Abstract
Double-sides polishing technology has the advantages of high flatness and parallelism, and high polishing efficiency. It is the preferred polishing method for the preparation of ultra-thin sapphire wafer. However, the clamping method is a fundamental problem which is currently difficult to solve. In this paper, a layer stacked clamping (LSC) method of ultra-thin sapphire wafer which was used on double-sides processing was proposed and the clamping mechanism of layer stacked clamping (LSC) was studied. Based on the rough surface contact model of fractal theory, combining the theory of van der Waals force and capillary force, the adhesion model of the rough surfaces was constructed, and the reliability of the model was verified through experiments. Research has found that after displacement between the two surfaces the main force of the adhesion force is capillary force. The capillary force decreases with the increasing of surface roughness, droplet volume, and contact angle. For an ultra-thin sapphire wafer with a diameter of 50.8 mm and a thickness of 0.17 mm, more than 1.4 N of normal adhesion force can be generated through the LSC method. Through the double-sides polishing experiment using the LSC method, an ultra-thin sapphire wafer with an average surface roughness (Ra) of 1.52 nm and a flatness (PV) of 0.968 μm was obtained.
Highlights
Sapphire is one of the main materials of light emitting diode (LED) substrate due to its excellent material properties [1,2,3]
Since the surface of various materials is not absolutely smooth, roughness becomes important for the force between solid surfaces [12,13], and the expression model of rough surface morphology has been the basis for studying rough surface forces
The theoretical and experimental adhesion forces obtained under the conditions of droplet volume of 50, 100, and 150 μL are shown in Figure 5a–c, respectively
Summary
Sapphire is one of the main materials of light emitting diode (LED) substrate due to its excellent material properties [1,2,3]. The real contact area of the deformed micro-bulge is Ar, and the van der Waals force in this area shows the interaction of two planes, the expression is shown in Equation (15): Aa =. When the micro-bulge is in the stage of plastic deformation, the relationship between the contact area ratio k and the pressure Pe shows as Equation (20), and the expression of ah shows in Equation (21): Pe. The per unit area of Van der Waals force work W’(h) is shown in Equation (22): JAWB log ( ) a1L−D/2 1−k1−D/2 h.
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