183 nm CW laser and inspection system

Patent metadata

Field	Value
Publication number	US-10429719-B2
Application number	US-201816205032-A
Country	US
Kind code	B2
Filing date	Nov 29, 2018
Priority date	Jan 3, 2017
Publication date	Oct 1, 2019
Grant date	Oct 1, 2019

Abstract

An inspection system/method in which first optics direct continuous wave (CW) light at 181-185 nm to an inspected article, and second optics redirect image information affected by the article to detectors. A laser assembly generates the CW light by generating fourth harmonic light from first fundamental CW light having a first wavelength between 1 and 1.1 μm, generating fifth harmonic light by mixing the fourth harmonic light with the first fundamental CW light, and mixing the fifth harmonic light with second light having a second wavelength between 1.26 and 1.82 μm. An external cavity mixes the first light and the fourth harmonic light using a first nonlinear crystal. The CW light is generated using a second cavity that passes circulated second fundamental or signal CW light through a second nonlinear crystal, and directing the fifth harmonic light through the second nonlinear crystal.

First claim

The invention claimed is:

1. An inspection system comprising:
a laser assembly configured to generate continuous wave (CW) laser output light having a wavelength in the range of approximately 181 nm to approximately 185 nm;
first optics configured to direct the laser output light from the laser assembly to an article being inspected;
second optics configured to collect an image information portion of said laser output light affected by the article being inspected, and to direct the image information portion to one or more detectors,
wherein the laser assembly comprises:
a first fundamental CW laser configured to generate a first fundamental CW light having a first fundamental frequency with a corresponding first fundamental wavelength between about 1 μm and 1.1 μm;
a fourth harmonic generation module coupled to receive a first portion of the first fundamental CW light, and configured to generate a fourth harmonic light having a fourth harmonic frequency equal to four times the first fundamental frequency;
a fifth harmonic generation module coupled to receive a second portion of the first fundamental CW light and to receive said fourth harmonic light from the fourth harmonic generation module, said fifth harmonic generation module being configured to generate a fifth harmonic light having a fifth harmonic frequency equal to five times the first fundamental frequency by mixing said fourth harmonic light and said second portion of the first fundamental CW light;
a frequency mixing module configured to generate said laser output light by mixing said fifth harmonic light with a second CW light having a second frequency with a corresponding second wavelength between 1.26 μm and 1.82 μm,
wherein the fifth harmonic generation module comprises a first cavity and a first nonlinear crystal, said first cavity being formed by a plurality of first mirrors that are configured to circulate the second portion of the first fundamental CW light such that circulated said first fundamental CW light passes through the first nonlinear crystal, said first nonlinear crystal being configured to mix said circulated first fundamental CW light with said fourth harmonic light received directly from said fourth harmonic generator to generate said fifth harmonic light,
wherein the frequency mixing module comprises a second cavity and a second nonlinear crystal, said second cavity being formed by a plurality of second mirrors that are configured to circulate the second CW light such that the circulated second CW light passes through the second nonlinear crystal, and the second nonlinear crystal being configured to receive said fifth harmonic light directly from said fifth harmonic generator such that said fifth harmonic light mixes with said circulated second CW light to generate said laser output light, and
wherein at least one of the first and second nonlinear crystals comprises one of an annealed cesium lithium borate (CLBO) crystal, a hydrogen-treated CLBO crystal and a deuterium-treated CLBO crystal.

2. The inspection system of claim 1 , wherein the laser assembly further comprises a second fundamental laser configured to generate the second CW light at a first power level,
wherein the frequency mixing module is configured to receive the second CW light from the second fundamental laser such that the second CW light is circulated in the second cavity, and the second cavity is configured to resonate at a second fundamental frequency of said second CW light such that a second power level of the circulated second CW light is greater than the first power level.

