Dual-photoresist complementary lithography technique for the formation of submicron patterns on sapphire substrates

Abstract

Dual-photoresist complementary lithography technique consisting of inorganic oxide photoresist and organic photoresist is applied to produce the submicron pit array patterns on a sapphire surface. The oxide photoresist is patterned by direct laser writing, and the developed pit size decreases to a smaller value than the laser spot size due to the thermal lithography. The oxide photoresist possesses strong etching resistance against oxygen plasma but shows no resistance against chlorine plasma. During the ion-coupled-plasma reactive-ion-etching process, chlorine plasma is a necessary component to etch the sapphire. Moreover, the characteristics of organic resist are opposite those of oxide photoresist and possess moderate resistance against chlorine plasma but no resistance against oxygen plasma. The thermal and developing characteristics of oxide photoresist are reported in this study. The dependence of laser power on the developed mark sizes and morphologies is examined by atomic force microscopy. The temperature distribution on the photoresist structure during the laser writing is simulated, and the thermal lithography concept is introduced to explain the effect of power on the developed oxide mark width. Images of patterned pit array on a commercial 4-inch-diameter sapphire substrate are also shown.