The ever-shrinking circuit device dimensions challenge lithographers to explore viable patterning for the 32 nm halfpitch
node and beyond. Significant improvements in immersion lithography have allowed extension of optical
lithography down to 45 nm node and likely into early 32 nm node development. In the absence of single-exposure
patterning solutions, double patterning techniques are likely to extend immersion lithography for 32 nm node
manufacturing. While several double patterning techniques have been proposed as viable manufacturing solutions, cost,
along with technical capability, will dictate which candidate is adopted by the industry.
Dual-tone development (DTD) has been proposed as a potential cost-effective double patterning technique.1 Dual-tone
development was reported as early as in the late 1990's by Asano.2 The basic principle of dual-tone imaging involves
processing exposed resist latent images in both positive tone (aqueous base) and negative tone (organic solvent)
developers. Conceptually, DTD has attractive cost benefits since it enables pitch doubling without the need for multiple
etch steps of patterned resist layers. While the concept for DTD technique is simple to understand, there are many
challenges that must be overcome and understood in order to make it a manufacturing solution.
This work presents recent advances and challenges associated with DTD. Experimental results in conjunction with
simulations are used to understand and advance learning for DTD. Experimental results suggest that clever processing
on the wafer track can be used to enable DTD beyond 45 nm half-pitch dimensions for a given resist process. Recent
experimental results also show that DTD is capable of printing <0.25 k1-factor features with an ArF immersion scanner.
Simulation results showing co-optimization of process variables, illumination conditions, and mask properties are
The development of next-generation exposure equipment in the field of lithography is now underway as the demand
increases for faster and more highly integrated semiconductor devices. At the same time, proposals are being made for
lithography processes that can achieve finer pattern dimensions while using existing state-of-the-art ArF exposure
Immersion exposure technology can use a high-refraction lens by filling the space between the exposed substrate and the
projection lens of the exposure equipment with a liquid having a high refractive index. At present, the development of
193-nm immersion exposure technology is proceeding at a rapid pace and approaching the realm of mass production.
However, the immersion of resist film in de-ionized water in 193-nm immersion exposure technology raises several
concerns, the most worrisome being the penetration of moisture into the resist film, the leaching of resist components
into the water, and the formation of residual moisture affecting post-processing. To mitigate the effects of directly
immersing resist in de-ionized water, the adoption of a top coat is considered to be beneficial, but the possibility is high
that the same concerns will rise even with a top coat.
It has been reported that immersion-specific defects in 193-nm immersion exposure lithography include "slimming,"
"large bridge," "swell," "micro-bridge," and "line pitch expansion," while defects generated by dry lithography can be
summarized as "residue," "substrate induced," "discoloration," and "pattern collapse." Nevertheless, there are still many
unexplained areas on the adverse effects of water seeping into a top coat or resist. It is vitally important that the
mechanisms behind this water penetration be understood to reduce the occurrence of these immersion-induced defects.
In this paper, we use top coats and resist materials used in immersion lithography to analyze the penetration and
diffusion of water. It is found that the water-blocking performance of protective-film materials used in immersion
lithography may not be sufficient at the molecular level. We discuss the diffusion of water in a top coat and its effects.
Utilizing de-ionized water as the medium between the wafer and lens of the exposure system and realizing high numerical aperture (NA), 193-nm immersion lithography is being developed at a great pace towards practical application. Recent improvements in materials, processing and exposure systems have dramatically reduced the defectivity levels in immersion processing. However, in order to completely eradicate immersion related defects and achieve defectivity levels required for ideal productivity, further investigation into the defect generation mechanism and full understanding of the improvements garnered so far is required. It is known that leaching of resist component materials during exposure and penetration of remaining water from the immersion scanning process are two key contributors towards immersion related defects. Additionally, the necessity to increase the hydrophobicity of the resist materials has had a signification effect on remaining resist residues. In order to more fully understand the generation of defects from the these contributions, it is necessary not only to analyze properties of the defects, but also investigate the change in composition originating from advanced processing techniques that have shown improvements in defectivity performance.
For immersion lithography at 193 nm, there is concern that the immersion of resist in water during exposure might cause water to penetrate the resist or resist components to dissolve into water, or that water remaining after exposure might affect subsequent processes. It is also thought that the same concerns are likely to be felt even if using a protective top coat. In this paper, we report on three key findings. First, after immersing resist in water using virtual immersion methods and evaluating the effect of water on critical dimension (CD) and defects, it was found that CD changes and defects increase. Second, as a result of performing the same evaluation when using a top coat, it was found that CD changes and defects increase despite top-coat application. Finally, a significant amount of knowledge can be obtained for the development of optimal 193-nm immersion lithography equipment as a result of wafer processing using real inline tools for immersion exposure and coating/developing.