Preparation and properties of intermetallic-bonded diamond grinding wheel for thinning SiC wafer
Objectives:Compared with Si-based materials,SiC has become an ideal substrate material for chip manu-facturing due to its good thermal conductivity,high breakdown electric field strength,and large bandgap width.However,the Mohs hardness of SiC wafer is as high as 9.5,which makes it difficult to grind.The thinning process of SiC single crystal wafers,reducing processing costs,and improving the processing quality of SiC chips have become ur-gent problems to be solved in the semiconductor industry.This study uses Cu3Sn and Cu6Sn5 intermetallic compounds as bonders to prepare rough and fine grinding diamond wheels for thinning SiC wafers.Methods:On the basis of the re-search and development of intermetallic compound bonding agent superhard material grinding wheels proposed earlier,the M5/10 diamond grinding blocks and the M1/2 diamond grinding wheel teeth were prepared using raw materials such as diamond,Cu3Sn,Cu6Sn5,graphite,and pore-forming agent through a 450℃hot pressing process.After grinding the upper and lower end faces of the diamond grinding wheel teeth flat,34 pieces were selected and uniformly bonded to the aluminum substrate tooth groove with universal strong adhesive,and the diamond coarse grinding and fine grinding wheels for silicon carbide wafer thinning were obtained.At the same time,the processing load and wear ratio of the sil-icon carbide grinding wheel,and the roughness and RTTV(total thickness deviation)of the silicon carbide wafer were systematically characterized.Results:(1)The bending strength and the impact toughness of Cu3Sn material subjected to 450℃hot pressing are 206.6 MPa and 0.45 J/cm2,respectively.The bending strength and the impact toughness of Cu6Sn5 material are 142.0 MPa and 0.31 J/cm2,respectively.(2)With the increase of pore-forming agent amount,the porosity of the grinding wheel teeth significantly increases,while its bending strength rapidly decreases.When the mass fraction of the added pore-forming agent is 20%,the porosity and the bending strength of the grinding wheel teeth are 35.0%and 42.5 MPa,respectively.(3)During the grinding process,the higher the bending strength of the grinding wheel teeth,the greater the holding force of the binder on the diamond,and the grinding wheel is prone to load alarms.However,too low bending strength of grinding wheel teeth will lead to excessive wear of the grinding wheel,easy edge breakage,and even broken teeth.(4)The wear ratio of M5/10 diamond rough grinding and thinning wheel with a mass fraction of 20%pore-forming agent for grinding 6-inch SiC chips reaches 1.0∶5.0,the surface smoothness of SiC chips reaches 0.011 µm,and the fragmentation rate is less than 0.2%.(5)When the mass fraction of the pore-forming agent added is 30%,the porosity and the bending strength of M1/2 fine grinding wheel teeth are 43.0%and 16.2 MPa,re-spectively.In addition,there are a large number of pores on the surface of the thinning grinding wheel,forming a honey-comb shape,ensuring that the grinding wheel has good chip holding and chip removal effects during the grinding pro-cess.At the same time,the wear ratio of the diamond wheel for grinding 6-inch SiC wafer is 1.0∶0.6,the surface smoothness of SiC wafer is 2.076 nm,and the RTTV is 2.55 µm.The process of grinding is smooth with a stable load.Conclusions:Cu3Sn material has high strength and can be used to prepare coarse grinding wheels for thinning SiC wafers.Cu6Sn5 material has good brittleness and can be used to prepare fine grinding wheels for thinning SiC wafers.During the grinding process,the pores in the grinding wheel can play a role in accommodating and removing chips,and can also accommodate failed and detached diamonds,thereby ensuring good surface quality of SiC wafers.The coarse and fine grinding diamond wheels prepared in this paper have obtained good grinding results.However,the diamond used in the grinding wheel for thinning SiC wafers is developing to M0/0.5 at present,which is hoped to achieve the bet-ter surface roughness and the lowest surface damage layer of SiC wafers,in order to reduce the processing amount of the CMP process.The follow-up work will further improve the brittleness of Cu6Sn5 material through ceramicization to en-hance the sharpness of the grinding wheel,and carry out research on M0/0.5 diamond precision grinding and thinning grinding wheels.
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