Kazuhide Yamashiro

SiC mask membrane for synchrotron radiation lithography

Abstract We have developed an excellent silicon carbide mask membrane with a hot wall type LPCVD using a SiH 2 Cl 2 - C 2 H 2 - H 2 reaction gas system. The internal stress can be precisely controlled by making a mixed crystal of poly β-SiC and poly Si. Surface roughness is less than about 50nm by STM measurement. The 2.0μm thick membrane shows excellent transparency of 53% by applying an AR coating. With regard to X-ray radiation durability, no change of stress is observed up to 120MJ/cm 3 of absorbed energy.

Evaluation of NLD mask dry etching system

An advanced photomask dry etching system (NLDE-9035 Prototype) has been evaluated. This system adopts new plasma source NLDE, and has a 230 mm mask capability. In this experiment, etching uniformity, selectivity and etching pattern profile were mainly evaluated. Etching uniformity of 20 nm (range) was obtained and good pattern fidelity was confirmed.

Smoothing Roughness of SiC Membrane Surface for X-Ray Masks

We have obtained a smoother surface of SiC membranes than that of as-deposited SiC using etch-back and polishing methods, and investigated the influence of surface roughness of SiC films on internal stress and film structure of X-ray absorber films and optical transmittance of SiC membrane. Surface roughness for the as-deposited SiC surface is 15 nm (Ra), whereas that for etch-backed SiC is 6.9 nm (Ra) and that for polished SiC is 4.3 nm (Ra). Optical transmittance of as-deposited SiC membrane is 48% (λ=633 nm) and increases by a few percent with decrease in the Ra value. Internal stress of sputtered Ta tends to show gentler change with increasing surface roughness of SiC film. Film structure of Ta film is largely influenced by the surface roughness of SiC films at low Ar pressure. Sub-half micron absorber patterns with vertical walls, however, have been obtained even on rough surface SiC.

Evaluation of loading effect of NLD dry etching

Recently, loading effect is becoming a great issue in mask dry etching process. It is well known that the effect is affected by pattern density. To improve the issue, an advanced mask dry etching system using neutral loop discharge was applied for next generation mask fabrication, because the tool make is possible to get high plasma density and low gas pressure.

Spray developer for ZEP 7000

ZEP7000 has been successfully used as EB resist for high-end photomask manufacturing where high dry etching resistance, high sensitivity and high resolution are required. ZED-500 is the common developer use din spray development process and ZED-750 for puddle development process. These developers are designed to suite particularly for dry etching pattern profile. In this paper, we introduce a new developer, ZED- 450 which performs equivalent to ZED-500 while requiring either lower dosage or shorter development time in spray development process.

Improvement of NLD mask dry etching system

An advanced photomask dry etching system (NLDE-9035) has been evaluated. The NLD plasma has an advantage to have a capability to control the plasma distribution and density. In our previous work, it has been confirmed to obtain excellent CD uniformity, CD linearity and good pattern fidelity. To improve the CD uniformity further, the neutral loop modulation etching technique has been evaluated. As a result, a further improvement of CD uniformity has been confirmed by using neutral loop (NL) diameter modulation etching technique.

Photomask blanks enhancement by optimizing resist baking and coating for advanced e-beam reticle fabrication

Advanced e-beam reticle fabrication, including phase-shifting mask (PSM) and optical proximity correction (OPC) reticle, has created a growing need for a resist system with wider process latitude, superior resolution and linearity, better CD uniformity. Some of aqueous-based DNQ-novolak resist systems, including chemical amplified one, have been proposed, however, their feasibility has not reached practical level yet. Accordingly, high-molecular polymer resist systems, conventional PBS for instance, are still the majors. We studied resist behavior to soft-baking conditions for the majors of high-molecular polymer resists in order to bring out their potential at its maximum. We also attempted to optimize coating thickness with an intention of superior linearity in conjunction with a risk of clear defects increase. We then examined very basic patterning features of each resist system in soft-baking latitude, coating thickness latitude, exposure dose latitude, develop latitude, adhesion and so on to make clear advantages and disadvantages of each the above resist system. This paper describes details of our findings on photomask blanks enhancement by optimizing soft-baking condition and coating thickness for the conventional high-molecular polymer resist systems for advanced e-beam reticle fabrication.