Method of etching silicon substrate at different etching rates for different planes of the silicon to form an air bridge

A method of etching a silicon substrate, for forming an air bridge by making use of differences in etching rates for respective crystal planes of a silicon substrate, comprising the steps of:

• forming a mask layer including an air bridge pattern on a (100 plane of a silicon substrate;
• generating isotropic defects in said silicon substrate by irradiating the silicon substrate with ions of an inactive element which is heavier than Si using a sputter etching process;
• and
• forming an air bridge by anisotropic etching of the irradiated silicon substrate.

A method of etching a silicon substrate, for forming an air bridge by making use of a difference in etching rate for each crystal plane of silicon in a silicon substrate, comprising the steps of:

• forming a mask layer including an air bridge pattern on a (100) plane of the silicon substrate;
• plasma etching isotropically to undercut the masked silicon substrate on opposite sides of the air bridge pattern, until a point of intersection between tangents of a peripheral plane surrounding a cavity undercut under the air bridge pattern, wherein each tangent is inclined at 54.74.degree. to the silicon substrate, is located just underneath a plane of the air bridge pattern;
• and
• forming an air bridge by anisotropic etching of the silicon substrate beneath the air bridge pattern.