Acoustic Emission Sensing for Chemical Mechanical Polishing (CMP) SFR Workshop November 8, 1999 Andrew K. Chang and David A. Dornfeld Berkeley, CA This work aims to investigate the feasibility of using acoustic emission to study the mechanical aspects of the material removal mechanism in CMP. 4/16/2019

Acoustic Emission Process Monitoring Pad condition monitoring End Point Detection (EPD) - Acoustic signature of material removal changes when polishing different materials Scratch Detection – Catastrophic scratching of the wafer surface caused by impurities embedded in the pad surface can be detected. Acoustic Emission Sources in CMP 4/16/2019

AE Ratio Signal Processing AE Ratios—A signal processing scheme that separates the raw signal into high and low band-pass regimes. During each sampling period (Dt), an average signal level (ASL) calculation is performed, and the ratio of the two peak values is calculated. HFpeak LFpeak ASL Dt High Pass Filter >100 kHz Ratio = Low Pass Filter 20-60 kHz Raw AE Signal AE Sensor 4/16/2019

Experimental Setup Sensor Integration – A laboratory-scale cmp machine was modified to attach the AE sensor on the backside of the wafer. 4/16/2019

ASL Ratio Sampling Period (Dt) Experimental Setup Workpiece Bare Silicon Wafer PSG Oxide Wafer Slurry De-ionized Water Nalco 2352 (particle size 70-90 nm) Polishing Pad IC 60 Linear Velocity 50 – 141 mm/sec ASL Ratio Sampling Period (Dt) 10 ms Sampling Duration 20 sec 4/16/2019

Results AE data obtained from polishing in the absence of abrasive particles. “Air polish” data point represents background level “noise” of environment without contact between pad and wafer Bare and Oxide Wafers Polished with Slurry 3.0 2.5 Average HF/LF Ratio 2.0 Air Polish 1.5 Bare Wafer Oxide Wafer 1.0 20 40 60 80 100 120 140 160 Linear Velocity (mm/s) 4/16/2019

Results AE data differentiating between polishing with (Nalco slurry) and without (DI Water) abrasive particle slurry. 20 40 60 80 100 120 140 160 1.0 1.5 2.0 2.5 3.0 Air Polish Bare Wafer Polished with Slurry and DI Water Wafer 1 with Slurry Wafer 2 with Slurry Wafer 2 with DI Water Average HF/LF Ratio Linear Velocity (mm/s) 4/16/2019

Progress vs Milestones Process Monitoring Year 1 Develop Acoustic Emission sensing for CMP. (Done) Year 2 Evaluate Acoustic Emission sensing for pad degradation, micro-scratching, and end-pointing for multi-layer stacks. (On-going) 4/16/2019

Future Work During the 2000-2002 period, we will extend the evaluation of the use of acoustic emission as applied to: AE Ratio sensitivity to CMP operating conditions Pad Type Slurry Type Pressure Correlation of AE to CMP material removal mechanism, multi-stack polishing, metal polishing Development of endpoint detection methodology 4/16/2019