Effects of various encapsulating films on laser recrystallization of silicon on SiO2

Abstract

Single-crystal silicon-on-oxide was produced by laser recrystallization of a 0.6-μm polysilicon film deposited on 1 μm of thermal SiO2. Oriented growth commenced where the polysilicon film was in contact with the silicon substrate, and proceeded laterally over the fully recessed SiO2. Typical dimensions of the single-crystal silicon-on-oxide film are 25 μm by 7 mm. The laser annealing was done with several different encapsulating films above the polysilicon, including 11.0, 16.4, and 32.9 nm of Si3N4, 25 nm of SiO2, 25 nm SiO2 +32.9 nm Si3N4, and uncapped samples. In addition, samples were laser annealed with and without an 1100 °C N2 preanneal of the structure. The 1100 °C anneal reduced the nucleation of misoriented grains in all samples, and extended the range of useable powers for the Si3N4 capped samples. The 32.9-nm Si3N4 cap produced the smoothest film and the most efficient coupling of the laser light into the silicon. The maximum distance of single-crystal growth was the same for all nitrogen-annealed samples, and showed a weak dependence on the melt width induced by the beam used for recrystallization. TEM micrographs of the recrystallized silicon show that the defects lie predominantly in the 110 direction. Their density increases away from the seed region, and they coalesce to form the grain boundaries at the transition to polysilicon growth.