Microstructural Characterization of Platinum Films Grown by MOCVD
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Pt bottom electrode. This results in the stress in the film becoming compressive, and relaxation of this compressive stress can cause hillock formation, as has been reported for Pt by many authors [2,3,13,14]. This can subsequently lead to device failure. Annealing studies were carried out on our samples to study this phenomenon. EXPERIMENTAL Oxidized Si (100) substrates were used in this investigation. In the first set of experiments using Pt(acac) 2 , the oxygen partial pressure was fixed at 0.086 Torr and the substrate temperature was varied from 350 to 450'C. The total system pressure was maintained at 1.2 Torr. In the second set of experiments, the substrate temperature was fixed at 400'C and the oxygen partial pressure was varied from 0 to 0.136 Torr. The Pt(acac)2 source temperature was maintained at 147°C for all depositions. Argon was used as the carrier gas and the growth period was 30 minutes. During the deposition, the carrier gas lines were heated to a temperature higher than the source temperature to prevent the precursor from condensing in the lines. A similar set of experiments was carried out using Pt(hfacac) 2 . The source temperature was kept at 37°C and the chamber pressure was 1.2 Torr under all conditions. In the first set of runs, the oxygen partial pressure was fixed at 0.186 Torr and the substrate temperature was varied from 210'C to 400'C. Helium was used as the carrier gas in this case and the deposition period was 60 minutes. In the second set of experiments, the substrate temperature was maintained at 275°C and the oxygen partial pressure was varied from 0 to 0.136 Torr. For the annealing studies, Pt films deposited using both Pt(acac)2 and Pt(hfacac) 2 were used. With Pt(acac) 2 , Pt was deposited at 400'C with an oxygen partial pressure of 0.086 Torr. With Pt(hfacac) 2 , Pt films were deposited at 275°C without oxygen. Atomic force microscopy (AFM) was used in the DC contact mode with silicon nitride tips in order to characterize the surface roughness of substrates and of films grown under different conditions. The Si0 2/Si(100) surface was found to be atomically flat. Field-emission scanning electron microscopy was performed to measure film thickness and study surface morphology. X-ray diffraction using Cu-Kax radiation was used to determine the film orientation on different substrates. Resistivity measurements were made with the four point probe technique. RESULTS AND DISCUSSION Substrate Temperature When Pt(acac)2 was used as the source, the lowest substrate temperature at which Pt films were obtained for P0 2 = 0.086 Torr was approximately 350'C. Figure 1 shows x-ray diffraction patterns for films deposited at different substrate temperatures at this PO. As can be seen in the spectra, Pt (111) was the predominant film orientation, although Pt (200) peak was also observed. Pt has an fcc structure and in the absence of lattice matching effects, Pt (111) would be the expected orientation. At 350'C and 400'C, the Pt (111) diffraction peak was not very intense, but these films were very
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