超薄閘極氧化層電荷傳輸和C-V模擬與特性

Abstract

此篇論文的主旨在於討論N型與P型金氧半場效電晶體當中的超薄(<30A)閘極氧化層之C-V與I-V特性的量測與計算，我們發展出一套量子模型用於模擬在直接穿隧模式下的表面量子化與電荷傳輸等現象，模擬所得到的I-V與C-V特性和量測結果極為符合，由模擬與量測結果得知，在相對較厚(>~18A)的氧化層中，氧化層厚度可經由C-V與I-V量測方法來估計，然而對於深次微米製程當中所需的超薄(<~18A)氧化層而言，I-V量測的方法較適合用來萃取氧化層厚度，I-V量測法包括Ig-V與Ib-V量測方法，在N型金氧半場效電晶體當中由於在正閘極偏壓時並沒有表面量子化的現象，故價帶電子穿隧電流(基極電流)較適宜用於厚度量測。 在本篇論文中，我們將解出波松和薛丁格聯立方程式。由薛丁格方程式可得到在反轉層中能量量子化和相對應的波函數。而藉著求解波松方程式，可觀察複晶閘極空乏效應。利用修正過後的WKB趨近式而得之傳導帶和價帶的電子穿透機率，可用來計算閘極與基極穿隧電流。因此，我們可以分別利用C-V， Ig-V和Ib-V得到基極、複晶閘極摻雜濃度和氧化層厚度。

The C-V and I-V characteristics in ultra-thin gate oxide (<30□ n- and p-MOSFETs and capacitors were measured and calculated. A quantum-mechanical model was developed to simulate surface quantization and charge transport across oxides in direct tunneling regime. Excellent agreement between the measured and simulated I-V and C-V characteristics is obtained. Based on the simulation and measurement, it has been shown that for relatively thick oxides (>~18□ the oxide thickness can be determined by either the C-V or the I-V methods. However, for ultra-thin oxides (<18□ which is necessitated in the sub-0.1mm technology, the I-V method is more suitable for the determination of oxide thickness. Two I-V methods, Ig-V and Ib-V, can be used to extract oxide thickness. Due to the absence of surface quantization at a positive gate bias in nMOSFETs, valence band electron tunneling current (substrate current) is preferable in the oxide thickness characterization. In this thesis, the Poisson and Schrodinger equations are solved self-consistently. The energy quantization and corresponding wave-functions in the inversion layer are obtained from the Schrodinger equation. The polygate depletion effect is investigated by solving the Poisson equation. A modified WKB approximation for the conduction-band and valence-band electron transmission probabilities is employed in the calculation of gate tunneling current and substrate tunneling current. The substrate doping, polygate doping and oxide thickness can be determined by the C-V, Ig-V and Ib-V separately. Abstract (English) ii Acknowledgments iv Contents v Figure Captions vi Chapter 1 Introduction 1 Chapter 2 Surface Quantization and Charge Transport Models 3 2.1 Simulation Model for Potential Distribution 3 2.2 Self Consistent Solution of Schrodinger's and Poisson's Equations 5 2.3 Results and Discussion 5 Chapter 3 C-V Simulation and Characterization 21 3.1 Gate Capacitance Modeling 21 3.2 Comparison between Simulation and Measurement 22 Chapter 4 Gate Current Modeling and Characterization 29 4.1 Transport of Conduction Band Electrons 29 4.2 Simulated and Measured Result 32 Chapter 5 Substrate Current Modeling and Characterization 40 5.1 Transport of Valance Band Electrons 40 5.2 Simulated and Measured Results 41 Chapter 6 Conclusion 49 References