Method for fabricating a self aligned contact which eliminates the key hole problem using a two step spacer deposition

Abstract

This invention provides a method for forming a self aligned contact without key holes using a two step sidewall spacer deposition. The process begins by providing a semiconductor structure having a device layer, a first inter poly oxide layer (IPO-,), and a conductive structure (such as a bit line) thereover, and having a contact area on the device layer adjacent to the conductive structure. The semiconductor structure can further include an optional etch stop layer overlying the first inter poly oxide layer. The conductive structure comprises at least one conductive layer with a hard mask thereover. A first spacer layer is formed over the hard mask and the IPO-,layer and anisotropically etched to form first sidewall spacers on the sidewalls of the conductive structure up to a level above the bottom of the hard mask and below the level of the top of the hard mask such that the profile of the first sidewall spacers are not concave at any point. A second spacer layer is formed over the first sidewall spacers and anisotropically etched to form second sidewall spacers, having a profile that is not concave at any point. A second inter poly oxide layer is formed over the second sidewall spacers, the hard mask, and the IPO-,layer, whereby the second inter poly oxide layer is free from key holes. A contact opening is formed in the second inter poly oxide layer and the first inter poly oxide layer over the contact area. A contact plug is formed in the contact openings.