Demonstration of stereophonic projection lithography using parabolic mirror optics and collimated illumination from one side

Abstract

Capability of stereophonic projection lithography on arbitrarily but gently curved surfaces was demonstrated using plastic spoons as a reticle and specimens to be patterned. It had already been clarified that the patterned area size was drastically enlarged by illuminating the transparent reticle obliquely upward by collimated light from one side. Here, it was confirmed at first that 200 μm line-and-space patterns in 10 mm square area on a flat reticle were stably replicated on Si wafers with large exposure-time and focus margins. Next, reticle patterns on a spoon concave were successfully replicated on convex surfaces of specimen spoons. On the other hand, it was clarified that resist pattern field was distorted in a warped trapezoid, and pattern sizes were also varied similarly. However, because the distortions are regular and systematic, they are probably no problem, if critical overlays are not required. And, the distortions can be compensated by modifying the reticle, if necessary.

Distortions of parabolic mirror optics for stereophonic lithography and prospects of compensations

“…[36][37][38] As a result, patterns on curved reticles were successfully replicated on curved specimen surfaces. 39,40) However, the shapes of the replicated patterns on the curved specimens were slightly different from the original ones on the reticle. For this reason, pattern shape distortions caused by the parabolic mirror optics composed of a pair of paraboloids of revolution were investigated 41) using a flat reticle and wafers.…”

Present situation of research on stereophonic lithography using a pair of parabolic mirrors

“…To realize the stereophonic projection lithography, characteristic optics composed of a pair of parabolic mirrors was applied [12][13][14][15][16] . And, owing to some distinguished ideas, it was demonstrated that patterns on curved reticles were successfully replicated on curved articles with the same shapes 17,18 . However, it was thought that reticles made by pasting transparent seals were insufficient for the practical use.…”