砷化鎵功率金屬半導體場效電晶體銅金屬化之研究

Abstract

本論文研究以濺鍍法成長奈米晶粒之β相金屬鉭膜(Ta)和奈米晶粒之氮化鉭膜(TaN,Ta2N)，做為砷化鎵金屬半導體場效電晶體(MESFETs)銅金屬化擴散障礙層之熱穩定研究。分別成長了：（1）Cu/Ta/GaAs，(2) Cu/TaN/GaAs，(3) Cu/Ta2N/GaAs等三種主要不同結構。所有試片皆在Ar氣氛圍中退火各30分鐘後，先做片電阻，X-光繞射，歐傑成分縱深分佈等分析測試，然後做成電子顯微鏡試片，放入配有X射線能量分佈儀(EDS)之穿透式電子顯微鏡進行觀察。結果顯示，以30 nm Ta為障礙層之多層結構可以承受500℃/30分鐘之退火，而以30 nm TaN及35 nm Ta2N為障礙層之結構則分別可以承受550℃和500℃各30分鐘退火。另外以10 nm Ta和以15 nm Ta2N為障礙層之結構，則可以承受400℃之退火。Ta主要的失效機制是由障礙層與砷化鎵反應產生砷與鎵的鉭化物所主導，而氮化鉭則是藉著晶界擴散效應，由銅與砷化鎵在氮化鉭與砷化鎵界面反應產生銅砷化合物，造成氮化鉭不穩定而失效。 此外為了實際測試金屬半導體場效電晶體銅金屬化後之熱穩定及其功率性能，亦先製作銅金屬化之元件，接著在300℃或200℃之溫度下進行2或3小時之熱應力退火，然後測試其各種電性與功率性能。結果顯示銅金屬化元件熱穩定相當良好，功率性能亦相當不錯，顯示銅可以取代金做為砷化鎵射頻元件之金屬化材料。

In this thesis, nano-crystalline beta phase tantalum (β-Ta) and nano-crystalline tantalum nitride (TaN, Ta2N) were sputtered on GaAs subtrate as the diffusion barrier for copper metallization of GaAs power MESFETs. The thermal stability of multiayer and copper metallized MESFETs were studied. Three different types of sample were processed：(1) Cu/Ta/GaAs (2) Cu/TaN/GaAs (3) Cu/Ta2N/GaAs. All samples were annealed for 30 min at different temperatures in Ar atmosphere. Sheet resistance, X-ray diffraction, Auger depth profile were measured, thereafter the transmission electron microscopy (TEM) samples were prepared and examined in transmission electron microscopes. The compositions of selected areas were analyzed with x-ray energy dispersive spectroscopy. The results showed that 30 nm Ta and 35 nm Ta2N barriers were stable up to 500℃, 30 nm TaN barrier were stable up to 550℃ annealing, while 10 nm Ta barrier and 15 nm Ta2N barrier were stable up to 400℃ annealing. The failure mechanism of Ta barrier was the reaction of Ta with GaAs to form compounds, and the failure mechanism of TaN and Ta2N barrier was the diffusion of Cu atoms through the grain boundary of TaN and Ta2N barriers to form compounds at TaN(Ta2N)/GaAs interface. The reactions of Cu and GaAs at TaN(Ta2N)/GaAs interface resulted in the unstability and failure of TaN and Ta2N barrier. The copper metallized monolithic microwave integrated circuits (MESFETs) were prepared and their thermal stability and power performance were evaluated. After 200℃/3 hr or 300℃/2r thermal stress annealing, the MESFETs showed good thermal stability and good power performance. These results clearly showed that copper instead of gold can be used for metallization of GaAs power MESFETs.