EUV lithography is the most promising technology for semiconductor device manufacturing of the 10nm node and
beyond. The image border is a pattern free dark area around the die on the photomask serving as transition area between
the parts of the mask that is shielded from the exposure light by the Reticle Masking (REMA) blades and the die. When
printing a die at dense spacing on an EUV scanner, the reflection from the image border overlaps edges of neighboring
dies, affecting CD and contrast in this area. This is related to the fact that EUV absorber stack reflects 1-3% of actinic
EUV light. To reduce this effect several types of image border with reduced EUV reflectance (<0.05%) have been
proposed; such an image border is referred to as a black border. In particular, an etched multilayer type black border was
developed; it was demonstrated that CD impact at the edge of a die is strongly reduced with this type of the black border
(BB). However, wafer printing result still showed some CD change in the die influenced by the black border reflection. It
was proven that the CD shift was caused by DUV Out of Band (OOB) light from the EUV light source. New types of a
multilayer etched BB were evaluated and showed a good potential for DUV light suppression.
In this study, a novel BB called ‘Hybrid Black Border’ (HBB) has been developed to eliminate EUV and DUV OOB
light reflection by applying optical design technique and special micro-fabrication technique. A new test mask with HBB
is fabricated without any degradation of mask quality according to the result of CD performance in the main pattern,
defectivity and cleaning durability. The imaging performance for N10 imaging structures is demonstrated on
NXE:3300B in collaboration with ASML. This result is compared to the imaging results obtained for a mask with the
earlier developed BB, and HBB has achieved ~3x improvement; less than 0.2 nm CD changes are observed in the
corners of the die. A CD uniformity budget including impact of OOB light in the die edge area is evaluated which shows
that the OOB impact from HBB becomes comparable with other CDU contributors in this area. Finally, we state that
HBB is a promising technology allowing for CD control at die edges.
EUV lithography is the most promising technology for semiconductor device manufacturing of the 10nm node and beyond. The EUV mask is a key element in the lithographic scanner optical path. The image border is a pattern free dark area around the die on the photomask serving as transition area between the parts of the mask that is shielded from the exposure light by the Reticle Masking (REMA) blades and the die. When printing a die at dense spacing on an EUV scanner, the EUV light reflection from the image border overlaps edges of neighboring dies, affecting CD and contrast in this area. To reduce this effect an etched multilayer type black border was developed, and it was demonstrated that CD impact at the edge of a die is strongly reduced with this type of the black border (BB). However, wafer printing result still showed some CD change influenced by the black border reflection. It was proven that the CD shift was caused by DUV Out of Band (OOB) light which is emitted from EUV light source. New types of a multilayer etched BB were evaluated and showed a good potential for DUV light suppression. In this study, a novel black border called Hybrid Black Border has been developed which allows to eliminate EUV and DUV OOB light reflection. Direct measurements of OOB light from HBB and Normal BB are performed on NXE:3300B ASML EUV scanner; it is shown that HBB OOB reflection is 3x lower than that of Normal BB. Finally, we state that HBB is a promising technology allowing for CD control at die edges.
In the semiconductor technology using the 193nm ArF excimer laser, the problem of radiation damage on photomask
becomes more serious. This phenomenon is regarded as serious issue for semiconductor device fabrication. Some
approaches have been tried to prevent the radiation damage. One of reports indicates that the radiation damage can be
reduced by using an exposure tool with ultra clean extreme dry air [1]. However, it is difficult to adopt dry air into all
exposure tools due to high cost. In our previous work, two facts were ascertained; radiation damage is caused by MoSi
film oxidation, and depends on MoSi film composition [2]. In this paper, radiation damage was tried to decrease by
MoSi film modification of att. PSM. MoSi film composition for PSM is optimized in consideration of cleaning durability,
mask defect repair and processability. The new PSM is named AID (Anti Irradiation Damage). Radiation damage of AID
PSM can be improved by 40[%] from conventional PSM. Cleaning durability can be also improved by AID PSM. The
other evaluation items such as CD performance, cross section, defect level and repair, are equal between the AID PSM
and conventional one. Additionally, the lithography performances by simulation of AID PSM are equivalent with that of
conventional PSM. Therefore, it can be expected that there is no difficulty in converting conventional PSM into AID
PSM. From these evaluation results, development of AID PSM was completed, and preparation for production is now
going.
