US 11,899,338 B2
Deep ultraviolet laser using strontium tetraborate for frequency conversion
Yung-Ho Alex Chuang, Cupertino, CA (US); Kelly Mauser, Santa Clara, CA (US); Baigang Zhang, San Jose, CA (US); Xuefeng Liu, San Jose, CA (US); John Fielden, Los Altos, CA (US); Yinying Xiao-Li, San Jose, CA (US); and Elena Loginova, Campbell, CA (US)
Assigned to KLA Corporation, Milpitas, CA (US)
Filed by KLA Corporation, Milpitas, CA (US)
Filed on Nov. 21, 2022, as Appl. No. 17/991,198.
Claims priority of provisional application 63/288,560, filed on Dec. 11, 2021.
Prior Publication US 2023/0185158 A1, Jun. 15, 2023
Int. Cl. G02F 1/35 (2006.01); G02F 1/355 (2006.01); G02F 1/39 (2006.01); G02F 1/37 (2006.01); G01N 21/47 (2006.01); G01N 21/95 (2006.01); H01S 3/16 (2006.01)
CPC G02F 1/3534 (2013.01) [G01N 21/4738 (2013.01); G02F 1/3507 (2021.01); G02F 1/3542 (2021.01); G02F 1/3548 (2021.01); G02F 1/3551 (2013.01); G02F 1/37 (2013.01); G02F 1/392 (2021.01); G01N 21/9501 (2013.01); G01N 2201/06113 (2013.01); G02F 2203/11 (2013.01); H01S 3/1625 (2013.01); H01S 3/1636 (2013.01)] 34 Claims
OG exemplary drawing
 
1. An inspection system comprising:
a light source configured to generate light having a wavelength in a range between 180 nm and 200 nm; and
an optical system configured to direct the light onto a sample,
wherein the light source comprises:
a first fundamental laser configured to generate a fundamental laser beam having a corresponding fundamental frequency;
one or more intermediate frequency conversion stages collectively configured to generate an intermediate frequency light using the fundamental laser beam, the intermediate frequency light having an associated intermediate frequency and a corresponding intermediate wavelength between 360 nm and 400 nm;
a final frequency doubling stage configured to pass the intermediate frequency light through a nonlinear crystal,
wherein the nonlinear crystal includes a plurality of strontium tetraborate (SBO) crystal plates disposed in a stacked configuration such that each first SBO crystal plate is adjacent to at least one second crystal plate, and
wherein the plurality of SBO crystal plates are cooperatively configured to form a periodic structure that achieves quasi-phase-matching (QPM) of the intermediate frequency light such that light exiting the nonlinear crystal includes laser output light having an output frequency with a corresponding wavelength in the range of approximately 180 nm to approximately 200 nm.