Emitter-Coupled Logic Ring Oscillators Implemented with GaAs/GaAlAs Single and Double Heterojunction Bipolar Transistors: A Comparison

Dubon‐Chevallier, C.; Desrousseaux, P.; Duchenois, A.M.; Besombes, C.; Dangla, J.; Bacot, C.; Ankri, D.

doi:10.1007/978-3-642-82979-6_30

High-Speed Electronics

1986

DOI: 10.1007/978-3-642-82979-6_30

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Emitter-Coupled Logic Ring Oscillators Implemented with GaAs/GaAlAs Single and Double Heterojunction Bipolar Transistors: A Comparison

C. Dubon‐Chevallier¹,

P. Desrousseaux²,

A.M. Duchenois³

et al.

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“…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.…”

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confidence: 99%

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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mentioning

confidence: 99%

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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Deposition and etching of refractory ohmic contacts to GaAs for self-aligned technology

Kétata¹,

Ketata²,

Dubon‐Chevallier³

et al. 1993

J. Phys. D: Appl. Phys.

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Refractory ohmic contacts to n-type GaAs have been developed for heterojunction bipolar transistors (HBTS) processed with self-aligned technology and including high-temperature anneals. We report the results on W and MoGe deposition, annealing and the reactive ion etching (RIE) operations necessary for HBTS' self-aligned processing. These refractory metallizations were fabricated on n-type epitaxial GaAs layers with a carrier concentration of 1018 cm-3. Ge was evaporated initially by an electron beam technique, while Mo and W films were deposited separately by sputtering in RF plasma. The MoGe ohmic contact formation is due to both an n+ layer created at the GaAs contact interface by Ge overdoping and molybdenum germanide stable phase formation. Low specific contact resistivities were obtained with experiments combining As-doped Ge and As overpressure. It was then possible to reduce the resistivity to 2*10-7 Omega cm2. Reactive ion etching of W, Mo and Ge is also described. Etch rates are compared using either photoresists or Pt masking materials. A Pt mask was found to be much more suitable than photoresist because it allows higher selectivities and etch rates. Surface contamination on the GaAs surface is a)so discussed and could be minimized for optimal device performance.

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Emitter-Coupled Logic Ring Oscillators Implemented with GaAs/GaAlAs Single and Double Heterojunction Bipolar Transistors: A Comparison

Cited by 2 publications

References 1 publication

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

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

Deposition and etching of refractory ohmic contacts to GaAs for self-aligned technology

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