Grain structure of thin electrodeposited and rolled copper foils

Planar and cross-section light optical and transmission electron microscopy (TEM) and X-ray diffraction analysis have been used to characterize the technologically relevant thin copper films and foils. The grain structure and grain orientation of (i) 1-15 mum deposit on the polyimide (PI) substrate, (ii) 5-35 mum free-standing foil and (iii) 200 mum sheet prepared by the industrial scale rolling or electrodeposit process have been examined. It is shown that the rolled foil structure is highly anisotropic due to grain stretching during rolling; the pancaked grains circumscribe a dislocation cell substructure. Thermal exposure in the 423-453 K range results in full anneal softening, while initiating the polygonization of cellular substructure, the formation of new large grains by discontinuous recrystallization and the transformation of the near (111) deformation textures into the near (100) anneal textures. The texture transformation is facilitated when the oxygen content of copper is reduced from the normal 100-400 ppm level or when a low level silver (similar to200 ppm) addition is made to copper. Depending upon the electrodeposition conditions or the nature of additives introduced in the electrolyte, it is possible to develop an electrodeposit with (a) a truly equiaxed, fine, twin-free, randomly oriented grain structure or (b) a relatively coarse grain structure, accompanied by extensive twinning, z (growth)-direction grain extension, columnar grain morphology and strong (220) crystallographic texture. Between (a) and (b), it is possible to tailor the processing to obtain a mix of fine and coarse grains, a large fraction of random orientation component (weak near (220) textures), moderate twinning, and vestiges of columnar grain morphology and z-direction grain extension. The anneal softening is not accompanied by significant grain structure modification or by texture change; somewhat above the softening temperature, an in situ grain growth ensues. For both rolled and electrodeposited (ED) foils, at 100 K or more above the softening temperature, grain growth is impeded by the foil surfaces. (C) 2004 Elsevier Inc. All rights reserved