Abstract: A method of manufacturing a display apparatus, the method including forming an amorphous silicon layer on a substrate, placing the substrate with the amorphous silicon layer in a chamber having a window on an upper portion thereof, and directing a laser beam toward the window, and converting the amorphous silicon layer into a polycrystalline silicon layer by irradiating the amorphous silicon layer with the laser beam while nitrogen gas is discharged from a nozzle located adjacent to an opening of a stabilizing room, wherein the laser beam reaches the amorphous silicon layer on the substrate after passing through the window, the stabilization room, and the opening of the stabilization room, wherein the opening faces the substrate.