Improving Standard Clean Particle Removal in a Wet Bench Process

When the Standard Clean process doesn’t result in improved silicon wafer yields, improved particle removal can be done with advanced processing equipment.

Standard Clean, or RCA Clean, was developed by RCA company in 1965 and it has remained pretty much the same since then. While it has been successful in cleaning wafers and removing most particles, with silicon wafers and structures decreasing in size and increasing product density on wafers, even the tiniest particles can cause device defects.

The submicron particles are hard to remove completely with chemicals or by rinsing. The use of megasonic cleaning technology to generate very high-frequency sound waves in the wafer bath provides the capability to dislodge all remaining particles, allowing them to be rinsed away. Megasonic cleaning improves Standard Clean particle removal process, ensuring defect-free production of microscopic structures on the silicon wafer.

How does megasonic cleaning work to improve standard clean particle removal? Here are the two steps that make up the RCA wafer cleaning process:

•  SC1 – It uses a mixture of ammonium hydroxide and hydrogen peroxide. It removes most of the contamination from the silicon wafer surface but introduces metallic ion contaminants that can influence subsequent wafer processing steps.
• SC2 – It uses a mixture of hydrochloric acid and hydrogen peroxide. It dissolves the remaining contaminants, allowing impurities to rinsed away as they float to the surface of the cleaning mixture.
  

Megasonic cleaning can remove the majority of these particles while also dislodging the few larger particles that may still be present. The process involves adding a megasonic transducer to the tank holding the wafers. The transducer converts very high-frequency signals from a megasonic generator into sound waves that travel through the rinsing water to strike the wafer surfaces.

As the sound waves travel through water, they create microscopic cavitation bubbles that form and burst in tune with sound wave frequency. As the bubbles burst, they produce tiny jets of water. The jets from the bubbles near the wafer surfaces dislodge any remaining particles, leaving them to be rinsed away at the surface of the bath. This results in an extremely low particle count on wafers that undergo both the RCA and megasonic cleaning.

Learn more about the wafer cleaning process by reading our recent article, Improving Standard Clean Particle Removal in a Wet Bench Process. Modutek, a leading semiconductor equipment manufacturer, is available if you have questions or would like to set up a free consultation. You may call 866-803-1533 or send an email to sales@modutek.com.