Characterization of Post-etch Residue Clean By Chemical Bonding Transformation Mapping Muthappan Asokan, Oliver Chyan*, Interfacial Electrochemistry and Materials Research Lab, University of North Texas Cheng-Hsien Wu +, Chih-Cheng Shih, Ting-Chang Chang, Departments of Physics, + Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung, Taiwan Present to SPCC-2018, *chyan@unt.edu
Objective: Utilize MIR-IR to optimize RIE etching and post RIE cleaning with minimum dielectric damages New MIR-IR Metrology Polymer residues Method for Wafer Characterization", U.S. Patent 9366601, 2016. ILD damages
Common Characterization Tools for ILD Nanostructure Physical Tools SEM: Decorated DHF Etch No Chemical Info TEM/EEL Labor intensive, Destructive. XPS : best for blanket wafer Atomic concentration % to assess F removal, take-off angle analyses to assess part of the side wall. Electrical Tools Hg Probe Non-contact, Contamination issues, For blanket wafer. MOS Structure Costly, Difficult locating sources of defects.
Ultra-clean Silicon Wafer Surface Preparation Front end (FEOL) Cleans MIR-R 4
Detect Trace organics (< ppb) Contamination in HF Solution Organics contamination MIR-IR Front end (FEOL) Cleans
MIR-IR : Apply to BEOL Processing Patterned ILD Wafer 6
MIR-IR is a Very Powerful Substantive Tool--- Isolate Low-k Film Stack only Spectra Oxide (50nm) Dense Low-k (50nm) Porous Low-k (300nm) Si sub ( ) Low-k Stack Si substrate Sample Spectrum Vs. Background Spectrum Low-k stack only Spectrum 7
Absorbance Chemical Bonding Transformation Map for Porous Low-k NanoStructure Carbon Doping a-ch 3 Low-k damage Residue removal Si-O cage Carbon Doping Si-O network Si-CH 3 (bend) Low-k Low-k Damage Si-CH 3 (rock Si-OH CH 2 O-SiH x SiH x Chyan, et al, ECS Solid State Lett., 3, N1 (2014) Wavenumber cm -1
0.02 0.04 0.06 0.08 0.10 0.12 0.14 Absorbance Identify Lowest Low-k Damage from four Strip Processes Four oxidative plasma strip processes screened by either adjusting process gases or by modulating chamber pressure for reduced O radical content Strip 1 Strip 2 Strip 3 Strip 4 Si-OH Strip process 1 induces minimal damage (lowest silanol) retaining maximal C-doping (highest CH 3 ) a-ch 3 Peak Heights (mabs) 130 125 120 115 110 Strip 1 Strip 2 Strip 3 Strip 4 Strip 1 Highest Carbon Dopping Lowest Water Sensitivity Si-OH 4000 3800 3600 3400 3200 3000 Wavenumber (cm -1 ) 2800 2600 2400
Identify Chemical Bonding Structure and Explore Cleaning Processes for Post-Etch Residues Patterned ILD Wafer 10
Absorbance (a.u.) Chemical Bonding Structure of Etch Residues 1x6nm 5x 28nm C=O FC=CF F 2 C=CF C=CF.... CF 3 t. Teflon (CF. 2 ). as (CF2 ) s CF. i 3 (CF 2 ) def (am). Polytetrafluoroethylene (Teflon) 2000 1600 1200 800 Wavenumber (cm -1 ) Mainly fluoropolymer backbone Significant branching/cross-linking Olefinic unsaturation (fluorinated) Carbonyl functional groups ECS Solid State Lett., 2, N11 (2013)
Monitor Wet Clean Efficiency on Post-etch Residue CF x, 1234 cm -1 CF x, 1234 cm -1 Post etch residues 1X Polymer
Evaluate Low-K Damages from Wet Clean Process Si-CH 3, 1278 cm -1 Si-CH 3, 1278 cm -1 Si-O-Si Si-O-Si Post etch residues Cleaning agent attacks ULK within 1 min of treatment. 1X Polymer
Quantitative Evaluation of Wet Clean Process Cleaning Efficiency Loss of Si-CH 3 Loss of ULK MIR-IR gives cleaning process evolution insights
Explore New Cleaning Processes for Post-Etch Residues Patterned ILD Wafer 15
UV-assisted Cleaning on Post-etch Residues No UV 10sec UV UV induced Polymer Residue Removal Hydrophobic No Wet Clean Hydrophilic Wet Clean workable UV UV How to access clean result?
MIR-IR can Assess UV Cleaning Process CF x =CF x Hydrophilic Wet Clean workable How effective? Low-k damages? Process evolution insights shorten R&D cycles 17
Super Critical Cleaning for Post-etch Residues (a) CF 4, CO 2 MUTHU: Search ther papers for a picture or scheme for SCC set up (3000 psi) H 2 O, H 2 O 2, Acetone (a) Reference: RSC Adv., 2017, 7, 11585 11590 (b) Reference: Appl. Phys. Lett. 104, 243508 (2014)
Comparison of three SCC-CO 2 Cleans (Differentials) SSC CO 2 SSC CO 2 + H 2 O SSC CO 2 + H 2 O + UV
Exploring new SCC-CF 4 Cleans (TEM Data) SSC-CF 4 + UV
Goal: Achieve better understanding of fundamental materials properties at the critical interfaces of practical applications. Group members: Muthappan Asokan Josh Caperton Issac Goutham, Kanwal JitSingh Alan M Myers Ian Brown Intel Intel TEL (now with SCREEN) 21
MIR-IR Applications in Advanced IC Fabrication FEOL, BEOL etching and cleaning, formulation development Monitor Post-etch residue removal & minimize Low-k damages Optimize Plasma Etch/Strip/Clean Process integration Monitor Low-k damages and optimize restoration process UV curing on porous Low-k dielectrics materials Evaluate TiN hard mask for Low-k pattern fabrication Flowable low-k dielectrics for gap filling in nanostructure Atomic Layer Deposition/Etching : provide critical interfacial chemical bonding info for better atomic layer control. PI: Oliver Chyan*, Chyan@unt.edu