Tian, Z (2021) Investigation of Material Removal Mechanism of SiC in Nano-scale Machining Using Molecular Dynamics Simulation. Doctoral thesis, Liverpool John Moores University.

Preview	Text 2021zigetianphd.pdf - Published Version Download (21MB) | Preview
	Archive Copyright permissions.zip - Supplemental Material Restricted to Repository staff only Download (1MB)

Abstract

Single crystal silicon carbide is widely used for microelectronics, optoelectronics and medicine sectors because of its specific properties. It is critical to completely eliminate the damaged layer and further reduce the surface roughness of the substrates to meet the requirements of epitaxy processes. Both mechanical removal and chemical removal play significant roles in the ultra-precision polishing. This research aims to investigate the nanomechanical performance, chemical reaction and removal mechanism of 4H-SiC and 6H-SiC polishing using molecular dynamics simulations and experimental validation. Material deformation in the forms of amorphous transformation and dislocations are found to be the primary mechanisms of material removal, which are evidenced in both MD simulation and experiments. The dislocations in the scratched 4H-SiC and 6H-SiC are prone to crack growth when the fractured bonds do not recover. During scratching, dislocations and slips could occur on both the C face and the Si face, mainly on the (0001) basal plane and the (10-10) plane. It is found that the stress peak of scratching on C face is lower, which means the dislocations at C face on the (0001) plane occur more easily. Material removal efficiency of the C face is higher than that of the Si face, and there is less subsurface amorphous deformation on the C face. Moreover, in both experimental and simulation results, machining conditions, such as shape of abrasive particles, scratching speed and scratching direction, also have significant effects on nanometric material removal performance. Setting the scratching cutting depth as an integer multiple of the height of a half lattice crystal may be more beneficial for removing materials and better subsurface quality of substrates. The occurrence of silicon dioxide when pure water is applied as the cooling liquid indicates that the 6H-SiC wafers can be oxidized by the water during polishing without any acid or alkali conditions. The occurrence and extent of the reactions between SiC and H2O are influenced by the destruction of the 6H-SiC lattice structures. The material on the C face of 6H-SiC is oxidized faster than that on the Si face, directly resulting in a larger removal efficiency of the C face than the Si face in the same conditions. The research methods introduced in this research could also be applicable for the investigation of different SiC polytypes and other brittle materials. Understanding these problems could be beneficial to nanomachining of these hard and brittle materials.

Item Type:	Thesis (Doctoral)
Uncontrolled Keywords:	Nano-scale Machining; Silicon carbide; Molecular Dynamics Simulation; Material Removal Mechanism; Material deformation mechanism
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Divisions:	Engineering
Date Deposited:	13 Dec 2021 14:14
Last Modified:	13 Dec 2022 00:50
DOI or ID number:	10.24377/LJMU.t.00015912
Supervisors:	Chen, X, Xu, X and Opoz, T
URI:	https://researchonline.ljmu.ac.uk/id/eprint/15912

View Item