Method of etching a deep trench in a substrate and method of fabricating on-chip devices and micro-machined structures using the same

A method of fabricating a device suspended on a substrate, comprising the steps of:

• forming the device on the substrate;
• and
• forming a cavity underneath the device to suspend the device on the substrate,
• wherein the second forming step comprises
• performing a first etching under a first etching condition, the first etching including anisotropically etching the substrate through a patterned masking layer to a first etch depth;
• and
• performing a second etching under a second etching condition, the second etching including semi-anisotropically etching the substrate through the patterned masking layer to a second etch depth, thereby forming the cavity underneath at least a portion of the device with precise control of lateral undercut.

A method of dry plasma etching a substrate to form at least one trench in the substrate, comprising the steps of:

• performing a first etching using an anisotropic etching agent and an isotropic etching agent to etch the substrate to a first etch depth, the first etching including alternately pulsing the anisotropic etching agent and the isotropic etching agent at respective first pulse durations;
• and
• performing a second etching using the anisotropic etching agent and the isotropic etching agent to etch the substrate to a second etch depth and form a re-entrant shape in the trench with approximately zero lateral undercut, the second etching including alternately pulsing the anisotropic etching agent and the isotropic etching agent at respective second pulse durations,
• wherein the second pulse duration of the isotropic etching agent is greater than the first pulse duration of the isotropic etching agent.