Andrew Chang, David Dornfeld Signal Processing and Analysis of Acoustic Emission Monitoring for Chemical Mechanical Polishing SFR Workshop May 24, 2001 Andrew Chang, David Dornfeld Berkeley, CA 2001 GOAL: To build integrated CMP model for basic mechanical and chemical elements. Develop periodic grating metrology by 9/30/2001. 5/24/2001

Motivation Alternative sensing methods are in-direct (motor current, pad temperature, etc.) or limited to localized areas of the wafer Endpointing for multi-material layer polishing creates tighter process control and minimizes overpolishing. Strategies for scratch detection and process control can be developed with acoustic emission sensing of the polishing process. 5/24/2001

Acoustic Emission Propagation in the Wafer Schematic view of abrasive particles during polishing (exaggerated view) Wafer Sensor Oil film couplant Wafer carrier Carrier ring Abrasives in slurry Pad Polishing plate Wafer Individual burst emission waves generated by abrasive particles contacting wafer produce a continuous acoustic emission source. 5/24/2001

Primary amplification Experimental Setup Pre-amplification & Primary amplification PC Data Acquisition Raw AE Signal Conditioning (60-100 dB) Raw Sampling Rate = 2 MHz CMP Tool Toyoda Float Polishing Machine Test Wafers Bare silicon & copper blanket wafers Slurry type ILD 1300, abrasive size (~100 nm) Alumina slurry, abrasive size (~100 nm) Pad type IC 1000/Suba IV stacked pad Polishing Conditions Pressure = ~ 1 psi Table Speed = 50 RPM Wafer Carrier Speed = Stationary Slurry flowrate = 150 ml/min 5/24/2001

Characterization of Acoustic Emission Silicon vs. Copper Characteristic raw acoustic emission signals produced by breaking a 0.5 mm lead on the surface of the material. 5/24/2001

Raw Acoustic Emission from CMP Process Low frequency noise due vibrations from table motor, pad pattern effects, etc. Filtered raw signal containing high frequency AE content 5/24/2001

Frequency Content: Bare Silicon vs. Copper Less high frequency content for bare silicon wafer. Increased high frequency content for copper wafer. 5/24/2001

Applications for AE in CMP Endpoint Detection The characteristics of the acoustic emission signal from various materials can be easily discernable during the polishing process. Outside noise sources, once characterized, can be minimized and filtered from disturbing the process signal. Scratch Detection Scratches and/or other mechanically induced flaws (large agglomeration of particles, contaminants on the pad, etc.) can be detected and used as feedback for purposes of real-time process control. Abrasive Slurry Design Energy of the AE signal can be correlated to the active number of abrasive particles during polishing for slurry concentration optimization 5/24/2001

2002 and 2003 Goals Integrate initial chemical models into basic CMP model. Validate predicted pattern development by 9/30/2002. Develop comprehensive chemical and mechanical model. Perform experimental and metrological validation by 9/30/2003. 5/24/2001