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* Work supported by Semiconductor Research Corporation

REACTION MECHANISM AND PROFILE EVOLUTION FOR CLEANING AND SEALING POROUS LOW- k DIELECTRICS USING He/H 2 AND Ar/NH 3 PLASMAS 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

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* Work supported by Semiconductor Research Corporation

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  1. REACTION MECHANISM AND PROFILE EVOLUTION FOR CLEANING AND SEALING POROUS LOW-k DIELECTRICS USING He/H2 AND Ar/NH3 PLASMAS 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 October 2010 *Work supported by Semiconductor Research Corporation AVS10_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 • Pulsing Effect On Etch Rate AVS10_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 to prevent diffusion into porous network. Ref: http://www.necel.com/process/en/images/porous_low-k_e.gif AVS10_03

  4. University of Michigan Institute for Plasma Science & Engr. LOW-kPROCESS INTEGRATION • Typical porous SiO2 has CH3 lineing pores with Si-C bonding – referred to as SiOCH. • Ave pore radius: 0.8-1.1 nm • Porosity: up to 50% • Etching and sealing SiOCH is an integrated, multistep process • Etch Ar/C4F8/O2 CCP • Clean Ar/O2 or He/H2 ICP • Activate He/H2 ICP • Seal Ar/NH3 ICP Mask Porous Low-k SiCOH Si AVS10_04

  5. University of Michigan Institute for Plasma Science & Engr. PORE SEALING PROCESS INTEGRATION • Step 1: Ar/C4F8/O2 CCP Etch trench leaving PR mask and CFn polymer • Step 2: Ar/O2 ICP Remove PR and CFn polymer with O radicals • O atoms diffuse into pore network to etch CH3 groups. • Degrades low-k material. AVS10_05

  6. University of Michigan Institute for Plasma Science & Engr. PORE PLASMASEALING MECHANISM • Step 3: He ICP Activate surface by sputtering and photo-detachment to create dangling bonds. • Step 4: Ar/NH3 ICP Seal pores with NHn radicals by forming C-N and Si-N bonds which bridges opening. AVS10_06

  7. University of Michigan Institute for Plasma Science & Engr. He/H2 CLEAN-ACTIVATE • Highly motivated to eliminate Ar/O2 step as degradation of SiOCH occurs. • Possible alternative is He/H2 ICP plasma cleaning. • Hot H atoms (> 1 eV) are produced by dissociative excitation and charge exchange. • H* remove PR and CFn while activating surface sites. • Low mass of H reduces likelihood for sputter of CHn. • Must optimize H* production AVS10_07

  8. 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) AVS10_08

  9. 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 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. • 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 AVS10_09

  10. University of Michigan Institute for Plasma Science & Engr. TYPICAL PLASMA PROPERTIES: H2/He ICP • Total ion density (cm-3): 1.5 x 1011 • Neutral densities(cm-3): H9 x 1012 H2 7 x 1013 H2(v=1,5) 1.5 x 1012 • Major fluxes to the substrate (cm-2 s-1): H6 x 1017 H23 x 1018 H2(v=1,3)6 x 1016 H+2 x 1015 • Conditions: H2/He = 25/75, 10 mTorr, 300 W ICP AVS10_10

  11. 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: • He/H2 plasmas without surface damage. • O2 plasmas that etch the CH3 groups. Porous Low-k SiCOH Si AVS10_11 Animation Slide-GIF

  12. 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 AVS10_12

  13. 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 polymer and masking PR layers as CH4, HF, and CxHyFz H**+ P(s)  CF + HF H**+ P(s)  CHF2 H2**+ P(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 AVS10_13

  14. 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 AVS10_14

  15. 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 C-N/Si-N NHy + SiNHx(s)  SiNHx-NHy(s) NHy + CHn-1NHx(s)  CHn-1NHx-NHy(s) AVS10_15

  16. 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-N bonds. • Initial Surface Pores • He/H2 Plasma Site Activation • Ar/NH3 Plasma Pore Sealing Animation Slide-GIF AVS10_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: Performs both activation and cleaning in a single step. Can seal with NH3 just after the clean. He/H2 Activation Sealing Si Si Animation Slide-GIF AVS10_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: Sealing is less sensitive to pore radius. Ar/O2 Clean He/H2 Clean Good Sealing Poor Sealing Animation Slide-GIF AVS10_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. AVS10_19

  20. PULSING EFFECT ON PR REMOVAL: He/H2 ICP • Duty cycle reduction increases ion to neutral flux ratios. • A low duty cycle can increase PR removal rate. PR SiCOH • Conditions: H2/He = 25/75, 10mTorr, 300 W ICP AVS10_20

  21. University of Michigan Institute for Plasma Science & Engr. CONCLUDING REMARKS • Integrated porous low-k material sealing was 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. • Pulsing can enhance the PR removal rate. • 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. AVS10_21

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