# US 4,398,964 A · Method of forming ion implants self-aligned with a cut

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- Number: US 4,398,964 A
- Document ID: US4398964A
- Status: Granted
- Kind: A
- Application number: 06/329,364
- Filed: 1981-12-10
- Granted: 1983-08-16
- Earliest claimed: 1981-12-10
- Assignees: Signetics Corporation
- Inventors: Manohar L. Malwah
- Web page: https://patentgrep.com/patent/US4398964A

## CPC

- H10W 10/10: Isolation regions comprising dielectric materials
- H10D 62/112: {for preventing surface leakage due to surface inversion layers, e.g. by using channel stoppers}
- H10P 30/22: using masks
- H10P 76/20: of masks comprising organic materials
- H10W 10/019: {using epitaxial passivated integrated circuit [EPIC] processes}
- H10W: GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
- H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10

## Abstract

A method of fabricating a thick field oxide isolation layer employs dual photoresist layers and selective ion implantation. A thick field oxide layer is grown on a silicon wafer and is covered with a negative photoresist layer followed by a thicker positive photoresist layer. The positive photoresist layer is exposed through a mask and developed to leave a portion remaining where an aperture in the field oxide is to be made. Boron ions are implanted into the silicon wafer through the layers not covered by positive photoresist. The remaining positive photoresist and the underlying negative photoresist are removed to expose the field oxide, after which the patterned negative photoresist is used as a mask to etch a hole in the field oxide that is self-aligned between the boron implants.

## Claims

### Claim 1

A method of implanting impurity ions in regions lying laterally spaced apart within a first stratum of a semiconductor body and offset and self-aligned with the edges of an opening formed within a second stratum of material lying above said first stratum, said method comprising:
(a) providing a semiconductor body having a first stratum therein and providing a second stratum of material adjacent to said first stratum,
(b) superimposing successive layers of a thin negative photoresist and a thicker positive photoresist over said second stratum in that order,
(c) removing only selected spaced portions of said positive photoresist layer by photolithographic means to produce voids therein,
(d) subjecting the structure thus formed to impurity ions of such velocity that impurity ions deposit in laterally spaced implanted regions of said first stratum that are aligned with said voids but are blocked from regions underlying said positive photoresist layer,
(e) removing the remaining positive photoresist layer and the underlying part of negative photoresist layer, and
(f) while using the remaining negative photoresist layer as a mask, removing material of said second stratum that is uncovered by said negative photoresist layer to produce an opening within said second stratum that is self-aligned with and disposed between said laterally spaced regions of implanted impurity ions.

### Claim 2 (depends on 1)

The invention according to claim 1, wherein said semiconductor body and said second stratum of material are made of different material.

### Claim 3 (depends on 1)

The invention according to claim 1, wherein said semiconductor body is silicon and said second stratum of material comprises silicon dioxide that is thermally grown on said silicon.

### Claim 4 (depends on 1)

The invention according to claim 1, wherein said second stratum of material comprises silicon nitride.

### Claim 5 (depends on 3)

The invention according to claim 3 wherein said silicon dioxide layer is about 4000-6000 angstroms thick.

### Claim 6 (depends on 5)

The invention according to claim 5 wherein said negative photoresist layer is about 3000 angstroms thick and said positive photoresist is about 15,000 angstroms thick.

### Claim 7 (depends on 1)

The invention according to claim 1, wherein said semiconductor body comprises P type silicon and said impurity ions comprise boron.

### Claim 8 (depends on 1)

The invention according to claim 1, wherein in step (e) said positive photoresist layer is removed by chemical stripping, after which said underlying part of the negative photoresist layer is removed with a developer solvent.

### Claim 9 (depends on 1)

The invention according to claim 1, wherein in step (f) the material of said second stratum is removed by chemical means.

### Claim 10 (depends on 1)

The invention according to claim 1, and further including the step of removing the remaining negative photoresist layer after said opening is produced.

### Claim 11 (depends on 10)

The invention according to claim 10, wherein said remaining negative photoresist layer is removed by chemical stripping.