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.

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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 b) Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor, Ann Arbor, MI October 2010 * Work supported by Semiconductor Research Corporation AVS10_01

 Sealing of Low-k Dielectrics  Modeling Platforms  Generation of Hot H  Polymer Removal and PR Stripping In He/H 2 Mixtures  Sealing Mechanism Using Ar/NH 3 Plasma Treatment  Sealing Efficiency  Pore Radius and Aspect Ratio  Pulsing Effect On Etch Rate AGENDA University of Michigan Institute for Plasma Science & Engr. AVS10_02

POROUS LOW-k DIELECTRICS  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.  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: University of Michigan Institute for Plasma Science & Engr. AVS10_03

 Typical porous SiO 2 has CH 3 lineing pores with Si-C bonding – referred to as SiOCH.  Ave pore radius: nm  Porosity: up to 50%  Etching and sealing SiOCH is an integrated, multistep process  EtchAr/C 4 F 8 /O 2 CCP  CleanAr/O 2 or He/H 2 ICP  ActivateHe/H 2 ICP  SealAr/NH 3 ICP LOW-k PROCESS INTEGRATION University of Michigan Institute for Plasma Science & Engr. Mask Si Porous Low-k SiCOH AVS10_04

 Step 1: Ar/C 4 F 8 /O 2 CCP Etch trench leaving PR mask and CF n polymer  Step 2: Ar/O 2 ICP Remove PR and CF n polymer with O radicals  O atoms diffuse into pore network to etch CH 3 groups.  Degrades low-k material. University of Michigan Institute for Plasma Science & Engr. PORE SEALING PROCESS INTEGRATION AVS10_05

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

He/H 2 CLEAN-ACTIVATE  Highly motivated to eliminate Ar/O 2 step as degradation of SiOCH occurs.  Possible alternative is He/H 2 ICP plasma cleaning.  Hot H atoms (> 1 eV) are produced by dissociative excitation and charge exchange. University of Michigan Institute for Plasma Science & Engr.  H* remove PR and CF n while activating surface sites.  Low mass of H reduces likelihood for sputter of CH n.  Must optimize H* production AVS10_07

MODELING : LOW-k PORE SEALING  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 PLASMA Porous Low-k Coils Wafer Substrate Metal Plasma Ar/NH 3 PLASMAS University of Michigan Institute for Plasma Science & Engr. AVS10_08

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. 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. AVS10_09

TYPICAL PLASMA PROPERTIES: H 2 /He ICP  Total ion density (cm -3 ): 1.5 x  Neutral densities (cm -3 ): H 9 x H 2 7 x H 2 (v=1,5) 1.5 x  Major fluxes to the substrate (cm -2 s -1 ): H 6 x H 2 3 x H 2 (v=1,3) 6 x H + 2 x  Conditions: H 2 /He = 25/75, 10 mTorr, 300 W ICP University of Michigan Institute for Plasma Science & Engr. AVS10_10

 CCP for trench etch.  Ar/C 4 F 8 /O 2 = 80/15/5  40 mTorr, 300 sccm  10 MHz  5 kW  CF x polymer deposited on the sidewalls efficiently seal the open pores. CF x polymers are harmful to diffusion barrier metals such as Ti and Ta.  Polymer layers can be removed by:  He/H 2 plasmas without surface damage.  O 2 plasmas that etch the CH 3 groups. Ar/C 4 F 8 /O 2 CCP TRENCH ETCH Animation Slide-GIF University of Michigan Institute for Plasma Science & Engr. Photo-Resist Si Porous Low-k SiCOH AVS10_11

HOT H GENERATION: He/H 2 ICP  Vibrational Excitation e + H 2 (v=0)  H 2 (v=1) + e e + H 2 (v=n)  H 2 (v=n+1) + e  Hot H Generation e + H 2 (v=n)  H ** + H ** + e  Charge Exchange Reactions H 2 (v=n) + H 2 +  H 2 (v=n) ** + H 2 + H 2 (v=n) + H 2 +  H ** + H 3 + H + H 2 +  H 2 (v=0) ** + H + H 2 (v=n) + H +  H ** + H 2 + H + H +  H ** + H +  Conditions: H 2 /He = 25/75, 10 mTorr, 300 W ICP University of Michigan Institute for Plasma Science & Engr. ** Translationally hot AVS10_12

