Patent Number: 
Section: claims

1. A method for supplying gas over a substrate in a reaction chamber wherein a substrate is placed on a pedestal, said reaction chamber having a gas-ejecting periphery on a plane, from which gas is ejected, said method comprising:supplying a first gas from the gas-ejecting periphery from a first side of the reaction chamber to a second side of the reaction chamber opposite to the first side in a horizontal direction passing through an axis of the reaction chamber so that the first gas travels over the substrate in a main stream from a first side of the substrate to a second side of the substrate opposite to the first side in a horizontal direction passing across a center of the substrate; andsupplying a second gas from the gas-ejecting periphery from sides of the reaction chamber other than the first side of the reaction chamber toward the main stream, wherein the first gas and the second gas are the same gas which is ejected in three or more directions, unevenly with respect to the gas-ejecting periphery, so that the second gas travels over the substrate in auxiliary streams from sides of the substrate other than the first side in a downstream direction of the main stream, said main stream being predominant relative to said auxiliary streams. 2. The method according to claim 1, wherein gas flow in total at the second side of the substrate is greater than gas flow in total at the first side of the substrate, and the gas flow has a flow rate gradient along the main stream. 3. The method according to claim 1, wherein the second gas is supplied from the sides, toward the center of the substrate. 4. The method according to claim 3, wherein the first and second gases are discharged from the reaction chamber through a circular duct arranged around the outer periphery of the pedestal. 5. The method according to claim 1, wherein the second gas is supplied from the sides, toward an axis passing the first and second sides of the substrate. 6. The method according to claim 5, wherein the first and second gases are discharged from the reaction chamber through a duct disposed in a vicinity of the second side of the reaction chamber. 7. The method according to claim 1, wherein the first and second gases are supplied from gas nozzles circularly arranged above and around the outer periphery of the pedestal and directed to the center of the substrate, wherein first gas nozzles supplying the first gas are disposed at the first side of the reaction chamber, and second gas nozzles supplying the second gas are disposed at the sides other than the first side of the reaction chamber. 8. The method according to claim 7, wherein the first gas nozzles have higher conductance than do the second gas nozzles. 9. The method according to claim 8, wherein the first gas nozzles are disposed at shorter intervals, have a larger diameter, and/or have a shorter nozzle length as compared with those of the second gas nozzles. 10. The method according to claim 7, wherein no gas nozzles are disposed at the second side of the reaction chamber. 11. The method according to claim 7, wherein the conductance of the first gas nozzles is about 1.5 to about 10 times higher than that of the second gas nozzles. 12. The method according to claim 7, wherein an exhaust port is disposed at the second side of the reaction chamber. 13. The method according to claim 7, wherein the first gas and the second gas are the same gas and supplied through the first and second gas nozzles via a common gas channel circularly disposed above and around the outer periphery of the pedestal. 14. The method according to claim 1, further comprising rotating the pedestal while supplying the first and second gases. 15. The method according to claim 1, wherein while supplying the first and second gases, the substrate is irradiated with UV light. 16. A UV irradiation apparatus comprising:a reaction chamber;a pedestal disposed inside the reaction chamber, for loading a substrate thereon;a UV irradiation unit disposed above the reaction chamber; anda circular flange disposed between the reaction chamber and the UV irradiation unit, said circular flange being provided with a UV transmission window disposed above the pedestal and gas nozzles,wherein the gas nozzles are provided along the circumference of the circular flange and directed to a center of a substrate when loaded and comprise first gas nozzles for supplying a first gas disposed at a first side of the flange and second gas nozzles for supplying a second gas disposed at sides other than the first side of the flange so that the first gas travels over the substrate in a main stream from a first side of the substrate to a second side of the substrate opposite to the first side in a horizontal direction passing across a center of the substrate, and the second gas travels over the substrate in auxiliary streams from sides of the substrate other than the first side in a downstream direction of the main stream, said main stream being predominant relative to said auxiliary streams, wherein the first gas and the second gas are the same gas which can be ejected in three or more directions, unevenly with respect to the circumference of the flange, to form the main stream and the auxiliary streams, wherein the first gas nozzles have higher conductance than do the second gas nozzles. 17. The UV irradiation apparatus according to claim 16, wherein the first gas nozzles are disposed at shorter intervals, have a larger diameter, and/or have a shorter nozzle length as compared with those of the second gas nozzles. 18. The UV irradiation apparatus according to claim 16, wherein no gas nozzles are disposed at the second side of the reaction chamber, and an exhaust port is disposed at the second side of the reaction chamber. 19. The UV irradiation apparatus according to claim 16, wherein the conductance of the first gas nozzles is about 1.5 to about 10 times higher than that of the second gas nozzles. 20. The UV irradiation apparatus according to claim 16, wherein the pedestal is rotatable.