砷化鎵元件銅金屬化製程可行性之研究

Abstract

在矽製程方面,銅金屬化製程已由IBM公司率先施行成功而應用在超大型積體電路之金屬化製程上,即使金屬化材料已逐漸被矽工業所應用,對於在砷化鎵單石微波積體電路上的應用仍未被研究。本論文中將研究Cu/W、Cu/Co、Cu/Mo、以及Cu/WNx在已經鍍上歐姆或蕭基金屬的砷化鎵基材上的熱穩定性,以及使用W、Co、Mo做為銅的擴散障礙層來取代Au/Pt成為閘極金屬或使用WNx做為銅的擴散障礙層和蕭基接觸來成為閘極金屬的可行性。 在W、Co、Mo三種擴散障礙層中,W是最好的,無論是在歐姆或蕭基金屬上經過300℃ 30分鐘後都保持穩定,而且Cu/W/Ti/n-GaAs結構的蕭基 二極體退火300℃ 2分鐘後仍具有0.828~0.832eV的位障高度和1.05~1.06的理想係數,至於Cu/WNx/n-GaAs結構的蕭基二極體,退火300℃ 2分鐘後仍具有接近理想的蕭基特性,其位障高度在0.672~0.739eV,理想係數在1.06,且由X-ray分析退火後並不會有化合物生成 。 根據這些結果,運用W和WNx做為銅的擴散障礙層可以應用在製作砷化鎵的傳輸線上,這樣的製程方法能降低產品的製作成本。

Copper interconnect technology has been developed and incorporated in commercial products ever since IBM announced its success in silicon VLSI process. Even though the use of copper as metallization metal has become very popular in silicon industry, the use of copper as metallization metal for GaAs monolithic microwave integrated circuit (MMIC) has not been studied thoroughly. In this study, we studied the thermal stability of Cu/W, Cu/Co, Cu/Mo and Cu/WNx on GaAs substrate with Ohmic metals and Schottky metals and the feasibility of the Cu/W/Ti, Cu/Co/Ti, Cu/Mo/Ti, and Cu/WNx as replacements of Au/Pt/Ti films for Schottky metal application. Our results showed W is the best diffusion barrier among the three materials studied because the Cu/W (40 nm)/Ohmic metal and Cu/W (40 nm)/Schottky metal structures were stable after annealing at 300℃ for 30 mins. The Schottky diode characteristics with the barrier height about 0.828~0.832 eV and the ideality factor about 1.05~1.06 for Cu/W/Ti/n-GaAs structure were obtained after annealing at 300℃ for 2 mins. Additionally, the Schottky diode with Cu/W2N/n-GaAs structure exhibited near-ideal I-V characteristics with the ideality factor about 1.06 and the barrier height between 0.672 and 0.739 eV after annealing at 300℃ for 2 mins. There was no compound formation in this annealed structure as indicated by XRD analysis. According to these results, copper metallization with tungsten and tungsten nitride as the diffusion barrier layers can be applied to the fabrication of GaAs transmission lines. This metallization scheme may reduce the cost of GaAs MMIC production.