Takeshi Koshiba

A character projection low energy electron beam direct writing system for device of small production lot with a variety of design

A character projection (CP)-type, low energy, electron beam direct writing (EBDW) system, for quick-turn-around-time and mask-less device fabrications of small production lots featuring a variety of designs has been developed. This system, named the EBIS (Electron Beam Integrated System), can satisfy a set of requirements for EBDWs, including higher throughput and mask-less exposure. A standardized CP aperture method that enables reduction in the number of EB shots without frequent aperture making has been applied as a means for attaining effective CP and mask-less fabrication. This breakthrough was able to be realized only by using low energy EB with the advantage of the free proximity effect. To resolve critical low energy EB issues, a compact EB column, equipped with monolithic deflectors and lenses for restricting beam blur caused by Coulomb interaction, was developed and put to use. Sufficient resolution, corresponding to 100 nm L/S patterns, was attained by using a thin-layered resist process. As the mark detection method, voltage contrast imaging using a micro channel plate was used. This method made it possible to detect buried marks when using low energy EB. The authors are currently verifying the basic performance of this EBIS. This paper outlines and discusses geometrical details and performance data of this system.

Process liability evaluation for EUVL

This paper concerns the readiness of extreme ultraviolet lithography (EUVL) for high-volume manufacture based on accelerated development in critical areas and the construction of a process liability (PL) test site that integrates results in these areas. The overall lithography performance was determined from the performance of the exposure tool, the printability obtainable with the resist, mask fabrication with accurate critical dimension (CD) control, and correction technology for mask data preparation. The EUV1 exposure tool can carry out exposure over the full field (26 mm × 33 mm) at a resolution high enough for 32-nm line-and-space patterns when Selete Standard Resist 3 (SSR3) is used. Thus, the test site was designed for the full-field exposure of various pattern sizes [half-pitch (hp) 32-50 nm]. The CD variation of the mask was found to be as good as 2.8 nm (3σ); and only one printable defect was detected. The effect of flare on CD variation is a critical issue in EUVL; so flare was compensated for based on the point spread function for the projection optics of the EUV1 and aerial simulations that took resist blur into account. The accuracy obtained when an electronic design automation (EDA) tool was used for mask resizing was found to be very good (error ≤ ±2 nm). Metal wiring patterns with a size of hp 32 nm were successfully formed by wafer processing. The production readiness of EUVL based on the integration of results in these areas was evaluated by electrical tests on low-resistance tungsten wiring. The yield for the electrically open test for hp 50 nm (32-nm logic node) and hp 40 nm (22-nm logic node) were found to be over 60% and around 50%, respectively; and the yield tended to decrease as patterns became smaller. We found the PL test site to be very useful for determining where further improvements need to be made and for evaluating the production readiness of EUVL.

Highly sensitive positive-working molecular resist based on new molecule

A highly sensitive positive-working molecular resist based on a new molecule, 1,3,5-tris[p-(p-hydroxyphenyl)-phenyl]benzene (THTPPB), was designed and synthesized. THTPPB showed a high glass transition temperature (Tg) of 145°C. Some acid-leaving groups were attached to THTPPB to realize positive-working performance developed by an alkaline aqueous developer. 70nm line-and-space (1:1) positive tone pattern was fabricated with high sensitivity (<1μC∕cm2) by the exposure to a low-energy electron beam (5keV).

Novel Molecular Resist Based on an Amorphous Truxene Derivative

A novel molecular resist based on a new amorphous molecule, a truxene derivative, was designed and synthesized. Truxene is characterized as an amorphous solid with a high glass transition temperature (Tg). 70 nm line-and-space (1 : 1) positive pattern was fabricated by the exposure of a low-energy electron beam (5 keV) using the new molecular resist. The new molecular design of resists based on the truxene derivative is promising with regard to development of more efficient molecular resists.

High resolution positive-working molecular resist attached with alicyclic acid-leaving group

Molecular resists are expected to offer the advantages of high resolution and low line width roughness (LWR) for the next-generation lithography. We developed a new molecular resist that showed high resolution by introducing an efficient acid-leaving group to an amorphous molecule, 1,3,5-Tris(p-(p-hydroxy- phenyl) phenyl) benzene (THTPPB). The lithographic properties such as sensitivity, developing rate, and adhesion are considered to be controlled using a suitable acid-leaving group. A molecular resist of THTPPB to which is attached with an alicyclic acid-leaving group, hyperlactyl vinyl ether group (HPVE) showed a high resolution for electron beam (EB) lithography and good etch resistance. Half-pitch 36 nm line-and-space (1:1) positive pattern was fabricated using 100 keV EB with chemically amplified molecular resist based on HPVETPPB.

