The invention discloses a method to control the etching rate and safety of materials, including but not limited to etching of silicon (Si) based materials. An etchant system that can etch silicon oxides (SiOx) but does not oxidize Si has been developed to effectively remove SiOx while keeping Si largely intact. The etchant system uses organic solvents as one of the additional components in etching medium. The organic solvents have the following properties: 1) they are not miscible with water and 2) etching agents can dissolve in such solvents. The candidates of organic solvents include but are not limited to aromatic compounds such as benzene, toluene, xylene, cumene, etc. and aliphatic compounds such as hexane, cyclohexane, pentane, decene, etc and a mixture of such solvents. Compared to conventional aqueous based etchants, this method leads to mild reaction with low heat generation rate and avoids the safety hazard associated with bubbling/spilling occurred in the conventional etching methods. It also increased etching yield of porous Si (Psi) by preventing over-etching of Si. In addition, the etching agent used in this etchant system is easy to be separated and recycles/reused so the total cost of etching process is largely reduced.