The Geometry of Amorphous Silicon Effect on Metal Induced Lateral Crystallization Rate
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The Geometry of Amorphous Silicon Effect on Metal Induced Lateral Crystallization Rate Y.-S. Kim, M.-S. Kim, and S.-K. Joo School of Materials Science and Engineering, College of Engineering, Seoul National University, Seoul 151-742, Korea, ABSTRACT
In this study, we observed that the MILC behavior changed when the amorphous silicon active pattern width was changed abruptly and explain that phenomena with novel MILC mechanism model. The 10nm thick Ni layers were deposited on glass substrate that has various amorphous silicon patterns on it. Then we annealed the sample at 550 oC with RTA (rapid thermal annealing) machine and measured the crystallized length with optical microscope. The MILC rate was reduced dramatically and stopped for several hours (incubation time). After the incubation time, the MILC started again and the incubation time increased as the amorphous silicon pattern width difference getting larger. We can explain these phenomena with the tensile stress that was caused by volume shrinkage due to the phase transform from amorphous silicon to crystalline silicon. INTRODUCTION
Poly-silicon is the key material for the integration of driving circuits and pixel transistors simultaneously in one glass substrate for large area LCD. However, it has been known that solid phase crystallization (SPC) of amorphous silicon (a-Si) requires furnace annealing at least 600 o C so that a plain glass could not be used as a substrate [1]. It has been reported earlier that the crystallization of a-Si thin films can be done at the temperature as lower as 450 oC by so called MIC (Metal Induced Crystallization) method [2]. For some metals such as Ag, Au, Al, Sn, Ti, Cu, Pd, Ni it is known that metal atoms dissolved in a-Si films may weaken Si bonds and enhance nucleation of crystalline silicon [3]. Uncommonly Ni, Pd is known that it can crystallize laterally a-Si thin films. It is called as Metal-Induced Lateral Crystallization (MILC) [4-5]. In this study, we reported abnormal MILC behavior when the MILC progressed through the patterned a-Si of which width was abruptly widened. And we investigated the relationship between the a-Si width change and Ni-MILC rate.
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(a) (b) Figure 1. Schematic diagram of the patterned a-Si EXPERIMENTAL DETAILS
A 300 nm thick SiO2 film was deposited on corning 1737 glass substrate for buffer oxide by plasma enhanced chemical vapor deposition (PECVD). And then a 50 nm thick amorphous silicon film was deposited by low pressure chemical vapor deposition (LPCVD) using disilane (Si2H4) gas. The deposition pressure and temperature were 200 mTorr and 450 oC, respectively. Then amorphous silicon was patterned by reactive ion etching (RIE) using SF6 and O2 gas as shown fig. 1 (a) and (b). The values of W1 were 12, 40, 46, 62
㎛
and W2 were 4.5, 10
㎛
and
we combine the W1 and W2 for the different W1/ W2 ratio. The 10nm thick Ni layers were deposited on silicon with by sputtering method and lift-off process was employed since Ni reacts with silicon even at room temperature. The anne
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