Experimental Study of the Microstructure and Stress of Electroplated Gold for Microsystem Applications

Abstract

Gold, used as an X-ray absorber for lithography and as a structural or conducting material in microsystems, was deposited from a commercially available sulfite electrolyte. The effects of current type and an arsenic additive on the gold microstructure and residual stress were studied. Using a simple bent strip method, good agreement with literature stress values determined via other methods was obtained. Without arsenic, residual stresses are tensile regardless of current type. With 25 ppm arsenic, the stress is compressive for direct current (ca. with pulsed current reducing the stress to compressive; this has been noted previously with thallium as an additive. The addition of arsenic does not appreciably change the film grain size but does lower the twin density and modify texture. Pores were observed in all the gold films, but were larger and less concentrated for films produced with arsenic; for the case of direct current with arsenic, the pores were concentrated at the grain boundaries. Consistencies in the microstructural observations and thin film stress theories are discussed. © 2003 The Electrochemical Society. All rights reserved.