金属氧化物薄膜光学常数计算物理模型应用研究

采用离子束溅射(IBS)方法制备了HfO₂和Ta₂O₅两种金属氧化物薄膜，通过测量薄膜的椭偏参数，使用非线性最小二乘法反演计算获得薄膜的光学常数。 在拟合过程中，采用L₈(27)正交表设计了8组反演计算实验，在初始选定Cauchy模型后，对HfO₂薄膜拟合影响最大的为表面层模型，对Ta₂O₅薄膜拟合影响最大的为折射率梯度模型。 确定了不同物理模型对拟合函数MSE的影响权重和拟合过程中模型选择的次序，按照确定的模型选择次序拟合，最后加入弱吸收模型反演计算两种薄膜的光学常数，反演计算的MSE相对初始MSE可下降79%和39%，表明拟合过程模型选择物理意义明确，具有广泛的应用价值。 在500 nm处，Ta₂O₅薄膜的折射率梯度大于HfO₂薄膜, 而HfO₂薄膜消光系数大于Ta₂O₅薄膜。 表明Hf金属与Ta金属相比容易氧化形成稳定的氧化物，HfO₂薄膜的吸收要高于Ta₂O₅薄膜。

Applied Research on the Physical Model for Calculating Optical Constant of Metal Oxide Films

In the present paper, two metal oxide films of HfO₂ and Ta₂O₅ were prepared by ion beam sputtering technology. Through measuring ellipsometric parameters of HfO₂ and Ta₂O₅ films, their optical constants can be inversion-calculated by nonlinear least squares techniques. In the fitting process, eight experiment groups were arranged by the orthogonal table L₈(27). After selecting Cauchy model, the largest influencing factor for fitting optical constant of HfO₂ is surface layer model and the largest influencing factor for fitting optical constant of Ta₂O₅ is refractive index gradient model. The impact of different physical model on MSE and the order for selecting model in the fitting process are determined. According to the selecting model and the determined fitting order, optical constants of the two metal oxide films were inversion-calculated with adding weak absorption model, and the obtained MSE can descend 79% and 39% according to the initial value. The results indicated that the selecting model possesses definite physical significance in the fitting process. The obtained method can be applied in inversion-calculating many metal oxide films with weak absorption. It has wide application value. At 500 nm, the refractive index gradient of Ta₂O₅ films is greater than HfO₂ films, while the extinction coefficient of HfO₂ films is greater than Ta₂O₅. It was shown that Hf metal is easier to form stable oxide than Ta metal. And the absorption of HfO₂ films is larger than Ta₂O₅ films.