Many semiconductor device manufacturers plan to make products with 157 nm lithography beginning in 2004. There is, at this time, no functional photoresist suitable for 157 nm exposure. Developing resist materials for 157 nm lithography is particularly challenging since water, oxygen, and even polyethylene are strongly absorbing at this wavelength. A modular approach to the design of a single layer resist for 157 nm has been undertaken. In this approach, the resist has been conceptually segmented into four functional modules: an acidic group, an acid labile protecting group, an etch resistant moiety, and a polymer backbone. Each of these modules has an assigned function and each must be transparent at 157 nm. Progress has been made toward finding candidate structures for each of these modules. We have demonstrated that acidic bistrifluoromethylcarbinols are very transparent at 157 nm and function efficiently in chemically amplified resists with both high and low activation energy protecting groups. Judicious incorporation of fluorine in acrylates and alicyclics has provided etch resistant polymers with greatly improved transparency at 157 nm. In particular, esters of poly͑␣-trifluromethylacrylic acid͒ are far more transparent than their protio analogs. The Diels-Alder adducts derived from reaction of these and other fluorinated alkenes with cyclopentadiene offer a route to a wide range of alicyclic monomers that show great promise as transparent, etch resistant platforms for the design of 157 nm resists. Polymers of this sort with absorbance below 2 per micrometer are reported.

Water is known to play a key role in the solubility switching reaction of novolac-diazonaphthoquinone photoresists and certain chemically amplified resists. In order to quantitatively study these effects, an environmental chamber was built in which the % RH could be controlled while the extent of acid catalyzed deprotection was monitored during the post exposure bake by reflectance FTIR spectroscopy. The extent of acid catalyzed deprotection of tBOC, KRS-XE, UV6, and a tBOCpoly(hydroxystyrene) copolymer have been measured as a function of time over a range of 0-60 % RH. For tBOC, the deprotection reaction rate was found to slow considerably as the %RH was increased. Also, the relative film shrinkage varied considerably with varying % RH. Several possible mechanisms for the dependence of the reaction rate and thickness loss on % RH were investigated. For KRS-XE, the deprotection reaction kinetics were found to increase as the % RH was increased, which was an expected trend. For UV6 and the tBOC-PHOST copolymer, no change in deprotection reaction rate was observed with changes in %RH.

A direct analytical technique for measuring the solution quantum efficiencies of photoacid generators (PAGs) is presented. The technique is based on the nonaqueous potentiometric titration of the photogenerated acid and does not require separate calibrations, or the addition of sensing materials such as dyes or bases. Solutions of PAGs in acetonitrile were irradiated at 248 nm and subsequently titrated with known concentrations of triethanolamine base. The only quantities required for an accurate determination of the quantum efficiency are the incident radiation energy and the titration equivalence point. A mathematical analysis that enables this calculation is derived, and a table with calculated quantum efficiency values for three classes of PAGs having a variety of counterions is presented. The method is simple, accurate, and applicable to any class of PAG molecules.

No abstract

Cationic graft polymerization lithography is a variation of top surface imaging schemes. This technique uses a spincoated, 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.