Metal (Al, Ni) Induced Lateral Crystallization of Amorphous Silicon

• Main Authors: Huang, Shih-Yang, 黃世陽
• Other Authors: Liu, Tzeng-Feng
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/c793fz

博士 === 國立交通大學 === 材料科學與工程學系所 === 103 === This dissertation mainly deals with the mechanism and optimization of metal-induced lateral crystallization of amorphous silicon. The first part elucidates the mechanism of aluminum-induced lateral crystallization (AILC), which has remained blurry to date. By means of a photoresist-based process, Al islands (100 nm) were thermally evaporated using parameters of 15 V, 3.5 A, and 25 V, 5.6 A onto a 100nm-thick amorphous silicon (a-Si) layer deposited on a glass substrate. Scanning electron microscopy (SEM) examinations indicated that the Al islands exhibited either smooth or crystalline-grain morphology. Annealing processes were carried out at 748 and 823 K for various periods of time. After annealing, AILC could be clearly observed in samples with crystalline-grain morphology, but not in the one with smooth Al island morphology. Transmission electron microscopy (TEM) analyses revealed that the mechanism of AILC is mainly dominated by two layer exchange processes. The Al islands first exchanged vertically with the underlying a-Si layer during AIC, and then the generation of Al particles accompanying AIC caused a lateral layer exchange with the remaining a-Si layer with further annealing. In the second part, the effect of compressive stress on nickel-induced lateral crystallization (NILC) of amorphous silicon thin films was investigated. Here, we described an alternative method enabling the metal-induced lateral crystallization (MILC) of a-Si films. Glass substrates coated with a-Si films were contacted with ground nickel sheets under compressive stresses ranging from 3.7 to 265.8 MPa at 823 K for 1 h. Subsequently, the nickel sheet and stress were removed and the specimens were annealed at 823 K for 1 to 4 h. The experimental results indicated that the extent of MILC decreased when the preliminary compressive stress was increased, while all specimens exhibited the same rate of lateral crystallization during annealing. The present study indicates that, by applying an appropriate compressive stress (~4 MPa), an effective method to reduce the residual Ni content in polycrystalline silicon (poly-Si) can be obtained. In the third part, we described another method for converting the amorphous silicon film into poly-Si film via MILC. Nickel nanoparticle containing solution prepared by microemulsion synthetic method with concentration of 10-3, 5 × 10-3, and 10-2 M was spin coated on a-Si deposited on glass substrate with spin speed of 500, 750, and 1000 rpm, respectively. The nickel nanoparticles (~200-500 nm) react with a-Si to form nickel silicide (NiSi2), which has very small lattice mismatch with crystalline silicon, thus, can trigger MILC at 823 K. Our results reveal that the MILC will occur if the Ni concentration is larger than 48 ppm. The combination of 500 rpm and 5 × 10-3 M gave rise to the most uniformly distributed poly-Si by controlling the distribution and amount of Ni nanoparticles. Moreover, after the annealing heat treatment, the residual nickel content can be reduced to very low ~38 ppm.