Improving Piranha Etch Process Results in Silicon Wafer Cleaning

Piranha etch, a popular process for silicon wafer cleaning, has to be tightly controlled in order to be effective. It consists of a mixture of about one-part hydrogen peroxide and three parts sulfuric acid, which quickly removes organic matter from silicon wafers. A heated quartz tank is used where both chemical concentration and temperature controls the etch rate.

Maintaining precise control of the original solution is difficult as it is exothermic. The temperature needs to be maintained between 130 and 180 degrees centigrade. The hydrogen peroxide decays to form water, diluting the solution, and the rate of decay depends on how high the temperature is. To prevent the solution from diluting, extra hydrogen peroxide is added to it. However, adding hydrogen peroxide also increases the temperature, which in turn speeds up the diluting process.

The mixture, with periodic spiking of the hydrogen peroxide, has a useful life of only one day. To address this Modutek introduced the "Bleed and Feed" process control strategy that improves the process while reducing chemical use. It also helps increase the useful lifespan of the mixture.

In the "Bleed and Feed" process, Modutek uses a two-tank "clean" and "dirty" tank design. When the hydrogen peroxide concentration in the "dirty" tank decreases, a small amount of mixture is drained from the tank and is replaced by the same amount from the "clean" tank. Then, the "clean" tank takes in a fresh amount of mixture.

The mixtures in the clean and dirty tanks are all programmable so that the desired concentrations can be maintained for an extended period. Using this method leads to the much longer lifespan of the Piranha mixture.

Below are the benefits of using Modutek's "Bleed and Feed" process control in Piranha etch process:

·         Better control of the process increases the reliability of strip results.

·         Replacing the mixture less often reduces downtime.

·         Chemical purchase and disposal costs become lower.

·         Precise temperature and concentration levels result in a constant strip rate.

·         Programmable dosage levels add control flexibility for predictable results.

·         Reproducing process parameters creates excellent repeatability.

·         Longer mixture life reduces chemical use.

·         The Risk of an accident from adding too much hydrogen peroxide is eliminated.

Learn more about how Modutek continues to improve their silicon wafer cleaning equipment by reading the entire article, “Improving Piranha Etch Process Results in Silicon Wafer Cleaning.” If you have questions, would like a free quote, or to set up a consultation, email Modutek at modutek@modutek.com or call 866-803-1533.