區域性應力通道之氧化鉿n型金氧半場效電晶體特性及可靠度之改善

Abstract

在本次的實驗中，我們成功的呈現了具高水準表現之區域性應力通道氧化鉿金氧半場效電晶體，而其區域性應力是由閘極多晶矽/非晶矽堆疊結構與覆蓋氮化矽所提供的。通道長度為0.35微米元件中，在維持住相同的關閉電流下，我們增加了約百分之九十的驅動電流與百分之七十的轉移電導，且隨著通道長度縮小其驅動電流與轉移電導的改善也隨之增加。另外一方面，當汲極引起能障下降(Drain Induced Barrier Lowering)現象獲得控制的同時，有氮化矽層覆蓋的元件其次臨限擺幅也能獲得相當程度的改善。而此高水準的表現與改善情形亦可在脈波電流電壓量測下觀察到相同的結果。 有覆蓋氮化矽之元件因為有氫去修補高介電氧化層與矽基板的介面，所以會有較小的充電泵(charge pumping)電流，這也代表具覆蓋氮化矽之元件會有較佳的高介電氧化層與矽基板之介面。相對地，大量矽-氫鍵的存在則導致了元件在熱載子惡化(hot carrier stress)量測下其臨限電壓的漂移更為明顯，且隨著覆蓋氮化矽層越厚其臨限電壓變化也隨之增加。在正偏壓溫度不穩定(Positive Bias Temperature Instability)量測方面，有覆蓋氮化矽的元件其臨限電壓變化與驅動電流下降都比較小，推測原因為氮進入了氧化鉿層去修補了氧化鉿的缺陷。最後，我們將覆蓋氮化矽的元件操作在動態臨限電壓(dynamic threshold voltage)的模式下，可以同時獲得高水準表現與低操作電壓的兩項優點。以通道長度0.35微米元件來看，其轉移電導增加了135％且次臨限擺幅(subthreshold swing)也改善了40%；在可靠度表現方面，以動態臨限電壓的模式作一萬秒熱載子惡化量測後，發現有覆蓋氮化矽層的元件其臨限電壓漂移與驅動電流下降都表現得相當傑出。

In this work, a high-performance local strain channel nMOSFETT with HfO2 gate dielectrics has been fabricated by using poly-Si/α-Si stacks and capping nitride layer. The driving current (ION) and transconductance (GM) can be increased about 90% and 70% for the 0.35μm device with keeping the quite low off current. Both improvements of ION and GM would be increased with channel length decreasing. On the other hand, the subthreshold swing could also be improved for the SiN-capped devices with negligible Drain Induced Barrier Lowering (DIBL) effect. Moreover, the increase in ION and GM can be also observed under pulsed-IV operation. The less charge pumping current can be observed for the SiN-capped devices due to hydrogen incorporation into HfO2/Si interface, indicating that the SiN-capped devices would have better HfO2/Si interface. However, the hot carrier stress induced threshold voltage shift and ION degradation would become more serious owing to extra Si-H bonds, and this distortion increased with increasing capping nitride thickness. On the other hand, the positive bias temperature instability (PBTI) characteristics would be improved for the SiN-capped devices such as ION degradation and Vth shift due to nitrogen incorporation into HfO2 thin films. Finally, the SiN-capped devices were operated under dynamic threshold (DT) voltage operation in order to get higher performance with quite low operation voltage. The GM can be increased about 135%, and subthreshold swing can be improved about 40% under DT operation mode for the 0.35μm device as compared with the conventional mode. Nevertheless, the tolerant VTH, ION and GM degradation can be observed for the SiN-capped HfO2 nMOSFETs even after 10000 seconds hot carrier stress with DT operation