Single Crystal TaN Thin Films on TiN/Si Heterostructure
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Single Crystal TaN Thin Films on TiN/Si Heterostructure H. Wang, Ashutosh Tiwari, X. Zhang, A. Kvit, J. Narayan Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7916 ABSTRACT We have successfully grown epitaxial cubic (B1-NaCl structure) tantalum nitride films on Si (100) and (111) substrate using a pulsed laser deposition technique. A thin layer of titanium nitride was used as a buffer medium. We characterized these films using X-ray diffraction, high resolution transmission electron microscopy and scanning transmission electron microscopy (Zcontrast). X-ray diffraction and high-resolution transmission electron microscopy confirmed the single crystalline nature of these films with cubic-on-cubic epitaxy. The epitaxial relations follow TaN(100)//TiN(100)//Si(100) on Si(100) and TaN(111)//TiN(111)//Si(111) on Si(111). We observed sharp interfaces of TaN/TiN and TiN/Si without any indication of interfacial reaction. Rutherford backscattering experiments showed these films to be slightly nitrogen deficient (TaN0.95). High precision electrical resistivity measurements showed excellent metallic nature of these films. We also tried to deposit TaN directly on silicon, the films were found to be polycrystalline. In our method, TiN plays a key role in facilitating the epitaxial growth of TaN. This method exploits the concept of lattice matching epitaxy between TaN and TiN and domain matching epitaxy between TiN and Si. We studied the diffusion barrier properties of these films by growing a thin layer of copper on the top and subsequently annealing the films at 500oC and 600oC in vacuum. Cu diffusion layer was about 2nm after 600oC annealing for 30min. This work explores a promising way to grow high quality TaN diffusion barrier on silicon for copper interconnection. INTRODUCTION Interests in structural and electrical properties of tantalum nitride thin films has been stimulated by its promising applications as diffusion barriers in ultra-large-scale integration (ULSI) of Si integrated circuit.1 Recently, Cu has been widely used as interconnect material due to its low resistivity, high electromigration and stress migration resistance, that are superior to Al and Al alloy interconnects.2 However, Cu is very easy to diffuse into SiO2 dielectric and subsequently into silicon region during device fabrication, which is deleterious to device operation. Various diffusion barriers for Cu diffusion have been extensively studied.3-5 But all of these diffusion barriers were around 100nm in thickness. For next generation ULSI devices, the thickness of barrier layers is expected to be within 10 nm, which should prevent Cu diffusion at temperatures above 600oC for 30mins. TaN barrier layers become promising candidates.6 In previous studies, polycrystalline TaN films have been deposited by a variety of techniques: Metal-organic chemical vapor deposition,7 radio-frequency sputtering method 8, DC magnetron sputtering9 and ionized metal plasma10. TaN has different stable phases suc
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