Applicability of projection exposure using a gradient-index lens array to thick resist patterning of more than 100-um

Applicability of scan projection lithography using a gradient-index (GRIN) lens array as a projection lens to printing of rough patterns in thick resist films with thicknesses more than 100 μm was researched by analyzing optics parameters and investigating actual patterning characteristics using a thick negative resist SU-8. From the analyses, it was found that the numerical aperture value of the GRIN lens array was considerably large as 0.28, and it was anticipated that the optics was not favorable for very thick resist processes. However, when upper limit of the resist thickness was investigated using 100-μm 1:1 line-and-space (L&S) patterns, very clear patterns with rectangular shape cross sections were obtained if the resist thickness was approximately 150 μm or less. Size miniaturization limits of 1:1 L&S patterns for 50- and 100- μm thick resists were investigated also. As a result, the limits were 25- and 40-μm, respectively, and aspect ratios of 2.3 were measured in both cases. It was clarified that the lithography using a GRIN lens array would be applicable to thick resist patterning within 150 μm. It was thought that the lithography was especially good for fabricating micro-fluidic devices and molds for electroplating, and others.