The mask part 41 includes a substrate 1, a patterning means 40 and a photoemissive layer 6. The patterning means 40 includes a mask pattern 2, 3 of apertures 3 and masking areas 2 and a modifying layer 4. Ultraviolet radiation 56 is patterned by patterning means 40 before effecting electron emission 60 from the photoemissive layer 6. There is electron emission from over the apertures 3 and the masking areas 2 as the masking areas are partially transparent to incident ultraviolet radiation. The ultraviolet transmitted by the apertures and the masking areas is modified in intensity dependent on the thickness R of the modifying layer. The resuting electron emission 60 is in a patterned beam which forms a proximity effect corrected electron image of the mask pattern in the electron sensitive resist layer 63. The masking areas 2 of chromium and the modifying layer 4 of resist may be made by modifications of known methods of chromium deposition and resist exposure and development. The use of the mask in the manufacture of a solid state device allows a single exposure of a resist layer 63 to form a proximity effect corrected image of the mask pattern 2, 3 in the resist layer 63.