Soft X-Ray Photoemission Measurement of Schottky Barrier Formation at The Pd-si Interface

Abstract

The binding energy of the bulk Si 2p levels observed with soft X-ray photoemission can be used to monitor the band bending in the silicon space charge region when a metal is deposited onto the silicon surface. Changes in the 2p binding energy with metal coverage can then be used to determine the change in the Schottky barrier height as the metal-silicon contact is formed. By tuning the photon energy and therefore the photoemitted electron escape depth, chemical shifts (atomic environment effects) at the interface can be separated from the bulk band bending effects. When combined with annealing to produce in-depth atomic intermixing, the result may reveal information on the distribution of metal atoms at the interface and its effect on the barrier height.Measurements of the Schottky barrier height change as a function of palladium deposition were made on (2 × 1) p-type and (7 × 7) n-type Si(111) surfaces by monitoring Si 2p core level shifts in a bulk sensitive mode. The barrier height change reached 1/e of its final value at a palladium coverage of 2.9 Å. Several experiments have made it possible to relate the measured Si 2p core level monitor of band bending to absolute Schottky barrier heights in a fully consistent fashion. Therefore, these results provide a means to measure the barrier height in the initial stages of Schottky barrier formation (i.e. at low metal coverage) and to compare these observations with the chemical behavior of the interface at low coverage and with electrical measurements on bulk contacts. Since the Pd/Si Schottky barrier height is established at the bulk value within a coverage of 3–5 Å (even before the overlayer is metallic), the role of interface chemical bonds in determining the barrier height is paramount.This work was supported in part by the U.S. Office of Naval Research.