Communication—Galvanic Deposition of Gold on Silicon from Au(I) Alkaline Fluoride-Free Solutions

Abstract

Deposition of gold from alkaline fluoride-free solutions containing Au(I) ions onto silicon surfaces has been demonstrated. This deposition takes place at room temperature and does not require the presence of a reducing agent in the solution. The results clearly show that Au(I) ions can be reduced to Au(0) by silicon and, as a consequence, gold metal can be deposited at the surface of the substrate. © The Author(s) 2016. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0991614jes] All rights reserved.Manuscript submitted September 28, 2016; revised manuscript received October 31, 2016. Published November 12, 2016 Using aqueous fluoride solutions, successful depositions of copper, silver or gold via the galvanic displacement reaction have been reported. [1][2][3][4] However, the fluorides represent a health hazard and as such are environmentally deleterious. Recent reports showed that silver 5 or copper 6 can be deposited from alkaline fluoride-free solutions directly onto silicon via the galvanic displacement reaction. It was clearly shown that the native SiO 2 films can be removed from the surface of a silicon wafer upon immersion into alkaline fluoride-free solutions. In this way, the direct deposition of silver or copper without a presence of any other reducing agent in the solution is realized via the galvanic displacement reaction. Similarly, this communication describes the observations of the deposition of gold onto silicon wafer from alkaline fluoride-free aqueous solutions containing Au(I) ions. Experimentalp-(B doped) and n-(P doped) single crystal (100) silicon wafers were used as substrates in the present work. As received, silicon substrates were very carefully washed with 3:1 (H 2 SO 4 -H 2 O 2 ) solution and then with water and absolute ethanol. Immersions were performed at pH 14 using a solution containing 30 g/L Na 2 S 2 O 3 and 1 g/L Au 2 S 2 O 3 . The pH of this solution was adjusted with NaOH.The specific immersion times are reported in the Results and discussion section. Experiments were carried out at room temperature (about 23• C). After the immersion, substrates were removed from the solutions and carefully washed with water, ethanol and then pressure dried with air at room temperature. Coated silicon substrates were analyzed by X-ray diffraction (XRD) using the CuKα radiation and by scanning electron microscopy (SEM). Results and DiscussionGold was deposited on both p-and n-Si substrates after immersion into alkaline Au(I) solutions at room temperature for 2 hours. Deposition of gold was observed on both polished and back sides of the silicon wafer. A prolonged exposure of silicon wafers to the investigated solutions obviously leads to the growth of gold particles. In Figure 1 are presented SEM images of the deposited gold onto p-and n-Si s...