Experimental Study Of The Lapping Based On Cluster Magneto-rheological Effect For Single Crystal SiC Wafer

As the third-generation semiconductor material, compared with Si and GaAs, SiC has some advantages of wide band gap, high thermal conductivity, large electronic saturated drift rate, chemistry stability which are very suitable for the production of high temperature, high frequency, radiation resistance, high power and high density integrated electronics.It requires ultra smooth, no damage, no defect surface for the application of SiC wafers, its processing quality directly influences the performance of the electronic devices.However, single-crystal SiC is typical of the hard brittle materials, and its moh’s hardness is second only to diamond, about9.2. It has a real good chemical stability, and does not react with acid and alkali at room temperature. It has low efficiency of conventional lapping process, and is easy to produce cracks and flaws as well. It is needed not only to remove cutting kerf and metamorphic layer quickly, but also to provide a good shape precision, size accuracy and surface quality for polishing in the lapping process, thus it is very important to improve the lapping efficiency on the basis of getting a good lapping quality.As to the earlier problems of single-crystal SiC lapping processing, exploratory research of single-crystal SiC lapping process was conducted, an improved scheme was put forward. As a result, even without scratches wafers were gained, and the feasibility of the lapping based on cluster magneto-rheological effect for single-crystal SiC wafers was verified. It increased the lapping efficiency significantly on the basis of maintaining a good processing surface, and with W14diamond powder as the abrasive particle, the material removal rate increased by21.2%compared to traditional lapping.Besides, the adsorption characteristics of magnetic particles in the lapping plane with different magnet specifications were compared, and abrasive constraint forms by magnetic particles were studied. The diameter matching experiment was carried out with similar shapes but different kinds of abrasives. The lapping effects of different particle diameter ratio were analyzed, and the best lapping effect was gained when the particle diameter ratio was about1.5.Experimental study was carried out to analyze the effects of the main parameters (concentration of iron powder, magnetic field intensity, lapping pressure, abrasive particle size, etc) in lapping based on cluster MR-effect of the material removal rate and surface roughness. According to it, the lapping effects of four important processing parameters (magnetic field intensity, lapping pressure, lapping plane rotational speed, workpiece speed) were studied through orthogonal experiment, and an optimized lapping parameters combine decision was realized. The optimized process parameters are workpiece speed of60r/min, plate reverse speed of90r/min, lapping pressure of70kpa, magnetic field strength of120Gs. It can get a maximum material removal rate of0.498μm/min and a surface roughness Ra value of86.3nm with6.63μm (D50) B4C and3.84μm (D50) carbonyl iron powder as the foundation of magnetic rheological lapping liquid under the optimized condition.