Sub 200nm laser pumped homonuclear excimer lasers

Patent metadata

Field	Value
Publication number	US-9735534-B2
Application number	US-201414571100-A
Country	US
Kind code	B2
Filing date	Dec 15, 2014
Priority date	Dec 17, 2013
Publication date	Aug 15, 2017
Grant date	Aug 15, 2017

Abstract

Disclosed are methods and apparatus for generating a sub-200 nm continuous wave (cw) laser. A laser apparatus includes a chamber for receiving at least a rare gas or rare gas mixtures and a pump laser source for generating at least one cw pump laser focused in the chamber for generating at least one laser-sustained plasma in the chamber. The laser apparatus further includes a system for forming an optical cavity in which the at least one laser-sustained plasma serves as an excitation source for producing at least one cw laser having a wavelength that is below about 200 nm. In one aspect, the at least one laser-sustained plasma has a shape that substantially matches a shape of the optical cavity.

First claim

What is claimed is:

1. A laser apparatus for generating continuous wave (cw) coherent output radiation having a wavelength below about 200 nm, comprising:
a chamber for receiving at least a rare gas or rare gas mixtures;
a pump laser source for generating at least one cw pump laser focused in the chamber for generating at least one laser-sustained plasma having excimer emissions in the chamber; and
a lens system positioned within the chamber, wherein the lens system provides an optical cavity for forming confocal or unstable resonators inside the chamber to provide feedback to the excimer emissions of the at least one laser-sustained plasma so as to generate at least one continuous wave (cw) laser having a wavelength that is below about 200 nm, wherein the at least one laser-sustained plasma has a shape that substantially matches a shape of the optical cavity, wherein the optical cavity comprises (i) a first mirror formed from materials that transmit wavelengths equal to or higher than the cw pump laser's wavelength and have a high reflectivity at wavelengths that include at least a portion of a wavelength range of the excimer emissions and (ii) a second mirror formed from materials that have a reflectivity at wavelengths that include at least a portion of the wavelength range of the excimer emissions.

2. The laser apparatus of claim 1 , wherein the chamber is configured to receive and maintain the rare gas or rare gas mixtures at a pressure that is above about 10 bars.

3. The laser apparatus of claim 1 , wherein the rare gas or rare gas mixture comprises one or more of the following gases: Xe, Kr, or Ar.

4. The laser apparatus of claim 1 , the laser apparatus further comprising a lasing medium positioned in the optical cavity, wherein the lasing medium is arranged so that excimer excited states are used to collisionally transfer energy to excited atomic states to produce the cw laser from the lasing medium.

5. The laser apparatus of claim 1 , wherein the cw laser has an ultraviolet (UV) or vacuum UV wavelength.

6. The laser apparatus of claim 1 , wherein the chamber is configured to receive and maintain the rare gas or rare gas mixtures at a pressure that is higher than about 10 atm.

7. The laser apparatus of claim 1 , wherein the pump laser source has a wavelength greater than or equal to either about 0.8 to 0.9 μm or about 1 μm and an average power equal to or higher than 1 kW.

8. The laser apparatus of claim 1 , wherein the pump laser source is a plurality of fiber bundles of incoherent diodes.

9. The laser apparatus of claim 1 , wherein the pump laser source is a plurality of fiber bundles of Yb based active media.

10. The laser apparatus of claim 1 , wherein the rare gas has at least a 51% relative fill pressure as compared to any heterodimeric gases in the chamber.

11. The laser apparatus of claim 1 , further comprising a pump for flowing the rare gas or rare gas mixtures through the chamber.

12. The laser apparatus of claim 1 , wherein the pump laser source and the lens system that provides the optical cavity are arranged to produce excimer emissions in the at least one laser-sustained plasma by having a small signal single pass gain of at least 0.2 so that every photon produced by the excimer emission between the first and second mirrors causes at least 2 photons to be generated.

13. The laser apparatus of claim 12 , wherein the gain is based on a concentration number of an excited population times an emission cross section times a length of the optical cavity and active laser medium having a range above 2.