The exposure tools have been advanced for finer patterns and higher throughput. However, it causes the increase of accumulation
of exposure dose on mask, which induces the mask CD growth. This issue has been reported as the radiation damage and
brought the low yield of device chips [1, 2, 3]. As the solution, the radiation damage can be reduced by the ultra extreme
dry air in exposure tool [4]. It is difficult to adopt dry air to all exposure tool due to cost. In this work, we tried to solve
the radiation damage from photomask making approach. The attenuated phase-shift mask (att. PSM) was chosen for this
evaluation because its damage is severest. The test plates of att. PSM were exposed by ArF laser, and the amount of CD
degradation and the composition change in damage area were investigated. By the analyses of TEM and EDX, it was
confirmed that the root cause of radiation damage is oxidation of MoSi film. Therefore, the approaches from mask
process and material were tried to prevent MoSi film from oxidation. As a result, the approach from mask material,
especially modification of MoSi film is effective. And the characteristics of new MoSi film, such as CD performances,
cross section, and cleaning durability, were compared with conventional att. PSM. These results show the characteristics
of two masks are equivalent. Att. PSM with new MoSi film is promising solution to improve radiation damage.
The miniaturization of pattern size on photomask is advanced year by year. It becomes more important to improve Line
Edge Roughness (LER) and resolution because of their impacts on lithography performances. When miniaturization is
advanced, high sensitivity inspection is also indispensable. Therefore, LER becomes the key factor to reduce the
nuisance defect for high sensitivity mask inspection. Basically, LER originates from resist materials and EB writer. If
resist pattern LER is good, final pattern LER can be good too. One of the easiest solutions for LER is using thick resist.
Thick resist can vertically smooth down the LER. However, it deteriorates resolution due to the high aspect-ratio.
Another solution for LER is using low sensitivity resist. Low sensitivity resist needs many electron exposures by EB
writer. Therefore, electronic density of EB pattern increases and pattern edge becomes clear. However, it deteriorates
throughput, which is essential to production. Only by mask resist, it is difficult to satisfy all items, that is mask LER,
resolution and throughput.
In this study, the improvement of LER without deterioration of resolution is tried by dry etching process. It is found that
remaining resist after Cr etching has its limitation for mask LER. And Cr over etching and source power of Cr and MoSi
etching are effective factors for mask LER. On the basis of these results, the optimal etching process is determined. It is
confirmed that mask LER can be improved without deterioration of resolution by the optimal etching process.
For 45nm and 32nm node technology, the challenges for resolution and CD control of mask patterns become the steeper
mountain path. Especially, Sub Resolution Assist Feature (SRAF) is the smallest pattern on mask and amplifies the
difficulty of mask fabrication. In order to improve the resolution of fine patterns, the influence of wet processing cannot
be neglected, because it causes the pattern collapsing. Wet processing of mask-making can be divided into resist
development and cleaning.
In this study, the root causes of pattern collapsing are investigated at each wet processing. It is confirmed that thin resist
can enhance the resolution limit of resist pattern and hard-mask blank, such as OMOG: Opaque MoSi On Glass, is
suitable for thinner resist under 1500A. The pattern collapsing of OMOG is compared with that of Att.PSM at the
cleaning before and after Cr stripping. Mask inspection finds that pattern collapsing can be suppressed by OMOG at both
cleanings. It is because OMOG has lower cleaning stress than Att.PSM due to lower aspect-ratio. This benefit is
demonstrated by cleaning stress simulation. Additionally, it is found that the SRAF size of OMOG can be wider than
Att.PSM by optical simulation. From these results, OMOG has much advantage of fine pattern fabrication and is the
optimal blank for 32nm node and beyond.
