Contact CD Uniformity and Hole Circularity Improvement in 32/28 nm Node: Effect of Substrate Properties and Chemical Material Baking Temperature

Abstract

Contact patterning is one of the critical steps in a state-of-the-art lithography process. One of the main challenges for developing contact patterning process in 32/28 nm technology node is to achieve better critical dimension uniformity (CDU) and smaller circularity of the contact holes. In this paper we study the CDU and pattern shape variation affected by material chemical properties and baking temperature. By employing DOE (Design of Experiment) methods, we have found that the contact holes CDU can be determined by the photoresist types and BARC (Bottom Anti-Reflective Coater) baking temperature. For one type photoresist, we have found that the circularity of contact holes falls into nearly linear relationship with the CD value, which can not be affected either by the baking temperatures of the photoresist and BARC materials or by the developing process. In addition, we have also found that contact layer defect scan results and final hole profile after etch can be altered by the sidewall angle and/or the profile of the photoresist, which is near vertical. To satisfy photoresist cross section profile sidewall angle requirement, the negative impact from the substrate films to the photoresist profile has to be studied and reduced. Finally, we will present the defect scan result for our experiments in CDU and pattern profile.