TSOM Method for Nanoelectronics Dimensional Metrology Ravikiran - - PowerPoint PPT Presentation

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TSOM Method for Nanoelectronics Dimensional Metrology Ravikiran - - PowerPoint PPT Presentation

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TSOM: R&D 100 Award Winner TSOM Method for Nanoelectronics Dimensional Metrology Ravikiran Attota Nanoscale Metrology Group Physical Measurement Laboratory National Institute of Standards and Technology Gaithersburg, USA *TSOM is

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TSOM Method for Nanoelectronics Dimensional Metrology

*TSOM is pronounced as “tee-som” ; A latest presentation on TSOM can be found here.

TSOM: R&D 100 Award Winner

Ravikiran Attota

Nanoscale Metrology Group Physical Measurement Laboratory National Institute of Standards and Technology Gaithersburg, USA

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Contents

What is TSOM ? Method to construct TSOM images Characteristics of TSOM images Applications

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Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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TSOM: Through-focus Scanning Optical Microscopy

TSOM transforms conventional optical microscopes into three-dimensional metrology tools with nanometer scale measurement sensitivity Not an image resolution enhancement method

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Analysis in lateral and vertical directions as large as over 50 m. Requirement for defining the "Best Focus" is eliminated.

TSOM: Through-focus Scanning Optical Microscopy

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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  • By using a set of through-focus images

instead of one “best focus” image

  • Going beyond edge-based imaging
  • Using the image as a signal/dataset

How does TSOM achieve this?

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Requires a TSOM Image

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Digital camera Motor for focusing

Optical Microscope Schematic showing through- focus scanning of the target 2D optical images at different through-focus positions Optical intensity profiles extracted from the optical images Constructed TSOM image using the

  • ptical intensities

Animation showing the TSOM image construction method using a conventional optical microscope

Color scale represents the optical intensity Computer acquires multiple digital images of targets Computer algorithms process the acquired digital images and produce the TSOM images

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Isolated line

LW=Linewidth; LH=Line height; SW=Sidewall angle

Isolated Si line on Si substrate; = 546 nm; LW = 40 nm; LH = 100 nm

Differential TSOM images are distinct for different dimensional variations

LW40-LW41 LH100-LH101 LW40LH100-LW41LH101 SW89-SW90

Sidewall angle Line width and height Linewidth Line height

Simulation

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Linewidth difference = 2 nm

Differential images appear similar for small changes in the same dimension

Simulation

Linewidth difference Line Height difference Difference = 2 nm Difference = 4 nm

LW100-LW104

MSD=35x10-6

LH100-LH104

MSD=37x10-6

LH100-LH102 LW100-LW102

MSD=10x10-6 MSD=11x10-6

(TSOM Image1 – TSOM Image2 )

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MSD Total number of pixels (TSOM Image1 – TSOM Image2 ) =

2

MSD

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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  • TSOM images change with target (assumed to be unique).
  • Differential TSOM images
  • Highlight nanometer scale dimensional differences using a

conventional optical microscope.

  • Appear distinct for different dimensional change (breaks the

correlation between parameters, e.g., height and width, in the

  • ptical signal).
  • Are additive.
  • Appear qualitatively similar for a change in the same dimension.
  • Integrated optical intensity of differential TSOM image indicates the

magnitude of the dimensional difference.

  • TSOM images are (assumed to be) unique.
  • Robust to optical aberrations and illumination variations.
  • Good quantitative agreement between measurement and simulation

is not established yet.

  • Trends observed in simulations generally match measurements.

Characteristics of TSOM images: Summary

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Two Applications

  • Requires good agreement

between measurement and simulation

  • TSOM images are

assumed to be unique

  • Simulation is not

necessary but useful Evaluate differences in dimensions

  • Requires two targets

Determine dimensions of a target

  • Requires a library of either

Accurate simulations

  • r

Measurements

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Some Example applications

  • f the TSOM method

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Linewidth = 152 nm, Line height = 230 nm, Pitch = 601 nm, Wavelength = 546 nm, Si line on Si substrate.

(a) (b) Simulation Experiment

Simulation to Experiment comparison

Line gratings

Experiment

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Simulation to Experiment comparison

Differential TSOM images for 3 nm difference in the line width Experiment Simulation

Experiment

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Experimental line width determination using simulated library

TSOM Matched target line width : 153 nm AFM measured line width: 145 nm

MSD MSD

Experimental TSOM image Determining the dimension using the library matching method

Experiment

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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SEM measured size = 103 nm TSOM measured size = 106 nm

MSIx10-6 MSIx10-6

Experimental TSOM image of 121 nm nanodot = 546 nm. Si nanodot on Si substrate.

Size determination of nanodots (nanoparticles, quantum dots) using experimental library

SEM image of 121 nm nanodot Experimentally created library.

