OSCILLATING CHEMICAL INSTABILITIES IN CONTACT ETCHING DIAGNOSED BY OPTICAL-EMISSION

This paper reports the observed optical emission during the plasma etc hing in a surface wave plasma, tool (SWP). In these experiments, the g as now was increased at constant pressure. The optical emission had a characteristic periodic behavior. As the gas flow is increased, the pe riod decreased and the amplitude increased. It will be shown that thes e optical emission oscillations interfere with endpoint detection for <5% open area wafers. These oscillations are consistent with a mechani sm involving two coupled auto-catalytic reactions, known in the litera ture as a ''chemical clock''. The optical emission spectra in the SWP is identical to that observed in a. transformer coupled plasma tool (T CP) and a high density plasma tool (HDP). However, similar optical emi ssion oscillations have not been seen in the TCP and the HDP. This dif ference is attributed to two causes: differing residence times and wal l temperature/chemistry. These two differences affect the auto-catalyt ic process involving SiFx products.