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ZYGO White Light Interferometry

Surface Roughness Measurement

August, 2015

Mechanics

• Three dimensional surface structure analyzer

• Light interferometric optical profiler

• Non Contact, non destructive

• Two light paths create interference.

• Vertical (Z axis) by light interference

• Lateral by pixel size calculation

• Data then analyzed and filtered

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New View 7100

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Filters

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Data Filter – 3 Bands

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Filter Settings

• Valuable date can be lost by high filtering.

• Recently, the IPC committee on Metallic Foil

Roughness Measurement decided that all high

frequency roughness data should be without

high filter to optimize results.

• The low frequency filter is useful for removing

any underlying surface “waviness” resulting

from the glass weave.

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Zygo Measurement Definitions

• Ra – The average surface roughness, or average

deviation, of all points from a plane to fit the surface,

measured in microns.

• Rz – Ten point height, or the average absolute value of

the five highest peaks and the five lowest valleys,

measured in microns.

• RSAR – Surface Area Ratio is equal to (surface

Area/Area) -1

• Rq - Root mean square of the average deviation

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Ra – Average Peaks & Valleys

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Rz – 10 Maximum Peaks & Valleys

Rz – Ten point height, or the average absolute

value of the five highest peaks and the five

lowest valleys, measured in microns.

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RSAR - Surface Roughness

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RSAR – Surface Area Ratio is equal to (surface Area/Area) -1

Rq (rms)

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Ra & Rz – Peaks & Valleys

• Ra measures average roughness.

• Rz measures 5 maximum peaks and 5

maximum valley heights.

• Both measure the Macro roughness of large

features

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RSAR – Surface Roughness Analysis

• RSAR data shows the increase in 3-D surface

area relative to the 2-D area - Micro-roughness

from Oxide Alternative.

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Measuring Roughness after Oxide Alternative

• Define the optimum parameters for measuring

the added roughness from Oxide Alternative

Process on different starting copper surfaces.

• Historical Ra and Rz results with RTF copper

after Oxide Alternative do not indicate the

added roughness after processing.

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Results – Before & After Oxide Alternative

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Measurements show the added micro-roughness from Alt. Oxide

No Filters Filter – High 0.6/ Low 500

RTF Cu Ra RSAR Rq Rz Ra RSAR Rq Rz

Start 1.45 1.56 1.78 11.28 1.48 1.59 1.78 11.07

After OA 1.35 2.15 1.69 11.62 1.37 1.97 1.69 10.82

VLP Cu Ra RSAR Rq Rz Ra RSAR Rq Rz

Start 0.29 0.30 0.38 3.77 0.29 0.30 0.37 3.1

After OA 0.49 1.35 0.62 8.26 0.48 1.15 0.6 6.74

RSAR shows the added roughness from Oxide Alternative on both RTF and VLP

Cu.

Results Summary

• Ra, Rz & Rq do not indicate the added

roughness from Oxide Alternative with RTF

copper.

• RSAR is suitable for measuring the micro

roughness from Oxide Alternative process on

both smooth and RTF copper.

• Ra, RSAR and Rq are suitable for measuring

roughness before and after Oxide Alternative

process on smooth copper foil.

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Typical Roughness Results

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Conclusions

Conclusions

• Using Ra and RSAR together will provide

improved measurement of copper surface

roughness.

• Ra and Rz measure the roughness of large

features - macro roughness.

• RSAR is the most suitable for measuring the

overall micro-roughness from Oxide Alternative

process on both smooth and RTF copper

surfaces.

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Conclusions

• Ra is an average roughness measurement of

large features - macro roughness.

• Rz is a maximum roughness measurement and

only reflects the 5 highest and 5 lowest points!

• Rz can have significant variation due to

scratches & dents.

• A perfectly uniform surface would have Rz =

10X Ra.

• Reducing or eliminating the high filter optimizes

roughness measurement.

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Limitations

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These surfaces have the same Ra and Rz but not the same RSAR

Limitations

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The surfaces have the same Rz, but not the same a Ra and RSAR