Non-destructive Measurement and Characterization of Damage Layer of Single-crystal Diamond Substrate after Ultra-precision Machining

doi:10.3901/JME.2024.04.239

Abstract

Abstract: Aiming at the characteristics of ultra-thin(the experiment involves only a few nanometers) and transparent damage layer on the surface of single-crystal diamond substrate after ultra-precision machining, a method based on spectral ellipsometry is proposed to achievenon-destructive measurement and characterization of the thickness and refractive index of the damage layer. Firstly, a two-layer model of “roughness layer + pure substrate” is established, and the seed crystal substrate before processing is measured by discrete Mueller matrix ellipsometry mode, and its optical constants are obtained by analyzing the measurement data, which are used for the ellipsometric numerical inversion of the subsequent processing damage layer. This can prevent the coupling of ellipsometric parameters between the damage layer and the substrate. Secondly, according to the characteristics of the substrate after processing, a three-layer optical model of “roughness layer + damage layer + pure substrate” is established, and a multi-point fitting analysis strategy is used to achieve non-destructive characterization of the damage layer of diamond substrate in two typical machining stages of rough grinding and fine grinding is realized, and the difference in the damage layer between single-sided grinding and double-sided grinding is further explored. The results show that the refractive index of the seed sample is very close tothe theoretical value of the diamond, and their variation trends with wavelength are consistent with each other, which indicates the measurement mode and the substrate refractive index fitting strategy are feasible. The thickness and refractive index of the damage layer after rough grinding are higher than those after fine grinding. The refractive index of the damage layer after double-sided grinding and single-sided grinding is almost the same in the infrared band, but different in the ultraviolet-visible band. The ellipsometry results of damage layer thickness are compared with those observed by transmission electron microscope(TEM), which has verified the accuracy of ellipsometry characterization. The proposed method can non-destructively measure the thickness and refractive index of the ultra-thin damage layer of the single-crystal diamond substrate, and characterize the surface quality of the substrate after ultra-precision machining, which will contribute to the process optimization of ultra-precision machining of diamond substrates.

Key words: single-crystal diamond substrate, ultra-precision machining, damage layer, spectral ellipsometry, non-destructive measurement

LI Ziqing, CUI Zhangcai, BIAN Subiao, LI Huihui, LU Jing, ORIOL Arteaga, XU Xipeng. Non-destructive Measurement and Characterization of Damage Layer of Single-crystal Diamond Substrate after Ultra-precision Machining[J]. Journal of Mechanical Engineering, 2024, 60(4): 239-249.

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