Process kit and wafer temperature effects on dielectric etch rate and uniformity of electrostatic chuck

Abstract

Etch rate and uniformity are two basic indicators of how rf power is coupled into the wafer. In reactive ion etch of dielectric layers, wafer temperature also appears as a key parameter, due to the innate deposition. When electrostatic chuck is introduced, we have to study and control both rf coupling and wafer temperature to maximize etch rate and minimize nonuniformity. We first review the basics of the electrostatic chuck (e-chuck) design and operation, and check them against Applied Materials’ polyimide monopolar e-chuck. Then a simple circuit model is developed and fitted to the experimental results. The model says to have higher etch rate, one needs to couple more energy through the wafer center. This is achieved by using a thicker insulating process kit with low dielectric constant. The uniformity study shows for a given wafer, its etch rate variation across the wafer can be divided into three sections—center, B-field corner, and very edge of the wafer, and each section is controlled by a key parameter. By optimizing these parameters, we are able to increase the etch rate and decrease its nonuniformity to 1.5% (1σ, 3 mm edge exclusion). Finally, wafer temperatures of both center and edge are studied and the delta between center and edge is reduced to ∼6 °C, and spin-on-glass etch rate nonuniformity is reduced to 1σ of 1.88%.