Robert Lavin Wood

Negative tone aqueous developable resist for photon, electron, and x-ray lithography

The use of negative acting photoresists has become a integral part of device fabrication strategy. In this paper we will. discuss a phenolic based photoresist which incorporates a crosslinkable resin and an acid generating sensitizer. When exposed and thermally treated, the resist forms a negative tone image which is developable in an alkaline medium. We will discuss the materials, processes and results from photon, electron and X-ray lithographic evaluations.

Shot-size reduction of photoresist formulations

The cost of expendable chemicals in the resist process is increasing and with this the economic impetus to conserve usage. The volume of liquid resist dispensed (shot size) determines the consumption rate and disposal volumes of liquid resist. The choice of resist solvent can influence the shot volume. Three formulation factors influence the shot size: (1) the surface tension of the resist and the interfacial energy of the coating surface, (2) the viscosity of the resist formulation, and (3) the evaporation rate of the solvent. The suitable resist formulation and subsequent solvent choice should be of the lowest surface tension and lowest viscosity and be balanced by an evaporation rate which allows a minimum shot volume to be spread on the surface without significant solvent loss. Of all the solvents examined, ethyl 3-ethoxy propionate (EEP) gave the lowest shot size relative to the old resist solvent standard of 2- ethoxy ethyl acetate (ECA).

Environmentally stable chemically amplified DUV resist based on diazoketone chemistry

This paper describes a resist that uses a polymer bound diazoacetoacetate as a photoacid generator in a two component system. The diazoacetoacetate is not used merely as a photoactive component, but its utility is extended to function as a photoacid generator for deprotection chemistry. The carboxylic acid generated upon exposure deprotects carboxylic acid-labile groups bound to another polymer backbone. This scheme has led to a resist with excellent performance like lithographically useful photospeed, resolution, environmental stability and aqueous base solubility combined with wide process latitudes. The resist does not require a topcoat or additives for stabilization towards airborne contaminants. The photo acid is a weak acid and hence allows fairly high concentrations of the acid generator to be used which helps in reducing contamination effects. Furthermore, being bound to a polymer backbone, diffusion into unexposed regions is limited and therefore exhibits greater stability towards PEB delay effects. Loss from surface due to volatility is also reduced in a polymeric acid generator compared to low molecular weight, monomeric compounds.

INR negative resist: a negative-tone I-line chemically amplified photoresist

INR, an I-line negative photoresist, is described. Acid catalyzed cross-linking of phenolic resins using a non-metallic photoacid generator, 2,6-bishydroxymethyl-p-cresol as a cross- linker, and 9-anthracene methanol as an I-line sensitizer results in a very high photospeed aqueous TMAH developable photoresist. Poly(p-hydroxystyrene) was found to have advantages over novolac resins for formulation of high performance negative I-line photoresist. Advantages obtained by using PHS rather than novolac include higher thermal stability, elimination of undercut on nuleophilic surfaces and compatibility with 2.38 percent TMAH puddle develop processes. A high resolution version, INR-X, is described. Resolution to 0.30 micrometers and linearity to 0.35 micrometers was obtained using a 0.54NA ASML I-line stepper. 0.35 micrometers line-spaces arrays had 1.2 micrometers depth of focus and 0.40 micrometers line-space arrays had a depth of focus greater than 1.6 micrometers . An unusual characteristic found in INR-X is a very low sensitivity to variation in PEB temperature. A 3nm/ degree(s)C line-width dependency was found.