I need to spin a 120um thick film. My current procedure consists of spinning the polymer (about 20um), uv exposure, plasma etch, and then spinning another 20um thick layer, uv again, plasma etch again, then spin the third layer, so on and so forth . I was able to build up to a 120um thickness but my transparent fill turned very yellow. any suggestions? I’m currently spinning at 1000rpm. I know I can change the concentration of the polymer or reduce the speed of the spinning, but is there any other more efficient way of achieving this?