Development of Chemical-Mechanical Polishing for

Superconducting Cavities

Shekhar Mishra, Fermilab

Mark J. Oreglia, Univ. of Chicago

Cliff Spiro, Cabot Microelectronics

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Project Summary

• High Gradient (~35 MV/m) and high yield of the SRF cavities are needed for

– International Linear Collider (ILC) and High Intensity Proton Accelerator (Project-X).

• State of the art cavity manufacturing and processing :– Electo-polishing and High Pressure Rinse

• Remove the damaged Niobium layer

– Average Gradient is 20% lower – Yield is less than 25%

• Limitation: – Complicated procedure, dangerous chemical, expensive– Niobium surface contamination and/or surface imperfection caused

by either manufacturing or processing (Sulfur contamination)

• Proposal: – Chemical-Mechanical Planarization technology to remove the

damaged Niobium layer

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9-cell Test Results

Average A6-8, AES2,4 = 32 MV/m A9 reprocess at Jlab

ILCGoal

Why alternate technique ?

• The electrolyte is a mixture of hydrofluoric and sulfuric acid. Details not fully understood.

• Manufacturing or acid related defect:

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1mm

θ

z

~600µm beadson Nb cavity

These two problems will require mechanical polishing that can make a smooth surface.

• Acid related contamination• Sulfur Deposit

• Surface Smoothness: RMS:

•1247 nm fine grain BCP

• 27 nm single crystal BCP

• 251 nm fine grain ep

Confidential

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© 2005 Cabot Microelectronics Corporation

Introduction to Cabot Microlectronics and Chemical Mechanical Planarization (CMP)

Non-planarized IC product Planarized IC product

• Leader in CMP slurries– Pioneer in CMP technology– Copper, Tungsten, Dielectric, Data Storage– CMP pad offering in early stage commercialization– ESF consumable and service offering in non-semiconductor applications

• Unparalleled track record– Deliver tens of millions of gallons to customers globally

• Outstanding technology and manufacturing infrastructure– Robust ramp of new products to high volume production– Provide global support and service

• World-class team of scientists and technologists

Confidential

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© 2005 Cabot Microelectronics Corporation

CMP of Nb 20X Field of View (approx. 230um x 300um)

AFTERRq = 3.5nm

Small islands appear to be grains.Highest point to lowest point around 18.6nm.

BEFORERq = 603nm

Heavily cratered surface from machining

Fermilab Tumbling Machine

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Design and Engineering needed to hold the cavity in place and liquid flow etc.

Not installed.

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New Vertical Test @ FNAL

• Recently commissioned (IB1)– Existing 125W@ 1.8 K Cryogenic plant– RF system in collaboration with Jlab– Capable of testing ~50 Cavities/yr– Evolutionary upgrades:

• Thermometry for 9-cells, 2 cavities at a time, 2 top plates, Cryo upgrades

• Plan for two additional VTS cryostats

– Ultimate capacity ~ 264 cavity tests/yr

VTS Cryostat:IB1

New RF & Control Room

Plan for 2 more VTS pits

Nine-cell Tesla-style cavity

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Plans and Possibilities

• Development of the chemical that would be used in the Chemical Mechanical Polishing (CMP) of Niobium

– Small sample test

• Accelerating Gradient Test:– Polish 1-cell (1.3 GHz) Nb cavity using the Fermilab Tumbling machine – Rinse with high purity water – RF test in the Fermilab Vertical Test Facility

• Possible Advantage• No dangerous chemical• A much simplified procedure that could lead to considerable cost saving• Could potentially reduce acid related defects and contamination• Could eliminate surface defects produced during manufacturing

• Small size R&D project with great potential• Excellent training opportunities for students in Accelerator R&D

Budget

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%FTE UofC Fermilab CabotSalary and Fringe Benefits

- Post-doctoral

-Graduate Student Assistant

-Undergraduate Student Assistant

-Engineers

-Technician

100%

5%

20%

$12,500

$6,500

$26,000Graduate Student Tution

Material and Supplies $1,000 $17,500 $35,000

Publication Cost (Conference) $1,500

Total Direct Cost $15,000 $50,000 $35,000

• Build on Surface science Research• Student training in Accelerator R&D (Fermilab Accelerator Ph.d Program)• Local Industry involvement• Leverage existing laboratory infrastructure