Kazunori Miyoshi

Patterning Characteristics of a Chemically-Amplified Negative Resist in Synchrotron Radiation Lithography

To explore the applicability of synchrotron radiation X-ray lithography for fabricating sub-quartermicron devices, we investigate the patterning characteristics of the chemically-amplified negative resist SAL601-ER7. Since these characteristics depend strongly on the conditions of the chemical amplification process, the effects of post-exposure baking and developing conditions on sensitivity and resolution are examined. The resolution-limiting factors are investigated, revealing that pattern collapse during the development process and fog caused by Fresnel diffraction, photo-electron scattering, and acid diffusion in the resist determine the resolution and the maximum aspect ratio of the lines and spaces pattern. Using the model of a swaying beam supported at one end, it is shown that pattern collapse depends on the resist patterns flexural stiffness. Patterning stability, which depends on the delay time between exposure and baking, is also discussed.

Extendibility of synchrotron radiation lithography to the sub‐100 nm region

This article discusses the resolution of synchrotron radiation lithography in the sub‐100 nm region, taking into consideration the mass production of large‐scale integrated circuits, under attainable conditions for the x‐ray mask, proximity gap, and resist processes. Resolution and exposure latitude for line‐and‐space patterns are markedly improved by using a mask with a contrast of only 2.5. Resolutions of 90, 80, 70, and 60 nm can be achieved with proximity gaps of 30, 20, 15, and 10 μm if a high‐contrast resist and a low‐surface tension developer are used. The latitude will be 10% for pattern sizes as small as 70 nm when the proximity gap is narrower than 15 μm. The effects of mask duty [which is defined to be the ratio of the absorber (line) width to the pattern pitch, i.e., duty cycle] on the optimum exposure dose and mask linearity are also evaluated.

Application of x‐ray lithography with a single‐layer resist process to subquartermicron large scale integrated circuit fabrication

The applicability of synchrotron radiation x‐ray lithography to future ultralarge scale integrated circuit fabrication processes is demonstrated by the test fabrication of subquartermicron bipolar‐ complementary metaloxide semiconductor devices (SRAM, gate arrays, and several test element groups) with a total size of two‐million transistors. Synchrotron radiation lithography is used at four critical levels: gate poly, first metal, via hole, and second metal. Both negative and positive chemically amplified resists are used with a single‐layer resist system to simplify the resist process. An overview of the lithography process is presented with emphasis on patterning and overlay performance.

Fabrication of 0.2 μm large scale integrated circuits using synchrotron radiation x‐ray lithography

In the last few years, we have made dramatic improvements in the key components of synchrotron radiation x‐ray lithography including a high‐brightness and compact synchrotron radiation source, high‐accuracy steppers, precise masks, and highly sensitive chemically amplified resists. These advances have been used in the test fabrication of complementary metal–oxide–semiconductor large scale integrated circuits using separation by implanted oxygen technology in the 0.2 μm regime. Synchrotron radiation lithography was used at the active, gate, contact, and four‐level metallization levels or at the gate level only. Fabricated gate array large scale integrated circuits, including a 48×48 bit multiplier, have excellent and fully functional characteristics. This article describes lithographic performance under device fabrication conditions, demonstrating an excellent critical dimension control of 0.02 μm (3σ), an overall overlay better than 0.15 μm (3σ) (including metallization levels), and a throughput of 12 waf...

Evaluation of Replicated Dynamic Random Access Memory Cell Patterns using X-Ray Lithography

We have evaluated the exposure latitude and the mask linearity of the lines and spaces (L/S), the isolated lines and the cell patterns used for DRAMs for various sizes down to 0.12 µ m. The exposure latitude was larger than 10% for all types of patterns with sizes larger than 0.12 µ m, using a mask of contrast of 3.7 in a mask-to-wafer gap of 20 µ m. We found that the mask linearity is insufficient and that mask pattern bias is required. The image shortening effect in the cell pattern was also evaluated. The results showed that the value of the shortening is higher when the design rule is smaller, the pattern density is sparser and the mask-to-wafer gap is larger. The value of the shortening in a 0.12-µ m- design- rule cell pattern was 13 nm, which is small enough to be corrected by simply giving a bias in the mask pattern.

