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Ultra Precision Engineering- some recent developments

Professor Pat McKeown OBE FREng

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What is Precision Engineering?

It is multi-disciplinary, based heavily on the application of metrology(dimensional and thermal) to manufacturing, and covers materials, machining and fabrication processes, design of high-precision machines, mechatronics and thus, microsensors, servo-drives, actuators, high speed control systems, etc.

Precision Engineering means working to tolerances from 1 part in 104

(McKeown, P.A.,1979) …. but now reaching 1 part in 108

this is “ Ultra-Precision Engineering “ “Precision Engineering involves working at the forefront of current

technology.” (Jones, RV 1979)….it still does! Precision Engineering has led to the ultra-precision technologies of

_ Micro-engineering.Engineering nanotechnology.

1970

1980

1990

2000

CNC controlCNC control

Radius toolsWaviness < 1 µm

Radius toolsWaviness < 1 µm

Waviness < 0.1 µmWaviness < 0.1 µm

Encoder feedback < 100 nmEncoder feedback < 100 nm

Ultra-precision air-bearing spindlesUltra-precision air-bearing spindles

Glass scale feedbackGlass scale feedbackMulti-axis machines and FTS turningMulti-axis machines and FTS turning

From Brinksmeier & Courtesy: Moore Nanotechnology Systems , ALMT

Non-circular cutting edgesNon-circular cutting edges

1960

Microtome knivesMicrotome knives

2010

Development of single point diamond machining

Development of spdt machinable geometries

Off-axis MirrorsOff-axis Mirrors

FTS-turned moulds and mirrorsFTS-turned moulds and mirrors

19601970

1980

1990

2000

Freeform surfacesFreeform surfaces

Triangular microprismsTriangular microprisms

Aspheric IR opticsAspheric IR optics

2010

From Brinksmeier & Courtesy: Moore Nanotechnology Systems , ALMT

Chemical wear in diamond machining

From Brinksmeier, Bremen

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Diamond turning process capability….nanotechnology

Ref, Ikawa & Donaldson, circa. 1990

Undeformed chip thickness of 1nmon amorphous copper

Ref, Technodiamant

7400 mm dia Axicon for space laser systems

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Diamond micro-tools manufactured using focussed ion beam machining

Ref. Adams, Sandia Nat. Labs. California

Diamond machining of prism arrays

1980sTriangular prisms

2010sHexagonal prisms

Fly-cutting of intersecting systems of V-grooves

Fly-cutting of intersecting systems of V-grooves

Micro-chisellingof corner cubesMicro-chisellingof corner cubes

From Brinksmeier, Bremen

The NION Nanocentre Diamond Machining Centre (1990)the world’s most accurate machine tool of its size

Thermal stability of the NION machineprovided by 5 advanced temperature control systems (+/- 0.001 deg C)

Ref, McKeown, Carlisle, Shore, 1990

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James Webb Space Telescope Infrared Spectrometer Image Slicer

Mirror 12 Mirror 11

29 mm

Mirror 1

Ref, Cranfield University Precision Engineering Centre

Individual mirrors: 12 x 1mm Form error: < 10nm RMSCurvature radius: 162.5mm

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James Webb Space Telescope – Launch 2017

Integrated ScienceInstrument Module ~

spectographic analysis

Infrared optimised space telescope searching for first galaxies formed in the Universe

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Ultra Precision Large Roll Diamond Turning Machines

designed and produced at Cranfield Precision (from 1992)

Workpiece Accuracy< 1 micron per metre

Workpiece weightup to 2000 Kg

Oil shower temp control

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Ultra Precision Manufacturing capability for structured drums

Purpose built facility @ OpTIC

Clean room class 10,000

Lab temperature control +/- 1ºC

Enclosure temperature control +/- 0.1ºC

Active vibration isolation

Replicating film from a structured drum

UV-curing Extrusion

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Applications for micro-structured films

Solar Energy

0

20000

40000

60000

80000

100000

120000

140000

1996

1998

2000

2002

2004

thermal collectors photovoltaics

Optical films: solar concentrators and antireflection film, increasing efficiency, reducing silicon costs

Displays

020406080

100120

US$

Bill

ions

tu

rnov

er

2003 2005 2007 2009

Flat panel CRT

Optical films are utilised in all flat panel displays for backlighting, depixelation, 3D displays etc.

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Applications for micro-structured films

Security

Identity fraud:~ 25 billion US$ p.a. Optical security devices business ~ 1.25 billion US$ growing 12% p.a. Applications - fraud prevention: note printing, securency, ID, etc.

