Morphology, Structure and Mechanical Properties of Copper Coatings Electrodeposited by Pulsating Current (PC) Regime on Si(111)

Abstract

Copper electrodeposition on (111)-oriented Si substrate was performed by the pulsating current (PC) regime at various average current densities in the range of 15-70 mA·cm −2 , obtained by varying either the frequency (30, 50, 80 and 100 Hz for the current density amplitude of 100 mA·cm −2 ) or the current density amplitude (120 and 140 mA·cm −2 at 100 Hz). The produced Cu coatings were examined by SEM, AFM and XRD techniques. The morphology of the coatings changed from those with large grains to fine-grained and globular, while the crystal structure changed from the strong (220) to the strong (111) preferred orientation by increasing the average current density. The mechanical characteristics of coatings were examined using Vickers micro-indentation tests, applying the Chicot-Lesage (C-L) composite hardness model for the analysis of microhardness. The maximum microhardness was obtained for the Cu coating produced at an average current density of 50 mA·cm −2 , with a current density amplitude of 100 mA·cm −2 and a frequency of 100 Hz. This copper coating was fine-grained and showed the smallest roughness in relation to the other coatings, and it was obtained in the mixed activation-diffusion control between the end of the effect of the activation control and the beginning of the dominant effect of diffusion control.

Implementation of the Chicot–Lesage Composite Hardness Model in a Determination of Absolute Hardness of Copper Coatings Obtained by the Electrodeposition Processes

“…During hardness analysis of the Cu coatings electrodeposited by the PC regime on Si(111), the calculated values of the coating hardness by the C-L model were multiple times larger than the composite hardness at the applied low indentation loads [21]. The similar situation was also observed during the hardness analysis of Cu coatings of various thicknesses electrodeposited by the same regime on the brass substrate [22].…”

“…All electrodepositions were performed in an open cell of cylindrical shape with an electrolyte temperature of 22.0 ± 0.50 • C. Two types of cathodes were used: Si(111), and brass (260 1/2 hard, ASTM B36, K&S Engineering). The preparation of Si(111) and brass cathodes for copper electrodeposition is described in previously published papers [21,22]. The cathodes of (1.0 × 1.0) cm 2 surface area were positioned in the center of the cell.…”

“…For an estimation of the preferred orientation of Cu coatings, methodology based on the determination of the "Texture Coefficient", TC(hkl) and the "Relative Texture Coefficient", RTC(hkl) was applied. The detailed description of a procedure for the determination of these coefficients is presented in [21,25,26].…”

“…The Vickers microhardness tester Leitz Kleinert Prufer DURIMET I (Leitz, Oberkochen, Germany) with applied loads (P) in the (0.049 − 2.942) N range and a dwell time of 25 s was used for a determination of a hardness of the Cu coatings. The measured (or so-called) composite hardness (H c ) including a contribution of the substrate hardness (i.e., cathode) is given by Equation (1) [21]:…”

“…The hardness values of Si(111) and brass cathodes have been already determined applying the PSR (Proportional Specimen Resistance) model [27], and they were 7.42 GPa for Si(111) [21] and 1.41 GPa for the brass B36 [22] substrates. The Chicot-Lesage (C-L) composite hardness model was used for a determination of the absolute hardness of the Cu coatings.…”