High Resolution, Steep Profile, Resist Patterns
01 May 1979
One of the more difficult problems with resist pattern generation is to achieve good linewidth control, high resolution, and good step coverage simultaneously. Often the requirements appear to be mutually exclusive; good step coverage requires thick resist; high resolution, however, is more easily obtained in thin resist. This is true for all resists, both positive and negative. With any resist, the ideal conditions to obtain high resolution and good linewidth control are a flat surface and a thin resist (3000-4000 A°). The flat surface means that the resist has very little variation in thickness and that, as a result, there will be little variation in resist line width. However, such resist line width variations will occur when lines traverse a step. As device wafers do have steps, thick resist (700015000 A) must be applied to achieve coverage over steps. We discuss here a method for generating high resolution, steep profile resist patterns by first preparing a flatter surface on the wafer.1 This is done by applying a layer of thick organic material that conforms with its lower surface to the wafer and is planar on its top. The thick 1027