Fabrication of flat silicon surfaces using ion-exchange particles in ultrapure water

A silicon etching process using an ultrafine particle dispersion is proposed. The ultrafine particles contain quaternary ammonium hydroxide groups as ion-exchange groups, giving an alkaline dispersion. In the etching process, the fine particles and impurity ions can be easily separated by filtration or dialysis. Dialysis led to a decrease in the concentration of impurities in the dispersion, which included heavy metal ions and alkali metal ions known to result in a rough etched surface and affect the electronic properties of the semiconductor. Our proposed method is applicable to the surface planarization of silicon single crystals, manufacture of semiconductor devices, and fabrication of MEMS (micro-electro and mechanical systems). In addition, the etching waste can be reused after removal of the impurity ions by dialysis. Thus, the method has low environmental burden. Using the proposed alkaline etching dispersion, cathodic electrochemical etching of a silicon single crystal was demonstrated. The etching characteristics, properties of the etched surface, and effects of particle size were evaluated. The roughness of a 2 μm × 2 μm etched p-Si(0 0 1) surface was measured to be 0.1228 nm Ra (center line average roughness) by AFM.