US4499656A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Deep mesa process for fabricating monolithic integrated Schottky barrier diode for millimeter wave mixers
Assignee: Unisys Corp
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Filing: 1983-08-15
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Granted: 1985-02-19
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Expires: 2003-08-15
Abstract
Abstract A method of fabricating gallium arsenide devices in which contact isolation is provided by a deep mesa step structure. Step coverage of deposited conductive films is facilitated by preferential orientation of the non-centrosymmetric crystal substrate and wet anisotropic etching that provides a sloped step. Problems of fine line definition of the Schottky anode contact in the photolithographic process are addressed by a two-step exposure of a single layer of thick photoresist followed by a chlorobenzene soak prior to development that ensures a retrograde resist profile needed for good lift-off of undesired evaporated metal. Mesas as deep as 7 μm have been obtained, which permit the fabrication of monolithic planar mixer millimeter-wave diodes with low series resistance and reduced parasitic capacitance.
Inventors
- 👤 Walter Fabian
- 👤 Frank H. Spooner
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 14:49
CPC Classifications
H; H10; H10P; H10P76/00; H10P76/20; H10P76/202; H10D; H10D8/00; H10D8/60; H10W; H10W20/00; H10W20/40; H10W20/41; H10W20/44; H10W20/4451; Y; Y10; Y10S; Y10S438/00; Y10S438/942; Y10S438/948; Y10S438/951
Claims Analysis
Total Claims: 39
Claim 1
Independent Claim
286 words
A method for fabricating semiconductor devices on a non-centrosymmetric semi-insulating substrate, comprising: disposing a heavily doped contact layer on said substrate, disposing a lightly doped active layer on said contact layer, orienting said substrate in a predetermined crystallographic direction, selectively removing a first region of said active layer and a portion of said contact layer underlying said first region, metallizing said contact layer in said first region to form an ohmic contact, preferentially removing a second region of said active layer, a portion of said contact layer underlying said active layer in said region, and a portion of said substrate underlying said contact layer in said region, said second region longitudinally disposed proximate to and spaced apart from said metallized region, a portion between said first and second regions defining a third intermediate region, the boundary between said second and third regions defining a step region disposed in said predetermined crystallographic direction, depositing an insulating layer over said metallized first region, said second region, said third region, and said step region, depositing a layer of photoresist over said insulating layer, exposing said photoresist through mask means in said second and third regions, said exposure selectively focused to pattern said second and third regions excluding said step region, exposing said photoresist through further mask means focused to pattern said step region, developing said photoresist, selectively removing regions of said insulating layer to expose said second patterned region, said step patterned region, and said third patterned region, metallizing said first, second, and third patterned regions, and further metallizing by means of an overlay disposed thereupon said second patterned region, a portion of said third patterned region, and said step patterned region, whereby said regions are integrally electrically contiguous.
Claim 2
Independent Claim
286 words
A method for fabricating semiconductor devices on a non-centrosymmetric semi-insulating substrate, comprising: disposing a heavily doped contact layer on said substrate, disposing a lightly doped active layer on said contact layer, orienting said substrate in a predetermined crystallographic direction, selectively removing a first region of said active layer and a portion of said contact layer underlying said first region, metallizing said contact layer in said first region to form an ohmic contact, preferentially removing a second region of said active layer, a portion of said contact layer underlying said active layer in said region, and a portion of said substrate underlying said contact layer in said region, said second region longitudinally disposed proximate to and spaced apart from said metallized region, a portion between said first and second regions defining a third intermediate region, the boundary between said second and third regions defining a step region disposed in said predetermined crystallographic direction, depositing an insulating layer over said metallized first region, said second region, said third region, and said step region, depositing a layer of photoresist over said insulating layer, exposing said photoresist through mask means in said second and third regions, said exposure selectively focused to pattern said second and third regions excluding said step region, exposing said photoresist through further mask means focused to pattern said step region, developing said photoresist, selectively removing regions of said insulating layer to expose said second patterned region, said step patterned region, and said third patterned region, metallizing said first, second, and third patterned regions, and further metallizing by means of an overlay disposed thereupon said second patterned region, a portion of said third patterned region, and said step patterned region, whereby said regions are integrally electrically contiguous.
Claim 3
Dependent Claim
33 words
The method in accordance with claim 1 in which said semi-insulating substrate comprises a compound selected from the Group III-V elements of the Periodic Table having a crystallographic structure similar to gallium arsenide.