3. The inspection system of claim 2 , wherein the second fundamental laser comprises one of a Yb doped fiber laser, a Nd doped solid state laser, fiber laser or fiber amplifier, and an erbium (Er) doped solid state laser, fiber laser or fiber amplifier.

4. The inspection system of claim 1 , wherein the laser assembly further comprises a pump laser configured to generate second laser light at a first frequency,
wherein the second cavity comprises one of a solid state laser cavity and an optical parametric oscillator cavity, said second cavity being configured to generate the circulated second CW light using the second laser light received from the pump laser such that the circulated second CW light has a second frequency that is lower than the first frequency.

5. The inspection system of claim 4 , wherein the frequency mixing module further comprises one of a Nd doped gain medium and an erbium (Er) doped gain medium.

6. The inspection system of claim 4 , wherein the second cavity further comprises an optical diode and an etalon.

7. The inspection system of claim 1 , wherein the first fundamental CW laser is configured such that the first fundamental frequency has a corresponding wavelength equal to one of approximately 1070 nm, approximately 1064 nm, approximately 1053 nm, approximately 1047 nm, and approximately 1030 nm.

8. The inspection system of claim 1 , wherein the first fundamental CW laser comprises one of an ytterbium (Yb) doped fiber laser or fiber amplifier, a neodymium (Nd) doped solid state laser and a Nd doped fiber laser or fiber amplifier.

9. The inspection system of claim 1 , wherein the fourth harmonic generation module comprises two frequency doubling cavity modules.

10. The inspection system of claim 1 , wherein the fifth harmonic generation module is configured such that the fourth harmonic light and the circulated first fundamental CW light are transmitted collinearly through the first nonlinear crystal.

11. A method of inspecting a sample, the method comprising:
generating continuous wave (CW) laser output light having a wavelength in the range of approximately 181 nm to approximately 185 nm, wherein generating said CW laser output light includes:
generating a first fundamental CW light having a first fundamental frequency with a corresponding first fundamental wavelength between about 1 μm and 1.1 μm;
converting a first portion of the first fundamental CW light to a fourth harmonic light having a fourth harmonic frequency equal to four times the first fundamental frequency;
generating a fifth harmonic light having a fifth harmonic frequency equal to five times the first fundamental frequency by mixing a second portion of the first fundamental CW light and the fourth harmonic light, wherein said mixing comprises circulating said second portion in a first cavity such that said circulated first fundamental CW light passes through a first nonlinear crystal that is also positioned to receive said fourth harmonic light; and
mixing the fifth harmonic light with second CW light having a second frequency with a corresponding wavelength between 1.26 μm and 1.82 μm to generate said CW laser output light, wherein said mixing comprises circulating said second CW light in a second cavity such that said circulated second CW light passes through a second nonlinear crystal that is also positioned to receive said fifth harmonic light;

directing the output laser light onto an article being inspected; and
collecting an image information portion of said laser output light affected by the article being inspected, and directing the image information portion to one or more sensors,
wherein at least one of the first and second nonlinear crystals comprises one of an annealed cesium lithium borate (CLBO) crystal, a hydrogen-treated CLBO crystal and a deuterium-treated CLBO crystal.

12. The method of claim 11 , further comprising:
utilizing a second fundamental laser to generate the second CW light as a second fundamental light at a first power level and having a second fundamental frequency; and
directing the second fundamental light fro

Assignees

• Kla Tencor Corp

Inventors

• Chuang Yung-Ho Alex
• Lu Xiaoxu
• Zhang Baigang
• Fielden John
• Dribinski Vladimir

Classifications

• G02F1/353 Primary

  Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams · CPC title

• G02F2201/16

  series; tandem · CPC title

• G02F1/3558

  Poled materials, e.g. with periodic poling; Fabrication of domain inverted structures, e.g. for quasi-phase-matching [QPM] · CPC title

• G02F1/3551

  Crystals · CPC title

• G02F1/3501

  Constructional details or arrangements of non-linear optical devices, e.g. shape of non-linear crystals · CPC title