Shunko Magoshi

Extreme Ultraviolet Lithography Using Small-Field Exposure Tool: Current Status

The small-field exposure tool (SFET) for extreme ultraviolet (EUV) lithography was manufactured by Canon and EUVA and installed in Selete. It is being used for developing mask, resist, and tool technologies. In this paper, we review the current status of SFET development and present some initial results on lithographic performance and tool stability.

Throughput enhancement strategy of maskless electron beam direct writing for logic device

A pattern design method for semiconductor circuits in logic device was developed, which realized an electron beam (EB) exposure with sufficient throughput. The number of EB shots can be decreased by repeating logic synthesis and P and R (place and route) by removing usable standard cells (SCs). By using the design method, a functional block with about 140 kGates could be generated with only 17 SCs, and the minimum number of EB shots was attained with 24 SCs. The increase in the total area of SCs and the consumed power of the chip was only 10%.

Character Projection EB Data Conversion System Combined with Throughput Analyzer

An electron beam (EB) data conversion system for a character projection (CP) writing method has been constructed. The system has been developed based on an EB data conversion system for a variable-shaped beam (VSB), and a formatting module for CP writing was added. In addition, several functions have been developed to analyze CP writing patterns, and combined with the system. The functions aim to select the CP writing patterns that best reduce writing time and to achieve the highest throughput. The new system was applied to a real LSI pattern to test the conversion function and to estimate the conversion speed. A model pattern of a 1 Gbit dynamic random access memory was successfully converted to EB data format. The conversion processing time was less than 14 min for each layer.

Recent progress of EUV full-field exposure tool in Selete

The Selete full-field EUV exposure tool, the EUV1, was manufactured by Nikon and is being set up at Selete. Its lithographic performance was evaluated in exposure experiments with a static slit using line-&-space (L&S) patterns, Selete Standard Resist 03 (SSR3), an NA of 0.25, and conventional illumination (σ = 0.8). The results showed that 25- nm L&S patterns were resolved. Dynamic exposure experiments showed the resolution to be 45 nm across the exposure field and the CD uniformity across a shot to be 3 nm, also 26-nm L&S patterns were resolved. Overlay performance of the EUV1 was showed as processed wafer mark alignment, the repeatability was under 1nm. Overlay accuracy using EGA (Enhanced Global Alignment) was below 4nm at the 3-sigma after liner correction. These results were good enough for an alpha-level lithography tool and test site verification.

Effects of aberration and flare on lithographic performance of SFET

The effects of aberration and flare on the lithographic performance of the EUV small-field exposure tool (SFET) were evaluated. Simulation results indicated that the effect of aberration on the image contrast of line-and-space (L&S) patterns should be small. In exposure experiments, 26-45-nm L&S patterns were successfully fabricated under annular illumination (σ=0.3/0.7). A key factor limiting resolution should be resist performance. Simulation results also indicated that the astigmatic aberration could produce a focal shift of about 60 nm between horizontal and vertical L&S patterns. The experimentally obtained focus shift agreed well with the simulation results. Dense 32-45-nm contact-hole (C/H) patterns were also successfully fabricated under annular illumination (σ=0.3/0.5). Due to astigmatic aberration, the C/H patterns were deformed at defocused positions, but they were almost circular at the best focus position. The flare of the projection optics measured by the Kirk method was 11% over a flare range of 1-100 μm. The effects of the 11% flare were evaluated using dark- and bright-field 32-nm L&S patterns. It was found that the top loss and line-width roughness (LWR) of the resist were larger for bright-field than for dark-field patterns. To reduce the impact of flare, we need EUV resists that are more robust with regard to flare. A comparison of the measured point spread function (PSF) of the flare and the calculated PSF revealed good agreement for long-range flare but some difference for short-range flare.

Resolution capability of SFET with slit and dipole illumination

A high-resolution EUV exposure tool is needed to facilitate the development of EUV resists and masks. Since the EUV small-field exposure tool (SFET) has a high numerical aperture (NA = 0.3), low aberration & flare, and excellent stage stability, it should be able to resolve fine L/S patterns for the half-pitch 22-nm & 16-nm nodes. In this study, we evaluated the resolution capability of the SFET and obtained 22-nm L/S patterns with x-slit illumination and clear modulation of 16-nm L/S patterns with x-dipole illumination. The resolution limit of the SFET seems to be about 15 nm. The main cause of pattern degradation in 16-nm L/S is probably resist blur. To obtain good shapes for this pattern size, the resist blur of less than 3.5 nm (σ) is required. The use of y-slit illumination was found to reduce the linewidth roughness (LWR) of resist patterns. Further reduction of the LWR requires a higher image contrast and a smaller flare. Due to the central obscuration, the image contrast of the SFET is sensitive to the change of pupil fill. The degradation in the collector & DMT should be reduced to ensure stable aerial images. This work was supported in part by NEDO.

Lithographic Performance of Extreme Ultravolet Full-Field Exposure Tool at Selete

The Selete full-field etreme ultraviolet (EUV) exposure tool, the EUV1, was manufactured by Nikon and is being developed at Selete. Its lithographic performance was evaluated in exposure experiments with a static slit using line and space (L&S) patterns, Selete Standard Resist 03 (SSR3), a numerical aperture (NA) of 0.25, and conventional illumination (σ= 0.8). The results showed that 25 nm L&S patterns were resolved. Dynamic exposure experiments showed the resolution to be 45 nm across the exposure field and the critical dimension (CD) uniformity across a shot to be 7 nm, which is sufficient for an alpha-level lithography tool.

Evaluation result of Selete's exposure tool: impact of the source performance

We have installed a small-field exposure tool (SFET) manufactured by Canon and EUVA with a discharge-producedplasma EUV source that employs Xenon gas. We investigated how the performance of the source affects lithographic performance. Electrode life has relation to the illumination uniformity of the exposure field on wafer surface. Also source power at the wafer surface has relation to the electrode life. Electrode life makes EUV power decreasing and larger illumination uniformity number. We examine the pupilgram test using high sensitivity resist. Actual pupil fill shape was observed and there was non-uniform distribution. Pupil fill shape was changed after exchanging electrode, also resist CD bias between parallel and horizontal line of the field. That was comparable to the simulation result. The source electrode requires periodic replacement, which impacts not only the performance of the source, but also the lithographic performance of the tool, such as the CD of resist patterns.

Throughput Enhancement in Electron Beam Direct Writing by Multiple-cell Shot Technique for Logic Devices

This paper reports a new pattern design method improving the throughput of the character projection electron beam direct writing (CP-EBDW) lithography for cell-based logic devices. The shot count decreases to approximately one fifth in a 90 nm CMOS technology by assembling the standard cells (SCs) in the physical design stage and exposing them at a time with multiple-cell shot technique. The operating frequency degradation of the logic devices is less than 5 %

Improved Electron-Beam/Deep-Ultraviolet Intralevel Mix-and-Match Lithography with 100 nm Resolution

We have developed a novel electron-beam (e-beam)/deep-ultraviolet (DUV) intralevel mix-and-match (ILM&M) lithography as a production-viable technology. The main feature of the ILM&M lithography is its use of a DUV biased exposure method for increased throughput and a combination of a variably shaped e-beam/character projection writer with a step-and-repeat DUV scanning system for accurate intralevel butting between e-beam and DUV patterns. It was demonstrated that the throughput of e-beam writing in the ILM&M lithography could reach about three times that of e-beam lithography, and that an intralevel butting accuracy of less than 50 nm could be achieved. The proposed ILM&M has been successfully applied to the development and early production of leading edge devices at our laboratory.