Claim 4
Dependent Claim
40 words
The method in accordance with claim 2, in which said compound is selected from the group consisting of gallium arsenide, indium antimonide, indium phosphide, gallium aluminum arsenide, gallium indium aluminum arsenide, indium arsenide, gallium phosphide, and gallium aluminum indium phosphide.
Claim 5
Dependent Claim
17 words
The method in accordance with claim 3, in which said compound is comprised of gallium arsenide material.
Claim 6
Dependent Claim
32 words
The method in accordance with claim 4, in which the step of disposing a contact layer on said substrate comprises vapor phase deposition of doped gallium arsenide material on said semi-insulating substrate.
Claim 7
Dependent Claim
34 words
The method in accordance with claim 5, in which the step of disposing an active layer on said contact layer comprises a further vapor phase deposition of doped gallium arsenide on said contact layer.
Claim 8
Dependent Claim
15 words
The method in accordance with claim 1, in which said insulating layer comprises silicon nitride.
Claim 9
Dependent Claim
23 words
The method in accordance with claim 7, in which said silicon nitride is deposited by the process of plasma enhanced chemical vapor deposition.
Claim 10
Dependent Claim
18 words
The method in accordance with claim 5, in which said contact layer is doped with n type material.
Claim 11
Dependent Claim
18 words
The method in accordance with claim 6, in which said active layer is doped with n type material.
Claim 12
Dependent Claim
26 words
The method in accordance with claim 1, wherein said first region of said contact layer is metallized with sequential layers of nickel, gold, germanium, and gold.
Claim 13
Dependent Claim
30 words
The method in accordance with claim 1, in which said first, second, and third patterned regions and said patterned step are metallized with sequential layers of titanium, palladium, and gold.
Claim 14
Dependent Claim
20 words
The method in accordance with claim 12, further comprising a metallizing overlay comprised of sequential layers of titanium and gold.
Claim 15
Dependent Claim
23 words
The method of claim 1, wherein said predetermined crystallographic direction comprises the [011] direction and said step is aligned parallel to said direction.
Claim 16
Dependent Claim
17 words
The method of claim 14, in which said step forms a sloped wall bounding a deep mesa.
Claim 17
Dependent Claim
16 words
The method of claim 15, in which said mesa is at least 4 μm in depth.
Claim 18
Dependent Claim
20 words
The method of claim 7, in which said insulating layer is deposited by the process of pyrolytic chemical vapor deposition.
Claim 19
Dependent Claim
20 words
The method of claim 1, further comprising soaking said photoresist in a chlorobenzene bath after exposure and prior to development.
Claim 20
Independent Claim
322 words
A method for fabricating semiconductor devices on a non-centrasymmetric semi-insulating substrate, comprising: disposing a heavily doped contact layer on said substrate, disposing a lightly doped active layer on said contact layer, orienting said substrate in a predetermined crystallographic direction, selectively removing a first region of said active layer and a portion of said contact layer underlying said first region, preferentially removing a second region of said active layer, a portion of said contact layer underlying said active layer in said region, and a portion of said substrate underlying said contact layer in said region, said second region longitudinally disposed proximate to and spaced apart from said metallized region, a portion between said first and second regions defining a third intermediate region, the boundary between said second and third regions defining a step region disposed in said predetermined crystallographic direction, depositing a first layer of insulating material over said first region, said second region, said third region and said step region, selectively removing a portion of said insulating material over said first region to expose said contact layer, metallizing said contact layer in said first region to form an ohmic contact, depositing a second layer of insulating material superposed on said first insulating layer and said metallized contact, depositing a layer of photoresist over said insulating layer, exposing said photoresist through mask means in said second and third regions, said exposure selectively focused to pattern said second and third regions excluding said step region, exposing said photoresist through further mask means focused to pattern said step region, developing said photoresist, selectively removing regions of said insulating layer to expose said second patterned region, said step patterned region, and said third patterned region, metallizing said first, second, and third patterned regions, and further metallizing by means of an overlay disposed thereupon said second patterned region, a portion of said third patterned region, and said step patterned region, whereby said regions are integrally electrically contiguous.
