低溫高介電係數材料於有機薄膜電晶體製程之研究

Abstract

在此論文裡，我們研究了高介電常數材料與薄膜電晶體在超臨界二氧化碳流體混合水的熱處理下其電性的改變並將此高介電常數薄膜為絕緣層製造有機薄膜電晶體。首先，在室溫下，利用真空濺鍍系統成長極薄的氧化鉿薄膜，厚度約為7奈米，為了取代傳統的高溫退火製程，我們使用了溫度約150°C超臨界流體混合水的技術，為了驗證超臨界流體混合水能有效的使水分子進入到氧化鉿，進而減少薄膜的缺陷密度，我們經由紅外線光譜儀、熱脫附常壓游離質譜儀與X射線光電子能譜來做材料分析，結果均顯示於氧化鉿薄膜內氧的含量增加，而厚度為7奈米氧化鉿薄膜在閘極電壓3伏特的操作下，其單位面積漏電流約為2×10-7 A/cm2，並且得到較高的崩潰電壓，崩潰電壓約為24伏特，傳導機制亦由原本未經過處理的量子穿隧效應轉換為熱放射效應，以上主要的原因是由於氧化鉿薄膜的缺陷密度減少。 此外，我們利用經處理過的氧化鉿薄膜為絕緣層去製作有機薄膜電晶體，發現經由超臨界流體技術的處理之後，有機薄膜電晶體有較好的元件特性，其有機薄膜電晶體中的臨界電壓、場效移動率、次臨界擺幅和開關電流比例都有顯著的提升。這些改善主要是因為超臨界流體的技術，能有效修補懸鍵，進而減少氧化鉿絕緣層的缺陷密度。 由這些結果均顯示，藉由超臨界流體混合水的技術，能減少薄膜的缺陷密度。可預期的，若超臨界流體的特殊特性整合在高介電常數材料與有機薄膜電晶體，將具有其優勢。

In this study, supercritical fluids (SCF) technology is employed originally to effectively improve the properties of low-temperature-deposited metal oxide dielectric films and fabricate organic silicon thin film transistors (OTFTs). In this work, 7 nm ultra-thin Hafnium Oxide (HfO2) films are fabricated by sputtering method at room temperature, and replacing the conventional high temperature annealing with supercritical fluids treatment at 150 °C. The supercritical fluids act a transporter to deliver H2O molecule into the HfO2 films for repairing defect states. After this proposed process, the absorption peaks of Hf-O-Hf bonding apparently raise and the quantity of oxygen in HfO2 film increases from FTIR and TDS measurement, individually. The leakage current density of 7 nm HfO2 film is cut down to 2×10-7 A/cm2 at |Vg| = 3 V, and the conduction mechanism is transferred from quantum tunneling to thermal emission because of the significantly reducing the defects in the HfO2 film. Moreover, the higher breakdown voltage is obtained, reaching |Vg| = 24 V. Additionally, supercritical fluids technology is also proposed to effectively passivate the defect states in HfO2 insulator of OTFTs at low temperature (150 °C). After the treatment of supercritical fluids mixed with water and propyl-alcohol, the characteristics of OTFTs are better. This proposed technology is also used to improve the transfer characteristics of OTFTs at 150 °C. From theses experimental results, the better sub-threshold swing, lower off-current, higher on/off current ratio and higher mobility are obtained, such that the supercritical CO2 treatment provide a novel method to enhance the transfer characteristics of Organic thin film transistors