Machining Silicon Wafers By Using Hydrodynamic Suspension Technology

Alone with development of LSI and SLSI quick, silicon wafers need high sur-face precision and machining effecency. Only improving actual technology is diffi-cult to solve the question. So people must research fresh machining theory and tec-hnics method, explore fresh function of silicon wafers surface and energy, motion,instrument. Especially function and combination of fresh energy break throughlimit of machining equipments.The new phase of super smooth surface processing technology is that a seriesof methods and noncontact polishing equipments. Noncontact is a bran-new meth-od including machining mechanism and machining method. The bran-new methodindicates developing direction of super smooth surface processing. Hydrodynamicsuspension super smooth surface processing is one of new technologies which areempoldered in allusion to super precison surface of burgeoning photoelectron com-ponent. Hydrodynamic suspension super smooth surface processing is a nanomet-er technique which is integret of mechanical polishing, particle dynamics, fluiddynamics and chemistry.On the basis of dynamical fluid theory and principle of EEM(Elastic emissionmachining), machnism of hydrodynamic suspension super smooth surface proc-essing is researched. It uses high velocity rotate tool that is nanometer and elastic todrive the nanometer suspension liquid, produces comprehensive functions asphysics﹑chemistry﹑elastic emission and machine concussion in workpiecesurface,to attain nanometer surface quality. Fig 1 is sketch of machining principle.Machining mould is a polyurethane tool. Distance between outer surface ofpolyurethane tool and surface of workpiece is 50um approximately. Polyurethanetool and workpiece emerge in suspension liquid placed in a container.Fig 1 Sketch of hydrodynamic suspension processing mechanismHydrodynamic suspension super smooth surface processing of silcon wafers iscomplicated multiphase reaction. It exists two course:(1) oxidant and acticator thatare absorbed in suspension liquid are redoxed with silicon on surface of silcon waf-ers, this is principal of chenmistry. (2) desorption is a course that reactant of workp-iece surface disengages from silcon wafers surface, in ord to come out responselesssilicon. Suspension liquid drived by Polyurethane tool is flow incessantly,consequently reactant of silicon wafers surface is disengaged incessantly, reactantis drived by suspension liquid. New silicon that come out is oxidatived, reactant isdrived again. It is a course of to-and-fro to attain super smooth surface.Chemistry ismostly that silicon wafers surface is eroded by lye of suspension liquid2Si + 2 OH ? + H 2 O ??→ SiO 3 ?+ 2H2Besides colliding and grinding workpiece surface, nanometer SiO2 is also acti-vator in suspension liquid. At machining temperature, SiO2 responses with siliconto produce SiO, then SiO redox with lye. Equations are:Si + SiO2 ??→ 2SiO2SiO + 2OH ? ??→ SiO3 ?+ H2↑Due to high velocity rotate of polyurethane wheel, elastic dynamical fluid isproduced between outer surface of polyurethane wheel and surface of workpiece insuspension liquid. Elastic dynamical fluid drives continuously nanometer SiC intoexiguity extent between polyurethane wheel and workpiece surface .One side, ela-stic dynamical fluid provides enough energy to drive nanometer SiC to concussatoms of workpiece surface. On the other hand, grads dynamical field is formedbetween outer surface of polyurethane wheel and workpiece surface, press fielduprights workpiece surface approximately. When suspension&turbid liquid is deli-vered to processing area, suspension liquid occurrs rheology under grads dynamicalfield, and produces soft solid state protuberance. Protuberance is a soft "grinder".Cutting strength is produced because "grinder" moves comparative fast on workp-iece surface. Since surface of optical glass is corroded by feeble alkalescence liq-uid , integrate energy of surface atomic layer becomes very weak. Going with frict-ion and cutting stress, crystal lattice of optical glass surface material is wiped off.Development of suspension liquid is first step of hydrodynamic suspensionsuper smooth surface processing of silicon wafers. Its performace decides surfacequality of silicon wafers machining. Suspension liquid offers chemistry and mechn-ical function. Suspension liquid is well-proportioned and stablilization formed bytiny nanometer particles being dispersed into liquid, moreover, it has very good rh-eology. Suspension liquid is consist of nanometer particle(SiO2), basic liquid(purewater), activitor( RO ( C 2 H 4O )nH ), organic lye etc. Basic liquid has very low visco-sity, very good heat stability,very low volatility, very wide difference in temperatu-re. Activitor must has the molecule structure. One of the molecule structure isabsorbed surface of nanometer particle, the other has a suitability length stretch keythat is dispersed into liquid easily. Lye adjusts PH of suspension liquid efficiently.Suspension liquid that has good performance ought of have suitabilityviscosity,good stability, good dispersity etc.In this paper, it is developed that processing system for hydrodynamic suspen-sion super smooth surface based on robot. The system is composed of YR-SV3-J00robot, machining equipment, speed variable motor, XY work table, WYKO andAFM, computer and so on.On the basis of theory analyzing about silicon wafers hydronamics suspensionsuper smooth surface processing,experimentation of silicon wafers has been doneby using developed suspension liquid. Fig 3, 4, 5 and 6 show results attained. Fig 3and 4 show 3-dimension visage(WYKO). From the two figs, we may see that surfa-ce roughnss degree is 1.55nm after being processed. Fig 5 and 6 show 2-dimension(WYKO). From the four figs we may see that surface quality and precision is impr-oved greatly, relatively to original surface.Measuring 30gSiO2UltrasonicvibratingAdding surfaceactivator and lyeSuspensionliquidUltrasonicvibratingwater200ml1hWater1LFig 2 Confecting flow of suspension&turbid liquid...