Measuring height variation over entire wafer surface with high lateral resolution

As the semiconductor industry progresses down the roadmap to smaller device geometries, precise metrology of the wafer nanotopography is increasingly needed by the wafer manufacturers and the semiconductor device manufacturers. To meet the demands, we have built an instrument that integrates our patented and proprietary white light interferometer with a motorized x-y stage. It measures height variation over the entire 200mm or 300mm wafer front surface with high lateral resolution and sub-nanometer height precision. This is accomplished by stitching together multiple maps obtained from a white light interferometer. Each individual map represents height variation over a part of the wafer surface. These individual maps are properly positioned to cover the entire wafer surface with sufficient overlapping area. With such properly arranged maps, we are able to produce an entire wafer surface by stitching them together. The map stitching expands the field of view available to our patented low coherence interferometer. This approach makes it possible to reveal more detail nanotopographic information over the entire wafer surface. In this paper, we will present the map stitching approach for the measurements of 200mm and 300mm wafers, including the theoretical foundations of stitching technique and the arrangements of individual measurements. We will also demonstrate measurement results on various wafers.