Etch uniformity in a CCl4plasma aluminum etch

The objective of this work was to develop and characterize a production-worthy plasma aluminum etch process. Major emphasis was placed on etch uniformity and aluminum to silicon etch ratio. Plasma aluminum etch processes typically suffer from both a radial etch rate variation ("bullseye") and a poor aluminum to silicon etch rate ratio. These defects have limited its application in the manufacture of integrated circuits. The process described herein overcomes these deficiences. This paper describes the use of an electrically floating shield surrounding the wafer to produce uniform etch rates within the wafer. The relationship between the characteristics of the floating plate and the observed etch uniformity is presented. High power (900 W) is used to initiate the etch while a lower power (100 W - 400 W) is used at completion to achieve a high aluminum to silicon etch ratio. A process producing etch rates on aluminum of 900Å/min, aluminum to silicon oxide etch ratios of >15:1 and aluminum to silicon etch ratios of >8:1 is described. The etch rate nonuniformity is less than 5%.