Bulk and SurfaceMircomachiningTuan Dang and Anita QuabiliENEE416October 6, 2009Wet Bulk Micromachining• Wet (etchant): aqueous solution that eatsaway Silicon.• Bulk: usually Silicon wafer where wetecthants remove material.• Micromachining: method of fabricatingmicrostructures using wet etchingtechniques.Wet Etching ProcessSiliconIsotropic Wet EtchingAnisotropic Wet EtchingBulk ApplicationsPros• Inexpensive• Done in bulk• Good for making micromechanical parts:holes, trenches, pits and MEMSCons• Not easily incorporated withmicroelectronic devices• Cannot be layered on the same waferSurface Micromachining• Bulk Micromachining: a silicon wafer isselectively etched to produce microstructures• Surface Micromachining is based on depositing and etching layers on top ofthe silicon substrateDry Etching Process• The main purpose of dry etching is to avoidisotropic etching associated with wet techniques• Realized using plasmaetching systems• Methods– Ion bombardment– Chemical Reactive• Environment– Vacuum chamberIon Bombardment (Sputtering)• Also known as Ion Beam Etching• Is performed in a low-pressure vacuumchamber.• Energetic gas particles are introduced into thechamber.• Gas particles hit the metalat the cathode, knockingthe metal particles loose– This deposits a layer ofmetal onto the unmaskedpart of the wafer• Requires very lowpressureReactive Ion Etching• Reverse polarity: Is like sputtering except the cathode is under thewafer and the anode is on top of the wafer• The gas particles hit the wafer and physically etch away theunmasked portion of the wafer• The wafer is usuallyheld at an angle sothat the etchedmolecules don’tredeposit themselvesonto the wafer• Is less anisotropicthan sputtering• Requires lessenergy thansputteringReactive Ion EtchantsO2, SF6, CF4CCl4, CF4, NF3, SF6CF4, C2F6, C3F8, CHF3CF4, C2F6, CHF3, SF6CCl4, Cl2, BCl3C2Cl2F4, CF4Cl2• Organic Materials:• Polysilicon:• Silicon Dioxide:• Silicon Nitride:• Aluminum:• Titanium:• Tungsten:Different etchants require different temperaturesand pressures to be effectivePros• High cost• Poor selectivity (compared to wet etching)• Potential radiation damageCons• Anisotropic• Capable of small feature sizes (<100nm)• Can be used for many layers• Insensitive to crystalline structuresSurface
View Full Document
Unlocking...