EUV Dry Resist Precursors
EUV dry resist technology, which was introduced by Lam Research, offers an innovative approach toward addressing critical high-volume manufacturing challenges of advanced logic and DRAM products, including resolution, productivity, and stochastic defectivity. Stochastic defectivity arises from unexpected, random photochemical events that can come from a combination of factors. Relative to ArF litho at 193nm, EUV uses a wavelength of light roughly 14 times shorter and, therefore, the energy of the EUV photons is about 14 times higher than that of ArF. That means for a volume element of resist of equal size and at an equivalent exposure dose there are far fewer EUV photons responsible for imaging. Therefore, there is a significantly higher propensity for error based on only a few errant photons or photochemical events stemming from secondary electrons triggered by EUV photons.
Relative to conventional chemically amplified resists (CARs), dry resists have less inherent variability. CARs have a primary component of a polymer matrix, which are generally random copolymers with a distribution of molecular weights and comonomer compositions. In addition, CARs are multicomponent formulations, containing photoacid generators, quenchers, and other components chosen to optimize the performance and process window of these materials. With these multiple degrees of freedom, and also considering the size of the features that are intended to be imaged with EUV, it becomes apparent that the relatively scarce EUV photons are more susceptible to stochastic defects that can manifest as broken patterns, microbridges, or missing features.
Unlike CARs that have a random distribution of components and a distribution of polymer chain lengths and compositions, dry resist is comprised of single component species of a finite and uniform size. These inherently homogeneous systems therefore overcome the inherent variability of CARs. In addition, the EUV dry resists are more effective at capturing the scarce EUV photons by nature of the high atomic cross section at the EUV wavelength of high EUV absorbing element relative to that of typical elements comprising CARs like carbon, hydrogen, and oxygen.
Combining these attributes – smaller, more discrete building blocks and the higher efficiency of photon absorbance – leads to higher density of imaging elements per volume element and therefore, less susceptibility to stochastic errors.
Dry resists are formed in situ in a dry deposition chamber by the introduction of a precursor under carefully engineered conditions. These materials undergo the formation of a cross-linked network upon exposure. They avoid diffusional effects induced by wet development by employing an anisotropic dry development process that selectively removes the unexposed areas of the resist, leaving a negative tone image on the wafer. By not using wet chemistries in either the film formation or the development steps, the waste stream is significantly reduced compared to conventional resist systems that employ either organic solvents or aqueous bases to render images on the wafer. This innovative new materials class offers a unique approach to directly address stochastics, while providing additional environmental benefits.
EUV lithography is becoming a mainstream technology for the manufacture of devices at the 7 nm logic node and beyond and is also rapidly gaining favor for use in advanced DRAM applications. To extend the utility of EUV to future generations of logic and DRAM devices, the industry is enabling high numerical aperture EUV to allow resolution below 30 nm pitch.
Dry resists are an enabling technology that offers a combination of unique attributes to achieve optimum performance from EUV.
For more information about dry resist precursors, please contact your local Entegris representative.
