Strategies in deep wet etching of Pyrex glass

This paper establishes the strategies for deep wet etching of one of the most common glasses: Pyrex. There are two way for increasing the etch depth: increasing the etch rate or increasing the resistance of the mask in the etching solution. The paper analyzes the methods for increasing the glass etch rate in HF solutions: annealing, concentration, ultrasonic agitation and temperature. The generation of the defects is investigated. The main factors that affect the degradation of the mask are: type, value and gradient of the residual stress and the hydrophilicity of the surface. Cr/Au mask is used for illustration. A new method for deep wet etching of glass using Cr/Au mask and photoresist is established. The result of this method is the best thus far as reported in the literature: 85 min deep wet etching in HF 49% which is equivalent to etching of more than 500 μm deep in the Pyrex glass material.