011 H2(v=5)3.0 x 1011 • Major fluxes to the substrate (cm-2 s-1): H6.0 x 1017 H23.0 x 1018 H2(v=1)2.0 x 1016 H2(v=2)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, 10 mTorr, 300 W ICP ICOPS10_12

  13. University of Michigan Institute for Plasma Science & Engr. HOT H GENERATION: He/H2 ICP • Vibrational Excitation e + H2(v=0) H2(v=1)+ e e + H2(v=n) H2(v=n+1)+ e • Hot H Generation e + H2(v=n) H** + H** + e • Charge Exchange Reactions H2(v=n) + H2+H2(v=n)** + H2+ H2(v=n) + H2+H** + H3+ H + H2+H2(v=0)** + H+ H2(v=n) + H+H** + H2+ H + H+H** + H+ • Conditions: H2/He = 25/75, 10 mTorr, 300 W ICP **Translationally hot ICOPS10_13

  14. University of Michigan Institute for Plasma Science & Engr. Ar/C4F8/O2 CCP TRENCH ETCH Photo-Resist • CCP for trench etch. • Ar/C4F8/O2 = 80/15/5 • 40 mTorr, 300 sccm • 10 MHz • 5 kW • CFx polymer deposited on the side-walls efficiently seal the open pores. CFx polymers are harmful to diffusion barrier metals such as Ti and Ta. • Polymer layers can be removed by one of the following: • He/H2 plasmas without surface damage. • O2 plasmas that etch the CH3 groups. Porous Low-k SiCOH Si Animation Slide-GIF ICOPS10_14

  15. University of Michigan Institute for Plasma Science & Engr. POLYMER REMOVAL AND PR STRIPPING PR • He/H2 plasma used for both polymer (P) removal and photoresist (PR) stripping. • Hot H, H2, H+ and H2+ remove polymers and masking PR layers as CH4, HF, and CxHyFz H**+ POLY(s)  CF + HF H**+ POLY(s)  CHF2 H2**+ POLY(s)  CH2F2 H**+ PR(s)  CH4 H2** + PR(s)  CH4. • CHn groups are also activated by H removal H**+ CHn(s)  CHn-1 + H2. Porous Low-k SiCOH Si Animation Slide-GIF **Translationally hot ICOPS10_15

  16. University of Michigan Institute for Plasma Science & Engr. POLYMER REMOVAL, CH3 DEPLETION • Ar/O2 plasma efficiently removes polymer. • Also removes CH3 groups in pores as O atoms diffuse into the porous network. • Net result is increase in pore size. • Pore openings can get too large to easily seal. • He/H2 plasma removes polymer without significantly depleting CH3. Low-k SiCOH Si ICOPS10_16

  17. University of Michigan Institute for Plasma Science & Engr. SEALING: WITH POLYMER REMOVAL AND PR STRIP He/H2 Activation Sealing • Ar/O2 Clean: additional He treatment is required for surface activation, followed by NH3 plasma sealing. • He/H2 Clean: can do both activation and cleaning in a single step. • Successive NH3 plasma exposure seals the surface pores forming Si-N and C-N bonds. He/H2 Activation Sealing Si Si Animation Slide-GIF ICOPS10_17

  18. SEALING EFFICIENCY: PORE RADIUS University of Michigan Institute for Plasma Science & Engr. • Ar/O2 Clean: sealing efficiency decreases with increasing pore size. • H2/He Clean: selective cleaning does not enlarge openings. Broad angular distribution of H improves surface activation and sealing. Ar/O2 Clean He/H2 Clean Good Sealing Poor Sealing Animation Slide-GIF ICOPS10_18

  19. University of Michigan Institute for Plasma Science & Engr. SEALING EFFICIENCY: ASPECT RATIO • O2 Clean: sealing efficiency on sidewalls decreases with increasing aspect ratio. • He/H2 Clean: sealing does not degrade with higher aspect ratio. • Hot H activates all of the surface sites due to its broad angular distribution. ICOPS10_19

  20. University of Michigan Institute for Plasma Science & Engr. CONCLUDING REMARKS • Integrated porous low-k material sealing was computationally investigated • Ar/C4F8/O2 Etch • H2/He Clean, PR Strip, and Surface Activation • Ar/NH3 Sealing • He/H2 plasmas clean polymer, strips off PR and activates surface sites in a single step. Higher activation and lower damage seal the surface better. • Si-N and C-N bonds formed by adsorption on active sites followed by one N-N bond linking C or Si atoms from opposite pore walls. • For Ar/O2 clean, sealing efficiency degrades when pore radius is >1 nm and aspect ratio >10. He/H2 clean enables sealing of larger pores and higher aspect ratio trenches. ICOPS10_20

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