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Page 1: Progress in understanding flatness measurements

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Progress in Progress in understanding flatness understanding flatness

measurementsmeasurements

Tom Diehl November 24, 2005Tom Diehl November 24, 2005

Draft as of 11/24/05Draft as of 11/24/05

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Micro-Epsilon Opto-NCDT 2400Micro-Epsilon Opto-NCDT 2400 We need to control the We need to control the

flatness of the focal plane.flatness of the focal plane. We need to measure We need to measure

components without components without touching their surfaces.touching their surfaces.

Using a DEMO version Jim Using a DEMO version Jim Fast determined that this Fast determined that this device could measure the device could measure the distance to the surface of a distance to the surface of a CCD mounted in the test CCD mounted in the test dewar through the dewar’s dewar through the dewar’s quartz window.quartz window.

100 micron spot diameter100 micron spot diameter 24 mm measurement 24 mm measurement

range at 222 mm distancerange at 222 mm distance ~1 micron resolution~1 micron resolution

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Power Power SupplySupply

PolychromaticPolychromatic

Light SourceLight Source

DSPDSP

SpectrometerSpectrometer

SensorSensor

On X-YOn X-Y

StagerStager

DigitalDigital

OutputOutput

To LabviewTo Labview

ControlsControls

Fiber OpticFiber Optic

CableCable CCDCCD

Micro-Epsilon Micro-Epsilon Opto-NCDT 2400Opto-NCDT 2400

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The MachineryThe Machinery

Labview controls Labview controls X and Y dimensionX and Y dimension

Stages w/ ~1 micron precisionStages w/ ~1 micron precision

On the scale of our devicesOn the scale of our devices

Micro-epsilonMicro-epsilon

imagerimager

SampleSample

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Silicon on a pedestalSilicon on a pedestal Example of a ¼ mm x ¼ mm scan of a part Example of a ¼ mm x ¼ mm scan of a part

with very reflective surface. Non-flat with very reflective surface. Non-flat surface features are evident.surface features are evident.

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Silicon Piece 6 cm x 3 cmSilicon Piece 6 cm x 3 cm Glued to aluminum nitride substrateGlued to aluminum nitride substrate Taped to a piece of unistrut. The device overlaps the unistrut by ~ 1 cm on each side.Taped to a piece of unistrut. The device overlaps the unistrut by ~ 1 cm on each side. Surface has observable grind marks from a thinning process. Surface has observable grind marks from a thinning process.

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2 Images2 Imagesof Same of Same DeviceDevice

• ½ mm x ½ mm grid½ mm x ½ mm grid• Offset by 0.1 mm in Offset by 0.1 mm in

Y direction illustrates the Y direction illustrates the

problem.problem.• One can see the warp in One can see the warp in

the surface but only the surface but only thatthat

general feature matches.general feature matches.

Individual points do not.Individual points do not.

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Systematic UncertaintySystematic Uncertainty The measurements of a point on the The measurements of a point on the

surface hold within about 1 micron.surface hold within about 1 micron. If I move off and move back on the If I move off and move back on the

measurement repeats.measurement repeats. If I move by off by 1/10 mm, the If I move by off by 1/10 mm, the

measurement is more different than what I measurement is more different than what I think is the height of the typical surface think is the height of the typical surface feature. Spurious reflections from the feature. Spurious reflections from the grind marks trick the system?grind marks trick the system?

A systematic unc’y is determined from 2 A systematic unc’y is determined from 2 measurements offset by 1/10 mm.measurements offset by 1/10 mm.• deltaZ=delta(ZdeltaZ=delta(Zaa-Z-Zbb)/sqrt(2)~15 microns)/sqrt(2)~15 microns

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““Greg’s Device” 6 cm x 3 cmGreg’s Device” 6 cm x 3 cm Average the measurements in ½ cm x ½ cm array. The total Average the measurements in ½ cm x ½ cm array. The total

uncertainty on mean in each of the 72 regions is ~ 1 micron.uncertainty on mean in each of the 72 regions is ~ 1 micron.

13/72 regions <z> gt 10 microns 13/72 regions <z> gt 10 microns

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The PlanThe Plan A few more improvements to the Labview A few more improvements to the Labview

programprogram• Automation is pretty good.Automation is pretty good.• Surface feature identification and Surface feature identification and

concentration is nearly doneconcentration is nearly done Bring into the CCD testing LabBring into the CCD testing Lab

• operate through a windowoperate through a window Incorporate results into the DES CCD Incorporate results into the DES CCD

databasedatabase• Develop a flatness grade for each CCDDevelop a flatness grade for each CCD

Develop a way to test the DES Focal plane Develop a way to test the DES Focal plane assemblyassembly