The Research On Kinetics Model Of Ultrasonic Enhancement On Liquid-solid Mass Transfer And Technology Of Silicon Echelle Grating Fabricated By Wet Etching

Silicon wet etching technology is the application that productsmicro-nanostructure on silicon materials by means of chemical solution corrosion. Inorder to reduce the surface roughness of the silicon devices, ultrasonic as theassistant means is widely used in silicon wet etching process. In the reaction processbetween silicon and corrosive liquid, the ultrasonic cavitation will enhance the masstransfer process, which could achieve the goal of improving the reaction rate andaccelerating the reaction process. In the wet etching process, the study of ultrasonicenhancement on mass transfer coefficient is still in the stage of qualitative, whichcauses the lack of quantitative analysis model and failure to guide the practical work.The silicon echelle grating is fabricated using the acisotropic etching behavior ofsingle-crystal silicon, which is an extension of the application of silicon wet etchingtechnique. The introduction of ultrasound has great influence to roughness on theblazed surface. The (111) crystal plane is usually used to be the blazed surface whenfabricating echelon grating by means of silicon wet etching. At present, the study ofroughness on blazed surface is little; especially there is no investigation on theinfluence between ultrasonic parameters and roughness on blazed surface. In view of the conditions mentioned above, the thorough researches of the mechanism ofultrasound to intensity mass transfer process in silicon wet etching and the wetetching technology of silicon echelle grating are maded in this paper. First, a newcomputational model to solve mass transfer coefficient quantitatively is put forwardbased upon the ultrasound field, flow field and mass transfer field module inCOMSOL Multiphysics software, which is including the study of the change ofdistribution of the liquid velocity under ultrasound effect, and the mathematicalrelationship between mass transfer coefficient and the distribution of solutionconcentration affected by liquid velocity. The changing law of mass transfercoefficient with ultrasonic parameters is discussed in detail through the study ofultrasonic field, solution flow rate and concentration gradient of the silicon surface,and the problem of such research cannot be quantitatively calculated mass transfercoefficient and the relationship between ultrasonic actions is solved. Second, thetheoretical formula between etching silicon wet etching process rate and masstransfer coefficient is given based on the theory of shrinking core. The numericalvalue of etching rate can be gotten through solving the mass transfer coefficient bythe model established which could solve quantitatively the relationship betweenultrasound and etching rate and realize the guidance to the wet etching process.Third, based upon the ultrasonic cavitation and wettability enhanced by IPA, theeffects of ultrasonic vibration and wettability enhancement on surface roughness onblaze plane of silicon echelle grating have been discussed systematically. Theexperimental results indicated that the combination of ultrasonic vibration andwettability and optimizing of experimental parameters could fabricate the siliconechelle grating with lower surface roughness.