A low volume showerhead in a semiconductor processing apparatus can include a porous baffle to improve the flow uniformity and purge time during atomic layer deposition. The showerhead can include a plenum volume, one or more gas inlets in fluid communication with the plenum volume, a faceplate including a plurality of first through-holes for distributing gas onto a substrate in the semiconductor processing apparatus, and a porous baffle positioned in a region between the plenum volume and the one or more gas inlets. The one or more gas inlets can include a stem having a small volume to improve purge time. The baffle can be porous and positioned between the stem and the plenum volume to improve flow uniformity and avoid jetting.