Investigation On Chemical Mechanical Planarization For The Functional Photoelectric Materials ZnO Thin Film

II-VI semiconductor material zinc oxide has been widely applied in the field of optoelectronics for UV, blue light emitting devices and lasers, piezoelectric transducers and sensors due to its excellent performance. However, the as-grown zinc oxide thin film is surface roughness and to some extent affects those devices’performance and its further application. How to obtain a highly flat surface by IC compatible process becomes one of the obstacles for the ZnO-based devices. As we all know, Chemical Mechanical Planarization (CMP) is the necessary and sole global planarization method for submicron device. Recently, the work of ZnO-CMP began to obtain attention. The Korean research group Gupta firstly began to study ZnO-CMP and obtained low surface roughness (6(?)), but the Removal Rate (RR) is only67nm/min, which is unable to meet the needs of efficiency in the production of semiconductor devices. How to improve the RR and at the same time to obtain the high planarization surface becomes one of the key technical problems.In the research, the colloidal silica was used as abrasives, the4inch silicon zinc oxide thin film was polished by6EC-nspire machine where the slurry and process parameters were optimized. The thickness of ZnO thin films before and after polishing was measured by The Dektak150system (Dektak150of Veeco Instruments, Inc) and surface topography was characterized by Atomic force microscope (5600LS of Agilent Technologies, Inc) respectively. The results of experiments are as follows:Firstly, the polishing slurry composition was optimized.(1) The RR was significantly larger using acid slurry than alkaline. The surface roughness first increases and then decreases with the pH increase (4â†'10). The scratch is observed on zinc oxide thin films surface at pH of7, the surface roughness achieve maximum6.3(?).(2) RR increases with the concentration of particle of slurry increasing; the maximum RR115.5nm/min was achieved at the concentration of slurry particle of12wt%, and the minimum surface roughness5.5(?) is obtained at4wt%. The effect of particle size for RR also has the same regular.Secondly, the polishing process parameter was optimized.(1) As the down pressure increases, the RR increases and the surface roughness decreases, the RR165.1nm/min and the surface roughness1.9(?) is achieved at pressure of5psi.(2) The RR increases with the rotation rate increased. The RR is126.9nm/min when the rotation rate is80rpm. The surface roughness is4.5(?).(3) As the slurry flow rate increases, the RR increases, the RR of128.Onm/min and the surface roughness7.4(?) is obtained at the slurry flow rate400ml/min.Finally, the polishing mechanism was analyzed both from mechanical and chemical viewpoint, the form of Preston equation was improved as follow:RR=KPV+Ro, Ro is a constant removal rate due to purely chemical reaction, Ro was calculated by experiment is4.69nm/min.To sum up, in this paper, the CMP slurry of zinc oxide thin films and polishing process were optimized. The polishing mechanism was explored and high RR and high-flat surface was obtained. It is great significance for the follow-up preparation of optoelectronic devices based on ZnO thin films.