Contamination control of particles smaller than 40 nm by thermophoretic force

As the miniaturization of semiconductor devices increases, the size of contamination particles that must be controlled becomes smaller. The effects of diffusion are stronger for smaller particles, so control becomes more difficult. We therefore evaluated the use of thermophoretic force in a new control technique. We confirmed that particle adhesion could be mostly prevented by simply heating the wafer to 5degC above the temperature of the air flow. Furthermore, we established a model of adhesion prevention behavior which predicts that the adhesion prevention effect of thermophoretic force is adequate, even for particles less than 40 nm in diameter. In addition, we actually confirmed that thermophoresis prevents adhesion even for 20 nm PSL particles.