Lighting / illumination

Film-based lighting market expected to total US$10 billion by 2010 including domestic and industrial applications using LED and OLED technologies

Ultra precision optics demands

Lithography - EUV [ASML] Microlithography Systems

Fusion - Focusing lens “wedge” optic

Space - IXO telescope mirrorTelescopes

E-ELT

European Extra Large Telescope (ELT)[the 400th year of the telescope…..Galileo 1609-2009]

E-ELT

42 metre diameterprimary mirror

Aspheric primarymirror design basedon 984 x 1.46 metre hexagonal segments

6 metre diametersecondary monolithicdeformable mirror adaptive optics

Ref: www.eso.org “operational by 2020” “estimated cost €950m”

E-ELT primary mirror design having ~ 9841.46 metre hexagonal segments

Form accuracy : 20 nm RMS, roughness 1 nm RMS

Ref, www.eso.org

1 part in 108 relative precision of form accuracy to size

Primary mirror• 42m diameter• Far off-axis ellipsoidal form• 984 segments @1.46m

7 Prototype Segments from peripheral region

Process Chain

Develop grinding and support technology for the aspherisation of large metre scale optics

Machine; Grinding Process; Metrology; Handling

Aspherisation

Grinding Requirement:

• 1 Segment per day

• 1mm material removed

• 1µm form accuracy

• No edge chipping or roll-off

Major new UK-based research initiative - processing time for large (1+ metre scale) freeform optical surfaces reduced from 100 hoursto 10 hours

Ultra Precision Machining Technologies

“ductile” mode grinding

0.01 0.1 1 10 100 1000

IBF RAPT

Fixed abrasivegrinding

Computercontrolledpolishing

MRF

1000

100

10

1

0.1

Removal Rate [mm3/minute]

Rou

ghne

ss [n

m] R

MS

diamond turning

1

2

3

Grinding machine• Free-form grinding capability

• Hydrostatic bearings

• 10 KW grinding power

• High performance thermal control (±0.1˚c)

• Integrated metrology capability

• Rapid material removal rate, (200 mm3/sec)

• Form accuracy < 1 µm/m RMS

• Low sub-surface damage < 10 µm

• Compact machine size

http://www.hembrug.com

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Cranfield University BoX® Machine

Ultra-precision, ultra stiff 3 axis freeform grinding machine for large optics up to 2 metres diameter

Truing/dressing

Grinding wheel

Grinding spindle

Metrology frame/optical straightedge

All axes/spindle oil hydrostatic

Laser interferometer / LVDT metrology

Ref: Shore/Morantz (2006)

Lowest control and structural eigenfrequencies > 100 Hz

Z axisMini-laser

interferometer

LVDT probes

Workpiece

Optical Straightedge

X axis

Workpiece metrology has full system

accuracy ~ 0.25 μm

Workpiece Metrology

www.cranfield.ac.uk

Low cost high performance temperature control Use a commercial unit to provide cooled water to

a pumped loop Divide cooled water between services using

mass flow control Complex algorithms to control cross-talk Total of 11 channels of temperature control

– mK resolution , << 0.1 °C accuracy Services located with machine (chilled water

supply is remote)

Grinding motion

20°

C X

Z

Free-form grinding

capability

• Novel 3 axes configuration

• R-theta grinding mode

• Toroidal shape grinding wheel

• Sophisticated toolpath software

XZ

C

Grinding technology

Grinding Conditions Grit size (µm)

Depth of cut (µm)

Feedrate(mm/rev)

Work speed

(mm/s)

Cutting speed

(m/s)

MMR

(mm3/s)

Rough cut (D76) 76 500 15 25 30 187.5

Semi‐finish cut (D46) 46 200 10 20 30 40

Finish cut (D25) 25 50 1.5 25 30 1.87

Multi-stage grinding process

Grinding Wheels• 325mm DIA• Resin bond• D25, D46, D76• 50 concentration

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Mirror segment (1)…CMM Metrology

• ELT segment SPN01 (15:15)

• Material – Zerodur

• 580,000 measurement points

• Data to within 0.5mm of the edge.