Claim 21
Independent Claim
322 words
A method for fabricating semiconductor devices on a non-centrasymmetric semi-insulating substrate, comprising: disposing a heavily doped contact layer on said substrate, disposing a lightly doped active layer on said contact layer, orienting said substrate in a predetermined crystallographic direction, selectively removing a first region of said active layer and a portion of said contact layer underlying said first region, preferentially removing a second region of said active layer, a portion of said contact layer underlying said active layer in said region, and a portion of said substrate underlying said contact layer in said region, said second region longitudinally disposed proximate to and spaced apart from said metallized region, a portion between said first and second regions defining a third intermediate region, the boundary between said second and third regions defining a step region disposed in said predetermined crystallographic direction, depositing a first layer of insulating material over said first region, said second region, said third region and said step region, selectively removing a portion of said insulating material over said first region to expose said contact layer, metallizing said contact layer in said first region to form an ohmic contact, depositing a second layer of insulating material superposed on said first insulating layer and said metallized contact, depositing a layer of photoresist over said insulating layer, exposing said photoresist through mask means in said second and third regions, said exposure selectively focused to pattern said second and third regions excluding said step region, exposing said photoresist through further mask means focused to pattern said step region, developing said photoresist, selectively removing regions of said insulating layer to expose said second patterned region, said step patterned region, and said third patterned region, metallizing said first, second, and third patterned regions, and further metallizing by means of an overlay disposed thereupon said second patterned region, a portion of said third patterned region, and said step patterned region, whereby said regions are integrally electrically contiguous.
Claim 22
Dependent Claim
23 words
The method in accordance with claim 19, further comprising the step of heating said contact layer after metallizing to 470° for 5 minutes.
Claim 23
Dependent Claim
24 words
The method in accordance with claim 19, wherein said first layer of insulating material is deposited by pyrolytic chemical vapor deposition of silicon nitride.
Claim 24
Dependent Claim
28 words
The method in accordance with claim 19, wherein said second layer of insulating material is deposited by the process of plasma enhanced chemical vapor deposition of silicon nitride.
Claim 25
Dependent Claim
18 words
The method in accordance with claim 19, in which said active layer is doped with n type material.
Claim 26
Dependent Claim
26 words
The method in accordance with claim 19, wherein said first region of said contact layer is metallized with sequential layers of nickel, gold germanium, and gold.
Claim 27
Dependent Claim
30 words
The method in accordance with claim 24, in which said first, second, and third patterned regions and said patterned step are metallized with sequential layers of titanium, palladium, and gold.
Claim 28
Dependent Claim
20 words
The method in accordance with claim 25, further comprising a metallizing overlay comprised of sequential layers of titanium and gold.
Claim 29
Dependent Claim
23 words
The method of claim 19, wherein said predetermined crystallographic direction comprises the [011] direction and said step is aligned parallel to said direction.
Claim 30
Dependent Claim
17 words
The method of claim 27, in which said step forms a sloped wall bounding a deep mesa.
Claim 31
Dependent Claim
16 words
The method of claim 28, in which said mesa is at least 4 μm in depth.
Claim 32
Dependent Claim
20 words
The method of claim 19, further comprising soaking said photoresist in a chlorobenzene bath after exposure and prior to development.
Claim 33
Dependent Claim
21 words
The method of claim 1, further comprising the step of heating said contact layer after metallizing at 470° for 5 minutes.
Claim 34
Dependent Claim
34 words
The method in accordance with claim 19 in which said semi- insulating substrate comprises a compound selected from the Group III-V elements of the Periodic Table having a crystallographic structure similar to gallium arsenide.
Claim 35
Dependent Claim
40 words
The method in accordance with claim 32, in which said compound is selected from the group consisting of gallium arsenide, indium antimonide, indium phosphide, gallium aluminum arsenide, gallium aluminum indium arsenide, indium arsenide, gallium phosphide, and gallium aluminum indium phosphide.
Claim 36
Dependent Claim
17 words
The method in accordance with claim 33, in which said compound is comprised of gallium arsenide material.
Claim 37
Dependent Claim
32 words
The method in accordance with claim 34, in which the step of disposing a contact layer on said substrate comprises vapor phase deposition of doped gallium arsenide material on said semi-insulating substrate.
Claim 38
Dependent Claim
34 words
The method in accordance with claim 35, in which the step of disposing an active layer on said contact layer comprises a further vapor phase deposition of doped gallium arsenide on said contact layer.
Claim 39
Dependent Claim
18 words
The method in accordance with claim 35, in which said contact layer is doped with n type material.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1988-02-19 | 1988-08-20 | 1989-02-19 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1992-02-19 | 1992-08-20 | 1993-02-19 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1996-02-19 | 1996-08-20 | 1997-02-19 | $7700.00 | Window Closed / Lapsed |