NOVELTY - Etching a silicon substrate comprises contacting the silicon substrate with an aqueous solution of a fluoride acid or a fluoride salt, metal salt (5-100, preferably 12.6-22.1 mM) (i.e. silver salt, optionally silver nitrate (0.2-16, preferably 0.75-0.7 wt.%)) capable of electroless deposition of the metal on the silicon in the presence of fluoride ions, and an alcohol (up to 40, preferably 15-30 vol.%), preferably ethanol. The fluoride acid comprises hydrogen fluoride whose content is between 3-20, preferably 12 or 13.6 wt.%.    USE - For etching a silicon substrate i.e. very large scale integration electronic grade single crystal wafers or their rejected samples, photovoltaic grade polycrystalline material, or crystalline metallical grade silicon, to create an etched silicon substrate used in an anode for a lithium rechargeable cell.    ADVANTAGE - The method provides an increasing pillar height of approximately 5 times that previously obtained and improves pillar uniformity over square centimeters. Thus, silicon based electrodes can be fabricated with uniform height and packing density across wafers of 10-15 cm in diameter.    DETAILED DESCRIPTION - Etching a silicon substrate comprises contacting the silicon substrate with an aqueous solution of a fluoride acid or a fluoride salt, metal salt (5-100, preferably 12.6-22.1 mM) (i.e. silver salt, optionally silver nitrate (0.2-16, preferably 0.75-0.7 wt.%)) capable of electroless deposition of the metal on the silicon in the presence of fluoride ions, and an alcohol (up to 40, preferably 15-30 vol.%), preferably ethanol. The fluoride acid comprises hydrogen fluoride whose content is between 3-20, preferably 12 or 13.6 wt.%. The substrate is allowed to stand in solution at 0-30, preferably 20degreesC for 5-50, preferably 10 minutes. The temperature of the solution is raised to 40-75degreesC; and the substrate is allowed to stand in the solution at the raised temperature for 30-100, preferably 45 minutes. The method comprises adding further silver salt e.g. silver nitrate, or a ferric salt e.g. ferric nitrate in 0.1-2, preferably 1 wt.%, upon raising the temperature, increasing the silver or ferric concentration of the solution by 2-6, preferably 2.85-5.45 mM.