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How Better KOH Etching Results Are Achieved Using Teflon Tanks



While KOH etching is widely used, the process controls and the process tanks can play a major role in obtaining the desired results. Improved KOH etching means precise control of the etch rate and a low particle count. When the etch rate is exact and consistent, the etched shapes in the silicon wafer will be as specified and the final semiconductor product will function as expected. When particle counts are low, the number of defective products will go down and yield will increase. Combining Teflon tanks with high-precision control systems can deliver superior etching results while reducing waste and increasing output quality.

How KOH Etching Can Be Controlled and Improved

KOH etching uses a solution of potassium hydroxide to etch silicon wafers. The etch rate is influenced by the bath temperature, the concentration of potassium hydroxide, the orientation of the silicon crystal lattice, and possible doping of the silicon. Each of these factors helps determine how quickly etching proceeds in the horizontal and vertical directions.

The cubic crystal lattice of the silicon has different atom densities in different directions. The wafer can be oriented in such a way that etching proceeds more quickly in a given direction. Doping, or adding impurities to the silicon, can be used to stop the etching at a particular location in the wafer. While both these factors can influence the etch rate and the microscopic silicon structures, they are fixed before the etching process begins.

Because the etch rate partly depends on the KOH concentration, it is critical to add the right amount of KOH to water. An accurate chemical delivery system can help ensure that the etching tank contains the right solution concentration before the etching process starts.

The etch rate speeds up with an increasing temperature. This means that the tank and solution temperature must be raised quickly to the specified level and must be maintained precisely at the set point for the duration of the etching process. Accurate temperature control is important for improved etching performance.

Modutek’s Teflon Tanks and Controls Help Achieve Better Etching Results

Modutek provides temperature-controlled Teflon tanks and precise chemical delivery systems needed for excellent etching rate control for improved KOH etching results. These two process variables determine the KOH etch rate once the doped silicon wafer is placed in the process tank with the correct lattice orientation. After the etching process begins, the temperature becomes the critical factor in obtaining the desired etching results.

Modutek’s Teflon tanks are designed to minimize particle contamination and deliver fast heating with accurate temperature control. The tanks have an all-Teflon liquid path and are available in circulating or static models. The heater can be located in the overflow weir or inline. Even heating throughout the tanks ensures that the etching rate is the same everywhere.

To facilitate etch rate control, Modutek’s Teflon tanks heat up quickly at a rate of 2 to 3 degrees centigrade per minute. Once the set point is reached, the temperature controller maintains the temperature at plus or minus 0.5 degrees centigrade. The tanks can operate at 30 to 100 degrees centigrade and temperature and level limit settings can be applied. KOH etching proceeds quickly and reliably to produce the desired microscopic silicon structures.

Modutek Designs Teflon Tanks to Match Customer Requirements

Modutek’s in-house team works closely with customers to ensure that their wet process equipment meets their needs. While standard Teflon tanks are available, Modutek will design and build custom sizes with special features as required. Whether standard or custom designs, the high-quality materials, and precision controls ensure that KOH etch results satisfy even the most demanding requirements and that the Teflon tanks deliver the expected performance. For a free quote or consultation to discuss your specific process requirements contact us or call 866-803-1533.

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