Abstract: A shadow mask particularly useful in ion implantation processes is disclosed. The mask is fabricated by doping a surface region of a semiconductor wafer to render that region resistant to a particular etchant, machining cavities in the surface of the wafer opposite the doped surface to a depth that does not quite reach the doped region, forming pattern openings in the webs remaining across the ends of the cavities, and thinning the webs by exposure to the particular etchant until the undoped material in the webs is removed. Thus, the ultimate thickness of the webs is controlled substantially by the doping depth.

Abstract: A method of precisely aligning a pattern on one side of an opaque substrate with a pattern on the opposite side thereof through the use of pattern-defining masks, wherein at least certain pattern areas previously not formed on the substrate, as defined selectively through the masks, are formed while the masks are aligned. The first mask is releasably secured to a first side of the substrate so as to define a particular orientation of a desired pattern therethrough, and is dimensioned such that at least one, but preferably several spaced peripheral areas thereof extend beyond adjacent peripheral edge portions of the wafer, with the extended mask areas including alignment indicia. A second mask is then positioned against a second side of the substrate, and is constructed with one or more outwardly extending peripheral areas and respectively associated alignment indicia corresponding in number, and spatial relationship, with those in the first mask.