In-situ UV absorption CF 2 sensor for reactive ion etch process control

In this article, we report the use of ultraviolet absorption spectroscopy for CF2 detection in a large area parallel plate capacitively coupled reactive ion etching system and correlation of data from this and other plasma sensors to the etch rate of SiO2 and a-Si in CF4/CHF3 plasmas. We present statistical models for estimation of a- Si etch rate in the operational regime in which the CF2 concentration is in the range of 0.4 approximately 1.6 volume % of total gas in the etch chamber. A small change in CF2 concentration translates into quite a large variation in terms of SiO2/a-Si etch selectivity, and this makes CF2 concentration a useful variable in process control. We will show statistically that silicon etch rates can be very well estimated by using sensors for CF2 and fluorine.