Experiment

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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6 5 4 3 2 1

Through Focus Distance, m

0 2.5 5.0

Distance, m

(a) (b) (c) (d)

0 2.5 5.0 0 2.5 5.0 0 2.5 5.0

Experimental defect analysis of four types

  • f 10 nm defects in dense gratings

Pitch = 270 nm, Linewidth = 100 nm, = 546 nm

Every 10th line smaller by 10 nm Every 5th line smaller by 10 nm Every 10th line larger by 10 nm Every 5th line larger by 10 nm Experiment

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Defect analysis: Random structure

Defect size: 25 nm, Defect height = 25 nm; Linewidth of the features= 100 nm, Line height =100 nm Wavelength = 365 nm, Si features on Si substrate

Defect X-Z plane Y-Z plane Defect X-Z plane Y-Z plane

Detected 25 nm defect that is 25 nm tall, (one fourth the height of the features) (XZ-plane reversed)

25 nm Defect Cross section

Simulation

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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High aspect ratio through silicon via (TSV) dimensional analysis

TSV Diameter = 5 m, Depth = 25 m, 20 nm change in the depth 20 nm change in the diameter

3D Metrology

5.0 m 25.0 m

= 546 nm

Simulation

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Photo mask application: Transmission microscope

Quartz

Chrome Photo mask target For line width measurements select low INA and TE polarization For line height measurements select low INA and TM polarization

Line width = 120 nm, Line height = 100 nm, Wavelength = 365 nm, UP=Unpolarized, TE=TE polarized, TM=TM polarized, MSD=Mean Square Difference

Dimension Diff. INA (nm) UP TE TM Line width 2 0.1 9.5 15.7 6.6 Line width 2 0.6 2.0 2.9 1.5 Line height 2 0.1 4.3 4.0 5.8 Line height 2 0.6 0.6 1.0 0.5 Chi Square, x10-6

MSD

Dimension Diff. INA (nm) UP TE TM Line width 2 0.1 9.5 15.7 6.6 Line width 2 0.6 2.0 2.9 1.5 Line height 2 0.1 4.3 4.0 5.8 Line height 2 0.6 0.6 1.0 0.5 Chi Square, x10-6

MSD

Simulated TSOM image Optimization of Illumination NA to obtain maximum sensitivity

Simulation

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Thin film metrology

1 nm 2 nm 3 nm Intensity normalized TSOM images at the edge of thin films for different film thickness

Calibration curve to measure films

  • f unknown thickness

Film Thickness

Area of analysis Simulation Experiment

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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  • 4 -2 0 2 4

OL=0 nm OL=2 nm

Overlay Targets for Double Patterning

First process Second process

Mean Square Difference

Simulations

Determination

  • f the overlay

value using the target

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Measured TSOM Image

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A simplified schematic of a MEMS device (fabricated at NIST) containing inner 20 mx20 m movable part and the outer fixed frame. Every time the device is powered the inner part moves 10 nm to the right side relative to the outer frame.

Differential TSOM image showing 10 nm movement of the inner part

Monitoring/Measuring Nanoscale Movements for MEMS/NEMS Devices

30 m 30 m 20 m 20 m Fixed frame Moving part 30 m 30 m 20 m 20 m Fixed frame Moving part

Simulation

Wavelength = 546 nm Calibration Curve Mean Intensity difference as a function of movement MD

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Advantages of the TSOM Method

  • Transforms conventional optical microscopes to truly 3D

metrology tools that provide excellent lateral and vertical measurement resolutions comparable to typical Scatterometry, SEM and AFM.

  • Has the ability to decouple vertical, lateral or any other

dimensional changes, i.e. distinguishes different dimensional variations and magnitudes at nanoscale with less or no ambiguity.

  • Has the ability to analyze large dimensions (over 50 m)

both in lateral and vertical direction.

  • Robust to optical and illumination aberrations.

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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  • Inexpensive, nondestructive, fast and simple, requiring

merely ubiquitous conventional optical microscopes and is perfectly suitable for industrial, high-throughput metrology.

  • Can be used with a variety of targets ranging from
  • paque (reflection mode) to transparent (transmission

mode) materials and geometries ranging from simple nanoparticles to complex semiconductor memory structures.

  • Applicability to a wide variety of measurement tasks.
  • Requirement for defining the "Best Focus" is eliminated.

Advantages of the TSOM Method

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Limitations of the TSOM Method

  • Optical system errors (for the second method)
  • Experiment to simulation agreement (for the second

method)

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Potential Applications (not exhaustive)

 MEMS  NEMS  Semiconductor industry  Biotechnology  Nanomanufacturing  Nanotechnology  Data storage industry  Photonics  Nanotechnology  Defect analysis  Inspection and process control  Quantum dots/nanoparticles/nanotubes  Critical dimension (CD) metrology  Overlay registration metrology  3D interconnect metrology (TSV)  FinFET metrology  Photo mask metrology  Film thickness metrology  Line-edge roughness measurement  Nanometrology  Relative movements of parts in MEMS/NEMS

Areas Industries

Companies openly collaborating or assessing the technology

SEMATECH, A large US Semiconductor Company, Veeco (Bruker), Toshiba, and several emerging companies

Any suggestions are welcome

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Conclusion

Through-focus scanning optical microscopy (TSOM) method provides 3D metrology with nanometer scale measurement sensitivity using a conventional

  • ptical microscope

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Acknowledgements

Michael Postek: Chief - Mechanical Metrology Division John Kramar: Leader - Nanoscale Metrology Group, discussions James Potzick: Discussions Richard Silver: Leader - For providing NIST optical microscope Rich Kasica and Lei Chen: NIST NanoFab – Fabrication Andras Vladar, Prem Kavuri and Bin Ming: SEM measurements Ronald Dixson: AFM measurements Andrew Rudack, Ben Bunday, Erik Novak , Victor Vartanian: For providing targets Mike Stocker, Yeung-Joon Sohn, Bryan Barnes, Richard Quintanilha, Thom Germer, Jayson Gorman, and Egon Marx

Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011

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Thank you

Ravikiran.attota@nist.gov Google search: Ravikiran, Attota, TSOM

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