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Scanning Near Infra-Red Microscopy (SNIRM) for the characterisation of defects in multi-crystalline Silicon

wafers

Lars Johnsen, SINTEF IKTKay Gastinger , SINTEF IKTStijn Roelandt, VUB (Vrije Universiteit Brussel)

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Outline

Optical inspection of mc-Si wafers at SINTEF ICT

Why NIR for Silicon?

Scanning Near Infra-Red Microscopy

Configuration

Transmission mode

Reflection (Confocal) mode

Experimental setup

Measurement results

Conclusions

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Quality control at SINTEF ICT, Optical Measurement systems and Data analysis (OMD)

Micro-cracks

Chipping

Inclusions

Geometry

Saw marks

Bow/warp

Thickness/TTV

Depositions (contamination)

In-line/offline

Main focus on in-line

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Tecniques at SINTEF ICT

Luminescence Polarisation Light scattering Camerabased inspectionMicroscopy

Scanning Near Infra-Red Microscopy (SNIRM)

Offline tool

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Why NIR?

Visible part of spectrum

156mm

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Why NIR?

Near Infra-Red part of the spectrum

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Why NIR?

At visible wavelengths: Penetration depth about 1 µm

Penetration depth increases fast beyond the wavelength corresponding to the band gap of Si

At 1300 nm the penetration depth is several 100 m

104/cm

Calculated from: Virginia Semiconductor, Inc., “Optical properties of silicon.” http://www.

virginiasemi.com/pdf/Optical%20Properties%20of%20Silicon71502.pdf.

1 km

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SNIRM configuration

Commercial instruments are available

Custom built setup allows for flexibility

MULE'STAGNO, P. TÖRÖK & L. “Applications of scanning optical microscopy in materials science to detect bulk microdefects in semiconductors .” Journal of Microscopy, Vol. 188, Pt 1, October 1997, pp. 1-16.

Transmission nonconfocal mode Reflection confocal mode

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Experimental setup

Laser, 1300nmChopper

Lock-in amplifiers

Reference

Transmission

Reflection

DUT on xyz-stage

NIR camera

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Experimental Setup

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Experimental results - Calibration sample

Testsample: 62.5 µm diameter dots in 125 µm grid

Spot diameter estimate: 13µm

Theoretical limit with current optics: 6.3µm

Potential for improvement of optics

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Experimental results - Transmission

Crack detection [Sondre Grønsberg]

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Experimental results - Transmission

Impurities

NIR camera SNIRM

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Experimental results - Reflection

Impurities, probably Si3N4, in Silicon

Depth scan through approximately 700µm

NIR camera SNIRM – confocal mode

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Experimental results - Reflection

Same as previous with transmission image overlay

NIR camera SNIRM – confocal mode

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Conclusions

Obtain same spatial resolution as NIR camera

”Low cost” setup <100kNOK

Applicable for large areas (current setup: 3x3cm2)

Programmable field of view

Programmable resolution

No stitching for large high resolution images

3D image through built-in z-scan

Possibility to measure in reflection and transmission

Attention! Confocal measurements require very accurate alignment

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Acknowledgement

Sondre Grønsberg – crack measurements

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Thank you for your attention