Current flash memory technology is facing more and more challenges for 45nm and 32nm node technology. To get good
CD and yield control, optimized RET, OPC modeling and DFM techniques have to be applied [1]. To enhance process
window (PW) and better CD control for main features, assist features (SB) have to be used. Simulation and wafer
evaluation show that the SB CD performance is very critical. Based on OPC simulation, we can get a very good
prediction about the CD size and placement of assist features. However, we can not always get what we want from mask
suppliers. For 45nm node technology and beyond, The SB CD size (~ 20nm at 1X) has almost pushed to the current
mask process limit. Wafer fabs have a very big concern about the stability of linearity signatures from different
suppliers and different products in order to keep high accuracy of OPC models. Actually the CD linearity signature
varies from one mask supplier to another and also varies from product to product. To improve the SB CD control, the
ideal goal is to make "flat" linearity for all mask suppliers. By working closely with TPI mask supplier, we come up
solutions to improve SB CD control to get "flat" linearity. Also technology development is causing more severe SB
printability, we proposed a methodology to use AIMS for predicting SB printability. Wafer results proved the feasibility
for these methodologies.
The development of semiconductor process for 32nm node is in progress. Immersion lithography has been introduced as
an extension of 193nm lithograpy. In addition, DPL (Double patterning lithography) is becoming a strong candidate of
next generation lithography. The extension of optical lithography increases more mask complexity and tighter
specification of photomasks.
CD performance is the most important issue in the advanced photomask technology. However, it is expected that
conventional mask cannot satisfy the required mask specifications for 32nm node and beyond. Most of CD errors are
contributed to the dry etching process. Mask CD variation is greatly influenced by the loading effect from dry etching of
the absorber.
As the required accuracy of the mask arises, Cr absorber thickness has been gradually thinner. CD linearity with the
thinner Cr absorber thickness has better performance. However, it is difficult to apply thinner Cr absorber thickness
simply under the condition of OD > 3, which is needed for wafer printing. So, we adopted MoSi absorber instead of
conventional Cr absorber, because MoSi absorber has less micro and global loading effect than that of Cr absorber. By
using MoSi absorber, we can reduce Cr thickness as a hardmask. The thinner Cr hardmask allows for reduce resist
thickness and become same condition for conventional EB resist lithography.
The lithography performances were confirmed by the simulation and wafer printing. The new MoSi absorber mask
behaves similar to the conventional Cr absorber mask.
The adoption of super thin Cr as a hardmask made it possible to reduce resist thickness. By the application of the thin
resist and the latest tools, we'll improve the mask performance to meet the 32 nm generation specification.
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.
The attenuated phase-shift mask (att. PSM) is one of resolution enhancement technologies (RET) and has been
widely adopted for several device layers. And the high-transmission att. PSM, which has various structures and
transmittances, can be expected to have the advantages in process window. In this paper, the lithographic performances
(Contrast, MEEF and DOF) of high-T att. PSM were evaluated by using the 3D electro-magnetic field simulator. The
results showed that high-T att. PSM has better MEEF and partially better DOF than those of 6%-transmission MoSi
type. As the transmittance is getting higher, the smaller line CD is needed for OPC adjustment especially at narrow
pitch. In respect of film structure, it is found that there is no large difference among three high-T att. PSMs except for
MEEF at specific pitch. Remaining chrome on the high-T films causes the trade-off between contrast and MEEF. The
simulation results are compared with AIMS results measured by AIMSTM 45-193i of Carl Zeiss. The AIMS results of
actual masks agree with no-Hopkins mode simulation very well, while they do not agree with Hopkins mode simulation
especially at narrow pitch. Because the azimuthal polarization does not cause contrast loss, the differences between
AIMS mode (conventional) and Scanner mode (vector effect emulation) are small.