Results: • Surface map (CMM)• RMS < 1 µm, P-V < 5.5 µm • No visible edge chipping• No attributable cavity effect • Some error attributable to the CMM

Mirror segment (2) CMM Metrology

• ELT segment SPN04 (16:15)

• Material – ULE

• Grinding cycle 20 hours

• Max MMR 187.5mm3/sec

•Results: • Surface map (CMM)• 580,000 measurement points• PV < 4.5 µm • RMS < 0.6 µm

Final figure correction

Figuring requirement:• 1 Segment per day

• Form accuracy < 20 nm RMS

• Surface roughness < 1 nm RMS

• Removal of process signatures

Major new UK-based research initiative – processing metre scale freeform optical surfaces

Reactive Atom Plasma Figuring

Developing RAP technology for the final figuring of large metre scale optics

RAP technology

Dimension (mm)

Sur

face

dev

iatio

n (n

m)

• Dry etch process – fluorine based gasAtmospheric pressure processing • Gaussian beam distribution• Dwell time based raster figuring algorithm• No induced SSD

Rapid nanometer dexterity surface process for figure correction of ultra precision metre-scaleoptics. Technology employs inductively Coupled Plasma Torch.

RAP facility

• 3 axes CNC Fanuc motion control• Low cost operation • 1.2 m capacity• Compact machine size

Refs1: Jourdain et al., (2011). “Fast 3D Figuring of Large Optical Surfaces Using Reactive Atom Plasma (RAP) Processing”, 2nd EOS Conference on Manufacturing of Optical Components, Munich (D), May 2011.2: Castelli et al., (2010). “Initial Strategies for 3D RAP Processing of Optical Surfaces Based on a Temperature Adaptation Approach” 36th Matador Conference, Manchester, section:18, pp 569-572 , July 2010

Processed materials: • Fused silica

• ULE

• SiC

• Silicon

• Borosilicate

Expected processing time for NIF focussing lens

• 420 mm x 420mm surface

• 2 iteration process

• Removal depth of 1µm

• Average MMR 1.5 mm3/min

• Figuring time ~ 3 hours

• x10 times faster than IBF

Contact: Prof Paul Shore, Precision Engineering Centre, Cranfield University, UK

Spherical surface results

rms: 80 nm

Spherical hollow

500 nm depth

Spherical form Residual error

18 nm RMS

146 nm PV

Courtesy of Paul Morantz –peacock butterfly (2004)

Thank you for your attention

Summary – Rapid production of large freeform surfaces

Acknowledgements:

The authors acknowledge funding support from the UK research councils’ Basic

Technologies Programme, the EPSRC Integrated Knowledge Centre in Ultra Precision

and Structured Surfaces (UPS2) and the McKeown Foundation.

• Polishing• Form accuracy < 16.8 nm RMS

• Reactive Atomic Plasma• Removal rates up to 1.5 mm3/s

• Grinding• Removal rates up to 187.5 mm3/s

• Grinding time 20 hours - 1.45 m ELT segment

• Form accuracy < 1 µm RMS, SSD < 10 µm

• Form accuracy < 16 nm RMS

• No induced SSD

Wheel form

Truing imparts toric wheel form using formed electroplate wheels

Dressing using AlO stick Wheel profile imprinted onto soft

dressing stick can be measured in-situ and used to compute wheel shape/wear

A full multi-pass grinding cycle may take 10 hours – wheel wear compensation critical to maintain accuracy

Inclined spindle configuration

Simulation of contact point compensation

Ref: Shore, P. et al., 2005

Mirror segment processingSegment fixture• Transportation• Metrology• Loading• Grinding• Location using master spheres

Grinding

• Input spherical form• 1mm material removed• Finish grind

• D25 wheel• 50 um depth of cut• Compensated path

Lithography is at the heart of i/c chip manufacturing

Repeat 30 to 40 times to build 3

dimensional structures

1 part in 108 relative precision of form accuracy to size

Advanced DUV Lithography Systemsemploy fused silica optics of up to 250 mm diameter having form accuracy of 2.5nm RMSand roughness < 0.5nm RMS ; 38nm linewidths……….the ASML TWINSCAN……………… Ref, Zeiss SMT

1nm

wavelength

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EUV / soft X-ray lithography scheme (ASML Veldhoven )

laserpump lens

reticle stage

wafer stage

illuminator

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EUV / soft X-ray lithography scheme reflective optics (ASML)

EUV (extreme ultraviolet)

– λ = 13 nm– linewidth < 35nm

(potentially 10nm)– reflective optics

essential (no available EUV transparent materials)

– tilt control of mirrors is highly critical

NXE:3100 first shipment Q4 20101st generation of the NXE platform

NA=0.25 Sigma=0.8 Resolution 27 nm SMO=4.5 nm MMO=7.0 nm Productivity

60wph at 10mJ/cm2 resist

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We’ve Come a Long Way in 60 years!

