氟摻雜對二氧化鉿堆疊式閘極P型金氧半場效電晶體其可靠性的影響

Abstract

本論文中，我們於源極/汲極摻雜前，先加入氟摻雜，使氟原子在後續的高溫摻雜活化過程中，擴散至通道和閘極介電層，以形成氟併入。藉此，我們深入探討氟對二氧化鉿/氮氧化矽閘極之P型金氧半場效電晶體可靠性的影響。我們發現，導入氟對元件之基本特性，並無明顯改變；但於固定電壓應力(CVS)和負偏壓-溫度應力(NBTS)量測時，有氟併入的元件具有較低的界面狀態產生、和較少的電荷捕捉，而明顯改善元件的穩定性和可靠性。 其次，我們探討電漿效應對二氧化鉿/氮氧化矽閘極之P型金氧半場效電晶體與負偏壓溫度不穩定效應的關連性、和氟併入對其影響。經由電荷泵浦電流量測，可發現不論在負偏壓-溫度應力(NBTS)前後，界面狀態密度均隨天線面積比而增加。因NBTS所導致的臨界電壓漂移，也因受到電漿充電損傷，而更形惡化，並造成嚴重的電洞缺陷。更重要的，電漿充電效應會使大天線面積比元件在二氧化鉿內的的電洞捕捉現象更為惡化，遠較界面產生的缺陷更嚴重。這和傳統以二氧化矽為閘極之P型金氧半場效電晶體，其惡化主因為電子捕捉，迥異其趣。利用氟併入，可有效增加對電漿充電損傷的免疫，因而降低具有大天線面積比元件在NBTS時的嚴重電洞捕捉現象。

In this work, F was incorporated before the source/drain implant step, which was subsequently diffused into the gate stack during later dopant activation. Effects of fluorine (F) on the reliabilities of pMOSFETs with HfO2/SiON gate stack have been thoroughly studied. We found that F introduction only negligibly impacts the fundamental electrical properties of the fabricated transistors. In addition, under constant voltage stress (CVS) and negative bias temperature stress (NBTS), lower generation rates of interface states and charge trapping are observed for devices with F incorporation, thus enhances high-k devices’ stability and reliability. Next, effects of plasma charging and fluorine incorporation on the NBTI of p-channel MOSFETs with HfO2/SiON gate stack were explored in this work. From charge pumping measurements, we confirm that the interface-state density is increased for devices with large antenna ratio, both before and after the BTS. It is clearly shown that the threshold voltage shift during negative bias-temperature stressing (NBTS) is deteriorated by plasma charging damage, causing severe hole traps. More importantly, we also found that hole trappings are aggravated in HfO2 film as compared to interface trap generation by plasma charging, even on virgin devices with large antenna area ratios prior to negative BTS. This result is different from that observed in traditional pMOSFETs with SiO2 gate dielectric where electron trapping is dominant. Fluorine incorporation would effectively improve plasma charging immunity, thus reducing the severe hole trapping under NBTS for devices with large antenna area ratios.