Molybdenum germanide ohmic contact to<i>n</i>-GaAs

Daoud‐Ketata, K.; Dubon‐Chevallier, C.; Besombes, C.; Bresse, J. F.; Hénoc, P.

doi:10.1049/el:19870012

Cited by 7 publications

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“…High-reliability refractory ohmic contacts are required to process devices such as self-aligned heterojunction bipolar transistors (HBTs), for which a stable contact is necessary to allow the annealing step (800~ for a few seconds), used to activate the p-type implant after the contact metal deposition (1). A schematic description of the selfaligned process is shown in Fig.…”

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confidence: 99%

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GeMoW Refractory Ohmic Contact for GaAs / GaAlAs Self‐Aligned Heterojunction Bipolar Transistors

Dubon‐Chevallier

Blanconnier

Besombes

et al. 1990

J. Electrochem. Soc.

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We have formed GeMoW and Ge(As)MoW ohmic contacts to n-type GaAs using different annealing techniques: rapid thermal annealing (RTA) or thermal furnace annealing under a forming gas, and sealed ampul or semi-open box technique under an As overpressure. A comprehensive study of both contacts is presented using electrical testing, Auger electron spectroscopy, secondary ion-mass spectrometry, and transmission electron microscopy. This study has led to the optimization of a new refractory ohmic contact, the As-doped Ge/Mo/W contact. Very low specific contact resistivities (10 -7 -cm2), have been obtained, when the contact included an As-doped Ge layer with a doping level of 102~ atm 9 cm -2 and was annealed using the semi-open box technique under an As overpressure. As doped GeMoW ohmic contacts have also been realized on GaAs/GaA1As heterostructures, the specific contact resistivity is 4 >< 10 -7 ~ -cm 2, which is a very low value for n-type refractory ohmic contact realized on GaAs/GaA1As heterostructure.High-reliability refractory ohmic contacts are required to process devices such as self-aligned heterojunction bipolar transistors (HBTs), for which a stable contact is necessary to allow the annealing step (800~ for a few seconds), used to activate the p-type implant after the contact metal deposition (1). A schematic description of the selfaligned process is shown in Fig. 1. The emitter ohmic contact is deposited first and delineated using reactive ion etching. The profile obtained after etching is a T-shape structure, where the undercut determines the distance between the emitter ohmic contact and the p-type implantation. The p-type implantation is then performed with the emitter contact acting as a mask. The following annealing step forms the ohmic contact and activates the p-type dopant. Then the HBTs are fully fabricated using a classical process (2). The classical AuGeNi alloyed ohmic contact, which has been extensively studied for n-type GaAs, cannot withstand such temperature cycles. Molybdenum germanide has already been investigated, because it provides a low specific contact resistivity and a good thermal stability on GaAs (3-5). The W film is used as a mask during the ion implantation process. The GeMoW contact can be etched selectively on GaAs, thus allowing a good dimension control. However, the published resistivities obtained for this contact on GaAs layers were always higher than 10 -8 ~ 9 cm 2. In this paper, we have investigated the formation of the refractory ohmic contact and correlated the electrical results and the metallurgical analysis. This study has led to the optimization of a new refractory ohmic contact using an As-doped Ge layer deposited by electron beam evaporation, followed by Mo and W films deposited by sputtering, which permitted the achievement of lower specific contact resistivities than pure Ge/Mo/W contacts. This contact has been formed on GaAs layers and also on GaAs/GaA1As heterostructure, allowing the realization of self-aligned HBTs. Experimental ProcedureOhmic contact sp...

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“…The classical AuGeNi alloyed ohmic contact, which has been extensively studied for n-type GaAs, cannot withstand such temperature cycles. Molybdenum germanide has already been investigated, because it provides a low specific contact resistivity and a good thermal stability on GaAs (3)(4)(5). The W film is used as a mask during the ion implantation process.…”

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confidence: 99%