US3823352A
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Field effect transistor structures and methods
Assignee: AT&T Inc
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Filing: 1972-12-13
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Granted: 1974-07-09
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Expires: 1992-12-13
Abstract
Abstract A field effect transistor is made in a mesa configuration with the top portion of the mesa being the source region and with the limits of the gate electrode being defined by a shadow mask that overhangs part of the mesa. A drift region layer of moderately high resistivity is included between the transistor channel region and the drain region and constitutes the upper wafer substrate surface from which the mesa extends. A thin implanted layer in the upper surface of the drift region layer limits the extent of the channel in the mesa, and a thick oxide over the drift layer reduces the coupling from the gate electrode to the drift region.
Inventors
- 👤 B Pruniaux
- 👤 T Riley
- 👤 R Ryder
- 👤 H Waggener
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 04:43
CPC Classifications
H; H10; H10D; H10D30/00; H10D30/60; H10D30/64; H10D30/66; H10D30/668; H10D30/80; H10D30/87; H10D30/873; H10D62/00; H10D62/10; H10D62/102; H10D62/112; H10D62/117; H10D62/13; H10D62/149; H10D62/151; H10D62/156; H10D62/159; H10D64/00; H10D64/20; H10D64/23; H10D64/251; H10D64/252; H10P; H10P95/00; H10D62/80; H10D62/83; H10D64/27; H10D64/311; H10D64/411; H10D64/511; H10D64/512; H10D64/513; H10D64/60; H10D64/62
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
119 words
A method for making field effect transistors comprising the steps of: forming on a semiconductor wafer surface drain, drift, channel and source layers; forming a mask layer over the source layer; shaping, by etching, the channel and source layers to a mesa configuration having tapered sides which are overhung by the mask layer, thereby to expose part of the drift layer; forming an insulative layer on the upper exposed surface of the drift layer which extends suBstantially at least to the junction between the drift and channel layers; and evaporating metal onto the mesa structure and insulative layer while shielding said source layer, thereby to form a gate electrode overlying the channel layer and insulated from the drift layer.
Claim 2
Independent Claim
119 words
A method for making field effect transistors comprising the steps of: forming on a semiconductor wafer surface drain, drift, channel and source layers; forming a mask layer over the source layer; shaping, by etching, the channel and source layers to a mesa configuration having tapered sides which are overhung by the mask layer, thereby to expose part of the drift layer; forming an insulative layer on the upper exposed surface of the drift layer which extends suBstantially at least to the junction between the drift and channel layers; and evaporating metal onto the mesa structure and insulative layer while shielding said source layer, thereby to form a gate electrode overlying the channel layer and insulated from the drift layer.
Claim 3
Dependent Claim
33 words
The method of claim 1 wherein: the source, drift and drain regions are formed to be of one conductivity type and the channel region is formed to be of the opposite conductivity type.
Claim 4
Dependent Claim
128 words
The method of claim 2 wherein: the step of forming the mask layer comprises the steps of forming a first mask layer on the upper surface of the source layer, forming a second mask layer on the upper surface of the first mask layer, etching part of the first mask layer such that the second mask layer overhangs the first mask layer; and the step of forming the insulative layer comprises the step of depositing insulative material on the upper surface of the drift layer from a location opposite the second mask layer such that the second mask layer shields the mesa surface from the deposited insulative material; and selectively dissolving the second mask layer, thereby leaving the first mask layer which overhangs part of the mesa surface.
Claim 5
Dependent Claim
57 words
The method of claim 3 wherein: the evaporating step takes place after the step of dissolving the second mask layer, and comprises the step of evaporating metal onto the mesa structure from a point opposite the first mask layer such that the overhanging portion of the first mask layer shields the source layer from the vaporized metal.
Claim 6
Dependent Claim
37 words
The method of claim 4 further comprising the step of: forming a thin layer on the upper surface of the drift layer, said thin layer being of a different conductivity type than that of the drift layer.
Claim 7
Dependent Claim
45 words
The method of claim 5 wherein: the step of forming the thin layer comprises the step of projecting material toward the drift layer from a location opposite the second mask layer, such that the second mask layer shields the mesa surface from the projected material.
Claim 8
Dependent Claim
47 words
The method of claim 6 further comprising the step of: ion implanting a channel region in the mesa surface of the channel layer using as an ion mask the first mask layer overhanging the mesa and the insulative layer on the upper surface of the drift layer.