POLYMER REMOVAL AND PR STRIPPING  He/H 2 plasma used for both polymer (P) removal and photoresist (PR) stripping.  Hot H, H 2, H + and H 2 + remove polymer and masking PR layers as CH 4, HF, and C x H y F z H ** + P(s)  CF + HF H ** + P(s)  CHF 2 H 2 ** + P(s)  CH 2 F 2 H ** + PR(s)  CH 4 H 2 ** + PR(s)  CH 4.  CH n groups are also activated by H removal H ** + CH n (s)  CH n-1 + H 2. University of Michigan Institute for Plasma Science & Engr. Animation Slide-GIF Si PR Porous Low-k SiCOH ** Translationally hot AVS10_13

POLYMER REMOVAL, CH 3 DEPLETION  Ar/O 2 plasma efficiently removes polymer.  Also removes CH 3 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/H 2 plasma removes polymer without significantly depleting CH 3. University of Michigan Institute for Plasma Science & Engr. Si Low-k SiCOH AVS10_14

SEALING MECHANISM IN Ar/NH 3 PLASMA  N/NH x species are adsorbed by activated sites 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) NH x + P * (s)  P(s) + 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) University of Michigan Institute for Plasma Science & Engr. AVS10_15

PORE-SEALING BY SUCCESSIVE He/H 2 AND NH 3 /Ar TREATMENT  Surface pore sites are activated by 610s He/H 2 plasma treatment.  Ar/NH 3 plasma treatment seals the pores by forming bridging Si-N, N-N and Si-N bonds. ·Initial Surface Pores University of Michigan Institute for Plasma Science & Engr. Animation Slide-GIF ·He/H 2 Plasma Site Activation ·Ar/NH 3 Plasma Pore Sealing AVS10_16

SEALING: WITH POLYMER REMOVAL AND PR STRIP  Ar/O 2 Clean: additional He treatment is required for surface activation, followed by NH 3 plasma sealing.  He/H 2 Clean: Performs both activation and cleaning in a single step. Can seal with NH 3 just after the clean. University of Michigan Institute for Plasma Science & Engr. Si Animation Slide-GIF He/H 2 Activation Sealing He/H 2 Activation Sealing Si AVS10_17

SEALING EFFICIENCY: PORE RADIUS  Ar/O 2 Clean: Sealing efficiency decreases with increasing pore size.  H 2 /He Clean: Sealing is less sensitive to pore radius. University of Michigan Institute for Plasma Science & Engr. Poor Sealing Good Sealing He/H 2 Clean Ar/O 2 Clean Animation Slide-GIF AVS10_18

SEALING EFFICIENCY: ASPECT RATIO University of Michigan Institute for Plasma Science & Engr.  O 2 Clean: sealing efficiency on sidewalls decreases with increasing aspect ratio.  He/H 2 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

PULSING EFFECT ON PR REMOVAL: He/H 2 ICP  Duty cycle reduction increases ion to neutral flux ratios.  A low duty cycle can increase PR removal rate.  Conditions: H 2 /He = 25/75, 10mTorr, 300 W ICP AVS10_20 SiCOH PR

CONCLUDING REMARKS  Integrated porous low-k material sealing was investigated  Ar/C 4 F 8 /O 2 Etch  H 2 /He Clean, PR Strip, and Surface Activation  Ar/NH 3 Sealing  He/H 2 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/O 2 clean, sealing efficiency degrades when pore radius is >1 nm and aspect ratio >10. He/H 2 clean enables sealing of larger pores and higher aspect ratio trenches. University of Michigan Institute for Plasma Science & Engr. AVS10_21