As a general rule of thumb, the ratio of the rate of etch-product formation to the flow rate of etch gas should be greater than 0.1 for uniform etching. Suppose a 7.5-cm diameter silicon wafer is etched at a rate of 50 nm/min in a CF4 plasma.
(a) How many atoms of Si are removed per minute?
(b) What evolution rate of SiF4 does this correspond to in standard cubic centimeters per minute (sccm)?
(c) What minimum CF4 flow rate should be maintained?