以Si2H6低壓氣相沉積之複晶矽研製低溫 (<=600℃)薄膜電晶體

Abstract

本論文首先研究在各種沉積壓力下，以460℃熱分解Si2H6來沉積非晶 矽，並以其所製備之複晶矽來研製低溫(<=600℃)薄膜電晶體。為了達到 低溫薄膜電晶體的要求，我們使用TEOS，以電漿輔助化學氣相沉積系統來 沉積閘極氧化層。為了了解薄膜電晶體的特性與沉積壓力之間的關係，我 們對Si2H6所沉積的複晶矽薄膜做進一步的材料分析。我們發現明顯的氧 雜質濃度差異是造成在越低的沉積壓力下有越差的特性表現之最主要因素 ，而並非受晶粒的大小以及表面的粗糙度所主控。由於較低的氧雜質濃度 ，所以100毫托耳所沉積的元件在NH3電漿鈍化後有最好的特性表現，其中 包括場效移動率約 68 cm2/Vsec 、開 /關電流比可達 5×10sup7以及漏 電流低於1 pA/mm。另外，我們進一步以缺陷密度及活化能來探討電性。 最後，關於以NH3電漿處理來改善複晶矽薄膜電晶體的電特性，我們發現 ，在 n通道元件，予體摻雜效果阻礙了對最小電流進一步的改善。較大晶 粒的Si2H6 薄膜減少了晶界的效應，包括減少了予體在晶界的析離以及晶 界對帶電載子的捕捉，這都使得薄膜更易被雜質所摻雜。 The characteristics of low temperature ( * 600℃ ) thin- filmtransistors ( TFTs ) with polycrystalline silicon (Poly-Si) filmsprepared from amorphous Si ( a-Si ) films deposited by pyrolysis of disilane ( Si2H6 ) gas at 460℃ are investigated at various pressures.The deposition of gate oxide films by plasma- enhanced chemical vapordeposition ( PECVD ) using Tetraethylorthosilicate ( TEOS ) was introduced tomake the low temperature TFT process possible. The material analysis of poly- Si films deposited from Si2H6 gas was investigated in order to comprehendthe relations between the TFT*s performances and the deposition pressure.It is found that the obvious difference in oxygen concentration rather thangrain size or surface roughness is the main dominating factor leading toapparatus performance degrades in the lower deposition pressure.Due to the lower oxygen concentration, the 100 mTorr device after NH3plasma passivation shows the best performances, including the field effect mobility ( mFE ) of about 68 cm2/Vsec, on/off current ratio of 5E7,and off current below 1 pA/mm. The electrical characteristics were alsoinvestigated by the density of states ( DOS ) and activation energy ( Ea ).NH3 plasma treatment was performed to improve the electrical characteristics of poly-Si TFTs. However, donor effect was shown to impede furtherimprovement on Imin in n- channel devices. The larger grain size in ourSi2H6 film reduces the grain boundary effects, including the grain boundarysegregation of dopants and the grain boundary trapping of charge carriers,and made it much easier to dope.