一种基于自适应差分进化算法的薄膜参数表征方法研究（特邀）

依据穆勒椭偏测量方法中偏振光的传输方式，文中提出了一种基于自适应差分进化算法（SADE）的各向同性纳米薄膜厚度与光学常数的表征方法。通过建立出射光强关于待测标准样片穆勒矩阵的最小二乘模型，用SADE算法对穆勒矩阵元素进行求解，并将拟合得到的穆勒光谱曲线与用双旋转补偿器穆勒矩阵椭偏仪(DRC-MME)测量得到的穆勒光谱图进行了比较，利用传输矩阵求解薄膜厚度。对标定值分别为(104.2±0.4) nm和(398.4±0.4) nm的SiO₂/Si标准样片进行仿真计算，实验表明:当分别迭代到80次和87次时，目标函数光强的残差平方和收敛到最小值0.97和1.01，得到的膜厚计算值分别是(103.8±0.6) nm和(397.8±0.6) nm，相对误差均小于1%。同时用计量型椭偏仪根据得到的折射率进行计算，得到膜厚的计算值分别为(104.1±0.6) nm和(398.2±0.6) nm，验证了SADE在相近收敛速度下对各向同性纳米薄膜参数求解过程中具有计算简单和可以准确的找到全局最优解的特点。

A characterization method of thin film parameters based on adaptive differential evolution algorithm (Invited)

According to the transmission mode of polarized light in Mueller ellipsometry, a characterization method for the thickness and optical constants of isotropic nano films based on Self-Adaptive Differential Evolution algorithm (SADE) was proposed. By establishing the least square model of the output light intensity with respect to the Mueller matrix of the standard sample to be measured, the elements of the Mueller matrix were solved by using the Sade algorithm, and the Mueller spectral curve obtained by fitting was compared with that measured by dual rotating-compensator Mueller matrix ellipsometer (DRC-MME), and the film thickness was calculated by using the transfer matrix. The SiO₂/Si standard samples with calibration values of (104.2±0.4) nm and (398.4±0.4) nm were simulated and calculated. The experiment shows that: when numbers of iterations accumulated to 80 and 87 respectively, the residual square sum of the light intensity of the objective function converges to the minimum values of 0.97 and 1.01. The calculated film thickness values are (103.8±0.6) nm and (397.8±0.6) nm respectively, and the relative errors are both less than 1%. At the same time, a metrological ellipsometer was used to calculate according to the obtained refractive index, and the calculated values of the film thickness were 104.1 nm and 398.2 nm. It is verified that SADE has the characteristics of simple calculation and accurate global optimal solution in solving the parameters of isotropic nano films at a similar convergence rate.