How Are Isotropic and Anisotropic Processes Used to Improve Silicon Wet Etching?

The microscopic structures produced by silicon wet etching can be created with a high degree of precision using both isotropic and anisotropic processes.

Hydrofluoric acid is one of the etchants used in isotropic etching. It etches at the same speed in all directions, independently of silicon atom density. For etchants used for anisotropic etching, such as potassium hydrochloride (KOH), the etching speed depends on the number of silicon atoms in a crystal lattice plane. It, therefore, depends on the direction of the different planes.

While isotropic etching is faster, it may etch under masks to create rounded shapes and is also harder to control. On the other hand, anisotropic KOH etching can be controlled more precisely and produce straight sides with precise dimensions.

In silicon wet etching, the etch speed also depends on the temperature. For precise control of etching processes Modutek's Teflon tanks provide rapid heating and tight temperature control. The tanks are either static or recirculating, and they can be built into any new wet bench configuration. The tanks have 360-degree overflow filtration and even heating throughout the bath. The heat-up rate is two to three degrees centigrade per minute. The temperature control accuracy is plus/minus 0.5 degrees centigrade, making these tanks ideal for both isotropic and anisotropic etching.

As for controlling etchant concentration, Modutek can provide for the injection of de-ionized water into the tanks. Because the etch speed depends on the etchant concentration, accurate concentration is essential for the final product quality and repeatability.

For more details read the recent article, “How are Isotropic and Anisotropic Processes Used to Improve Silicon Wet Etching?” . If you would like to set up a consultation, or would like to receive a free estimate, contact Modutek at 866-803-1533 or email Modutek@modutek.com.