Experimental Study On Surface Quality Dispersion Of Sapphire Wafers By Multi-wire Saw And Its Effect On Lapping

Sapphire was widely used as LED substrate material now.Sapphire substrate manufacturing processes are mainly include wire saw,lapping,polishing.The wire saw is the first step in the processing of the sapphire substrate.The effect of the sawn wafer quality has obvious influence on the subsequent process.In this paper,the surface quality dispersion of sapphire wafers sawing by multi-wire rocking with reciprocating motion that was widely used in enterprises at present and its effect on the subsequent lapping process were studied.Firstly,the rationality of the sampling and inspection of sapphire wafers was analyzed.Then,the influence of machines,batches of wires,wire consumption per wafer and sawing wires on wafers surface quality were further analyzed.The variation of sawn wafer quality at different positions of the wire web in wire sawing was analyzed.Through lapping sawn wafers on at different positions of the wire web with different parameters,the surface quality and morphology of sapphire wafers on at different positions of the wire web were observed and the effect of wire web position on the subsequent lapping was analyzed.The main research results are summarized as follows:1.It is found that it is unreasonable to inspect wafers quality according to sampled the fixed number of wafers for the company due to the variation of the sapphire ingot length and the multiple detection parameters.The effect of sampling estimated confidence,sampling permissible error,sapphire ingot length and the sample variance with different detection parameters on the number of samples are analyzed.Reasonable suggestions on sampling method for wafer sawn quality inspection are put forward to the company.2.The variation and the dispersion of sawn surface quality are roughly similar with different machines and different batches of wires.The variation and the surface quality dispersion are roughly similar.However,the surface quality of the sawn wafers is significantly decentralized with the reduction of the wire consumption per wafer and the use of secondary wires.The observation of the wire surface shows that the wire wear is the main reason of the high surface quality dispersion of the sawn wafers.3.It is found that the surface quality of the sawn wafers at both ends of the wire web is worse than that in the middle position of the wire web with the same processing conditions.The surface roughness of the sawn wafer are gradually reduced from the front of the wire web to the back of the wire web.The surface roughness of the sawn wafers at the inlet of wire are higher than other positions,which has a certain relationship with the wear of the abrasive particles in the wire sawing process.4.The dispersion of total thickness and surface flatness of the wafers after lapping process are is greatly improved compared to sawing process.However,the dispersion of wafers' s warpage increases.The variation of wafers thickness removal rate and the warpage at different positions of the wire web are different with the same lapping conditions.The quality of sawn wafers has a certain influence on subsequent lapping.5.Lapping pressures have a significant effect on the wafers quality.The appropriate lapping parameters should be selected regardless of the sawn wafer quality with different position of wire web.