As high-volume manufacturing (HVM) of photomasks of various types and processes expands, defects and their origin are of particular concern. Organic materials are present in many aspects of a photomask's lifecycle, from carriers and tool hardware to resists and chemical residues. Characterization of organic materials to determine their origin and mitigate their yield impact is quintessential to throughput time (TPT). With the emergence of atomic force microscopy-infrared spectroscopy (AFM-IR) failure analysis techniques, distinguishing organic defects and thin films with high resolution is limited only by the size of the AFM probe. Using the AFM-IR lab instrument, we collect IR spectra of many common materials found in our process to build a database, allowing future defects to be matched to our known materials and general external IR databases. To expand our capabilities, an in-line automated AFM with spectra acquisition capability is required, with cleanliness and recipe reliability required for factory use. Supporting this automated toolset, an automated reporting function has been developed to quickly provide customers with a complete picture of a defect, from AFM scan to IR spectra, complete with IR imaging at wavelengths of interest. This paper seeks to decode the nature of AFM Nano-IR and its place as a critical in-line defect analysis technique to increase yield and proactively prevent excursions in the HVM environment.
The increasingly tight overlay requirements to support high-NA EUV lithography are driving specifications for mask metrology tools. Precise and accurate mask registration measurements with optical proximity corrections are challenging but essential to enable scanner on-product overlay requirements. To achieve this, it is necessary to improve registration tool capability to enable resolution and highly repeatable measurements of small features. Close cooperation between equipment vendors and mask shops is required to keep pace with those requirements. The latest generation of the Carl Zeiss registration tool PROVE® neXT provides an illumination wavelength of 193 nm and a numerical aperture of 0.8 to provide inherent repeatability and resolution advantages on smaller features. The present paper reports the performance of a fleet of PROVE® neXT tools. The readiness to meet the requirements of upcoming technology nodes, notably high – NA EUV lithography, is reviewed. Related application cases are discussed from a mask shop point of view.
With EUV Attenuated Phase Shift Masks (aPSMs) rapidly approaching maturity, actinic metrology soon will be required to ensure phase accuracy, uniformity, and stability. The target phase shift is carefully designed to an optimized value, which is not 𝜋, but typically around 1.2𝜋 for optimal printing at critical feature sizes. The additional 0.2𝜋 phase shift is necessary due to mask 3D effects (M3D), which increasingly distort the nearfield scattering and phase as the feature size is reduced. Therefore, EUV attenuated phase shift masks require metrology, not only for the relative Fresnel phase shift between large-area multilayer and absorber regions, but also for the feature-dependent pattern phase shift in the near-field scattering. We demonstrate a metrology solution for measuring the in-pattern phase shift using spectroscopic variable angle scatterometry. The measurements are performed using the commercially available EUV Tech ENK (EUV n/k tool), based on a compact continuously tunable laser-produced plasma light source. In this presentation we describe experiments validating the accuracy and precision of actinic scatterometry-based pattern phase measurements conducted on the ENK platform on seven samples of EUV attenuated phase shift absorbers of varying thickness. We demonstrate good agreement with simulation on measurements of phase vs absorber thickness and phase vs grating pitch, validating the suitability of this measurement for measuring the actinic phase shift of an EUV mask.
Anamorphic High-Numerical Aperture (NA) EUV photomask manufacturing presents some unique challenges and opportunities in Critical dimension (CD) Scanning electron microscope (SEM) metrology. Novel methods of beam scanning condition are needed to improve image resolution and reduce image blurring to enable reliable metrology for the curvilinear mask era. Additionally, electron optics stigmation monitoring plays a major role in ensuring the horizontal to vertical (X-Y) CD Average to target (ATT) tool matching is not drifting due to aberrations, which are key for anamorphic EUV mask metrology. In this paper, we show the correlation between offsets in Condenser lens, Aperture balance, and electron beam Stigmation offset and its impact on horizontal and vertical feature CD ATT and CD uniformity measurements. Using Advantest E36xx Scanning electron microscopes we also present preliminary results, from improving measurement repeatability (ATT and CDU) on different mask substrates by incorporating Shadow reduction scanning (SRS), enhanced charge suppression using Charge neutralization technology and modulating dose of the beam (which is a function of scan condition and beam condition) In conclusion, we summarize the key metrology advances needed for next generation CD-SEM tools for High NA EUV photomask metrology, such as automated column optics monitoring, shadow reduction scan, design-based site focusing, high degree of measurement precision better than 0.5 nm, charge mitigation capabilities, high Throughput (TPT), enhanced stage performance accuracy, among others.
