Recrystallization of Silicon Film on Nitride/Oxide Double Insulating Structure by CW Laser Irradiation

Abstract

Double layer structure of thin nitride on thick oxide is used as an insulating material in order to get a good quality of silicon layer on insulator by laser recrystallization. This structure makes deposited polycrystalline silicon (polysilicon) more resistant to stripping off at high power laser irradiation and results in large grains of silicon layer with random crystal orientations. Laser scanning steps of 20 to 30 µm/step are obtained as optimum values for the largest grain size and smooth surface by investigation of grain growth and surface features. A fully oxide isolated bipolar transistor is fabricated in recrystallized silicon film on the substrate with the double insulating structure, and it shows following characteristics; typical values of hFE, BVCBO, BVCEO, and BVEBO are 29, 73 V, 30 V and 5.2 V, respectively. This is the first demonstration of the bipolar transistor in silicon layer on insulator. Quite similar results in grain sizes after laser irradiation and electrical characteristics of transistors are obtained between two kinds ofpolysilicon by conventional LPCVD furnace and an epitaxial reactor at relatively high temperatures, while original grain sizes of the latter are apparently larger than that of the former.