Three types of high transmission attenuated phase shift masks were evaluated. The attenuating materials were obtained from commercial and non-commercial sources. Various key performance metrics were investigated. Blanket film transmission and reflection was measured at various wavelengths. Laser durability and cleaning durability were
measured. Standard dry etch processes were used for each film and the profile and surface properties were compared. Final mask transmission and phase were also measured. The summarized results show clear benefits of using some high transmission materials relative to others.
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.
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.
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.
We have investigated new materials for 157nm attenuated phase-shifting mask (Att-PSM). The structure of the Att-PSM is based on the bi-layer film in which a transparent film (TF) is deposited on an absorptive film (AF) on quartz substrate. We evaluated the optical property and the durability against F2 laser irradiation for 157nm Att-PSM materials, for which we prepared the modified ZrSixOy films and SiOx film as a TF and the Cr film and the modified ZrSixOy films as an AF. For a TF, the SiOx and modified ZrSixOy films achieve high transparency and robust durability against F2 laser light. For an AF, the Cr film achieves robust irradiation durability. Furthermore, we investigated the feasibility of defect inspection in consideration of the various combinations of TF and AF. From the calculation of the transmittance at inspection wavelength (193nm and 248nm), it is expected that the defect inspection is feasible in the combination of the SiOx or ZrSixOy transparent films with any absorptive film.
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.
We propose zirconium silicon oxide (ZrSiO) film as a powerful candidate for attenuated phase-shift mask (Att-PSM) materials. A bi-layer structure of this material with an absorptive film (AF) and a transparent film (TF) can effectively control the transmittance and phase. We confirmed the durability of the ZrSiO film in ArF laser irradiation. The lifetime with the change in transmittance and phase after irradiation at 30 kJ(DOT)cm-2 is equivalent to a total dose of 3 years in future ArF exposure systems. We investigated the resolution performance of the Att-PSM with ZrSiO film for a 130 nm pattern. The depth of focus with the Att-PSM was larger than that of the binary mask. Therefore, an Att-PSM with ZrSiO is promising for developing a 130-nm-technology node with ArF lithography. Controllability of the critical dimension on the wafer is discussed from the viewpoint of the mask error factor (MEF).
This paper reports optimization of Zirconium-Silicon-Oxide (ZrSiO) films for attenuated phase shift mask (Att.PSM) concerning Zr/Si compound ratio. ZrSiO films were deposited by RF magnetron co-sputtering in Ar mixed with O2 gas using separated dual cathode of Zr and Si. Researched were the relationships between chemical durabilities, optical property, and Zr/Si compound ratio determined with XPS analysis. As a result, it was confirmed that controllability of optical property, chemical durabilities, and spectroscopic property would be improved by optimizing Zr/Si compound ratio. Consequently, by composing appropriate optical constants and thickness of bi-layer ZrSiO films, various transmitting Att.PSM can be obtained.
An aptitude for attenuated phase shift mask (AttPSM) blank of zirconium silicon oxide (ZrSiO) films for excimer laser lithography use was evaluated. ZrSiO films were deposited by dc or rf sputtering in Ar mixed with 02 gas using ZrSi2 target. Since optical constants of ZrSiO films vary with sputtering parameters, their bi-layer structures can fulfill optical quality required AttPSM. They have high durability to heating conc. H2SO4 independent of their optical constants. Internal stress varies from initial compression to tensile side by annealing to obtain conveniently a low stressed blank. Sheet resistance and surface roughness are sufficiently small to fabricate AttPSM pattern including sub- micron features. They are etched by chlorine-based gases, resulting in high dry etch selectivity to quartz substrate. Although they are expected to have potential in durability to excimer laser, it should be evaluated under the conditions similar to exposure system.
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