Low volume showerhead with faceplate holes for improved flow uniformity

A showerhead for use in a semiconductor processing apparatus, the showerhead comprising:

• a plenum volume having a first surface and a second surface opposite the first surface, the first surface and the second surface at least partially defining the plenum volume of the showerhead;
• a faceplate including a plurality of faceplate through-holes, the plurality of faceplate through-holes extending from a first side to a second side of the faceplate, the first side of the faceplate defining the first surface of the plenum volume, the plurality of faceplate through-holes including central through-holes and edge through-holes surrounding the central through-holes, the edge through-holes positioned at the second side of the faceplate circumferentially at a diameter larger than a diameter of a substrate for which the showerhead is configured for use;
• a backplate opposite the faceplate, wherein a side of the backplate defines the second surface of the plenum volume;
• a stem connected to the backplate and in fluid communication with the plenum volume, wherein the stem has an inner diameter defined by a tube extending through the stem and an outer diameter defined by the outermost surface of the stem greater than the inner diameter of the stem;
• and
• a baffle plate including a plurality of baffle through-holes, the baffle plate being configured to distribute gas flow around edges of the baffle plate and through the baffle plate, the baffle plate being positioned at least partially within or fully within a region that is recessed into the side of the backplate and forms a discrete transition space between the plenum volume and the stem that extends at least partially through a thickness of the backplate, the discrete transition space being in direct fluid communication with the stem and with the plenum volume, the discrete transition space having an outer diameter defined by the outer diameter of the stem.