When microscopic particles remain on the surface of silicon wafers during a wet bench process, the resulting semiconductor products may be of reduced quality or even defective. As semiconductor geometries and microscopic structures become smaller and are packed more densely on a silicon wafer, the presence of particles can influence the etch rate around the particle and compromise semiconductor fabrication. The smallest structures and conductor paths can be influenced by particles in the submicron size range and these particles are especially difficult to remove completely.
Modutek has developed innovative solutions that achieve particle reduction through reduced handling of wafers and excellent particle removal. The single chamber IPA Vapor Dryer and the use of megasonic cleaning deliver excellent results. The reduced particle count produces better yields and higher quality output. At the same time, Modutek’s solutions save money through the reduced use of chemicals.
The Single Chamber IPA Vapor Dryer Keeps the Particle Count Low
Modutek’s single chamber IPA Vapor Dryer incorporates rinsing and drying in a single system to save space, reduce costs, and minimize the handling of silicon wafers. The system initially rinses the wafers with de-ionized water and then introduces IPA vapor into the drying cabinet. The vapor comes from a one-gallon bottle that is located in the exhaust compartment for easy changing.
IPA vapor is introduced into the drying chamber from the top to ensure even distribution and reduce the amount of IPA required. When the IPA vapor condenses on the wafers, a surface tension gradient develops between the IPA and the remaining water. When water flows off the wafer surfaces it can remove the contaminating particles. The dry wafer surface doesn’t have any water marks and no particles are added.
One source of particles is the handling of wafers during transfers between stations. Reducing the number of transfers eliminates a source of particle contamination. Modutek’s Single Chamber IPA Vapor Dryer can handle an optional etching feature and drying in the same system. The wafers are rinsed and dried without transferring them to a new station. Since no additional particles are introduced during this process the particle count is kept to a minimum.
Megasonic Cleaning Effectively Removes Particles Without Toxic Chemicals
Megasonic cleaning relies on high-frequency sound waves in the cleaning solution to remove contaminating particles from wafer surfaces. Modutek has partnered with Kaijo Corporation, a world leader in megasonic cleaning systems to incorporate this technology in their wet bench equipment.
A megasonic generator feeds a high-frequency signal to a transducer immersed in the cleaning tank liquid. The transducer converts the signal into sound waves that travel throughout the tank. The sound waves generate microscopic cavitation bubbles that produce a scrubbing action to clean wafers. Particles on the surface of the wafer are dislodged and washed away.
The higher the megasonic frequency, the smaller the cavitation bubbles and the gentler the cleaning action. The microscopic structures etched into silicon wafers are very delicate and could be damaged with rough cleaning. Megasonic cleaning uses frequencies of 950 kHz and higher. The tiny bubbles of megasonic cleaning deliver gentle cleaning action without damaging fragile silicon structures.
Although megasonic cleaning works well with DI water or an SC1 process, adding a mild detergent or solvent can improve cleaning performance. Particles on silicon wafer surfaces often adhere to the surface and can be difficult to remove. Submicron particles may stay within a surface boundary layer, resisting removal. The microscopic bubbles can dislodge such particles, but the addition of solvents or detergents helps dissolve the bonds holding the particles to the surface and can improve particle removal.
Modutek Innovates to Help Meet Customer Challenges
Modutek works closely with customers to identify issues with wet process applications and continually works on developing new innovative solutions. The Single Chamber IPA Vapor Dryer and the megasonic cleaning process are innovations that help reduce particle counts while reducing chemical use and lowering costs. Modutek’s experience with wet processing equipment ensures customers will continually be able to improve their process performance results. Contact Modutek to schedule a free consultation to discuss your specific process requirements.
