The Cu metalized GaAs pHEMTs using developed Pd/Ni/Ge/Mo/Cu and Cu/Ge based ohmic contacts and Ti/Mo/Cu 150 nm T-shape gate has been successfully fabricated for the high-frequency applications. The fabricated Cu metalized GaAs pHEMTs with Pd/Ni/Ge/Mo/Cu and Ge/Cu ohmic contacts had a transconductance peak of 440 and 320 mS/mm, maximum stable gain value was about 18.8 and 14.5 dB at frequency 10 GHz and current gain cut-off frequency was about 100 and 60 GHz, accordingly. The performance of the fully Cu metalized atomic hydrogen treated GaAs pHEMT with Cu/Ge ohmic contacts and Ti/Mo/Ge/Cu based T-gate was investigated. 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 reduce the contact resistance of Ge/Cu ohmic contacts by 1.6 times. The reduction in specific contact resistance is apparently caused by the action of the hydrogen atoms which minimise the rate of the oxidizing reactions and activate solid phase reactions forming the ohmic contact during the thermal treatment process. The fabricated fully Cu metalized GaAs pHEMT with atomic hydrogen processing had a transconductance peak of 380 mS/mm and current gain cut-off frequency was about 80 GHz. It is similar with performance of conventional gold base devices. The experimental results allow to consider the copper as perspective gold replacement in the GaAs MMIC production.
The influence of atomic hydrogen treatment on two-layer thin-film Cu/Ge system deposited on i-GaAs substrate was investigated. It was established that the treatment in an atomic hydrogen flow with density 1015 at./(cm2•s) at a room temperature for 5 min results the solid state interdiffusion of Cu and Ge thin films and polycrystalline CuGe alloy formation with the vertically oriented grains.
The work investigated the formation processes of Ge/Cu ohmic contacts to n-GaAs with a germanium content of 30-55% in the film. A comparative analysis was undertaken of the influence of the conditions of a first preliminary annealing carried out in situ with the metallization deposition process, on the value of the specific contact resistance obtained after a second annealing carried out ex situ in a nitrogen environment. It was shown that when the first preliminary annealing is carried out in a flow of atomic hydrogen with a flow density of atoms of 1013-1016 at. cm2 s-1 a reduction in specific contact resistance of 2-2.5 times is observed, and also a more homogeneous metallization is formed with a finer microcrystal structure, in comparison with when the first, preliminary annealing is carried out under vacuum.
The reduction in specific contact resistance is apparently connected with the action of the hydrogen atoms which minimise the rate of the oxidizing reactions and activate solid phase reactions forming the ohmic contact during the thermal treatment process.
Conference Committee Involvement (1)
The International Conference “Micro- and Nanoelectronics – 2012”
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