Correlation of morphology and electrical properties of nanoscale TiSi₂ epitaxial islands on Si (001)

The morphology and electrical properties of nanoscale epitaxial islands of TiSi₂ are explored. The TiSi₂ islands are prepared by ultra-high vacuum (UHV) deposition of ultra-thin Ti (0.3-2 nm) on both smooth and roughened Si (001) substrates. The roughened substrates are prepared by etching with atomic H produced in a plasma. The island formation is initiated by annealing to 800-1000°C. The morphologies of the substrate before and after island formation are examined by atomic force microscopy (AFM). In particular, the influence of surface-roughness on both the formation of islands and the size distribution of islands is investigated. Islands with a lateral dimension of ∼35 nm and a vertical dimension of ∼2.5 nm on a roughened substrate (RMS = 12 nm) were observed, with a uniform distribution of 120 nm spacing between the islands. It was found that for similar processing conditions the size distribution of islands formed on a rough surface was smaller than islands formed on smooth surfaces. The results are discussed in terms of surface energy, diffusion and the strain field around the islands. The island structures can affect the electrical characteristics of the interface and the Schottky barrier was obtained from diodes formed with a Pt layer deposited over the islanded interface. The Schottky barrier was lowest for interfaces with the smaller TiSi₂ islands.