Hideaki Mitsui

Improvement of total quality on EUV mask blanks toward volume production

Total quality on EUV mask blanks have to be improved toward future volume production. In this paper, progress in EUV blank development and improvement in flatness, bow and ML blank defects as critical issues on EUV blanks were reported. Steadily progress in flatness improvement was made in the past five years by improving polishing processes. A LTE substrate with a high flatness of 78 nm PV in 142 mm square area was achieved in average. Annealing process was developed to make small bow of less than 600 nm after ML coating. It was confirmed that annealed ML blank has stable performance in bow and centroid wavelength values through mask making process. Small bow of less than 300 nm was successfully demonstrated using annealing process and a CrN back side film with high compressive stress. Low defects of 0.05 defects/cm2 at 70 nm SiO2 sensitivity inspected by a Lasertec M1350 was demonstrated on a multilayer (ML) blank with a LTE substrate as best. Small defects over 50 nm in a M7360 were effectively reduced by improvement of polishing process consisting of local polish, touch polish and cleaning.

Development of attenuating PSM shifter for F2 and high-transmission ArF lithography

A new att-PSM shifter for both F2 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 ultimate chrome absorber in photomask making

193nm-immersion lithography is the most promising technology for 32nm-node device fabrication. A new Cr absorber (TFC) for 193-nm attenuated phase-shift blanks was developed to meet the photomask requirements without any additional process step, such as hardmask etching. TFC was introduced with a design concept of the vertical profile for shorter etching time, the over etching time reduction. As a result, the dry-etching time was dramatically improved by more than 20% shorter than the conventional Cr absorber (TF11) without any process changes. We confirmed that 150nm-resist thickness was possible by TFC. The 32nm technology-node requirement is fully supported by TFC with thinner CAR, such as resolution and CD performance.

Ion beam sputter-deposited SiN/TiN attenuating phase-shift photoblanks

Improving microprocessor speed, design and density are mainly determined by the minimum feature size that can be imaged on the wafer [1]. On the other hand, the latter is limited by the optics, the lithographic wavelength and the process used. Phase shift photomasks were introduced to extend the usefulness of any optical lithographic generation [2,3]. As smaller feature sizes are required by the IC industry, the use of phase shift masks is expected to increase for a specific stepper generation.

Development of halftone phase-shift blank and mask fabrication for ArF lithography

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 films 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.

Characteristics of Ta4B/SiC x-ray mask blanks

Stress controllability and stress distribution of Ta4B absorber on polished SiC films have been investigated. Dry etching behaviors of Cr and Si02 films have been characterized as etch-masking and etch-stopping materials. Xe gas sputtering was found to be effective to obtain higher stress controllability and more uniform stress distribution for Ta4B film compared to Ar gas sputtering. Cr film has been found to have high etching selectivity of more than 15 to the Ta4B film during the ECR etching with Cl2 gas, which is proven to be suitable for etch-masking and etch-stopping layers of the Ta4B absorber.

Advanced binary film for 193nm lithography extension to sub-32-nm node

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.

Hyper-thin resist system for photomask-making in double-patterning generation

Double-patterning generation at 32-nm node and beyond raises many subjects for photomask blanks. We especially focus on the resolution improvement by hyper-thin resist combined with the hardmask process called the hyper-thin resist system (HTRS). Cr-hardmask has been specially developed for the HTRS, and this Cr material shows an extremely high etching rate. Additionally, we confirmed that a 55-nm resist thickness was available to etch the Cr-hardmask and last then the resolution of MoSi-absorber patterns was improved by HTRS, such as 45-nm LS, 60-nm isolated line and hole, and 35-nm isolated space. Moreover, the Cr-hardmask showed almost no film stress, which is necessary to achieve the image placement accuracy required for the double patterning. MoSi-binary with HTRS meets the photomask technology requirements for 32-nm node and beyond.

Development of embedded attenuated phase-shifting mask (EAPSM) blanks for ArF lithography

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.

The art of photomask materials for low-k1-193nm lithography

The resolution of photomask patterns were improved with a hardmask (HM) system. The system which is thin Sicompounds layer is easily etched by the hyper-thin resist (below 100nm thickness). The HM material has sufficient etching selectivity against the chrome-compounds which is the second layer chrome absorber for the phase-shifter. This hardmask layer has been completely removed during the phase-shifter etching. It means that the conventional phase-shit mask (PSM) has been made with the ultimately high-resolution without configuration changes. Below 50nm resolution of PSM was made with 90nm thickness resist on HM layer in this paper. The CD bias between a resist feature CD and a chrome feature CD was almost zero (below 1nm) in the optimized etching condition. We confirmed that the mask performances were the equal to COMS (Cr-HM on MoSi binary mask) in resolution and CD linearity. The performances of hardmask blanks will be defined by resist performance because of almost zero bias.