Spatial atomic layer deposition

Systems and methods are provided herein to improve the efficiency of an atomic layer deposition (ALD) cycle by providing an improved purge block design. The improved purge block prevents gas mixing, regardless of the rotational speed of the platen, by providing a lower cavity on an underside of the purge block, and in some embodiments, by providing an upper cavity on a topside of the purge block. The lower/upper cavity provides a gas conduction path that distributes purge gas evenly beneath/above the purge block and provides uniform gas flow conductance within the lower/upper cavity. Compared to conventional purge block designs, the improved purge block design described herein provides a narrower, yet more effective isolation barrier, which prevents gas mixing even at high rotational speeds of the platen.