A new dry-etching method for fabricating anisotropic deep grooves on a borosilicate glass wafer is reported. The method uses a 200 µm thick bulk silicon wafer bonded to a borosilicate glass wafer by anodic bonding as an etching mask and inductively coupled plasma generated by C4F8 or CHF3 gases for etching. The measured etching rate showed that the deep reactive ion etching conditions for achieving a high etching rate are low gas pressure, high gas-flow rate, high antenna power and high bias power. The measured groove profile revealed that the sidewall angles of the etched grooves were less than 80° and C4F8 plasma provided a slight difference in width between the mask opening and etched groove. These results indicate that C4F8 plasma is suitable for precise groove fabrication. Even after fabrication of a 430 µm deep groove, enough silicon mask (135 µm thickness) remained to fabricate a deeper groove. Consequently, our etching method using an anodically bonded silicon mask and C4F8 plasma enables the fabrication of very deep grooves in borosilicate glass.

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