Local Wafer Shape Characterization

Abstract

The shape of a silicon wafer is one of the key wafer characteristics. It is not only impacted by wafering and epitaxial processes but also highly modulated by device manufacturing processes, such as film deposition, CMP, lithography, and thermal process. Wafer shape can be best described and visualized by a complex 3D contour map, which contains both global (low spatial frequency) and local (high spatial frequency) wafer shape components. Unfortunately, the 3D contour map is not practical to guide wafer shape control in high volume production. To quantify and control the wafer shape, two global shape metrics, bow and warp, have been used for a few decades. These two metrics, however, are too simplified to capture local wafer shape. In this study, the limitations of traditional global shape metrics, bow and warp, are addressed, and different global and local shape metrics are explored. A novel shape metric of Site Slope-Radial Range (SSRR) reveals unique local wafer shape characteristics in the slope domain and may help us to better understand the impact of local wafer shape to device manufacturing processes, particularly lithography and CMP.