Deep Reactive Ion Etching Raj Bhattacharya Alex Reis Overview Concept behind DRIE DRIE processes and technology Bosch process Cryogenic process DRIE applications Concept of DRIE Reactive ion etching RIE Etch gas is converted to plasma Electrode beneath wafer accelerates ions Ions etch substrate through both chemical and physical reactions DRIE Expands on RIE technology Can produce vertical sidewalls High aspect ratio High etch rate More precise than RIE useful for micromachining The Bosch Process Developed in Germany in 1994 Alternates etching and passivation layer deposition allows for high aspect ratio etching SF6 to etch fluorocarbon to passivate PR Si After etch step Passivation layer deposition After second etch step The Bosch Process cont d Technology High density plasma HDP is needed for high etch rates inductively coupled plasma ICP systems produce the required density plasma at low pressure Typical ICP system used for Bosch process The Bosch Process cont d Technology cont d Specific hardware High capacity gas pump fast pumping is required to achieve high etch rates Fast response mass flow controllers required to accommodate fast switching of injected gas Purely inductive plasma coupling capacitive coupling causes variations in plasma density uniformity The Cryogenic Process Uses ICP system to produce HDP One step etching etch gas and passivation gas are released at the same time SF6 to etch and SiOxFy to passivate Cryogenic temperatures 110o to 130oC are used to reduce the etch rate on the passivated sidewalls The Cryogenic Process cont d Technology Hardware Cryogenically cooled stage Mass flow controller for oxygen very small amounts of oxygen can have significant effects on etch profile Bosch vs Cryogenic Bosch process advantages Can be conducted at room temperature Low temperature sensitivity Cryogenic process advantages Lower power requirements less attack on mask and therefore higher selectivity Smooth sidewalls Less specialized hardware is required Rough sidewall from Bosch process DRIE Applications Micromachining Bosch process Printer heads Accelerometer for air bags Cryogenic process Preferred for through wafer etching Fluid transport smooth sidewalls Questions
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