Patent ID: 8628677

Claim:
A process for forming dents in a substrate, comprising: attaching a bottom surface of a shadow mask to a top surface of the substrate, the shadow mask including a plurality of through-holes, each through-hole leading from a top surface of the shadow mask to the bottom surface of the shadow mask and having a respective lower portion adjacent to the bottom surface and a respective upper portion closer to the top surface of the shadow mask than the respective lower portion, the respective lower portion of the through-hole having a respective bottom opening in the bottom surface of the shadow mask, the respective upper portion of the through-hole having a respective upper opening in the top surface of the shadow mask, and a vertical projection of the respective upper opening along a direction perpendicular to the top surface of the shadow mask on the bottom surface of the shadow mask falling entirely within the respective bottom opening without a peripheral of vertical projection overlapping with a peripheral of the respective bottom opening; exposing the top surface of the substrate to isotropic plasma etching through the through-holes of the shadow mask to form curved dents in the top surface of the substrate, each curved dent having a width narrower than a width of the respective bottom opening; and removing the shadow mask after the curved dents have been formed to a predetermined size in the top surface of the substrate.