extending lateral resolution of optical profiling beyond ... · going beyond the optical...

$: Extending Lateral Resolution of Optical Profiling Beyond ... · Going Beyond The Optical Diffraction Limit in Optical Profilometry Keywords: optical profiling, optical profilometry,$
Extending Lateral Resolution of Optical Profiling Beyond the Optical Diffraction Limit

Dr. Erik Novak

Director of Technology Development

Bruker Nano Surfaces Division-- Stylus and Optical Metrology Unit

• Lateral Resolution of Microscopes

– Basics of resolution

– Methods of increasing lateral resolution

• Bruker’s ContourGT 3D Microscope

– Principle of Operation

– Enabling Technologies for resolution enhancement

• AcuityXR Measurement Mode

– How the measurement is made

– Visualization of fine features

– Improved metrology on narrow linewidths

• Conclusions

June 16, 2011 Slide 2© Copyright 2011, Bruker Inc. All Rights Reserved


Optical Systems All Blur The Objects They Image

• Two Fine Lines Become Blurred Together

• Width of the blurred image is given by

– This criteria means the first zero of one feature corresponds to the maximum of the neighboring feature

– Optical resolution improved by moving to smaller wavelengths

– Optical resolution improved by collecting more light with lenses


ObjectOpticalSystem

Image

δ = 0.61λ / NA


Two Cases Will Ultimately Limit Resolution

• Detector-limited resolution

– Not enough pixels to resolve a feature

– Typical for lower magnifications (<20X)

• Optical (Diffraction) Limited Resolution

– Blur of the system limits ability to resolve a feature

– Typical for high magnification (>20X)



Several Methods Increase Lateral Resolution for Detector Limited Systems

• Move to higher pixel cameras

– Slows down acquisition

– Not possible in most situations

• Combine multiple images together

– Translate object with respect to imaging system

– Determine amount translated between images and recombine

• Either case can result in superior images



Diffraction Limited Resolution Presents Greater Challenges

• Fluorescent Systems Can Improve Resolution by only lighting one pixel at a time

– Technique can take hours/days to image a sample

– Only appropriate for 2D, biological data

– Zeiss has implemented this commercially with good results



If the Blurring Function is Perfectly Known The Effect Can Be Removed

• Some success has been shown by changing the illumination to add additional data

– Inappropriate for general optical systems due to noise and the complexity of the structured illumination

– 100nm holes modeled here

• More common techniques are to iterate results to guess the optical blur

– Practical results have limited success due to noise and image complexity



Bruker’s ContourGT 3D MicroscopesProduce 3D Images of Objects

• Microscope with specialized objectives to gain information about sample height• Scan the optics so all of the object in the field of view passes through focus• Analyze the focus scan to determine height information



Bruker’s ContourGT 3D Microscopes Contain Design Feature for Enhancing Lateral Resolution

• Ultra-low noise CCD Camera

– Can achieve repeatable height maps results to below 0.01nm

• Most Stable mechanical design– Repeatable, small motions from vibration/acoustics

• Precise Focus Scan

– PZT or 0.1nm resolution stepper motor for the focus scan

• High Quality XY staging with 0.5 µm encoders

• Parfocal/Parcentric objectives for easy magnification changes

• Advanced, 64 bit software for maximum computing power



AcuityXR Enhances Lateral Resolution at All Magnifications

• AcuityXR Measurements:

– Operate on measurements using phase information from the sample (PSI or HDVSI modes)

– Scan the object multiple times (at least 10)

– Combine the information from those multiple height maps

– Use advanced modeling of the optical system with the combined height map information to improve resolution

• Works for both detector limited and diffraction limited measurements

– Provides a final image with twice the pixel count provided by the camera



AcuityXR Can Enhance Many Measurements

• AcuityXR Measurements are appropriate for:

– Smooth and flat samples (mirrors, wafers, polymers, thin film solar or batteries)– Smooth and curved samples (medical implants, lenses)– Smooth and stepped samples (MEMS devices, etched semiconductors…)

• AcuityXR is Not Appropriate for some samples:

– Samples with Roughness >10nm (paper, cloth, unpolished wafers, silicon solar)– Samples with large areas of missing data (PSS wafers, metal with drilled holes…)June 16, 2011 Slide 11© Copyright 2011, Bruker Inc. All Rights Reserved


AcuityXR Improves Results at Low Magnifications

• 5X Measurement of Semiconductor Wafer



Cleaner Edges and Finer Detail Possible on MEMS Devices

• 10X (pixel limited) magnification was used

• Superior metrology on widths, heights, area, volume is achievable



June 16, 2011 15

Standard Resolution Resonator Ridges Are Highly Pixelated

© Copyright 2011, Bruker Inc. All Rights Reserved


June 16, 2011 16

AcuityXR Resolution Resonator Ridges are Sharp

Bruker Confidential Information© Copyright 2011, Bruker Inc. All Rights Reserved


At High Magnifications 130nm Lines Can Be Distinguished

• Bruker’s 115X objective used

• Detection is 3 times higher than the diffraction limit


150nm lines with 150nm spacing

130nm lines with 130nm spacing


June 16, 2011 18

Grating, Textured Bumps, and 250nm linewidth with PSI (left) and AcuityXR (right)

• 200nm grating

• 5 µm semiconductor features

• 150nm line pair



AcuityXR Enhances Narrow Features



June 16, 2011 20

AcuityXR Visually Sharpens Images



June 16, 2011 21

AcuityXR Visually Sharpens Images



Greater Detail on Polymer Films is Evident


Feature height is 90nm, width about 8 µm


AcuityXR Improves Metrology of Narrow Features

• Vision64 Image Segmentation Used to Characterize Linewidths of 350nm Features

June 16, 2011 Slide 23Bruker NSB Stylus and Optical Unit R&D Status Update 08OCT10 V1.4





Standard Contour Image Shows Rounded, Blurred Features




AcuityXR Contour Image Shows Sharp, Distinct Lines



Multi-Region Analysis




Standard Deviations of Results Improves Significantly

Line Width

(nm)

Volume

(um^3)

Standard Measurement

35.1631 0.0051

AcuityXR 5.2725

(6.6 times lower)

0.0014

(3.6 times lower)





Lateral Resolution Can Be Enhanced Using AcuityXR

• Bruker’s ContourGT 3D microscopes are designed to support AcuityXR

• Multiple measurements are made on smooth samples

• Results are combined intelligently to improve resolution even when limited by diffraction

• Features down to 130nm can be imaged

• Measurement repeatability of fine features is significantly improved


16.06.2011 29

AcuityXR is Available On Various Models

Increasing Functionality and Automation

GT-K1 GT-X8GT-X3GT-K0

NPFlex Dektak D150SP9900

VCM Confocal Microscope


QUESTIONS?

• Our website: www.bruker-axs.com

• For additional product information e-mail: [email protected]

• To find your local office: http://www.bruker-axs.com/nano_surfaces_business.html

• My e-mail: [email protected]

• Also, please fill out the exit survey at the end so our future webinars can be improved


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