複晶矽薄膜電晶體通道摻雜與氫化效應之研究

Abstract

一般複晶矽薄膜電晶體若未經過氫化及通道摻雜之手續其臨限電壓及漏電 流均大到無法令人接受，故適當的氫化和通道摻雜過程往往是必需的。在 本論文中我們研究了未摻雜及硼、砷摻雜之p通道薄膜電晶體。從實驗的 資料我們發現較厚的薄膜(86nm)可得到預期的結果–即在適當之通道離子 佈植條件下，其臨限電壓隨著砷摻雜量之增加而增加；隨著硼摻雜量之增 加而減小。但是較薄之薄膜(26nm)在很少量之通道離子佈植條件下，卻表 現出鈍化的特性。此外，我們發現當複晶矽薄膜愈薄時其源極／汲極電阻 經過氫化後有愈明顯增大的現象。所以較薄之薄膜電晶體雖然具有較佳的 電特性，但是由於氫化後源極／汲極電阻有劇烈的變化(當通道厚度小 於20nm時可能變大7∼8倍)，導致導通電流提早飽和，從而降低了轉移電 導和場效移動率，故在製造很薄之薄膜電晶體時，應盡量地縮短源極／汲 極電阻的長度，使其對電性之影響減至最低。 With regard to the unpassivated poly-Si TFTs with undoped channel, the magnitude of the threshold voltage is greater than 5V and the leakage current is usually not available. Thus the necessary channel doping and hydrogenation are required to reduce threshold voltages to acceptable values. In this thesis , we have studied the characteristics of the p-channel TFTs with boron and arsenic implantation doses before and after hydrogenation. From the experimental results, it is seen that the thicker films of 86nm exhibit the characteristics just as those we have predicted that the threshold voltage increases with the channel arsenic dose and decreases with the channel boron dose for properly channel implantation. However, the thinner films of 26nm show the features of passivation for very lightly channel implantation. In addition, it is seen that the increase of the Source/Drain resistance after hydrogenation becomes more significant as the thickness of the polysilicon is scaled down. Therefore, though the TFT with thinner channel thickness(26nm) exhibits better characteristics, its on current is limited by the drastically increased Source/Drain resistance after hydrogenation. In view of the reason mentioned aboved, it is recommended that the length of Source/Drain region should be decreased in order to minimize the influence of Source/Drain resistance on electrical characteristics.