複晶矽薄膜電晶體製程效應之研究

Abstract

首先，以受到氮離子植入的複晶矽膜製作薄膜電晶體並研究其電特性，結 果顯示，混入的氮具有鈍化缺陷的效果。此外，熱載子可靠度也可獲得改 善。同時也發現，氮離子植入複晶矽膜並退火後所引起的授電子效應，會 稍減緩p-通道複晶矽薄膜電晶體改善的幅度。接著是探究使用薄堆疊式閘 介電層─氧化物/氮化物/氧化物之複晶矽薄膜電晶體的電漿鈍化效應，並 以用傳統熱氧化層為閘介電層的複晶矽薄膜電晶體作為對照標準。結果顯 示，用氧化物/氮化物/氧化物為閘介電層的複晶矽薄膜電晶體對電漿鈍化 的響應較佳，因此可得到較好的電性，並且也較能抵擋電漿損傷。另一項 與前面相關聯的研究是，在閘氧化層成長前後施以不同溫度的氨氣退火處 理，以將氮混入元件中。結果顯示，氨氣退火溫度愈高則氮混入量愈多且 元件性能愈佳，加上氫化，可使經氨氣退火過的元件有更為顯著的改善。 我們也以N2O退火製程對複晶矽薄膜電晶體電性的影響為主題進行了研究 ，實驗結果發現N2O退火時的氮化與氧化效應，是改善元件電性的兩大主 因。除上述與氮或氮氧化物相關的研究外，論文中，亦對於用氟離子佈植 技術來增加非晶矽結晶後晶粒大小並製成複晶矽薄膜電晶體後所得的特性 ，進行了廣泛的研究。以二次離子質譜儀及穿透式電子顯微鏡分析材料特 性，經對照元件電性分析後發現，晶粒增大和氟本身可鈍化缺陷的雙重效 應是電性改善的主因，尤其是前者使得載子移動率可大幅度地增加。氫化 後載子移動率可再進一步提高。為避免因氟離子植入而引起的雙閘極效應 ，使用較薄厚度的膜並配合較高能量的氟離子佈植是必要的。最後，我們 對複晶矽薄膜電晶體的輻射效應進行研究。發現輻射照射會使氫化前的n- 和p-通道複晶矽薄膜電晶體及氫化後的p-通道複晶矽薄膜電晶體的臨界電 壓往負向偏移，卻使氫化後的n-通道複晶矽薄膜電晶體的臨界電壓往正向 偏移。這是因為氫化後的輻射照射打斷了部份鍵結較弱的矽氫鍵，而使氫 化處理過之複晶矽薄膜電晶體的次臨界特性大幅劣化所致。關於氫化前臨 界電壓會往負向偏移，主要是因輻射照射在氧化層中引起的正電荷所致。 先預作一次輻射照射可以提高氫化元件的抗幅射能力。 Firstly, electrical characteristics of thin-film transistors fabricated on nitrogen-implanted poly-Si were investigated. Results showed that incorporated-nitrogen had a passivation effect. Hot-carrier reliability was also improved. A donor effect of the nitrogen in poly-Si was found which affected overall passivation effect on the p- channel TFT's. Then, effects of plasma passivation on poly-Si TFT's using thin stacked oxide/nitride/oxide (ONO) gate-dielectrics were explored. Results showed that compared to O devices, ONO devices can be improved more after H2-plasma , and obtain better electrical characteristics. Moreover, the ONO devices could be more resistant to plasma-induced damage. NH3-annealing is another choice to incorporate nitrogen. Results showed the higher the NH3-annealing tem- perature, the more the incor- porated nitrogen and the better the device performance. With hydrogenation, the NH3-annealed TFT had the more remarkable improvement. The reliability was also improved. Electrical characteristics of poly-Si TFT's using N2O-annealed gate-oxide were also studied. It is shown that both n- and p-channel poly- Si TFT's can be improved for this N2O-anneal process. The improvement is possibly due to the simultaneous nitridation and oxidation effect of N2O. A comprehensive study on characteristic of n- and p-channel poly-Si TFT's fabricated on fluorine- implanted-then-crystal- lized a-Si was presented. It was found that field-effect mobilities of both n- and p-channel devices were improved by the fluorine implantation due to the enhanced grain size and the fluorine passivation effect. Finally, radiation effects on n- and p-channel poly-Si TFT's was investigated. Negative Vth shift is mainly attributed to the presence of positive oxide charges after irradiation. For the hydrogenated n-channel devices, the Vth shift of n-channel device became positive due to the seriously degraded sub- threshold character istic. The radiation hardness of the hydrogenated