标题: 量子修正模式在奈米级金属氧化物半导体元件特性模拟之研究
Quantum Correction Modeling and Simulation of Nanoscale Metal-Oxide-Semiconductor Devices
作者: 汤干绍
赵天生
电子物理系所
关键字: 半导体;devices
公开日期: 2003
摘要: 随着半导体产业的发展,积体电路要求速度快、低功率、小面积,许多新元件结构用来替代单闸极金氧半场效电晶体 (Single-Gate MOSFET),本论文中介绍了常见的两种新结构元件:双闸极金氧半场效电晶体 (Double-Gate MOSFET)、全闸极金氧半电晶体 (Gate-All-Around MOSFET或称Surrounding-Gate MOSFET),并将此两种结构和绝缘式矽单闸极金氧半场效电晶体 (Single-Gate MOSFET Silicon-on-Insulator) 做物理特性和电特性的比较。当金氧半电晶体氧化层厚度低于三奈米 (3nm) 以下时,在氧化层和半导体接面处会有明显量子化效应的产生,古典的模式用来计算电子特性已经失真,必须加入量子化修正模式来表现真实电子在半导体中运动行为和电位在整个半导体结构中的分布。
水丁格-泊松 (Schrödinger-Poisson) 方程式包含了波动和粒子的二元性,可以真实描述半导体中电子的物理特性,进一步的可以探讨电子分布的机率和位置及电子浓度的分布和大小。利用数值方法离散物理方程式写入电脑程式叠代计算收敛出答案,更能有效率且准确的得到所要的结果。然而在计算二维 (Two-Dimensional) 和三维 (Three-Dimensional) 水丁格-泊松方程式时太过费时,我们引用了其他不同种的量子化修正模式来近似真实结果。其中密度梯度 (Density Gradient) 不仅迅速容易收敛,和水丁格-泊松方程式的真实描述比较也非常准确,吾人用此法做二维电性特性分析与不同半导体元件特性之比较。
经过程式模拟和特性分析,对于次二十奈米 (Sub-20nm) 全闸极金氧半电晶体在相同特性条件下和其他两种奈米元件相比较物理特性,有较好的闸极控制通道能力、较大的电子迁移率、较高的电子浓度,较低的功率消耗。在电性特性比较方面,全闸极金氧半电晶体有较好的开/关电流比 (On/Off Current Ratio),受比较小的汲极电压所造成之能障降低效应 (Drain Induced Channel Barrier Height Lowing),较低的次临界震荡 (Subthreshold Swing),及较小的临界电压 (Threshold Voltage) 变化。
Diverse device structures have been recently proposed explored, and found better characteristics than that of conventional used single-gate (SG) metal-oxide-semiconductor field-effect-transistors (MOSFETs). Among them, the double-gate (DG) MOSFETs and gate-all-around MOSFETs (GAA) have been paid of great interest in recent years. Comparing with the SG silicon-on-insulator (SOI), these structures suppress short channel effects, have high transconductance, and sustain subthreshold swing. They have a superior ability in channel control that drain induced channel barrier height lowing (DIBL), threshold voltage roll off, and off state leakage are greatly improved.
We compare the electrical characteristics for the three structures by using the quantum-mechanical (QM) simulation. In this comparison, the different gate voltage, various oxide thickness, and different channel doping concentration are designed. A comprehensive comparison leads to a conclusion that MOSFETs with a gate oxide thinner than 3nm should be carefully corrected with QM model when modeling their physical transport phenomena. The three nanoscale structures SG, DG, and GAA are explored numerically with various theoretical approaches that have been considered to study the quantum confinement effects. Those are full quantum mechanical model (e.g. nonequilibrium Green’s function) and quantum corrections to the Boltzmann transport and classical drift-diffusion (DD) and hydrodynamic (HD) transport models. In the beginning of this work, a set of Schrödinger-Poisson equations has been applied to study the quantum effect in the inversion layers, but it is a time-consuming task in the application to realistic device two-dimensional (2D) and three-dimensional (3D) simulations. In considering with the computational efficiency and simplicity, other quantum correction models are more attractive and greatly used in industrial application.
In comparison, the different quantum correction models such as the Hänsch, the modified local density approximation (MLDA), the density gradient (DG), and the effective potential (EP) model are introduced and studied. Comparing of the 2D electrical characteristics for the three structures, we use the DG method to calculate them. It is easy to converge and can be demonstrated good accuracy in physical characteristics. Finally, we get GAA has the best quality, high mobility, low threshold voltage, superior channel controllability.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT009121520
http://hdl.handle.net/11536/51968
显示于类别:Thesis