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A new-type 10-Gbps VCSEL-TOSA (vertical cavity surface emitting laser transmitter optical sub-assembly) was demonstrated with single-mode-fiber direct coupling optics and a flexible substrate platform. The TOSA showed high fiber coupling efficiency (-1.6 dB) and clear 10-Gbps eye-opening with -2.6 dBm average optical power and 6 dB extinction ratio.

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.

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.

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.

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 φ≥-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.

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.

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 pattern's flexural stiffness. Patterning stability, which depends on the delay time between exposure and baking, is also discussed.