Tadashi Saga

Improvement of CD variation control for attenuated phase-shift mask

As the required accuracy of the mask arises, Cr shading film thickness has been thinner gradually. CD linearity with the thinner Cr film thickness has better performance. However, it is difficult to apply thinner Cr film thickness simply under the condition of OD > 3, which is needed for wafer printing. So, we tried to develop new shading film. We adopted MoSi film, because MoSi film has almost no micro loading effect compared with Cr film. MoSi shading film with att.PSM satisfied OD > 3 at 193nm wavelength with good resist profile. But the issue was dry-etching selectivity, because shading layer material was the same of att. PSM layer material. Therefore super thin Cr etching stopper was inserted between MoSi shading layer and MoSi att.PSM layer. The mask CD performance of new blank was evaluated for CD linearity, CD through pitch, and global loading effect. This blank and mask process reduce loading effect, therefore the mask CD performance is improved remarkably. In conclusion, the mask manufacturing process margin was able to be expanded by this new blank and method, and it is expected that we can achieve the required specifications for att.PSM in 45nm node and beyond.

ZrSiON as a material for high-transmittance attenuated PSM

ArF lithography which is a leading technology for 100nm node device fabrication is approaching the stage of practical use, where resolution enhancement techniques (RET) represented by attenuated phase shift mask (att.PSM) are expected to be used from the beginning. ON the other hand, in order to obtain higher depth of focus and resolution, it is said that att.PSM with high transmittance (HT-PSM) will be adopted to KrF and ArF lithography. We have developed zirconium silicon oxide (ZrSiO) att.PSM and reported its utilities toward practical use of ArF lithography. In this paper, we present examination results of possibility of ZrSiON att.PSM to be applied to HT-PSM for KrF and ArF lithography. Consequently, we confirmed the possibility and effectiveness of ZrSiON for HT-PSM as follows; ZrSiON films are convenient to control optical properties required for HT-PSM because of its distribution of optical constants (n;refractive index, k;extinction coefficient) with deposition conditions. Bi- layer HT-PSM having transmittance of 15% for ArF of KrF lithography show such good spectral transmittance that they can be inspected with currently available inspection tool. ZrSiON blanks are also proved to have high durability against cleaning chemicals of not only acid but alkali. Moreover, ZrSiON shifter has good dry-etching durability against Cr dry-etching stacked on ZrSiON film, which makes it easy to control phase angle in fabricating tri-tone-type HT-PSM.

Study of mask-induced polarization effects on att. PSM in immersion lithography

The immersion lithography for 45 nm generation has been developing aggressively for smaller critical dimension of semiconductor devices. The polarization lithography system is indispensable to have an advantage to use the immersion lithography with hyper NA (>1.0). As pattern size becomes smaller, mask induced polarization effects to polarization of exposure image seems not to be negligible. There are several issues about mask induced polarization. But dominant factor for mask induced polarization effect is not understood well. In this paper, in case of monolayer mask of att.PSM, degree of polarization (DoP) strongly depends on film thickness and extinction coefficient from simulation and experimental results. DoP depends on material factor. And in case of double layer mask, DoP depends on total film thickness and extinction coefficient of both upper layer and bottom layer. So, DoP depends also on structure of mask.

Realization of mass production for 130-nm node and future applicatiton for high transmission using ZrSi-based attenuated phase-shift mask in ArF lithography

Attenuated phase shifting mask (att-PSM) is one of the key technologies for 130 nm and below device fabrication. We have proposed zirconium silicon oxide (ZrSiO) as a suitable material for next-generation att-PSM material. Through our optimization process both for film deposition and dry etching condition, we confirmed that we could control its phase shift and transmittance precisely. Because of its low film stress, we could neglect registration degradation. From its excellent spectral property, we can apply currently available defect inspection systems. Defect repair is easily performed by gas assisted etching. Further, we were successful to make high-transmittance material (16 %) at ArF laser source even keeping inspectability.

Development of ZrSiO attenuated phase-shift mask for ArF excimer laser lithography

We have reported that Zirconium Silicon Oxide (ZrSiO) film is one of the most promising materials for attenuated phase shift mask (att. PSM) for ArF excimer laser lithography. In this paper, we report on practical mask characteristics of ZrSiO att.PSM through its fabrication process. Optical constants (refractive index n/extinction coefficient k) of ZrSiO sputtered films vary continuously according to Ar/O2 flow ratios. A reasonable solution to improve spectroscopic property including transmittance at inspection wavelength can be obtained by a bi-layer structure, consisting of two films having different optical constants, that is absorptive film (AF) and transmissive film (TF). By selecting a pair of appropriate optical constants and adjusting thickness of each layer, we developed the bi-layer structure suitable for optical and other required properties. ZrSiO films are etched by chlorine-based gases, especially AF (bottom layer) dry etching using BCl3 gas has high selectivity to quartz substrate. By optimizing dry etching conditions, cross sectional profile has been attained to over 80 deg, moreover no remarkable residues and edge roughness can be seen. These masks are confirmed to have sufficient tolerance to conventional cleaning process by monitoring the change of transmittance or reflectance curve. Consequently, both transmittance and phase shift through fabrication process approached the required specification, plus or minus 0.3% and plus or minus 2 deg, respectively. Inspection or measurement tools for conventional masks are also applicable. In addition, ZrSiO att.PSM is proved to have sufficient durability for ArF excimer laser irradiation.