The Effect of pH on Sapphire Chemical Mechanical Polishing

Abstract

In this paper, the effect of pH on sapphire chemical mechanical polishing (CMP) was investigated. The sapphire removal rate increased with ascending pH until 8. To investigate the electrostatic force between colloidal silica abrasive and sapphire surface, the zeta potential of sapphire surface and colloidal silica abrasive were studied. The sapphires immersed into the slurry containing 20 wt% colloidal silica were observed with scanning electron microscopy (SEM). For further insights into the mechanism of sapphire CMP with different pH values, particle size of the colloidal silica was used to analyze the mechanical function. Finally, the chemical actions between sapphire (Al 2 O 3 ) and colloidal silica (SiO 2 ) during sapphire CMP as a function of pH value were discussed.Sapphire, which is a single crystal form of α-alumina (corundum), is an important ceramic material widely used in a range of applications such as optics, electronics and temperature sensing. 1 In manufacturing light-emitting diode (LED), sapphire is widely applied as the substrate of gallium and indium nitride films. The development of LED technology leads to an exponential increase in device efficiency and light output over the past thirty years, which promotes the LEDs to become the light source of choice for virtually all applications. All of the applications request sapphire high removal rate, no damaged near-surface layer and surface defects and a low working surface roughness. To achieve these surface quality of sapphire, the chemical mechanical polishing (CMP) of sapphire plays a significant role.Some researchers have investigated sapphire CMP. Zhu et al. 1,2 used alumina slurry to polish sapphire (0001) wafers. It was admitted the fact of a coupling effect of the chemo-mechanical reaction between the sapphire and alumina accelerated the material removal. Silica slurries were mostly used as the ultimate polish run because they can produce the required surface quality. Liu et al. 3 provided the silica-based slurry containing a chelating agent to polish sapphire. The results showed that the removal rate was 9.96∼18 μm/h and the surface roughness was 0.1∼0.3 nm. Zhang and colleagues investigated the process parameters effect on sapphire CMP using silica-based slurry. Wang et al. 4 achieved a MRR of 5 μm/h (approximate 83.3 nm/min) but the surface quality was not mentioned. However, there is still a dearth of detailed research on the effect of pH on sapphire CMP.In this paper, we investigated the effect of pH on sapphire CMP using slurry only containing colloidal silica. The removal rate of sapphire reached maximum at pH 8 and the CMP mechanism of the sapphire at this pH was analyzed with mechanical abrasion of the abrasive abrasion and the chemical action of the chemical agent. The effect of pH on mean particle size of colloidal silica indicated that an increase of the mean particle size of colloidal silica contributed little to the sapphire removal rate. The chemical actions between sapphire and colloidal silica resulted in accelerating inc...

Effect of surfactant and electrolyte on surface modification of c-plane GaN substrate using chemical mechanical planarization (CMP) process

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Green synthesis of Ag nanoparticles in large quantity by cryomilling

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