I get that. You will need a halftone screen.
You can buy a "contact halftone screen". Check auction site completed listings. It's like a sheet of film with a negative of a bunch of fuzzy dots. For that you will need a vacuum back.
I've never seen a glass halftone screen on an auction site, but I know they used to exist. This is what I think you can get your photolith department to conjure up. It won't be light sensitive, it will be a checkerboard.
You'll hold this glass checkerboard a very slight distance away from your sensitive plate. Just enough that the shadows don't overlap, but make a continuous pattern of dark to light. As each dot under the screen opening gets hit by more light, first a small dot forms, then it grows as more light hits it.
For now, just hold a windowscreen over a sheet of paper, you'll be able to see the effect.