3D Shape Measurements of Patterned Silicon Wafers

Wave Front Phase Imaging (WFPI), a new technique that can measure the free form wafer shape of a patterned silicon wafer using only the intensity of the reflected light is presented. In the WFPI system, the wafer is held either horizontally or vertically, depending on the configuration of the optical system. The wave front phase is then measured by acquiring only the 2-dimensional intensity distribution of the reflected non-coherent light at two or more distances along the optical path using a digital imaging sensor. This method allows for very high data acquisition speed, equal to the camera's shutter time, and a high number of data points with the same number of pixels as available in the digital imaging sensor. In the measurements presented in this paper, we acquired 7.3 million data points on a full 200mm patterned silicon wafer with a lateral resolution of 65µm when the wafer was held vertically and 3.4 million data points on the system where the wafer was resting horizontally with a 96µm lateral resolution. The vertical system presented can also acquire data on a 300mm silicon wafer in which case 16.3 million data points with the same 65µm spatial resolution were collected.