氫含量對於矽鍺閘極元件之特性與可靠度分析

Abstract

在本研究中，我們探討了不同氫含量對於具有矽鍺閘極的深次微米電晶體的性能影響和可靠度分析。使用矽鍺當P型金氧半場效電晶體(PMOSFETs)之閘極有許多優點，包括有效降低閘極空乏效應並且改善閘極片電阻。為了改變在電晶體中的氫含量，元件分成三種不同的製程條件。對照的樣本是使用氮氫混合氣體退火(forming gas anneal)，另一種條件則是採用氮氣退火，第三種條件則是在的TEOS覆蓋層之前先使用電漿增強式化學氣相沈積一層氮化矽。我們研究不同條件的P型金氧半場效電晶體的負偏壓溫度不穩定特性(NBTI)。氮氫混合氣體退火和具有氮化矽覆蓋層的元件都可以有效地修補界面的缺陷，但是二者具有不同的臨界電壓。雖然氮化矽覆蓋層可以大量地降低界面狀態密度，並且增加反轉層的電容，但從結果可看出覆蓋的氮化矽層會使得NBTI特性變得更差。使用電漿增強式化學氣相沈積的氮化矽含有大量的氫，也就是使可靠度惡化的主要原因。然而，使用氮氫混合氣體退火展現出不同的行為。值得注意的是，使用氮氫混合氣體退火或氮氣退火在基本電性以及負偏壓溫度不穩定特性上具有幾乎相同的趨勢，唯獨在一開始的界面狀態密度界不同。而具有氮化矽覆蓋的元件，不論使用氮氫混合氣體退火或氮氣退火皆具有相同的特性。電性回復效應可以有效降低界面狀態的產生，因此動態負偏壓溫度不穩定性與交流應力也被用來模擬電路中元件的操作特性。我們觀察到，交流應力頻率強烈影響具有氮化矽覆蓋層元件之臨界電壓改變、與界面態位之產生。

In this work, the effect of hydrogen species on the performance and reliability of deep submicron transistors with SiGe gate was studied. Using SiGe as gate material of PMOSFETs has numerous advantages, including reduced gate depletion effect and improved gate sheet resistance. To set various hydrogen contents in the test transistors, wafers were split three ways. Specifically, the control split was annealed in forming gas, while the N2-split was annealed in nitrogen ambient and the SiN-split received an extra PE-SIN layer in addition to the normal TEOS passivation. Negative bias temperature instability (NBTI) characteristics of PMOSFETs of all splits were investigated. Both forming gas and SiN capping can effectively passivate interface states, and result in threshold voltage difference. Although SiN capping would greatly reduce interface state density and increase inversion capacitance, our results indicate that the SiN capping may simultaneously aggravate the NBTI characteristics. An abundant hydrogen species contained in the PE-SiN layer may be the culprit for the worsened reliability. However, forming gas anneal shows a different behavior. In particular, forming gas and N2 anneals result in almost identical electrical characteristics and NBTI behaviors, albeit their fresh Dit is quite different. Unlike SiN capping, the NBTI characteristics of PMOSFETs receiving either forming gas or N2 gas anneal are nearly identical. Dynamic NBTI and AC stress characteristics were used to simulate the switching operation of PMOSFETs in circuits, the electric passivation effect effectively reduces the interface states generation. Both threshold voltage shift and interface states generation are strongly dependent on frequency for devices with SiN capping layer.