US3761785A
Expired / Lapsed
US
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Methods for making transistor structures
Assignee: AT&T Inc
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Filing: 1971-04-23
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Granted: 1973-09-25
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Expires: 1991-04-23
Abstract
Abstract A high frequency field effect transistor is made by first epitaxially growing semiconductor channel and drain layers over a source layer. An oxide layer is formed on the upper drain layer which acts as a mask during etching of the epitaxial layers. Anisotropic etching of the semiconductor forms a mesa configuration of the channel and drain layers which is overlapped by the upper oxide layer. Metal is then evaporated onto the mesa from a point opposite the oxide layer. The overhanging oxide layer masks part of the mesa, particularly the drain layer, to define precisely the area covered by the evaporated gate contact, as required for high frequency operation. Other embodiments are also described.
Inventors
- 👤 B Pruniaux
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 16:20
CPC Classifications
H; H10; H10D; H10D62/00; H10D62/10; H10D62/13; H10D62/149; H10D62/151; H10D30/00; H10D30/60; H10D30/63; H10D30/80; H10D30/87; H10D30/871; H10P; H10P50/00; H10P50/60; H10P50/64; H10P50/642; H10P50/644; H10P95/00; Y; Y10; Y10S; Y10S148/00; Y10S148/037; Y10S148/051; Y10S148/085; Y10S148/106; Y10S438/00; Y10S438/942; Y10S438/944
Claims Analysis
Total Claims: 18
Claim 1
Independent Claim
122 words
A method for making transistor devices comprising the steps of: forming on a semiconductor wafer successive first, second and third layers, at least one layer having a different conductivity type from that of another layer; forming a smaller area oxide mask on the surface of the third layer; selectively etching the semiconductor layers to form a mesa structure that is overlapped by the oxide mask layer; forming an insulative layer on the etched surfaces of the first, second and third layers; and evaporating metal onto the mesa structure, including at least part of the insulative layer overlying the second layer, from a point opposite the oxide mask layer such that the mask layer shadow masks the third layer from the vaporized metal.
Claim 2
Independent Claim
122 words
A method for making transistor devices comprising the steps of: forming on a semiconductor wafer successive first, second and third layers, at least one layer having a different conductivity type from that of another layer; forming a smaller area oxide mask on the surface of the third layer; selectively etching the semiconductor layers to form a mesa structure that is overlapped by the oxide mask layer; forming an insulative layer on the etched surfaces of the first, second and third layers; and evaporating metal onto the mesa structure, including at least part of the insulative layer overlying the second layer, from a point opposite the oxide mask layer such that the mask layer shadow masks the third layer from the vaporized metal.
Claim 3
Dependent Claim
29 words
The method of claim 1 wherein: the step of etching the second and third layers comprises the step of anisotropic etching the said layers to form the mesa configuration.
Claim 4
Dependent Claim
58 words
The method of claim 2 wherein: the semiconductor is silicon, the upper surface of the wafer is oriented along the (100) crystallographic plane and the Mask layer is oriented to give anisotropic etching along the (110) plane, whereby the etching undercuts the mask layer to form the overhang and the mesa sides taper at a 45 degree angle.
Claim 5
Dependent Claim
45 words
The method of claim 2 wherein: the mask layer overhangs the junction between the second and third layers, but does not overhang the junction between the first and second layers, whereby at least part of said evaporated metal is deposited adjacent to the second layer.
Claim 6
Dependent Claim
35 words
The method of claim 4 further comprising the step of: forming an insulative layer on the mesa surface prior to the metal evaporation step, whereby the finished structure may be operated as an IGFET device.
Claim 7
Dependent Claim
117 words
The method of claim 4 wherein: the step of forming the mask layer comprises the steps of forming a first mask layer on the upper surface of the third 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; depositing the insulative material on the horizontal upper surface of the wafer 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 8
Dependent Claim
27 words
The method of claim 4 wherein: the second and third layers constitute channel and drain layers formed by epitaxial growth, thereby permitting extremely small active channel lengths.
Claim 9
Independent Claim
106 words
A method for making IGFET devices comprising the steps of: forming on a semiconductor wafer successive source, channel, and drain layers; forming a smaller area oxide mask layer on the drain layer; selectively etching the semiconductive layers to form a mesa structure that is overlapped by the oxide mask layer; forming an insulative layer on the etched surface of the source, channel, and drain layers; and evaporating metal onto the mesa structure, including at least part of the insulative layer overlying the channel layer, from a point opposite the oxide mask layer such that the mask layer shadow masks the drain layer from the vaporized metal.
Claim 10
Independent Claim
106 words
A method for making IGFET devices comprising the steps of: forming on a semiconductor wafer successive source, channel, and drain layers; forming a smaller area oxide mask layer on the drain layer; selectively etching the semiconductive layers to form a mesa structure that is overlapped by the oxide mask layer; forming an insulative layer on the etched surface of the source, channel, and drain layers; and evaporating metal onto the mesa structure, including at least part of the insulative layer overlying the channel layer, from a point opposite the oxide mask layer such that the mask layer shadow masks the drain layer from the vaporized metal.
