Two-step etching process for small-size pattern

When pattern size on the mask is getting smaller, wet etching can not control the CD well enough and it is also difficult to add CD bias by using wet etch, especially at the contact layer. Dry etching process is therefore used to meet these requirements. This paper is to report the problems we have encountered during the development of dry etching process and to introduce a two-step, wet then dry etching process, which we used to solve these problems.