Challenges in high-aspect ratio contact (HARC) etching for DRAM capacitor formation

Abstract

In the HARC etching to form capacitor in DRAM fabrication, many essential requirements such as CD uniformity, vertical profile, process margin and etc. should be satisfied. The CD uniformity not only of the contact hole but also of the space between adjacent contact holes determines the distribution of the cell capacitance and leakage characteristics. The CD uniformity is mainly determined by the mask etching. Recently, it was found that the CD uniformity of the space between contact holes becomes worse along with the design rule shrinkage. And the worse CD uniformity comes from the tilted profile of the hard mask. Obtaining vertical contact profile is a traditional problem in HARC etching. To achieve large enough bottom CD fundamentally erodes side surface of the upper part of the contact and thus forms so called bowed profile. Serious bowed profile decreases the minimum space between adjacent contact holes and induces electrical leakage. In this paper, these issues and related challenges will be presented. And various approaches to understand the mechanism of the issues and to resolve them will be touched.