Patent Number: 050935798
Section: summary

FIELD OF THE INVENTION AND RELATED ART This invention relates to a substrate holding device for holding a substrate on a predetermined holding surface, through a difference between pressures respectively applied to a surface of the substrate, facing the holding surface, and another surface of the substrate remote from the holding surface. In another aspect, the invention is concerned with an exposure apparatus for manufacture of semiconductor microcircuit devices, having such a substrate holding device for holding a semiconductor wafer at a predetermined exposure position. In the field of manufacture of semiconductor microcircuits, as such a substrate holding device, a vacuum chuck is known wherein a semiconductor wafer is held through a difference between pressures applied respectively to both sides of the semiconductor wafer. Also, proposals have been made to control the temperature of a wafer chuck, holding a semiconductor wafer at an exposure position in an exposure apparatus, thereby to control the temperature of the wafer so as to prevent expansion/contraction of the wafer resulting from changes in temperature of the wafer during the exposure operation or to correct distortion of the wafer caused by any other process. An example is illustrated in FIG. 5, wherein a wafer chuck 6 is arranged to hold a wafer 5 by a vacuum applied thereto through an evacuation passageway 12 and wherein the wafer chuck 6 is formed with a flow passageway 7 through which temperature controlled circulating water flows to perform temperature control of the wafer 5. In X-ray lithography for manufacture of microcircuits, a mask and a wafer are disposed close to each other with a clearance on an order of a few tens of microns. Thus, the temperature of the mask easily follows the temperature of the wafer and, therefore, temperature rise in the wafer easily produces thermal distortion of the mask. This necessitates exact temperature control of the wafer, as compared with conventional lithography using light other than X-rays. In this respect, a vacuum applying system such as shown in FIG. 5 wherein a vacuum is simply or uncontrollably applied to the back of the wafer is not desirable. This is because mere application of a vacuum through a vacuum pump or the like substantially completely removes gas inside of the wafer chuck and in the interspace between the wafer and the wafer chuck, wherein such gas serves as a heat transfer medium. This easily results in an increase in the contact thermal resistance between the wafer and the wafer chuck. In this regard, experiments were performed wherein a wafer chuck made of an SUS material was used and, by using a vacuum pump, a vacuum was applied to the back of a wafer. The result is that the contact thermal resistance was increased to 10.sup.2 deg.multidot.cm.sup.2 /W. This means that, even if the temperature of the wafer chuck is constant, the application of energy of 100 mW/cm.sup.2 to a wafer in the X-ray exposure, for example, causes a temperature rise in the wafer by a few degrees. Since the temperature rise in the wafer causes a temperature rise in the mask, there is a possibility of thermal distortion of the latter which results in positional deviation of a pattern. SUMMARY OF THE INVENTION It is accordingly an object of the present invention to provide a substrate holding device in which the temperature of a substrate, being held by the substrate holding device, can be controlled precisely. It is another object of the present invention to provide a substrate holding device suitably applicable to an exposure apparatus for manufacture of semiconductor microcircuits, wherein a semiconductor substrate is held at an exposure position through a difference between pressures applied respectively to both sides of the substrate and wherein any temperature rise in the substrate which otherwise might be caused by the exposure operation can be reduced. It is a further object of the present invention to provide an exposure apparatus by which, through the control of the temperature of a wafer chuck, holding a wafer, any temperature rise in a mask and a wafer which otherwise might be caused by the exposure operation can be reduced, whereby correct transfer of a pattern of the mask to the wafer is ensured. These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.