Ulrich Schaedeli

Bilayer resist approach for 193-nm lithography

Tremendous efforts to extend optical lithography beyond the quarter micrometer boundary, which is currently achievable with KrF-excimer laser lithography, are ongoing. One-hundred- ninety-three nm lithography, using ArF-excimer lasers, is believed to be the technology of choice to approach the ambitious sub-0.2 micrometer resolution target. Single layer, positive tone resist systems, which can be developed with aqueous base, would be preferred. However, it might well turn out that the targeted requirements can only be fulfilled by resist systems which involve some type of dry etch steps. This paper focuses on a positive tone bilayer resist system, which is based on novel silicon containing methacrylate polymers bearing acid labile side groups. Due to a unique combination of monomeric building blocks, polymers with high silicon concentrations and, at the same time, high thermal flow stability are obtained. Hardbaked novolac is used as the planarizing layer. Resists systems based on the new silicon containing polymers demonstrated 0.175 micrometer resolution capability, a thermal flow stability greater than 120 degrees Celsius, and an etch selectivity ratio greater than 20.

Relationship between physical properties and lithographic behavior in a high-resolution positive-tone deep-UV resist

A chemically amplified positive tone resist system, based on new maleimide polymers and a photoacid generator, has been developed, called MISTRAL (Maleimide-Styrene based Resist for Advanced Lithography). These polymers, which are insoluble in aqueous base, consist of two different types of monomers: blocked p- hydroxystyrenes and N-substituted maleimides. In the irradiated zones of the resist film, the phenols are regenerated by the presence of a photoacid, thereby making the resist soluble in an appropriate developer. The maleimides, on the other hand, are needed to introduce high thermal stability and good film properties. The maleimides can further be used to tailor the dissolution properties of the resist. A variety of different MISTRAL polymers have been prepared, starting from the corresponding monomers. Changes in the molecular weight, the types of monomers used and their ratio in the feed have been analyzed: a correlation study between the physical properties of the MISTRAL polymers and their lithographic behavior was systematically performed, revealing quarter micron resolution capabilities.

1,3-dioxolyl acetals as powerful crosslinkers of phenolic resin

The principle of chemical amplification has proven to be successful for the design of highly sensitive, high resolution resist materials of both positive and negative tone, respectively. This paper discusses our new approach to a high resolution, aqueous base developable deep-UV negative tone resist. It is based on the acid catalyzed cleavage of acetal blocked aromatic aldehydes, which, if treated with strong Broensted acid, react with the surrounding phenolic resin in a Friedel-Crafts type reaction, thereby leading to matrix crosslinking. Resists based on this type of crosslinking chemistry show good deep-UV transparency, have high sensitivity, and can be developed with an aqueous base.