Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having schottky gate
Reexamination Certificate
2001-06-04
2002-10-01
Smith, Matthew (Department: 2826)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having schottky gate
C438S181000, C438S195000, C438S572000
Reexamination Certificate
active
06458640
ABSTRACT:
RELATED APPLICATIONS
NONE
TECHNICAL FIELD
The present invention is directed to the general field of forming gallium arsenide (GaAs) semiconductor devices. More particularly, it is directed to forming GaAs Metal-Semiconductor Field Effect Transistors (MESFETs).
BACKGROUND OF THE INVENTION
FIG. 1
illustrates a simplified structure of a conventional GaAs MESFET
100
. The MESFET
100
has a GaAs substrate
102
, a source region
104
, a drain region
106
, an n-type channel
108
, and a p-type background region
110
and. A source electrode
112
is formed above the source region
104
, a drain electrode
114
is formed above the drain region
106
and a gate electrode
116
is formed between the source and drain electrodes on a surface of the GaAs substrate, and above the n-type channel
108
. As seen in
FIG. 1
, the gate electrode
116
is formed in a depressed area
118
formed in the upper surface of the device. When a voltage is applied to the gate electrode
116
, the width of the n-type channel changes, thereby affecting the flow of current between the source electrode
112
and the drain electrode
114
.
In conventional ion implanted, or epitaxially grown, GaAs MESFET devices, such as that depicted in
FIG. 1
, the channel
108
is doped uniformly between the source
104
and drain
106
regions. The result is that the p-type background forms a p-n junction with the n-type channel doping underneath the channel. When the MESFET
100
is used as an amplifier, it normally operates with high electrical field intensity in the gate-drain region. In high RF power amplifiers, the electrical field in the gate-drain region may be high enough to initiate impact ionization, in which both excessive electrons and holes are generated. In such case, the holes become trapped in the p-n junction, thereby forming a virtual back-gating, which results in a pinch-off the n-channel
108
. This phenomenon is termed a power transient in RF amplifiers, which is detrimental to normal operation.
SUMMARY OF THE INVENTION
The present invention uses selective ion implantation techniques to create a GaAs MESFET device with non-uniform doping profiles in the conduction channel. In the Source-Gate region of the MESFET, a conventional p-type implantation is used as the background, and one or more n-type implantations form the conduction channel. In the Gate-Drain region of the device, there is either no, or a reduced, background p-type implantation, and the n-type implantation dose is also reduced, resulting in lower doping concentration between the gate and the drain.
The present invention is also directed to a method for forming a GaAs MESFET having non-uniform doping profiles in the conduction channel. This is accomplished by forming a lightly-doped first conduction channel of a first type, forming a moderately doped second conduction channel of the first type along a first portion of the first conduction channel, forming a background region of a second type beneath the second conduction channel, forming source and drain regions at opposite ends of the first conduction channel, forming source and drain contacts over corresponding source and drain regions, and forming a gate contact between the source and drain contacts, the gate contact being positioned approximately over an end of the second conduction channel.
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Anadigics Inc.
Luu Chung Auh
Pennie & Edmonds LLP
Smith Matthew
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