# US 5,344,787 A · Latid implants for increasing the effective width of transistor elements in a semiconductor device

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- Number: US 5,344,787 A
- Document ID: US5344787A
- Status: Granted
- Kind: A
- Application number: 08/126,626
- Filed: 1993-09-24
- Granted: 1994-09-06
- Earliest claimed: 1993-09-24
- Assignees: VLSI Technology, Inc.
- Inventors: Samuel J. S. Nagalingam; Yu P. Han; Ravi Jhota
- Web page: https://patentgrep.com/patent/US5344787A

## CPC

- H10P 30/222: {characterised by the angle between the ion beam and the crystal planes or the main crystal surface (characterised by the angle between the ion beam and the mask H10P30/221)}
- H10P 30/221: {characterised by the angle between the ion beam and the mask}
- H10W 10/0126: {introducing electrical active impurities in local oxidation regions to create channel stoppers}
- H10W 10/13: formed using local oxidation of silicon [LOCOS], e.g. sealed interface localised oxidation [SILO] or side-wall mask isolation [SWAMI]
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
- H10W: GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10

## Abstract

The diffusion of P-type channel-stop implants into regions where P-type channels are to be formed which will connect N-type source and drain regions of a transistor element on a P-type substrate is effectively compensated for through angled implantation of an N-type dopant material into these regions. Angle implantation is performed by tilting and rotating the wafer in the presence of an N-type ion beam.

## Claims

### Claim 1

A method for increasing the effective width of a P-type channel connecting N-type source and drain regions of a transistor element further comprising a gate which transistor element is located on the surface of a P-type substrate and is separated from other transistor elements on the substrate by field oxide and P-type channel-stop implants which method comprises the steps of:
(a) tilting a transistor-free substrate having P-type field stop implants and field oxide regions which substrate contains a silicon nitride layer over all portions of the substrate surface except over the field oxide regions wherein said substrate is tilted at an angle of from greater than 0.degree. to less than 90.degree. relative to the direction of an N-type ion beam;
(b) ion-implanting N-type ion dopant into the tilted substrate;
(c) rotating the substrate while retaining or later reestablishing the tilt and repeating step (b) until all of the substrate has been exposed to ion-implantation;
(d) thermally treating the substrate produced in step (c) above so as to activate the dopants; and
(e) completing fabrication of said transistor element on the surface of said substrate
wherein sufficient N-type dopant is implanted into the substrate so that the threshold voltage in the boundary of the P-type channel of said transistor element is reduced.

### Claim 2 (depends on 1)

The method according to claim 1, wherein said P-type dopant material is boron and said N-type dopant material is phosphorus or arsenic.

### Claim 3 (depends on 2)

The method according to claim 2, wherein the concentration of the N-type dopant material angle implanted is sufficient to reduce the threshold voltage at the boundary of the P-type channel such that the ratio of the threshold voltage at the channel boundary to the threshold voltage at the center of the channel is from 1:1 to no more than 1.5:1.

### Claim 4 (depends on 1)

The method according to claim 1, wherein the temperature of the thermal anneal is less than about 1000.degree. C..

### Claim 5 (depends on 4)

The method according to claim 4, wherein said temperature is from about 900.degree. C. to about 1000.degree. C..

### Claim 6 (depends on 1)

The method according to claim 1, wherein the N-type dopant material is implanted at an angle ranging from about 30.degree. to about 60.degree. relative to the direction of an N-type ion beam.

### Claim 7 (depends on 6)

The method according to claim 6, wherein said angle ranges from about 40.degree. to about 50.degree..

### Claim 8 (depends on 6)

The method according to claim 6 wherein the ion implantation angle is adjusted during implantation.