應用在低雜訊InAlAs/InGaAs變異型高電子遷移率電晶體之前端銅金屬化製程

Abstract

本次研究中探討應用在InAlAs/InGaAs變異型高電子遷移率電晶體(MHEMTs)銅金屬化蕭基接觸以及銅導線製程。鈦/鉑/銅閘極金屬取代低雜音假晶高電子遷移率電晶體中傳統的鈦/鉑/金閘極金屬。此前端MHEMTs銅金屬化製程針旨在降低成本以及簡化銅導線製程，並獲良好的熱穩定性以及電導特性。

鈦/鉑/銅金屬結構中，鉑作為擴散阻擋層，避免銅擴散進入鈦而形成金屬化合物。本實驗中針對鈦/鉑/銅蕭基二極體做不同溫度之熱處理以探討其熱穩定性質。透過XRD，AES，TEM以及直流電性的檢測，鈦/鉑/銅蕭基二極體在退火350度仍保有蕭基特性。且展現了足以和鈦/鉑/金媲美的特性。銅金屬化蕭特基結構具有優良的電性及熱穩定性，並且可應用於砷化鎵元件的蕭特基金屬製程。

再則，在歐姆以及蕭基接觸金屬上銅的使用，使得金半接面以及銅導線之間無須另一擴散阻擋層，簡化了銅導線製程。最後則在銅導線上沉積氮化矽薄膜來避免銅金屬氧化。

在元件特性方面，前端銅金屬化低雜訊變異型高電子遷移率電晶體其在此次的研究中其汲極飽和電流密度為673 mA/mm，而電流在1.5 V的汲極偏壓下最大的互導係數可達750 mS/mm。元件的電流增益截止頻率為90 GHz。

因此，本次研究成功的研發出應用在低雜訊變異型高電子遷移率電晶體元件之前端銅金屬化製程。應用此製程之元件具有優越的電流以及高頻特性。結果顯示鈦/鉑/銅之閘極結構以及銅金屬化空氣橋製程可以整合應用在低噪音變異型高電子遷移率電晶體之製程上。

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.