TN5nm HVM where EUVL was implemented on started in the middle of 2020, but EUV mask pattern inspection is still not ready in terms of fully satisfying customers' requirements. There are three tool candidates; optical, actinic, and e-beam inspection. The E-beam tools have high resolution and sensitivity, but have a low throughput.
To better address market requirements, NuFlare has optimized its multi e-beam optics to inspect EUV masks, and apply D2DB method into the e-beam tool to achieve the throughput target. We describe the latest results of verification about main technologies to achieve throughput required for EUV mask inspection.
High volume manufacturing of semiconductors using extreme ultraviolet lithography (EUVL) is off to a good start, and development of high-NA EUVL tool has started; however, EUV mask pattern inspection, one key technology supporting EUVL, is still not ready in terms of fully satisfying customers' major requirements, such as 1) defect sensitivity, 2) throughput, and 3) cost of ownership (CoO). There are three tool candidates that have the potential of meeting these requirements: optical inspection, actinic inspection, and e-beam inspection. The resolution of the optical inspection tool has almost reached its limit. The actinic inspection tool satisfies both defect sensitivity and throughput requirements, but the cost is high and it needs to support D2DB inspection capability. The e-beam tool has high resolution and sensitivity, but its low throughput which is a key issue. With this background, NuFlare has optimized its multi e-beam optics system to inspect EUV masks, and has made progress in verifying a POC tool as well as develop new image processing technology. From these verifications, the development has moved on to the feasibility study of inspecting EUV mask pattern defects with D2D and D2DB for the 5nm node and beyond. In this paper, we will present our technology for EUV mask inspection as well as our latest results.
Using a POC tool, we are continuing a feasibility study for an EUV mask pattern inspection tool having multibeam electron optics with D2D and D2DB functions. In this paper, we will discuss our technologies in addition to our latest results on our POC tool.
Mask inspection tool with DUV laser source has been used for Photo-mask production in many years due to its high sensitivity, high throughput, and good CoO. Due to the advance of NGL technology such as EUVL and Nano-imprint lithography (NIL), there is a demand for extending inspection capability for DUV mask inspection tool for the minute pattern such as hp4xnm or less. But current DUV inspection tool has sensitivity constrain for the minute pattern since inspection optics has the resolution limit determined by the inspection wavelength and optics NA.
Based on the unresolved pattern inspection capability study using DUV mask inspection tool NPI-7000 for 14nm/10nm technology nodes, we developed a new optical imaging method and tested its inspection capability for the minute pattern smaller than the optical resolution. We confirmed the excellent defect detection capability and the expendability of DUV optics inspection using the new inspection method. Here, the inspection result of unresolved hp26/20nm pattern obtained by NPI-7000 with the new inspection method is descried.
Various technologies such as multiple patterning (MP) are being developed to extend the current DUV optical
lithography to deal with the delay of next generation lithography such as EUV and NIL. Likewise, it is necessary to
continue to develop technologies for mask inspection tools for masks fabricated for the DUV optical lithography so that
they can be appropriately inspected, until the next generation EB or EUV actinic inspection tools is put into practical use.
To fabricate 1x nm devices with the present lithography process, the industry will likely further extend double
patterning (DP) to multiple patterning (MP). For MP, the requirements for the inspection sensitivity of traditional defects
such as intrusions or extrusions do not change much, but those for CD control and overlay tolerances will become more
critical.
In this paper, we will discuss the main features of NPI-7000, a DUV based mask inspection tool for the 1x nm node
devices, and our challenges in enhancing the CD error sensitivities to enable the inspection of masks.
EUV lithography is expected to be not only for hp 2Xnm node device production method but also for hp 1X nm
node. We have already developed the mask inspection system using 199nm wavelength with simultaneous transmitted
and reflected illumination optics, which utilize p-polarized and s-polarized illumination for high defect detection
sensitivity, and we developed a new image contrast enhancement method which changes the digitizing rate of imaging
sensor depending on the signal level. Also, we evaluate the mask structure which improve the image contrast and defect
detection sensitivity. EUVL-mask has different configuration from transmitted type optical-mask. A captured image
simulator has been developed to study the polarized illumination performance theoretically of our inspection system.
Preferable mask structure for defect detection and possibility of miss defect detection are considered.
With continued shrinkage of the semiconductor technology node, the inspection of mask with a single preset defect
detection sensitivity level becomes impractical because of the increase occurrence of false capturing of defects.
Inspection of leading-edge masks with conventional defect detection method, redundant detection of defects such as
pseudo defects, or anomalies such as slightly deformed OPCs caused by assist features tend to increase the Turn Around
Time (TAT) and cost of ownership (COO).
