利用大氣壓電漿輔助化學氣相沉積製備不同比例之銦鎵鋅氧薄膜電晶體與雷射退火處理之電性研究

Abstract

二氧化矽過去以來用來當作閘極介電層是因為它在矽基板上的物理和電性,但是閘極漏電流會變高當閘極長度及閘極氧化層的大幅微縮時,用高介電常數閘極介電材料來代替二氧化矽可以解決氧化層微縮這個問題,用氧化物薄膜電晶體有良好的電性和高的穿透率,非晶銦鎵鋅氧化物則有相對較高的電子遷移率和好的化學穩定性的優點。 本論文旨在新製程技術開發透明氧化物半導體，藉由新穎式大氣壓電漿輔助化學氣相沉積銦鎵鋅氧化物薄膜電晶體，利用較無環境危害水溶液式硝酸金屬鹽類的前驅物，可直接在大氣環境下沉積。 首先,沉積高介電係數氧化鋯和氧化鉿來製作電容和銦鎵鋅氧電晶體,由實驗可以知道高介電係數氧化層在退火溫度500度時是最佳的,因為他有較高的電容值和較低的漏電流,之後我們利用銦鎵鋅氧當作主動通道層。很多方式被用來改善電性的效能,而其中通道層銦鎵鋅氧的比例會對元件有很大的影響,而銦鎵鋅的莫耳比例為1:1:1,1:1:2,和3:1:2,其中莫耳比例為1:1:2表現出比較好的電性效能,好的電性達到為臨限電壓0.628V、次臨界擺幅0.365V/dec、遷移率可達到19.8cm2/V-s、開關電流比達到7.34x106。 最後我們研究雷射退火在銦鎵鋅氧電晶體的作用,因為雷射退火可以提高溫度在極短的時間內和特一定點,而且可以減少電荷在閘極絕緣層裡面或通道和絕緣層的介面。結果顯示電晶體的漏電流全部都減少,銦鎵鋅莫耳比為1:1:2有最佳的電性效能,移率可達到14.36cm2/V-s 臨限電壓0.16V、次臨界擺幅0.286 V/dec、開關電流比達到6.34x107。

Silicon dioxide (SiO2) has been gate dielectric because of its physical and electrical properties on silicon substrate. But gate leakage current becomes higher when shrinking of the gate length and gate dielectric thickness. Using high dielectric constant material for gate dielectric instead of SiO2 will solve the problem of the gate dielectric thickness. The oxide-based thin film transistors have good electrical properties and high transparency. Amorphous indium gallium zinc oxide (a-IGZO) has advantages of relatively high electron mobility and good chemical stability. In this thesis, new process technology is developed to deposit IGZO films. Atmospheric pressure plasma jet (APPJ) is proposed to fabricate IGZO thin film transistors. Also, water-based metal salt solution, which is an eco-friendly precursor, is adopted, and the thin film can be deposited in atmospheric environment. First, HfO2 and ZrO2 were deposited to fabricate capacitor and IGZO TFTs. According to the experience, we discover that the annealing temperature 500°C has the best condition because of higher capacitance and lower leakage current. Then we fabricated TFTs using IGZO as active channel layer. Many approaches have been studied to improve electrical performance. The channel composition of the IGZO has a large impact on device. The atomic mole ratio of In:Ga:Zn=1:1:1,1:1:2, and 3:1:2 were used as channel layer. The atomic mole ratio of In:Ga:Zn=1:1:2 exhibit a excellent electrical performance. The good electrical characteristics were achieved, including a VT of 0.628V, a subthreshold swing (SS) of 0.365 V/dec, a mobility of 19.8 cm2/V-s and a large Ion/Ioff ratio of 7.34x106. Finally, we investigate the effect of laser annealing on the IGZO TFTs. Because laser annealing can raise the temperature for a short period at a precise position, and can reduce the charge trapping in the gate insulator or the channel/insulator interface. The results show the leakage current of TFTs were all decreased. The molar ratio of In:Ga:Zn=1:1:2 has the best electrical performance with high mobility of 14.36 cm2/V-s, a threshold voltage of 0.16, subthreshold swing (SS) of 0.286 V/dec, and an on/off current ratio of 6.34×107.