Non-ionic photo-acid generating (PAG) compounds were prepared that contain an aryl ketone group. The disclosed non-polymeric PAGs release a strong sulfonic acid when exposed to high energy radiation such as deep UV or extreme UV light. The photo-generated sulfonic acid has a low diffusion rate in an exposed resist layer subjected to a post-exposure bake (PEB) at 100° C. to 150° C., resulting in formation of good line patterns after development. At higher temperatures, the PAGs undergo a thermal reaction to form a sulfonic acid.