A first resist mask is formed on a rail, covering an area where none of a shallow surface and a deep surface are formed. A first etching process is performed to etch the rail not covered with the first resist mask to a depth corresponding to the shallow surface. Next, without removing the first resist mask, a second resist mask is formed covering an area where the shallow surface is formed. A second etching process is performed to etch the rail not covered with the first and second resist masks, to a depth corresponding to the deep surface. After the first and second etching processes, the first and second resist masks are removed from the rail.