Characterization of Films Formed during the Corrosion of Copper in Dilute Solutions of Cupric Chloride
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ABSTRACT Microstructural differences in copper deposited by four techniques commonly used in the microelectronics industry were previously reported. Grain size, preferred orientation, and near surface chemistry were considered. [1] Prediction of the reaction rates were made based on these differences and then correlated with actual measurements. [2] In aerobic conditions the grain size dictated the reaction rate, the smaller the size the faster the rate.[3] The composition of the surface film formed during etching was examined. The trends in chemical concentrations on the surface film vary for each sample, but the relative constituent amounts correlate to the grain size of the original copper samples. Thus, there is further evidence that during exposure to aqueous solutions of cupric chloride, copper corrosion, in terms of both etch rate and film composition, is dictated by grain size of the original copper and not other microstructural factors.
I. INTRODUCTION Copper is a choice metallization for semiconductor devices and packages because of its low resistivity, resistance to electromigration, solderability, and low cost.
Copper lines for
interconnections are fabricated using different techniques and substrates chosen by its final device or package application and manufacturing cost. Each copper film has its own characteristic microstructure dependent on deposition technique and substrate. [4-10] These differences influence the copper film's physical and electrical properties such as resistivity, mechanical strength, hardness, and fatigue resistance. In actual processing, the deposition technique will most likely be chosen by its ability to economically adapt to the size of the substrate. For example, large substrates or circuit boards are routinely plated in aqueous baths while smaller substrates are easily inserted into vacuum chambers for either evaporation or sputter metal deposition. Currently the following deposition techniques are used in the microelectronics industry: electroless, electroplate, evaporate, and sputter deposition. Each is known to produce films with differences in grain size, preferred grain orientation (texture) and surface topography. Thus each of these films will be distinct. The overall objectives of this research were to measure the microstructural differences of films typically used in the microelectronics industry and to predict their influence on the wet etching of copper during patterning of the microelectronic circuits. Variations in the microstructure of these lines and subsequent processing will influence the reliability and performance of the resulting interconnects. Microstructure differences of the films, a method to determine etching kinetics, and the relationship of the microstructure to etching
117 Mat. Res. Soc. Symp. Proc. Vol. 390 01995 Materials Research Society
kinetics are reported elsewhere.[1,2,3] residue are reported here.
Results relating the microstructure and the corrosion
II. EXPERIMENTAL The copper samples for this study are thin films formed using two
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