This report describes a new method for the inspection of mask. It assigns defect detection sensitivity levels to local area
inspections and is named as Regional Sensitivity Applied Inspection (RSAI). Then, the sensitivity information from each
local area is converted into a format that can be fed into a Mask Data Rank (MDR) which is represented on the basis of
pattern prioritization determined at the device design stage. Core technologies employing this concept resulted in the
shortening of TAT where samples of actual device mask patterns were used.
Printability verification functions (PVF) were applied to the advancement of technologies such as to Source Mask
Optimization (SMO) technology. We report on the shortening of TAT that was achieved by the implementation of a new
inspection technology that combines RSAI with MDR, and employs printability verification functions.
Lithography potential expands for 45nm node to 32nm device production by the development of immersion
technology and the introduction of phase shift mask. We have already developed the mask inspection system using
199nm wavelength with simultaneous transmitted illumination and reflected illumination optics, and is an effectual
candidate for hp 32nm node mask inspection. Also, it has high defect sensitivity because of its high optical resolution, so
as to be utilized for leading edge mask to next generation lithography. EUV lithography with 13.5nm exposure
wavelength is dominant candidate for the next generation lithography because of its excellent resolution for 2x half pitch
(hp) node device. But, applying 199nm optics to complicated lithography exposure tool option for hp2x nm node and
beyond, further development such as image contrast enhancement will be needed. EUVL-mask has different
configuration from transmitted type optical-mask. It is utilized for reflected illumination type exposure tool. Its
membrane structure has reverse contrast compared with optical-mask. This nature leads image profile difference from
optical-mask. A feasibility study was conducted for EUV mask pattern defect inspection using DUV illumination optics
with two TDI (Time Delay Integration) sensors. To optimize the inspection system configuration, newly developed Nonlinear
Image Contrast Enhancement method (NICE) is presented. This function capability greatly enhances inspectability
of EUVL mask.
Highly reliable DUV light sources are required for semiconductor applications such as a photomask inspection. The
mask inspection for the advanced devices requires the UV lightning wavelength beyond 200 nm. By use of dual fiber
lasers as fundamental light sources and the multi-wavelength conversion we have constructed a light source of 198nm
with more than 100 mW. The first laser is Yb doped fiber laser with the wavelength of 1064 nm; the second is Er doped
fiber laser with 1560 nm. To obtain the robustness and to simplify the configuration, the fundamental lights are run in
the pulsed operation and all wavelength conversions are made in single-pass scheme. The PRFs of more than 2 MHz
are chosen as an alternative of a CW light source; such a high PRF light is equivalent to CW light for inspection
cameras. The light source is operated described as follows. Automatic weekly maintenance within an hour is done if it is
required; automatic monthly maintenance within 4 hours is done on fixed date per month; manufacturer's maintenance is
done every 6 month. Now this 198 nm light sources are equipped in the leading edge photomask inspection machines.
A novel EUV mask inspection tool with 199nm laser source and super-resolution technique has been developed.
This tool is based on NPI-5000PLUS, which is a photo-mask inspection tool for hp2X nm node and beyond. In order to
implement EUV mask inspection with only a short time for mask set-up, reflected illumination type alignment optics to
guide alignment mark and adjust mask coordinate with visible illumination light are equipped. Moreover, to inspect EUV
masks for hp2X nm and beyond, the image detection optics with the novel polarized illumination technique is
incorporated in this tool. Image contrast enhancement was confirmed by experiments and simulations.
In this paper, we will report on our experimental results on the impact of inspection system optics on mask defect
detection sensitivity. We evaluated the capability of detecting defects on the EUVL masks by using a new inspection
tool (NPI6000EUVα) made by NuFlare Technology, Inc. (NFT) and Advanced Mask Inspection Technology, Inc.
(AMiT). This tool is based on NPI-5000 which is the leading-edge photomask defect inspection system using 199nm
wavelength inspection optics. The programmed defect mask with LR-TaBN absorber was used which had various sized
opaque and clear extension defects on hp-180nm, hp-128nm, and hp-108nm line and space patterns. According to the
analysis, to obtain optimum sensitivity for various types of defects, using both C- and P-polarized illumination
conditions were found to be effective. At present, sufficient defect-detection sensitivity is achieved for opaque and clear
extension defects in hp128nm (hp32nm at wafer). For hp108nm (hp27nm at wafer), using both C- and P- polarized
illumination is effective. However, further developments in defect-detection sensitivity are necessary.
