Rapid x-ray reflectivity (XRR) characterization and process monitoring of multilayer Ta/Al2O3/Ta/SiO2/Si

We have developed a rapid XRR system that is capable of acquiring the reflectivity data in the angular range of 0.1 - 1.6 degree in less than 20 sec. The data were analyzed to obtain the thickness, density and roughness of the film of interest in a few seconds. The system consisted of an x-ray source with a tungsten target and a Si monochromator, a sample stage, and a 1024-pixel photo-diode array. The system was used to characterize the multiple film stack of Ta/Al 2 O 3 /Ta/SiO 2 /Si. The Ta and Al films were sputtered onto the SiO 2 /Si substrate and the Al was oxidized to form the film of Al 2 O 3 . The thickness of the Ta layers was about 100 angstrom while the thickness of Al 2 O 3 varied from 40 angstrom to 200 angstrom. The XRR sensitivity to parameters such as thickness, density, and roughness of the Ta and Al 2 O 3 layer was also studied. We found that the XRR can measure the thickness and density of each layer with a standard deviation less than 0.5% and 1.5% of the target thickness and density, respectively. The roughness was found to have a standard deviation better than 1 angstrom. We also found that the density of the film of Al 2 O 3 varied from 2.7 - 4.0 g/cm 3 , indicating that the stoichiometry of the Al 2 O 3 films ranged from the non-oxidized pure Al to the fully oxidized Al 2 O 3 . The information of the thickness, density and roughness of each of the Ta and Al 2 O 3 films from XRR is particularly useful to nondestructively monitor the thin film deposit conditions in real time.