Technical Research On The Processing Of Sapphire Substrate By Flexible Polishing Tool With Mixed Abrasive~*

Due to its excellent physical and chemical properties,single crystal sapphire??-Al₂O₃?has become the main substrate material of light-emitting diode?LED?.The surface quality of sapphire substrate has an important influence on the quality of the epitaxial growth nitride films.Its surface is required to achieve ultra-smooth and defect-free quality after processing.Owing to the intrinsic nature of sapphire,including high hardness,high brittleness and corrosion resistance,the traditional copper-resin plate polishing and chemical mechanical polishing?CMP?methods have many disadvantages,such as low processing efficiency,high cost and environmental pollution.Therefore,polishing methods for sapphire substrate with high efficiency and low damage have become the focus of research.Based on the principle of solid phase reaction,a new idea of polishing sapphire substrate with soft and hard mixed abrasives is proposed,and the studies on mixed abrasives polishing technology for sapphire substrate are carried out.The reactivity between different kinds of soft abrasive and sapphire is studied by theoretical and experimental methods.The results show that under the condition of friction induced,the silica abrasive has higher reactivity with sapphire than magnesium oxide and iron oxide abrasive,in which the silica is the most easily to react with sapphire to generate aluminosilicate with the structure of mullite.Flexible polishing pad,which contains hard and soft abrasives,is prepared for the polishing experiment on sapphire substrate to evaluate the processing performance of the flexible polishing tool with mixed abrasives.Results show that the material removal rate of mixed abrasives is more than 52.63%of that of single hard abrasives and the decrease in surface roughness Sa is more than19.55%of that of single hard abrasives when the effect of mechanical removal of hard abrasives and the chemical corrosion effect of soft abrasives are in dynamic equilibrium,and the ideal processing performance for sapphire substrate with high removal rate,good surface quality and pollution-free can be achieved.The material removal mechanism of soft-hard mixed abrasive is studied and a model that describes the material removal process of sapphire with mixed abrasives is proposed.During the mixed abrasive processing,the active abrasives create constant friction with micro-convex on the sapphire substrate surface.The friction at the local contact region makes the reactivity between the active abrasive and micro-convex increased.The solid state reaction between the soft abrasive and micro-convex happens and the passivation layer is formed when the obtained energy exceeds the required activation energy for the reaction.The passivation layer has lower hardness than sapphire and can be easily removed from sapphire surface by the mechanical cutting of hard abrasive.Then,the fresh surface of sapphire is exposed to generate another corrosive thin layer.The sapphire wafer can be polished effectively along with the continuous development of this cycle.In order to further improve the processing performance of the mixed abrasive,the hybrid abrasive with core/shell structure is used to change the receiving force mode of the soft abrasive.The results show that core/shell structured diamond/akageneite hybrid abrasives can effectively reduce the scratch and subsurface damage.The presence of akageneite layer is conductive to enhance the binding force between the matrix and the abrasives.Meanwhile,the enhanced binding force can reduce the amount of abrasive particles shedding from polishing pad during the processing,as well as prolong the life of the polishing pad.A novel surface finish process sequence,using the flexible polishing tool with mixed abrasives and gas-liquid assisted chemical mechanical polishing?GLACMP?instead of general Cu-resin plate polishing and CMP to obtain ultra-smooth substrate surface with damage-free,is proposed.For the proposed surface finish process sequence,the qualified surface can be obtained within 50 minutes in the rough polishing stage,and the processing efficiency is increased by 65%.The new surface finish process sequence can effectively improve the processing efficiency for sapphire substrate and reduce environmental pollution.The research of this paper enriches the ideas and methods of polishing technology for sapphire substrate by mixture of soft and hard abrasives,and has some practical guiding significance for the realization of the sapphire substrate with high efficiency and high quality and pollution-free polishing.