Richard Vicari

Modified polyhydroxystyrenes as matrix resins for dissolution inhibition type photoresists

It is generally accepted that the production of shrink versions of the 16 MB DRAM and the 64 MB DRAM generations will be patterned using deep UV radiation. This provides a new challenge to the photoresist suppliers, as the standard photoresist formulations are not suitable for this technology, mainly because the presently used novolak resins are highly opaque in the 200 - 300 nm region. This is especially true for the 248 nm wavelength of KrF eximer lasers. Poly 4- hydroxystyrene [PHS] has several advantages in transmission and thermal stability; however, its dissolution rate in commercial grade developers is unacceptably high. We report some recent results on modified, alkyl-substituted PHS derivatives. These polymers combine reduced alkaline solubiity with adequate optical and thermal properties, making them acceptable for future deep UV based production processes. Selected data of these new (co)polymers are discussed.

Methylated poly(4‐hydroxystyrene): A new resin for deep‐ultraviolet resist application

Positive photoresists which function on the basis of dissolution inhibition are the mainstay of optical lithographic technology at long wavelength. Described in this paper is a new type of material which permits the dissolution inhibition mechanism to be extended to deep‐UV wavelengths. Methylated poly(4‐hydroxystyrene) resins are prepared by a copolymerization reaction which results in a final product whose dissolution properties can be defined by the ratio of the two monomers used in the reaction. The deep‐UV optical absorbance of the methylated resin is about one‐half the absorbance of novolac at 248 nm which makes these materials attractive for application in deep‐UV resist formulations. Binary photoresists using diazo compounds as dissolution inhibitors have been prepared with the methylated poly(4‐hydroxystyrene) as the host resin. These materials function very similarly to the familiar diazonaphthoquinone/novolac photoresists at long wavelength. For deep‐UV application, both binary and three component resists have been evaluated. The three component system has high sensitivity ( 3). The high contrast is due in part to the induction effect observed from dissolution data. Projection printed images have steep wall profiles indicative of high contrast photoresists.

Non-chemically amplified 248-nm resist materials

Remarkable progress has been made in the formulation of chemically amplified resists for deep-UV (DUV or 248 nm) lithography. These materials are now in general use in full scale manufacturing. One of the deterrents to rapid and universal adoption of DUV lithography has been the combination of high cost of ownership and a narrow process latitude when compared to conventional i-line process alternatives. A significant part of the high cost of the DUV process is associated with installing and maintaining special air handling equipment that is required to remove basic contaminants from the ambient. Manufacture process latitude demands this special air handling. The chemically amplified resists were developed originally to support mercury lamp powered exposure systems. The sensitivity realized by chemical amplification is required to enable useful productivity with such systems that generate very little DUV flux at the wafer plane. With the advent of high powered excimer laser based illumination systems for 248 nm steppers and step-and-scan systems, it is appropriate to re-examine the applicability of non-chemically amplified DUV resist systems. These systems are less sensitive but have the potential to offer both lower cost of ownership and improved process latitude. A series of photoactive compounds (PACs) have been synthesized and auditioned for use in the formulation of a non-chemically amplified 248 nm resist. The most promising of these materials are analogs of 3-oxo-3-diazocoumarin. This chromophore displays photochemistry that is analogous to that of the diazonaphthoquinones (DNQ) that are the basis of i-line resist formulations, but it bleaches at 248 nm. Several structural analogs of the chromophore have been synthesized and a variety of ballast groups have been studied with the goal of enhancing the dissolution inhibition properties of the molecule. The diazocoumarin PACs have been formulated with customized phenolic resins that were designed to provide the combination of optical transparency, dry etch resistance and the dissolution characteristics that are required for manufacturing applications. The resins are copolymers of poly(4-hydroxystyrene) and blends of these polymers with novolac.

Synthesis and lithographic performance of highly branched polymers from hydroxyphenylmethylcarbinols

A new synthesis pathway for 4- and 2-hydroxymethylcarbinol (4- and 2-HPMC) has made a new class of highly branched polymers readily available. The polymers, which are isomers of polyhydroxystyrene, show unexpected dissolution behavior in aqueous bases which differs from the solubility characteristics seen for the linear polymers obtained by free-radical polymerization. This behavior is traced back to the influence of the changing bond types in the co-polymerization series on the kinetic parameters. With respect to lithography, the absorption of the polymers is too high to make them attractive as DUV resist materials. Although their bond structure shows all bond types that also exist in novolaks, the HPMC polymers are found to be more PHS-like than novolak-like in their performance with DNQ sensitizers. However, they are compatible with DNQ/novolak resists, and can be used in resin blends with novolaks without phase separation.