Through Glass Vias by Wet-etching Process in 49% HF Solution Using an AZ4620 Enhanced Cr/Au Mask

Through glass vias on a high-quality borosilicate glass wafer (i.e., BOROFLOAT® 33) of $500\ \mu \mathrm{m}$ in thickness were accomplished in 49% HF solution using an AZ4620 enhanced Cr/Au mask, without pin holes or defects on the surface. Here, the dehydrated AZ4620 photoresist film plays an important in etching process, which not only enhances the Cr/Au masks by filling micro cracks on them, but also resists the etchant as the first barrier for a longer etching time (e.g., 150 min for $6\ \mu \mathrm{m}$ thick AZ4620 photoresist in 49% HF solution). No peeling off of AZ4620 photoresist film occurs due to its excellent adhesive properties to Au film. The etching rate of borosilicate glass wafer in depth, which is found to be significantly affected by the dimension of masks, decreases with increasing etching time due to the deposition of etching products. The undercut etching rate of glass wafers can be twice of that in depth, resulting in an inclination of the side wall of the vias (or cavities), which ranges from 45° to 50° and is found to be slightly depended on the quality of the masks, the adhesive strength between the interface, for example.