Investigation of peculiarities of cobalt and its alloys electroless deposition

As new technological tasks arise, electroless coatings on the basis of cobalt have come into use in microelectronics and micromechanics in order to form a protective layer against copper migration in integral schemes. Copper possesses a low specific resistance, however it also has some disadvantages, such as a low corrosion resistance and a high diffusion coefficient into So and SiO2 as well as into other substances. These problems can be diminished by using a thin barrier layer protecting from copper diffusion. The barrier properties of CoP and CoB layers which can be further improved by addition of tungsten would be suited for this purpose. At present, investigations of this kind are being carried out in many countries. Recently much attention is given to the search of new substances, which could be used in direct borohydride fuel cells as catalysts for the borohydride oxidation reaction. The aim of our work was to investigate the peculiarities of electroless cobalt coatings deposition in glycine solutions using sodium hypophosphite and morpholine borane as reducing agents, as well as to determine the composition of the coatings obtained and the possibilities of their employment for the formation of barrier layers on copper and application for fuel cells production. It has been determined that using hypophosphite as a reducing agent the rate of CoP and CoWP coatings deposition and the quantity of P in them increases with increase in solution pH. After appropriate conditions were selected high-quality cobalt coating were obtained, which contain 2.9 to 6.3 at. % of P and up to 5 at.% of W. It has been determined that dicarbonic acids improve the buffer properties of the solutions, accelerate the deposition of cobalt coatings and increase the quantity of phosphorus in them. The buffer properties of the solutions improve with an increase in the number of -CH2- groups in the chain of dicarbonic acid. The XRD and XPS data obtained suggest that thin CoWP coatings deposited in the glycine solution are an appropriate barrier against Cu migration into adjacent layers. When morpholine borane was used as a reducing agent at a relatively low temperature (30˚), both nearly pure cobalt coatings free from boron and coatings containing up to 13 % of boron can be obtained. It has been determined that in cobalt coatings boron can be in two forms: elemental boron (binding energy 187.7 eV) and boron in its oxycompounds (binding energy193 eV). An increase in glycine concentration in electroless cobalt plating solutions diminishes nonproductive consumption of morpholine borane. Nanostructured Au/Co/Cu and Au/Co/Cu catalysts obtained after Co/Cu and CoB/Cu coatings were plated with Au nanoparticles using the immersion method can be used in direct borohydride fuel cells. The highest catalytic activity towards the borohydride oxidation reaction was shown by the CoB catalyst with a gold load of 3.1 μg cm-2 on the CoB surface, when Au particles were deposited in a 5 mmol l-1 Au citrate complex solution (pH 5.0)