New Principle For Image Enhancement In Single Layer Positive Photoresists

Abstract

Positive photoresists containing a dissolution inhibitor as the photoactive compound (PAC) are potentially high resolution materials. For the case of PAC materials with two or more diazonaphthoquinone (DAQ) groups attached to the same ballast molecule (a poly-DAQ PAC), the DAQ groups can photolyze essentially independently in a sequential manner to form a distribution of photoproducts containing both DAQ groups and indene-carboxylic acid groups (ICA) bonded to the ballast molecule, and ultimately, a poly-ICA photoproduct. Equations are deduced for the concentrations of these photoproducts with dose. Dissolution rate is taken to be a function of the relative contributions of each photoproduct to the dissolution rate. These equations show that poly-DAQ PACs can enhance resolution, with maximum resolution occurring in the specific case of ideal selectivity: when the poly-ICA photoproduct has a large contribution to the dissolution rate and the intermediate photoproducts have a negligible contribution to the dissolution rate. This process we call Polyphotolysis*. The difficulty in approaching ideal selectivity is discussed in terms of dissolution rates required to maintain photospeed. Polyphotolysis is experimentally demonstrated for a resist with ideal selectivity. Analytical expressions for approximate treatment of gamma, E0 and absorption are,given as a function of PAC functionality. SAMPLE has been modified to include these basic equations and model profiles are generated. These profiles are compared with experimental patterned resists in which the number of DAQ groups per ballast molecule have been varied between 1 and 6.