# US 4,392,932 A · Method for obtaining uniform etch by modulating bias on extension member around radio frequency etch table

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- Number: US 4,392,932 A
- Document ID: US4392932A
- Status: Granted
- Kind: A
- Application number: 06/320,386
- Filed: 1981-11-12
- Granted: 1983-07-12
- Earliest claimed: 1981-11-12
- Assignees: Varian Associates, Inc.
- Inventors: David J. Harra
- Web page: https://patentgrep.com/patent/US4392932A

## CPC

- H01J 37/32623: {Mechanical discharge control means}
- C23F 4/00: Processes for removing metallic material from surfaces, not provided for in group C23F1/00 or C23F3/00
- H01J 37/32706: {Polarising the substrate}
- H01J 37/34: operating with cathodic sputtering (H01J37/36 takes precedence {; methods of cathodic sputtering C23C14/34})
- H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H)
- 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

A method for etching a semiconductor wafer on an RF etch table employs a succession of different biases on an extension member positioned adjacent the periphery of the table. The extension member is electrically conductive, but is insulated from the etch table. The extension member is positioned with respect to the periphery of the table in a manner such that the plasma sheath induced above the etch table is continued beyond the periphery of the table, thereby eliminating the focusing of ions on the edges of an item being etched on the table. As different bias voltages are applied to the extension member, different etch profiles are experienced on the semiconductor wafer. The aggregation of etch profiles produces a more uniform overall etch.

## Claims

### Claim 1

A method for obtaining a uniform etch on a semiconductor wafer being etched on an RF etch table in a plasma etch system, comprising,
placing said semiconductor wafer on said RF etch table, said table having an extension member positioned adjacent its periphery, said extension member being electrically conductive and being insulated from the structures surrounding said table,
generating a plasma above said etch table to thereby etch the surface of said wafer,
protecting the surface of said extension member from ions extracted from said plasma to prevent the generation of unwanted metallic impurities, applying a bias potential to said extension member whereby the sheath of said plasma generated above said etch table is extended beyond the periphery of said etch table and above at least a portion of said extension member, and
modulating said bias potential so as to produce a more uniform overall etch on said semiconductor wafer.

### Claim 2 (depends on 1)

A method of obtaining a uniform etch in accordance with claim 1 wherein said step of applying a bias potential is accomplished by the step of applying a DC bias potential.

### Claim 3 (depends on 1)

A method for obtaining a uniform etch in accordance with claim 1 wherein said step of generating a plasma is accomplished by the steps of introducing a sputtering gas above said etch table and impressing an RF voltage on said etch table.

### Claim 4 (depends on 3)

A method for obtaining a uniform etch in accordance with claim 3 wherein said step of modulating said bias potential is accomplished by the step of modulating said bias potential within the range of 0.1 to 0.4 times the self bias potential of said etch table.

### Claim 5 (depends on 4)

A method for obtaining a uniform etch in accordance with claim 4 wherein said step of modulating said bias potential is accomplished by the step of switching said bias voltage among a series of discrete voltages.

### Claim 6 (depends on 5)

A method for obtaining a uniform etch in accordance with claim 5 wherein said step of switching said bias voltage among a series of discrete voltage is accomplished by the step of switching said bias voltage between two discrete voltages.

### Claim 7 (depends on 4)

A method for obtaining a uniform etch in accordance with claim 4 wherein said step of modulating said bias voltage is accomplished by the step of applying a continuously changing voltage to said extension member.

### Claim 8 (depends on 4)

A method for obtaining a uniform etch in accordance with claim 4 wherein said step of modulating said bias potential within the range of 0.1 to 0.4 times said self bias potential of said etch table is accomplished by the step of modulating said bias potential within the range of 0.2 to 0.3 times said self bias potential of said etch table.