以雙(二乙基醯胺)矽烷輝光放電製備之有機無機混成介電薄膜性質之研究及其於氧化鋅薄膜電晶體之應用

Abstract

本研究針對雙二乙基醯胺矽烷(以氬氣作為載流氣體)與氧氣於電漿輔助化學氣相沉積系統中沉積之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，同時將其應用在氧化鋅薄膜電晶體之閘極介電層，並分析薄膜電晶體之特性。此外，也針對薄膜阻水阻氧特性進行研究，以應用於薄膜封裝。 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，同時藉由水接觸角量測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，隨著基板溫度的提升，薄膜中的無機Si-O-Si鍵結量也會隨之提升，使薄膜趨向於無機之二氧化矽；而O2/Ar流量比例的提高，也同樣地會增加材料中Si-O-Si的鍵結量，所得到的結果與水接觸角之分析相符合。接著我們利用奈米壓痕儀量測薄膜之楊氏係數與硬度，當無機鍵結逐漸增多，薄膜之楊氏係數及硬度逐漸的增大，符合無機薄膜較脆硬的特性。為瞭解薄膜的電性，文中利用平面電容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。隨著基板製程溫度的提升或是製程的O2/Ar流量比例的增加，皆使漏電流密度降低，介電常數也隨之下降，最後趨近於無機二氧化矽的相對介電常數值3.9。 接著將所製備之有機無機混成薄膜作為氧化鋅薄膜電晶體之閘極介電層，偏向無機的介電薄膜較為緻密，使電晶體擁有較低的閘極漏電流，以及較低的關電流值；而使用偏向有機之閘極介電層的電晶體，介電層與通道層之間表面性質較佳，因此有較小的次臨界擺幅。最佳的介電層製程參數為基板製程溫度135℃，O2/Ar=50以及電漿功率55 W。當電晶體的介電層厚度為400 nm，電晶體W/L=320

In this thesis, we investigate the properties of organic-inorganic hybrid films deposited from a mixture of oxygen and newly-emerging organosilicon precursor, bis(diethylamino)silane, using Ar as the carrier gas by plasma enhanced chemical vapor deposition (PECVD). These organic-inorganic hybrid materials are then used as the gate dielectrics for ZnO thin-film transistors (TFTs) and applied as a permeation barriers in the thin-film encapsulation applicaiton. The results from Fourier transform infrared spectroscopy and contact angle measurement reveal that the films are more inorganic-like (SiO2-like) when either the substrate temperature or the O2/Ar flow rate ratio increases. More inorganic-like films have lower leakage current and their relative dielectric constants approach 3.9 as SiO2. Nanoindentation is used to analyze the Young’s modulus and hardness of the hybrid thin film. As the film becomes more inorganic-like, it’s Young’s modulus and hardness increase. The hybrid material is then used as the gate dielectrics for ZnO TFTs. An on/off current ratio of 〖10〗^7, threshold voltage of 9.6 V, subthreshold swing of 1.6 Vdec-1, gate leakage current of 2.07×〖10〗^(-10) A, and field-effect carrier mobility of 70 cm2V-1s-1 are achieved for the TFT using the gate dielectric deposited at a substrate temperature of 135℃, O2/Ar flow rate ratio of 50, and process power of 55 W. In comparison with pure SiO2 in TFT applications, the appealing feature of the organic-inorganic hybrid material is its adjustable composition. The organic component seems to offer better interface between the gate dielectric and ZnO channel, resulting in a lower subthreshold swing, while the inorganic component possesses lower gate leakage current. In the application of thin-film encapsulation, inorganic compounds serve as permeation barrier while organic compounds offer mechanical flexibility and reduce the physical defect formation. With the optimized process condition, same as that for gate dielectrics, a water vapor transmission rate of 7×〖10〗^(-6)g/m2-day and an optical transparency higher than 90% in visible region are obtained in a 1.5