In addition to the conventional demands for high sensitivities with which the mask inspection system detects the minute
size defects, capability to extract true defects from a wide variety of patterns that should not be counted as pseudo
defects has been quite demanding. It is necessary to ascertain suppression of MEEF incurred by the combination of
parameters such as LER and defects of SRAF.
NFT and Brion are jointly developing a mask-image based printability verification system with functions combining
their respective technologies with the results from ASET's research. This report describes such defect detection results
and introduces the development of a mask inspection system with printability verification function.
We report the development of Mask-LMC for defect printability evaluation from sub-200nm wavelength mask
inspection images. Both transmitted and reflected images are utilized, and both die-to-die and die-to-database inspection
modes are supported. The first step of the process is to recover the patterns on the mask from high resolution T and R
images by de-convolving inspection optical effects. This step uses a mask reconstruction model, which is based on
rigorous Hopkins-modeling of the inspection optics, and is pre-determined before the full mask inspection. After mask
reconstruction, wafer scanner optics and wafer resist simulations are performed on the reconstructed mask, with a wafer
lithography model. This step leverages Brion's industry-proven, hardware-accelerated LMC (Lithography
Manufacturability Check) technology1. Existing litho process models that are in use for Brion's OPC+ and verification
products may be used for this simulation. In the final step, special detectors are used to compare simulation results on the
reference and defect dice. We have developed detectors for contact CD, contact area, line and space CD, and edge
placement errors. The detection results on test and production reticles have been validated with AIMSTM.
In this paper, we will report on our experimental and simulation results on the impact of EUVL mask absorber
structure and of inspection system optics on mask defect detection sensitivity. We employed a commercial simulator
EM-Suite (Panoramic Technology, Inc.) which calculated rigorously using FDTD (Finite-difference time-domain)
method. By using various optical constants of absorber stacks, we calculated image contrasts and defect image signals as
obtained from the mask defect inspection system. We evaluated the image contrast and the capability of detecting
defects on the EUVL masks by using a new inspection tool made by NuFlare Technology, Inc. (NFT) and Advanced
Mask Inspection Technology, Inc. (AMiT). This tool is based on NPI-5000 which is the leading-edge photomask defect
inspection system using 199nm wavelength inspection optics. The programmed defect masks with LR-TaBN and LRTaSi
absorbers were used which had various sized opaque and clear extension defects on hp-160nm, hp-225nm, and hp-
325nm line and space patterns. According to the analysis, reflectivity of EUVL mask absorber structures and the
inspection optics have large influence on image contrast and defect sensitivity. It is very important to optimize absorber
structure and inspection optics for the development of EUVL mask inspection technology, and for the improvement of
performance of EUV lithographic systems.
We report the development of Mask-LMC for defect printability evaluation from sub-200nm wavelength mask
inspection images. Both transmitted and reflected images are utilized, and both die-to-die and die-to-database inspection
modes are supported. The first step of the process is to recover the patterns on the mask from high resolution T and R
images by de-convolving inspection optical effects. This step uses a mask reconstruction model, which is based on
rigorous Hopkins-modeling of the inspection optics, and is pre-determined before the full mask inspection. After mask
reconstruction, wafer scanner optics and wafer resist simulations are performed on the reconstructed mask, with a wafer
lithography model. This step leverages Brion's industry-proven, hardware-accelerated LMC (Lithography
Manufacturability Check) technology1. Existing litho process models that are in use for Brion's OPC+ and verification
products may be used for this simulation. In the final step, special detectors are used to compare simulation results on the
reference and defect dice. We have developed detectors for contact CD, contact area, line and space CD, and edge
placement errors. The detection result has been validated with AIMSTM.
The lithography potential of an ArF (193nm) laser exposure tool with high numerical aperture (NA) will expand its
lithography potential to 45nm node production and even beyond. Consequently, a mask inspection system with a
wavelength nearly equal to 193nm is required so as to detect defects of the masks using resolution enhancement
technology (RET). A novel high-resolution mask inspection platform using DUV wavelength has been developed, which
works at 199nm. The wavelength is close to the wavelength of ArF exposure tool. In order to adapt 199nm optics for
hp2x nm node and beyond defect detection on next generation mask with appropriate condition, further development
such as the illumination condition modification technique has been studied. The illumination optics has the advantageous
feature that super-resolution method is applied by adding the optics. To evaluate the super-resolution effect of
illumination condition control optics, the interaction of light with mask features is calculated rigorously using RCWA
(Rigorous Coupled-Wave Analysis) method.
