Based on the record for reasonable throughput, 19x nm wavelength inspection is one of the strongest candidates available today for the initial EUV (Extreme Ultraviolet) mask inspection approach until high-throughput E-Beam or actinic inspection is ready. However, there are several key challenges with 19x nm optical inspection of EUV masks. In the previous study, it was demonstrated that a 19x nm inspection system was capable of detecting programmed 15nm edge defects and 7nm CD errors on the programmed defect mask (PDM) containing EUV device designs, and inspected at maximum sensitivity. However, in that study, the inspectability on the product mask was not considered. In this study, EUV product mask inspection with a 19x nm inspection system is demonstrated, with special attention paid to defect sensitivity and inspectability on the product mask. In our results, we discuss whether inspection conditions, such as focus, can be employed to create a trade-off between defect sensitivity and inspectability. In addition, we discuss how defect measurement definitions affect the programmed defect size and the printability on EUV AIMS.
Two different mask inspection techniques are developed and compared for 14 nm node and beyond photomasks, High
resolution and Litho-based inspection. High resolution inspection is the general inspection method in which a 19x nm
wavelength laser is used with the High NA inspection optics. Litho-based inspection is a new inspection technology.
This inspection uses the wafer lithography information, and as such, this method has automatic defect classification
capability which is based on wafer printability. Both High resolution and Litho-based inspection methods are compared
using 14 nm and 7 nm node programmed defect and production design masks. The defect sensitivity and mask
inspectability is compared, in addition to comparing the defect classification and throughput. Additionally, the Cost /
Infrastructure comparison is analyzed and the impact of each inspection method is discussed.
A variety of repairs were conducted on extreme ultraviolet (EUV) multilayer, including protection against pattern degradation in manufactural use, in order to evaluate feasibility of multilayer repair and subsequent protection schemes. The efficacy of postrepair protection techniques is evaluated to determine the lifetime of multilayer repairs. Simulations were used to select the optimal material thicknesses for repair protection, and the simulation results are verified with the lithographic results. The results showed a high correlation coefficient. Finally, all repaired sites were cleaned multiple times to quantify repair durability and impact on wafer critical dimension (CD). Aerial imaging of the repair sites before and after cleans showed a dramatic degradation of wafer CD. However, we show that applying a surface protection material after multilayer repair successfully mitigates the influence of multilayer degradation during extensive manufacturing operations.
Native acting phase-programmed defects, otherwise known as buried program defects, with attributes very similar to native defects, were successfully fabricated using a high-accuracy overlay technique. The defect detectability and visibility were analyzed with conventional amplitude and phase-contrast blank inspection at 193-nm wavelength, pattern inspection at 193-nm wavelength, and scanning electron microscopy. The mask was also printed on wafer, and printability is discussed. Finally, the inspection sensitivity and wafer printability are compared, leading to the observation that the current blank- and pattern-inspection sensitivity is not enough to detect all of the printable defects.
A variety of repairs on EUV multilayer were conducted including protection against pattern degradation in manufactural use in order to evaluate feasibility of multilayer repair and the protection schemes. The efficacy of post-repair protection techniques are evaluated to determine the lifetime of multilayer repairs. Simulations were used to select the optimal material thicknesses for repair protection, and the simulation results are verified with the lithographic results. The results showed a high correlation coefficient. Finally, all repaired sites were cleaned multiple times to quantify repair durability and impact on wafer CD. Aerial imaging of the repair sites before and after cleans shows a dramatic degradation of wafer CD post-cleaning. However, we show that applying a surface protection material after multilayer repair successfully mitigates the influence of multilayer degradation during extensive manufacturing operations.
NAP-PD (Native Acting Phase – Programmed Defects), otherwise known as buried program defects, with attributes very similar to native defects, are successfully fabricated using a high accuracy overlay technique. The defect detectability and visibility are analyzed with conventional phase contrast blank inspection @193 nm wavelength, pattern inspection @193 nm wavelength and SEM. The mask is also printed on wafer and printability is discussed. Finally, the inspection sensitivity and wafer printability are compared, leading to the observation that the current blank and pattern inspection sensitivity is not enough to detect all of the printable defects.
