Effect of isopropyl alcohol, acetic acid and sodium dodecyl sulfate on the etching rate and surface roughness of Z-cut quartz etched by BOE solution

Quartz crystals, with their unique piezoelectric, mechanical, and electrical insulation properties, are a popular choice for Micro-Electro-Mechanical System (MEMS) resonators. Z-cut quartz, in particular, is the most promising for fabricating microsensors and microactuators because of its high etching rate. Wet etching is the most common patterning process for quartz, and the buffered oxide etch (BOE) solution is the commonly used etchant, but its low etching rate and high surface roughness of the etched quartz blanks can affect the electrical properties of the subsequently fabricated quartz devices. To address this issue, three additives were tested: isopropyl alcohol (IPA), glacial acetic acid, and sodium dodecyl sulfate (SDS). Each additive was added at varying concentrations ranging from 5% v/v to 20% v/v, while the etching temperature was maintained at 80±1°C. The BOE solution was used as a mixture of 49 wt% HF and 40 wt% NH4F with a volume ratio of 1:6. The study investigated the effects of the different additives with different concentrations on the etching rate and surface morphology of quartz. The results indicated that all three additives contributed to accelerating the etching rate and reducing the surface roughness of quartz to a certain degree. However, excessively high additive concentrations could lead to poor etching results. The addition of 10% v/v IPA to the BOE solution resulted in the fastest etching rate, increasing it from 10.71µm/h to 27.73µm/h. On the other hand, the lowest surface roughness occurred when 15% v/v SDS was added to the BOE solution, reducing the quartz surface roughness from 416nm to 125nm, which is approximately two-thirds of the original value. This finding presents a promising new approach to elevate the surface quality of etched quartz, with potential implications for the further development of quartz MEMS devices.