Non-critical phase matching in CLBO to generate sub-213nm wavelengths
View Patent ↗A laser illuminator and illumination method for use in an inspection system, such as a semiconductor wafer inspection system or photomask inspection system is provided. The design comprises generating fundamental frequency laser energy at different fundamental wavelengths, such as 998 nm, converting a portion of the fundamental frequency laser energy to 2 nd harmonic frequency laser energy, further converting the 2 nd harmonic frequency laser energy to 4 th harmonic frequency laser energy, and mixing the 4 th harmonic frequency laser energy with a portion of the fundamental frequency laser energy to produce laser energy at a sum frequency. Mixing is accomplished by non-critical phase matching in a crystal of Cesium Lithium Borate (CLBO). Alternately, the design may employ shifting a portion of the fundamental frequency laser energy to laser energy at a Raman line and/or mixing the 2 nd harmonic frequency laser energy with a portion of the fundamental frequency laser energy to produce 3 rd harmonic frequency laser energy.
1. A method for producing light energy, comprising:
generating fundamental frequency laser energy at a wavelength of approximately 998 nm;
converting a portion of the fundamental frequency laser energy to 2 nd harmonic frequency laser energy;
further converting the 2 nd harmonic frequency laser energy to 4 th harmonic frequency laser energy; and
mixing the 4 th harmonic frequency laser energy with a portion of the fundamental frequency laser energy to produce laser energy at a sum frequency, wherein the mixing is accomplished by non-critical phase matching in a crystal of Cesium Lithium Borate (CLBO).
2. The method of claim 1 where the fundamental frequency laser energy is generated by a fiber laser.
3. The method of claim 1 where at least one from a group comprising a CLBO crystal, a BBO crystal, an LBO crystal, a BiBO crystal, and a periodically polled material is used to convert fundamental frequency laser energy to 2 nd harmonic frequency laser energy.
4. The method of claim 3 where two crystals are used to convert fundamental frequency laser energy to 2 nd harmonic frequency laser energy.
5. The method of claim 1 where the temperature of the CLBO crystal is controlled to maintain a phase matching condition.
6. The method of claim 1 where the CLBO crystal is processed according to at least one from a group comprising:
ion polishing a surface of the CLBO crystal to remove sub surface damage and standard polishing contaminants;
MRF polishing the surface to remove sub surface damage and standard polishing contaminants;
processing the starting material using an aqueous solution before sintering;
stirring the solution during crystal growth; and
baking the CLBO crystal for at least 100 hours to remove any residual moisture.
7. A method for producing light energy, comprising:
generating fundamental frequency laser energy;
converting a portion of the fundamental frequency laser energy to 2 nd harmonic frequency laser energy;
further converting the 2 nd harmonic frequency laser energy to 4 th harmonic frequency laser energy; and
mixing the 4 th harmonic frequency laser energy with a portion of the fundamental frequency laser energy to produce laser energy at a sum frequency, wherein the mixing is accomplished by non-critical phase matching in a crystal of Cesium Lithium Borate (CLBO).
8. The method of claim 7 where the fundamental frequency laser energy is generated by a fiber laser.
9. The method of claim 7 where at least one from a group comprising a CLBO crystal, a BBO crystal, an LBO crystal, a BiBO crystal, and a periodically polled material is used to convert fundamental frequency laser energy to 2 nd harmonic frequency laser energy.
10. The method of claim 9 where two crystals are used to convert fundamental frequency laser energy to 2 nd harmonic frequency laser energy.
11. The method of claim 7 where the temperature of the CLBO crystal is controlled to maintain a phase matching condition.
12. The method of claim 7 where the CLBO crystal is processed according to at least one from a group comprising:
ion polishing a surface of the CLBO crystal to remove sub surface damage and standard polishing contaminants;
MRF polishing the surface to remove sub surface damage and standard polishing contaminants;
processing the starting material using an aqueous solution before sintering;
stirring the solution during crystal growth; and
baking the CLBO crystal for at least 100 hours to remove any residual moisture.
13. The method of claim 7 where the CLBO crystal is processed according to at least one from a group comprising:
ion polishing a surface of the CLBO crystal to remove sub surface damage and standard polishing contaminants;
MRF polishing the surface to remove sub surface damage and standard polishing contaminants;
processing the starting material using an aqueous solution before sintering;
stirring the solution during crystal growth; and
baking the CLBO crystal for at least 100 hours to remove any residual moisture.
14. A method for producing light energy, comprising:
converting a portion of a fundamental frequency laser energy to 2 nd harmonic frequency laser energy;
further converting the 2 nd harmonic frequency laser energy to 4 th harmonic frequency laser energy; and
employing non-critical phase matching in a crystal of Cesium Lithium Borate (CLBO) to combine the 4 th harmonic frequency laser energy with a portion of the fundamental frequency laser energy to produce laser energy at a sum frequency.
15. The method of claim 14 where at least one from a group comprising a CLBO crystal, a BBO crystal, an LBO crystal, a BiBO crystal, and a periodically polled material is used to convert fundamental frequency laser energy to 2 nd harmonic frequency laser energy.
16. The method of claim 15 where two crystals are used to convert fundamental frequency laser energy to 2 nd harmonic frequency laser energy.
17. The method of claim 14 where the temperature of the CLBO crystal is controlled to maintain a phase matching condition.