# US 4,392,938 A · Radio frequency etch table with biased extension member

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- Number: US 4,392,938 A
- Document ID: US4392938A
- Status: Granted
- Kind: A
- Application number: 06/320,385
- Filed: 1981-11-12
- Granted: 1983-07-12
- Earliest claimed: 1981-11-12
- Assignees: Varian Associates, Inc.
- Inventors: David J. Harra; Frederick T. Turner
- Web page: https://patentgrep.com/patent/US4392938A

## 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 37/32697: {Electrostatic control}
- 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

An RF etch table has a biased extension member positioned adjacent its periphery. The extension member is electrically conductive, but is insulated from other conductive members in the system. The extension member is positioned with respect to the periphery of the table in a manner such that the boundary of the plasma induced above the etch table is continued beyond the periphery of the etch table, thereby eliminating the focusing of ions onto the edges of an item being etched on the table. The potential impressed upon the extension member produces a dark space above its surface having a sufficient height so that the horizontal configuration of the sheath above the etch table is continued beyond its edges. More uniform etching is accomplished.

## Claims

### Claim 1

An RF etch table for uniformly etching a semiconductor wafer by sputtering, comprising,
a table structure adapted to receive and hold a generally circular semiconductor wafer to be subjected to sputter etching;
an RF power supply electrically connected to said table structure;
an extension member positioned adjacent the periphery of said table, said extension member being electrically conductive and being insulated from other conductive members;
a bias power supply means for applying an electrical potential to said extension member whereby the plasma generated above said table structure extends horizontally beyond the periphery of said etch table and above at least a portion of said extension member; and
a shielding member placed over said extension member, but not in electrical communication with said extension member, whereby said biased extension member is protected from unwanted sputtering to thereby avoid metallic contamination of said semiconductor wafer.

### Claim 2 (depends on 1)

An RF etch table in accordance with claim 1 wherein said RF power supply is capacitively coupled to said etch table.

### Claim 3 (depends on 1)

An RF etch table in accordance with claim 1 wherein said table structure includes means to produce active cooling of said semiconductor wafer.

### Claim 4 (depends on 3)

An RF etch table in accordance with claim 3 wherein said means to produce active cooling comprises means to accomplish gas conduction cooling.

### Claim 5 (depends on 1)

An RF etch table in accordance with claim 1 wherein said extension member is positioned above the level of the top surface of said table structure and below the low boundary of the plasma sheath produced above said table structure.

### Claim 6 (depends on 5)

An RF etch table in accordance with claim 5 wherein said extension member is positioned from 2 mm to 4 mm above the level of said table structure.

### Claim 7 (depends on 1)

An RF etch table in accordance with claim 1 wherein said bias power supply means applies electrical potential in the range of 0.1 to 0.4 times the potential on said table structure.

### Claim 8 (depends on 7)

An RF etch table structure in accordance with claim 7 wherein said bias power supply means applies an electrical potential in the range of 0.2 to 0.3 times the potential on said table structure.

### Claim 9 (depends on 1)

An RF etch table in accordance with claim 1 wherein said table structure is circular in shape and wherein said extension member comprises a ring positioned in annular, concentric fashion around said circular table structure.

### Claim 10 (depends on 1)

An RF etch table in accordance with claim 1 wherein said shielding member is connected to ground.

### Claim 11 (depends on 10)

An RF etch table in accordance with claim 10 wherein said bias power supply applies a negative potential to said biased extension member.