Extreme ultraviolet lithography at a wavelength of 13.5 nm has been prepared for next generation lithography for several
years. Of primary concern in EUV lithography is line edge roughness as well as high sensitivity. In recent years, various
types of resist, such as protected PHS resin resist and molecular resist, have been investigated. In order to reduce LER,
we have studied novel molecular resists which are promising alternative to polymeric photoresists for use as imaging
materials with improved resolution and line edge roughness. The work reported in this paper has focused on the
development of a new class of chemically amplified molecular resists that are composed of a single molecule which
contains all of the different functionalities desired in a chemically amplified resists. For the purpose of improvement of
the resist performance, we have designed the resist material of a protected polyphenol derivative (protected Compound
A). PAG moiety is bonded to Compound A to achieve uniform PAG density and to control the acid diffusion length in a
resist film. We analyzed uniformity of PAG density in a resist film by using gradient shaving preparation and TOF-SIMS
analysis. From the TOF-SIMS spectra, the ions intensities of the PAG moiety are almost constant from the surface to the
bottom of the film. Therefore, we can conclude that PAG is distributed homogeneously. Under e-beam exposure, a
100nm thick film of the PAG bonded molecular resist resolved lines down to 100nm. We also discussed the new design
for molecular resists, their synthesis and lithographic performance.
Our recent research effort has been focused on new top coating-free 193nm immersion resists with regard to leaching of
the resist components and lithographic performance. We have examined methacrylate-based resins that control the
surface properties of ArF resists thin films by surface segregation behavior. For a better understanding of the surface
properties of thin films, we prepared the six resins (Resin 1-6) that have three types fluorine containing monomers, a new
monomer (Monomer A), Monomer B and Monomer C, respectively. We blended the base polymer (Resin 0) with Resin
(1-6), respectively. We evaluated contact angles, surface properties and lithographic performances of the polymer blend
resists. The static and receding contact angles of the resist that contains Resin (1-6) are greater than that of the base
polymer (Resin 0) resist. The chemical composition of the surface of blend polymers was investigated with X-ray
photoelectron spectroscopy (XPS). It was shown that there was significant segregation of the fluorine containing resins
to the surface of the blend films. We analyzed Quantitative Structure-Property Relationships (QSPR) between the surface
properties and the chemical composition of the surface of polymer blend resists. The addition of 10 wt% of the polymer
(Resin 1-6) to the base polymer (Resin 0) did not influence the lithographic performance. Consequently, the surface
properties of resist thin films can be tailored by the appropriate choice of fluorine containing polymer blends.
With no apparent showstopper in sight, the adoption of ArF immersion technology into device mass production is not a matter of 'if' but a matter of 'when'. As the technology matures at an unprecedented speed, many of initial technical difficulties have been cleared away and the use of a protective layer known as top coat, initially regarded as a must, now becomes optional, for example. Our focus of interest has also sifted to more practical and production related issues such as defect reducing and performance enhancement. Two major types of immersion specific defects, bubbles and a large number of microbridges, were observed and reported elsewhere. The bubble defects seem to decrease by improvement of exposure tool. But the other type defect - probably from residual water spots - is still a problem. We suspect that the acid leaching from resist film causes microbridges. When small water spots were remained on resist surface after exposure, acid catalyst in resist film is leaching into the water spots even though at room temperature. After water from the spot is dried up, acid molecules are condensed at resist film surface. As a result, in the bulk of resist film, acid depletion region is generated underneath the water spot. Acid catalyzed deprotection reaction is not completed at this acid shortage region later in the PEB process resulting in microbridge type defect formation. Similar mechanism was suggested by Kanna et al, they suggested the water evaporation on PEB plate. This hypothesis led us to focus on reducing acid leaching to decrease residual water spot-related defect. This paper reports our leaching measurement results and low leaching photoresist materials satisfying the current leaching requirements outlined by tool makers without topcoat layer. On the other hand, Nakano et al reported that the higher receding contact angle reduced defectivity. The higher receding contact angle is also a key item to increase scan speed. The effort to increase the receding contact angle become very important issue for not only defectivity but also scanner throughput. Some of our experimental results along this line of study are also included in the report. The last topic covered is LWR (Line Width Roughness) as an essential leverage for performance improvement, especially for the smaller CD that immersion lithography is aiming to define. Our recent effort to find effect and working concept to reduce LWR with low leaching materials is also described.
The lithographic performance of a single layer 193nm resist platform, Sumitomo PAR707, was evaluated for 100nm node patterns for thicknesses ranging from 313nm to 60nm. We first demonstrated that the standard resist formulation could not be used for sub-200nm thicknesses because of unacceptable line edge roughness (LER). We then evaluated the influence of the concentration of photo acid generator (PAG) in the resist formulation of LER over the thickness range of 313nm to 60nm. High PAG loading was found to decrease LER significantly for sub-200nm thicknesses. Using the optimal formulation for minimal LER for a given thickness, process latitudes for 100nm node patterns were determined. The overall dose-focus latitudes were found to remain very close for all thicknesses, with slightly larger latitude for thicker imaging layers.
For the sub 130nm technology nodes, 193nm(ArF) lithography has become the technology path of choice. Similar to the 248nm technology set, the resist systems being used for 193nm lithography are based on chemical amplification to achieve high throughput at the low exposure energy at 193nm. The current ArF resist systems have experienced problems with etch selectivity and line slimming during CD-SEM measurement. Both of these issues are related to the resist platform and constituents used to achieve the desired lithographic performance. This investigation evaluates electron beam stabilization as a way of addressing both the etch selectivity and line slimming issues associated with some of the current 193nm resist systems. Varying levels of electron beam dose were evaluated in an attempt to understand the effects of energetic electrons on ArF resist materials. Chemical changes in the resist were monitored for blanket resist films by FTIR, film shrinkage, and changes in index of refraction, all as a function of dose level. An increase in modification of the resist is seen with increasing dose. Blanket resist etch rate studies were performed as a function of stabilization condition. The etch rate of the resist was found to decrease with increasing dose as compared to untreated resist. Correlation of the chemical changes and etch rate reductions are proposed for the resists considered. The CD changes induced by the electron beam stabilization were monitored as a function of dose applied. Minimal CD change was seen as a result of the stabilization process. The impact of the electron beam process on line slimming was evaluated by performing repeated measurements on resist features with different levels of electron beam dose. The line slimming was found to be significantly reduced for the higher dose levels considered. Etch selectivity was evaluated by cross-section SEM measurements after etch of features with different levels of stabilization. An increase in the etch selectivity and pattern stability were observed with increasing stabilization dose.