IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Thursday Sessions
       Session SS2-ThA

Paper SS2-ThA9
Characterization by XPS, LEED and STM of Silicon Deposited onto HfB@sub 2@ (0001)

Thursday, November 1, 2001, 4:40 pm, Room 122

Session: Nucleation & Growth
Presenter: R. Singh, University of Illinois at Chicago
Authors: R. Singh, University of Illinois at Chicago
W. Hayami, National Institute for Materials Science, Japan
T. Tanaka, National Institute for Materials Science, Japan
M.W, Trenary, University of Illinois at Chicago
Correspondent: Click to Email
In the microelectronics industry, transition metal diborides like TiB@sub 2@ and HfB@sub 2@ have received a great deal of attention as possible diffusion barriers because both diborides are refractory materials that have high melting points, high degrees of hardness, and are chemically very stable. While studies have been done to assess the ability of these materials to prevent the diffusion of copper into silicon, there have not been any studies of the actual bonding, or interface, between silicon and a diboride. Since the structures and composition of the interfacial region necessarily dictate the properties and morphology of the subsequent film, this region is of great importance. Also, while HfB@sub 2@ on Si more closely resembles the actual application of a diffusion barrier, many experimental advantages are gained from studying Si on HfB@sub 2@, while yielding the same results as HfB@sub 2@ on Si. Silicon was deposited onto a clean and well ordered single crystal by the reaction of silane, SiH@sub 4@(g), at 800C. Two phases of hafnium and silicon, were identified on the surface. The Hf@sub 5@Si@sub 3@ phase has a hexagonal unit cell and was found to form hexagonal islands that were more than 100Å in width and scattered over the surface. This surface exhibited a complex (@sr@7x@sr@7)R19.1 LEED pattern and two distinct XPS peaks in the Si2p region at 99.8 and 99.4 eV assigned to silicon and the silicide respectively. The HfSi@sub 2@ phase has an orthorhombic unit cell and formed nanometer-wide lines which, at higher coverages, form a "wagon wheel" structure. STM also shows rows of silicon dimers both before and after the 900C anneal, growing side by side the silicide features. These dimers are "bean-like" protrusions that have a (@sr@7x@sr@3) silicon structure. After annealing the dimer covered surface to 1300C the Si-Si bond was cleaved and the individual silicon atoms relaxed to form a honeycomb-type structure, occupying the three fold hollow sites.