A process for etching silicon to form silicon pillars on the etched surfaces, includes treating silicon with an etching solution that includes 5 to 10M HF 0.01 to 0.1M Ag+ ions and 0.02 to 0.2M NO3− ions. Further, NO3− ions in the form of alkali metal, nitric acid or ammonium nitrate salt is added to maintain the concentration of nitrate ions within the above range. The etched silicon is separated from the solution. The process provides pillars, especially for use as the active anode material in lithium ion batteries. The process is advantageous because it uses an etching bath containing only a small number of ingredients whose concentration needs to be controlled and it can be less expensive to operate than previous processes.