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 (R_a) of 1.52 nm and a flatness (PV) of 0.968 μm was obtained.

Elliptical elements are essential optical surfaces for modifying optical systems. For polishing the whole elliptical surface using doughnut-shaped MCF polishing tool with variable tilt angle, an experimental investigation was conducted in this work. Firstly, a flat workpiece was polished to determine the polishing feasibility. It was found that the middle portion of the polishing tool had optimal ability to remove materials, and the surface roughness S_a at the material removal peak was changed from 134 nm to 17.5 nm within 50 min of polishing. A smoother surface could be obtained using MCF2 slurry and MCF3 slurry, but the use of MCF1 slurry resulted in a rough surface. Then, the effects of working gap h, revolution speed of MCF polishing tool and polishing time on the polishing results were tested to study the polishing characteristics. S_a 9.6 nm and glossiness 278 Gu were obtained, and form error improved from 2.3 μm to 1.3 μm. Finally, the MCF polishing tool was dried to observe the microstructure of the MCF polishing tool after polishing. Abrasive particles were distributed evenly after polishing. It was seen that the abrasive particles were grabbed by the ferric clusters, and the α-celluloses were interleaved between the clusters.

Ultra-thin sapphire wafer processing is receiving increasing attention in the LED substrate industry. In the cascade clamping method, the motion state of the wafer determines the uniformity of material removal, while the motion state of the wafer is related to its friction coefficient in the biplane processing system, but there is little relevant literature discussing the relationship between the motion state of wafer and friction coefficient. In this study, an analytical model of the motion state of sapphire wafers in the layer-stacked clamping process based on the frictional moment is established, the effect of each friction coefficient on its motion is discussed, the base plate of different materials and different roughness are experimentally studied, the layer-stacked clamping fixture is prepared in this way, and finally the failure form of the limiting tab is analyzed experimentally. The theoretical analysis shows that the sapphire wafer is mainly driven by the polishing plate, while the base plate is mainly driven by the holder, and the rotation speed of the two is not the same; the material of the base plate of the layer-stacked clamping fixture is stainless steel, the material of the limiter is glass fiber plate, and the main form of failure of the limiter is to be cut by the edge of the sapphire wafer and damage the material structure.

Ultrathin sapphire wafer is of great significance in the semiconductor field. In order to explore the effective clamping method of ultrathin sapphire wafer in double-side polishing, this paper studied the characteristic of Layer stacked clamping (LSC) method on polishing ultrathin sapphire wafer with double-side polishing machine. A self-made friction force test platform was built for learning the friction force between sapphire wafer and baseplate with different baseplate (stainless steel, cast iron, aluminum alloy) and different baseplate surface roughness (R_a 3.6 nm, 68.2 nm, 210.1 nm, 517.9 nm). Single factor polishing experiments were carried out on baseplate with different flatness (PV value 5.3 µm, 9.8 µm, 19.9 µm, 29.7 µm) and different thicknesses (0.082 mm, 0.104 mm, 0.119 mm). The double-side polishing experiments were carried out to compare the polishing performance on the ultrathin sapphire polishing between LSC method and traditional paraffin bonding method. The results show that the friction force of stainless steel and iron increase under the adsorption of droplets. Stainless steel performs higher friction force and is more suitable for making the baseplate. The inner fringe of limiter was cut off by the edge of the sapphire wafer and a slope was thereby formed. According to polishing results, LSC method has higher processing efficiency per unit time. The surface roughness, flatness and material removal rate are better than paraffin bonding. Finally, a smooth surface with surface roughness (R_a) 1.3 nm and flatness (PV) 0.988 µm was obtained with LSC method.

With the development of the electronics industry, the requirements for chips are getting higher and higher, and thinner and thinner wafers are needed to meet the processing of chips. In this study, a model of the adhesion state of semiconductor wafers in the stacking–clamping process based on microarray adsorption was established, the composition adhesion was discussed, the microarrays of different materials and pressures were experimentally studied, and a molecular dynamics model was established. The molecular dynamics analysis showed that the adhesion force was only related to the type of atom, and the applied pressure did not change the adhesion force. According to the simulation results, the tangential adhesion between the metal and the wafer is greater than that between the ceramic and the wafer, the adsorption force between the aluminum–magnesium alloy and the silicon wafer is shown in the normal direction, and the repulsion force between other materials and the silicon wafer is shown in the normal direction. During the pressure process, the metal is in the elastic deformation stage between the metal and the wafer, the wafer is plastically deformed in the silicon carbide ceramic and wafer, and the wafer is elastically deformed in the alumina ceramic and wafer. In this paper, the adhesion between the substrate and the wafer is studied, a method of constructing microarrays to enhance adhesion is proposed, and the tangential deformation of the array unit under pressure is studied, which provides theoretical support for increasing the adhesion by constructing microarrays.