Evaluation of lithography process or stepper involves very large quantity of CD measurements and measurement
time. In this paper, we report on an application of Scatterometry based metrology for evaluation of EUV photomask
lithography. Measurements were made on mask level with Ellipsometric scatterometer for develop-check CD (DCCD)
and final check CD (FCCD). Calculation of scatterometer profile information was performed with in-situ library-based
rigorous coupled wave analysis (RCWA) method. We characterized the CD uniformity (CDU) and metal film thickness
uniformity. OCD results show that high precision CD measurement EUV absorber and resist is possible with this
method.
A series of simulations were also performed to investigate the feasibility of Ellipsometric scatterometry for various
pitches/line CD sizes, down to 11nm half-pitch at 1x magnification. The data showed that Scatterometry provides a
nondestructive and faster mean of characterizing mask CD performance for various EUV process generations.
As technology nodes go down to 45nm and below, mask metrology becomes more important as the critical features
decrease in size, while, at the same time, the number of measurements that need to be performed increases. OPC and
RET put further burden on metrology as it is typical to measure more than one dimension on a single feature. In order to
maximize the throughput of metrology tools and to keep up with the demand for more measurements, we have
implemented the ability to measure multiple CD sites within a field of view without any stage movement in fully
automated ways in a production environment. This in turn reduces total mask measurement time and helps to increase
tool capacity
As PSM (Phase Shift Mask) process moves toward 45nm and 32nm node, phase control is becoming more important
than ever. Both attenuated and alternating PSM need precise control of phase as a function of both pitch and target
sizes. However conventional interferometer-based phase shift measurements are limited to large CD targets and requires
custom designed target in order to function properly, which limits clear understanding and control of small target PSM
features.
New type of Phase metrology tool created by Zeiss, in collaboration with Intel has been introduced and Intel's 45nm
node PSM targets have been measured.
In this paper we present test results from AAPSM/EAPSM targets with space CDs down to 45nm a wafer-level.
Smallest pitch was 300nm print pitch, 150nm CD at mask (75nm pitch at wafer). In addition to this, phase and
transmission matching between conventional phase metrology tool and new tool has been investigated and shown.
As lithography mask process moves toward 45nm and 32nm node, phase control is becoming more important than ever.
To ensure an accurate printing both attenuated and alternating PSMs (Phase Shift Masks) need precise control of phase
as a function of both pitch and target sizes. However critical target CDs fall much below conventional phase metrology
tools capabilities. Interferometer-based phase shift measurements are limited to large CD targets and require custom
designed features in order to function properly, which limits phase measurement. AFM (Atomic Force Microscopy)
methods are able to capture small feature sizes but do not consider any diffraction effects which are caused by the
topography of the features itself when getting close to the used wavelength.
Imaging simulations, both, in a rigorous and a Kirchhoff regime, show the dependency of the phase in the image plane
of a microlithography exposure tool on numerical aperture and pitch due to the loss of phase information in the imaging
pupil. Additionally, for small features the phase is strongly impacted by polarization and 3D mask effects. For these
feature sizes, the image phase does not coincide with the etch depth equivalent phase calculated from the nominal depth
and optical constants of the shifter material. Deviations up to 20° have been observed leading to strong variations in the
imaging quality and process window variations during scanner printing. Considerations of CD variation between 0 and
pi features by simulation show lowest 0/pi CD variation and therefore largest process window if the scanner relevant
phase is at 180°. The simulation results illustrate the importance to measure the scanner relevant phase, effective in the
image plane of the scanner.
Consequently Zeiss, in collaboration with Intel, has developed a laterally resolving Phase Metrology Tool - Phame® -
for in-die phase measurements. The optical metrology tool is able to perform in-die phase measurement on alternating
PSM, attenuated PSM and CPL masks down to 120nm half pitch at mask. On-axis measurement results have already
been published.
In this paper we elaborate on off-axis phase measurement theory and procedure. Furthermore we present first off-axis
measurement results over varying features sizes using different illumination conditions.
As lithography mask process moves toward 45nm and 32nm node, phase control is becoming more important than ever.
