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

The main purpose of this study was to evaluate ozone chemistry in NH 4 OH solutions in terms of oxidizing power compared with H 2 O 2 -based NH 4 OH 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 NH 4 OH solutions. The slow decrease in pH and the increase in redox potential were measured as functions of ozone injection time in NH 4 OH solutions at 10°C. The half-life times of peroxide were 40 min and 4 h in 1:1:5 (volume ratio) NH 4 OH:H 2 O 2 :H 2 O (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 NH 4 OH solutions. The addition of peroxide and ozone significantly reduced the etch rate of silicon in NH 4 OH solutions. When Al 2 O 3 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.