As the design rule of the semiconductor shrinks, the CD MTT (Critical Dimension Mean-to-Target) specification for photomask becomes tighter. So, more precise control of CD MTT is required. We have investigated the CD MTT control and applied it to the attenuated PSM (Phase Shift Mask) successfully for several years. We can control the CD MTT of MoSi pattern by measuring Cr/MoSi pattern to estimate MoSi pattern CD and additional etch to shrink MoSi pattern as reported in previous study. At first, the MoSi pattern CD can be estimated with the Cr/MoSi pattern CD because the CD gap between MoSi pattern and Cr/MoSi pattern is relatively constant. Additional MoSi etch is performed to shrink the MoSi pattern CD after then. The CD gap alwasys exists and the variation of the CD gap is enough small to be not considered in conventional photomask production until now. However, the variation of the CD gap is not ignorable in case of sub-20 nm tech.
In this study, we investigated new method to measure MoSi pattern CD before Cr strip process to eliminate the CD gap between MoSi pattern and Cr/MoSi pattern. To eliminate the CD gap, we attempt three solutions – 1) Optimize etch process to perform perfect Cr/MoSi pattern profile without the CD gap, 2) Improve CD measurement accuracy by developing new SEM measuring mechanism, 3) Develop of new process to modify Cr/MoSi pattern profile to be measured without the CD gap. It was found that the CD gap can be eliminated and MoSi pattern CD can be measured perfectly. Finally, MoSi pattern CD control was improved because of CD gap elimination.
EUV (Extreme Ultraviolet) Lithography has been delayed caused by several technical problems such as
EUV mask, source power and etc. So ArF immersion lithography has been continued with adopting new
technology. Especially, the wafer lithography tends to increase rapidly NTD(Negative Tone Develop) process
for overcoming high resolution such as small hole type patterns. For wafer NTD process, the pattern shape in
mask has changed from hole pattern to dot pattern. Also the local CD uniformity of aerial image is getting
more important. In this paper, we studied local CD uniformity with analyzing aerial images of high
transmittance HT-PSM (attenuated phase-shift mask) and conventional 6% HT-PSM from AIMS (Aerial Image
Measurement System) tool. Additionally, several cell sizes were analyzed to find an optimum target cell size
which has good wafer performance and AIMS aerial image. And we analyzed NILS(Normalized Image Log
Slope) factor which represent wafer photolithographic performance. Furthermore, we analyzed not only AIMS
NILS simulation, but also wafer lithographic performance.
As the device design rule shrinks, photomask manufacturers need to have advanced defect controllability during the
ARC (Anti-Reflection Coating) and ABS (Absorber) etch in an EUV (extreme ultraviolet) mask. Therefore we studied
etching techniques of EUV absorber film to find out the evasion method of particle generation. Usually, Particles are
generated by plasma ignition step in etching process. When we use the standard etching process, ARC and ABS films are
etched step by step. To reduce the particle generation, the number of ignition steps need to decrease. In this paper, we
present the experimental results of in-situ EUV dry etching process technique for ARC and ABS, which reduces the
defect level significantly. Analysis tools used for this study are as follows; TEM (for cross-sectional inspection) , SEM
(for in-line monitoring ) and OES (for checking optical emission spectrum)
During EUV exposure, more frequent mask cleaning is essential for removing not only particles from lack
of pellicle but also the carbon contamination due to accumulative EUV exposure. Because of this reason,
process improvement for minimize corrosion and etching of the Ru capping layer is urgently needed. In this
work, the influence of TaBN absorber etch condition on Ru integrity followed by repetitive cleaning was
evaluated and the effects on long-term durability of Ru are compared under various cleaning conditions.
Consequently, it was shown that Ru durability was strongly influenced by the gas contents and over etch time
of absorber dry etch, not only as a function of cleaning conditions.
As technical advances continue, the pattern size of semiconductor circuit has been shrunk. So the field of the photomask needs the processing more strictly. It is critical to the photomask which contained considerably shrank circuit and ultra high density pattern for sub-20 nm tech device, although a small defect is negligible in the conventional process. Even if some defect can be repaired, it is not satisfied with a strict pattern specification. Stricter fabrication process and pattern specification increase the manufacture cost. Furthermore, EUV photomask manufacture cost is several times expensive than the conventional photomask. Therefore the effort to decrease defects is important for the photomask fabrication process. In addition, when defects are generated, it is obviously important that the repaired patterns have better pattern reliability. In this paper, we studied about advanced processes that control and remove hard defects minutely .on ArF attenuated phase-shift mask. This study was accomplished for 4 areas. First of all, we developed advanced Mosi etch process. Defects are generated under this etch process are not fatal. The thickness of hard defects were controlled thinner under this etch process compared with conventional etch process. Secondly, we studied cleaning process that has good performance on Cr : MoSi surface and a poor hydrophilic contrast to control side effect by etch process. Thirdly, we made inspection technique for detecting thin thickness hard defects. Lastly, we researched a repair technology that is effective in hard defects of thin thickness. The performance of the repaired pattern was verified by AIMS. In this study, it is researched that control shape, properties of defects to prepare a reliable repair and improved repaired photomask pattern reliability by 30% over.
