a method for curing spin - on - glass formed on a wafer film which insulates the metal layers and flattens any step difference in the process for manufacturing a multi - layered metal layer of a highly integrated semiconductor device which comprises establishing a predetermined initial temperature in a heating chamber with an ultraviolet light source . a wafer , on which a sog film to be cured is formed , is then introdued into the heated chamber and the temperature gradually increased to a predetermined maximum temperature . the sog film is irradiated with ultraviolet light at a predetermined wavelength simultaneously with the application of heat at the maximum temperature for a predetermined time . the wafer is then cooled .