Over the last two decades, very important research has been made on the Si/SiO2 interface both because of its practical importance in the MOS technology and because of its fundamental interest. The non-crystalline character of the SiO2 overlayer and the inability of the usual experimental tools to investigate the atomic structure at the interface without interaction, which in turn modifies the structure, are the main reasons for using the atomic scale simulation. By means of Lennard-Jones and Axilrod-Teller potential functions and energy minimization by the Metropolis test, an ultrathin alpha SiO2 layer 10 Angstrom thick is deposited on a Silicon unit lattice. The structure is relaxed for temperatures ranging from 300 to 1700 K. We find a variation of the position roughness with the temperature and the crystalline orientation. On the contrary, the potential roughness does not depend on the temperature but varies with crystalline orientation and the depth in the Si/SiO2 interface.