先進材料應用於低溫複晶矽薄膜電晶體和金氧半場效電晶體之研究

Abstract

在本論文中，我們利用了先進的高介電常數材料來製造高效能的低溫複晶矽薄膜電晶體。擁有高效能N型通道薄膜電晶體以不同的高介電常數介電層材料：包括二氧化鉿（HfO2）、矽酸鉿（Hf-silicate）、氧化鋁鉿（Hf-aluminum oxide）被提出，以有機金屬高介電薄膜沉積系統沉積的高介電常數介電層在低溫環境中被製作出來，分別參雜不同比例的矽或鋁組成比作為我們互相比較的主軸，並且研究其效應與可靠度。 我們發現高介電常數材料在電性上的表現有著普遍性的改善：包括有較低的臨界電壓、較好的次臨界擺幅、較高的驅動電流；在研究中，我們發現擁有複晶結構的二氧化鉿 (HfO2)薄膜會導致較大的漏電流；相對地，矽酸鉿 (HfSiOx)薄膜則表現出比較優異的熱穩定度，在高溫退火處理後仍維持其非晶狀態的結構。氧化鋁鉿 (HfAlOx)薄膜則隨著鋁的參雜量越多，亦可提高其結晶溫度。當然，矽酸鉿薄膜相較於二氧化鉿薄膜較低的介電常數，則為矽酸鉿薄膜的缺點。另外，具有較低介電常數的介面層自然形成於高介電氧化層薄膜和矽基板之間，將會導致等效氧化層厚度降低的問題。 我們也研討了有關使用高介電薄膜當作閘極介電層的複晶矽薄膜電晶體所引起的嚴重漏電流現象。我們認為高介電薄膜所產生的較高電場是引發嚴重的閘極誘發汲集漏電流(GIDL)的原因，而場發射電流為其主要的漏電流機制。不同介電層的複晶矽薄膜電晶體，其中矽酸鉿在目前的測試中展現了較佳的可靠度，主要原因在於其有較高的結晶溫度、較好的薄膜品質與較少的介面狀態密度。 最後，我們嘗試將此新開發的高介電係數材料應用在金氧半場效電晶體，並且探討較薄介電質層的結構和電性。

In this thesis, advanced High-κ materials were employed to fabricate high performance low-temperature polycrystalline silicon thin film transistors (TFTs). High performance n-channel poly-Si thin film transistors (TFTs) are demonstrated using the different High-κ dielectric with hafnium dioxide (HfO2), hafnium silicate (HfSiOx) and hafnium aluminum oxide (HfAlOx) layer are demonstrated by metal organic chemical vapor deposition system with low temperature processing. We compare with different composition ratio High-κ materials layer for our main shaft and the effect and reliability are also studied. It is found the electrical characteristic of High-κ dielectric TFTs that improve obviously：including the lower threshold voltage, the better subthreshold swing, the higher driving current. However, the large leakage current would be caused by the polycrystalline structure of HfO2 film. In contrast, HfSiOx films exhibit better thermal stability and retain the amorphous structure even after high temperature annealing. In addition, as Al content increasing of HfAlOx films that could be to raise crystalline temperature. Certainly, the lower κ compared with HfO2 film is the disadvantage of the HfSiOx films. Besides, the native interfacial layer with lower κ value always exists between the High-κ gate dielectric and Si substrate, which defeats the purpose of EOT lowering. Moreover, the higher leakage current of poly-Si TFTs using High-κ gate dielectric was also studied. Aggravated gate-induced drain leakage (GIDL) current was thought to arise from the higher induced electric field by the introduction of High-κ films, and field-emission current would be the dominant leakage mechanism. We found the HfSiOx dielectric TFTs have the better reliability due to it has the better interface, higher crystalline temperature and lower density of states. Finally, we also tried to apply the newly-developed High-κ films to the Metal-oxide semiconductor field-effect transistors (MOSFETs). And the structural and electrical properties of the thinner High-κ films were discussed.