基于遗传算法的透射光谱法测量薄膜光学常量

目前的实际生产加工需求中，需要一种高精度、简单易行的薄膜参数检测方法。但是，传统的基于透射光谱法的单纯形法只能够得到薄膜的厚度信息，无法获取准确的薄膜的折射率。本文基于多光束干涉理论建立了单层薄膜的透射率模型，并且得到了薄膜透射率T与厚度d及折射率n之间的关系的数学模型。进而利用遗传算法求解该数学模型。由于薄膜透射光谱数学模型的特殊性，按照实际的精度需求，有针对性的选取了遗传算法中的关键参数：种群大小、交叉概率和变异概率。并且针对透射光谱的具体情况，设计了离散化的适应度函数。最终的拟合结果表明，基于遗传算法的透射光谱法能够快速、准确的得到薄膜的光学参数。

Methods based on genetic algorithm for the determination of the optical constants of thin films from transmission

For the practical productive demands, a highly-accuracy easy-to handle method was in need of determination of optical film constants. Traditional method which was based on simplex optimization, could work out thickness of the optical film, however, refractive index was unavailable. In this paper, mathematic model of the transmitted spectrum was established by multi-beam interference. And the function relationship between transmittance and thickness, refractive index is built. Then the mathematic model could be solved through the genetic algorithm. In consideration of the special character of the optical film, value of key parameters of genetic algorithm need special choice. Key parameters include: population size, crossover probability and mutation probability. Fitness function was designed to be discretized. Finally, the fitting results proved that the method could calculate the constants of optical films at the same time.