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.
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.
Recently, extremely-high-quality-quartz substrates have been demanded for advancing ArF-lithography. HOYA has
developed a novel inspection method for interior defects as well as surface defects. The total internal reflection of the
substrate is employed to produce an ideal dark field illumination. The novel inspection method can detect a "nano-pit" of
12nm-EDS, the Equivalent of the Diameter of a Sphere (EDS). It will meet the sensitivity for 32nm node and beyond.
Moreover, a type of unique defect is detected, which induces Serious Transmittance Error for Arf-LiTHography. We call it
the "STEALTH" defect. It is a killer defect in wafer printing; but it cannot be detected with any conventional inspection in
the mask-making process so far.
In this paper, the performance of the novel inspection method for quartz substrates and the investigation of "STEALTH" are reported.
Hyper-NA lithography with polarized light illumination is introduced as the solution of 45nm or 32nm node
technology. In that case, consideration of new characteristics of masks and substrates has been required. One of these is
birefringence of quartz substrates. It has been said that birefringence of substrates affects printed CD on the wafer and is
required to control on the masks or substrates. Current birefringence measurement system requires some millimeters
windows if it measures on the masks. So, it is impossible to measure the birefringence on the entire field of the patterned
masks. And it is said that birefringence is caused by inside stress of the material. That of quartz substrate may be affected
by film stress, thermal effect during bake process or pressure of pellicle mounting.
In order to confirm birefringence variation during mask process, we measured the birefringence in between each mask
processes. We have prepared ultra low birefringence quartz substrates to check the small volume of birefringence change.
Number of measurements for each mask and each process was 11 X 11 = 121 locations which covers 126mm square on the
mask. 4mm square window for each measurement locations were opened at the mask process. It was enabled to measure
birefringence after mask process as well as before and after pellicle mounting. Substrate's birefringence is typically called
as a maximum birefringence value. We analyzed maximum birefringence change and calculated the shift of birefringence
for each process to confirm the effect of birefringence change for each processes.
The CD requirements for the 45nm-node will become tighter so as it will be difficult to achieve with 65nm node
technologies. In this paper, a method to improve resolution by using DRECE (Dry-etching Resistance Enhancement
bottom-Coating for Eb) will be described. After all, DRECE has five times as high dry-etch resistance than the EB resist,
and this enables to accept higher anisotropic dry etching condition. By optimizing dry etching conditions, the CD
iso-dense bias dropped to 1/3 and the CD shift was reduced to 1/2. Also, there was no negative effect to CD uniformity.
From these results, we propose the use of DRECE for the 45nm-node technology.
To control the CD precisely, inorganic "Hard-Mask" which we expect one of the candidates for 45nm-node and beyond
technology was evaluated. Hard-Mask which is inserted between resist and Cr layer of a photomask blank enable us to
use high anisotropic etch condition. Also it enhances the resist resolution because it can avoid the interaction between
resist and Cr. This time, we confirmed the benefit of Hard-Mask which could reduce the etch bias and proximity process
error. Especially proximity process error was reduced down to 1/4. And resolution enhancement effect was observed. We
also confirmed the blank quality such as defects, film stress, sheet resistance, optical properties and so on, and found that
Hard-Mask blank would not be a showstopper for this development.
The mask-making process for 45nm-node and beyond demands higher resolution and CD accuracy. To meet the requirements, the multi-layer resist system is developed as one of the solutions. BIL (Bottom Insulating Layer) can correct the profile of CAR (Chemically Amplified Resist). CAR shows profile degradation by photo-acid loss at the boundary of chrome and resist. The photo-acid loss induces excess footing in positive-tone CAR and under-cutting in negative-tone CAR. BIL reduced the profile degradation to less than half of the conventional resist system. BIL requires no extra mask process steps. Final CD linearity of isolated lines was improved by BIL. It is very beneficial for the patterning of sub-resolution assist features. Moreover, BIL with a hard-mask layer showed superior dry-etching bias performance.
