Surface Loss in Ozone-Based Atomic Layer Deposition Processes

The recombinative surface loss of O3 was investigated and its effects on the initial growth, film uniformity, and film conformality in atomic layer deposition (ALD) processes were illustrated. To determine O3 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 O3 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 O3 loss observed during the initial growth of O3-based ALD Pt on Al2O3 and vice versa. Next, we studied the uniformity of O3-based ALD using ZnO ALD as a model system. Changes in the spatial uniformity of the ALD ZnO films and the O3 concentration in the reactor as a function of the O3 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 O3 recombination probability in O3-based ALD processes using reasonable cycle times.