Unique spin coat process for positive photoresists

A unique spin coat process was developed which improves the coating uniformity and extends the range of applicable resist thicknesses typically encountered for a one viscosity photoresist. This spin coat process involves a high speed, short term initial coat followed by a low speed dry cycle. Advantages are seen in better standard deviation of coating uniformity and coating thicknesses achieved over a 1 micron range (1.2 to 2.4 microns) for positive photoresists on 6' wafers. In this paper the authors discuss the application of this unique resist processing approach to three types of photoresists which differ in solvent composition (utilizing ethyl lactate, propylene glycol mono methyl ether acetate, and 3-ethoxy-ethyl propionate). Comparison of coating uniformity at various resist thicknesses with a standard coating process is made and emphasis is placed on analysis of residual solvent and PAC content in resist films.