New Particle Removal System Patent Allowed
By Susan English
Mountain View, CA–On June 26, YieldUP International Corporation announced the U.S. Patent Office has allowed a patent for its CleanPOINT particle removal system, a water filtration method based on the principle of electrostatic attraction. Using electrostatically charged filters, the point-of-use water cleaning technology removes microscopic particles down to less than 0.1 µm. YieldUP, founded in 1993, develops, manufactures and markets wafer cleaning, rinsing and drying equipment for the semiconductor and other defect-sensitive industries. It completed its initial public offering last November. The recently patented CleanPOINT system is a major component of the company`s Omega2000 and Omega4000 wafer wet processing cleaning systems. The Omega systems combine non-mechanical, motionless wafer rinsing and drying with significantly reduced particle contaminants. “Elimination of particle contamination is the most important factor in improving semiconductor yields today and in the future. CleanPOINT could well be the foundation for obtaining high yields for technologies below 0.35 µm,” suggests Raj Mohindra, President and CEO of YieldUP.
Conventional filtration techniques rely on the passage of liquids through a series of filters with holes or pores of decreasing size. In order to maintain acceptable liquid flow as the size of the filter pores are decreased, expensive pumps must be used to increase pressure through the filters. (Fine particles in DI water include bacteria, yeast, suspended solids, viruses, colloidal silica, pyrogens, enzymes, colloids and other charged particles.) Use of fine filters below 0.1 µm can result in excessive microcontamination and microbubbling, which ultimately decrease yield. According to the company, the electrostatic filter techniques used in the CleanPOINT achieve significant particle reductions with only a small drop in pressure across the filter. In fact, the smaller the size of the charged particle in deionized (DI) water, the easier it is to remove. In addition, notes Mohindra, YieldUP`s systems have been able to achieve reduced surface roughness, improved oxide integrity and elimination of water spots. The company claims a decrease in particle counts to zero adds, an improvement in oxide integrity of 2 coulombs/cm2 470Åof oxide, and up to a 50-percent improvement in wafer sort yields. The system also virtually eliminates VOCs, a major concern for semiconductor manufacturers. The technology, says the company, can also reduce the need for expensive distribution systems required to transport clean water from the main system filters for use in other areas of the fab.
YieldUP markets its products for application at several points in the IC fabrication process–prior to deposition and photolithography and following etching. Although the company believes the main application of the technology will be in semiconductor manufacturing, it also intends to investigate its potential in other industries where ultrapure water is a necessity, such as magnetic and optical disks, flat panel displays, liquid crystal displays, photomasks, chemicals, pharmaceuticals, drinking water and steam turbines.n