Both attenuated and alternating Phase Shifting Masks (PSM) need precise control of phase as a function of both pitch
and target sizes. However conventional interferometer-based phase shift measurements are limited to large CD targets
and require custom designed patterns in order to function properly, which limits phase measurement Zeiss is currently
developing an optical phase measurement tool (PhameTM), providing the capability of extending process control from
large CD test features to in-die phase shifting features with high spatial resolution. The necessity of designing this
optical metrology tool according to the optical setup of a lithographic exposure tool (scanner) has been researched to be
fundamental for the acquisition of phase information generated from features close to the size of the used wavelength. It
was found by simulation that the image phase of a scanner depends on polarization and the angle of incidence of the
illumination light due to rigorous effects. Additionally, for small features the phase value is strongly influenced by the
imaging NA of the scanner due to the loss of phase information in the imaging pupil.
Simulations show that the resulting scanner phase in the image plane only coincides with the etch-depth equivalent
phase for large test features, exceeding the size of the in-die feature by an order of magnitude.
In this paper we introduce the PhameTM phase metrology tool, which enables the industry to perform in-die phase
control for Alternating PSM, Attenuated PSM and CPL masks. The PhameTM uses a 193nm light source with the optical
capability of phase measurement at scanner NA up to the equivalent of a NA1.6 immersion scanner, under varying,
scanner relevant angle of incidence for Attenuated PSMs and CPLs, and with the possibility of polarizing the
illuminating light. New options for phase shifting mask process control on in-die features will be outlined with first
phase measurement results for varying states of polarization.
As lithography mask process moves toward 45nm and 32nm node, phase control is becoming more important than ever.
Both attenuated and alternating PSMs (Phase Shift Masks) need precise control of phase as a function of both pitch and
target sizes. However conventional interferometer-based phase shift measurements are limited to large CD targets and
requires custom designed target in order to function properly, which limits phase measurement.
Imaging simulations, both, in a rigorous and a Kirchhoff regime, show the dependency of the phase in the image plane
of a microlithography exposure tool on numerical aperture, polarization, and on the so-called balancing of the mask for
features close to the size of the used wavelength. For these feature sizes, the image phase does not coincide with the
etch depth equivalent phase calculated from the nominal depth and optical constants of the shifter material.
Additionally, for PSMs generating phase jumps deviating from 180°, the resulting phase in the image plane of a
microlithography exposure tool depends on the transmitted diffraction orders through the aperture of the imaging
system.
Consequently Zeiss, in collaboration with Intel, has started the development of a laterally resolving Phase Metrology
Tool (Phame) for in-die phase measurements.
In this paper we present this optical metrology tool capable of phase measurement on individual line/spaces down to
120nm half pitch. Alternating PSM, Attenuated PSM, Cr-less masks were measured on various target sizes and
simulations were performed to further demonstrate the capability and implication of this new method to measure the
scanner relevant phase in-die, taking into account NA, polarization, and rigorous effects.
Evaluation of lithography process or stepper involves very large quantity of CD measurements and measurement
time. In this paper, we report on a application of Scatterometry based metrology for evaluation of binary photomask
lithography. Measurements were made on mask level with ODP scatterometer then on wafer with CD-SEM. 4 to 1
scaling from mask to wafer means 60nm line on wafer translates to 240nm on mask, easily measurable on ODP.
Calculation of scatterometer profile information was performed by a in-situ library-based analysis (5sec/site). We
characterized the CD uniformity, linearity, and metal film thickness uniformity. Results show that linearity measured
from fixed-pitch, varying line/space ratio targets show good correlation to top-down CD-SEM with R2 of more than
0.99. ODP-SEM correlation results for variable pitch shows that careful examination of scatterometer profile results in
order to obtain better correlation to CD SEM, since both tools react differently to the target profile variation. ODP
results show that global CD distribution is clearly measurable with less outliers compared to CD SEM data. This is
thought to be due to 'averaging' effect of scatterometer. The data show that Scatterometry provides a nondestructive and
faster mean of characterizing lithography stepper performanceprofiles. APSM 1st level (before Cr removal) 'dual-space'
CDs and EPSM rectangular contacts were also measured with and results demonstrates that Scatterometer is capable of
measuring these targets with reasonable correlation to SEM.
Design Based Metrology (DBM) requires an integrated process from design to metrology, and the very first and key
step of this integration is to translate design CD lists to metrology measurement recipes. Design CD lists can come from
different sources, such as design rule check, OPC validation, or yield analysis. These design CD lists can not be directly
used to create metrology tool recipes, since tool recipe makers usually require specific information of each CD site, or a
measurement matrix. The manual process to identify measurement matrix for each design CD site can be very difficult,
especially when the list is in hundreds or more. This paper will address this issue and propose a method to automate
Design CD Identification (DCDI), using a new CD Pattern Vector (CDPV) library.
