Specific Process Knowledge/Etch/Etching of Bulk Glass

At Danchip, we have two types of bulk glass substrates: Borosilicate glass (Borofloat 33 (like pyrex)) and fused silicate glass which in cleanliness is similar to quartz. Both types are etched wet in a special set-up placed in a fumehood using a strong HF-solution (isotropic etch).

Masking materials and pre-treatment of the glass surface prior to the deposition of the masking material is a special concern in particular for deep etchings (> 10µm).

40% HF 3µm/min Beaker Maske?

Wet HF-etch of bulk glass

	Wet Silicon Oxide etch (BHF and SIO Etch (wetting agent))	RIE	AOE
General description	Isotropic etch	Anisotropic etch: vertical sidewalls	Anisotropic etch: vertical sidewalls, especially good for deep etch and high aspect ratio etch
Possible masking materials	Photoresist Silicon nitride	Photoresist (Poly)Silicon Aluminium Chromium (ONLY RIE2!) Other metals that covers less the 5% of the wafer area (ONLY RIE2!)	Photoresist (Poly)Silicon Aluminium
Etch rate	~75 nm/min (Thermal oxide) in BHF ~90 nm/min (Thermal oxide) in SIO Etch	Typically 40-120 nm/min can be increased or decreased by using other recipe parameters.	Typically 200-600 nm/min can be increased or decreased by using other recipe parameters.
Batch size	1-25 wafers at a time	1 wafer at a time	1 wafer at a time
Size of substrate	4" wafers	4" wafers or smaller pieces	6" or 4" depending on the setup (smaller pieces if you have a carrier wafer)
Allowed materials	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist Blue film Gold (Au) and Nickel (Ni) (but only in BHF2 (KOH)!)	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist E-beam resist Aluminium Chromium (ONLY RIE2!) Other metals that covers less the 5% of the wafer area (ONLY RIE2!)	Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist E-beam resist Aluminium