Influence of different additives on the copper electroplating onto Au(111) and Cu(111) substrates

Abstract

Electrochemical deposition of metals on metals is a widely used industrial process and understanding its basics is the subject of numerous studies. In the following copper electrodeposition onto two substrates - Au(111) and Cu(111) - will be presented. The applied experimental techniques were cyclic voltammetry and in situ Scanning Tunneling Microscopy (STM). Addition agents are used in the industrial copper plating from acid sulphate solutions in order to achieve the desired deposit quality. The effect of different additives (three functionalized thiols - MPSA, SPS, MPA, polyethylene glycol + chloride) on Cu electrodeposition will be discussed. They have been chosen because of their use into the electroplating baths, especially in microelectronics. It is known that the additives affect deposition and crystal formation processes as adsorbates at the cathode. Therefore special attention is given on the adsorption of the studied molecules onto the substrates. The initial stages of Cu deposition in the presence of different additives have been investigated. Their adsorption on the substrate surface and differences in the growth peculiarities will be presented. Substrate preparation played a very important role and therefore will be also briefly addressed. In the case of Au single crystals, annealing in a hydrogen flame at yellow heat yielded a clean surface with large terraces. In comparison to Au, Cu has proven to be a more difficult substrate, especially because of its tendency to form an oxide layer in the air. Two preparation methods have been used for the Cu(111) surface: electrochemical polishing and annealing in an inert atmosphere, using inductive heating. It was the first time when annealing with inductive heating has been used for preparing Cu single crystal surfaces.