Claim 11
Dependent Claim
34 words
The method of claim 8 wherein: the step of forming the channel and drain layers comprises the step of epitaxially growing said channel and drain layers, thereby permitting an extremely small active channel length.
Claim 12
Dependent Claim
65 words
The method of claim 9 wherein the oxide mask layer overhangs the mesa structure by a distance Wo that conforms to the relation T1 + T2/tan theta > Wo > T1/tan theta where T1 is the thickness of the drain layer, T2 is the thickness of the channel layer, and theta is the angle that the sides of the mesa forms with the wafer surface.
Claim 13
Independent Claim
176 words
A method for making transistor devices comprising the steps of: forming on a semiconductor wafer successive first, second and third layers, at least one layer having a different conductivity type from that of another layer; forming a smaller area oxide mask layer on the surface of the third layer; selectively etching the semiconductor layers by using said mask layer to form a mesa structure having tapered sidewalls extending from the surface of the third layer to said first layer, with part of the tapered sidewalls being defined by an etched surface of the second layer, and the remaining portion of the third layer being completely overlapped by the oxide mask layer; forming an insulative layer on the exposed surface of the first layer, including that portion which is closely adjacent the second layer; and evaporating metal onto the insulative layer, the mask layer and exposed portions of the tapered sidewalls of the second layer from a point opposite the oxide mask layer such that the mask layer masks the third layer completely from the vaporized metal.
Claim 14
Independent Claim
176 words
A method for making transistor devices comprising the steps of: forming on a semiconductor wafer successive first, second and third layers, at least one layer having a different conductivity type from that of another layer; forming a smaller area oxide mask layer on the surface of the third layer; selectively etching the semiconductor layers by using said mask layer to form a mesa structure having tapered sidewalls extending from the surface of the third layer to said first layer, with part of the tapered sidewalls being defined by an etched surface of the second layer, and the remaining portion of the third layer being completely overlapped by the oxide mask layer; forming an insulative layer on the exposed surface of the first layer, including that portion which is closely adjacent the second layer; and evaporating metal onto the insulative layer, the mask layer and exposed portions of the tapered sidewalls of the second layer from a point opposite the oxide mask layer such that the mask layer masks the third layer completely from the vaporized metal.
Claim 15
Dependent Claim
119 words
A transistor made by the steps of: forming on a semiconductor wafer successive first, second and third layers, at least one layer having a different conductivity type from that of another layer; forming a smaller area oxide mask on the surface of the third layer; selectively etching the semiconductor layers to form a mesa structure that is overlapped by the oxide mask layer; forming an insulative layer on the etched surfaces of the first, second and third layers; and evaporating metal onto the mesa structure, including at least part of the insulative layer overlying the second layer, from a point opposite the oxide mask layer such that the mask layer shadow masks the third layer from the vaporized metal.
Claim 16
Dependent Claim
119 words
A transistor made by the steps of: forming on a semiconductor wafer successive first, second and third layers, at least one layer having a different conductivity type from that of another layer; forming a smaller area oxide mask on the surface of the third layer; selectively etching the semiconductor layers to form a mesa structure that is overlapped by the oxide mask layer; forming an insulative layer on the etched surfaces of the first, second and third layers; and evaporating metal onto the mesa structure, including at least part of the insulative layer overlying the second layer, from a point opposite the oxide mask layer such that the mask layer shadow masks the third layer from the vaporized metal.
Claim 17
Dependent Claim
173 words
A transistor made by the steps of: forming on a semiconductor wafer successive first, second and third layers, at least one layer having a different conductivity type from that of another layer; forming a smaller area oxide mask layer on the surface of the third layer; selectively etching the semiconductor layers by using said mask layer to form a mesa structure having tapered sidewalls extending from the surface of the third layer to said first layer, with part of the tapered sidewalls being defined by an etched surface of the second layer, and the remaining portion of the third layer being completely overlapped by the oxide mask layer; forming an insulative layer on the exposed surface of the first layer, including that portion which is closely adjacent the second layer; and evaporating metal onto the insulative layer, the mask layer and exposed portions of the tapered sidewalls of the second layer from a point opposite the oxide mask layer such that the mask layer masks the third layer completely from the vaporized metal.
Claim 18
Dependent Claim
173 words
A transistor made by the steps of: forming on a semiconductor wafer successive first, second and third layers, at least one layer having a different conductivity type from that of another layer; forming a smaller area oxide mask layer on the surface of the third layer; selectively etching the semiconductor layers by using said mask layer to form a mesa structure having tapered sidewalls extending from the surface of the third layer to said first layer, with part of the tapered sidewalls being defined by an etched surface of the second layer, and the remaining portion of the third layer being completely overlapped by the oxide mask layer; forming an insulative layer on the exposed surface of the first layer, including that portion which is closely adjacent the second layer; and evaporating metal onto the insulative layer, the mask layer and exposed portions of the tapered sidewalls of the second layer from a point opposite the oxide mask layer such that the mask layer masks the third layer completely from the vaporized metal.
References Cited (Backward Citations)
US3244555A
Cited
US3506502A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-09-24 | 1977-03-26 | 1977-09-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-09-24 | 1981-03-26 | 1981-09-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-09-24 | 1985-03-26 | 1985-09-25 | $7700.00 | Window Closed / Lapsed |