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.
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.
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.
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.
193nm-immersion lithography is the most promising technology for 32nm-node device fabrication. At the 32nm
technology-node, the performance of photomasks, not only phase-shift masks but also binary masks, needs to be improved,
especially in "resolution" and "CD accuracy". To meet sub-100nm resolution with high precision, further thinning of resist
thickness will be needed.
To improve CD performance, we have designed a new Cr-on-glass (COG) blank for binary applications, having OD-3
at 193nm. This simple Cr structure can obtain superior performance with the conventional mask-making process. Since the
hardmask concept is one of the alternative solutions, we have also designed a multilayered binary blank.
The new COG blank (NTARC) was fully dry-etched with over 25% shorter etching time than NTAR7, which is a
conventional COG blank. Thinner resist (up to 200nm) was possible for NTARC. NTARC with 200nm-thick resist showed
superior resolution and CD linearity in all pattern categories.
On the other hand, the multilayered binary stack gives us a wide etching margin for several etching steps. Super thin
resist (up to 100nm) was suitable by using a Cr-hardmask on a MoSi-absorber structure (COMS). The COMS blanks
showed superior performance, especially in tiny clear patterns, such as the isolated hole pattern.
We confirmed that these new photomask blanks, NTARC and COMS, will meet the requirements for 32nm-node and
beyond, for all aspects of mask-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.
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 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.
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.
The introduction of 193-nm lithography is expected to provide a one-generation improvement in lithographic imaging capability. This will only happen if all of the enhancements presently being used for 248-nm lithography are also available at 193 nm. Attenuating phase shift materials have been developed by a few mask vendors for use at 193 nm. A molybdenum silicide phase shifting absorber has been developed by Hoya and evaluated by IBM and Hoya. Transmission and phase uniformity have been evaluated, and the contribution to these values from film thickness and etch variations have been identified. Plate-to-plate uniformity of phase and transmission have been measured. Durability of the film has been tested against 193-nm radiation exposure and chemical cleaning methods. Defect levels have been measured in the unprocessed film and the finished mask. The inspectability of masks made with this material has been evaluated on commercial inspection systems. The 193-nm molybdenum silicide film is compatible with etch and repair processes developed for 248-nm molybdenum silicide mask absorbers. The 193-nm molybdenum silicide film has a transmission of 6%, which is suitable for most attenuating phase shift applications. The film may be extendable to higher transmission values.
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.
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.
A novel material system of W/Si film which consisted of W, Si and their oxides has been developed for the single-layered attenuated phase- shifter (SAttPS) for the KrF excimer laser lithography. The W/Si film was deposited on quartz substrate by an RF sputtering, using WSi2 as a target and Ar and O2 mixtures as sputtering gases. The W/Si film has been shown to have excellent properties for the SAttPS such as controllability of the optical transmittance, electric conductivity, chemical durability and adequate adhesion to quartz substrate, in the same way as the film for i-line lithography previously reported. As- deposited W/Si film with the thickness of 975 angstrom and the transmittance of 7.1% at 248 nm showed no changes in the refractive index and some changes in the extinction coefficient after the KrF excimer laser irradiation up to 200 kJ/cm2. Annealing at 350 degree(s)C for 60 min under atmospheric He environment, however, let to no degradation in the extinction coefficient after the laser irradiation. The annealed W/Si film is expected to be a promising material of the KrF SAttPS.
A novel material system of metal W corpuscles dispersed in silicon dioxides layer (W/Si film) has been developed for the single-layered attenuated phase-shifting mask (SAttPSM) for i-line. The W/Si film has been proved to have a wide flexibility in designing the optical transmittance and the film thickness by changing the sputtering conditions such as the O2 ratio to the sputtering gas (O2 and Ar) flow rate and the RF power supplied. The W/Si shifter film are also found to have some electric conductivity, which again depends on the sputtering conditions, tough chemical durability against both hard acid and basic solutions, and sufficient adhesion to quartz substrate SAttPSM, fabricated with the W/Si film and having the thickness of 1575 angstroms and the transmittance of 6.3%, showed the phase-shifting angle of 177.9 at i-line wavelength. The depth of focus around 0.35 micrometers hole pattern was widened from 0.6 micrometers to 1.4 micrometers .
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