1 Progress in understanding flatness measurements Tom Diehl November 24, 2005 Draft as of 11/24/05

2 Micro-Epsilon Opto-NCDT 2400 We need to control the flatness of the focal plane. We need to control the flatness of the focal plane. We need to measure components without touching their surfaces. We need to measure components without touching their surfaces. Using a DEMO version Jim Fast determined that this device could measure the distance to the surface of a CCD mounted in the test dewar through the dewar’s quartz window. Using a DEMO version Jim Fast determined that this device could measure the distance to the surface of a CCD mounted in the test dewar through the dewar’s quartz window. 100 micron spot diameter 100 micron spot diameter 24 mm measurement range at 222 mm distance 24 mm measurement range at 222 mm distance ~1 micron resolution ~1 micron resolution

3 Power Supply Polychromatic Light Source DSP Spectrometer Sensor On X-Y Stager DigitalOutput To Labview Controls Fiber Optic Cable   CCD Micro-Epsilon Opto-NCDT 2400

4 The Machinery Labview controls Labview controls X and Y dimension Stages w/ ~1 micron precision On the scale of our devices Micro-epsilonimager Sample

5 Silicon on a pedestal Example of a ¼ mm x ¼ mm scan of a part with very reflective surface. Non-flat surface features are evident. Example of a ¼ mm x ¼ mm scan of a part with very reflective surface. Non-flat surface features are evident.

6 Silicon Piece 6 cm x 3 cm Glued to aluminum nitride substrate Glued 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.

7 2 Images of Same Device ½ mm x ½ mm grid ½ mm x ½ mm grid Offset by 0.1 mm in Offset by 0.1 mm in Y direction illustrates the problem. One can see the warp in One can see the warp in the surface but only that general feature matches. Individual points do not.

8 Systematic Uncertainty The measurements of a point on the surface hold within about 1 micron. The measurements of a point on the surface hold within about 1 micron. If I move off and move back on the measurement repeats. If I move off and move back on the measurement repeats. If I move by off by 1/10 mm, the measurement is more different than what I think is the height of the typical surface feature. Spurious reflections from the grind marks trick the system? If I move by off by 1/10 mm, the measurement is more different than what I think is the height of the typical surface feature. Spurious reflections from the grind marks trick the system? A systematic unc’y is determined from 2 measurements offset by 1/10 mm. A systematic unc’y is determined from 2 measurements offset by 1/10 mm. deltaZ=delta(Z a -Z b )/sqrt(2)~15 micronsdeltaZ=delta(Z a -Z b )/sqrt(2)~15 microns

9 “Greg’s Device” 6 cm x 3 cm Average the measurements in ½ cm x ½ cm array. The total uncertainty on mean in each of the 72 regions is ~ 1 micron. Average the measurements in ½ cm x ½ cm array. The total uncertainty on mean in each of the 72 regions is ~ 1 micron. 13/72 regions gt 10 microns

10 The Plan A few more improvements to the Labview program A few more improvements to the Labview program Automation is pretty good.Automation is pretty good. Surface feature identification and concentration is nearly doneSurface feature identification and concentration is nearly done Bring into the CCD testing Lab Bring into the CCD testing Lab operate through a windowoperate through a window Incorporate results into the DES CCD database Incorporate results into the DES CCD database Develop a flatness grade for each CCDDevelop a flatness grade for each CCD Develop a way to test the DES Focal plane assembly Develop a way to test the DES Focal plane assembly