TEM Analyses of Cu-Ta And Cu-Tan Interfaces
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Mat. Res. Soc. Symp. Proc. Vol. 564 ©1999 Materials Research Society
chamber was < 1 x 10' Torr. In particular, ion-metal-plasma (IMP) deposition was utilized for the film depositions, as that is the preferred technology for deposition of the barrier (Ta or TaN) and copper seed layers for electroplating using the damascene scheme for formation of the interconnects[7]. The thermal annealing (400-500'C) of the wafers with the multilayered stacks was carried out in a chamber with < I x 10' Torr base pressure, and using high purity argon gas for conduction of the heat from the pedestal to the wafer. TEM samples were prepared using the wedge technique which provides a fast and efficient way of preparing TEM samples[8]. Then the sample underwent 3 to 5 minutes ionmilling using a Gatan Precision Ion Mill, followed by immediate TEM analysis. Transmission electron microscopy was carried out on Philips' CM200 and Philips' FEG CM200 microscopes. TEM samples were then exposed to air for ten days prior to the observation of any oxidation effect. RESULTS AND DISCUSSION X-ray diffraction analysis of the as deposited Ta and TaN films indicated that while the Ta film was crystalline, occuring in the 13-phase, the TaN film was amorphous with no crystalline peaks[4]. Furthermore, from Rutherford backscattering analysis, the nitrogen composition in the TaN films was determined to be 30% atomic. Figures la and lb are the bright-field and dark-field images of as-deposited Cu/Ta films, showing highly textured Cu grains. Figures 2a and 2b show the images of the Cu/Ta films after 400'C one hour anneal, again, showing strong Cu (111) texture. As will become more evident in the following figures, there is no sign of any interfacial layer formation between Ta and Cu. It is also important to note that the nanocrystalline Ta coalesced and became a large single grain after annealing as indicated in figure 2b. The Ta grains are illuminated under the same Bragg condition as the copper grains.
;
Z=21
Zt70.00nm
Figure la. Bright field images of as deposited Cu/Ta. Figure lb. Dark deposited Cu/Ta film stacks show preferred orientation of copper grains.
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Figure 2a. Bright field images of Cu/Ta films annealed at 400'C for one hour. Figure 2b. Dark field images of 400'C annealed films. The copper grains are highly textured. In addition, the Ta nano crystals also coalesce forming one large single grain. High resolution TEM analysis has been performed to further study the interface structure of Cu/Ta films, especially for the ones which underwent one hour annealing at 400'C and 500*C. Figures 3a, 3b, and 3c show interface structures of Cu/Ta for all three conditions, respectively. It is clear that all of them have clean and atomically sharp interface structures, regardless of annealing conditions. Among them, figure 3c, the sample processed at 500'C is significantly important because the interface maintained its crystallinity at the grain boundary triple junction area after one hour heat treatment. This is a strong indication that Cu/Ta has a
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