US Patent 8012365 Deep anisotropic silicon etch method

A method of anisotropic plasma etching of a silicon wafer, maintained at a temperature from −40° C. to −120° C., comprising alternated and repeated steps of:etching with injection of a fluorinated gas, into the plasma reactor, andpassivation with injection of silicon tetrafluoride, SiF4, and of oxygen into the plasma reactor, the flow rate of the gases in the plasma reactor being on the order of from 10% to 25% of the gas flow rate during the etch step.