A UV/hydrogen procedure performed in vacuo is able to remove adsorbed hydrocarbons from a protective silicon oxide layer prior to its sublimation. The efficiency of UV/H-2-cleaning increases with increasing substrate temperature, with the time of treatment, and with increasing partial pressure of hydrogen. At least three different mechanisms give rise to the observed removing of carbon-containing contaminants : (i) thermal desorption due to the higher substrate temperature, (ii) a direct interaction between the high energy UV photons and the adsorbed species (photochemical degradation), and (iii) a mechanism based on the presence of the activated hydrogen atoms. Each single process has its own temperature dependence. This moderate in situ procedure removes preferentially weakly bonded species. It can be successfully used to clean the protective layer prior to sublimation. All wet chemical treatments before introducing the wafer into the deposition equipment can be avoided and silicon substrates as-received from the producer can be used to grow high quality epitaxial layers, which seems to be a good alternative to highly sophisticated wet chemical procedures, where recontamination during wafer loading hardly can be avoided.