Tribochemical mechanisms of abrasives for SiC and sapphire substrates in nanoscale polishing.

Strong acid, alkali, or active chemicals are generally employed in chemical mechanical polishing (CMP) slurry for the ultra-precision machining of semiconductor substrates, obstructing further improvement in machining accuracy and reduction in damaged layers. Understanding the material removal behavior of abrasives, which combines mechanical and chemical actions during nanoscale abrasive polishing, poses a significant challenge. In this study, the interfacial interaction mechanisms between abrasives and substrates during nanoscale polishing with only deionized water used as coolant were analyzed by utilizing concerned experiments and molecular dynamics (MD) simulations. The results showed that ultra-smooth SiC and sapphire substrate surfaces only with damage layer thicknesses of 2.06 nm and 0.76 nm were obtained by employing diamond abrasive and alumina abrasive, respectively. Tribochemical reactions could occur on substrate surfaces under the repeated interfacial fiction of fine abrasives without any chemical reagents during nanoscale polishing. The tribochemical reactions mainly depended on the chemical compatibility between the abrasives and substrates when the material removal size of abrasives was limited to nanoscale, not abrasive hardness. Furthermore, a new method of abrasive selection is proposed and widely applied in the ultra-precision polishing of semiconductor substrates, which could not only improve removal efficiency but also ensure good surface quality.

Understanding the Mechanisms of SiC-Water Reaction during Nanoscale Scratching without Chemical Reagents.

Microcracks inevitably appear on the SiC wafer surface during conventional thinning. It is generally believed that the damage-free surfaces obtained during chemical reactions are an effective means of inhibiting and eliminating microcracks. In our previous study, we found that SiC reacted with water (SiC-water reaction) to obtain a smooth surface. In this study, we analyzed the interfacial interaction mechanisms between a 4H-SiC wafer surface (0001-) and diamond indenter during nanoscale scratching using distilled water and without using an acid-base etching solution. To this end, experiments and ReaxFF reactive molecular dynamics simulations were performed. The results showed that amorphous SiO2 was generated on the SiC surface under the repeated mechanical action of the diamond abrasive indenter during the nanoscale scratching process. The SiC-water reaction was mainly dependent on the load and contact state when the removal size of SiC was controlled at the nanoscale and the removal mode was controlled at the plastic stage, which was not significantly affected by temperature and speed. Therefore, the reaction between water and SiC on the wafer surface could be controlled by effectively regulating the load, speed, and contact area. Microcracks can be avoided, and damage-free thinning of SiC wafers can be achieved by controlling the SiC-water reaction on the SiC wafer surface.