Spin-coating of photoresist on convex lens substrates

Spin coating of photoresist on flat substrates is a quick and well-known method to generate a homogeneous layer, which is necessary for many lithographic fabrication processes. An important field of application besides the semiconductor industry is the fabrication of diffractive optics. These optical components provide unique properties like negative dispersion or the possibility to realize aspheric phase modifications on surface heights of some micrometers only, which makes them attractive for integration also in optical imaging systems. The fabrication of such micro-structures on curved lens surfaces would provide an additional degree of freedom and thereby enhance the performance of optical systems. To evaluate the abilities of standard spin coating regarding curved substrates, we applied different sets of typical parameters on different convex lenses and found acceptable homogeneity even at angles of more than 20 degrees. The data were acquired with an automated measuring station we realized for this task. In this publication the measurement device and the resulting coating measurements are presented.