利用電漿增強型原子層沉積技術製作摻氮氧化鋅薄膜電晶體

Abstract

氧化鋅透明氧化物半導體近來有逐漸取代傳統非晶矽來當作薄膜電晶體通道層的趨勢，但經由原子沉積技術所沉積出的氧化鋅薄膜，具有高電子濃度的缺點(1019 cm-3~1020 cm-3)，易使的薄膜電晶體無法關閉，且易有漏電流的產生，所以須摻雜受體來壓制這些高電子濃度。對於氧化鋅而言，氮、磷、砷，皆是屬於受體，本論文選用氮來當作受體摻雜在氧化鋅中，並選用氨氣來當作氮的來源，並找出最佳的氧化鋅薄膜成長條件:當氨氣摻雜百分之五十時，可將電子濃度降低到1017 cm-3，並擁有霍爾移動率: 15 cm2/V-sec。 利用摻雜百分之五十氮的氧化鋅所製作的薄膜電晶體，利用鈦來當作源極與集極的金屬，且將通道層的厚度降低至30 nm時，可以有效改善所製成薄膜電晶體之電性。而且其最好之開/關電流可以達到6個數量級，最好之場效電子遷移率可以達到20.7 cm2/V-sec，並擁有turn-on電壓: 3 V。此薄膜電晶體元件在利用電子束沉積技術( E-gun)沉積二氧化矽來當作保護層，具有相當不錯的保護效果，沉積完後的薄膜電晶體特性能可維持: 開/關電流達6個數量級，場效電子遷移率可達到18.6 cm2/V-sec。當元件暴露在大氣中，其電子特性經過一個月變化很少。

Zinc oxide (ZnO) thin film is a promising transparent oxide to replace amorphous silicon used in thin film transistor (TFT), but the ZnO thin film deposited by atomic layer deposition (ALD) has high electron concentration (1019~1020 cm-3). Thin film transistor could not be turned off and exhibited large leakage current. It is necessary to add acceptor into ZnO thin film to suppress electron concentration. For ZnO, nitrogen, phosphorus, and arsenic are acceptors. When choosing ammonia as the precursor of nitrogen, the best performance is achieved when delta doping concentration of NH3 is 50%. It can reduce electron concentration to 1017 cm-3 and has hall mobility around 15 cm2/V-sec. TFT using the doping condition from above and using Ti as source and drain contact achieves the best on/off current ratio of 6 order of magnitude and the mobility could attain 20.7 cm2/V-sec with Vth=3 V. The ZnO:N TFT that use E-gun silicon oxide (SiOx) as passivation layer has good performance. The on/off current ratio can still remain 6 order of magnitude and the mobility could attain 18.6 cm2/V-sec after deposition SiOx as passivation layer. The electrical properties change very little when the passivated TFT was exposed to atmosphere for 30 days.