Illuminance distribution measuring method, exposing method and device manufacturing method

An exposing method for forming a pattern on a substrate by irradiating a luminous flux from an optical illumination system onto said substrate through a pattern of mask, while said substrate is being positioned on a substrate stage;

• which is characterized in that said method comprises a step of reciprocatively moving said substrate stage in such a manner that a detecting sensor positioned on said substrate stage is moved forward along a route during which said detecting sensor is intermittently stopped at a plurality of locations within an exposure region of the surface of said substrate, and, after reaching a turning location among said plurality of locations, moved to return along said route during which said detecting sensor is intermittently stopped again at said plurality of locations within said exposure region;
• in that measurement of illuminance is performed an even number of times at each of said plurality of locations except said turning location;
• in that said illuminance distribution in said exposure region of the surface of said substrate is determined based not only on a measured value of illuminance obtained at each of said plurality of locations during the forward movement of said detecting sensor but also on a measured value of illuminance obtained at each of said plurality of locations during the returning movement of said detecting sensor;
• and
• in that a light volume of said luminous flux from said optical illumination system is determined based on said illuminance distribution thus determined.