Metal-Induced Low-Temperature Crystallization of Amorphous SiGe on Insulating Films
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Metal-Induced Low-Temperature Crystallization of Amorphous SiGe on Insulating Films M. Miyao, H. Kanno, I. Tsunoda, T. Sadoh, and A. Kenjo Department of Electronics, Kyushu University, 6-10-1 Hakozaki, Fukuoka 812-8581, JAPAN ABSTRACT o
Metal-induced low temperature ( ≤ 550 C) crystallization of a-Si1-xGex ( 0 ≤ x ≤ 1 ) layers on SiO2 films has been investigated. For low Ge fractions below 20 %, Ge-doping enhanced plane growth was observed. This realized strain-free poly-Si0.8Ge0.2 films with large grains (18 µm). On the other hand, dendrite growth was dominant for intermediate Ge fractions with 40-60 %. Directions and widths of dendrites became straight and narrow with decreasing annealing temperature. As a result, very sharp needlelike crystals (width: 0.05 µm, length: 10 µm) were obtained at the optimized growth conditions (x: 0.4, annealing: o 450 C, 20 h). These new polycrystalline SiGe films on insulators should be used for the advanced system-in-displays and novel one-dimensional wires. INTRODUCTION o
Low temperature ( ≤ 550 C) formation of Si1-xGex ( 0 ≤ x ≤ 1 ) hetero-semiconductors on insulating films has been expected to realize advanced system-in-displays and three-dimensional ultra-large scale integrated circuits (ULSI). To achieve this, crystallization processes of amorphous SiGe (a-SiGe) on SiO2 have been widely investigated. However, only poly-SiGe with small grains (~1 µm) was obtained by solid-phase crystallization (SPC) [1,2]. The melt-grown process such as laser annealing achieved poly-SiGe with large grains (~5 µm). However, Ge atoms were not distributed uniformly in the films, and surface ripples with ~15 nm height were observed [3]. o Recently, low temperature (~550 C) SPC of a-Si was realized by using the catalytic effect of some metals [4-7]. This metal-induced lateral crystallization (MILC) has achieved poly-Si with large grains (~10 µm) on insulating films. In addition, high-performance thin film transistors with electron mobility of 120 cm2/Vsec have been successfully fabricated [8]. The key question is whether a-SiGe can be recrystallized by such a MILC method. In order to examine this possibility, we have investigated the MILC process of a-Si1-xGex ( 0 ≤ x ≤ 1 ) on SiO2. The present paper reports our new findings of the Ge fraction dependence of MILC. EXPERIMENTAL PROCEDURES In the experiment, p-type Si substrates with (100) orientation were used. They were covered with SiO2 films (160 nm thick), and then a-Si1-xGex ( 0 ≤ x ≤ 1 ) layers (50 nm thick) were deposited on the SiO2 films by using a molecular beam epitaxy system (base pressure: 5 x 10-11 Torr). Here Si and Ge atoms were evaporated by using Knudsen cells at a rate of 0.1 nm/sec by keeping substrates at room temperature. The composition ratio (x) in a-Si1-xGex was controlled by monitoring Si and Ge fluxes, and confirmed by using Auger electron spectroscopy. Subsequently, Ni films (5 nm thick) were deposited on the a-SiGe films and then patterned by
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using the photolithography technique. Finally, the sample
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