Michael Sworin

High-resolution fluorocarbon-based resist for 157-nm lithography

Lithography with 157 nm fluorine lasers is rapidly emerging as the next evolutionary step in optical lithography and is clearly seen as the likely successor to 193 nm lithography. In fact, it may become the technology of choice for the sub-100-nm node features. The photoresists used for this technology will be required to be extendable to less than 70 nm. As has been demonstrated with the transition to shorter wavelengths in the past, the photoresist materials that were developed for the longer wavelength applications are too absorbent for practical use as high-resolution single layer resist with 157 nm radiation. This high absorbency will force the coated resist thicknesses to be well under 100 nm. Fluorine containing polymers have been demonstrated to be more transparent in this spectral region than pure hydrocarbon polymers. We have developed and evaluated a number of unique 4-hexafluoroisopropanol styrene based polymer systems which we previously termed FESCAP resists and have developed new acetal partially blocked 4-hexafluoroisopropanol styrene based copolymers. These resists can have absorbencies of under 3 micrometers -1 at 157 nm which could allow imaging to thicknesses of 150 nm. Our recent resist designs are shown to have imaging capability down to 70 nm with a 0.60 NA microstepper.

Experimental VUV absorbance study of fluorine-functionalized polystyrenes

A number of fluoro-functionalized poly(4-hydroxystyrene) derivatives, consisting of both blocked and unblocked hexafluoroisopropanol-substituted stryrenes, were prepared and their vacuum-ultraviolet absorption spectra were measured. From our efforts, we find that a wide range of synthetic flexibility exists and allows for a variety of fluorinated analogs of APEX-like and ESCAP-like copolymers and terpolymers with 157nm absorption coefficients less than 4.0micrometers . From these findings, we conclude that facile routes to high-performance 157nm resins are possible with optimum imaging thicknesses of 100 to 130nm.

High resolution fluorocarbon based resist for 157-nm lithography

Lithography at 157nm represents the next evolutionary step in optical lithography and is clearly seen as the likely successor to 193nm lithography. If successful, the photoresists used for this technology must be initially capable of 100nm resolution and be extendable to less than 70nm. As with the transition to shorter wavelengths in the past, the photoresist materials developed for longer wavelengths appear to be too absorbent for practical use as a traditional high resolution single layer resist imageable with 157nm radiation. The high 157nm absorbance of polyacrylate, polycyclic, and polyhydroxystyrene copolymer resists, will force the coated resist thickness to be under 100nm. It has been shown that some fluorine-functionalized polymers are more transparent in this spectral region than pure hydrocarbon polymers. This has led us to investigate the use of fluorocarbon polymers in resists specially designed for 157nm lithography. We have synthesized and evaluated a number of unique 4-hexafluoroisopropanol1 styrene based polymer systems that yield resists in which the 157nm absorbance ranges from 3.0 to 4.0micrometers . Resists of this type are potentially capable of imaging at resist thickness of 150nm. Examples of the high performance imaging capability of our resist design are shown to have imaging capability of 150nm with 0.50NA microstepper and 40nm employing interference lithography.

Encapsulated inorganic resist technology applied to 157-nm lithography

In order to increase plasma etch selectivity in traditional single layer organic resists SiO2 nanoparticles have been added to typical 248nm resist formulations. Formulation modifications are necessary due to the dissolution acceleration effect of the particles. Surface functionalization of the nanoparticle surfaces with organic groups lessens this effect and allows the inclusion of acid labile groups. This allows for a wider formulation window and limits unexposed film thickness losses (UFTL). Both t- butyl ester groups and poly(t-butyl acrylate) have been used to achieve this effect. Encapsulated inorganic resist technology (EIRT) can be used as a single layer hard mask compatible with existing resist processing steps and replace complex and costly multilevel resist approaches. Lithogrpahic evaluations have been performed with electron beam, and with 248nm and 157nm projection systems. Greater transparency at 157nm is achieved by the addition of these materials, thus enabling the use of thicker films. High resolution imaging is demonstrated at these wavelengths.