Effect of Deposition Condition of Precursor Amorphous Silicon Thin Films on the Behavior of Milc
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EFFECT OF DEPOSITION CONDITION OF PRECURSOR AMORPHOUS SILICON THIN FILMS ON THE BEHAVIOR OF MILC Y.-G. Yoon, G.-B. Kim, H.-H Park, S.-W Lee, and S.-K. Joo School of Materials Science and Engineering, College of Engineering, Seoul National University, Seoul 151-742, Korea, [email protected] ABSTRACT We studied on the effect of a deposition condition of precursor a-Si thin films on the shape and micro-structure of MILC. The a-Si thin films were prepared by Plasma Enhanced Chemical Vapor Deposition (PECVD) with silane and hydrogen as a source gas and the deposition temperature was varied from 100 to 400 . The a-Si films deposited at a lower temperature showed a tendency to (111) crystals and leaving some a-Si residues in MILC region, while those with higher deposition temperature tended to be crystallized to (110). These differences were explained in terms of original hydrogen content and following structural changes by the dehydrogenation during annealing.
INTRODUCTION Poly-silicon is the cardinal material for the integration of driving circuits and pixel transistors simultaneously in one glass substrate for large area LCDs. However, it has been well-known that solid phase crystallization (SPC) of amorphous silicon (a-Si) requires furnace annealing at least 600 , so that plane glass cannot be used as a substrate [1]. There have been many attempts to lower crystallization temperature and it has been reported earlier that the crystallization of a-Si thin films can be done at temperatures as low as 450 by so-called MIC ( Metal Induced Crystallization ) method [2]. For some metals such as Ag, Au, Al, Sn, Ti, Cu, Pd and Ni it is known that metal atoms dissolved in a-Si films may weaken Si bonds and enhance the nucleation of crystalline silicon [3]. But these metals have very harmful influences on the electrical properties of TFT devices by contaminating channel area of TFTs. Unlike other metal, Ni and Pd can crystallize “laterally” a-Si thin films with less metal taint and it is called as Metal-Induced Lateral Crystallization (MILC) [4,5]. Many research groups could make excellent TFTs most successful in terms of device characteristics and mass production applicability with MILC poly-Si. [7] Even though MILC behavior varies according to the precursor formation conditions, such as deposition temperature, method, and source gas, not much attention has been paid to these conditions. In this paper, we studied on the effect of a deposition temperature of precursor a-Si D3.3.1
thin films on the shape and rate of MILC. EXPERIMENTAL METHODS The a-Si thin films were prepared by Plasma Enhanced Chemical Vapor Deposition (PECVD) with silane and hydrogen as a source gas and the deposition temperature was varied from 100 to 400 . On top of a-Si films, 50 -thick nickel films were deposited selectively for the purpose of MILC. These samples were annealed for various time at 450 -550 in N2 ambient in order to observe MILC behavior. MILC length was measured with optical microscopy, and microstructure was inspected with TEM. RESULTS A
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