Multiprobe End-Point Detection for Precision Control of the Copper CMP Process
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Multiprobe End-Point Detection for Precision Control of the Copper CMP Process Thomas Laursen and Malcolm Grief SpeedFam-IPEC, Inc. 305 North 54th Street Chandler, AZ 85226, U.S.A.
ABSTRACT Sentinel is an optical multiprobe endpoint detection (EPD) system that has been developed by SpeedFam-IPEC (SFI) for the 200-mm and 300-mm Momentum orbital polishers. Sentinel EPD for copper CMP is based on monitoring the visible spectrum of light from a Xenon (Xe) flash lamp, which has been reflected by the wafer surface during polish. Large representative areas of the wafer are monitored from multiple locations in the pad continuously throughout the polish process. Spectra of reflected light from cleared and uncleared copper on a pattern wafer demonstrate a clear transition from copper to the underlying dielectric layer. With the Sentinel EPD system, the wafer is probed at optimized multiple locations constantly throughout the polish process by small-diameter light spots. The coverage of the monitoring is extensive and the radial coverage is substantial on a real-time basis. The EPD call is made based on an EPD signal, which displays the fractional copper coverage as a function of polish time. The detection of copper clearing on the SFI Momentum tools is very reliable and predictable, and not sensitive to process changes.
INTRODUCTION A reliable EPD system is critical for maintaining an optimal and well-controlled CMP process. Sentinel EPD controls the delicate point in process optimization ensuring that the overburden being polished is removed everywhere across the wafer, while minimizing overpolish. There are several types of EPD systems which potentially can be applied for copper CMP, based on either motor current, pad temperature or optical monitoring of the wafer surface. Optical-based EPD systems provide the most direct monitoring of the polish state of the wafer. Probing the wafer surface while being polished requires means of mounting a probe either in the pad itself or in the platen, allowing light to be transmitted through the pad and slurry film. The light source can be either lamps or lasers, while the detection equipment usually involves photo diodes or spectrometers. The present paper provides a short description of the Sentinel optical endpoint system used for the SFI 200-mm and 300-mm Momentum orbital polishers on the copper CMP process.
EXPERIMENTAL Sentinel EPD for copper CMP is based on monitoring the visible spectrum of light from a Xe flash lamp, which has been reflected off the wafer surface during polish. The Sentinel EPD system has a total of three probes continuously monitoring the wafer during polish. This probe M7.6.1
placement, in conjunction with the orbital motion of the platen, allows for large representative areas of the wafer to be monitored continuously throughout the polish process. Spectra of reflected light from cleared and uncleared copper on a pattern wafer demonstrates a clear transition. This is best seen by studying the normalized copper spectra, which initially are approximately
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