| Summary: | 碩士 === 國立交通大學 === 材料科學與工程系所 === 94 === In this dissertation, the feasibility of using Cu-metallized Schottky contact and interconnects for an InAlAs/InGaAs metamorphic high electron mobility transistors (MHEMTs) is studied. The front side Cu metallization process was performed to reduce the production cost and to simplify the Cu interconnect process of the GaAs MHEMTs. The finished front-side copper metallized MHEMTs exhibit good thermal stability and electrical performances.
In this study, Pt was used as diffusion barrier to prevent the interaction between Ti and Cu for MHEMTs. The Ti/Pt/Cu Schottky diodes were annealed at different temperatures to investigate the thermal stability of the material system. XRD, AES, TEM analysis and I-V measurement were performed to examine the diffusion behavior of Cu in this metal system in details. It revealed that the Ti/Pt/Cu structure was thermally stable up to 350 ℃. The electrical performance of the Ti/Pt/Cu Schottky diode was comparable to that of the performance of Ti/Pt/Au Schottky diodes. Overall, the Cu-metallized Schottky structure has excellent electrical characteristics and thermal stability, and can be used as the Schottky metals for GaAs MHEMTs.
In addition, using the Ti/Pt/Cu Schottky contact is the simplification of the copper metallization process when Cu interconnects was introduced. The silicon nitride film was deposited on the copper airbridge to prevent copper surface from oxidation.
The front-side Cu metallized low noise MHEMT has a saturated drain current of 663 mA/mm and a maximum transconductance of 750 mS/mm. The device demonstrates a cutoff frequency fT of 90 GHz.
In summary, the front-side Cu metallization process for high-frequency low noise MHEMTs was successfully developed. The fabricated MHEMTs show superior DC and RF performances. It is shown that the Ti/Pt/Cu gate structure and Cu-metallized airbridge process can be integrated into the front-side metallization process for the InAlAs/InGaAs/GaAs MHEMTs.
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