Five EUV film stacks were prepared and evaluated from the multiple viewpoints of mask repair process: etching property, CD control and wafer print. Etching property results revealed a thicker lower reflective (LR) layer stack showed good performance. Some types of defects were repaired and a CD comparison done with both CD-SEM and EUV microscope. It was found thinner total film stack (LR plus absorber) performs better than thicker ones for CD control. In addition, thicker LR performed better than thinner LR. Wafer print performance on the repaired site was evaluated through focus by imaging on an EUV microscope. Wafer printability performance showed that thinner total film stack performed better than a thicker one. Finally the best stack for EUV mask repair performance was determined to be a thinner total film stack and thicker a LR from all the various points of view.
EUV blank defect is one of the key issues the industry has to overcome to implement EUV lithography for HVM
(high volume manufacturing). Several inspection techniques for EUV blank defect detection have been proposed, but the
blank defect criteria for EUV mask is assumed to be very tight, thus, high sensitivity performance is required for blank
inspection. However, it is important how the blank inspection tool to be assessed with appropriate test blanks with
properly characterized defects. New programmed defect fabrication method has been introduced and verified that the
method enables to fabricate natural-like programmed defects. In this study, it was attempted to fabricate more complex
shape defects and investigated how multilayer defects are grown during multilayer deposition. Then, printability
simulation was conducted for 3 different defect transition models, and critical multilayer defect shapes and sizes were
discussed based on the simulation work.
EUV lithography is the most promising candidate for semiconductor device manufacturing of 1x nm half pitch and
beyond. For the practical use, EUV mask with a thin absorber could be adopted because of less shadowing effect. EUV
reflectivity from the thin absorber is about 1~3%. It would cause CD change on wafer especially at the exposure field
edge due to the leakage of the EUV light from neighboring exposure shots.1 To avoid this phenomenon, light shield
black border is needed at the edge of pattern area on mask. Stacked absorber type and ML-etched type of light shield
black border have been proposed in the past.2 The most important things for these black borders are that there is no
reflection of EUV light and no defect which affects pattern CD on wafer. ML-etched black border is considered to be
applied for early practical use from a viewpoint of manufacturability. Because CD degradation and defect increase might
happen due to 2nd litho and etch process on its main pattern area in manufacturing process of stacked absorber type.
In this paper, we will show several evaluation results regarding
ML-etched black border we have developed. It has a
good light shield performance for EUV and low DUV light reflection. Defect inspection in black border area can be
performed successfully by three kinds of inspection tools. As a result, most of the defects seemed not to be printable to
wafer. We also evaluated CD change, flatness change linked to mask IP shift and particle contamination on main pattern
area. What it comes down to is that there is no show-stopper for
ML-etched BB process for now.
EUV blank inspection is the key technology for EUV mask fabrication. To assess blank inspection tools, it is
important to obtain appropriate test blanks with properly characterized defect types. In this study, new programmed
defect blank was fabricated with conventional programmed defect fabrication and several new methods for natural-like
programmed defects. And defect characterization work has been conducted to verify the difference of conventional
programmed defects and natural-like programmed defects, and confirmed wide range of defect sizes from minimum
below 1nm-height × 18nm-width to micron order defects were successfully fabricated. Furthermore, the blank was
inspected by Actinic Blank Inspection (ABI) tool and evaluated the effectiveness of the new defect fabrication methods.
And it was confirmed that the new programmed defect showed similar characteristics as natural defects.
Photomask Japan each year hosts a meeting inviting the conference attendees to actively participate in a discussion on a
selected topic. The topic selected for this year is on new mask inspection and metrology techniques that are just
emerging in the market, namely, aerial/wafer image based inspection and metrology, and optical high sampling
frequency CD uniformity measurement. The panel discussion hopes to identify potential values of each technique and
at the same time discover any challenge if the industry were to adopt such technique.