In this study, the method to achieve the precise CD MTT (critical dimension mean to target) correction in
manufacturing attenuated PSM (phase-shift mask) is investigated. There has been a growing demand for
more precise Mask CD MTT control in recent years. The CD correction method has been developed and
applied to meet the tighter CD MTT specification . However, the efficiency of the CD correction is greatly
affected by the repeatability of the CD measurement. The factors, which can have an influence on the CD
measurement, are the fluctuations of the pattern profile and the electron current of the SEM.
The conventional CD MTT correction method is basically to correct MoSi CD MTT by applying the
additional dry etch for MoSi based on Cr CD value. Therefore, the repeatability of the Cr CD MTT is the
crucial point for the accuracy of the final CD MTT correction. Although the Cr CD MTT is the crucial factor for
the successful CD MTT correction, it has the fluctuation due to the Cr pattern profile. If the Cr pattern profile
has low patterned angle after MoSi etch process, it can cause the focusing error in the CD measurement
using CD SEM. Therefore, a method to improve the reliability of the Cr CD MTT should be developed.
The IS and the normalized Delta CD concepts are adopted to obtain more reliable Cr CD MTT. The IS
refer the variation of the Cr CD MTT according to the difference in CD values with CD measuring thresholds.
The normalized Delta CD is obtained from the correlation of IS and Delta CD. Finally, the normalized Delta CD
is applied to correct the MoSi CD MTT by dry etch process.
The reduction of the Cr CD MTT fluctuation range is achieved by using the new CD correlation process
including IS and the normalized Delta CD. Consequently, the final MoSi CD MTT is improved 60% of range by
using the new CD correlation process.
As the feature size is smaller, the overlay budget of lithography for the rigorous manufacturing control becomes so small.
And, overlay accuracy has become more important due to small overlap margin and double patterning process. Recently,
a scanner maker has developed several effective solutions to correct the errors of overlay in field. But, the error induced
by photomask still remains, so the accuracy of photomask image placement is required below than several nm for the HP
3X nm memory device generation. But, current e-beam writers don't meet this specification. There are various sources of
image placement errors. Many papers report their analysis of those errors, so we focus on e-beam charging effect and
compensation. Especially, their compensating methods are too complex to apply to production. So, it is need a simple
way to compensate to image placement errors effectively.
We have investigated self-aligned resist patterning for a patterning accuracy of photo mask. Self-aligned resist
pattern can be formed by backside flood exposure on photo-mask. It had been already proved by the experiments with
248 nm light source exposure on binary (Cr on Quartz) and KrF attenuated phase shift masks. Attenuated phase shift
masks are generally composed of Cr/MoSiN/Quartz, MoSiN/Quartz, and Quartz layers. MoSiN layers of attenuated
phase shift mask have the optical property of 6% transmittance at 248 nm light source, and the interference of the 6%-
transmitted light makes the undesirable resist pattern profile on MoSiN-Quartz boundary. This paper shows the fresh
possibility of the self-aligned resist pattern fabrication on attenuated phase shift masks using backside flood exposure. To
solve the optical property of MoSiN layer, self-aligned resist patterns of KrF attenuated phase shift mask was fabricated
using 193 nm wavelength backside flood exposure and ArF attenuated phase shift mask used 172 nm wavelength. The
shorter wavelength than generally applied wavelength could minimize transmittance on MoSiN area. Besides we used
Negative PR to make the self-aligned resist pattern on exposed regions. These experimental concepts help to form the
selective PR patterning on only quartz regions of attenuated phase shift mask.
As the design rule of the semiconductor circuit shrinks, the specification for photomask becomes tighter. So, more
precise control of CD MTT (Critical Dimension Mean to Target) is required. We investigated the CD MTT control of the
attenuated PSM (Phase Shift Mask) by additional Cr dry etch. In conventional process, it is difficult to control CD MTT
precisely because about 5 factors - Blank Mask, E-beam writing, Resist develop, Cr dry etch, MoSiN dry etch - affect
CD MTT error. We designed the new process to control CD MTT precisely. The basic concept of the new process is to
reduce the number of factors which affect the CD MTT error. To correct CD MTT error in the new process, we
measured CD before MoSiN dry etch, and then additional corrective Cr dry etch and MoSiN dry etch was performed. So,
the factors affecting CD MTT error are reduced to 2 steps, which is additional corrective Cr dry etch and MoSiN dry
etch. The reliability of CD measurement before MoSiN dry etch was evaluated. The generable side-effect of the
additional corrective Cr dry etch was analyzed. The relationship between 'CD shift' and 'additional corrective Cr dry
etch time' was found for various patterns. As a result, accurate CD MTT control and significant decrease of CD MTT
error for attenuated PSM is achieved.
