Wet etch suitable for creating square cuts in si

A method of creating a lateral shelf in single crystal silicon, the method comprising:

• aligning a mask on a single crystal silicon along the <110> direction, the mask having at least one opening therein;
• exposing the single crystal silicon to an isotropic etchant through the at least one opening in the mask to form at least one trench in the <100> direction therein;
• forming a structure over unrecessed portions of an upper surface of the single crystal silicon and sidewalls of the at least one trench, while leaving a portion of the single crystal silicon exposed within the at least one trench;
• and
• contacting the exposed portion of single crystal silicon at a bottom of the at least one trench with a solution comprising a fluoride component, an oxidizing agent and an inorganic acid to form at least one square undercut without beveled edges.

A method of etching a single crystal silicon wafer, the method comprising:

• etching the single crystal silicon wafer to form at least one trench in the <100> direction;
• forming a structure over unrecessed portions of an upper surface of the single crystal silicon and sidewalls of the at least one trench, while leaving a bottom of the at least one trench exposed;
• and
• contacting an exposed portion of the single crystal silicon wafer at the bottom of the at least one trench with a solution that etches the (110) and (111) planes of the single crystal silicon faster than the (100) plane of the single crystal silicon
• the solution comprising a fluoride component, an oxidizing component and an inorganic acid to form an undercut cavity defined by concave square corners.

A method of creating a lateral shelf in single crystal silicon, comprising:

• aligning a mask on a single crystal silicon along the <110> direction, the mask having at least one opening therein;
• exposing the single crystal silicon to an anisotropic etchant through the at least one opening in the mask to form at least one trench in the 100> direction therein;
• forming a structure over unrecessed portions of an upper surface of the single crystal silicon and sidewalls of the at least one trench, while leaving a bottom of the at least one trench exposed;
• and
• contacting the exposed single crystal silicon at the bottom of the trench with a solution comprising a fluoride component, an oxidizing agent and an inorganic acid, while the sidewalls of the trench remain substantially covered by the structure, to form an undercut cavity having square corners.