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.

How the Silicon Nitride Wet Etching Process Is Improved by Modutek

Silicon nitride is used as a mask when etching silicon wafers as part of the semiconductor manufacturing process. Before the silicon wafer goes to the next fabrication steps, the silicon nitride needs to be removed from the wafer surface using a solution of DI water and phosphoric acid.

To optimize the silicon nitride wet etching process, the phosphoric acid solution is kept at a high temperature. This means some of the DI water boils off as steam and must be replaced. Adding water to the phosphoric acid is extremely dangerous as it can explode. Keeping the solution at a constant temperature is essential for accurate control of the stripping process.

Modutek has made significant improvements to both the safety and the control of the nitride wet etching process with its Nb series silicon nitride wet etching baths. Here, the heater that boils the solution is always switched on, which leads to the solution being heated up to the boiling point and further heating will not increase the temperature, just the boiling rate.

Just in case the temperature increases, a thermocouple in Modutek's bath gives the signal that the DI water should be added. Then, the DI water is added slowly to the boiling solution (since the acid boils rapidly) to make sure that it's mixed in immediately and doesn't form a water film on the solution's surface. If the water is added to the solution too quickly, the water film will form and mix itself with the acid, which leads to a very strong reaction and an explosion is possible.

This control strategy employed in Modutek’s system ensures the temperature of the solution is always maintained at its boiling point.Modutek’s silicon nitride wet etching baths also have additional safety features which ensure that no water is added if the solution is not boiling. Using its advanced control system with additional safety interlocks, Modutek has improved the accuracy, control and safety of the silicon nitride wet etching process.

For more details read the complete article titled “How the Silicon Nitride Wet Etching Process Is Improved by Modutek”. If you have questions or would like further information, please call Modutek at 866-803-1533 or email to modutek@modutek.com.