In order to maintain the lithographic margin and to have sufficient image resolution, attenuated phase shift masks are widely used as a resolution enhancement technique. To improve the radiation durability of the phase shift film, we have developed low oxidation MoSi shifters, such as A6L2, as one option for improving radiation durability. But to provide the best radiation durability, we have developed a new approach eliminating the molybdenum from the phase shift film and introduced a Silicon-Nitride (Si-N) based attenuated phase shift film. Traditionally the transmittance of the phase shift layer is usually around 6%. In the case of a pure Si3N4 film, the transmittance with 180 degree phase shift is around 18%. But, by controlling film structure with a combination of Si-N the transmittance can be tuned to the customers desired transmission value for high durability Mo free attenuated phase shift films.
The proportion of mask fabrication in the total cost budget for IC production is increasing, particularly for the double
patterning generation. Prolonging mask lifetime is very effective in reducing the total mask cost. The factors shortening the
mask lifetime principally damage by cleaning and by 193nm excimer laser irradiation during wafer exposure. In order to
solve these issues, Advanced Binary Film (ABF) was developed that is more durable against 193nm irradiation during
wafer exposure, and has superior cleaning durability. We confirmed the dry etching characteristics of the ABF, using
100nm thick Chemically Amplified Resist and exposure by 50keV EB tool. We obtained impressive results from the ABF
evaluation, through cycle cleaning tests (simulating cleaning during pellicle re-mounting), ArF irradiation damage and the
effects on Critical Dimension changes.
A high flatness of 50 nm, zero defects at more than a size of 30 nm and a high reflectivity of more than 66% for
extreme ultraviolet (EUV) light are critical issues related to EUV mask blanks. In this paper, progress on these issues
and the recent performance of EUV blanks is reported. Steady progress in defect reduction was achieved in the past six
years by improving fabrication processes. When inspected by a Lasertec M1350, defect quality as low as 0.02
defects/cm<sup>2</sup> at 70-nm sensitivity was demonstrated on a multilayer (ML) blank with a quartz (QZ) substrate. A QZ
substrate with a high flatness of around 90 nm peak-to-valley (P-V) on both sides and a high defect quality of 0.006
defects/cm<sup>2</sup> at 60-nm sensitivity was obtained using a newly developed polishing process consisting of local polishing,
touch polishing and cleaning. The cleaning process was developed for low thermal expansion (LTE) glass to reduce the
defects associated with it. Using the cleaning process, the ULE<sup>TM</sup> substrates showed defectivity similar to the QZ
substrates. An average flatness of 117 nm P-V, and best flatness of 84 nm P-V on the front side and 56 nm P-V on the
back side were obtained on ULE substrates using the new polishing process. Multilayer (ML) blanks with a high defect
quality of 0.08 defects/cm<sup>2</sup> at 80-nm sensitivity were produced on a ULE substrate. The ML blanks, consisting of 50 bilayers,
have high peak reflectivity of more than 66% and excellent uniformity of less than 0.04 nm in centroid wavelength, which meets the desired specifications.
Absorber layer patterning process for low reflectivity tantalum boron nitride (LR-TaBN) absorber layer and
chromium nitride (CrN) buffer layer were improved to satisfy high resolution pattern and high level critical dimension
(CD) control. To make 100nm and smaller pattern size, under 300nm resist thickness was needed because of resist
pattern collapse issue. We developed absorber layer dry etching process for 300nm thickness resist. Absorber layer
patterning was done by a consequence of carbon fluoride gas process and chlorine gas process. We evaluated both gas
processes and made clear each dry etching character. Sufficient resist selectivity, vertical side wall, good CD control and
low buffer layer damage were obtained. Then, we evaluated how buffer layer dry etching affects EUV reflectivity.
Finally, we evaluated EUV mask pattern defect inspection and defect repair. Sufficient contrast of mask pattern image
and good repair result were obtained using DUV inspection tool and AFM nano-machining tool, respectively.
Low damage processes for an EUV mask consisting of an LR-TaBN absorber and a thin CrN buffer layer with a thickness of 10-nm have been successfully demonstrated through a dry etching process with high selectivity for the absorber, AFM and EB repair processes, and damage less dry etching process of the CrN buffer layer. Deploying an ICP etching process using CHF<sub>3</sub> gas, we achieved high etching selectivity of 40 between the LR-TaBN absorber and the CrN buffer and LR-TaBN absorber patterns with nearly vertical sidewalls of a feature size of 150-nm in width. Damage to the multilayer film and the CrN buffer induced by repair process was evaluated using a LR-TaBN mask with a 10-nm thick CrN buffer layer via AFM machining and EB etching techniques. Cross sectional TEM analysis of the repaired mask indicated that the multilayer film showed no significant structural damage, against optimized AFM and EB repair processes. Since the CrN buffer lost a mere 1 nm in thickness in the EB etching process, EB repair appear to represent a promising damage-free repair technique for EUV masks with CrN buffer layers. The reflectivity loss on the multilayer film, caused by dry etching of CrN buffer layer with Cl<sub>2</sub> and O<sub>2</sub> mixed gases, was improved by an etching process under relatively high pressure. The CrN buffer layer can be etched for the patterns of 150-nm in width without footing at 50% overetch. The results confirm that the reflectivity losses on multilayer film are within 1% after undergoing the improved CrN buffer etching process.
A new att-PSM shifter for both F<sub>2</sub> and high-transmittance ArF lithography was developed. This shifter consists of SiON / TaHf in stacked layers. SiON for phase shift layer has a moderate transmittance and refractive index, and has sufficient laser durability. The TaHf film, which is a transmittance control layer, was effective as a functional layer in mask dry etching. Adopting the 3 step etching procedure, low damage of the quartz surface and less impact to CD shift was realized. It was confirmed that a new shifter has also sufficient feasibility to the mask inspection and repair process.
The halftone phase-shift mask (HtPSM) has been in practical use for i-line and KrF lithography. In ArF lithography, the HtPSM is also considered to be a promising resolution enhancement technique for its simple structure and fabrication process required. We in HOYA have attempted to expand the applicability of our MoSi-based HtPSM blank technology to ArF lithography, helping extend the life of the existing infrastructure for conventional HtPSM fabrication. We have completed tuning our new MoSi-based film for ArF application. The film’s optical properties, chemical durability and ArF laser irradiation durability meet industry requirements; and it is compatible with conventional mask-making processes and repair techniques for the KrF HtPSM.
The halftone phase-shift mask has been in practical use for i-line and KrF lithography. In ArF lithography, the HtPSM is also considered to be a promising resolution enhancement technique for its simple structure and fabrication process required. We in HOYA have attempted to expand the applicability of our MoSi-based HtPSM blank technology to ArF lithography, helping extend the life of the existing infrastructure for conventional HtPSM fabrication. We have completed tuning our new MoSi-based film for ArF application. The film's optical properties, chemical durability and ArF laser irradiation durability meet industry requirements; and it is compatible with conventional mask-making process and repair techniques for the KrF HtPSM.
The embedded attenuated phase-shift mask (EAPSM) has been in practical use for i-line and deep UV lithography. In 193 nm lithography, too, the EAPSM is considered to be a promising resolution enhancement technique for its simple structure and fabrication process required. We at HOYA have attempted to extend the applicability of MoSi-based EAPSM blanks to 193 nm lithography, helping extend the life of the existing infrastructure for conventional EAPSM fabrication. We have completed tuning our new MoSi-based film for 193 nm lithography and characterized its optical properties, chemical durability, ArF laser exposure durability and mask- making process compatibility.