KEYWORDS: Scanning electron microscopy, Critical dimension metrology, Photomasks, Atomic force microscopy, Binary data, 3D modeling, Cadmium, Metrology, 3D acquisition, 3D metrology
Scatterometers are widely used for line/space or 2D structure measurements in both wafer and mask industries. This
technology is now gaining more acceptance and is being applied 3D structures such as contacts and pads. Contact CDs
and trench depth in photomasks are critical monitoring parameters in mask industry and are discussed here.
We are reporting contact CDs and profile results measured from targets from Binary, PSM, and Crless plates. The
strategies of model creation such as using simple trapezoid versus more advanced shapes affect how well SWA and
footings can be measured and reported from these structures. We are reporting CD and profile information obtained
with Scatterometer, and then comparing CD SEM, AFM, and cross section SEM. Multiple different modeling
configurations were used with different levels of complexity, and we report on optimum modeling strategy to obtain
profile information from 3D structures. The relationship between the modeling strategy versus cross correlation between
different parameters is discussed. CD linearity, uniformity, and other correlation parameters to the reference CD SEM
tool are reported. Target CDs ranged from 60nm up to 600nm. CD uniformity reported from Scatterometry is 20~30%
less than that from CD SEMs. This CD uniformity improvement is due to the fact that scatterometer beam samples
dozens to hundreds of samples and 'averages' profile parameters, thus eliminating local effect such as line edge
roughness. Contact depth are also measured and compared to AFM, in which the bias between the two tools are usually
around 3nm or less. In terms of smallest target CD measurable, in this paper we report routine measurement of small
contacts with middle CD down to 65nm (bottom CD close to 50nm) with both RP and SE mode.
Application of scatterometry method to mask contacts and pads leads to accurate and fast measurement of 3D profiles,
and opens up possibility of in-line monitoring of profile information due to the higher runrate compared to traditional
metrology tools.
Linewidth and etch depth control on the photomask is rapidly becoming a major concern in mask processing. In this paper, we report on a Scatterometry based metrology system that provides line width and etch profile measurements on Embedded PSMs on Intel's 65nm and 45nm node test masks. Measurements were made with Nanometric's Atlas-M reticle measurement system. Spectrum data obtained from plates were analyzed using Timbre Technologies' ODP analysis software. We characterized the CD uniformity, linearity, sidewall angle and thickness uniformity. Significant reduction in time per measurement is achieved when compared to CD-SEM. ODP Scatterometry reported a 2x reduction in the CD Uniformity compared to that reported from the SEM. This reduction is typically due to outliers reported by the CD-SEM that is averaged out in ODP Scatterometry. Good correlation to top-down CD-SEM and cross-sectional SEM is reported. R-squared correlation of >0.99 (ODP scatterometry to top down CD-SEM) is reported. Profile measurements from ODP show excellent match to cross-section SEM. The data show that Scatterometry provides a nondestructive way to monitor basic etch profile combined with relatively little CD metrology lag.
Control of line width and profile is gaining more importance in photomask processes as the industry moves toward 45nm node and beyond. In this paper we report scatterometer measurements of CD and profile data from chrome-less mask profile processed using Intel's 65nm and 45nm node technology. As opposed to the highly charging nature of chrome-less plate during CD SEM measurements, scatterometry provides a non-charging optical alternative to measure critical CDs. As for trench depth measurement, scatterometry has big advantage over AFM with its much higher throughput (about 5 seconds vs. >2min). Since quartz plate is very transmittive to lights, we use eliipsometer-based scatterometry instead of conventional reflective-photometer based one. Parameters characterized in this study include line/space CD, contact CD, and trench depth. Correlation to top-down CD-SEM, cross-sectional SEM, and AFM is reported. Line CD uniformity reduction is more than 30% compared to that from CDSEM, due to averaging effect of scatterometry as well less lack of charging during measurements. Depth bias to AFM was around 3nm in both DCCD and FCCD height measurements we performed. The data show that Scatterometry provides a nondestructive way to
monitor basic etch profile combined with relatively little time loss from measurement step.
