Research on influences of contact force in chemical mechanical polishing (CMP) process

Abstract

A series of simulations of chemical mechanical polishing (CMP) were conducted to investigate the contact force between abrasive particles and specimens by using the finite element method (FEM). In this paper, a micro-contact model, which only involves the mechanical interactions, was set up to simulate the polishing process by changing the processing parameters, including the downward pressure, abrasive size, and polishing speed. Simulation results show that the contact force becomes larger when the downward pressure increases. In addition, when the downward pressure and abrasive size increase, the fluctuation of the contact force becomes large, whereas it declines with decreases in the polishing speed. In addition, corresponding CMP experiments were done to investigate the material removal rate (MRR) and polished average roughness (Ra) under different simulation conditions. Through the establishment of the contact force properties in the simulation and the MRR and Ra in the CMP experiment, qualitative research has been done on the relationship between the contact force in the simulation and experimental results. Experimental results indicate that the MRR and surface roughness are influenced by the contact force. A high MRR can be obtained by a large contact force and dramatic fluctuations can lead to poor surface-finish quality. The investigation contributes to obtaining higher polishing efficiency and lower surface roughness through optimization of the polishing parameters.

Investigation of silicon carbide ceramic polishing by simulation and experiment

“…[19][20][21] For example, Wang et al 22 used FEM simulations to study the effects of wheel speed, grinding depth, apex angle of abrasive grain, and workpiece feed rate on the material removal rate and grinding force in brittle material grinding. Li et al 23 investigated the brittle-ductile transition of ceramics in high-speed grinding by the simulation of single-grit scratch test and achieved better surface quality and machining efficiency.…”

Development of a novel two-dimensional ultrasonically actuated polishing process

“…These include magnetorheological finishing, 8,9 bonnet polishing with precessions, 10,11 magneto-rheological jet finishing, 12 stressed lap polishing, 13 and ultrasonic two-axis vibration assisted polishing, 14,15 as well as other composite finishing processes. [16][17][18][19][20][21][22][23] The magneto-rheological finishing (MRF) process was first developed by the Center for Optics Manufacturing of the University of Rochester (USA) and QED Technologies, and since then serialized MRF machines have been successfully commercialized and widely used in aspheric and freeform optics fabrication (William I. Kordonski). 24 In the MRF process, magneto-rheological fluid based polishing slurry between the workpiece and polishing tool is formed into a flexible ribbon along the circumferential direction of a rotating polishing tool under a graded magnetic field.…”

Computational analysis and chemical mechanical polishing for manufacturing of optical components

“…Effects of pressure on the non-uniformity and surface roughness have been investigated by many researchers [22,26,31,38,39,[51][52][53][54][55][56][57][58][59]. In traditional CMP, when pressure increases, MRR increases linearly, non-uniformity is slightly reduced [26,31], and the surface roughness increases [54]. The head load also causes the wafer deformation, especially when the wafer becomes thinner in ultraprecision machining [60].…”

“…When the pad speed increases, the larger centrifugal force pushes the slurry out of the pad surface and reduced the amount of slurry necessary to create high quality surfaces [26,41,75]. The surface roughness decreases [54], and the uniformity is decreased [27,71], or unchanged [39,53]. Yuh et al have shown that the non-uniformity decreases when the pad and head speed increases from 30 rpm to 60 rpm.…”

“…Abrasive particles are a primary factor of CMP processes. The particle shape is spherical in some researches, and is hexagonal or non-spherical in other researches [24,54]. The irregularity of the particle shapes has affected the surface roughness and caused a fluctuation of the contact forces between the substrate and the particles.…”