應用鈀/鍺/銅歐姆接觸至全面銅金屬化之磷化銦鎵/砷化鎵異質接面雙載子電晶體

Abstract

在這篇論文中，成功的發展出使用鈀/鍺/銅歐姆接觸至N型砷化鎵上，且成功的運用至全面銅金屬化磷化銦鎵/砷化鎵異質接面雙載子電晶體中。 在低溫退火(250°C)下，鈀/鍺/銅歐姆接觸即具備了低接觸電阻(5.73 x 10-7 Ω-cm2)。經由X光繞射儀、穿透式電子顯微鏡、二次離子質譜儀和原子力顯微鏡的分析結果，鈀/鍺/銅歐姆接觸形成機制和微結構反應都已被研究了解；且鈀/鍺/銅歐姆接觸經過250°C、24小時的熱穩定測試後，其接觸電阻幾乎沒有變化。 接著將鈀/鍺/銅歐姆接觸應用至全面銅金屬化磷化銦鎵/砷化鎵異質接面雙載子電晶體，並使用鉑/鈦/鉑/銅為P型砷化鎵歐姆接觸、鈦/鉑/銅為連接導線（其中鉑為銅之擴散阻障層）。量測結果顯示，全面銅金屬異質接面雙載子電晶體的直流特性和使用傳統金金屬化的特性相當；在微波特性方面，射極面積為3x20-μm2之元件，其fT為38GHz。此外，將元件施以250°C、24小時的熱處理後都很穩定，且在高電流密度140kA/cm2之電流加速測試24小時後，其元件特性也並沒有明顯改變。這些結果顯示將鈀/鍺/銅歐姆接觸應用至全面銅金屬化磷化銦鎵/砷化鎵異質接面雙載子電晶體其元件特性十分的優異。

In this study, a low contact resistivity Pd/Ge/Cu ohmic contact to n-type GaAs has been successfully developed. The Au-free fully Cu-metallized InGaP/GaAs HBTs using Pd/Ge/Cu ohmic contact to n-type GaAs also has been successfully fabricated for the first time. The Pd (150 Å)/Ge (1500 Å)/Cu (1500 Å) ohmic contact exhibits a very low contact resistivity of 5.73 x 10-7 Ω-cm2 at a low annealing temperature (250 °C). The ohmic contact formation mechanisms and microstructure evolution were investigated using x-ray diffraction (XRD), secondary ion mass spectrometry (SIMS), transmission electron microscopy (TEM), atomic force microscopy (AFM) and energy dispersive spectrometer (EDX). The thermal stability test of the Pd/Ge/Cu ohmic contact was also performed at 250 °C for 24 hours and showed no obvious degradation on Pd/Ge/Cu ohmic contact after the annealing. The Pd/Ge/Cu ohmic contact was applied to fully Cu-metallized InGaP/GaAs HBTs. In this fully Cu-metallized HBT, Pt/Ti/Pt/Cu was used as the base metal, SiNx was used for passivation, and Ti/Pt/Cu was used for interconnect metals with Pt as the diffusion barrier. The common emitter I-V curves and Gummel plot of these Cu-metallized HBTs using Pd/Ge/Cu ohmic contact showed similar electrical characteristics as those for HBTs metallized with conventional Au-metallized HBTs. The cutoff frequency (fT) of 3x20-μm2-emitter-area devices was about 38GHz. During both the current-accelerated stress test (110 kA/cm2 stress for 24h) and the thermal stability test (annealing at 250°C for 24 hours), for the fully Cu-metallized HBT with Pd/Ge/Cu ohmic contact showed almost no obvious degradation in electrical characteristics. The results show that the novel Pd/Ge/Cu ohmic contact can be used on Au-free fully Cu-metallized InGaP/GaAs HBTs, and exhibit good device performance.