The atomic structure of Σ = 1 and Σ = 3 NiSi₂/Si interfaces

Abstract

The high-resolution imaging technique is applied systematically to study the Σ=1 (type A) and Σ = 3 (type B) NiSi₂/Si interfaces. Possible structural models for Σ = 1 (type A) and Σ = 3 (type B) NiSi₂/Si interfaces can be completely deduced from the dichromatic constrained coincidence site lattice (CCSL) patterns. For the Σ = 1 NiSi₂(001)/(001)Si interface, new interface structures have been found and a 2 × 1 reconstructed interface structure involving a difference in composition has also been observed. The new interface structures were confirmed from through-focal series of high-resolution images from two orthogonal 〈110〉 beam directions. Domain-related interface structures coexisting in Σ = 1 NiSi₂(001)/(001)Si interfaces were found to be separated by a ¼〈111〉 type of dislocation which is associated with a demi-step. There is only one interface structure observed in both Σ = 1 and Σ = 3 NiSi₂(111)/(111)Si interfaces where the interfacial Ni atoms has been determined to be sevenfold coordinated. Two DSC dislocations associated with steps were identified in a Σ = 3 NiSi₂(111)/(111)Si interface. The Burgers vectors of the DSC dislocations were determined to be 1/12[111]Si and ⅓[111]_Si. Both DSC dislocations are associated with a complete step with the vector being ½[110]_Si. The long-period boundaries of Σ = 3 NiSi₂(111)/(115)Si and NiSi₂(221)/(001)Si have been shown to decompose into short period of symmetrical NiSi₂(111)/(111)Si and NiSi₂(112)/(112)Si atomic facets which resembles the asymmetrical tilt grain boundary case. The coexistence of two domain-related atomic faceting interfaces in the Σ = 3 NiSi₂(111)/(115)Si and NiSi₂(221)/(001)Si has also been observed in different areas of an interface. They are separated by a ¼〈111〉 type dislocation associated with a demi-step. The Burgers vector and step of a dislocation required to separate two domain structures and that of DSC dislocations in the Σ = 3 NiSi₂/Si interface can be derived from consideration of the CCSL model.