Silicon wet etching technology is the application that products micro-nanostructure on silicon materials by means of chemical solution corrosion. In order to reduce the surface roughness of the silicon devices, ultrasonic as the assistant means is widely used in silicon wet etching process. In the reaction process between silicon and corrosive liquid, the ultrasonic cavitation will enhance the mass transfer process, which could achieve the goal of improving the reaction rate and accelerating the reaction process. In wet etching process, the study of ultrasonic enhancement on mass transfer coefficient is still in the stage of qualitative, which causes the lack of quantitative analysis model and failure to guide the practical work. The silicon echelle grating is fabricated using the acisotropic etching behavior of single-crystal silicon, which is an extension of the application of silicon wet etching technique. The introduction of ultrasound has great influence to roughness on the blazed surface. The (111) crystal plane is usually used to be the blazed surface when fabricating echelon grating by means of silicon wet etching. At present, the study of roughness on blazed surface is little; especially there is no investigation on the influence between ultrasonic parameters and roughness on blazed surface. In view of the conditions mentioned above, the thorough researches of the mechanism of ultrasound to intensity mass transfer process in silicon wet etching and the wet etching technology of silicon echelle grating are maded in this paper. First, a new computational model to solve mass transfer coefficient quantitatively is put forward based upon the ultrasound field, flow field and mass transfer field module in COMSOL Multiphysics software, which is including the study of the change of distribution of the liquid velocity under ultrasound effect, and the mathematical relationship between mass transfer coefficient and the distribution of solution concentration affected by liquid velocity. The changing law of mass transfer coefficient with ultrasonic parameters is discussed in detail through the study of ultrasonic field, solution flow rate and concentration gradient of the silicon surface, and the problem of such research cannot be quantitatively calculated mass transfer coefficient and the relationship between ultrasonic actions is solved. Second, the theoretical formula between etching silicon wet etching process rate and mass transfer coefficient is given based on the theory of shrinking core. The numerical value of etching rate can be gotten through solving the mass transfer coefficient by the model established which could solve quantitatively the relationship between ultrasound and etching rate and realize the guidance to the wet etching process. Third, based upon the ultrasonic cavitation and wettability enhanced by IPA, the effects of ultrasonic vibration and wettability enhancement on surface roughness on blaze plane of silicon echelle grating have been discussed systematically. The experimental results indicated that the combination of ultrasonic vibration and wettability and optimizing of experimental parameters could fabricate the silicon echelle grating with lower surface roughness.
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