metrologia smart metrology. spectel’s mission improve accuracy, physical understanding, and...

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


Built-in statistical analysis of all data


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


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


Built-in statistical analysis of all data


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


The software that allows you to correctly set your top-down CD SEM and laboratory SEM

SEM Focus MeasurementsSEM Focus Measurements


Fourier transform-based image

sharpness analysis


Parameter set for correct sharpness

analysis

SEM Astigmatism MeasurementsSEM Astigmatism Measurements


Shows the original image and 2D

Fourier magnitude distribution


Primary electron beam shape monitor

and sharpness parameters

Real Time SEM Sharpness MeasurementsReal Time SEM Sharpness Measurements


Real time beam

shape monitoring


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


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


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


Library of modeled structures helps to

find the best fit


Plots the measured and best fit

modeled line width over the measured

structure


Automatically finds the best fitting real structure and the beam diameter


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


• 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


• 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


• 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


• 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


• 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

metrologia smart metrology. spectel’s mission improve accuracy, physical understanding, and...

Documents

measurement stability

primary measurement

sem settings

relative accuracy

measurement processwe

measurement algorithm

severe optical measurements

sharpness analysisbased