One transistor/cm2

Dec. 23, 1947Today: Each die contains 500

million transistors/cm2

Process Chain

Computer control polishingMachine; Polishing Process; Metrology; Fixturing

Polishing

Requirement:

• 20µm material removed

• 20nm RMS form accuracy

• No edge roll-off

Major new UK-based research initiative – processing metre scale freeform optical surfaces

Next generation of large telescopes

Hale(1948)

Keck(1993)

GMT(2018)

TMT(2018)

E-ELT(2018)

Mirror technology

36 segments Production rate: 1 per

month

Active segmented mirror technologypioneered through the Keck telescope

Optical Test Tower• Segment radius of curvature 84m

• Test tower 10m

• Folded path using spherical mirror

• 45˚ fold mirror near intermediate focus (central

obscuration)

• Focus relayed to interferometer by pair of

aspheric lenses

• Spherical aberration corrected by aspheric plate

off-axis and a pair of cylindrical lenses.

• Option for final residual aberrations to be

corrected by CGH

• Located over polishing machine

Acknowledgement: Dr John Mitchell, Cranfield Ultra Precision and Structured Surfaces (UPS2)

Master spherical segment (MSS)

Source: David Walker, University of Wales Professor of Optics at Glyndwr University , Professorial Research Associate, University College London, Research Director, Zeeko Ltd

• Composite measurements constructed from lateral and rotational shears

• Form 16.8 nm ± 2nm RMS

• Mid spatial frequencies < 5nm RMS

• 1.490 m across corners

• 200 mm thickness

• Spherical form 84 m ROC

Sub-surface Damage

Evaluation technique:• Polished tapered grooves

• Etched HF, target removal 1µm• Groove depth - contact profilometery

• Crack observation using optical microscope

Grinding Conditions Cluster depth (µm) Last fracture depth(µm)Zerodur® ULE® Zerodur® ULE®

Rough cut (D76) 5 8.5 8 18.5Semi‐finish cut (D46) 4 4.5 7.5 9Finish cut (D25) 3 4 4 8

Ref: Tonnellier, T. et al. 2008, Sub-surface damage issues for effective fabrication of large optics, Proc of SPIE Vol. 7018, pg 701836-1 to 701836-10

Micro-textured cylindrical mould

Cutting a varying

included angle:

corner sharpness

Flat Lens Parquets

Arrayed flat fresnellenses on optical film

Laminate in ‘one shot’to support frame

Manufacture Conical Lenses

Diamond cut master

Lens Film in r2r process

Fold assemble and glue lens structure

Thin Film

Solar Power technologies

Thin Film Flat Panel Concentrated

Lenses Mirrors

ThermalPhotovoltaic

Solar Power

Advanced Surface Structuring

Micro-texturedlight diffusers

Micro-textured light reflectors

Advanced Surface Structuring

Micro-textured retro-reflecting surfaces

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SummaryAccuracy capability a 1 part in 108

(metre class surfaces in 10 hours)

BoX® -Ultra Precision fixed abrasive Grinding & Measuring System, Cranfield

IRP1200 –Ultra Precision 7 axes free abrasive polishing system, UCL & Zeeko Ltd

RAP –Re-active atom plasmasurface figuring system, Cranfield and RAPT Industries

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High Precision Diamond Turning of Structured / Textured Surfaceson rolls for large scale replication of plastic films

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Textured roll

Plan view

Side view

Diamond turned micro-structured surface

Structured / Textured Surfaces on rolls

CPV installations growth forecast 1.5GW capacity will be installed in 2014 Equates to 7 million m2 of solar units

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Reactive Atomic Plasma Processing

Ar Ar

CF4

FF

FFF

FC

CC

ArArAr

ArArAr

ArArAr

Ar

Excitation Region

Plasma Discharge

Copper coils for Inductively-coupled energy source

Plasma (main) gas

Reactive precursor gas

Si, SiO2, SiC…

Quartz tube

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Shallow trench, approximately 15 nm deep, created by 4 passes

Segmented mirrors

Pioneered by Keck

Repeated by GTC, SALT, JWST etc.

Image credit: A. Miller

New process chain for large optics

Major new UK-based research initiative*– processing time for large (1+ metre scale) freeform optical

surfaces reduced from 100 hours to 10 hours– 3 step process chain

Stage 1

Fixed abrasive Grinding

Stage 3

Reactive atom

Plasma

1 mm form accuracy

1 μm form accuracy

10 nm form accuracy

Stage 2

Computer control polishing

* Ultra Precision Surfaces: A New Paradigm – Cranfield/UCL collaboration (2004-2008)

1st ESO segment in ground condition