Characterization of Dilution Effect of Mix Acids on Rough Silicon Etching Irregularities : CFM: Contamination Free Manufacturing

Abstract

Mix acids for rough silicon etch (RSE) is made up of approximately 75 – 90% of sulfuric acid (H 2 SO 4 ) as medium, and some different ratio of nitric acid (HNO 3 ) and hydrofluoric acid (HF) as effective etchant. Different ratio of these 3 mix acids would lead to different characteristics of the silicon surface, especially when these mix acids are diluted by water. The chemical properties such as H 2 SO 4 of the mix acids are characterized by thermometric titration using barium chloride (BaCl 2 ) precipitation method. There is a delta of approximately 10% of the as prepared and the as measured samples for the H 2 SO 4 measurement. The response of the titrated % H 2 SO 4 value on the dilution of the acids is not consistent. The physical properties of the mix acids can be characterized using a self-made PTFE based capillary viscometer. The change of the viscosity of the mix acids (as a function of min/mL) respond correspondingly to the dilution of acids. Experiment has shown that as the % of dilution of mix acid is increased, bigger and denser bubbles are produced on the silicon surface during the etching reaction, causing significant ‘burn mark’ defect (irregularities) on the silicon surface.