1. Acoustic and Thermal Methods in Detecting Endpoint during Chemical Mechanical Polishing of Metal Overlay for Nanoscale Integrated Circuits Manufacturing
H. Hocheng & Y.L. Huang
Department of Power Mechanical Engineering
National Tsing Hua University
Hsinchu, TAIWAN ROC

2. Semiconductor Roadmap
Year
2001
2002
2003
2004
2005
2006
2007
Minimum Feature Size (nm)
130
115
100 90 80 70 65
Maximum Substrate Diameter (mm)
200
300
DRAM
Numbers of Metal Levels 3 4 5
Contacts (nm)
165
140
110
Memory Size (mega bits)
512
2,000
6,000
MPU
Numbers of Metal Llevels 7
7-8 8
8-9 9
122 75
Microprocessor Speed (MHz)
1,684
5,173
11,511
Depth of Focus (mm)
0.7
0.6
0.5
0.4

3. What is Planarization? Unplanarized Smoothing Local Planarization
Global
Planarization

4. Why Chemical Mechanical Planarization?
Achieve global planarization for lithography
Increase reliability, speed and yield of sub-micron circuits
No hazardous gas is used
Expected to be a low cost process
Reference: Steiferwald, J. M., et al., “Chemical Mechanical Planarization of Microelectronic Materials,”
New York, John Wiley & Sons, 1997

5. CMP Application
Metal
Dielectric
Without CMP
With CMP

6. Chemical Mechanical Planarization
Down Force
Wafer
Carrier
Slurry Dispenser
Slurry
Pad
Platen

7. Endpoint Needs Monitoring
Metal CMP
Endpoint !

8. Monitoring Principle :
Difference in Coefficients of Friction
 between the pad and dielectric layer
0.35
 between the pad and the copper overlay
0.7
 different acoustic and thermal signals

9. Polishing Conditions Series No. 1 2 3 4 Down Pressure 4.0 psi
Backside Pressure
0.2 psi
Slurry Flow Rate
100 ml/min
Platen Speed
70 rpm
50 rpm
Carrier Speed
30 rpm

10. Acoustic Signal Emissions
Energy Index
Root-Mean-Square =

11. Acoustic Signal Transfer Test
(a) Wafer to Carrier
AE Sensor
Spindle
Backing Film
Carrier
Retaining Ring
Wafer
Calibration AE Sensor
(b) Pad to Carrier
Pad
Calibration AE Sensor
AE Sensor
Platen

12. (a) Platen Speed= 70 rpm, Carrier Speed= 50 rpm
Endpoint
Endpoint
(a) Platen Speed= 70 rpm, Carrier Speed= 50 rpm
(b) Platen Speed= 70 rpm, Carrier Speed= 30 rpm
Endpoint
Endpoint
(c) Platen Speed= 50 rpm, Carrier Speed= 50 rpm
(d) Platen Speed= 50 rpm, Carrier Speed= 30 rpm

13. (a) Platen Speed= 70 rpm, Carrier Speed= 50 rpm
Endpoint
Endpoint
(a) Platen Speed= 70 rpm, Carrier Speed= 50 rpm
(b) Platen Speed= 70 rpm, Carrier Speed= 30 rpm
Endpoint
Endpoint
(c) Platen Speed= 50 rpm, Carrier Speed= 50 rpm
(d) Platen Speed= 50 rpm, Carrier Speed= 30 rpm

14. Thermal Monitoring Strategy
Time
Temperature Rise on Pad B C
A: Beginning of polishing of metal film
B: Beginning of co-polishing of metal and dielectric films
C: End of co-polishing of metal and dielectric films
AB: Linear regression
BC: Second-order regression
Beyond C: Linear regression A

15. B C A
Thermal Signals C B A
AB: the pad polishes the metal layer only, the temperature rises steadily with time.
BC: the pad polishes both metal and dielectric film. Since the coefficients of friction for dielectric film is lower than copper, the temperature rises less rapidly than in the previous phase and varies with the relative amount of metal film left on wafer surface.
Beyond C: the metal film on wafer surface is fully removed, the temperature rises steadily and milder as compared to polishing metal film in the AB period.

16. Signal Processing  Endpoint.
pad temperature is constantly measured, the least-square regressions of the first and second order are continuously calculated and compared.
the error of linear regression is found larger than the second-order regression for five continuous measurements at the beginning of transition.
the error of the linear regression is found less than the second-order regression for five continuous measurements at the end of transition
 Endpoint.

17. (a) Platen Speed= 70 rpm, Carrier Speed= 50 rpm
(b) Platen Speed= 70 rpm, Carrier Speed= 30 rpm
(c) Platen Speed= 50 rpm, Carrier Speed= 50 rpm
(d) Platen Speed= 50 rpm, Carrier Speed= 30 rpm

18. Comparison of Endpoint by Thermal and Acoustic Methods
Platen=70 rpm
Carrier=50 rpm
Carrier=30 rpm
Platen=50 rpm
Thermal Method
40 sec
42 sec
41 sec
62 sec
AE Method
35 sec
34 sec
55 sec

19. Slight Delay of the Thermal Method
-- less agile heat transfer in the system
(including the slurry and polymer pad)
than the acoustic wave propagation
-- time required for regression errors check in
thermal method

20. Conclusions CMP indispensable for nano-scale IC
Endpoint detection essential for yield
Exploit the difference in COF for monitoring
Acoustic and thermal signals both effective
Acoustics more agile

21. Thank you!