Research On Depth Measurement Of The High Aspect Ratio Trenches Based On Spectral Reflectometry

With the development of MEMS,optical measurement technology can be used as a non-contact,high-precision,high-speed,on-line and non-destructive testing method in MEMS technology,especially in the detection of high aspect ratio(HAR)micro trench structure processing technology.Generally,the HAR micro trench structures of MEMS are about(1?10)μm in width and(10?300)μm in height.The aspect ratios are generally between 5 : 1 and 20 : 1.The HAR micro trench structures can usually be measured by the existing measuring instruments under the condition that the MEMS device structures are cross-sectioned.Because the measurements are very inefficient and the operations are complex,they cannot be used as the on-line and non-destructive testing technology.Therefore,the research and development of a convenient,rapid and nondestructive testing method for the MEMS device with deep trench depth and side wall morphology have urgent practical needs and important scientific significance.Focusing on a convenient and rapid nondestructive testing technology for MEMS device of trench depth.This paper uses discrete Fourier transform(DFT)algorithm to transform the reflective light signal from the trench bottom,based on the spectral reflection technology,a measure method for the depth of the trench with high aspect ratio in MEMS devices is proposed,at the same time,a spectral reflection measurement system is built and verified,According to the sequence of work,the research content of this paper can be summarized as follows:(1)Based on the analysis of the spectral reflection measurement principle,a new measurement scheme is proposed for the on-line and nondestructive testing of MEMS trench depth with high aspect ratio.The principle of processing spectral reflection intensity signal basing on DFT algorithm is analyzed,and the Wiener filter using as the noise suppressing method is proposed.(2)In order to meet the experimental requirements of(37)3 mm incident beam and(37)30 μm outgoing beam diameter,the beam shaping optical system for the light source is designed,and the achromatic aberration is corrected by using doublet lens.(3)According to the spectral reflection measurement technology,the measurement process is simulated and analyzed.The trench sample with the aspect ratio of 10 : 1 is modeled;The simulation results of single trench and trench array are analyzed;The influence of the roughness of the trench bottom on the experimental results is analyzed;Finally,the influence of noise on the experimental results is analyzed,and Wiener filter is used to eliminate the noise.(4)According to the simulation results,the measurement experiment platform system is built.By using silicon-based MEMS trench samples,the measurement effect of the experimental system is verified.The measurement results show that the spectral reflection technology can be applied to the non-destructive and rapid measurement of the depth for HAR structures on MEMS devices.