次微米MOS元件中因熱載子效應引起氧化層傷害之探討

Abstract

小幾何MOS元件的汲極與閘極附近的熱載子效應(Hot carrier effect)為 元件可靠性的重要議 題之一. 氧化層的破壞如界面狀態 (Interface States)和固定電荷 (Fixed Oxide Charge) 是由熱載子效 應所引起, 它 們對元件或電路的可靠性甚為重要. 基本上, 有兩種 方法可 以被用來探 討界面狀態和氧化層固定電 荷 , 第一種是閘極電流(Gate current)的特 性化 ;另一種是基片電流(Substrate Current) 的特性化 . 本論文 研究 目的是藉由電荷幫浦法 (Charge pumping technique),發展 出界面 狀態 的空間分佈和固定捕捉 電荷的特性關係 . 其中我們 採用了三 種不同的 方法 , 決定界面狀態 的空間分佈以及探討元件氧化層在不同操作電壓下 的性質 . 其一係利用 傳統電荷幫浦法,變化汲極電壓,藉由二維元件模擬 器,模擬出空乏區域位置 , 以決定汲極 附近Nit的界面狀態分佈 .第二種 是利用改善的電荷幫浦法 , 找出空間分佈. 最後一種是採用一種 新穎的 轉換法.計算出界面狀態的空間分佈 . 同時, 實驗的分析過程,可 將氧化 層的界面狀態和固定電荷特性化出來,此一方法亦可擴展到靜態和 動態元 件特性退化的分析 , 最後將所得到的界面狀態 空間分佈放入二維元件模 擬器 可以驗證實驗結果的可靠性。 Channel hot electron effect in the vicinity of the drain region small geometry MOS devices has become an important device reliability issue. Oxide damages such as the interface traps (Nit) and the fixed oxide charge (Qox) caused by the hot- carrier stressing are of critical importance to the reliability of devices or circuits. Basically, two approaches can be employed to investigate the interface state and the oxide trap charge. The first one is to characterize the gate current (Ig). Another one is to characterize the substrate current (Ib). The objective of this research is the development of the interface state distribution by way of charge-pumping method and the characterization of the associated oxide trap charge. Three different approaches have been employed to determine the spatial distribution of interface states and been used to evaluate the quality of oxide for devices operated under different stress conditions. The first one is to use conventional charge pumping method by varying source/drain voltages.Two-dimentional (2-D) device simulator is used to simulate the depletion layer position such that the spatial of Nit distribution in the near drain neghborhood can be determined.