Cationic graft polymerization lithography

Cationic graft polymerization lithography is a variation of top surface imaging schemes. This technique uses a spin-coated, inert polymer film as a photoacid generator carrier. UV exposure is used to generate acid in the top surface of the film. A vapor-phase reaction between the generated acid and a silicon-containing monomer occurs in the exposed areas. The silicon-containing polymer formed, or grafted, on the surface is used as an oxygen etch mask for subsequent pattern transfer through the underlying film. A modular approach can be employed in material design, allowing optimization of characteristics of each component. A key criterion is introduced by the interaction between the transfer layer and the graft monomer. The solubility of the monomer into the inert polymer layer influences the growth behavior, and should be minimized to prevent background silylation and potential swelling. The solubility of the monomer in the inert polymer is characterized by measuring the equilibrium sorption of the vapor into the polymer. Solubility behavior can also be estimated from group contribution theories. These estimates guide the rational design of materials for this lithography process. Based on this analysis method, a new monomer, bis(vinyloxymethyl)dimethylsilane, has been designed and tested. Its sorption into a typical polymer layer has been characterized experimentally. Kinetic growth rate data have been obtained on a quartz crystal microbalance system, and preliminary imaging results using 248 nm exposure are presented.