以六甲基二矽氧烷與氧氣輝光放電製備之閘極絕緣層於氧化鎂鋅薄膜電晶體之應用

Abstract

本論文針對六甲基二矽氧烷與氧氣於電漿輔助化學氣相沉積系統中沉積的有機無機混成薄膜進行了薄膜製程條件及材料性質的研究，同時進一步應用在氧化鎂鋅薄膜電晶體的閘極介電層，並評估薄膜電晶體的特性。 實驗上首先利用傅立葉轉換紅外線光譜儀來檢視薄膜成分隨製程參數的變化，同時運用水接觸角來佐證紅外線光譜儀的結果。在傅立葉轉換紅外線光譜中發現，隨著O2/HMDSO流量比例的提高，介電薄膜中的無機Si-O-Si鍵結量會跟著提升，使薄膜趨向於無機的二氧化矽，而製程功率提高也同樣提增加材料中的Si-O-Si的鍵結量，所得到的結果與水接觸角的分析相符合。同時為了瞭解薄膜的電性，文中利用平面電容三明治電極結構來分析不同薄膜成分下的漏電流密度與相對介電常數，以獲得相關的電性參數。漏電流會隨著薄膜製程的O2/HMDSO流量比例的增加而下降。隨著鍍膜功率的上升，漏電流也隨之降低。隨著O2/HMDSO流量比例上升及鍍膜功率的上升，介電常數則隨之下降，使薄膜介電常數趨近於無機二氧化矽的相對介電常數值3.9。 所製備的有機無機混成薄膜應用於氧化鎂鋅下閘極薄膜電晶體之閘極介電層。可以發現隨著O2/HMDSO流量比例的提高，薄膜電晶體的暗電流則被有效的降低，進而拉高電流開關比，同時臨界電壓也會跟著增加。當電晶體的介電層厚度為350 nm，電晶體W/L=80 m/15 μm，開關比則到達2.6×10^5，臨界電壓約為9.07伏特，而閘極漏電流也低於5.8×10^(-10)安培。我們也嘗試了三種不同的方式來沉積介電薄膜並觀察電晶體的表現，分別為升溫法、分段鍍膜法以及漸變鍍膜法，由於高溫與電漿轟擊對於薄膜會有所傷害，因此前兩種方式效果較差，而漸變鍍膜法所鍍出的介電薄膜則具有較低的閘極漏電流。

This thesis reports the experimental results of organic-inorganic hybrid dielectric layer deposited from HMDSO and oxygen by Plasma Enhanced Chemical Vapor Deposition. The films deposited under various O2/HMDSO flow ratios and power are examined and applied to the gate dielectric layer of bottom gate MgZnO thin film transistors (TFTs). Fourier transform infrared spectroscopy (FTIR) is used to analyze the bonding characteristics of the films. The portion of Si-O-Si bonding increases with the increases of the O2/HMDSO flow ratio and the deposition power. The results are confirmed by contact angle experiments. As the deposition power and O2/HMDSO flow ratio increase, the films become more inorganic-like and the leakage current is also lowered. The relative dielectric constant also approaches 3.9 of SiO2. The organic-inorganic hybrid films are also used as the gate dielectrics for bottom gate MgZnO thin film transistors. MgZnO TFTs with dielectric films deposited at relatively high power exhibit poor transfer characteristics. With our current deposition apparatus, the best dielectrics for MgZnO TFTs are deposited at O2/HMDSO=40 and 45 W rf-power. For a TFT of W/L=80 μm/15 μm and a gate dielectric thickness of 350 nm, the on/off current ratio can reach 2.6× 10^5; the threshold voltage is around 9.07 V; the leakage current is below 5.8×10^(-10)A.