複晶矽薄膜及其電晶體之研究

Abstract

利用雷射退火方式所形成的複晶矽薄膜電晶體，由於其有較大的晶粒故其臨界電壓與載子遷移率均優於傳統爐管退火方式所形成的複晶矽薄膜電晶體，但其表面平坦度及在同一晶片上的均勻性卻是所需要改善的地方。 在本論文中，我們利用雷射來作為摻雜質活化的方法，此方法有降低整體製程溫度的效用。但經此方法處理後的元件電性均有些微劣化情形，且在通道與汲極和源極介面處會使晶粒產生不連續的現象而使電晶體的漏電流上升。在於較薄通道的元件中，由於雜質為完全活化及較容易跑入通道中形成元件特性劣化情形，而雷射退火方式卻有改善其摻雜質活化的現象而使電晶體的效能上升。 在本論文中發現經過雷射活化後的元件可靠度較傳統爐管活化方式處理的元件差；加大電壓stress後，發現經過雷射活化後的元件特性有較大的變動值─臨界電壓變大、次臨界波動變大、漏電流上升等。

In this thesis, excimer laser (KrF) processes are introduced to improve the performance of TFTs. The laser crystallized poly-Si TFTs have larger grain size but rougher surface which yield more variations on device characteristics, comparing to SPC poly-Si TFTs. The performance of laser crystallized TFTs is better than that of SPC TFTs. However, the mobility of laser crystallized TFTs is similar to that of SPC TFTs , which is due to larger surface roughness in laser crystallization in spite of larger grain size obtained. Laser activation method after ion implantation can lower the process temperature, and the TFT performance of laser activation is similar to that of conventional furnace activation. However, the leakage current for laser activation is higher than that for furnace activation, which is caused by grain modification near S/D side and will result in increased trap state density.