Claim 9
Dependent Claim
82 words
The method of claim 7 wherein: a plurality of field effect transistors are made simultaneously and substantially identically on a single semiconductor wafer; and further comprising the steps of: masking the wafer so as to expose only limited regions on the wafer back surface opposite each mesa; etching a cavity in the wafer opposite each mesa by exposing the masked wafer to an etchant; filling the cavity with metal which constitutes a drain contact; and separating the individual field effect transistor devices.
Claim 10
Dependent Claim
52 words
The method of claim 8 wherein: the step of etching said cavities comprises the steps of: illuminating one side of the wafer while the wafer is exposed to the etchant; observing the other side of the wafer, and removing the wafer from the etchant when light spots representing the cavities are observed.
Claim 11
Dependent Claim
16 words
The method of claim 9 wherein: the wafer is silicon and the light is red light.
Claim 12
Independent Claim
311 words
A method for making a field effect transistor comprising the steps of: forming a plurality of semiconductor layers on one surface of a semiconductor wafer, the top layer overlying a channel layer; forming over the top layer first and second mask layers, the second mask layer overlying the first mask layer; selectively etching part of the first mask layer such that the second mask layer overhangs the first mask layer; anisotropically mesa etching the top and channel semiconductor layers such that the etch undercuts the second mask, thereby to form a mesa that extends at an angle from a flat semiconductor surface and is overhung by the first and second mask layers; forming an anti-channel layer in the flat semiconductor surface comprising the step of projecting impurities toward the flat surface from a location opposite the second mask layer, such that the second mask layer shields the mesa surface from the projected impurities; forming a relatively thick insulative layer over the flat surface comprising the step of depositing insulative material on the flat surface from a location opposite the second mask layer such that the second mask layer shields the mesa surface from the deposited insulative material; selectively dissolving the second mask layer, thereby leaving the first mask layer which overhangs part of the mesa surface; forming a channel region in the channel layer comprising the step of projecting the second impurities toward the mesa surface from a location opposite the first mask layer such that the first mask layer and the relatively thick insulative layer expose only the channel layer to the second impurities; and forming a gate electrode over the channel region comprising the step of evaporating metal onto the mesa structure from a point opposite the first mask layer such that the overhanging portion of the first mask layer shields the top semiconductor layer from the vaporized metal.
Claim 13
Independent Claim
311 words
A method for making a field effect transistor comprising the steps of: forming a plurality of semiconductor layers on one surface of a semiconductor wafer, the top layer overlying a channel layer; forming over the top layer first and second mask layers, the second mask layer overlying the first mask layer; selectively etching part of the first mask layer such that the second mask layer overhangs the first mask layer; anisotropically mesa etching the top and channel semiconductor layers such that the etch undercuts the second mask, thereby to form a mesa that extends at an angle from a flat semiconductor surface and is overhung by the first and second mask layers; forming an anti-channel layer in the flat semiconductor surface comprising the step of projecting impurities toward the flat surface from a location opposite the second mask layer, such that the second mask layer shields the mesa surface from the projected impurities; forming a relatively thick insulative layer over the flat surface comprising the step of depositing insulative material on the flat surface from a location opposite the second mask layer such that the second mask layer shields the mesa surface from the deposited insulative material; selectively dissolving the second mask layer, thereby leaving the first mask layer which overhangs part of the mesa surface; forming a channel region in the channel layer comprising the step of projecting the second impurities toward the mesa surface from a location opposite the first mask layer such that the first mask layer and the relatively thick insulative layer expose only the channel layer to the second impurities; and forming a gate electrode over the channel region comprising the step of evaporating metal onto the mesa structure from a point opposite the first mask layer such that the overhanging portion of the first mask layer shields the top semiconductor layer from the vaporized metal.
Claim 14
Dependent Claim
65 words
The method of claim 11 wherein: the channel layer contains impurities of a first type such as to give the channel layer a first conductivity type; the step of forming the channel stop comprises the step of ion implanting impurities of the first type; and the step of forming the channel region comprises the step of ion implanting second impurities of a second conductivity type.
Claim 15
Dependent Claim
11 words
A field effect transistor made by the process of claim 1.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-07-08 | 1978-01-07 | 1978-07-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-07-08 | 1982-01-07 | 1982-07-09 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-07-08 | 1986-01-07 | 1986-07-09 | $7700.00 | Window Closed / Lapsed |