The Mechanism of Layer Stacked Clamping (LSC) for Polishing Ultra-Thin Sapphire Wafer

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.

Performance assessment of ultrathin sapphire wafer polishing with layer stacked clamping (LSC) method

“…An amount of water was dropped onto a surface of the baseplate, and thereby, the water lm was formed after the workpiece was placed inside the limiters. Since the two contacted surfaces were not extremely smooth, van der Waals forces and capillary forces [27,28] between the baseplate and workpiece were obtained, which induced a great normal adhesion force of workpiece to baseplate. Because the workpiece was also radially limited by the limiter, the movement of the workpiece can be totally restrained.…”

“…In addition, the investigation on processing sapphire wafer is now focused on the process optimization [24][25][26], the discussion on the clamping issue was rarely carried out. To further improve the polishing e ciency of ultra-thin sapphire wafers, we propose a novel clamping method for ultra-thin wafers based on the layer stacked clamping (LSC) [27]. The adhesion mechanism and the numerical model of adhesion force were studied, and the validity of the adhesion model was veri ed through experiments.…”

Molecular Dynamics Analysis of Adhesive Forces between Silicon Wafer and Substrate in Microarray Adhesion

“…Planetary wheel clamping demands high material requirements for the fixture, and wax-free adsorption is unable to adhere to ultra-thin workpieces. Additionally, Chen and others proposed a stacked clamping method, establishing a numerical model based on fractal theory and experimentally verifying the model's effectiveness [17]. They also experimentally validated the polishing performance of stacked clamping [18] and studied the failure mode of limit pieces, attributing it to edge cutting causing the fracture of limit pieces [19].…”

Research on the Preparation and Application of Fixed-Abrasive Tools Based on Solid-Phase Reactions for Sapphire Wafer Lapping and Polishing

“…Single-crystal sapphire specimen (α-Al 2 O 3 ) are currently one of the most widely applied materials in the fields of defense, aerospace, microelectronics, and the medical domain [ 1 , 2 , 3 , 4 ] due to their excellent physicochemical properties and material characteristics, such as high hardness (Mohs hardness 9), high melting point (2045 °C), high light transmittance, high chemical stability, and high thermal stability [ 5 , 6 , 7 , 8 , 9 , 10 ]. Sapphire has not only become the most widely used substrate material for traditional LEDs [ 11 , 12 , 13 , 14 ] but also has a large number of applications in mini/micro-LEDs, which are currently very popular.…”