A New Materials-based Pitch Division Technique

Several techniques have been proposed to achieve higher resolution from 193 nm optical lithography [1]. Most of these techniques require the design of new exposure tools or implementation of costly extra process steps. A new pitch division technique is reported, which doubles the resolution of conventional lithography tools by simply adding one component to the photoresist formulation. This technique creates a resist system that involves a series of linked photochemical reactions (A -> B -> C) in which a photoacid generator (PAG) produces an intermediate species (B) that is a strong acid, which in turn undergoes a reaction that produces a neutral and inert compound (C) that is the final product. The intermediate acid concentration is low at lower doses, but it is largely consumed at higher doses. At moderate doses, the acid concentration reaches its maximum. This property could, in principle, be exploited to double the frequency of a grating on a mask. One formulation that provides this sort of resist response incorporates both a photoacid generator and a photobase generator. This system was studied by simulation and a test formulation was demonstrated to produce the expected resist response.