Residual Stress, Defects, and Electrical Properties of Epitaxial Copper Growth on GaAs

Abstract

The residual stress in Cu films epitaxially grown on GaAs(001) singlecrystalline substrates has been compared to polycrystalline Cu growthon (111) textured Au substrates, both grown via the same galvanostaticelectrodeposition process. Optimized Cu/GaAs epitaxial nucleationand growth was obtained with a substrate pre-etch in dilute ammonium-hydroxidefollowed by electrodeposition in a pure Cu sulfate aqueous electrolyteat elevated temperatures. The resulting films are single crystalline,and strain relaxed, as measured by X-ray and electron diffraction.The (001) surfaces developed square pyramidal facets that increasein average size with increasing current density. In situ wafer curvaturemeasurements found that the Cu/GaAs films followed the commonly observedchange from compressive to tensile and finally to compressive stress(-200 MPa) that quickly relaxed once growth was interrupted. In contrast,polycrystalline Cu/Au films developed a smaller and constant tensilestress (+10 MPa) that relaxed more slowly. Given the similar growthrates of the two systems, differences in residual stress are relatedto differences in the density and nature of the coalescence boundariesand associated surface adatom processes. The resulting electricalproperties of Cu/GaAs diodes show an interfacial capacitance thatis consistent with interdiffusion and the reaction layer detectedby electron microscopy.