A projection exposure apparatus for projecting a pattern of a reticle upon a wafer by use of a projection lens system, is disclosed. The apparatus is arranged so that a mark illuminating light is projected upon the wafer from between the projection lens system and the wafer and not by way of the projection...http://www.google.com/patents/US4814829?utm_source=gb-gplus-sharePatent US4814829 - Projection exposure apparatus
