Real time temperature monitoring of Si substrate during plasma processing and its heat flux analysis
Actual Si wafer temperatures during plasma etching processes were temporally measured using a real time wafer temperature monitoring system with autocorrelation type frequency domain low coherence interferometry. Indeed, the Si wafer temperature, which was 20 degC before the process, rapidly increased in 10 s. Then, the temperature rise gradually slowed, but continued to increase and reached 45 degC after 600 s. This can be due to the fact that there exists a heat source for the wafer other than the plasma. Reasonably, the Si wafer was found to be sensitive to the temperature of the disk covering the area around the wafer, i.e. the focus ring. Usually, the temperature of the focus ring is not controlled and causes the radial distribution of Si wafer temperature. Consequently, the Si wafer temperature should be controlled with the temperature increase of other heat sources, especially the focus ring.