Stress Analysis and Optimization on Saddle-shape Warpage by Direct Patterning of Stressed Film

Abstract

As the stacks of the three-dimensional integrated circuits (3D-ICs) increases, the mechanical stress issues are challenging due to the increases in the asymmetry saddle-shape warpage. Various approaches to decrease asymmetric warpage were proposed by forming trenches of tens of micrometers or laser annealing treatment on the backside of wafer, but they had low throughput or lack of improved value. In this paper, we present a novel method to decrease the mechanical stress depending on the shape of the warpage by applying direct coating to the backside of wafer. The proposed method is to release the warpage by patterning a photo-sensitive polyimide (PSPI) with the inkjet-printing to adjust the surface characteristics and the steps, and then depositing tetraethylorthosilicate (TEOS) film with high compressive stress. We measured the changes in the asymmetric bow alongside the x-axis and y-axis before and after the process on the bare wafer by a finite element analysis using ABAQUS. Through the experiment and simulation, the x-y skew of about 230μm was obtained when 10μm-thick TEOS film was partially deposited on a 300mm wafer. In addition, by taking advantage of this process, the localized bow (warpage) can be released according to the changes in the thickness and area of the TEOS film. These results provide an effective guideline to solve unusual warpage caused by stacking process and can be applied to 3D integration in advanced packaging.