以晶圓接合與金屬誘發使非晶矽薄膜結晶

Abstract

在本實驗中利用晶圓接合及金屬誘發的方式，使沈積在玻璃基板上的非晶矽薄膜經低溫退火產生結晶，並探討矽結晶的形態與可能的形成機制，以期得到高品質的複晶矽薄膜。 以直接鍍覆在矽晶片上的鎳金屬薄膜在接合過程中可在500~550℃下經過六小時的退火過程使非晶矽薄膜轉變成複晶矽。所得的複晶矽薄膜為長板狀的矽晶粒所堆疊而成。其形成的原因可能是由於鎳原子擴散至非晶矽薄膜後形成非連續的矽化鎳薄膜之後開始誘發結晶，所以在初步結晶的區域是呈局部性，但結晶晶粒比直接鍍覆金屬在非晶矽薄膜上所得的晶粒大。 若預先將鍍覆在矽晶片上的鎳金屬經過不同的熱退火處理，再與非晶矽薄膜接合誘發結晶，則所得的複晶矽薄膜結晶會有不同的形態產生。 在長時間（一小時）高溫（800℃）下使鎳薄膜預先反應成矽化鎳後接合誘發結晶，在經過同樣的退火溫度與時間所得結晶程度會比直接以鎳金屬誘發所得的結晶差，由實驗中可證實是因長時間的預先退火使鎳金屬擴散至矽基板導致表面鎳原子濃度的不足，形成的矽化鎳核減少所造成的。 而以快速退火（RTA）的方式預先對鎳薄膜做退火，所得到的矽化鎳晶粒分佈密集且晶粒大，所以在誘發非晶矽時結晶密集且呈不規則的結晶形態，雖然可以大幅縮短製程時間（約2~3小時）就可得到複晶矽薄膜，但會有大量的矽化鎳殘留在複晶矽薄膜內而影響到薄膜品質。

In the study, the amorphous silicon thin film deposited on glass was crystallized during annealing process at low temperature by wafer bonding and metal-induced crystallization. If we directly deposited nickel on silicon wafer and bonded it with a-Si film to induced the form of silicon crystallization, we could get the poly-silicon thin film after annealing at 500~550℃ 6 hour. The poly-Si film was stacked with long plank crystals. At the initial stage, the crystal was partial and had larger grain size than directly deposited nickel on amorphous silicon film to induce crystallization at the same annealing temperature and manufacture time. The partial crystal region should be due to the form of un-continuous silicide film. The morphology of poly-silicon film would be different by means of bonding a-Si film with a silicide layer made by thermal annealing process. From the experiment, the degree of crystallization was worse if we bonded a-Si film with a silicide layer formed by nickel layer on silicon wafer annealing at 800℃ 1hr. At high temperature and long annealing time, the nickel atoms would diffuse from surface to silicon substrate. That leaded to the lack of nickel atoms to form silicide nucleuses. Forming silicide layer by rapid thermal annealing, the grain of silicide distributed closely and the size was about 300~500Å. The silicon crystal formed by bonding with the above-mentioned silicide layer and annealed at shorter time. The crystal type was not long plank but irregular and the quality of silicon thin film would be affected because of a larger number of residual silicide.