opened to move the substrates 1 and the holder 1 39 to the reaction chamber 2 and the gate valve 6 was closed to partition the reaction chamber 2 and the preparation chamber 4 later in order to prevent mixing of the reactive gases into the light source by the reverse nonproduct gases were introduced first to the light source chamber and the heating chamber at the flow rate of 100 to 1 500 cc min and at the same time a nonproduct gas for example nh 3 was supplied to the reaction chamber in a similar manner it was left standing in this state for about 30 minutes and photo cleaning of the formed surface of the substrate was carried out by generating active hydrogen and fluorine by the photo decomposition of the gases later the product gases among the reactive gases were supplied through a nozzle 30 as the light source for reaction use was made of a low voltage mercury lamp 9 made of synthetic quartz tube with water cooling 32 the source of the ultraviolet rays consisted of 16 of low voltage mercury lamp with illumination length of 40 cm irradiation intensity of 20 ma cm 2 and lamp power of 45w that can radiate light with 185 nm and 254 nm made of synthetic quartz the ultraviolet rays irradiate through transparent covering plate 10 made of synthetic quartz reactive gases 31 and the formed surface 1 39 of the substrates 1 in the reaction space of the reaction chamber 2 for the heater 3 34 deposition up 34.