超薄先進閘極介電層之成長與特性研究：氮氧化矽與氧化鋯及其矽酸鹽

Abstract

在本論文中，我們對於超薄先進閘極介電層在奈米級金氧半導體元件（CMOS）上的可行性進行研究。我們所研究的超薄先進閘極介電層包含氮氧化矽、氧化鋯及鋯的矽酸鹽。我們分別應用不同的化學氣相沈積（CVD）系統，成功地來成長氮氧化矽（ECRCVD）、氧化鋯及鋯的矽酸鹽（MOCVD）。藉由XPS, AFM, MEIS, HRTEM等設備，我們對這些先進閘極介電層進行物性的分析與探討。此外，我們也探討及顯示沈積後退火（post deposition anneal）的效應與改善的電性結果。 首先，我們提出一個利用XPS來分析氮氧化矽的組成，並且計算出其等效氧化層厚度的方法。利用電漿氮化處理形成的氮氧化矽及低壓化學氣相沈積形成的氮氧化矽在經過N2O退火處理後，其厚度可以藉由分析矽基板與氮氧化矽的XPS Si2p譜線來決定。至於氮氧化矽的組成，則可藉由分析N1s 與 O1s的譜線得到。這個方法可以同時提供臨場（in-situ）厚度與組成量測。電漿氮化處理形成的氮氧化矽在經過N2O退火處理後，也較傳統的二氧化矽具有較佳的電性表現。 其次，我們提出利用氧分子及一種新的六配位之鋯先驅物（precursor）Zr(Oi-Pr )2(thd)2來成長超薄氧化鋯介電層。藉由液態注入（liquid injection）系統，我們可以使用脈衝模式（pulse mode）在金屬有機化學氣相沈積（MOCVD）系統內成長氧化鋯。我們針對介電層的結構、鍵結的化學態及形態（morphology）進行研究，發現沒有Zr-C與Zr-Si的鍵結形成。但介電層具有複晶結構的晶粒，這會造成電性上的衰退。對於界面層（interfacial layer）的形成機制，我們也提出一個模型來解釋。此外，我們評估沈積後退火（post deposition anneal）對介電層的影響，並且在電性上獲得顯著的改善。 最後，我們提出利用新的鋯和矽的先驅物，搭配一氧化氮（NO）來沈積超薄之鋯的矽酸鹽。我們使用脈衝模式（pulse mode）在具備液態注入（liquid injection）系統的金屬有機化學氣相沈積（MOCVD）系統內成長鋯的矽酸鹽。我們針對介電層的結構、鍵結的化學態及形態（morphology）進行研究，發現一氧化氮可以有效減少界面層的成長；且鋯的矽酸鹽可以在低於900 ºC的退火下，維持非晶性的結構。在經過最佳化的沈積後退火（post deposition anneal）處理後，我們可以得到明顯改善的電性。對於未來的金氧半元件而言，鋯的矽酸鹽具備相當有潛力的物性與電性特質。

In this dissertation, we have investigated the feasibility of ultra-thin advanced gate dielectrics for nanometer CMOS devices. The advanced gate dielectrics include oxynitride, ZrO2 and Zr silicate. The deposition techniques for oxynitride, ZrO2 and Zr silicate are ECRCVD and MOCVD, respectively. The physical characteristics of these advanced gate dielectrics are studied by XPS, AFM, MEIS, HRTEM. The effects of post deposition anneal are also explored, and promising electrical characteristics are demonstrated. First, we propose a methodology to analyze the equivalent oxide thickness (EOT) and composition of oxynitride by XPS. The thickness of N2O-annealed oxynitride films produced by plasma nitridation and low-pressure chemical-vapour deposition (LPCVD) can be determined by analysis of the Si2p (substrate) and Si2p (bonded) XPS lines, and their composition can be determined by analysis of the N1s and O1s lines. This methodology can provide an in-situ thickness and composition measurements simultaneously. Compared to conventional SiO2, promising electrical characteristics of N2O-annealed oxynitride films produced by plasma nitridation are also demonstrated. Next, we report the first investigation of the physical and electrical properties of ultra thin ZrO2 films deposited in pulse mode using molecular oxygen and a recently developed six coordinate mixed alkoxide/β-diketonate compound, Zr(Oi-Pr )2(thd)2 (Oi-Pr is isopropoxide and thd is 2,2,6,6-tetramethyl- 3,5-heptanedionate), which are introduced into the MOCVD chamber with a liquid injection system. The film structure, chemical sates, and morphology have been studied. No evidence of Zr-C and Zr-Si bonds is found, however, the grain is polycrystalline that can lead to degraded electrical characteristics. The mechanism of the growth of interfacial layer has also been explored. The effects of post deposition anneal have been examined. Promising electrical characteristics have been investigated and demonstrated. Finally, We report, for the first time, the deposition of ultra-thin Zr silicate films using Zr(Oi-Pr)2(thd)2, Si(Ot-Bu)2(thd)2 and nitric oxide in a pulse-mode metallorganic chemical-vapour deposition apparatus with a liquid-injection source. The film structure, surface roughness, chemical state and composition of the films have been thoroughly investigated. It is found that nitric oxide can reduce the growth of interfacial layer significantly and the amorphous structure of Zr silicate can be maintained, if the annealing temperature is kept below 900 ºC. With the optimized post deposition anneal, improved electrical properties have been demonstrated. The silicate films exhibit promising physical and electrical characteristics for future nanometer metal-oxide-semiconductor devices.