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LSST detector components and assemblies: Metrology issues

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Detector Metrology Issues. Focal plane flatness requirements - from proposal draft doc 2/9/05 ... Raft assembly metrology considerations ... – PowerPoint PPT presentation

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Title: LSST detector components and assemblies: Metrology issues


1
LSST detector components and assembliesMetrology
issues
  • Peter Z. Takacs
  • Brookhaven National Laboratory
  • 23 March 2005
  • LSST Camera Project Meeting
  • SLAC

This research was sponsored (in part) by the U.S.
Department of Energy under Contract No.
DE-AC02-98CH10886.
2
Detector Metrology Issues
  • Focal plane flatness requirements - from proposal
    draft doc 2/9/05
  • Measure over temperature range and at various
    angular attitudes
  • What does it take to insure these requirements
    are met?

1 µm 0.000040 2.5 µm 0.0001 1 ?
0.6 µm
3
Example of what could happen
  • Several microns of bow and twist possible in
    detector surface

4
FPA Metrology Error Budget
  • Goal - Focal plane planarity 10 µm PV over 64cm
    dia. area
  • Maintain planarity at -100C and at 45 tilt
    attitude angle.
  • FPA comprised of
  • CCD modules
  • Raft plates
  • Raft assemblies
  • Integrating structure
  • Adjustable kinematic mounts
  • Other items hanging from raft assemblies
  • Specified tolerances
  • CCD module planarity 5µm PV
  • Raft plate planarity and parallelism 1.0µm
  • Raft assembly planarity 6.5µm PV
  • Integrating structure planarity 1.0µm,
    attitude deflection 1.0µm
  • Measurements on individual components and
    subassemblies required to insure final tolerances

5
FPA component structures
5 µm
1 µm
1 µm
6
CCD module metrology
Require non-contact measurement methods
  • PMI Interferometer for surface flatness -
    aperture 60mm
  • White-light micro PMI for edge height
    discontinuity
  • Gauge block reference for absolute height
  • Vendor guarantee on absolute height (?)

PMI ? Phase Measuring Interferometer
7
CCD module metrology considerations
  • 201 live individual sensor modules
  • Planarity 5µm over 40x40 mm2 area
  • Datum plane defined by shoulders on 3 pins
  • Absolute height (piston) and tilt relative to
    datum is important
  • General case is warped CCD surface --gt not flat
  • Do we believe vendor???
  • Warping and distortion after cryo test cycles?
  • Height measurement requires non-contact optical
    method
  • Use gauge block as absolute standard
  • White-light micro PMI needed for comparison
    measurement
  • Conventional PMI required for non-contact 2D
    topography measurement
  • Useful for in-situ measurement through dewar
    window during cryotesting

8
Raft plate metrology
  • Area 120 x 120 mm2
  • Measure before any items assembled onto it
  • Thickness tolerance 1µm

Unknowns Kinematic mount configuration - impact
on thickness tolerance??? Measure plate with
kinematic mount assembled?
9
Raft plate metrology considerations
  • Raft construction - 120 x 120 mm2
  • Double-sided plates, top surface lapped plano to
    1µm
  • Thickness secondary issue. Adjust with kinematic
    mounts?
  • Is 1µm PV parallelism tolerance too tight?
  • Insure planarity - want no bowing or twisting
  • Changes vs. time and temperature -- causes
    deformation
  • Measure surface 2D topography
  • Easiest method by conventional PMI -- 200mm
    aperture
  • Require top surface to be specular reflector --
    lapped smooth
  • Full aperture in one measurement - short time
  • Contact probe if non-specular surface -- discrete
    points
  • Need CMM with lt 1µm accuracy
  • Not good for in-situ cryotesting
  • Takes time for complete surface measurement

10
Raft assembly metrology
  • Flat and coplanar 6.5 µm PV
  • Absolute height with kinematic mounts attached,
    ZR
  • Distortion at cryo temperatures and off-normal
    attitudes
  • Surface deformation of modules after assembly -
    torque effects from pins
  • ZR

11
Raft assembly metrology considerations
  • CCD module mounting pins - force and torque
    transmission into surface
  • Easy with 200mm PMI
  • Kinematic mount static height adjustment
  • Need to know absolute height of detector plane
    above IS surface
  • Require dummy IS reference surface during
    assembly
  • Gauge block standard with micro PMI for absolute
    edge heights
  • Edge discontinuity between modules ? height
    ambiguity
  • Requires white light PMI
  • Full aperture (200mm) PMI for dynamic surface
    distortions
  • Configure for viewing through dewar window and at
    45

12
FPA Integrating Structure metrology
Nominal max OD 1 meter
  • Planarity tolerance 1 µm PV
  • Interface to raft assemblies through kinematic
    mounts
  • Map topography of interface surfaces
  • Measure distortion vs. temperature and attitude
  • Testing with unassembled raft plates installed???
  • Requires BIG interferometer

13
FPA metrology
  • Assemble rafts onto IS
  • Edge height continuity
  • Dynamic distortion vs. attitude and temperature
  • Monitor changes over time
  • Full aperture measurement requires steerable
    750mm dia aperture PMI

14
Major optical instrumentation required
  • White-light micro PMI
  • Eliminates edge height ambiguity
  • Microscope-based system
  • ADE Phase Shift MicroXAM w/200mm stage
  • 200mm aperture PMI
  • Add beam steering for attitude testing
  • (Fisba stock item, on order)
  • 750mm aperture white-light Fizeau PMI
  • with variable optical delay line
  • 4D Technology concept with Jim Burge, UofA

15
FPA instrumentation issues
  • 200mm aperture Twyman-Green PMI interferometer
  • Available from Fisba, currently on order, 110K
  • Customize for variable attitude, variable
    stand-off distance
  • White-light micro PMI
  • FOV 3.3x2.5mm2 at 2.5x magnification
  • Essential for edge discontinuity problem
  • Available from several sources, start at 55K,
    87K as shown
  • Large aperture (750mm) white-light Fizeau
    interferometer
  • Remote sensing of module problems within FPA
  • New concept, licensed by Zeiss to 4D Technology
  • Will require significant development work,
    collaboration with Jim Burge, UofA
  • Cost TBD
  • Surface plates for clean room workstations
  • Gauge blocks
  • Fixtures for cryotesting and variable attitude
    testing

16
Reference herein to any specific commercial
product, process, or service by trade name,
trademark, manufacturer, or otherwise, does not
necessarily constitute or imply its endorsement,
recommendation, or favoring by Brookhaven
National Laboratory, the Department of Energy, or
the United States Government. The views and
opinions expressed herein do not necessarily
state or reflect those of Brookhaven National
Laboratory, the Department of Energy, or the
United States Government, and may not be used for
advertising or product endorsement purposes
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