Process liability evaluation for extreme ultraviolet lithography

This work concerns the readiness of extreme ultraviolet lithography (EUVL) for high-volume manufacturing based on accelerated development in critical areas, and the construction of a process liability (PL) test site that integrates results in these areas. Overall lithography performance is determined from the performance of the exposure tool, the printability obtainable with the resist, mask fabrication with accurate critical dimension (CD) control, and correction technology for mask data preparation. The EUV1 exposure tool can carry out exposure over the full field (26 × 33 mm) at a resolution high enough for 32-nm line-and-space patterns when Selete Standard Resist 3 (SSR3) is used. The effect of flare on CD variation is a critical issue in EUVL, so flare is compensated for based on the point spread function for the projection optics of the EUV1 and aerial simulations that take resist blur into account. Production readiness of EUVL based on the integration of results in these areas is evaluated by electrical tests on low-resistance tungsten wiring. We find the PL test site to be very useful for determining where further improvements need to be made and for evaluating the production readiness of EUVL.

What is the strongest candidate in lithography for 2x nm HP and beyond

We have investigated three candidate lithography technologies for 2x nm HP generation and beyond for the application to LSI, namely, double patterning technology (DPT), EUV lithography (EUVL) and nanoimprint lithography (NIL). In terms of lithography unit technologies and lithography integration technologies, each technology has advantages and disadvantages from the viewpoint of difficulty, development resources, extendability, process cost, and so on. Using a development matrix consisting of development steps and development stages, we clarified the current development status for each technology. This matrix indicates the items for which technological critical breakthroughs are necessary to realize LSI production. From this study, we made three lithography development scenarios for the feasibility stage and the production stage for 2x nm HP generation and beyond.

A study of voltage contrast image using Monte Carlo simulation

Using Monte Carlo simulation, we studied voltage contrast (VC) image caused by negative charging. In order to simulate the VC image, we have developed an electron scattering program based on a consideration of the spatial charge conduction model. Also we have established a cluster computing system of 60 CPUs to shorten the processing time. Using a Monte Carlo simulator, we succeeded in obtaining the simulated VC image. Comparison between simulated images and experimental images reveals that the simulated images are in good agreement with some experimental images.

Exposure characteristics of character projection-type low-energy electron-beam direct writing system

We have developed a character projection (CP)-type low-energy electron beam (EB) direct writing (EBDW) system called EBIS (Electron Beam Integrated System). A low-energy EB of less than 5 keV has the potential to expose by the CP-method without intra- and inter-layer proximity effect corrections. In this paper, the advantages of the proximity effect of the low-energy EBDW system of 5 keV with the CP exposure are discussed. The experimental results to compare the intra-layer proximity effect between 5 keV and 50 keV showed that the low-energy EB has an advantage over high-energy EB in terms of small shot size deviation at the pattern edge. The experimental results of inter-layer proximity effect of 5 keV indicate that no proximity effect corrections for structures in underlying layers are necessary in the case of the combination of low-energy EB and multi-layer resist. On the other hand, in response to concern about the Coulomb interaction effect, which is a critical problem of low-energy EB, a dose correction function of each shot was proposed for the EBIS system. We are convinced that the low-energy EBDW is useful for exposure of practical patterns of logic devices by the CP exposure with higher throughput, because the proximity effect is so small that complicated corrections due to the adjacent pattern and structures of substrate under exposure layer are unnecessary.

Recent progress of a character projection-type low-energy electron-beam direct writing system

We have developed a Character Projection (CP)-type, low-energy Electron-Beam Direct Writing (EBDW) system for a quick turnaround time and mask-less device fabrication of small production lots with a variety of designs. The exposure time has been decreasing because the irradiation time of electrons is being reduced by development of high-sensitivity resist and by decrease in the number of EB shots with the CP method, and the amplifiers of the deflectors have attained specifications required by EBIS. In order to further increase the throughput, overhead time, that is, the exposure waiting time, must be shortened. This paper describes our strategy for reducing the exposure waiting time. The reduction ratio of the exposure waiting time was about 60% and the throughput was increased about 20%.