Study On Sapphire Substrate CMP Materials Of Different Crystal Plane For LED

For LED photoelectric device,the processing quality of sapphire substrate has a direct impact on light transmittance,reliability,superior products,composite cost and product competitiveness.At present,the requirement of sapphire substrate processing efficiency and precision is higher and higher.However,due to the characteristics of high hardness,brittleness and corrosion resistance,the theory and techniques research on surface chemical mechanical polishing?CMP?has become an international recognized problem.Meantime,since the c-plane sapphire substrate is polar plane,the strong built-in electric field inside the the GaN epitaxial film grown on it can be produced.But on other crystal planes,the luminous efficiency of the thin film can be significantly improved.In order to improve the processing efficiency and precision of different crystal plane sapphire substrate,the optimization of polishing process parameters,selection and optimization of slurry component and generation mechanism analysis of reactant were studied thoroughly.In order to gain better utilization rate of slurry and better polishing effect,the effects of polishing rotational speed,slurry flow rate and polishing pressure on removal rate and surface roughness for sapphire substrate were systematically studied by using the self-developed slurry.From the results it indicated the removal rate increased first and then decreased with the increasing of polishing rotational speed,slurry flow rate and polishing pressure.When polishing head speed was 40 r/min,platen rotation speed was 45 r/min,slurry flow rate was 160 mL/min,c-plane sapphire polishing pressure was 4 psi and r-plane sapphire polishing pressure was 7 psi,the optimal polishing result was obtained.Such rule is of great significance to guide industrial sapphire ultra-precision machining.Based on the analysis of component role and selection in slurry by applying chelating theory and DLVO theory,the new type slurry for different crystal plane sapphire substrate was studied.The optimized c-plane sapphire slurry component was as following:FA/O II chelating agent and KOH solution mixing ratio was 1:15,the mixture was used to adjust the pH value to 10.5,KNO₃ concentration was 0.1 wt%,and anionic surfactant concentration was 0.3 vol%;r-plane sapphire slurry component was as following:FA/O I chelating agent concentration was 0.6 vol%,the surfactant concentration was 0.2 vol%,and the wafers were soaked in the FA/O I chelating agent one week for pretreatment.For c-plane sapphire,removal rate and surface roughness Sq can reach 3.6 um/h and 0.184 nm respectively;for the soaked r-plane sapphire,removal rate and surface roughness Sq can reach 2.48 um/h and 0.148 nm.The r-plane sapphire removal rate is significantly improved,and the surface roughness can be stable at low level to meet industrial production requirements.Such result can provide guiding significance for the development of industrial sapphire ultra-precise processing.According to the experiment results,the formation and reaction mechanisms of diaspore and aluminum silicate have been verified and analyzed by AFM,XRD and XPS testing method,and the rationality of the rule was proved.Meantime,different removal rate for different crystal plane was analyzed,which will lay the foundation for other crystal plane sapphire CMP.