Pattern profiles achieved in composite resists of a polymer and a bisazide compound tend to be rectangular, in spite of electron backscattering from substrates. This phenomenon is explained by the bisazide concentration dependence of the composite resist sensitivity to electron beam and the depth profile of bisazide distribution in a polymer film. An optimum amount of bisazide compound, needed to obtain the highest sensitization, exists. It does not depend on molecular weight, but on the kind of polymers used. An excessive amount of bisazide compound incorporation is found to reduce sensitivity. Bisazide compounds distribute to a great extent in the vicinity of a substrate during a prebaking process. These factors reduce the backscattering problem taking place in electron beam lithography to obtain resist patterns with vertical walls.