次微米MOS SOI元件之分析與設計

Abstract

近年來，矽磊晶絕緣體(Silicon-on-Insulator, SOI) 金氧半電晶體由於 較矽基片元件有很多優點，因此在極大型積體電路 (ULSI) 的應用上極具 發展潛力， SOI元件不僅提供了較快的速率，較高的包裝密度，更簡單的 製程，避免 latch-up 的 CMOS 結構，而且也改善了元件特性。然而， SOI 金氧半場效體的隔離結構會產生浮動基體效應 ( floating-body effects)，如電流紐結 (kink) 和早期崩潰，而這些效應在矽基片元件 中並不會發生。 所以，在本文中我們著眼在深次微米 SOI 元件之浮動基 體效應及崩潰機構的分析與研究。本論文中，結果顯示薄膜完全空乏 (fully-depleted) SOI 金氧半場效體不能完全免於寄生雙極性接面電晶 體效應( parasitic BJT effect )，而完全空乏 SOI 元件的崩潰機構和 部分空乏 ( partially-depleted )元件不同。在部分空乏 MOS 結構的 SOI 元件中，寄生雙極性電晶體電流主控陡增的崩潰電流；另一方面，完 全空乏 MOS 結構 SOI 元件由於有比較高的橫向電場，因此撞擊游離電 流 (impact ionization current) 主宰崩潰特性。因此，為了要改善浮 動基體效應和早期崩潰而不犧牲驅動電流大小的情況下，我們提出一個採 用薄膜非對稱輕摻雜汲極 (asymmetric lightly doped drain) 結構的高 效能深次微米 SOI 元件。 In recent years , Silicon-on-Insulator MOS transistors are attractive candidates for use in ULSI circuits owing to numerous advantages over bulk-Si devices . The SOI devices provide not only faster speed , latch-up-free CMOS structure , but also improved other device performance . However , the electrically isolated silicon film structure of SOI MOSFET's creates floating-body effects such as current kink and early breakdown . Therefore, we focus on the analysis of the floating-body effects and the breakdown mechanism for deep-submicron SOI devices. In the thesis,we have shown that fully-depleted SOI MOSFET's do not always have the immunity from the parasitic BJT effect. The parasitic BJT current dominates the steep breakdown current in partially- depleted MOS structure SOI. On the other hand , the impact ionization current dominates the breakdown phenomena in the fully-depleted MOS structure SOI devices owing to its higher lateral field as compared with partially-depleted counterpart. In order to improve floating-body effects and breakdown without sacrificing the current drivability , we propose a thin-film asymmetric lightly doped drain structure SOI device which is a promising candidate for high-performance SOI MOSFET's.