In this paper, image contrast enhancement effect using newly designed super-resolution optics which is applied to
transmitted and reflected light image acquisition system are presented with simulation and experiment.
In this paper, we will report on our experimental and simulation results on the impact of EUVL mask absorber
structure and of inspection system optics on mask defect detection sensitivity. We employed a commercial simulator
EM-Suite (Panoramic Technology, Inc.) which calculated rigorously using FDTD (Finite-difference time-domain)
method. By using various optical constants of absorber stacks, we calculated image contrasts and defect image signals as
obtained from the mask defect inspection system. We evaluated the image contrast and the capability of detecting
defects on the EUVL masks by using a new inspection tool made by NuFlare Technology, Inc. (NFT) and Advanced
Mask Inspection Technology, Inc. (AMiT). This tool is based on NPI-5000 which is the leading-edge photomask defect
inspection system using 199nm wavelength inspection optics. The programmed defect masks with LR-TaBN and LRTaSi
absorbers were used which had various sized opaque and clear extension defects on hp-160nm, hp-225nm, and hp-
325nm line and space patterns. According to the analysis, reflectivity of EUVL mask absorber structures and the
inspection optics have large influence on image contrast and defect sensitivity. It is very important to optimize absorber
structure and inspection optics for the development of EUVL mask inspection technology, and for the improvement of
performance of EUV lithographic systems.
We evaluated the capability of a commercially available DUV system equipped with
reflective inspection optics with the shortest inspection wavelength of 199nm in detecting
pattern defect on EUVL mask of hp45nm programmed defect pattern. The sensitivity of the
system for opaque extension defects for hp45nm node was quite acceptable but for clear
extension defects the sensitivity of the system was rather poor. In this paper, the influence of
base pattern size on inspection sensitivities for opaque and clear extension defects is discussed.
The lithography potential of an ArF (193nm) laser exposure tool with high numerical aperture (NA) will expand
its lithography potential to 65nm node production and even beyond. Consequently, a mask inspection system with a light
source, whose wavelength is nearly equal to 193nm, is required so as to detect defects of the masks using resolution
enhancement technology (RET). Wavelength consistency between exposure tool and mask inspection tool is strongly
required in the field of mask fabrication to obtain high defect inspection sensitivity. Therefore, a novel high-resolution
mask inspection platform using DUV wavelength has been developed, which works at 198.5nm. This system has
transmission and reflection inspection mode, and throughput using 70nm pixel size were designed within 2 hours per
mask. In this paper, transmitted and reflected light image acquisition system and high accuracy focus detection optics are
presented.
We have developed a mask inspection system using 199nm inspection light wavelength. This system performs
transmission and reflection inspection processes concurrently within two hours per plate. By the evaluation result of
mask images and inspection sensitivity, it is confirmed that the 199nm inspection system has the advantage over the
system using 257nm and has the possibility corresponding to next generation mask inspection. Furthermore, advanced
die-to-database (D-DB) inspection, which can generate high-fidelity of a reference image based on the CAD data for
alternating phase shift mask (PSM) or tri-tone, is required for next generation inspection system, too. Therefore, a
reference image generation method using two-layer CAD data has been developed. In this paper, the effectiveness of
this method is described.
The usage of ArF immersion lithography for hp 65nm node and beyond leads to the increase of mask error enhancement factor in the exposure process. Wavelength of inspection tool is required to consistent with wavelength of lithography tool. Wavelength consistency becomes more important by the introduction of phase shift mask such as Tri-tone mask and alternating phase shift mask. Therefore, mask inspection system, whose inspection light wavelength is 199nm, has been developed. This system has transmission and reflection inspection mode, and throughput, using 70 nm pixel size, were designed within 2hours per mask. The experimental results show expected advantages for Die-to-Die and Die-to-Database inspection compared with the system using 257nm inspection optics. Shorter wavelength effect makes transmission inspection sensitivity increase, and realizes 40nm size particle inspection. As for the phase shift mask, the difference of gray value between the area with phase defect and without phase defect was clear relatively. In this paper, specifications and design, experimental results are described.
High-Definition DVD 15 GB/side recording capacity is realized by using violet laser diodes, and it is expected to be the next generation optical disc. However, the shortening in the wavelength of laser diode and increase in recording density lead to a tighter margin for allowable disc tilt due to the wavefront aberration. Therefore, a tilt servo system using a 4-axis lens actuator has been developed. It controls the object lens not only in tracking and focusing directions but also in two axes tilt directions corresponding to disc tilt. This paper describes features of the tilt servo system and the experimental results of its tilt compensation effect.
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