In this study, the method for achieving precise CD MTT (critical dimension mean to target) in manufacturing attenuated PSM (phase shift mask) was investigated. As the specification for photomask becomes tighter, more precise control of CD is required. There are several causes to result in CD MTT error. In general mask patterning processes which are from blank material to dry etch, it is difficult to detect CD MTT error before final CD measurement and correct it. It is necessary to apply new process to mask production to correct CD error and control CD MTT precisely. Reducing number of factors which can have an effect on CD and introducing reliable method to correct CD error are important to achieve accurate CD MTT. For the correction of CD error, the reliability of CD in each measurement step such as resist CD or Cr CD before and after resist removal and effect on items related with CD like CD uniformity, isolated-dense CD difference, etc should be considered and evaluated. In this method to correct CD MTT error, Cr CD after removing resist was measured before MoSiN dry etch and additional corrective Cr dry etch using Cr CD information was applied to cancel CD error and then MoSiN dry etch was followed. In this case, factors affecting final CD are additional corrective Cr etch and MoSiN etch. The relationship between CD shift and corrective Cr etch time for masks with various pattern densities was found and necessary corrective Cr etch time was applied to CD correction process. The CD MTT error is canceled by additional corrective Cr dry etch step. As a result, accurate CD control and significant decrease of CD MTT error for attenuated PSM is achieved through the use of this CD correction method.
As a minimum pattern size on photomask decreases, a patterning accuracy is very important. Especially pattern repair
needs the perfect positioning accuracy. But the positioning accuracy of equipment stage has its limit and therefore cannot
meet a required accuracy. We can form the resist patterns with no positioning error on Cr or MoSiN patterns of
photomask. We named this process 'the self-aligned resist patterning' and investigated the various patterning
performance. In this process, a photoresist is coated on Cr/MoSiN pattern side and the photomask is exposed to KrF light
on a backside and is developed. The principle of this self-aligned resist patterning is the difference between the
transmittances of Cr and quartz. This self-aligned resist patterning can form the resist patterns on sub-patterns of Cr or
MoSiN which had been formed on photomask. First of all, the alignment accuracy of this process is perfect and the
alignment error is zero.
ZEP is a field-proven stable E-Beam resist for photo-mask manufacturing. The spin-spray develop method has been widely used for ZEP resist processing. Recently, we have successfully adopted the spin-stream develop process for ZEP resist by using modified TEL MARK-8 wafer process track. This paper presents a comparison result of CD uniformity between the conventional spin-spray method and new spin-stream method on 6-inch production halftone phase shift masks. In this process, we apply low temperature(18 deg. C) develop solution in room temperature ambient. The spin-stream process with low temperature solution is found to be a suitable recipe for high-end phase shift mask manufacturing with under 10 nm CD uniformity (3sigma) in 120mm X 120mm area. Moreover, the modified MARK-8 track can provide both of a FEP and a ZEP process module in one unit, and this advantage reduces the cost of ownership for a high-end mask manufacturing facility.
CD control of FEP-171 is difficult due to abnormal CD variation in single puddle development. Fogging analysis patterns show that space CD in large open region is smaller than that in small open region. That is caused by develop loading effect, which is largely affected by developer dispensing condition in single puddle method. Double puddle development improves the abnormal CD trend and has a good CD uniformity (3sigma 5.4nm). Contrary to FEP-171, abnormal CD trend is not observed in UV-82(CAR). The low dissolution rate of FEP-171 is the cause of the abnormal CD trend. The yield of CD uniformity and MTT increases with applying double puddle method to FEP-171 process.
It is intended to evaluate the feasibility of 0.15μm generation mask fabrication with a KrF photomask repeater. Inter-field registration accuracy(3sigma) is 28nm in X direction and 45nm in Y direction on a daughter mask in the KrF photomask repeater process and that is out of the registration specification(3sigma 30nm) of 0.15μm generation mask. The intra-field registration accuracy(3sigma) within a 18.4mm × 23.0mm field on a daughter mask is about 9nm with compensation of mis-registration to a mother mask. Inter-field CD uniformity(3sigma) is 8nm on a daughter mask and intra-field CD uniformity(3sigma) can be improved into 15nm with the compensation of CD error to a mother mask. Pattern fidelity in the KrF photomask repeater is inferior to that of the e-beam process. Hence it is necessary to apply OPC pattern to a mother mask in order to fabricate the 0.15μm generation mask.
