Research On The Deterioration Layer Of Silicon With Specific Crystallographic Plane Cut By WEDM

In today's era of rapid development of science and technology,there is a strong demand for monocrystalline silicon materials with specific crystal orientation in the military,precision instruments,optical instruments and other areas,because of its special physical and chemical properties.In the production of these areas,single crystal silicon with specific crystal orientation as the main raw material in the processing,which surface need to be smooth,clean and without any damage,the surface crystal orientation accuracy also need to meet the requirements.However,the most common way to process monocrystalline silicon wafers is to use WEDM(Wire Electrical Discharge Machining).This method will cause machining damage such as electric erosion pits,cracks,small and deep holes in the machined surface,so there is a layer of machining damage on the machined silicon wafers' surface.Andin the latter stage of these materials' processing,the damage layer needs to be removed.In this paper,the damage layer of monocrystalline silicon after WEDM has been studied,including the thickness and correlation detection technology of the damage layer on the silicon wafer,different material removal methods in the process and their influence on the silicon wafers,structural features of machining damages,the measures of reducing the depth of damage layers and clarified the division of the damage layer under different erosion modes.Also,apply these results of damage layer detection to the removal of the damage layer.A platform of silicon damage layer removal,which based on the method of spray electrolysis,was build.The experimental data of removal processing were selected and optimized.The main work is as follows:(1)The technique of determining the thickness of the damage layer on the monocrystalline silicon with specific crystal orientation,which based on the X-ray swing curve method,is proposed.And its feasibility is proved by experiment.The influence of the pulse width on the thickness of the damage layer is studied.It is found that the larger the pulse width is,the thicker the damage layer is.Also found that the damage layer thickness are different among monocrystalline silicon with different crystal orientation,although the processing parameters of these silicon wafers are the same.And the thickness of the damage layer decreases with the increase of the bond density between adjacent crystal planes.(2)The method of X-ray swing curve method combined with microscopic observation was used to study the different erosion modes in WEDM processing of single-crystal silicon,and the method ofreducing the depth of processing damage was proposed.(3)The machining damages,cause of these damages and structure characteristics of silicon wafers' damage in different erosion modes during WEDM process are studied.The type and microstructure of the damage are determined.The hierarchical structure of damage layers which were formed under two cases: normal erosion(the mainly discharge erosion of which are melting and gasification)and composite erosion(another erosion which is thermal spalling happened on the basis of normal erosion)were divided.(4)The results of damage layer detection are applied to the study of monocrystalline silicon's damage layer removal.A platform of silicon damage layer removal,which based on the method of spray electrolysis,was build.And the selection and optimization of the basic experimental parameters of removal processing were completed.The loss of the silicon substrate material is reduced,under the premise that the damage layer is completely removed.Also the surface quality of the single crystal silicon,after the damage layer removal,is improved.