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Device Isolation And Backgating Reduction by Dual Oblique Implantations

IP.com Disclosure Number: IPCOM000100583D
Original Publication Date: 1990-May-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

de Souza, JP: AUTHOR [+3]

Abstract

A simple method to achieve three-dimensional electrical isolation around a discrete device or an array of devices in III-V semiconductors is described. The method involves two or more oblique implantations around a device such that the trajectories of the implants intersect under the device in a manner shown in the figure. The device is protected by a layer of photoresist during the implants. In order to (Image Omitted) obtain intersecting ion trajectories under a GaAs FET of 0.7 mm gate length and a total width of 5.5 mm width (from the far edge of the source to the far edge of the drain) with the lowest ion energy, two oblique implants (along a non-crystallographic direction) of H+ at 330 keV at 60o with respect to the wafer normal would be required.

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Device Isolation And Backgating Reduction by Dual Oblique Implantations

       A simple method to achieve three-dimensional electrical
isolation around a discrete device or an array of devices in III-V
semiconductors is described.  The method involves two or more oblique
implantations around a device such that the trajectories of the
implants intersect under the device in a manner shown in the figure.
The device is protected by a layer of photoresist during the
implants.  In order to

                            (Image Omitted)

 obtain intersecting ion trajectories under a GaAs
FET of 0.7 mm gate length and a total width of 5.5 mm width (from
the far edge of the source to the far edge of the drain) with the
lowest ion energy, two oblique implants (along a non-crystallographic
direction) of H+ at 330 keV at 60o with respect to the wafer normal
would be required.  Standard photoresist of thicknesses of a few
microns can therefore be used as a masking material over the device.

      Typical doses to achieve good electrical isolation in GaAs
(>1e6 ohm-cm) by H+ are 1e13 - 1e14 cm-2.  The backgating in GaAs
MESFETs has been shown to improve by a factor of 3 - 5 after two
oblique implantations of H+.  To achieve intersecting trajectories
under an array of devices with dimensions of tens of microns, high
implant energies (several hundred/thousand kilovolts) are required
and the standard photoresist or a dielectric layer can no longer be
us...