次臨界區奈米級金氧半場效電晶體之隨機擾動訊號切換強度之建模化

Abstract

隨著金氧半場效電晶體(MOSFET)逐漸微縮趨勢的科技世代中， 隨機擾動訊號(RTS)在元件發展之中變成重要的課題。這些訊號透過 載子在矽與氧化層的接面或氧化層內缺陷捕捉-釋放的過程而產生。 這種捕捉-釋放的行為會導致源極／汲極的電流在兩個層級上波動。 此切換的強度會對元件效能有負面的影響，而我們將ΔId/Id 做為分析 RTS 的一項指標。 在實驗中不容易觀察到源極／汲極電流的波動，此外通常會在不 止兩個層級上波動，多層級的現象會複雜化RTS 的分析，而這也不 是這篇論文研究的方向。更重要的是，要控制影響RTS 現象的參數， 諸如基層參雜濃度、元件大小、缺陷的位置是相當困難的，然而我們 可以透過TCAD 模擬建造各式各樣的元件，進而輕易的調整這些參 數。 傳統的RTS 模型建立在通道的位能是平的前提下，而這在次臨 界區是行不通的。問題在於當閘極電壓很小時，位能障礙在通道中央 是最大的。在此篇論文中，我們透過擷取沿著通道方向及寬度方向的 傳導帶能量，將本質的位壘納入考量。為了得到RTS 指標ΔId/Id 我們 建立了兩個很類似的結構，一是有缺陷的，另一個則沒有。ΔId/Id 可 以透過萃取兩個結構的汲極端電流計算而得。 我們之前的研究，將源極／汲極電流的切換強度，在次臨界區及 過臨界區分別表示為與等效長度及等效區域有關。而在此次的研究， 不僅是涵蓋一些RTS 的模型，也將缺陷的位置因素ηs1 及隨機參雜濃 度係數ηs2 及ηc 考慮進去。

With the technology generation down-scaling trend of metal-oxide-semiconductor field effect transistors (MOSFETs), random telegraph signals (RTS) turn into an essential issue in device development. These signals take place through the carrier capture-emission process via a defect at the silicon/oxide interface or in the oxide layer. The capture-emission behavior of the defect causes the witching of source/drain current between high and low level. The switching magnitude may have negative impact on device performance of MOSFETs, and it can be displayed by calculating ΔId/Id as an index to analyze the characteristic of RTS. In the experiment, it is not easy to observe the two-level switching magnitude of source/drain current. Besides, it usually appears in terms of more than two levels. Multiple levels would make the issue more complicated, which is not the major issue in this thesis. Most important of all, dealing with all the parameters, which may affect RTS phenomenon, such as the substrate doping concentration, the device size, and the IV position of defect into control through experiment, are quite difficult. However, we can easily modify these parameters by building all kinds of device characteristics in TCAD simulations. A conventional RTS magnitude model was derived in flat potential distribution across the whole channel, but now fails in subthreshold region. The reason is that the potential barrier is highly localized in the middle of channel under a small gate voltage. In this thesis, we establish a new model taking the local barrier into account, which is shown as conduction band energy along channel length and channel width direction. To obtain RTS index ΔId/Id, we run two cases in device simulations: one of a defect at the silicon/oxide interface or in the oxide layer, and one of no defect. Then, corresponding drain terminal currents are simulated to determine ΔId/Id. In our previous work, the switching magnitudes of source/drain current measured in both subthreshold and above-threshold regions were separately transformed into the effective size of the affected region and the effective area of the percolation path. In this work, many of well-known RTS models are considered, by taking into account the defect position factor ηs1 and the random discrete doping coefficient (percolation effect) ηs2 and ηc.