Feasibility of stereophonic projection lithography applying a parabolic magic mirror system

Abstract

A new stereophonic projection lithography applying a parabolic magic mirror system was proposed. An aperture was also opened at the bottom of lower mirror, and a transparent reticle was placed in place of a reflective object article used in the conventional magic mirror system. Toward the transparent reticle, illumination light was irradiated obliquely upward from the bottom. Thus, images of curved reticle patterns were projected at the aperture center of the upper mirror, and 200 μm line-and-space resist patterns were actually printed on a silicon wafer when a flat reticle was used. On the other hand, it was clarified by tracing light rays in the meridional plane that the resolution depended on the field size, the extent of used mirror parts, and the defocus. It is considered that aimed 50 μm patterns will be printable if the illumination system is improved. The new method is feasible and hopeful.

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

“…The prototype stereophonic projection exposure system developed and renovated in past research [25][26][27][28][29][30] was used in this research. The system is shown in Fig.…”

“…However, in the stereophonic exposure system, an aperture was opened also at the bottom center of the lower mirror, and patterns on a curved transparent reticle placed at the lower mirror center were projected on a curved specimen with the same surface shape by illuminating the reticle obliquely upward from the bottom. [25][26][27][28][29][30] In this paper, patterning characteristics of the parabolic mirror optics illuminated by a collimated light from one side are investigated in detail using a flat reticle with 200 μm line-andspace patterns and 4 inch silicon wafers. In addition, actual stereophonic patterning is demonstrated for the first time using plastic spoons.…”

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

“…[28][29][30][31][32][33][34][35] For this reason, in the present study, the authors began the research and development of lithography systems applicable to the patterning of large patterns on arbitrarily but gently curved surfaces using optics known as a magic mirror system. [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.…”

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.…”

“…On the other hand, it was considered that fabrication and preparation of accurate curved reticles were not easy. For this reason, applicability of conventional flat reticles is investigated here 19 . Feasibility of using flat reticles is discussed.…”