15 when the active layer is converted into a membrane of the reticle blank the doped phosphorus concentration for this purpose is for example approximately 1 u00d7 10 18 atoms cm 3 thus a reticle blank 20 fig1 a for use in fabricating a cpb microlithography reticle is manufactured the cpb microlithography reticle is fabricated by forming a reticle pattern not shown in the figures in or on the membrane 15 pattern elements are formed u201c in u201d the membrane by forming respective apertures in the membrane 15 thereby forming a stencil reticle pattern elements are formed u201c on u201d the membrane by forming a layer of a suitable heavy metal on the membrane 15 followed by patterning the heavy metal layer according to the arrangement and configurations of the pattern elements thereby forming a continuous membrane reticle patterning the membrane in either manner is performed lithographically in this embodiment since a silicon support substrate 12 having a thickness of e g approximately 5 mm is used for supporting the membrane warping is reduced substantially compared to conventional reticle blanks in which an 8 in diameter support substrate has a thickness of approximately 725 u03bcm 0 725 mm this decreased warp correspondingly reduces distortion caused by chucking the reticle onto a reticle stage as well as positional distortion caused by application of resist to the membrane various modifications can be made to this embodiment for example in the discussed embodiment a silicon support substrate having a thickness of 1 5 mm was used alternatively another range of thickness can be used so long as the minimum thickness is about 1 mm in contrast to the maximum.