複晶矽薄膜之結晶成長與雜質活化及複晶矽薄膜電晶體特性之研究

Abstract

在本論文中,我們探討了複晶矽薄膜之結晶成長,植入離子的活化機構,並 探討了複晶矽薄膜電晶體的電特性與鈍化技術.在低溫爐管退火下,非晶矽 薄膜可獲致比複晶矽薄膜較大的晶粒.這是因為非晶矽薄膜在結晶過程中 有較少的成核中心,故可以得到較大的晶粒.當雷射功率足以熔融矽薄膜 時,結晶進入液相晶粒成長的機構,此時,不論是非晶或多晶矽薄膜,都可獲 致極大的成長晶粒.在植入離子的活化研究中,對於不同的活化溫度,我們 發現砷攙雜試片之片電阻在退火溫度介於 650~850 ℃ 之間會隨著退火溫 度的增加而上升.這種逆向熱退火(reverse annealing)的現象主要是由於 活化離子擴散到晶界析出(segregation)的結果.對於低溫活化 P-型攙雜 的試片,二氟化硼攙雜的試片,其中的氟離子俱備填補晶格缺陷的功能,在 低溫活化N-型攙雜試片的研究中,我們發現晶粒成長的孕育期會隨佈值濃 度的增加而延長.對於磷,砷佈植的試片,適當的攙劑量會促進晶粒成長.但 是過高的佈值劑量則會造成佈植離子叢聚(cluster formation),阻礙晶界 向外擴長,造成較小的成長晶粒.在氫/氮電漿鈍化處理方面,我們發現添加 氮氣的氫化處理可獲致比傳統氫氣電漿鈍化更佳的電性提昇.最後,本論文 又提出一種雙通道複晶矽薄膜電晶體之新型結構.在傳統通道區域內加入 一層薄的埋藏介電質,可以降低垂直電場強度,減少載子散射機率,得到比 傳統結構更高的等效移動率及電流趨動力.此外,我們也發現一種奇特的雙 電晶體特性,這是由於上層通道累增崩潰造成電荷累積進而引發下層通道 導通的結果.此種雙通道電晶體特性將可應用在多元邏輯及控制電路等用 途上. In this thesis, the grain growth mechanisms of low-pressure chemical vapor deposition (LPCVD) silicon films, the dopant activation of implanted ions in poly-Si layers,and the electrical characteristics as well as the passivation effects of the poly- Si thin film transistors (poly-Si TFTs) have been investigated. The lower density of nuclei formation of the a-Si layer could result in the larger final grain size. Significant large grain sizes can be achieved for large laser powers.An increase in sheet resistance have been observed for the As+- implanted specimens within the annealing temperature ranging from 650 to 850 ℃. For the BF2+-implanted specimens, the fluorine ions can passivate the trap states.Too high of the doping level may cause the dopant cluster formation for the N- type dopants. Which will inhibit the expansion of grain boundaries. For the H2/N2 plasma passivation, the nitrogen- containing hydrogen (H2/N2) plasma treatments show better passivation effects on the electrical characteristics of the poly-Si TFTs than the pure H2 hydrogenation. The vertical electrical field can be reduced by inserting a thin buried oxide within the traditional channel region and the higher effective mobility as well as the larger drivability can be achieved for the DAL poly-Si TFTs.