蓝宝石衬底损伤层厚度和折射率的椭偏测量

为了定量测量蓝宝石衬底在化学机械抛光过程中产生的损伤层厚度d和折射率n，提出了一种光谱椭偏测量法。首先，测量蓝宝石衬底反射光谱（波长范围：250~1650 mm）偏振态的改变量（即振幅比和相位差）：然后，通过光学建模和测量数据反演，获得损伤层d和n。实验研究了Al，0。和SiO，两种磨料加工蓝宝石衬底损伤层d和n的变化趋势，前者d呈现波动趋势且最小值（约1.4mm）出现在40min左右，后者d持续下降，在20min接近1mm；二者损伤层n均小于蓝宝石晶体n。另外，实验和仿真分析结果表明相位差与厚度变化趋势一致，因无需建模反演，可作为快速表征损伤层 d变化趋势的参量。总之，所提方法作为光学无损测量模式，适用于加工过程监测。

Ellipsometric measurement of subsurface damaged layer thickness and refractive index of sapphire substrates

To quantitatively measure the thickness d and refractiveindex n of the damage layer on sapphire substrate produced during chemical mechanical polishing,a spectral ellipsometric method is proposed. First, the change of spectral polarization state(i.e., amplitudes ratio and phases difference) of light(from 250 to 1650 nm) reflected on sapphire substrate is measured. Then, the thickness and refractive index of damaged layer are extracted by optical modeling and inversion of measured data. The d and n of substrates polished by Al,O% and SiO, abrasives are measured. Thed of the former fluctuates with the better result about 1.4 nm after 40 min, and the latter continues decreasing with the better result1 nm after 20 min. The n produced by two abrasives is both smaller than that of sapphire crystal. Meanwhile, the experiment and simulation analysis indicate that the change of phase difference is similar with d,which can be used to quickly evaluate the change of damage layer thickness because of no requirements for modelling and inversion. Therefore, the proposed method can be utilized tomonitor the machining process as a nondestructive optical way.