Excimer Laser Crystallization of Amorphous Silicon Film with Artificially Designed Spatial Intensity Beam Profile

Abstract

A method of forming polycrystalline silicon film with large grains at a controlled location using a single irradiation of an excimer laser beam is proposed. The excimer laser beam is modified to have a specific spatial intensity profile, periodic spatial variation of intensity maxima ͑I max ͒ and minima ͑I min ͒, by means of a specially designed mask composed of transparent and opaque patterns. It is noted that the evolution of polycrystalline silicon microstructure is critically dependent on the melt depth of amorphous silicon at I min , which we categorized as "partial melting," "near-complete melting," and "complete melting" regimes. While the lateral grain growth of polycrystalline silicon increases in proportion to the fluence gradient as the energy density is increased, surprisingly we find that it decreases in the complete melting regime due to the "secondary nucleation" occurring at I max . By judicious selection of optimum intensity modulation and the spacing between I max and I min , we have obtained the maximum lateral grain size of 7.0 m at controlled position.

Seed-Free Fabrication of Highly Bi-Axially Oriented Poly-Si Thin Films by Continuous-Wave Laser Crystallization with Double-Line Beams

“…In the polycrystal with small grains, the Si film was partial-melted. 16 In the lateral crystallization, linearly-arranged bands were observed along the laser-exposed area. In the polycrystal region, the color of the Si film was changed uniformly along the laser-exposed area.…”

“…Figures 3a-3c show the micrographs of the three typical crystallization morphologies, that is, the lateral crystal with void, the lateral crystal, and the polycrystal with small grains, respectively. In the lateral crystal, the Si film was complete-melted, 16 and void was induced by agglomeration. In the polycrystal with small grains, the Si film was partial-melted.…”

Superlateral Growth of Silicon by Artificially Designed Spatial Intensity Laser Beam Profile

“…The mechanism of the microstructure evolution was reported in our previous work. 22 Overall, the evolution of the microstructure with the energy density can be classified into the following three regimes based on the melt depth of a-Si at the location of I min : ͑i͒ in the partial melting regime ͑ Յ1.00 J/cm 2 ͒, explosive crystallization 27,28 occurs vertically at the location of I min and the grains grow laterally ͑Fig. 5a͒; ͑ii͒ in the near-complete melting regime ͑=1.05 J/cm 2 ͒, the grains grow bilaterally by SLG at the location of I min ͑Fig.…”

“…22 Using a single irradiation of this spatial beam intensity modulation on a-Si films, the melt depth can be varied spatially, which can result in the evolution of a range of microstructures. In particular, it was reported that SLG grains as large as 7.0 m can be obtained in the "near-complete melting" regime.…”

“…In previous work, an ELC method was proposed based on the modulation of the spatial intensity beam profile of the excimer laser with periodic maximum ͑I max ͒ and minimum ͑I min ͒ intensities using a specially designed mask structure. 22 Using a single irradiation of this spatial beam intensity modulation on a-Si films, the melt depth can be varied spatially, which can result in the evolution of a range of microstructures. In particular, it was reported that SLG grains as large as 7.0 m can be obtained in the "near-complete melting" regime.…”