# US 5,346,586 A · Method for selectively etching polysilicon to gate oxide using an insitu ozone photoresist strip

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- Number: US 5,346,586 A
- Document ID: US5346586A
- Status: Granted
- Kind: A
- Application number: 07/996,074
- Filed: 1992-12-23
- Granted: 1994-09-13
- Earliest claimed: 1992-12-23
- Assignees: Micron Semiconductor, Inc.
- Inventors: David J. Keller
- Web page: https://patentgrep.com/patent/US5346586A

## CPC

- H10P 50/287: {by chemical means}
- H10P 50/268: {of silicon-containing layers}
- H10P 50/71: {using masks for conductive or resistive materials}
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10

## Abstract

In semiconductor manufacture, a method of etching a polysilicon layer to a gate oxide in a semiconductor structure is provided. The method is performed insitu in a plasma etch chamber. Initially, an oxide hard mask is formed on the semiconductor structure by etching a deposited oxide layer through a photoresist mask. The photoresist mask is then stripped in the same etch chamber using a high pressure ozone plasma. With the photoresist mask stripped from the semiconductor structure, the polysilicon layer can be etched through the oxide hard mask to the gate oxide with a high etch selectivity.

## Claims

### Claim 1

In semiconductor manufacture, a method for etching a silicide layer and a polysilicon layer to a gate oxide layer formed on a substrate, comprising:
forming an oxide layer on the silicide layer;
forming a patterned photoresist mask on the oxide layer;
forming an oxide hard mask by etching the oxide layer through the photoresist mask in an etch chamber of a reactive ion etcher (RIE) using a first gas etchant;
removing the photoresist mask insitu in the etch chamber using an ozone plasma;
etching the silicide layer insitu in the etch chamber using the oxide hard mask and a second gas etchant; and
etching the polysilicon layer insitu in the etch chamber using the oxide mask and a third gas etchant.

### Claim 2 (depends on 1)

The method as claimed in claim 1 and wherein the first gas etchant includes a species of gas selected from the group of gas species consisting of fluorocarbon, chlorine or fluorine species.

### Claim 3 (depends on 1)

The method as claimed in claim 1 and wherein the silicide layer is formed of tungsten silicide.

### Claim 4 (depends on 1)

The method as claimed in claim 1 and wherein the third gas etchant includes a species selected from the group of species consisting of a fluorine, bromine, or chlorine species.

### Claim 5 (depends on 1)

The method as claimed in claim 1 and wherein the second gas etchant includes SF.sub.6, Q.sub.2 and He.

### Claim 6

In a semiconductor structure including a substrate, a gate oxide layer formed on the substrate, a polysilicon layer formed on the gate oxide, and a silicide layer formed on the polysilicon layer, a method of etching the silicide and polysilicon layers, comprising:
forming an oxide layer on the silicide layer;
forming a photoresist mask on the oxide layer;
etching the oxide layer through the photoresist mask in an etch chamber of a reactive ion etcher (RIE) using a first gas etchant to form an oxide hard mask;
stripping the photoresist mask insitu in the etch chamber using an ozone plasma;
etching the silicide layer insitu in the etch chamber using a second gas etchant; and
etching the polysilicon layer insitu in the etch chamber using a third gas etchant.

### Claim 7 (depends on 6)

The method as recited in claim 6 and wherein the first gas etchant is a fluorocarbon gas.

### Claim 8 (depends on 7)

The method as recited in claim 7 and wherein the first gas etchant includes CF.sub.4 and CHF.sub.3.

### Claim 9 (depends on 6)

The method as recited in claim 6 and wherein the silicide layer is tungsten silicide.

### Claim 10 (depends on 6)

The method as recited in claim 6 and wherein the second gas etchant includes SF.sub.6 and He.

### Claim 11 (depends on 6)

The method as recited in claim 6 and wherein the third gas etchant includes Hbr and Cl.sub.2.

### Claim 12

In a semiconductor structure including a silicon substrate, a gate oxide, a polysilicon layer and a silicide layer, a method for etching the polysilicon layer to the gate oxide, comprising;
forming an oxide hard mask by depositing an oxide layer on the silicide layer, forming a photoresist mask on the oxide layer and etching the oxide layer in an etch chamber of a reactive ion etcher (RIE) using a first etching gas;
stripping the photoresist mask insitu in the etch chamber using an ozone plasma;
etching the silicide layer in the etch chamber using the oxide hard mask and a second etch gas; and
etching the polysilicon layer to the gate oxide in the etch chamber using the oxide hard mask and a third etch gas.

### Claim 13 (depends on 12)

The method as recited in claim 12 and wherein the second etch gas contains a gas species selected from the group of species consisting of a fluorine, chlorine or bromine gas species.

### Claim 14 (depends on 12)

The method as recited in claim 12 and wherein the third etch gas contains HBr and Cl.sub.2.

### Claim 15 (depends on 12)

The method as recited in claim 12 and wherein the first etch gas contains a fluorocarbon gas species.

### Claim 16 (depends on 12)

The method as recited in claim 12 and wherein the etch selectivity of the polysilicon to the gate oxide is about twenty eight to one.