利用交直流陽極氧化補償技術改善超薄閘極氧化層品質

Abstract

近年來由於積體電路元件尺寸不斷縮小，對閘極氧化層的要求也越嚴格，對於超薄閘極氧化層的研究，當縮小氧化層厚度的同時也能降低漏電流並提高穩定度方面議題也相形重要。本篇論文乃提出室溫陽極氧化備製來補償快速熱製程氧化層的缺陷，利用此方法所長出來的氧化層將會有較小的漏電流。我們先介紹直流陽極氧化的成長機制，接著以交直流的技術以補償超薄閘極氧化層，由實驗結果可看出這種技術能改善氧化層的特性。 論文首先簡述對閘極氧化層的研究及整篇論文的動機。在第一章中，對實驗的設備及所使用的量測儀器做簡單的介紹。第二章首先回顧過去對定電壓陽極氧化機制的基本理論，這些模型提出在陽極氧化過程中可能發生的電化學反應。此外，本章利用不同交直流氧化條件來補償快速熱製程氧化層的不完全。探討的效應包括：1. 交流切換頻率。2. 補償時間長短。3. 直流振幅大小。 接著，在第三章我們對無陽極氧化與經過陽極氧化補償後的氧化層做比較，比較在反轉區與聚積區的電流密度，發現在陽極氧化補償後反轉區雖有比較小的漏電流，但隨著時間經過，電流降低速度比較慢。我們所製備氧化層在聚積區的漏電流，與世界標準非常接近，也肯定了交直流陽極氧化補償技術的功效。

The scale of the VLSI device has downsized in recent years. The studies of the ultra-thin gate oxide have progressed rapidly due to strict requirement of the gate dielectric. When gate oxide becomes thinner, it is important to lower the leakage current and improve the reliability. This work proposes room temperature anodic oxidation or anodization (ANO) to compensate the defects existed in the oxides grown by rapid thermal oxidation (RTO). By this method, we can get oxide with lower leakage current and better performance. First, we introduce the mechanism of the direct current ANO. Then, compensate the ultra-thin gate oxide with direct-current superimposed with alternating-current anodization (DAC-ANO) technique. We can find the quality of the oxide has been improved. In the beginning of this work, we introduce study of the gate oxide and the motivation of this thesis. In chapter 1, the experimental setup and the measurement system are also briefly described. In chapter 2, basic theories about the mechanism of the constant voltage ANO of silicon are reviewed. These models suggest possible electrochemical reactions during the ANO. Besides, we utilize different DAC-ANO conditions to compensate the defects in RTO oxides. The conditions including 1. frequency effect, 2. duration effect, and 3. DC amplitude effect are inspected. Next, in chapter 3, we compare the current densities in inversion region and accumulation region of the RTO oxides with and without ANO-DAC. We found that the leakage current in inversion region is smaller with ANO-DAC compensated, but the current density lowering is slower with time past. We also can get similar current scale with the world level in accumulation region. It confirms the contribution of DAC-ANO.