Reduction of Metal Residual in MILC Poly-Silicon Thin Film by Wafer Bonding Method~ Ni Filter & Ni Gettering ~
YewChung Sermon Wu
我們將論文分為兩個方向 : (1) 降低誘發結晶前鍍覆的鎳濃度。(2) 減少誘發結晶後複晶矽薄膜中的殘餘鎳含量。
Among various techniques of fabricating Low Temperature Polycrystalline Silicon thin film, Nickel metal-induced lateral crystallization (Ni-MILC) attracted considerable interest for their better uniformity and crystal quality acquired at lower annealing temperature and shorter annealing time. In the poly-Si thin film, however, Ni trapped by the grain boundaries and defects leads to introduce deep level states and results in degradation of the device performance. Therefore, the Ni contamination should be reduced to fabricate high performance thin film transistors. This study was divided into two parts : (1) Reduction of Ni concentration for inducing crystallization before MILC.(2) Reduction of Ni residual in poly-Si thin film after MILC. The first part is to carry out Ni-induced crystallization of amorphous silicon by using a Si wafer as a filter substrate. Deposited different thickness of Ni film on the front or back of the Si wafer and then the Ni concentration diffusing into amorphous silicon was reduced by pre-annealing process. It is found that reduction of nucleation sites、increase of MILC grain size and improvement in Ni contamination resulted from the drop in Ni concentration. In addition, as Ni deposited on the back of the wafer, the grain size increase with decrease in thickness of Ni indicated that the Ni concentration lowered. The second part is to bond an a-Si coated Si wafer utilized as Ni-gettering substrates with MILC poly-Si and successfully get the Ni to the gettering substrate because of the difference between Ni concentration and free energy of thermal dynamics. Apparently the Ni concentration was diminished. The leakage current of GETR TFT has reduced evidently by more than one order as compared with NILC TFT because of reduction of Ni concentration and therefore the on/off ratio was enhanced by one order.
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