Patent Number: 051611767
Section: summary

FIELD OF THE INVENTION AND RELATED ART This invention relates to an exposure apparatus and, more particularly, to an exposure field angle limiting means for use in an exposure apparatus of step-and-repeat type wherein one wafer is repeatedly subjected to zone exposure. The manufacture of integrated circuits or semiconductor devices involves repetition of a process of transferring a pattern of a mask to a wafer which is coated with a photosensitive material. Particularly, in consideration of decreasing linewidth of a pattern, an exposure apparatus which uses X-rays as a light source means for the exposure, has been developed. As an example of such an X-ray exposure apparatus, there is a step-and-repeat type exposure apparatus wherein the surface of one wafer is divided into plural zones to reduce the size of each exposure region to which the pattern transfer is effected by a single exposure operation. To these divided exposure regions, exposures are executed sequentially while moving the wafer stepwise relatively to the mask. This step-and-repeat method is effective for a high-precision X-ray exposure apparatus. In this method, it is necessary to use a specific means for limiting the exposure zone so as to prevent a surrounding portion of the wafer from being exposed. Such exposure zone limiting means may be provided by covering the outside of a circuit pattern area defined on a mask with an aperture member having large X-ray absorbency. Since the necessary exposure zone is determined by the circuit pattern of the mask, the aperture member for limiting the exposure zone has to be positioned with respect to the circuit pattern of the mask. If the positioning precision is not good, the exposure zone is expanded excessively, which leads to enlargement of the spacing between adjacent exposure zones on the wafer. This results in expansion of a blank portion of each wafer, having no circuit pattern, and thus the efficiency decreases. Accordingly, the aperture member for limiting the exposure zone has to be positioned with good precision. Generally, around a circuit pattern area of a mask, there are formed alignment marks for attaining alignment between the circuit pattern of the mask with a circuit pattern already printed on the wafer. The exposure apparatus is equipped with detecting means for detecting positional deviation related to these alignment marks. In order to prevent exposure of such alignment marks, the aperture member for limiting the exposure zone should cover these alignment marks against the exposure illumination light. If the aperture member is maintained in this state, however, it blocks the light path for an optical system of the positional deviation detecting means. Therefore, it is necessary to provide a function for moving the aperture member, at the time of positional deviation detection, from the position covering the alignment mark against the exposure illumination light to a position not covering the alignment marks. Examples of exposure apparatus are disclosed in Japanese Laid-Open Patent Applications, Laid-Open Nos. Sho 62-262428, Sho 52-5504 and Sho 60-45252, for example. SUMMARY OF THE INVENTION Japanese Laid-Open Patent Application, Laid-Open No. Sho 62-262428 discloses a specific film structure for a mask which has large X-ray absorbency at a region outside a circuit pattern area. But, it does not mention prevention of exposure of an alignment mark area. Japanese Laid-Open Patent Application, Laid-Open No. Sho 52-5504 discloses a solution for preventing exposure of an alignment mark area. However, if X-rays are used as a light source, the disclosed solution cannot be applied easily. To avoid such inconveniences, illumination zone limiting means (means for defining an aperture) separate from a mask may be provided as disclosed in Japanese Laid-Open Patent Application, Laid-Open No. Sho 60-45252. However, even this publication does not mention the manner of relatively positioning such limiting means and an edge of the pattern area of a mask, with good precision. It is accordingly an object of the present invention to provide an exposure apparatus, by which the exposure zone can be limited at high precision without exposure of an alignment mark on a mask. In accordance with an aspect of the present invention, to achieve this object, there is provided an exposure apparatus including means for detecting positional deviation between a mask and a wafer, and light blocking means capable of limiting an exposure zone to the mask, wherein the positional relationship between the light blocking means and the circuit pattern area of the mask can be detected by using the detecting means, whereby the light blocking means can be positioned with good precision. 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.