Electroless silver deposition in 100 nm silicon structures

A new and simple method is described to plate silicon structures with metallic silver for ultralarge-scale integration in dimensions down to 100 nm at an aspect ratio of 4.25. The silver deposition is initiated by an exchange reaction of silicon with silver ions, and the subsequent layer growth of the activated wafers occurs by electroless plating from supersaturated aqueous silver salt solutions at pH similar to 11. No extra reducing agents are needed since silver ions are reduced at the catalytic silver surface by hydroxyl ions. The "spontaneous" ion-metal transition only proceeds at pH similar to 11 and is likely mediated by the formation of subnanometer-sized [Ag-4(OH)(2)](2+) clusters. The silver plating proceeds more easily in smaller structures and yields void-free, crystallized deposits. (C) 2000 The Electrochemical Society. S0013-4651(00)02-082-6. All rights reserved.