Method of manufacturing a semiconductor device

A method of manufacturing a semiconductor device comprising the steps of:

• defining a selected surface of a semiconductor substrate on which a semiconductor device is to be formed, p1 forming an insulating film on said selected surface of said semiconductor substrate having a plurality of diffusion windows through which corresponding portions of the said selected surface of the semiconductor substrate are exposed,
• applying a polycrystalline semiconductor layer on said insulating film and extending through said diffusion windows thereof to contact the said corresponding portions of the surface of the semiconductor substrate,
• applying a protective mask selectively over portions of said polycrystalline semiconductor layer associated with predetermined said diffusion windows with respect to which regions of a first junction depth are to be formed, the remainder of said polycrystalline silicon layer being exposed at least as to the portions thereof extending through other of said diffusion windows with respect to which diffusion junctions of a second junction depth deeper than said first junction depth are to be formed,
• reducing the thickness of said polycrystalline semiconductor layer in the exposed portion thereof,
• removing said protective mask, and
• simultaneously forming said diffusion regions of both said first and said second junction depths by diffusing impurities through said polycrystalline semiconductor layers of said first and second depths, associated with said diffusion windows, and into the corresponding said substrate portions.