We proposed the use of Si 2 H 6 /H 2 chemistry for selective silicon epitaxy growth by low-pressure chemical vapor deposition(LPCVD) in the temperature range 600 710 ? C under an ultraclean environment. As a result of ultraclean processing, an incubation period of Si deposition only on SiO 2 was found, and low temperature epitaxy selective deposition on Si was achieved without addition of HCI. Total gas flow rate and deposition pressure were 16.6sccm and 3.5mtorr, respectively. In this condition, we selectively obtained high-quality epitaxial Si layers of the 350~1050 \AA thickness. In older to extend the selectivity, we kept high pressure H 2 environment without Si 2 H 6 gas for few minutes after first incubation period and then we conformed the existence of second incubation period.