Fabrication of the microfluidic channels in silicon wafers using isotropic wet etching method: the impact of the composition of HNA solution on etching

Isotropic wet etching is a popular technique to fabricate microfluidic channels in silicon wafers that are used in various fields of engineering and medicine. In this work, SiO2 and Cr thin films, along with positive photoresist (SiO2/Cr/PR), is employed as a novel masking layer on 3-inch silicon {100} wafers. SiO2 and Cr thin films are deposited through thermal oxidation and DC sputtering, respectively, and the photoresist is deposited by spin coating, followed by patterning using UV-photolithography. Here, a mixture of HF, HNO3, and CH3COOH, known as hydrofluoric acid-nitric acid-acetic acid solution (HNA solution), is used to fabricate microfluidic channel on silicon wafers via isotropic wet etching. The volume of HF is maintained constant, and the volumes of HNO3 and CH3COOH are varied in the HNA solution. The etching of the silicon wafers is performed in various compositions of HNA solution for 5, 10, and 15 min, respectively, and the resultant etching parameters and surface features are investigated. The vertical and lateral etch rates increased with the increment of HNO3 volume in HNA solution. Among all HNA solutions, the solution of composition 10:20:20 (HF: HNO3: CH3COOH) delivered a better outcome in terms of surface quality. The derived microfluidic channel using the mentioned 10:20:20 HNA solution comprised sharp edges and a defect-free surface.