# US 4,400,257 A · Method of forming metal lines

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- Number: US 4,400,257 A
- Document ID: US4400257A
- Status: Granted
- Kind: A
- Application number: 06/451,818
- Filed: 1982-12-21
- Granted: 1983-08-23
- Earliest claimed: 1982-12-21
- Assignees: RCA Corporation
- Inventors: Gordon C. Taylor
- Web page: https://patentgrep.com/patent/US4400257A

## CPC

- H10D 30/0612: {of lateral single-gate Schottky FETs}
- C23F 1/02: Local etching
- G03F 7/36: Imagewise removal not covered by groups G03F7/30 - G03F7/34, e.g. using gas streams, using plasma
- G03F 7/40: Treatment after imagewise removal, e.g. baking
- H10D 64/0125: {characterised by the sectional shape, e.g. T or inverted T}
- H10P 76/202: {for lift-off processes}
- H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
- C23F: NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE (working metal by laser beams B23K26/00; desurfacing by applying flames B23K7/00; working of metal by electro-erosion B23H; producing decorative effects by removing surface material, e.g. by engraving, by etching, B44C1/22; electrolytic etching or polishing C25F); INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G)
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10

## Abstract

A method of forming metal lines is described for semiconductor processing wherein a line mask is initially ion milled to provide a mask contour which promotes the onset of chemical etching at the base of the mask. This produces a metal line that has a tapered cross-sectional dimension wherein the base of the line is narrower than the top.

## Claims

### Claim 1

A process for forming a conductive line on a substrate, comprising steps of:
forming a conductive layer on the substrate;
forming an apertured masking layer on the conductive layer, the aperture having a first dimension at the surface of the masking layer adjacent the conductive layer and a narrower dimension at its opposite surface;
depositing a line masking layer on the exposed surface of the metal layer;
removing the apertured masking layer;
ion milling the line masking layer and the exposed portions of the conductive layer for a period of time sufficient to form trenches on either side of the line masking layer and to simultaneously redeposit a portion of the line masking material and the conductive layer on the sides of the line masking material to form projecting wings thereon; and
chemically etching the exposed conductive layer and a portion of the conductive layer under the line masking layer.

### Claim 2 (depends on 1)

The process of claim 1, wherein the step of forming an apertured masking layer comprises:
forming a first layer of masking material on the conductive layer;
exposing a portion of the first layer to delineate a first area which will represent a first aperture;
forming a second layer of masking material on the first layer;
forming a third layer of masking material on the second layer;
exposing a portion of the third layer to delineate another area which will represent a second aperture in alignment with the first aperture;
developing and removing the second delineated area in the third layer to form an aperture and to expose portions of the second layer of masking material;
removing the exposed portion of the second masking layer to form an aperture and to expose the first delineated area; and
removing the exposed portion of the first delineated area to form an aperture in the first masking layer.

### Claim 3 (depends on 2)

The process of claim 2, wherein:
the first and third layers of masking material are layers of photoresist;
the first layer being deposited to a thickness of about 1.5 microns;
the third layer being deposited to a thickness of about 1.0 microns; and
the second layer of masking material is a metal layer deposited to a thickness of about 0.01 microns.

### Claim 4 (depends on 3)

The process of claim 3, wherein the step of depositing a line masking layer, comprises:
depositing successive metal layers;
depositing the first and second layers to a thickness of about 0.1 microns;
depositing a third layer to a thickness of 1.8 microns; and
depositing a fourth layer to a thickness of about 0.4 microns.

### Claim 5 (depends on 4)

The process of claim 4, wherein:
the conductive layer is titanium;
the first and fourth metal layer of the line masking layer are titanium;
the second metal layer of the line masking layer is platinum; and
the third metal layer of the line masking layer is gold.

### Claim 6 (depends on 5)

The process of claim 5, wherein:
the ion milling step is maintained at:
______________________________________ Accelerating voltage 500v Ambient pressure 8 .times. 10.sup.5 Torr. Beam current 20 ma Suppressor grid 250v ______________________________________

### Claim 7 (depends on 6)

The process of claim 6, wherein the ion milling step comprises:
maintaining the substrate normal to the incident beam of ions; and
maintaining the substrate in the ion beam for a period of about 30 minutes.