UCRL-PROC-215104

Fabrication of Planar LaserTargets with Sub-MicrometerThickness Uniformity

M. Bono, C. Castro, L. Griffith, R. Hibbard, J.Kass, J. Satcher

September 7, 2005

2005 Tri-Lab Engineering ConferenceMonterey, CA, United StatesSeptember 12, 2005 through September 15, 2005

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This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. 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 the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes.

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---TitleTitleTitleFabrication of Planar Laser Targets with

Sub-Micrometer Thickness UniformityThe Cu EOS Targets

Matthew Bono, Carlos Castro, Lee Griffith, Robin Hibbard, Jeff Kass, Joe Satcher

This work was performed under the auspices of the U.S. Department of Energy by the University of CaliforniaLawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.

Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94551

Presented to:2005 Tri-Lab Engineering Conference

September 12-15, 2005

UCRL-PROC-215104

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The selection of target specifications requires close collaboration between Target Fab and Physics

To make the targets manufacturable, the specifications were re-examined and revised several times.

To make the targets manufacturable, the specifications were re-examined and revised several times.

Polystyrene (CH) ablatorthickness uniformity ±0.3 µm

Iodine-doped polystyrene (ICH) preheat shieldthickness uniformity ±0.25 µm

Al baseplate thickness uniformity ±0.25 µm

Quartz window

Cu sample thickness uniformity ±0.1 µm

Bond < 0.5 µmmeasured to 0.1 µm

Bond < 3 µm

35 102 62 100 µm

43

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The target specifications necessitate a very The target specifications necessitate a very precise manufacturing strategyprecise manufacturing strategy

The required level of precision is approximately 10× that of most laser targets

The required level of precision is approximately 10× that of most laser targets

CH ablatort = 32.5 µm

ICH pre-heat shieldt = 102 µm

Al baseplatet = 62 µm

Cu Sample t = 43 µm

Quartz windowst = 100 µm

Au support ring

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The specified thickness uniformities of the The specified thickness uniformities of the components require highcomponents require high--precision fixturing methodsprecision fixturing methods

100 mm workpiece100 mm workpiece

Diamond toolDiamond tool

Coolant nozzleCoolant nozzle

A batch of targets is built on a 6 mm thick 100 mm diameter Al disk. Both sides of the disk are diamond turned so that the faces are parallel to 0.1-0.2 µm.

Diamond turning machine spindle

Vacuum chuck

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To meet the specifications for the To meet the specifications for the baseplatebaseplate--sample joint, the Cu sample is sample joint, the Cu sample is

deposited onto the Al baseplatedeposited onto the Al baseplate

• Cu-Al interface must be < 0.1 µm• Outside the 25 µm region on either side of the edge of the Cu, all flaws

must be < 0.1 µm• Al disk must not be warped, scratched, pitted, or otherwise damaged• Cu must have adequate adhesion for diamond turning• Cu must be placed on Al disk in a band with radial tolerance of ±10 µm

The requirements for the Cu-Al interface are very demanding.

A great deal of research has gone into identifying an acceptablemethod of depositing Cu onto the Al disk.

A great deal of research has gone into identifying an acceptablemethod of depositing Cu onto the Al disk.

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The masking process is designed to accommodate The masking process is designed to accommodate flaws created in the electroplating processflaws created in the electroplating process

The selected deposition process sputters 3-5 µm of Cu onto the Al and then electroplates additional Cu.

The 100 mm Al disk is masked with precisely placed Kapton tape prior to sputtering.

Kapton with diamond turned edges

Exposed Al

Reference surface

Al disk

Kapton tape

Cu

Cross sectional view

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After sputtering 3After sputtering 3--5 5 µµm of Cu, additional Cu is m of Cu, additional Cu is electroplated onto the sputtered Cuelectroplated onto the sputtered Cu

Electroplating mask

Al disk

Plated Cu

Electroplating mask

Al disk

Plated Cu

Disk masked with Kapton tape after sputtering 3-5 µm of Cu

Disk in the hardmask that is used to electroplate additional Cu

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The deposited Cu is diamond turned to a The deposited Cu is diamond turned to a thickness of 43 thickness of 43 µµmm

A band of Cu of thickness 43 µm and width 1 mm is left on the surface of the Al.

SPDT

43 µm < 1 µm, measured to 0.2 µmMachining may leave a 1 µm

step in the Al, but it must be known to within 0.2 µm

The Cu is then carefully measured in several locations with an LVDT mounted on the machine tool.

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The CuThe Cu--side of the disk is placed against another side of the disk is placed against another precision narrowprecision narrow--land vacuum chuckland vacuum chuck

Al plate

Centering guide

100 mm Al disk

Vacuum chuck~100 µm

Cap probe

Cu

Centering guides allow the ring of Cu to fit precisely into a groove in the chuck.

SPDT

Vacuum chuck

The Al disk is machined to a thickness of 62 µm to form the baseplate.

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Pads of iodinePads of iodine--doped polystyrene are bonded doped polystyrene are bonded and machined to form the preand machined to form the pre--heat shieldsheat shields

Precise pads of iodine-doped polystyrene (ICH) are bonded to the Al using a special assembly station.

An LVDT measures the thickness of the adhesive in 4 spots.

Air bearing

Force transducer

Height adjustment

Component mount

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After finishing the preAfter finishing the pre--heat shields, pads heat shields, pads of polystyrene are bonded and machined of polystyrene are bonded and machined

to form the ablators to form the ablators

Vacuum chuck

SPDTThe pads of iodine-doped polystyrene are diamond turned to the required thickness to complete the pre-heat shields.

The pre-heat shields are then measured again with the LVDT in 4 spots.

SPDT

Vacuum chuck

To form the ablators, the process of bonding, measuring, machining, and measuring is repeated with pads of polystyrene (CH).

Diamond turned pad

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Targets are laser cut from the Targets are laser cut from the 100 mm100 mm disk and disk and bonded to windows and support ringsbonded to windows and support rings

The “ablator – preheat shield – baseplate – sample” subassemblies are laser cut from the 100 mm disk

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UNCLASSIFIEDSummary Summary -- close collaboration between close collaboration between Target Fab and physicists is crucial to Target Fab and physicists is crucial to

designing manufacturable targetsdesigning manufacturable targets

• Metrology is almost as labor-intensive as the fabrication process.

• The required level of precision is approximately 10× that of most laser targets. Extreme care must be taken at each step of the process.

• Appropriate fixturing of the workpiece is critical to achieving the manufacturing and metrology tolerances.

• The seating of the workpiece against the vacuum chucks must be verified at each step.

• A great deal of research has gone into identifying an acceptablemethod of depositing Cu onto the Al disk. Sputter-seeded electroplating was identified as an acceptable method of depositing the Cu.

• Batch processing allows several targets to be produced from each100 mm disk.