Two types of blanks, EUV A and EUV B, are the leading EUV blanks contenders. They are evaluated and compared
with OMOG blank for their suitability as a photomask blanks. For defect inspection evaluation, contrast for pattern
image and sensitivity for detection were evaluated using the newly developed inspection tools. With these tools, it is
learnt that the sensitivity varies according to a set of conditions. For repair performance evaluations, EUV mask was
assessed through E-beam repair tools, those that are most widely used. The results on both types of masks demonstrate
good repair shape that is almost same quality as repair on OMOG mask. Moreover, under the two types of repair
conditions used in this study, no degradation on pattern was found for the optimized condition as result of repair work.
As a result of demand for ever decreasing of feature sizes in photomasks, inspection has become more
important as a key element of manufacturing 32nm node and beyond. In order to provide a better solution for
it, we have developed a new method to create programmed defects having attributes very similar to those
seen in natural defects. We have named the new method as NLPD (Natural-Like Programmed Defect). One
of the noteworthy features of NLPD is that it is possible to make reticles with different heights which have
never been made by conventional method. Natural like defects are desirable for new inspection modes
including ones using shorter wavelength and aerial plane inspection technology. These new inspection
modes are equipped with recently released inspection tools. They are expected to meet the requirements
which are needed by future advanced masks, and these requirements have been inadequately fulfilled with
inspection tools for current generation masks. Those requirements include responding to currently dominant
reticle types for 32nm node: CoG: 6% EPSM: and OMOG (Opaque MoSi On Glass). Other possible reticle
types for 32nm node contain EUV, Enhancer, complex tri-tone, high transmission, and CPL. In the future,
aggressive model based OPC (Optical Proximity Correction) will be typically used which include jogs, serifs,
and SRAF (Sub-Resolution Assist Features) accompanying extremely small gaps between adjacent structures.
When those advanced technologies are adopted, NLPD definitely contributes to making inspection more
efficient and effective as evaluation method dealing with advanced inspection tools.
This paper provides NLPD results with comparison of newly released inspection tools equipped with new
inspection modes. The new inspection modes include hi-resolution inspection and aerial inspection which are
designed to fulfill the requirements of inspection for advanced masks. These results confirm that hi-resolution
inspection is suited for process development or improvement and aerial inspection is good for the volume
production.
The application of aggressive optical proximity correction (OPC) has permitted the extension of advanced lithographic
technologies. OPC is also the source of challenges for the mask-maker. Sub-resolution features, small shapes between
features and highly-fragmented edges in the design data are difficult to reproduce on masks and even more difficult to
inspect. Since the inspection step examines every image on the mask, it is required to guarantee the total plate quality.
The patterns themselves must be differentiated from defects, and the ability to recognize small deviations must be
maintained. In other words, high inspectability at high defect sensitivities must be achieved simultaneously. This must be
done without restricting necessary OPC designs features. Historically, transmitted light has been deployed for mask
pattern inspection. Recently, the inspection challenge has been both enhanced and complicated by the introduction of
reflected light pattern inspection. Reflected light reverses the image contrast of features, creating a new set of design
limits. This paper introduces these new reflected inspection limits. Multiple platform capabilities will be incorporated
into the study of reflected and transmitted inspection capability. The benefits and challenges of integrating a combination
of transmitted and reflected light pattern inspection into manufacturing will be explored. Aerial Image Measurement
System (AIMS) analysis will be used to help understand how to leverage the enhanced inspection capability while
avoiding unnecessary restrictions on OPC.
The increase of MEEF(Mask Error Enhancement Factor) as well as the life prolonging of the ArF lithography with low k1 makes the demand for the mask quality more and more severe . Alt-PSM (Alternating Phase-Shifting Mask) is one of the most effective approaches to the resolution improvements of the ArF lithography. In addition, the improvement of MEEF can be expected in Alt-PSM . In this study, firstly Alt-PSM was manufactured containing programmed phase defects.
