The preferred embodiment of the present invention provides a method for defining three regions on a
semiconductor substrate using a single masking step. The preferred embodiment uses a
photoresist material having, simultaneously, both a positive tone and a negative tone response to
exposure. This combination of materials can provide a new type of
resist, which we call a
hybrid resist. The
hybrid resist comprises a positive tone component which acts at a first actinic
energy level and a negative tone component which acts at a second actinic
energy level, with the first and second actinic energy levels being separated by an intermediate range of actinic energy. When
hybrid resist is exposed to actinic energy, areas of the resist which are subject to a full
exposure cross link to form a negative tone line pattern, areas which are unexposed form remain photoactive and form a positive tone pattern, and areas which are exposed to intermediate amounts of
radiation become soluble and wash away during development. This exposes a first region on the
mask. By then
blanket exposing the hybrid resist, the positive tone patterns become soluble and will wash away during development. This exposes a second region on the
mask, with the third region still be covered by the hybrid resist. Thus, the preferred embodiment is able to define three regions using a single masking step, with no chance for
overlay errors.