metrologia smart metrology. spectel’s mission improve accuracy, physical understanding, and...
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METROLOGIAMETROLOGIA
SMART METROLOGYSMART METROLOGY
Spectel’s Mission
• Improve Accuracy, physical understanding, and stability for metrology through software products
• Provide offline measurement software for failure analysis, OPC rules determination metrology, inverse scattering methods, and metrology on research lines.
When is accuracy important
• Building standard artifacts
• Failure Analysis
• Determining OPC corrections using empirical methods
• Focus exposure matrix analysis
• Sometimes in in-line production monitoring
Are Top-Down SEM Images Accurate
• The industry consensus is that without calibration the accuracy of top-down SEMs is limited to about 20nm.
• With calibration to some de-facto standard, relative accuracy depends on process variability, SEM settings, and measurement algorithm type. Basically it’s an unknown.
• So the consensus answer is no, top-down SEM measurements are not accurate today.
What are the hopes for better CD accuracy?
• Cleaved cross-sectional SEM measurements
• Ion-beam-milled cross sectional measurements
• Advanced Atomic Force Microscope tool with good tip deconvolution algorithm
• Inverse scattering method with top-down SEM
Accuracy requirement for photomask CDs is also getting more severe
• Optical measurements with calibration to NIST standards are still the primary measurement done on photomasks and reticles
• Top-down SEMs and AFMs are coming into use
Where Does Metrologia Fit In?
• We simulate the image for optical or SEM images
• We measure linewidths with state of the art algorithms
• We are perfecting inverse scattering measurement algorithms for using simulations in the measurement process
• We help improve the measurement stability with Fourier Transform based sharpness tools.
Simulation
• Optical Systems– Classical Brightfield and Darkfield Microscopes
– Confocal - Ideal as well as finite pinholes
– Coherence Probe - complex mutual coherence function
– Reflection and Transmission cases covered
– Diffraction Gratings
– Multilayer Film Stacks
– Spherical aberration, coma, and illumination decenter
Simulation
• Scanning Electron Microscopes– Backscatter electron Model
– Secondary electron Model
– Transmission and reflection modes
– Material database
– Future support for NIST’s Monsel model
– Graphical Display of Simulation Data
– Measurement of Simulated Data
Fourier Transform Sharpness Analysis
• Based on the research of Postek and Vladar at NIST
• Gives estimates of sharpness and beam eccentricity
• Provides feedback for adjusting an SEM
• Has database for storing results
• Can be used for quantifying vibration and noise as well
• Requires an isotropic, high resolution, and stable sample
Fourier Transform Sharpness Analysis Continued
• Can be used to quantify the relative degree of granularity of a specimen as well, and so could be used for surface tribology in top-down SEM images.
• Can be used with optical microscopes to measure and quantify resolutoin and asymmetry in the imaging optics. Could be use to qualify objective lenses or stepper lenes.
Measurement
• Measurement algorithms are provided which can be used on SEM or optical images
• Images can be taken from tif, jpeg, bmp , or other file formats, or can be acquired from a video feed by using a frame grabber supported by our software
Measurement
• CD measurements are provided using several options:– Threshold between max and min using linear regression
– Sidewall-base crosspoint, sometimes known as “regression to a baseline”, for measuring bottom widths of lines
– Peak of edge signal for measuring tops of lines approximately
Optical Film ThicknessOptical Film Thickness
• Builds multi-layer stacks
• Plots reflection, absorption, & transmission
• Plots vs. angle, wavelength, layer thickness
• Inputs material models
Diffraction Grating ScatterometryDiffraction Grating Scatterometry
• Calculates diffraction efficiencies and
phases for gratings
• Plots scattered rays
• Tests reciprocity for accuracy
• Uses Analytic Wave-guide method
Analytic Wave-guide MethodAnalytic Wave-guide Method
• Uses exact eigenfunctions rather than
Fourier approximation
• Proven faster, more accurate, and more
convergent than rigorous coupled wave
• Similar to the “Botten Method”.
Optical Image SimulationOptical Image Simulation
• Simulates classical optical microscopes
• Simulates confocal microscopes
• Simulates coherence probe microscopes
• Uses Analytic Wave-guide method.
Classical MicroscopeClassical MicroscopeImage Plane
Laser Confocal MicroscopeLaser Confocal Microscope
Ilumination pinhole
Image pinhole
Linik Coherence Probe MicroscopeLinik Coherence Probe Microscope
Real-time Confocal MicroscopesReal-time Confocal Microscopes
Nipkow Disks and Large
Non-ideal Pinholes
Alignment error due to coma
Stepper Aerial Image SimulationStepper Aerial Image Simulation
• Rigorous vector simulation of aerial images
• Uses Analytic Waveguide method, proven to be
accurate and convergent for reticles.
