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

Abstract

The influence of various electrolysis parameters, such as the type of cathode, composition of the electrolyte and electrolysis time, on the morphology, structure and hardness of copper coatings has been investigated. Morphology and structure of the coatings were analyzed by scanning electron microscope (SEM), atomic force microscope (AFM) and X-ray diffraction (XRD), while coating hardness was examined by Vickers microindentation test applying the Chicot–Lesage (C–L) composite hardness model. Depending on the conditions of electrolysis, two types of Cu coatings were obtained: fine-grained mat coatings with a strong (220) preferred orientation from the sulfate electrolyte and smooth mirror bright coatings with a strong (200) preferred orientation from the electrolyte with added leveling/brightening additives. The mat coatings showed larger both measured composite and calculated coating hardness than the mirror bright coatings, that can be explained by the phenomena on boundary among grains. Independent of electrolysis conditions, the critical relative indentation depth (RID) of 0.14 was established for all types of the Cu coatings, separating the zone in which the composite hardness can be equaled with the coating hardness and the zone requiring an application of the C–L model for a determination of the absolute hardness of the Cu coatings.

Structural, Mechanical and Electrical Characteristics of Copper Coatings Obtained by Various Electrodeposition Processes

“…Copper coatings were produced using constant galvanostatic regime (DC mode) without and with application of ultrasound (US) for mixing of electrolytes at current densities of 33, 67 and 150 mA cm −2 . The electrodeposition process was performed from the following electrolytes [5]: The electrolytes were prepared using double distilled water and reagents of p.a. quality (Sigma-Aldrich, Darmstadt, Germany).…”

“…Electrodeposition was performed at a temperature of 22.0 ± 0.50 °C. The thickness of coatings was 20 μm, and was controlled by the mechanical comparator with electronic reader on display (model: Iskra, type: NP37 (Iskra Avtomatica, Ljubljana, Slovenia) with the accuracy of the vertical shift of ±1 μm [5]. All conditions applied for a production of uniform Cu coatings are summarized in Table 1.…”

“…Various processes of copper electrodeposition on different bulk materials were devel-oped for micro electro mechanical systems devices (MEMS), through-hole plating for printed circuit boards (PCBs), as well as for all other conventional functional plating processes on silicon, brass, steel, copper, etc. [3][4][5]. Copper coatings are the most commonly used material for interconnections within microelectronics.…”

“…The most commonly used additives in Cu electrodeposition from sulfate electrolytes are: chloride ions, bis(3sulfopropyl) disulfide (SPS), polyethylene glycol (PEG), 3-mercapto-1-propanesulfonic acid (MPSA), Janus Green B, thiourea, etc. [5,[7][8][9][10][11]. It was shown recently [5] that a combination of the additives such as chloride ions, PEG and MPSA added to the basic sulfate electrolyte drastically affected a change of the topography of the copper coatings compared to the coatings obtained from the basic sulfate electrolyte.…”

“…[5,[7][8][9][10][11]. It was shown recently [5] that a combination of the additives such as chloride ions, PEG and MPSA added to the basic sulfate electrolyte drastically affected a change of the topography of the copper coatings compared to the coatings obtained from the basic sulfate electrolyte.…”