Safely Controlling the Silicon Nitride Etching Process

Silicon nitride etch removes silicon nitride from silicon wafers during the fabrication process of semiconductor components. It consists of a solution of phosphoric acid in water which etches silicon nitride. When the temperature of the solution and the concentration of phosphoric are kept constant, the etching will be carried out rapidly and consistently.

The silicon nitride wet etching process uses silicon nitride as a mask to produce the micro-structures and connections in semiconductor devices. In most etching applications the etch rate can vary by changing the temperature or chemical concentration, but the ideal conditions for a successful etch rate consist of a boiling point and a concentration of 85% phosphoric acid in a de-ionized water solution.

The high temperature will lead to water evaporation and will increase the acid concentration in the solution. Adding water is dangerous because if too much water is added at once, the solution stops boiling, and the added water will create a film above the acid. The temperature will rise again, and the acid starts boiling, the large quantity of the water from the film mixes with the acid and this may cause an explosive reaction.

That is why the accurate monitoring of the solution is extremely important for safe control of the process.

Modutek's Nb Series Wet Etching Baths ensure the safe operation of silicon nitride etching process. Here, the phosphoric acid solution is kept boiling with a heater that's constantly on which maintains the solution at the boiling point.

One of its features is the heater which constantly keeps the phosphoric acid solution at the boiling point.

Other key features are the thermocouples – the first one detects the rise of temperature (as the water evaporates and the acid concentration increases). In this case, a small amount of water is added to the solution to bring the concentration to back its manageable levels. There's also a second thermocouple which detects the presence of steam above the bath liquid and blocks the addition of water when no steam is present. The third thermocouple monitors the bath temperature to switch off the heater if the solution overheats.

The advanced features of the Modutek's Nb Series Wet Etching Baths allow semiconductor manufacturers and research labs to control the silicon nitride wet etching process safely while achieving optimum consistency characteristics.

The complete article, “Safely Controlling the Silicon Nitride Etching Process,” explains in more details. For a free quote or consultation contact Modutek at 866-803-1533 or email Modutek@modutek.com.