Charge Exchange Processes during the Open-Circuit Deposition of Nickel on Silicon from Fluoride Solutions

Abstract

Electrochemical deposition of metals has been used to obtain high quality Schottky diodes on compound semiconductors like GaAs 1 and InP, 2 but less attention has been dedicated to silicon despite its wider use in microelectronics. A few studies have been published recently about Pt, Au, Fe, Ni, and Cu deposition, 3-8 some of them including in situ scanning tunneling microscopy (STM) imaging, as in the case of Zn 5 and Pb. 6 Others focused on the fundamentals of nucleation and growth modes as well as the chargetransfer mechanism during electrochemical deposition. 7-9 The application of an external potential to a sample immersed in an electrolyte somehow diminishes the main advantage of the wet chemical methods for industrial purpose. Regarding metal deposition, it is both desirable and convenient for some applications to have a method that produces deposition on the sample without the need for an electrical contact, thus allowing deposition by simple immersion of the sample in a solution containing the appropriate metallic ions. This paper reports on the electrochemical study of nickel deposition at the open-circuit potential (OCP) on silicon from fluoride solutions of pH 1.2 and 8.0. The charge-transfer processes involved in the deposition mechanism and the role of surface states are also discussed, using a complete study under potentiostatic control. It is shown that this approach provides first-hand information for the analysis of the deposition mechanism.Hydrofluoric acid solutions are known to etch the insulating oxide that may form on the silicon surface under certain conditions. The presence of relatively high fluoride concentrations thus guarantees the cleanness of the substrate and its intimate contact with the solution, and simplifies the analysis of charge-exchange processes with the species in solution. Beyond this justification, a posteriori for basic research purposes, the interest in the study of metal deposition from fluoride solutions arises from several fields in the microelectronics industry, to evaluate the damaging effects of metal trace contaminants in the cleaning solutions 9,10 and to delineate p-n junctions 11,12 and reveal defects in semiconductor wafers. 13,14 In the metal coatings industry, these solutions are also employed to predeposit the samples to be subsequently coated by other electrochemical methods. 15Charge transfer at semiconductor electrodes.-In order to be reduced and deposited as metal on the surface, the metal ions in solution must draw electrons from the silicon substrate. The corresponding electrons can in principle be obtained in different ways, namely, by accumulating them at the surface of an n-type electrode under negative bias or by photogenerating them at the surface of a depleted p-type electrode. Another possibility is extracting them from the bonding levels of the substrate atoms (i.e., by oxidizing the silicon atoms). In the formalism of semiconductor electrochemistry, the first two processes involve free electrons in the silicon conduction band (CB), and the...

Electroless Nanoparticle Film Deposition Compatible with Photolithography, Microcontact Printing, and Dip-Pen Nanolithography Patterning Technologies

“…Deposition proceeds via galvanic displacement 20 in the absence of fluoride, pH buffers, complexing agents, or external reducing agents, in contrast to earlier work. [21][22][23][24][25][26][27][28][29][30] Patterning of these particle film assemblies is essential for their subsequent incorporation into higher order architectures and devices. 31,32 The first patterning motif tested, photolithography, was carried out as outlined in Figure 2a.…”

FeNi alloys electroplated into porous (n‐type) silicon

“…It can be seen that the onset potential for the Ni/Fe deposition on n-Si (100) is around -0.7 V. The extra over potential for the deposition of Ni/Fe on Si is required to overcome the energy barrier, according to the energy distribution model at the semiconductor/electrolyte interface [10,11], such that the charge transfer would not occur for passing a Faradayic current until the flat band potential is reached at a certain value of the cathodic potential.…”

Electrochemistry of metals and semiconductors in fluoride media

“…Using this process a thick and stable tin deposits can be obtained [204]. The physicochemical properties of gold deposited on porous Si by a similar procedure have also been described [205]. The pH of the electrolyte medium has a significant effect on the electroless deposition of Ni on porous Si.…”