利用雙重微影成像法製作P型金氧半場效電晶體之元件特性和可靠度研究

Abstract

在本篇論文中，我們利用先前所開發的一種雙重微影成像技術，以I射線光學步進機，成功製作出80奈米閘極線寬的P型金氧半場效電晶體。這方法使用了兩個不同光罩，藉由兩次微影和蝕刻製程來形成閘極圖形。雖然製程步驟較傳統標準作法複雜，但是可以打破傳統I射線光學解析度的限制，並且能夠實現非對稱元件的製作。我們藉由電腦輔助軟體模擬，可以檢視非對稱延伸區的摻雜分佈來形成超淺接面。在本篇論文中，我們使用並分析不同閘極堆疊模組對於元件特性上的影響，包含硼穿透和可靠度問題，也使用不同方式形成超淺接面。 我們發現，由於氧增強硼擴散效應的作用，屏蔽氧化層無助於形成超淺接面。而利用大分子化合物離子像BF2+和低能量佈植，並且改善後續熱退火處理是可改善超淺接面製作的方法。事實上，氟會增加硼穿透能力，而且造成較大的閘極空乏區，減少驅動電流能力。然而在可靠度方面，氟的摻入是對減少負偏壓溫度不穩定性有益的。最後，我們比較負偏壓溫度不穩定模式和通道熱載子模式下造成的變化差異，負偏壓不穩定性的影響是較為嚴重而且必須加以重視的。

In this thesis, we have employed a double-patterning technique previously developed by our group to fabricate PMOSFETs with gate length down to 80 nm using only a conventional I-line stepper. The DP method takes advantages of two distinct masks which are used in the litho-etch-litho-etch (LELE) process to form the gate patterns. Although more process steps are needed than conventional single patterning method, LELE process breaks the resolution limit of conventional I-line lithography and enables the feasibility of asymmetric MOSFETs. With the aid of technology computer-aided design (TCAD) simulation, the doping profiles of asymmetric ultra shallow extensions are designed. In this work, we have also investigated and analyzed the effects of gate stack modules on the device characteristics, including boron penetration and reliability issues. We have found that the screen oxide prevalently used for suppressing channeling effect may have negative impact on the formation of ultra-shallow junctions owing to the occurrence of oxygen enhanced diffusion (OED). Use of molecular ion species such as BF2+, lowering the implant energy, and carefully adjusting the post-implant annealing conditions are feasible to achieve ultra shallow junction. Fluorine incorporation is advantageous of reducing NBTI effect in short channel devices. However, as fluorine is involved, enhanced boron penetration and poly gate depletion that reduces the drive current are potential issues that should be concerned. We’ve also assessed the NBTI and CHI reliability characteristics of the fabricated devices. The results indicate that the NBTI effect is more serious than the latter.