The programmed phase defects are variable type and multiple phase angles. The phase differences of these defects are 180,120 and 60degree. Two types of chrome line width were placed (280nm and 400nm) with four different pitches (1:1.1:1.5,1:2,1:5). Two programmed phase defects type (divot and bump) placed on isolated and on edge.
The printability of the phase defect was evaluated by using Aerial Image Measurement System (AIMS-fab193 of Carl Zeiss Co.) In this study, the printable defect was defined to be a defect, which CD error size is within +/-5% and DOF was +/-100nm on wafer.
And, the defect detection capability was confirmed by using TeraScan( KLA-Tencor Co.)
Finally, the real existence situation of the natural phase defect in imitated 65nm node production mask was estimated by using TeraScan with optimized inspection condition.
In addition, the detected phase defect verified the printability. As a result of this verification, it turned out that a practical inspection was possible of Alt-PSM for 65nm technology node.
As the ArF lithography technology is going to progress to 90nm node from 130nm node, it has been more difficult to inspect all types of mask defects, which influence wafer. Photomask for 90nm node, the aggressive OPC mask and Phase Shift Mask (PSM) might be inevitable in production devices due to the slow progresses in lithography equipment itself compared to shrinkage speed in device manufacturing.
Recently, due to the similiar effect such like MEEF (Mask Error Enhancement Factor) phenomenon many mask defects become to detect difficult even printable defects even the lots of improvements mask inspection equipments. In this paper, we will present the inspection capability of advanced DUV inspection tool LM7000 (NEC) with various programmed defect masks (e.g. aggressive OPC masks, half-tone PSM, tri-tone PSM) with, and discuss the relationship between inspection sensitivity and mask defect printability.
The KrF12% tri-tone PSM (phase shift mask) was designed with the programmed defects on the chrome (Cr) and phase shift (PS) layers. From the lithography simulation, the PS defects, generated on the PS layer, were estimated to fluctuate the CD of the contact holes on the wafer more than the defects in the same size on the conventional EAPSM (half-tone PSM). The printability of the PS defects and Cr defects on the contact holes were investigated by the print-test on the wafer. The Cr residues on the PS layer slightly changed the CD of the contact holes on the wafer. The PS defects showed the great influence to the CD variation of the contact holes. The light calibration of the defect inspection was optimized to detect the PS and Cr defects. For the detection of the PS defects in the die-to-die inspection mode, the UV inspection system SLFX7 showed the high performance with the PS/SiO2 calibration, in which the boundary of the PS layer and SiO2 substrate was used as the light calibration point. The SLFX7 also available to detect the Cr defects in the die-to-die mode. For the die-to-database mode to detect the Cr defect, the KLA351, the visible light inspection system, was available by the Cr/PS calibration. The sensitivity of the SLFX7 and KLA351 was adequate for the Cr defects, however, that was not enough to the specification of the PS defects estimated from the print-test. The sensitivity of the SLFX7 showed a slight difference between the tri-tone and binary layout in the specific defect types.
We have improved DUV laser reticle inspection system LM7000 for 90 nm technology node devices. To increase inspection sensitivity, we developed a reflected light inspection as a supplementary method to transmittance light inspection. We have also strengthened inspection algorithm to distinguish between real defects and very small features from optical proximity effect correction (OPC). Finally, we have improved reference image for die to database inspection. With the merit of short wavelength of LM7000 (266 nm), the inspection sensitivity of the high-transmittance half-tone phase shift mask (HTPSM) does not deteriorated so severely compared to that of binary mask. With the help of these series of improvements, LM7000 could shows inspection capability for OPC masks and HTPSM for ArF lithography. The inspection capability of LM7000 was proved with the programmed defect masks and printability experiment using ArF scanner.
Won Kim, Shinji Akima, Christopher Aquino, Charika Becker, Mark Eickhoff, Tsuyoshi Narita, Soo-Kim Quah, Peter Rohr, Robert Schlaffer, Junichi Tanzawa, Yoshiro Yamada
As our chip producing industry rapidly ramps to mass production of the 130nm device technology node and wrapping up the final stages of 90nm node process technology development, the ability to inspect all types of 130nm node masks and early identification of shortcomings in 90nm node mask inspection are extremely important.
