Fully Cu-Metallized InGaP/GaAs HBTs Using Pd/Ge/Cu Ohmic Contact to N-type GaAs
Edward Yi Chang
在低溫退火(250°C)下，鈀/鍺/銅歐姆接觸即具備了低接觸電阻(1 x 10-6 Ω-cm2)。經由X光繞射儀、歐傑電子縱深分析、穿透式電子顯微鏡和能量分散式X射線分析的分析結果，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。
The Pd/Ge/Cu ohmic contacts to n-type InGaAs is investigated. The Au-free fully Cu-metallized InGaP/GaAs HBTs using Pd/Ge/Cu ohmic contact to n-type InGaAs also has been successfully fabricated for the first time. Low specific contact resistivity of 1x10-6 Ω-cm2 was achieved at a low annealing temperature (250 °C). The ohmic contact formation mechanisms and microstructure evolution were investigated using x-ray diffraction (XRD), Auger electron spectroscopy (AES) depth profiles, transmission electron microscopy (TEM) and energy dispersive spectrometer (EDX). The thermal stability test of the Pd/Ge/Cu ohmic contact on InGaAs was also performed at 250 °C for 72 hours and showed no obvious degradation on Pd/Ge/Cu ohmic contact after the annealing. In addition, the sheet resistance got to high temperature of 550 °C for 20min also showed no obvious rising. The Pd/Ge/Cu ohmic contact was applied to the fully Cu-metallized InGaP/GaAs HBTs as the emitter and collector metals. The base metal was Pt/Ti/Pt/Cu, 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 current gain (β) of these Cu-metallized HBTs using Pd/Ge/Cu ohmic contact on InGaAs cap layer showed similar electrical characteristics as those for conventional Au-metallized HBTs. The high current test was performed at a high emitter current density of 100kA/cm2 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 InGaAs Cap layer of fully Cu-metallized InGaP/GaAs HBTs exhibit good device performance.
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