多晶矽閘極滲雜濃度對以超薄氧化層製作的深次微米元件可靠度之研究

Abstract

對超大型積體電路來說，閘極氧化層的可靠性是一相當重要的課題。這篇論文主要是關於不同閘極摻雜濃度對閘極氧化層可靠性的影響。電漿蝕刻以及電阻灰化過程產生的電漿傷害也是我們研究的主要課題之一。 近幾年前人的研究發現，多晶矽閘極的摻雜離子濃度對閘極氧化層的可靠性的影響很大。在這篇論文中，用以研究的元件氧化層厚度從2.5nm到6 nm 不等。研究發現，在正閘極偏壓下的累積崩潰電荷（Qbd）會隨著閘極摻雜濃度增加而有顯著提升；而負閘極偏壓下的累積崩潰電荷卻和濃度沒有顯著關係。高低摻雜濃度的累積崩潰電荷差距，也隨著氧化層厚度降低而降低，顯示這種現象在氧化層變薄後會更加明顯。這個現象主要由於閘極多晶矽和氧化層間的界面受到摻雜離子的改變。 在另一方面，多晶矽閘極的摻雜濃度和電漿傷害間的關係也是這次實驗的主要課題。和之前所提到的結論相反，在低摻雜濃度的元件我們只觀察到很小的電漿傷害；反之對高摻雜濃度的元件而言，其受到之電漿傷害卻非常大。這結果顯示製程中的電漿環境表現較類似電壓源，在調整電位能時對元件所導致的傷害，可能因為閘極濃度的降低而受到壓制所致。

Reliability of ultra-thin gate oxides (Tox < 10 nm) is a major concern for ULSI manufacturing. The thesis reports about the evaluation of reliability of ultra-thin oxide devices with various poly-gate doping concentrations. Charging damage effects from plasma etching and subsequent ashing were used to explore effects of poly-gate doping concentration on plasma charging damage. Recent studies have found that the conditions of the polysilicon gate can play an important role in the reliability of thin gate oxides. In this thesis, the impact of gate doping concentration on the ultra-thin gate oxide reliability was investigated for oxides with thickness ranging from 2.5 to 6 nm. It was observed that charge-to-breakdown (Qbd) under substrate injection stress shows a notable improvement as the doping concentration increased while charge-to-breakdown under gate injection stress shows independent of the doping concentration. The difference of Qbd between high and low doping concentrations becomes much more significant as the oxide is scaled down. Such findings could be ascribed to the dopant-related stress/strain at the gate/oxide interface. On the other hand, effects of poly-gate doping concentration on plasma charging damage were also investigated. Contrary to those findings above, negligible charging damage was observed on device with lower gate doping concentration (5x1014cm-2). Plasma process-induced oxide degradation increases with poly-gate doping concentration. These interesting findings suggested that the plasma environment act more like a voltage source, which is due to the potential adjustment between plasma and substrate potentials, rather than a current source.