利用接觸蝕刻停止層以及下凹式源極和汲極對電晶體載子遷移率提升之研究

Abstract

在本論文中，我們將n 型電晶體製作於(110)的基板上，加上接觸蝕刻停止層以及下凹式源極和汲極的結構，來提升通道的應力，進而改善載子遷移率。 其中，我們的元件活化是使用微波退火方式活化離子佈值。 另外，我們從材料分析中發現，氮化矽(接觸蝕刻停止層)材料經過微波退火過程之後，會提高伸張應力， 所以我們將此項方法加入製程之中，來提升接觸蝕刻停止層的伸張應力，可以有更高的載子遷移率。 之後，我們再對電晶體做熱載子測試，針對元件的可靠度做一簡單的分析。 在實驗結果中，我們發現接觸蝕刻停止層經由微波活化提升伸張應力可以明顯改善驅動電流。而在閘極線寬縮小至0.2 微米以後，下凹式源極和汲極的結構加上微波活化提升伸張應力，可以提高驅動電流。而在氮化矽沉積的過程之中，因沉積氧化矽的反應氣體含有大量的氫元素，氫元素在沉積過程中擴散進入通道，修補矽與氧化矽交界的懸浮鍵，因而降低了表面陷阱密度。在熱載子分析部分，熱載子對元件介面的破壞對於下凹式源極和汲極的結構是相當嚴重的。因為在測試過程中，熱載子會被捕捉在閘極與spacer 之中，造成在做完熱載子測試後的驅動電流量測中，電子經過有大量電子被捕捉的閘極與spacer 附近，會產生散射，而我們會發現驅動電流有明顯的衰減。並且在等效電壓變動(threshold voltageshift)對熱載子測試時間的結果之中，下凹式源極和汲極的結構的等效電壓明顯的變動也證明此項結果。

In this thesis, we fabricate nMOSFET with recess source/drain and CESL(contact etch stop layer) on (110) substrate for channel strain and carrier mobility enhancement. Dopant activation is executed by the microwave anneal. Besides, from the result of material analysis, SiN film annealed by microwave shows with a tensile stress shift. This technique is used in device fabrication for tensile strain and mobility enhancement. From the result, CESL with microwave anneal for tensile enhancement technique improves driving current obviously. As gate length scales down to 0.2μm, recess source/drain structure with CESL with microwave anneal for tensile enhancement technique significantly enhances driving current. During SiN deposition, hydrogen diffuses to the interface of silicon and oxide to passivate dangling bonds. From charge pumping measurement, interface state density of SiN split is smaller than that of control split. From hot carrier stress analyses, the recess source/drain device shows a serious degradation after the hot carrier stress. In the process, channel hot electron would be trapped in the spacer. When the electrons flow through the spacer, Coulomb scattering would become serious in current-voltage measurement. As a result, current-voltage curves show a serious degradation. This phenomenon is confirmed from the result of shift of threshold voltage versus time under stress.