- 學位論文
砷化鎵經電漿表面處理與歐姆接觸之研究
The study of ohmic contact on GaAs surface passivated by plasma treatment
摘要
砷化鎵材料一直是高頻通訊ICs的主流，因為其具有低雜訊、超高載子移動率及半絕緣基板等優勢，但近年來在IBM的領先研究下SiGe一直在特性上突飛猛進，挾著Si低生產成本優勢下已經對砷化鎵材料構成威脅，所以砷化鎵材料當務之急除了保持高頻特性上的優勢之外，更應降低生產成本，才能在未來通訊ICs世界裡繼續佔有一席之地。降低砷化鎵生產成本，最直接的方式是導入與矽相容的積體電路製程。其第一個需要克服的是避免使用黃金系列接觸金屬，因為鋁線和黃金會產生可靠度(purple plague)問題。本研究就是發展非黃金系列接觸金屬，並且運用SF6來披覆砷化鎵表面，以減少其特有的高密度表面狀態，在硫披覆過程中以提高晶片溫度(-30~80℃)效果最明顯， 從0.863eV降到0.559 eV，增加SF6硫披覆時間(15~45秒) 最低可得到0.608eV，而增加SF6電漿製程壓力(10~60mTorr)最低可得到0.607eV。一般n型砷化鎵所使用接觸金屬是Ni/AuGe，我們以Co取代Ni，用Al取代Au，最後再結合硫披覆技術，成功的獲得一個非黃金系列的歐姆接觸金屬Co/Ge/Al，雖然ρc=4.1×10-6(Ω-cm2)並不會比傳統的AuGe/Au的接觸電阻值低，但是在熱的穩定性及金屬表面平坦度上均遠較AuGe/Au佳，且本實驗所開發出來的Co/Ge/Al的歐姆接觸金屬，不使用Pd、Pt、Au等貴重金屬，成本上更是一大優勢。
並列摘要
GaAs related compound material system dominates the applications of modern high frequency communication devices because of its low noise, high electron mobility and nature of semi-insulating substrate. Recently SiGe technologies developed by IBM, which can be integrated with low cost Si process tremendously progress and affect the mainstream position in GaAs of high frequency ICs. The most important mission for GaAs systems is to promote the high frequency performance and maintain lowers production cost at the mean time. To lower the production cost of GaAs processes new methods need to adopt the process of Si integrated circuits. The first problem often found in the processing of Si integrated circuits is to avoid using gold-alloyed contact meal. When using Al for contact metal in the GaAs material system the problem of “purple plague” will arise. In this study, we develop methods of non-gold alloyed contact metal for GaAs material system and surface treatment of GaAs to reduce the surface density of states. During the processing of S passivation it is found that the higher temperature(-30~80℃) GaAs been passivated the less surface density of states GaAs shows. For example, from 0.559eV increases to 0.836eV. By increased the passivation time (15~60 second) of SF6 , the best result was found about 0.68ev for . By increasing the pressure (10~60mTorr) of SF6 plasma process, the best result was found about 0.607eV for . After the passivation experiment, Co is used to replace Ni that is the common part for Ni/AuGe ohmic contact metal of n-GaAs. Finally non-gold alloyed ohmic contact metal Co/Ge/Al was formed as well as S passivation. The contact resistance ρc as low as 4.1×10-6(Ω-cm2) is found in Co/Ge/Al which is not lower than tradition ohmic contact Ni/AuGe for GaAs. However, superior performance of thermal stability and surface flatness for Co/Ge/Al is found compared to those of Ni/AuGe as well as the consideration of processing cost.