14. The laser apparatus of claim 1 , wherein the optical cavity has a length between about limn and 10 cm and a diameter having a range of about 100 μm to 3 mm.

15. The laser apparatus of claim 1 , wherein the lens system that provides the optical cavity comprises one or more line-narrowing elements.

16. An inspection system for inspecting a photolithographic reticle or wafer for defects, comprising:
a laser apparatus as recited in claim 1 ;
imaging optics for directing the output beam towards a reticle or wafer;
a detector for receiving a detected signal or image in response to an output beam being reflected from or transmitted through the reticle or wafer in response to the output beam being reflected or scattered from the reticle or wafer; and
a processor and memory that are configured to analyze the detected signal or image to thereby detect defects on the reticle or wafer.

17. A photolithography system for transferring a pattern from a reticle onto a wafer, comprising:
a laser apparatus as recited in claim 1 ; and
imaging optics for directing an output beam through a reticle onto a wafer.

18. A laser apparatus for generating continuous wave (cw) coherent output radiation having a wavelength below about 200 nm, comprising:
a first second chamber for receiving at least a rare gas or rare gas mixtures;
a pump laser source for generating at least one cw pump laser focused in the first chamber for generating at least one laser-sustained plasma having excimer emissions in the first chamber; a lens system positioned within a second chamber for receiving an extruded portion of the at least one laser-sustained plasma, wherein the lens system provides an optical cavity for forming confocal or unstable resonators inside the second chamber to provide feedback to the excimer emissions of the at least one laser-sustained plasma so as to generate at least one continuous wave (cw) laser having a wavelength that is below about 200 nm, wherein the at least one laser-sustained plasma has a shape that substantially matches a shape of the optical cavity; and
the second chamber having an orifice, wherein the first chamber is configured to have a first pressure and the second chamber is configured to have a second pressure that is substantially lower than the first pressure so as to cause extrusion of an extruded portion of the at least one laser-sustained plasma from the first chamber, through the orifice, to the second chamber.

19. The laser apparatus of claim 18 , wherein the first pressure is above about 10 bars and the second pressure is below about 1 torr, wherein the orifice has a diameter between about 30 to 200 μm.

20. The laser apparatus of claim 18 , wherein the pump laser source comprises a plurality of fiber bundles for generating a plurality of cw lasers for forming a plurality of laser-sustained micro-plasmas aligned along the length of the optical cavity.

21. A method of generating output radiation having a wavelength below about 200 nm, comprising:
receiving a rare gas or rare gas mixture within a first chamber;
with a pump laser source, generating at least one laser-sustained plasma so as to cause excimer emissions within a laser cavity that forms confocal or unstable resonators inside the first chamber to provide feedback to the excimer emissions, wherein the laser cavity is positioned within the chamber;
outputting an excimer laser from the laser cavity based on the excimer emissions and feedback from the laser cavity;
directing the excimer laser towards a semiconductor sample; and
inspecting the semiconductor sample based on output light that is reflected or scattered from the semiconductor sample in response to the excimer laser on the semiconductor sample,
wherein the at least one laser-sustained plasma has a shape that substantially matches a shape of the optical cavity, wherein the optical cavity comprises (i) a first mirror formed from materials that transmit wavelen

Assignees

• Kla Tencor Corp

Inventors

• Solarz Richard W
• Bezel Ilya
• Shchemelinin Anatoly

Classifications

• H01S3/036

  Means for obtaining or maintaining the desired gas pressure within the tube, e.g. by gettering, replenishing; Means for circulating the gas, e.g. for equalising the pressure within the tube {(H01S3/031 takes precedence)} · CPC title

• H01S3/094053

  Fibre coupled pump, e.g. delivering pump light using a fibre or a fibre bundle · CPC title

• H01S3/2207 Primary

  Noble gas ions, e.g. Ar+>, Kr+> · CPC title

• H01S3/0941

  of a laser diode · CPC title

• H01S3/225

  comprising an excimer or exciplex · CPC title