An air bearing assembly includes: an upper portion having a plurality of air supply and vacuum holes therethrough; a lower portion; and a plurality of spacers disposed between and maintaining the upper and lower portions in spaced relation, wherein a density of the air supply and vacuum holes is high enough to provide an air bearing for a substrate, but low enough such that at least one of: (i) a sufficient number of the spacers are employed, and (ii) the spacers are located in close enough proximity, to maintain a substantially uniform flatness of the upper portion relative to the lower portion.