Control schemes using emission endpoint in a borderless oxide contact etch process

Emission endpoint is a convenient way to compensate for incoming film variations in many reactive ion etch (RIE) processes. Variations in film thickness and composition which change the etch rate do not adversely affect the product since etch times are automatically adjusted by the endpoint system. Emission endpoint systems are also useful in borderless contact etch processes which depend heavily on etch selectivity to underlying nitride films. Loss of selectivity damages isolation structures in CMOS devices, while excessive selectivity causes etch-stop in the oxide and open circuits. The onset of these phenomena is evident in the emission endpoint signal. This paper describes detection of etch-stop and selectivity loss by analysis of plasma emission. A control scheme to monitor selectivity is also discussed.