利用晶圓接合技術降低金屬誘發側向結晶之複晶矽薄膜中殘餘金屬~鎳過濾與鎳捕捉~

Abstract

在製作低溫複晶矽薄膜電晶體的技術中，利用鎳之金屬誘發側向結晶法能在較低退火溫度與較短退火時間下，得到均勻且品質佳的晶粒而倍受矚目。但在複晶矽薄膜中，鎳會被晶界及缺陷所捕捉，並產生深層能階而造成漏電流等元件電性的衰退。因此減少鎳的殘餘量是製作高品質薄膜電晶體的重要前提。 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。 第一種方向是利用矽晶圓當過濾基板進行鎳誘發結晶，在製作出圖形的矽晶圓正面或背面鍍覆不同厚度的鎳金屬，並進行預退火的步驟減少與非晶矽膜接觸進行退火誘發結晶時的鎳濃度。結果證實進行預退火步驟後，鎳濃度確實降低導致成核點減少，而誘發結晶之晶粒大小變大且鎳矽化物的汙染獲得改善。而將鎳鍍覆在背面且厚度越薄者其鎳濃度也會越低，所以晶粒尺寸增加。 第二種方向則是將鍍覆非晶矽的晶圓做為捉聚基板與金屬誘發側向結晶的複晶矽接合，由於兩者鎳含量之差異以及熱力學上的因素，成功的把殘餘鎳捕捉至基板，顯著的降低了複晶矽中鎳含量。 比較捉聚前後的元件特性發現因為鎳含量減少而使得漏電流顯著的降低的一個數量級以上，開關電流也因此提高一個數量級。

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.