宽带膜厚实时监控过程中膜层折射率的确定方法

为了准确计算出镀膜过程中每层膜的折射率，介绍了实时监控过程中确定膜层折射率的2种方法：一种是由实测的透射比光谱直接反算出膜层的折射率；另一种是用最小二乘法的优化算法实时拟合折射率。试验结果表明：在线反算适合单点监控，所得折射率误差小于2%。然而在实际镀膜过程中,由于宽带内膜层参数误差较大,一般大于25%。为此，采用最小二乘法拟合，即在整个宽光谱范围内采集每个波长点的信息，所得结果误差很小，一般都在2％～5%之间,有时可达到10%,在很大程度上提高了实际镀膜时膜厚监控的精度。

Determination of the film refractive index in real time monitoring for wideband thin-film thickness monitoring

To calculate the refractive index of every layer accurately in coating process,two methods are introduced to determine the refractive index of layers in real time monitoring.The first method calculates the refractive index of the film inversely with the measured transmittance spectrum.The other one fits the refractive index of the film with the estimation algorithm in the least square method(LSM).The results of the test indicate the online inverse calculation method is more suitable for single point monitoring and the error of calculated refractive index is less than 2%.However,in real coating process,the first method is not preferred because the layers' parameters differ a lot from each other,which makes the error greater than 25%.Meanwhile,the latter one can collect the information from whole wideband spectrum and make the error smaller,which is normally less than 10%.Therefore,it can improve the precision of the film thickness monitoring significantly.