Stepper Aerial Image SimulationStepper Aerial Image Simulation
Based on rigorous vector solutions
Aberrations Simulated
• Spherical Aberration
• Coma
• Illumination decentering
Bitmap representation of pupil
Aperture decentering
SEM Monte Carlo SimulationSEM Monte Carlo Simulation
• Backscattered and secondary electron simulationBackscattered and secondary electron simulation
• Measurement capabilityMeasurement capability
• Compatible with inverse scattering codeCompatible with inverse scattering code
• Checked with NIST Monte Carlo code - MONSEL - Checked with NIST Monte Carlo code - MONSEL -
under SEMATECH contract.under SEMATECH contract.
Detector Properties
• Left and Right Detectors for Backscattered Electrons
• Minimum and maximum angle for detector
• Minimum and maximum energy for detector as % of beam
SEM Geometry Editor
SEM Geometry Editor
Increase the number of polygons to the desired
number
SEM Geometry Editor
Change the Edit polygon number to the polygon
you wish to edit
Polygon Editor
Polygon Editor
Makes a rectangle ofgiven height and width
Polygon Editor
Corners,click on to select
Polygon Editor
Press Modify to changecorner to new values
Polygon Editor
Press “Add Point” to adda new corner point at end
Polygon Editor
Press “Insert” to adda new corner point at
selected position
Polygon Editor
Press Delete Pointto remove the selected
point.
Polygon Editor
Create rounded cornersand insteps to a foot
with the “Round Corner”button.
Polygon Editor
Press “Material Selection” button to select a material
Polygon Editor
Press “SelectPoints” button to select the
polygon
Material Selection Database Navigator
Measurement of Simulated SEM Line ScansMeasurement of Simulated SEM Line Scans
Animated Ray Tracing of Monte Carlo- Animated Ray Tracing of Monte Carlo- Simulated SEM DataSimulated SEM Data
Material Properties DatabaseMaterial Properties Database
• Several n & k databases are included
• A database for atomic scattering parameters
is also included for use with SEM Monte
Carlo analysis.
SEM MonitorSEM Monitor
• Cross sectional dimensional measurements
• Top-down SEM CD measurements
• SEM focus measurements
• SEM astigmatism measurements
SEM Monitor/MeasureSEM Monitor/Measure
• Measures distances with various edge criteria:– Side wall and base line cross point
– Threshold and peak
• Measures the apparent primary electron beam width
• Saves data in compatible file
The software that allows you to correctly measure your sample in a top-down CD SEM and a laboratory
SEM
Cross Sectional Dimensional MeasurementsCross Sectional Dimensional Measurements
Cross Sectional Dimensional MeasurementsCross Sectional Dimensional Measurements
Built-in statistical analysis of all data
Cross Sectional Dimensional MeasurementsCross Sectional Dimensional Measurements
All data are saved in compatible text
files
SEM Monitor/MeasureSEM Monitor/Measure
• Measures distances with various edge criteria:– Side wall and base line cross point
– Threshold and peak
• Measures the apparent primary electron beam width
• Saves data in compatible file
The software that allows you to correctly measure your sample in a top-down CD SEM and a laboratory
SEM
Top-down CD SEM MeasurementsTop-down CD SEM Measurements
Top-down CD SEM MeasurementsTop-down CD SEM Measurements
Built-in statistical analysis of all data
Top-down CD SEM MeasurementsTop-down CD SEM Measurements
All data are saved in compatible text
files
SEM Monitor/SharpnessSEM Monitor/Sharpness
• Fourier analysis measures image sharpness and
astigmatism of the primary electron beam
– Gives quantitative measure of SEM performance
– Real time analysis while you set the SEM
• Saves data in compatible file
The software that allows you to correctly set your top-down CD SEM and laboratory SEM
SEM Focus MeasurementsSEM Focus Measurements
SEM Focus MeasurementsSEM Focus Measurements
Fourier transform-based image
sharpness analysis
SEM Focus MeasurementsSEM Focus Measurements
Parameter set for correct sharpness
analysis
SEM Astigmatism MeasurementsSEM Astigmatism Measurements
SEM Astigmatism MeasurementsSEM Astigmatism Measurements
Shows the original image and 2D
Fourier magnitude distribution
SEM Astigmatism MeasurementsSEM Astigmatism Measurements
Primary electron beam shape monitor
and sharpness parameters
Real Time SEM Sharpness MeasurementsReal Time SEM Sharpness Measurements
Real Time SEM Sharpness MeasurementsReal Time SEM Sharpness Measurements
Real time beam
shape monitoring
Real Time SEM Sharpness MeasurementsReal Time SEM Sharpness Measurements
Real time image sharpness and astigmatism calculation
SEM Monitor/AdaptiveSEM Monitor/AdaptiveMonte Carlo SimulationMonte Carlo Simulation
