Mems Substrate Thickness Of The Laser Ultrasonic Measurement Technology Research

As the part of micro-detected technology, the 3D geometrical size measure of micro-structure is of great importance, which is composed of length measure, width measure and depth measure. The height measure, especially the thickness measure is hardly achieved. Usually the 3D geometrical size measure of micro-structure is realized by the optical method. But when the situation become to the micro-structure distributed at the inner of the chip, the optical method won't work well. Along with the development of Micro Electrical Mechanical System (MEMS) technology, the MEMS manufacture technology will take on diversification, and the structure of MEMS chip will become more and more complex. So in order to measure the thickness of these structures (especially thin films) we have to explore a new way.In the article, the fundamental of laser-based ultrasound(LBU), the design scheme of the system and the analysis method of data is researchedOn the fundamental of LBU, The excite theory of laser-based ultrasound especially ultra-short pulse laser-based ultrasound, the modulate technology of laser in order to enhance the SNR of the system and the fundamental theory of pump-probe technology is researched. On the design of the system, the thickness measure system of MEMS chip is built based on LBU and pump-probe technology. On the analysis of data, the reflectivity curve is analyzed using the law of reflectivity change induced by ultrasound, and the thickness is calculatedUsing the system designed by the article, to aluminum film the size of about 20nm can be measured , when the film be measured is single layer, the relative error of the system is less than 2%, when the film be measured is double layer, the relative error of the system is less than 10%.