GREEN™ Nitride Etch
Most integrated circuits are passivated with a protective layer of silicon nitride. The most common method of removing silicon nitride is by plasma or reactive ion etching. Plasma etching is relatively expensive and comes with the disadvantages of plasma charging damage and lack of selectivity to etching silicon. GREEN™ is a safe, easy to use solution containing less than 5% of the active ingredient, ammonium fluoride. However, GREEN™, heated to 120°C will remove typical silicon nitride passivation in about 14 minutes. GREEN™ can be reused several times.
The nitride etch rate of GREEN™ increases with temperature from about 90 to 140 degrees Celsius. Etch rate selectivity of nitride to oxide is about 1.5 to 1.0 at 120°C. Selectivity of nitride to oxide decreases with temperature. Aluminum etch rate is insignificant throughout the temperature range.
The best uniformity is achieved if the solution is constantly agitated during etching. If a magnetic stirrer/hot plate is available, a Teflon coated stir bar will to cause sufficient motion in the liquid. A small stir bar (STRBR), 1/2″ x 5/16″, leaves plenty of room in the beaker to hold a small IC sample with locking tweezers.
Stainless steel beakers (SS125, SS250) are recommended for superior temperature distribution and chemical non-reactivity.