Taper etching without re-entrance profile

摘要

A method is described for forming tapered contact via holes in large scale integrated circuit structures which avoids the formation of a re-entrance profile. The re-entrance profile can form at the entrance to the contact via hole when a dry etch is used as a first etching step by redepositing material removed during the dry etch at the entrance of the contact via hole. This re-entrance profile makes the angle of entrance into the contact via hole greater than 90 DEG and the step coverage of metal filling the hole poor. This invention uses wet etching with a greater lateral etch rate than vertical etch rate as a first etching step in the formation of the contact via hole and avoids the formation of the re-entrance profile. The edges of the resulting contact via hole are smooth and the entrance angle into the contact via hole is substantially less than 90 DEG . The step coverage of metal later filling the contact via hole is substantially improved.