• Automatically finds the best fit of measured and
modeled line scans
– Extensive modeled library of production samples possible
– Finds the best fit depending on:
• the beam parameters of the SEM
• specimen geometry
• Possibility of accurate measurements based on physical first principles
Applications
• New class of potentially rigorously accurate linewidths
• Sidewall angle information from top-down SEM
• Can determine the beam shape
• Can be used to measure other non-obvious dimensions and shapes, chemical compositions, etc. as the technique is very general
Description of Method
• First one precalculates a library of Monte Carlo runs which illustrate the process variability that is addressed by the Metrology
• Then one takes a line scan of data from an SEM
• The software uses an Adaptive Least Squares Method
• Alignment is achieved by shifting the Monte Carlo signal relative to the scan signal and using Least Squares to test for best alignment
Description of Method
• All of the files in the search set are tested for best fit
• The best fitting Monte Carlo simulation wins and is reported in the output. The widths and other parameters used in the simulation are attributed to the measured object.
Adaptive Monte Carlo SimulationAdaptive Monte Carlo Simulation
Adaptive Monte Carlo SimulationAdaptive Monte Carlo Simulation
Select the file which contains there scan data
Press this button to plot the selected scan file
Plot of acquired data
Sliders adjust the area to be used for
camparison
Adaptive Monte Carlo SimulationAdaptive Monte Carlo Simulation
Possibility to accommodate to
electron beam and detector parameters
Beam Shape Formula
• The beam is parametrized as a Guassian which is modulated by a multiplicative polynomial function
Adaptive Monte Carlo SimulationAdaptive Monte Carlo Simulation
Library of modeled structures helps to
find the best fit
Adaptive Monte Carlo SimulationAdaptive Monte Carlo Simulation
Plots the measured and best fit
modeled line width over the measured
structure
Adaptive Monte Carlo SimulationAdaptive Monte Carlo Simulation
Automatically finds the best fitting real structure and the beam diameter
Adaptive Monte Carlo SimulationAdaptive Monte Carlo Simulation
Changing waveforms due to various primary electron beam diameters (nm)
Dimensional Metrology Application
• In development, planned for 1999.
• Automatic offline measurement of SEM images and data
• Will include automatic fine alignment to allow operatorless batch processing of a directory of image files or line scans.
Applications for Dimensional Metrology Application
• Measurements on cross-sectional, ion beam milled, and off-line top-down SEM measurement.
• Failure analysis
• Developing Rules for Optical Proximity Correction
• Research and prototype lines
• Reverse engineering laboratories
• Mask metrology
Measurement Tool Features
• Linewidth or CD measurements
• Contact Hole measurement
• Angles
• Corner rounding
• Overlay
• pitch
• Edge roughness
Measurement Tool Features
• CD measurement with a large number of possible algorithm choices:– Threshold based on regression
– Regression to a baseline or “sidewall-base crosspoint”
– Peak to peak width
– Sygmoidal fit to data
– Apparent beam width
Measurement Tool Features
• Contact Holes– Upper and bottom rim measurement
– Operator assisted to help deal with poor signal to noise
– Shape and size of the contact hole and assessment of whether it is open or closed
– A video clipping warning will be included to indicate if there is image clipping (either high or low) in the area of interest
Measurement Tool Features
• Cross-sectional measurement– Vertical and horizontal dimensions of multilayer
structures
– Roundness of corner and foot
– Surface roughness estimated with RMS algorithm
– Will handle focused ion beam milled samples as well
Measurement Tool Features
• Will measure rotation of lines from horizontal/vertical and will apply a geometrical correction to CD measurements
• Will give estimates of signal to noise ratios
• Extensive graphical analysis of results database
• Fully documented
Measurement Tool Features
• Work from image file or acquired image from video feed with a frame grabber
• Will include software to control and utilize a frame grabber
• Compatibility with non-standard line-scan data formats as the need arises
• Operating system: Windows NT, Windows 95/98
Measurement Tool Features Cont’d
• Push-button image swapping with Adobe Photoshop so that all the power of photoshop can be available for metrology
• Database storage for training and results files
• Automatic batch mode available