In this paper, we report on a Scatterometry based metrology system that provides line width, line thickness, and
trench depth measurements on APSM and EPSM photomasks. Measurements were made with scatterometer in DUV to
visual wavelength range. Calculation of profile information was performed by a library-based analysis software. We
characterized the CD uniformity, linearity, trench depth uniformity. Results show that linearity measured from fixed-pitch,
varying line/space ratio targets show good correlation to top-down CD-SEM with R2 of more than 0.99. EPSM
FCCD data was obtained from both scatterometer and CDSEM. Results show that MEEF calculation based on
scatterometer CD shows about 40% improvement in removing mask-induced CD non-uniformity, compared to
calculation based on CD SEM data. This is thought to be due to 'averaging' effect of scatterometer. Depth measurements
from APSM show that scatterometer makes good correlations to AFM, generally within 3nm of each other. The data
show that Scatterometry provides a nondestructive means of monitoring PSM profiles combined with relatively little
time loss.
We have developed and characterized a stack of TaN (absorber) and TaON (ARC) using reactive magnetron sputtering method. Two DOE (design of experiments) were performed with varying gas and power parameters and their effects on the various film parameters are discussed. We characterized the stress, uniformity, reflectivity (for defect inspection and EUV wavelengths), defect adders, and etch performance. Film property characterization was performed with AFM, Optical reflectance measurement tool, Particle inspection tool and profilometer. Optimized film stack met or exceeded ITRS guideline for EUV lithography mask with film stress less than 200MPa, inspection wavelength reflectivity at 9%, and thickness uniformity less than 5%. Defect adder number (< 0.5 / cm2) was a strong function of underlying film surface roughness and cleanliness of surface as well as deposition parameters.
In this paper, we report on a Scatterometry based metrology system that provides line width and thickness measurements on binary, APSM, EPSM masks both on FCCD (final check CD) and DCCD (develop check CD), fabricated on 193nm process. Measurements were made with scatterometer in DUV to visual wavelength range. Calculation of profile information was performed by a library-based analysis software. We characterized the CD uniformity, linearity, trench depth uniformity. Results show that linearity measured from fixed-pitch, varying line/space ratio targets show good correlation to top-down CD-SEM, meanwhile linearity from wide range of different pitch generally does not correlate well and therefore post-measurement calibration is needed. Depth measurements from APSM show that scatterometer makes good correlations to AFM. The effect of optical properties of the film layers on metrology performance is discussed. The data show that Scatterometry provides a nondestructive of monitoring basic etch profile combined with relatively little time loss from CD measurement step.
At Intel Mask Operations (IMO), Standard Mechanical Interface (SMIF) processing has been employed to reduce environmental particle contamination from manual handling-related activities. SMIF handling entailed the utilization of automated robotic transfers of photoblanks/reticles between SMIF pods, whereas conventional handling utilized manual pick transfers of masks between SMIF pods with intermediate storage in Toppan compacts. The SMIF-enabling units in IMO's process line included: (1) coater, (2) exposure, (3) developer, (4) dry etcher, and (5) inspection. Each unit is equipped with automated I/O port, environmentally enclosed processing chamber, and SMIF pods. Yield metrics were utilized to demonstrate the effectiveness and advantages of SMIF processing compared to manual processing. The areas focused in this paper were blank resist coating, binary front-end reticle processing and 2nd level PSM reticle processing. Results obtained from the investigation showed yield improvements in these areas.
The silicon/silicon dioxide (Si/SiO2) materials system provides a high index contrast waveguide platform compatible with existing monolithic microelectronic fabrication processes. The large index difference between the Si and SiO2 ((Delta) n approximately equals 2.0) allows the miniaturization of waveguide cross-sectional dimensions: single-mode strip waveguides with 0.2 X 0.5 micrometers cross-sections are possible. Additionally, right angle waveguide bends with radii of 2.0 micrometers can be fabricated with insertion loss of less than 1.0 dB. Bend radii of 250 micrometers or more are required to achieve the same performance in less confined waveguide systems such as GaAs/AlGaAs. The high confinement of the Si/SiO2 system also allows Y-branch power splitters with splitting angles greater than 20 degree(s) to operate with low loss. The combination of small cross- section, small bend radius, and large splitting angle provides a highly compact light guiding technology. Calculations of the loss due to 90 degree(s) bends in these waveguides and preliminary loss measurements for bends from 2.0 to 100.0 micrometers in radius are reported. Y-branch power splitters are analyzed and measurements of branches from 2 degree(s) to 40 degree(s) are presented.
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