Semiconductor processing tool and methods of operation

A diffusion plate, comprising:

• a body;
• a first plurality of holes through a central region of the body;
• a second plurality of holes through a first annular region of the body that surrounds the central region;
• and
• a third plurality of holes through a second annular region of the body that surrounds the first annular region,
• wherein a first size of a first hole of the first plurality of holes, a second size of a second hole of the second plurality of holes, and a third size of a third hole of the third plurality of holes are different sizes.

A semiconductor processing tool, comprising:

• a processing chamber comprising sidewalls, an upper cover, and a chamber floor that define an internal area of the processing chamber;
• a chuck within the internal area and located adjacent to the chamber floor;
• vent ports in the chamber floor under the chuck;
• a diffusion plate within the internal area,
• wherein the diffusion plate is located above the chuck and adjacent to the upper cover,
• wherein the diffusion plate comprises:
• a body,
• wherein a central region of the body is located further away from the upper cover than from a perimeter of the body;
• and
• a plurality of holes through the body;
• and
• a gas inlet in the upper cover above the diffusion plate.