Optimizing UV/VUV Transmission Through Capillary-array Windows From Utilizing Statistical Experimental Designs

Capillary-array windows have gained interest in semiconductor industries for plasma-assisted materials processing applications. They enable the transmission of desired optical radiation such as UV/VUV photons to the processing chamber while protecting the target sample from producing damage by bulky debris, thus leading to enhanced quality of plasma processing. Here, we report a new approach in which a capillary-array window can show its efficacy over conventional solid thin films in the transmission of UV and VUV photons in an ECR plasma reactor. By benchmarking windows of varying capillary size and thickness as a key factor of three levels (nanometer-sized pore, micrometer-sized pore, and millimeter-sized pore), we demonstrated that the transmission could achieve as high as 58.93%. This optimized transmission can be attained by carrying out a factional-factorial design to examine the interaction of various factors, namely, pore diameter, window thickness, window area, and incident angle of radiation properties. In addition, the windows can hold pressure differentials from 10^-6 torr to 20 mtorr and 20 mtorr to 760 torr without mechanical failure. The capillary-array windows also survived the tests of differential pressure of several hundred psi. Overall, our approach to use capillary windows for plasma UV/VUV transmission in a processing chamber with differential vacuum levels is very promising.