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

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

What is Planarization? Unplanarized Smoothing Local Planarization Global Planarization

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

CMP Application Metal Dielectric Without CMP With CMP

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

Endpoint Needs Monitoring Metal CMP Endpoint !

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

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

Acoustic Signal Emissions Energy Index Root-Mean-Square =

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

(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

(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

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

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.

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.

(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

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

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

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

Thank you!