Photoresist reflow method of microlens production Part I: Background and experiments

We present a two part study of melted microlens arrays. This first part concentrates on the production and measurement of microlens arrays while the second part examines attempts to model the microlens profiles. In this paper we first review some of the fabrication techniques used over the past twenty years to produce lens arrays. Some applications of microlens arrays are then discussed. Particular emphasis is placed on the photoresist reflow method of microlens production that was suggested by Popovic et al., as this was the method used to produce the microlens examined in this study. Lenses produced using this method can have large deviations from the spherical case, i.e. the profile that would be expected from a simple minimisation of the surface energy. These deviations have not been explained to date in the literature, however a number of possible causes for this deviation are given in this paper. Therefore the fundamental questions we wish to explore here are: (1) Why physically do dips occur? and (2) Can the resulting surface profile be predicted? Any model developed to quantitatively estimate the optical effects of surface shape will depend on the physical assumptions made regarding the surface formation mechanism. However as we shall indicate at this point only an informed guess regarding the relative importance of a number of possible mechanisms can be made.