Surface Loss in Ozone-Based Atomic Layer Deposition Processes

The recombinative surface loss of O 3 was investigated and its effects on the initial growth, film uniformity, and film conformality in atomic layer deposition (ALD) processes were illustrated. To determine O 3 recombination probabilities over a wide range, a method was developed using high aspect ratio capillaries at the inlet to a mass spectrometer. Using this method, we measured O 3 recombination probabilities ranging from <10 −6 to >10 −3 depending on the composition and temperature of the capillary surface. We utilized these measurements to understand dramatic variations in O 3 loss observed during the initial growth of O 3 -based ALD Pt on Al 2 O 3 and vice versa. Next, we studied the uniformity of O 3 -based ALD using ZnO ALD as a model system. Changes in the spatial uniformity of the ALD ZnO films and the O 3 concentration in the reactor as a function of the O 3 exposure were explained by a transition from reaction- to recombination-limited growth. This explanation was validated using a simple plug-flow model. Finally, we estimated the maximum aspect ratios that can be coated for a given O 3 recombination probability in O 3 -based ALD processes using reasonable cycle times.