In this paper, we share our experience of mask inspection for the 90nm and 130nm nodes, using the advanced TeraStar mask inspection system (KLA-Tencor) with the SEMI programmed defect standard masks, comprising three substrate types (binary, 248nm-KrF MoSi and 193nm-ArF MoSiON). Both Die-to-Die (D2D) and Die-to-Database (DDB) inspections were carried out and the results are presented with our assessments of benefits and shortcomings of those methods. To verify the resulting defects actually impact device functionality, we also carried out systematic printability experiments with our proprietary 130nm and 90nm nodes lithography processes. The wafer results were then compared with mask inspection results and mask measurement data to draw our final conclusions. In addition, we will also present inspection performance of the TeraStar system on our 130nm production masks and very challenging 90nm node (ArF EAPSM/AAPSM) development masks.
For the latest photomask fabrication, critical dimension (CD) control is required more for ArF lithography. To satisfy the requirement, Alternating Phase-Shifting Mask (Alt.PSM) is expected to be the most effective approach for resolution enhancement. We investigated the optimization of shifter structure and evaluated phase defect detectability for 130 to 100nm node ArF Alt.PSM. Considering the process and defect control, shifter trench type is the most popular approach. However, in order to achieve smaller CD on reticle, dual trench type becomes also necessary. Therefore, we investigated the performance of the two types of shifter structure, and we compared the optical characteristics. On the other hand, Using test reticles contained programmed phase defects of various shape and size, phase defect printability was analyzed with the Aerial Image Measurement System, MSM193, and phase defect detectability was evaluated with some inspection tools. As a result, the manufacturing technology of ArF Alt.PSM for 100nm node was established.
Be accompanied with gate length will tend to be smaller in LSI manufacturing, assist bar type OPC masks are vigorously investigated to take into mass production. In this research, we examined problems about manufacturing and guarantee of assist bar type OPC masks. We applied 50KeV-accelerated Vector-type E-beam system to mask manufacturing that is going to be a major equipment from now on. Firstly, we remarked the CD error that occurred in mask manufacturing, and the error was valuated. Secondly, we estimated the influence of mask accuracy to false defect occurrence. Lastly, we made the masks for defect check. The defects of the masks were measured using SEM, and wafer printability of the defects was checked by simulation. And we estimated the sensitivity of inspection. As results, it is proved to be possible that manufacturing and inspecting the assist bar type OPC masks in 100 nm node.
Alternating Phase-Shift Mask (Alt-PSM) is one of the key technologies for 0.15 micrometer or below rule device fabrication. But it is not yet widely utilized because of difficulty on phase controllability and defect controllability. Through more than 7 years at our commercial base operation and feedback from customers, we have improved our Alt-PSM both on its performance on wafer resist image and defect minimization. We have focused on the two elements, defects detection and repair, that made it difficult to control defect quantity on Alt-PSMs. In this paper, we describe results of experiment and optimization method that aims to assure zero defect on Alt-PSM for DUV lithography. We prepared evaluation plates. The plates contain series of programmed quartz defect on 0.6 micrometer line & space, each has phase errors of 60, 120 and 180 degrees at KrF wavelength. We used several latest models of inspection tools to evaluate phase shift quartz defect detectability, which are KLA353UV, STARlight, 9MD84SR(i). Micrion8000 was used as the repair tool. MSM-100/AIMS was used to evaluate wafer CD error of defect area before and after repair. As results, we found that inspection by short wavelength, especially by 9MD84SR(i), was effective for detection of phase shift defects, and that if this method were combined with STARlight inspection, detectability of the phase shift defect would be improved. With combination of this inspection method and our FIB repair, which is optimized for premeasured height of each phase shift defect by use of AFM, we would be able to supply zero defect Alt-PSMs for 0.15 micrometer design rule devices.
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