Wet etch stop resist evaluation for MCM-D packaging

An investigation was carried out to evaluate positive resists which would be used in subtractive etching of Cr and Cu in MCM-D applications. This resist must be able to withstand the alkaline and acidic chemistries used in the metal etch solutions. It must meet certain spin application requirements in order to produce a uniform and consistent coating. It also must be compatible with an alkali metal hydroxide develop chemistry. Another requirement is the ability of the resist to tolerate a large soft-bake temperature range. These stipulations are, in part, necessary to provide a robust MCM thin film interconnect build process. This paper shows results collected on a variety of commercially available novolac based positive resists. Their photolithographic properties, including spin application observations, soft bake temperature effect on unexposed developer etch rates, contrast, and minimum dose effects are discussed. This paper gives observations on the performance of the resists in the metal etch solutions. The capability of some of these resists in Al etching is also discussed. The results of loss of resist adhesion during Al etch are shown. Bake parameter effects on resist adhesion in the Al etch bath are presented. Selection of a resist to meet overall thin film MCM process requirements often involves a trade-off between several resist characteristics. This selection process is discussed.