It is intended to clarify the feasibity of 0.15 μm generation mask fabrication with the photomask repeater that is based on a KrF stepper(step-and-repeat exposure system). In a photomask repeater patterning, a daughter mask is exposed to KrF light through a mother mask. Inter-field registration accuracy(3sigma) is 14 nm in X direction and 28nm in Y direction within a 80mm ×100mm area on a daughter mask and intra-field registration accuracy(3sigma) is 21nm in X direction and 26nm in Y direction within a 18.4mm ×23.0mm field on a daughter mask. Inter-field CD uniformity (3sigma) is 8nm in 100mm ×100mm area on a daughter mask and intra-field CD uniformity (3sigma) is 24nm within a 18.4mm ×23.0mm field on a daughter mask.
The errors of registration and CD within a field can be improved by compensating for these errors to a mother mask. With the compensation, the intra-field registration error can be reduced to about 13.5nm and the intra-field CD uniformity (3sigma) can be improved into 15nm. Pattern fidelity in the KrF photomask repeater is inferior to that in the e-beam process. So we need to apply OPC pattern to a mother mask in order to get an equivalent pattern fidelity to profiles in the e-beam process.
It is intended to clarify the feasibility of 0.15μm generation mask fabrication with the photomask repeater that is based on a KrF stepper(step-and-repeat exposure system). In a photomask repeater patterning, a daughter mask is exposed to KrF light through a mother mask. Inter-field registration accuracy(3sigma) is 14.9nm in X direction and 29.1nm in Y direction within a 100mm×100mm area on a daughter mask and intra-field registration accuracy(3sigma) is 21nm in X direction and 26nm in Y direction within a 18.4mm×23.0mm field on a daughter mask. The registration error within the field on a daughter mask can be reduced to about 13.5nm(range) by compensating for the registration error to a mother mask. Inter-field CD uniformity(3sigma) is 8nm in 100mm×100mm area on a daughter mask and intra-field CD uniformity (3sigma) is 24nm within a 18.4mm×23.0mm field on a daughter mask. The intra-field CD uniformity (3sigma) can be improved into 15nm by compensating for the CD error to a mother mask . In order to satisfy the 30nm registration and 15nm CD uniformity specification of a 0.15μm generation mask, we need to reduce the inter-field registration error with removing the backside defect of a daughter mask and improve the intra-field CD uniformity by changing the dose distribution of the photomask repeater.
To solve the very low throughput of an e-beam writer in mask fabrication, a new patterning method based on a step-and-repeat exposure system, that is a photomask repeater, has been developed. In this paper, we intended to clarify the feasibility of 0.15 micrometers generation mask fabrication with the KrF photomask repeater. Inter-field registration accuracy (3sigma) in the photomask repeater is 14.9 nm in X direction and 29.1 nm in Y direction and can meet the registration specification (30 nm) of a 0.15 micrometers generation mask. Intra-field mis-registration caused by stepper lens distortion is 14 nm (3sigma) in X direction and 12 nm in Y direction for a 12 mm X 12 mm field and gets larger with an increase of a field size. Inter-field CD uniformity (3sigma) is 15.7 nm in 122.5 mm X122.5 mm mask area and intra-field CD uniformity is 10.3 nm in 12 mm X 12 mm field area. The sum of inter-field and intra-field value in the KrF photomask repeater don't currently satisfy the 30 nm registration and 15 nm CD uniformity specification of a 0.15 micrometers generation mask. So we need to reduce the registration and CD errors with optimizing PR coating and development process, using a small field size and compensating the errors of intra-field factors to a mother mask.
To solve very low throughput of e-beam writer, a new patterning method based on stepper, photomask repeater has been developed. For the KrF photomask repeater development we have modified a wafer-exposing stepper to expose photomasks. In this paper, we intended to clarify the feasibility of 0.15 micrometers generation mask fabrication with KrF photomask repeater. Interfield registration almost satisfied the 28 micrometers specification. Intra-field mis- registration was 10 nm in 18 mm by 18 mm field area and so we have to use a small field size and basically improve this intra-field mis-registration. CD uniformity could not meet the 13 nm specification. Though the evaluated results of KrF photomask repeater process have not satisfied the specification of 0.15 micrometers generation mask, we have found the mask fabrication with KrF photomask repeater is feasible with optimization of field and process, we have found the mask fabrication with KrF photomask repeater is feasible with optimization of field and process.