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 Al2O3 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.