# US 7,465,946 B2 · Alternative fuels for EUV light source

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- Number: US 7,465,946 B2
- Document ID: US7465946B2
- Status: Granted
- Kind: B2
- Application number: 11/406,216
- Filed: 2006-04-17
- Published: 2006-11-09
- Granted: 2008-12-16
- Earliest claimed: 2004-03-10
- Assignees: Cymer, Inc.
- Inventors: Norbert R. Bowering; Oleh V. Khodykin; Alexander N. Bykanov; Igor V. Fomenkov
- Web page: https://patentgrep.com/patent/US7465946B2

## CPC

- H05G 2/0094: {Reduction, prevention or protection from contamination; Cleaning}
- B82Y 10/00: Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
- H05G 2/0035: {the material containing metals as principal radiation-generating components}
- G21K 2201/061: characterised by a multilayer structure
- H05G: X-RAY TECHNIQUE (investigating or analysing materials by the use of X-rays G01N23/00; apparatus for X-ray photography G03B42/02; X-ray tubes H01J35/00; TV systems having X-ray input H04N5/321)
- B82Y: SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- G21K: HANDLING OF PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES

## Abstract

An EUV light source is disclosed which may comprise at least one optical element having a surface, such as a multi-layer collector mirror; a laser source generating a laser beam; and a source material irradiated by the laser beam to form a plasma and emit EUV light. In one aspect, the source material may consist essentially of a tin compound and may generate tin debris by plasma formation which deposits on the optical element and, in addition, the tin compound may include an element that is effective in etching deposited tin from the optical element surface. Tin compounds may include SnBr4, SnBr2 and SnH4. In another aspect, an EUV light source may comprise a molten source material irradiated by a laser beam to form a plasma and emit EUV light, the source material comprising tin and at least one other metal, for example tin with Gallium and/or Indium.

## Claims

### Claim 1

An EUV light source, said source comprising:
at least one optical element having a surface;
a laser source generating a laser beam; and
a source material irradiated by said laser beam to form a plasma and emit EUV light, said source material consisting essentially of a tin compound and generating tin debris by plasma formation which deposits on at least one optical element, wherein said tin compound includes an element effective in etching deposited tin from said surface; and
a heater to heat tin deposits on said element surface to a temperature greater than 150° C. to increase a rate of chemical reaction between said deposited tin and the etchant.

### Claim 2 (depends on 1)

An EUV light source as recited in claim 1 wherein said optical element is a multi-layer mirror.

### Claim 3 (depends on 1)

An EUV light source as recited in claim 1 wherein said tin compound is SnBr4.

### Claim 4 (depends on 1)

An EUV light source as recited in claim 1 wherein said tin compound is SnBr2.

### Claim 5 (depends on 1)

An EUV light source as recited in claim 1 wherein said tin compound is SnH4.

### Claim 6 (depends on 1)

An EUV light source as recited in claim 1 wherein said optical element is selected from the group of elements consisting of a collector, a laser input window and a metrology window.

### Claim 7 (depends on 1)

An EUV light source as recited in claim 1 wherein said heater is selected from the group of heaters consisting of an ohmic heater, a radiative heater, a radio-frequency heater and a microwave heater.

### Claim 8 (depends on 1)

An EUV light source as recited in claim 1 further comprising a droplet generator system for creating droplets of source material.

### Claim 9 (depends on 8)

An EUV light source as recited in claim 8 wherein said system heats said source material to a temperature above room temperature.

### Claim 10 (depends on 9)

An EUV light source as recited in claim 9 wherein said tin compound is SnBr4 and said temperature is above 35 degrees C.

### Claim 11 (depends on 9)

An EUV light source as recited in claim 9 wherein said tin compound is SnBr2 and said temperature is above 216 degrees C.

### Claim 12 (depends on 8)

An EUV light source as recited in claim 8 wherein said system cools said source material to a temperature below room temperature.

### Claim 13 (depends on 12)

An EUV light source as recited in claim 12 wherein said tin compound is SnH4 and said temperature is below minus 52 degrees C.

### Claim 14 (depends on 1)

An EUV light source as recited in claim 1 wherein said laser source comprises a CO2 laser source.

### Claim 15 (depends on 14)

An EUV light source as recited in claim 14 wherein said laser source produces radiation having a wavelength of about 10.6 μm.

### Claim 16

An EUV light source said source comprising:
a source material comprising at least one tin bromide.
a heater for heating said source material above the melting point of said tin bromide;
a CO2 laser source generating a laser beam for irradiating said liquid source material to produce a plasma therefrom and emit EUV radiation;
at least one optical element having a surface; and
a heater to heat tin deposits on said element surface to a temperature greater than 150° C. to increase a rate of chemical reaction between said deposited tin and the bromide.

### Claim 17 (depends on 16)

An EUV light source as recited in claim 16 wherein said source material comprises SnBr2.

### Claim 18 (depends on 16)

An EUV light source as recited in claim 16 wherein said source material comprises SnBr4.

### Claim 19

An EUV light source, said source comprising:
a source material comprising SnH4,
a cooling system for cooling said source material below the boiling point of SnH4; and
a CO2 laser source generating a laser beam for irradiating said liquid source material to produce a plasma therefrom and emit EUV radiation.

### Claim 20 (depends on 19)

An EUV light source as recited in claim 19 wherein said cooling system uses Nitrogen to cool said source material.

### Claim 21

An EUV light source, said source comprising:
an etchant;
a laser source generating a laser beam;
a molten source material irradiated by said laser beam to form a plasma and emit EUV light, said source material comprising tin and at least one other metal, said source material having a melting point lower than pure tin;
at least one optical element having a surface; and
a heater to heat tin deposits on said element surface to a temperature greater than 150° C. to increase a rate of chemical reaction between said deposited tin and the etchant.

### Claim 22 (depends on 21)

An EUV light source as recited in claim 21 wherein said molten source material consists essentially of metals.

### Claim 23 (depends on 21)

An EUV light source as recited in claim 21 wherein said molten source material comprises Gallium.

### Claim 24 (depends on 21)

An EUV light source as recited in claim 21 wherein said molten source material comprises Indium.

### Claim 25 (depends on 21)

An EUV light source as recited in claim 21 wherein said molten source material comprises Gallium and Indium.

### Claim 26 (depends on 21)

An EUV light source as recited in claim 21 wherein said molten source material comprises a eutectic tin alloy.

### Claim 27 (depends on 21)

An EUV light source as recited in claim 21 wherein said laser source comprises a CO2 laser source producing radiation having a wavelength of about 10.6 μm.

### Claim 28 (depends on 21)

An EUV light source as recited in claim 21 wherein said optical element is selected from the group of elements consisting of a collector, a laser input window and a metrology window.

### Claim 29 (depends on 28)

An EUV light source as recited in claim 28 further comprising a droplet generator system for creating droplets of source material.

### Claim 30 (depends on 28)

An EUV light source as recited in claim 28 wherein said reactant is selected from the group of reactants consisting of HBr, HI, I2, Br2, CI2, HCI, H2 and combinations thereof.

### Claim 31 (depends on 21)

An EUV light source as recited in claim 21 wherein said source material melting point is lower than 150° C.

### Claim 32 (depends on 21)

An EUV light source as recited in claim 21 wherein said source material comprises tin in the range of 13 to 19 percent by weight, Indium in the range of 19 to 25 percent by weight and Gallium in the range of 59 to 65 percent by weight.