Particle Removal and Its Mechanism on Hydrophobic Silicon Wafer in Highly Diluted NH4OH Solutions with an Added Surfactant

Abstract

Wafer cleaning in semiconductor processes is one of the most critical steps because of the rapid increase in the device integration density and its direct impact on device yield. Highly diluted NH4OH solutions to which a nonionic polyoxy-alkylene alkylphenyl ether surfactant was added were evaluated to measure their cleaning efficiency and to determine the particle removal mechanism. The particle removal experiment was performed in a 0.2 vol% NH4OH solution, which has a pH value equivalent to that of conventional SC1 (1 : 1 : 5, NH4OH : H2O2 : H2O mixture) solution, as a function of solution temperature. A surfactant of critical micelle concentration of 50 ppm was added to NH4OH solution. The etch rate of silicon in 0.2 vol% NH4OH solution decreased to 2.4 Angstrom /min from 92 Angstrom /min at 80 degreesC by the addition of the surfactant due to die adsorption of the surfactant on the surface. The particle removal efficiency increased as the temperature of the solutions increased. Particle removal of over 95% was observed when wafers were treated in surfactant-added NH4OH solution at 80 degreesC. This can most likely be attributed to the slight increase of the etch rate and better passivation of the surfactant on the silicon surface at a higher temperature.