US4472871A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method of making a plurality of MOSFETs having different threshold voltages
Assignee: STMicroelectronics lnc USA
•
Filing: 1980-11-19
•
Granted: 1984-09-25
•
Expires: 2000-11-19
Abstract
Abstract An integrated circuit using MOSFETs having varying threshold voltages permitting improved performance and reduced area utilization on a monolithic semiconductor chip is produced by selectively varying ion implantation doses in the channels of the MOSFETs. By repeated masking and implanting steps, selected MOSFETs are implanted with differing doses of ions and combinations of doses, thereby forming circuit portions with MOSFETs having threshold voltages tailored to optimize different characteristics associated with different circuit portions.
Inventors
- 👤 Robert S. Green
- 👤 Harold W. Dozier
- 👤 Vernon D. McKenny
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 15:55
CPC Classifications
H; H10; H10D; H10D84/00; H10D84/01; H10D84/0123; H10D84/0126; H10D84/0128; H10D84/02; H10D84/03; H10D84/038
Claims Analysis
Total Claims: 5
Claim 1
Independent Claim
380 words
A method of making an integrated circuit including an inverter circuit having a plurality of MOSFETs on a single semiconductor substrate of a first conductivity type comprising: preparing a body of semiconductor material with a plurality of transistor sites, identifying first, second, third, and fourth groups of sites, selectively masking said second and fourth groups of sites against ion implantation while leaving said first and third groups unmasked, a first exposing of the semiconductor material to a source of ions of a conductivity altering material to implant said ions in said first and third groups of sites, selectively masking said first and fourth groups of sites against ion implantation while leaving said second and third groups of sites unmasked, a second exposing of the semiconductor material to a source of ions of a conductivity altering material to implant ions into said second and third groups of sites, forming a MOSFET in each site, whereby four different types of MOSFETs are formed, each type corresponding to one of the four groups of sites, the types being distinguishable on the basis of differing threshold voltages, forming a connection from the drain of a MOSFET of said first type to a drain voltage and forming a connection from the source of said MOSFET of said first type to an output node, forming a connection from the drain of a MOSFET of said second type to a drain voltage and forming a connection from the source of said MOSFET of said second type to its respective gate and the gate of said MOSFET of said first type, forming a connection from the drain of a first MOSFET of said fourth type to the source of said MOSFET of said first type and forming a connection from the source of said first MOSFET of said fourth type to a source voltage, and forming a connection from the drain of a second MOSFET of said fourth type to the source of said MOSFET of said second type, forming a connection from the source of said second MOSFET of said fourth type to a source voltage, and forming a connection from the gate of said second MOSFET of said fourth type to the gate of said first MOSFET of said fourth type and to an input node.
Claim 2
Independent Claim
380 words
A method of making an integrated circuit including an inverter circuit having a plurality of MOSFETs on a single semiconductor substrate of a first conductivity type comprising: preparing a body of semiconductor material with a plurality of transistor sites, identifying first, second, third, and fourth groups of sites, selectively masking said second and fourth groups of sites against ion implantation while leaving said first and third groups unmasked, a first exposing of the semiconductor material to a source of ions of a conductivity altering material to implant said ions in said first and third groups of sites, selectively masking said first and fourth groups of sites against ion implantation while leaving said second and third groups of sites unmasked, a second exposing of the semiconductor material to a source of ions of a conductivity altering material to implant ions into said second and third groups of sites, forming a MOSFET in each site, whereby four different types of MOSFETs are formed, each type corresponding to one of the four groups of sites, the types being distinguishable on the basis of differing threshold voltages, forming a connection from the drain of a MOSFET of said first type to a drain voltage and forming a connection from the source of said MOSFET of said first type to an output node, forming a connection from the drain of a MOSFET of said second type to a drain voltage and forming a connection from the source of said MOSFET of said second type to its respective gate and the gate of said MOSFET of said first type, forming a connection from the drain of a first MOSFET of said fourth type to the source of said MOSFET of said first type and forming a connection from the source of said first MOSFET of said fourth type to a source voltage, and forming a connection from the drain of a second MOSFET of said fourth type to the source of said MOSFET of said second type, forming a connection from the source of said second MOSFET of said fourth type to a source voltage, and forming a connection from the gate of said second MOSFET of said fourth type to the gate of said first MOSFET of said fourth type and to an input node.
Claim 3
Dependent Claim
72 words
A method according to claim 1 further including selecting said source of ions in said first exposing of the semiconductor material and selecting said source of ions in said second exposing of the semiconductor material to be of a second conductivity type, and selecting the dosage of ions in said first exposing of the semiconductor material to be different than the dosage of ions in said second exposing of the semiconductor material.
Claim 4
Dependent Claim
59 words
A method according to claim 2 wherein the starting semiconductor material is selected to be P-type conductivity and the ions are selected to be of an N-type material, such that the depletion mode MOSFETs are formed by ion-implant doses sufficient to convert the semiconductor material in the channels of the depletion mode MOSFETs from P-type conductivity to N-type conductivity.
Claim 5
Dependent Claim
127 words
A method according to claim 3 wherein the ion dosage to said first site is adjusted to form an area which is slightly depletion type having a threshold voltage in the range 2.4 volts to zero volts, the ion dosage to said second site is adjusted to form an area which is standard depletion type having a threshold voltage in the range of 2.4 volts to 4.3 volts, the ion dosage to said third site is adjusted to form an area which is highly depletion type having a threshold voltage in the range from 4.3 volts to 5.3 volts, and said fourth site is adjusted to form an area which is standard enhancement type having a threshold voltage in the range from zero volts to 1.5 volts.
References Cited (Backward Citations)
US3895966A
Cited
US3775693A
Cited
US3898105A
Cited
US3868274A
Cited
US3868274B1
Cited
US4052229A
Cited
US4052229B1
Cited
US4276095A
Cited
US4274105A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1987-09-25 | 1988-03-26 | 1988-09-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-09-25 | 1992-03-26 | 1992-09-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1995-09-25 | 1996-03-26 | 1996-09-25 | $7700.00 | Window Closed / Lapsed |