In situ laser reflectometry for multilayer thin film deposition with dynamic target adjustment

In order to enable the monitoring method to work for thin film systems with a large number of layers, the value of the target reflectivity should be dynamically adjusted. We report a new monitoring technique to solve problems related to the current method: necessity of change of witness samples, poor dynamic range and sensitivity, applicability to nonquarter-wave layers, limitation of light source, and restriction of incident angle, etc. In our scheme, only one witness sample is used for multiple layers by the direct in-situ monitoring with a shifted monitor wavelength to avoid the DBR effective range. Furthermore, the target point is dynamically adjusted by controlling the phase thickness of each layer instead of its physical thickness, which is insensitive to the index fluctuation. With a proper calibration, the method gives us a considerable flexibility to be adaptive to arbitrary chamber size and layout