Shrinking design rules have decreased film thickness specifications and are creating challenges as multi-layer structures and new materials are introduced. Film thickness measurement is one of these challenges that must be addressed. Not only are the structures and materials challenging to measure but in the 300mm wafer process it is required to implement these measurements on small test pads to eliminate dummy wafers and save costs. To meet these requirements, Dainippon Screen Mfg. Co., Ltd. has developed a spectroscopic ellipsometer, RE-3200, which can measure several parameters with a spot size down to 30um. This state-of-the-art film thickness measurement tool has a unique design to support spectroscopic ellipsometry and also optical interferometry and monochromic ellipsometry(optional). The advantages include high long-term repeatability, high accuracy, short measurement time, and low COO. The simple optics does not require any components between polarizers and ensure high optical efficiency and stability. The high-precision aspheric mirrors are developed specifically for this system and allow the measurement of the small areas on the device. In addition, the use of high-contrast polarizers minimizes measurement errors. The RE-3200 system is also strongly recommended for scatterometry applications.
In this paper, the optical design and performance of RE-3200 including measurement results will be presented.