Chemical oxides formed on silicon surfaces by the wet cleaning agents [H2SO4-H2O2 (SPM), HNO3, NH4OH-H2O2-H2O (SC1), HCl-H2O2-H2O (SC2) solutions] of the RCA standard cleaning procedure were characterized by infrared reflection absorption spectroscopy (IR-RAS) by the longitudinal optical phonon and transverse optical phonon modes arising from Si-O stretching vibration. These oxides were found to each have their own distinct IR-RAS spectrum. By using these wet cleaning agents in sequence, we found that the chemical oxide IR-RAS spectrum corresponds to the spectrum of one of the single treatments. That is, SC2 has no effect on chemical oxides formed by other treatments. Otherwise, we found the last treatment to prevail, except in the case of HNO3 following SPM, where SPM prevailed. Thus, we found the SC2 cleaning solution to be the least effective at removing previous oxides. SC1, SPM, and HNO3 were all very effective at removing previous oxides.