Reaction of Ozone and H2O2 in NH4OH Solutions and Their Reaction with Silicon Wafers

Abstract

The main purpose of this study was to evaluate ozone chemistry in NH4OH solutions in terms of oxidizing power compared with H2O2-based NH4OH solutions. The solubility of ozone in the solutions tested was almost nil at room temperature when the solution pH was higher than 9. However, the decrease in solution temperature to 10°C resulted in a dissolved ozone concentration at the ppm level in NH4OH solutions. The slow decrease in pH and the increase in redox potential were measured as functions of ozone injection time in NH4OH solutions at 10°C. The half-life times of peroxide were 40 min and 4 h in 1:1:5 (volume ratio) NH4OH:H2O2:H2O (SC1, standard clean 1) solution at 80 and 50°C, respectively. However, the half-life of ozone at room temperature was less than 2~ 5 min at the concentrations investigated. The contact angles of bare silicon changed from 72° to less than 5° within 10 s in SC1 at 80°C. In ozonated solutions, change of contact angle to hydrophilic took longer than 3 min depending on the concentration of ozone in NH4OH solutions. The addition of peroxide and ozone significantly reduced the etch rate of silicon in NH4OH solutions. When Al2O3 particles were deposited on silicon wafers, ozonated NH4OH combined use with megasonic power at room temperature could remove more than over 90% of particles from the wafer surface.