KOH Etching of Silicon - 1
• Typical and most used of the hydroxide etches.
• A typical recipe is:
– 250 g KOH
– 200 g normal propanol
– 800 g H2O
– Use at 80°C with agitation
• Etch rates:
– ~1 mm/min for (100) Si planes; stops at p++ layers
– ~14 Angstroms/hr for Si3N4
– ~20 Angstroms/min for SiO2
• Anisotropy: (111):(110):(100) ~ 1:600:400
• Simple hardware:
– Hot plate & stirrer.
– Keep covered or use reflux condenser to keep propanol from
evaporating.
• Presence of alkali metal (potassium, K) makes this
completely incompatible with MOS or CMOS processing!
• Comparatively safe and non-toxic.