# US 4,396,479 A · Ion etching process with minimized redeposition

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- Number: US 4,396,479 A
- Document ID: US4396479A
- Status: Granted
- Kind: A
- Application number: 06/355,445
- Filed: 1982-04-30
- Granted: 1983-08-02
- Earliest claimed: 1980-11-14
- Assignees: Rockwell International Corporation
- Inventors: Addison B. Jones
- Web page: https://patentgrep.com/patent/US4396479A

## CPC

- H10P 50/287: {by chemical means}
- C23C 14/35: by application of a magnetic field, e.g. magnetron sputtering {(C23C14/3457 takes precedence)}
- C23F 4/00: Processes for removing metallic material from surfaces, not provided for in group C23F1/00 or C23F3/00
- H10P 50/262: {by physical means only}
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
- C23C: COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04)
- 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

## Abstract

The invention is a method of minimizing redeposition of thin film material being removed by ion impact via a patterned resist mask, which invention determines the resist mask etching rates in selected atmospheres and determines the material etching rates in selected atmospheres. Then the mask thickness is selected relative to the material thickness, the ambient gases, and the ion beam parameters to cause the resist mask to be faceted to the edges of underlying material as the unprotected layer is removed such that no resist walls remain to receive redeposited material. A different embodiment of the invention employes a getter mask material between the resist mask and said material where the thickness and etching rates of resist, said material and getter material are relatively selected to cause the unprotected getter material to be removed shortly prior to faceting of the resist down to the protected getter material in a first environment, and continues etching the thin film material in a different environment which also causes resist removal while eroding the getter mask very slowly. The getter mask can thus be very thin to minimize redeposition.

## Claims

### Claim 1

The method of minimizing redeposition of thin layer material being removed by ion impact via a patterned resist mask having rectangular cross section, comprising the steps of:
determining the resist mask etching rates in selected atmospheres;
determining the material etching rates in selected atmospheres;
selecting the mask thickness relative to the material thickness and the atmosphere for ion impact to cause the resist mask to be faceted to the edges of underlying material as the unprotected portions of the layer of material are removed such that no resist walls remain to receive redeposited material at the completion of etching said material, and said faceting is simultaneously completed with the removal of the last of the exposed material.

### Claim 2 (depends on 1)

The method of claim 1, wherein:
said material is metal; and
ion impact is caused by ion milling.

### Claim 3 (depends on 1)

The method of claim 1, wherein:
ion impact is caused by sputter etching.

### Claim 4 (depends on 1)

The method of claim 1, wherein:
the thickness of the ion etch resist mask, X.sub.R, is determined for normal incidence ion etching by the formula: ##EQU4## where: X.sub.M =thickness of material to be etched
R.sub..theta..sbsb.p.sup.R =rate of erosion of the bevels of the resist mask
.theta..sub.p.sup.R =angle of maximum ion erosion rate for the resist material (bevel normal to ion direction)
R.sub.0.degree..sup.M =rate of erosion of the material to be etched at normal (0.degree.) incidence.