Jose Corona Advisors: Lin You and Joseph Kopanski Engineering - - PowerPoint PPT Presentation

COMSOL SIMULATION STUDY OF THE EFFECT OF PROBE TIP SHAPE ON THE MEASUREMENT OF AN ELECTRICAL FIELD GRADIENT GENERATED BY MICROELECTRONIC TEST STRUCTURES

Jose Corona Advisors: Lin You and Joseph Kopanski Engineering Physics Division, PML Summer 2016

OUTLINE

Ø Theory

Ø Scanning Kelvin Force Microscopy (SKFM)

Ø Motivation Ø COMSOL Model Builder Ø Results

Ø Importance of tip shape Ø Cantilever Effect Ø Importance of Tip Shape Ø Clearance Effect Ø Differential Voltage Ø Different Size Ratios

Ø Conclusions Ø Future Work Ø References

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MOTIVATION

ØPrecise nano-scale measurements ØUse of Scanning Kelvin Force Microscopy (SKFM) ØElectric Field Measurements are HIGHLY dependent on the shape of the probe ØDesign an Electrical Tip Shape Profiler Reference Material

Image from Semiconductor Manufacturing & Design Community 3

WORKING PRINCIPLES OF SKFM

ØTapping Mode vs. Mode Lift

Image credit: Kaja

(Kaja’s PhD THESIS 2010)

Scanning Kelvin Force Microscope (SKFM)

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15°

COMSOL MODEL BUILDER

• Fig. 5

Domain Probe

Image credit: Kaja

(Kaja’s PhD THESIS 2010)

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COMSOL MODEL BUILDER

Materials

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Air Copper Glass

Electrostatics

ØCharge Conservation ØZero Charge ØFloating Potential ØBiasing ØGround

COMSOL MODEL BUILDER

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+10V Ground

Floating Potential

Meshing

COMSOL MODEL BUILDER

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Parametric Sweep

COMSOL MODEL BUILDER

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∠𝑢𝑗𝑞

Clearance

ØThe Surface Potential dependency on the shape of the tip ØSharper vs. Blunter tips Ø5°

Ø(-2.52 , 0.140)

Ø(2.66 , -0.149) Ø35° Ø(-2.52 , 0.101) Ø(2.66 , -0.113)

IMPORTANCE OF TIP SHAPE

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

• 5
• 4
• 3
• 2
• 1

1 2 3 4 5

Surface Potential [V] Position [µm] Surface Potential of Lateral Scan

5° 20° 35° 12.5° 27.5°

• 0.2
• 0.15
• 0.1
• 0.05

0.05 0.1 0.15 0.2

• 5
• 4
• 3
• 2
• 1

1 2 3 4 5

Derivative Surface Potential [dV] Derivative Position [dµm]

Instantaneous Surface Potential at any Given Point

5° 12.5° 20° 27.5° 35°

10

FP +10V

• 10V

GRD Glass

• 0.15
• 0.1
• 0.05

0.05 0.1 0.15

• 15
• 10
• 5

5 10 15

Surface Potential [V] Position [um]

Cantilever Effect

5deg 25deg 45deg

• 0.25
• 0.2
• 0.15
• 0.1
• 0.05

0.05 0.1 0.15 0.2 0.25

• 15
• 10
• 5

5 10 15

Surface Potential [V] Position [um]

Cantilever Effect

5deg 25deg 45deg

CANTILEVER EFFECT

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CLEARANCE EFFECTS ON SURFACE POTENTIAL

0.1 0.2 0.3 0.4 0.5 0.6

• 2.5
• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 2.5

Surface Potential [V] Position [µm]

5º Cone Angle KFM Scan

10nm 43nm 77nm 110nm 144nm 177nm 210nm 244nm 277nm 310nm 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

• 2.5
• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 2.5

Surface Potential [V] Position [µm]

35º Cone Angle KFM Scan

10nm 43nm 77nm 110nm 144nm 177nm 210nm 244nm 277nm

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Glass +10V GRD

+10V Glass GRD

CLEARANCE EFFECTS ON SURFACE POTENTIAL

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

• 6
• 5
• 4
• 3
• 2
• 1

1 2 3 4 5 6

Surface Potential [V] Position [µm] 5º Cone Angle KFM Scan

10nm 20nm 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

• 6
• 5
• 4
• 3
• 2
• 1

1 2 3 4 5 6

Surface Potential [V] Position [µm]

35º Cone Angle KFM Scan

10nm 20nm

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DIFFERENTIAL VOLTAGE

Ø 5º Cone Angle highest SP and most narrow width Ø Coherent results as before Ø Smaller lift height, higher SP

• 0.02
• 0.015
• 0.01
• 0.005

0.005

• 15 -14 -13 -12 -11 -10 -9
• 8
• 7
• 6
• 5
• 4
• 3
• 2
• 1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Differential Voltage [dV] Position [µm]

Determining the Width of the Tip

5° 35° 20° 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

• 15
• 10
• 5

5 10 15

Surface Potential [V] Position [µm]

Surface Potential of Rectangular Scan with Conical Tip

5°(10nm) 5°(20nm) 35°(20nm) 35°(10nm) 20°(20nm) 20°(10nm)

(20-10)nm

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DIFFERENT SIZE RATIOS

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

• 6
• 5
• 4
• 3
• 2
• 1

1 2 3 4 5 6

Surface Potential [V] Position [µm]

Lateral Scan of 5:1 Eccentric Cone

longside shortside 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

• 6
• 5
• 4
• 3
• 2
• 1

1 2 3 4 5 6

Surface Potential [V] Position [µm]

Lateral Scan of 2:1 Eccentric Cone

10nm longside 10nm shortside

Ø Noticeable gap Ø Indicates the direction of scan

Long side Short side

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SUMMARY AND OUTLOOK

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ØExtract: ØBase shape ØTip angle ØHeight ØFuture work: ØCompare

THANK YOU!

• How AFM

Works: Scanning Kelvin Probe Microscopy (SKPM), Web. (http://www.parkafm.com/index.php/medias/nano-academy/how-afm- works#prettyPhoto).

• Khaled Kaja. Development of nano-probe techniques for work function

assessment and application to materials for microelectronics. Physics. Universite Joseph-Fourier - Grenoble I, 2010. English. <tel-00515370>

• http://semimd.com/insights-from-leading-edge/2010/10/02/iftle-18-

the-3d-ic-forum-at-2010-semicon-taiwan/

References Any Questions?

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CONCLUSIONS

Ø COMSOL’s ability to simulate SKFM Ø Effect of Tip on the Surface Potential Measurement

Ø Seen through development of many DUTs Ø IF SLOPE DETERMINED INSERT HERE

Ø Various lift heights affect Surface Potential

Ø Differential Voltage Produced

Ø V

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GOALS

• 3D COMSOL Simulation of Scanning Kelvin

Force Microscopy (SKFM)

• SKFM à Electric field measurements
• Determine the field distribution to design

Electrical Tip Shape Profiler Reference Material

• Cone Angle
• Base
• Height

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THEORY OF SURFACE POTENTIAL

Electric Potential – work per unit charge to move a point charge Coulomb’s Law – Electric force between charges Gauss’s Law – Used to determine the Electric field of a Gaussian surface Image from HyperPhysics Image from HyperPhysics Image from HyperPhysics

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elewor.html#c2

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VAN DER WAAL’S FORCES

http://www.eng.usf.edu/~tvestgaa/ThinFilm/ Image by

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http://mathworld.wolfram.com/FullWidthatHalfMaximum.html

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