X-Ray Phase-Shifting Mask for 0.1-µm Pattern Replication under a Large Proximity Gap Condition

The effects of Fresnel diffraction on the patterning characteristics in synchrotron radiation lithography are greatly influenced by X-ray phase shift in the absorber, especially when a low-contrast X-ray mask is used. We show that the resolution in sub-quarter-micron region can be markedly improved without reducing the proximity gap by utilizing the phase-shifting effects in the absorber. By controlling the absorber thickness within a suitable range (1.5≤mask contrast≤4.0, -30°≥phase shift ≥-120°), fine patterns as small as 0.1 µm can be replicated with a large exposure latitude at a large proximity gap of 30 µm. Based on these results, we propose a novel X-ray phase-shifting mask with shallowly etched patterns (L in width) at the absorber edge as a phase shifter. This mask can be fabricated by a simple self-alignment process and also offers the possibility of 0.1-µm pattern replication at the 30-µm proximity gap by using 0.02≤L≤0.1 µm.

Recent progress in synchrotron radiation lithography

Abstract An infrastructure for synchrotron radiation (SR) x-ray lithography has now been completed as a result of dramatic advances in the key components of this technology, including compact SR sources, vertical steppers, x-ray masks, and resist materials. This paper presents NTTs recent progress in SR lithography. The lithographic performance of the integrated system is presented with emphasis on patterning characteristics, overlay and throughput performance, and the feasibility of using SR lithography in the future LSI fabrication is demonstrated.

Proximity Effect on Patterning Characteristics of Hole Patterns in Synchrotron Radiation Lithography

This paper reports the results of analyzing the proximity effect on the patterning characteristics for plural neighboring hole patterns in synchrotron radiation lithography. Fresnel diffraction simulation was used and pattern replication experiments were performed with pattern pitch, proximity gap, and mask contrast as parameters. Even when the pattern pitch (hole:space) is 1:1, pattern sizes down to 0.2 ? m can be replicated with a large dose margin under a large proximity gap condition up to 40 ? m, irrespective of the mask contrast. A low-contrast (2.5) mask has an advantage over the conventional-contrast (7) mask in that it allows the use of a larger proximity gap when replicating hole patterns with a size of 0.1?0.2 ? m. Moreover, the phase-shifting mask we previously proposed improves the exposure latitude and widens the proximity gap, so that it is possible to use a 20-? m gap to replicate 0.1-? m hole patterns for a pitch of 1:1 and to use a 30-? m gap for a pitch of 1:2.

Patterning Characteristics of 0.1-µm Line-and-Space Pattern in Synchrotron Radiation Lithography

A detailed analysis is performed to investigate the effects of mask contrast, mask-pattern size error and proximity gap on resolution and exposure dose margin for replicating 0.1-µm-region line-and-space (L&S) patterns using synchrotron radiation lithography. The analysis is performed by comparing Fresnel diffraction simulation and pattern replication experiments. When a conventional-contrast (7) mask is used, designing the pattern size of a Ta mask absorber to be slightly narrower than the specified value is a great advantage for faithful pattern replication of 0.1-µm L&S patterns. A large dose margin is obtained for proximity gaps of 15 µm or less. On the other hand, a low-contrast (2.5) mask has an advantage over the conventional mask in that it allows the use of a larger proximity gap for replicating 0.1-µm L&S patterns. A relatively large margin is obtained by limiting the Ta size error to the range of -0.05 µm to +0.03 µm for proximity gaps smaller than 25 µm, and ±0.02 µm for a 30-µm gap.

Resolution Enhancement of Hole Patterns in Sychrotron Radiation Lithography

This paper analyzes the influence of Fresnel diffraction on the patterning characteristics of isolated hole patterns in synchrotron radiation lithography by comparing Fresnel diffraction simulation extended to 2-dimensional patterns and pattern replication experiments with mask contrast as a parameter. It is possible to replicate hole patterns down to 0.1 µm at a large proximity gap of 30 µm by keeping the mask contrast at 2.5-7. However, the exposure latitude for fine patterns below 0.1 µm diminishes abruptly. It also becomes clear that the phase-shifting mask which we previously proposed offers the possibility of replicating ultra-fine hole patterns (<0.1 µm) with a large exposure latitude at the 30-µm proximity gap. Moreover, by using an X-ray mask with a circular absorber pattern instead of the conventional square pattern, it should be possible to solve the problem of pattern deformation and improve the exposure latitude.