Deep Reactive Ion EtchingOverviewConcept of DRIEThe Bosch ProcessThe Bosch Process (cont’d)The Bosch Process (cont’d)The Cryogenic ProcessThe Cryogenic Process (cont’d)Bosch vs. CryogenicDRIE ApplicationsDeep Reactive Ion EtchingRaj BhattacharyaAlex ReisOverview Concept behind DRIE DRIE processes and technology Bosch process Cryogenic process DRIE applicationsConcept 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 micromachiningThe Bosch Process Developed in Germany in 1994 Alternates etching and passivation layer deposition – allows for high aspect ratio etching SF6 to etch, fluorocarbon to passivateSiPRAfter etch stepPassivation layer depositionAfter second etch stepThe 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 pressureTypical ICP system used for Bosch processThe 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 uniformityThe 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 (-110oto -130oC) are used to reduce the etch rate on the passivated sidewallsThe 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 profileBosch 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 requiredRough sidewall from Bosch processDRIE Applications Micromachining Bosch process Printer heads Accelerometer for air bags Cryogenic process Preferred for through-wafer etching Fluid transport – smooth
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