Diffusion barrier of sputtered W film for Cu Schottky contacts on InGaP layer

To improve the thermal stability of Schottky performances, a refractory diffusion barrier layer of W is used for impeding the indiffusion of Cu into the JnGaP layer. From the atomic force microscopy measurements for W/Cu Schottky contacts to the InGaP layer thermally annealed at various temperatures, both the surface roughness and mean particle size increase with increasing annealing temperatures. Meanwhile, there is also an obvious change in the surface color for the Schottky diodes thermally annealed at 500 degreesC. This change in surface color reveals that the metallic CW is unstable and tends to react with the ambient nitrogen as annealing temperature reaches 550 degreesC. However, transmission electron microscopy measurement represents a well-defined W layer between the Cu and InGaP layer under annealing temperature of 550degreesC. The interface of W/InGaP is obvious and no indiffusion of Cu appears in the InGal? layer. Therefore, the metallic W acts as a diffusion barrier layer and results in a higher thermal stability of Schottky performance. As annealing temperature reached 600 degreesC, an obvious spike-toothed indiffusion appears around the W/InGaP interface. According to energy dispersive X-ray spectroscopy analyses, the spike-toothed region is attributable to the penetration of Cu into the InGaP layer through the grain boundaries of W, and results in the degradation of the Schottky performance. (C) 2004 Elsevier B.V. All rights reserved.