ELECTROCHEMICALLY REDUCED POLYCRYSTALLINE TIN OXIDE THIN-FILMS - SURFACE-ANALYSIS AND ELECTROPLATED COPPER ADHESION

In previously reported work, a conductivity enhancement effect in poly crystalline tin oxide thin films, which are widely used for the front electrodes in flat panel displays, has been achieved by electroplating copper onto the 300 nm high sidewalls of the electrode. Recent experi ments show that if an electrolytic reduction is introduced as a surfac e modification process just before electroplating then excellent adhes ion between copper and tin oxide can be achieved. In this paper, the c hemical, physical and surface morphological changes of tin oxide elect rodes have been characterized by using atomic force microscopy, x-ray diffraction, x-ray photoelectron spectroscopy and surface sheet resist ance measurements by a four-point probe method. The electrolytic reduc tion was found to result in an increase in the intensity of the x-ray reflection from the (110) planes of tin oxide, and compositional nonun iformity of: the tin oxide surface layers, where metallic tin is trapp ed at the surface, and oxygen is enriched in the subsurface region. Th ese results, taken together, suggest that the observed adhesion improv ement may be due to a combination of tin oxide surface roughening due to preferential etching and the increased (110) orientation, in situ c leaning, and chemical bonding introduced by surface chemical changes.