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THRESHOLD VOLTAGE TRIMMING OF GaAs MESFETS

IP.com Disclosure Number: IPCOM000039281D
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Buchmann, P: AUTHOR [+3]

Abstract

Method for adjusting the threshold voltage of GaAs MESFET devices, particularly for MESFET fabrication processes, that allows characterization of the FET channel prior to device completion. Trimming is accomplished by controlled and, where needed, repeated removal of thin surface layers of the MESFET channel using oxidation and subsequent oxide etching until the desired threshold voltage is obtained. The threshold voltage of MESFETs is determined by the amount of charge in the channel. By removing part of the channel, the threshold becomes more positive. This can be achieved by first exposing the implanted GaAs channel surface to a microwave oxygen plasma (2.4 GHz), thereby oxidizing a thin surface layer. Subsequently, the oxide is removed in a wet chemical etch process (HCl).

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THRESHOLD VOLTAGE TRIMMING OF GaAs MESFETS

Method for adjusting the threshold voltage of GaAs MESFET devices, particularly for MESFET fabrication processes, that allows characterization of the FET channel prior to device completion. Trimming is accomplished by controlled and, where needed, repeated removal of thin surface layers of the MESFET channel using oxidation and subsequent oxide etching until the desired threshold voltage is obtained. The threshold voltage of MESFETs is determined by the amount of charge in the channel. By removing part of the channel, the threshold becomes more positive. This can be achieved by first exposing the implanted GaAs channel surface to a microwave oxygen plasma (2.4 GHz), thereby oxidizing a thin surface layer. Subsequently, the oxide is removed in a wet chemical etch process (HCl). When further trimming is required, these process steps can be repeated. It has been found, that the resulting change in threshold voltage is in the order of 10 mV per minute of oxygen plasma treatment. This figure varies, e.g., from 7 mV/min for a deep implant channel (220 kV) to 11 mV/min for a shallow channel (85 kV), the latter being more sensitive because the doping profile is nearer the surface. When the removal of a surface layer of a thickness of 2 nm or more is required, the oxidation-etching processes need to be repeated since the oxide formation in oxygen plasma is self-limiting in its thickness - the oxide thickness was found to stabiliz...