In the field, each customer uses their owned designed reticle case as for shipping, storage. To modify the case is so expensive that it is very difficult to improve, especially in time respect. At the blank suppliers, they ship their mask blanks packing into their owned designed multiple shipper, however the market needs single shipper with next generation blanks to prevent from particle and outgas of case material damage. At the mask shops, most of them use MP567 (Trade mark of Dainichi Shoji K.K.) single case which was designed about 15years ago to ship their products to their customers. It is not designed for robot handling, so contamination from manual handling makes reticle damaged. Adhesive tape is also required to seal it, so chemical contamination will be occurred on quartz glass, i.e. haze. At the IC fabs, scanner case such as Nikon, Canon and ASML case is the most common in their process. However these cases are not airtight, so they cannot be handled under class 10000 circumstances. RSP (Reticle SMIF Pod) has a capability of automatic transportation, however it is not airtight case. We develop new mask case named Universal Reticle Pod (URP) at affordable price, airtight and chemical tight so as to be used as shipping, storage and process case. We evaluate it as blanks shipping case, so we would like to report its results.
For advanced reticle fabrication, a resist thinning technique continues a promising trend of the resolution enhancement. To bring out thin resist performances, a new chrome absorber has been developed for the second layer of 193nm att-PSM. The new chrome absorber is thinner and has a higher dry-etch rate than our current products, such as NTAR5. This new chrome absorber can utilize a super thin resist application because of a reduction in dry-etching time. Additionally, a technique of film stress reduction was also developed to reduce placement shift by film stress relaxation. The new chrome absorber with super thin resist (TF blanks) exceeds current products in the mask-making metrics of resolution and CD performance. This performance will meet the requirements of 65nm-node and beyond.
DUV (Deep Ultra-Violet) laser reticle writers were released to the market for advanced reticle fabrication in 2002, AZ-DX1100P resist (for KrF lithography) has historically been employed for these tools. To respond to further high-end requirements, a new resist more friendly to DUV reticle fabrication is needed. FEP171 is a positive-type CAR (Chemically amplified resist) developed for EB reticle fabrication, which is sensitive to DUV as well. In this paper, we have investigated the applicability of FEP171-coated blanks for DUV reticle fabrication. As the results show, FEP171 could achieve 200 nm patterns by DUV exposure. FEP171 blanks showed superior performance in resolution and profile as compared to AZ-DX1100P. FEP171 blanks are promising for DUV reticle fabrication as well as EB reticle fabrication.
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 advanced photomask dry etching system using neutral loop discharge (NLD) has been thought as a promising candidate for the next generation technology, because the NLD plasma has a capability to control the plasma distribution and density. In previous work, we improved CD uniformity for 130nm node technology using the neutral loop modulation etching technique. However, 100nm node lithography requires tighter specification, thus we set a target to achieve CD accuracy of 6nm (3 sigma) by improving CD uniformity and loading effect of the NLD dry etching system. First, we changed the system configuration: exhaust place, reactor size, and electrode shape. Especially, by optimizing the antenna configuration, we improved the unevenly distributed plasma. Additionally, we introduced a new etching technique to reduce CD shift from resist profiles by enhancing Cr/Resist sensitivity. Consequently, the NLD dry etching system for 100nm node technology was confirmed the effectiveness to improve CD performance using the above techniques.
The dry etching process by using NLD (Neutral Loop Discharge Plasma) has been evaluated. The loading effect was measured applying the CAR (Chemically Amplified Resist) negative resist process in the low pressure etching condition, where an excellent CD (Critical Dimension) uniformity was obtained.
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.
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.
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.
Embedded phase-shift mask (EPSM) has an advantage in comparison with several other phase-shifting mask approaches because of its simple structure and fabrication process. We tried to modify MoSi-based EPSM blanks by re-examining the material and by optimizing sputtering condition in order to produce more useful EPSM blanks for Deep UV lithography technology. New MoSi-based EPSM blanks for which Nitrogen gas is used as the reactive sputtering gas has been developed. And it has been confirmed that the New MoSi-based EPSM (MoSi-N) blanks are superior to HOYA previously developed one (MoSi-ON) in chemical durability, manufacturing stability and Dry Etching property.
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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