1. 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

2. 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

3. 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

4. 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

5. ASL Ratio Sampling Period (Dt)
Experimental Setup
Workpiece
Bare Silicon Wafer
PSG Oxide Wafer
Slurry
De-ionized Water
Nalco 2352
(particle size 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

6. 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

7. 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

8. 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

9. Future Work
During the 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