MINIMIZATION OF PARTICLE CONTAMINATION DURING WET-PROCESSING OF SI WAFERS

The minimization of particle contamination during wet processing of Si wafers, such as from particles in solutions with surfactants, was studied. It was demonstrated that particle deposition on wafer surfaces in solutions is determined by an attractive or a repulsive electrostatic force through the zeta potentials of particles and substrates. In practice, wafer surfaces consist of materials such as Si, poly-Si, SiO2, Si3N4, Al-alloy, and photoresist, and all these materials exhibit different zeta potentials in wet chemical solutions. In solutions with a pH < 5, the Si surface exhibits a negative zeta potential while SiO2 and Si3N4 surfaces have positive zeta potentials. This means that particle deposition will always occur either on Si surfaces or on SiO2 and Si3N4 surfaces in acidic solutions that contain particles. Therefore, in order to suppress particle deposition on the wafer surfaces, it is essential, that the wafer surface and the particles must have the same polarity of the zeta potential. This can be achieved by adding an anionic or cationic surfactant, where the wafer surfaces and the particles exhibit the same polarity of the zeta potential.