A comparison between MOCVD grown AlGaAs/GaAs and InGaP/GaAs HBTs showed a relatively constant DC current gain as a function of temperature upto 300/spl deg/C for the latter devices. A novel high temperature ohmic contact using ZrB/sub 2/ diffusion barrier has been developed and found to be suitable for HBTs operating at elevated temperatures. This barrier has been successfully employed in the fabrication of InGaP/GaAs HBTs which operated at 200/spl deg/C for 18 hours without any significant change to device performance.

Characteristics of AlGaAs/GaAs and InGaP/GaAs HBTs at high temperature

This paper presents a comparative analysis of the parameters of non-alloyed Pd/Ge/Ta/Cu and alloyed Ge/Au/Ni/Ta/Au ohmic contacts to n+-GaAs, both with planar as well planar and sidewall diffusion barriers based on Ta films formed by magnetron sputtering. It has been found that use of sidewall diffusion barriers reduces the value of specific contact resistance of ohmic contacts of both types and improves the thermal stability of the edge morphology of the contact pad in the case of alloyed Ge/Au/Ni/Ta/Au ohmic contacts. The effects observed for the samples with effective diffusion barrier are explained by limiting diffusion, as well as limiting the interaction of Au or Cu atoms with underlying metallization layers and with gallium arsenide, taking place along the sidewall surfaces of the ohmic contact.

Ohmic contacts to n + -GaAs with refractory metal sidewall diffusion barrier

The DC and RF performance of the fully Cu/Ge metalized GaAs pHEMT and pHEMT with Cu/Ge ohmic contacts and Ti/Mo/Cu based T-gate were investigated. The Cu/Ge compound was formed by the atomic hydrogen treatment of Cu/Ge/GaAs two layer system. It was found, that such processing in an atomic hydrogen flow with density 1015 at. cm2 s−1 at room temperature during 5 min leads to the solid state interdiffusion of Cu and Ge thin films and polycrystalline CuGe compound formation with the vertically oriented grains. The fully Cu/Ge metalized pHEMT with 170 nm T-gate had a saturation drain current of I dss = 660 mA/mm, off-state gatedrain breakdown of BV gd = 7 V and a transconductance peak S m = 380 mS/mm at V ds = 3 V. The maximum stable gain of the fully Cu/Ge based pHEMT was about 17,5 dB at frequency 10 GHz and the current gain cut-off frequency was about 80 GHz at U ds = 3V and I ds = 1/4I dss . The transistor with Cu/Ge ohmic contacts and Ti/Mo/Cu based 170 nm T-gate had a worse DC and RF parameters. The thermal stability test of both GaAs pHEMTs was performed in nitrogen environment at a temperature T = 250 °C for a period 5–120 min. The gold free fully Cu/Ge-metalized pHEMT fabricated with an atomic hydrogen treatment demonstrated superior thermal stability performance than the pHEMT with Cu/Ge ohmic contacts and Ti/Mo/Cu T-gate fabricated without atomic hydrogen treatment. The experimental results allow to consider the CuGe compounds, as perspective gold replacement in the GaAs MMIC production.

A gold free fully Cu/Ge metalized GaAs pHEMT for the high frequency applications

The influence of the modes and conditions of deposition of the Ti film of the diffusion barrier on the parameters of the Ge/Au/Ni/Ti/Au ohmic contacts to n-i-GaAs were investigated. Deposition modes of the Ti films, in which a 50-fold increase in the reduced contact resistance, as well as an increase in thermal stability of the morphology of the edge of contact pads, are determined. The factors affecting the reduced contact resistance are the angle under which the Ti atoms enter the substrate surface, the deposition rate of the Ti film, and the pressure of the residual atmosphere during deposition of the film of the diffusion barrier. The factor affecting the thermal stability of the morphology of the edge of the contact pads is apparently the angle under which the Ti atoms enter the substrate surface.

Features of the formation of a low-resistance Ge/Au/Ni/Ti/Au ohmic contact to n-i-GaAs

The thermal stability performance of the fully Cu/Ge metalized GaAs pHEMT and pHEMT with Cu/Ge ohmic contacts and Ti/Mo/Cu based T-gate were investigated. The CuGe compound was formed by the atomic hydrogen treatment of Cu/Ge/GaAs two layer system. It was found that such processing in the atomic hydrogen flow with density of 1015 at. cm2 s−1 at room temperature for 5 min leads to the solid state interdiffusion of Cu and Ge thin films and polycrystalline CuGe compound formation with the vertically oriented grains. The fully Cu/Ge metalized pHEMT with 170 nm T-gate had a saturation drain current of I dss = 660 mA/mm, off-state gate-drain breakdown voltage of BV gd = 7 V and a transconductance peak S m = 380 mS/mm at F ds = 3 V. The maximum stable gain of the fully Cu/Ge based pHEMT was about 17.5 dB at the frequency of 10 GHz and the current gain cut-off frequency was about 80 GHz at U ds = 3 V and I ds = 1/4I dss . The transistor with Cu/Ge ohmic contacts and Ti/Mo/Cu based 170 nm T-gate had worse DC and RF parameters. The thermal stability test of both GaAs pHEMTs was performed in a nitrogen environment at the temperature of T = 250 °C for a period of 5–120 min. The gold free fully Cu/Ge-metalized pHEMT fabricated with an atomic hydrogen treatment demonstrated more superior thermal stability performance than the pHEMT with Cu/Ge ohmic contacts and Ti/Mo/Cu T-gate fabricated without atomic hydrogen treatment. The experimental results allow considering of CuGe compounds as a perspective gold replacement in the GaAs MMIC production.

http://ieeexplore.ieee.org/iel5/6089237/6102757/06102797.pdf

Thermal stability of gold free fully Cu/Ge metalized GaAs pHEMT

Barrier layers have been used on top of Ni-Au-Ge alloyed and Pd-Ge ``non-alloyed'' ohmic contacts for GaAs MESFET integrated circuits. They prevent diffusion of subsequent interconnection layers and so maintain stable low resistance (0.05 ohm. mm) contacts. The assessment of these contact structures, both electrically and using AES and TEM, is presented. The results show that the barrier action is effective in producing uniform and reliable contacts and good yields of MSI high speed digital circuits.

/pdf/diffusion-barrier-layers-for-ohmic-contacts-to-gaas-4iph7zv0i3.pdf

Diffusion Barrier Layers for Ohmic Contacts to GaAs

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Diffusion Barrier Layers for Ohmic Contacts to GaAs