1 BROOKHAVEN SCIENCE ASSOCIATES 1nm R&D plan K. Evans-Lutterodt Contributions from: C. Jacobsen, N....

1 BROOKHAVEN SCIENCE ASSOCIATES

1nm R&D plan

K. Evans-Lutterodt

Contributions from: C. Jacobsen, N. Bozovic, I. Bozovic, J.Maser, A.Snigirev, C. Schroer, O.Hignette, and many others


Current Trends in X-ray optics

Points courtesy of C. Jacobsen

Bottom Line: • It can be done; there is no physical reason we cannot get to 1nm• However, it will take resources and a targeted effort.


Basic Issues

Metrics1. Numerical Aperture and resolution2. Depth of field3. Aperture4. Efficiency5. Chromaticity6. Modulation Transfer Function

If resolution is 1nm=> then DOF =27nm


Implications of Goals/SourceNSLS2 has a 6μm x 39μm source size in low straight.If resolution is 1nm, and =0.1nm, => NA = 0.1

F(mm) Aperture Image Size

1 100μm 0.72x1.1nm

10 1mm 1.3x8nm

100 10mm 12x80nm

Focal Length

Spo

t S

ize Diffraction limit

Demagnification2

Demag2

DL


Paths to 1nm

Optic Type Comment

1. Single bounce Solid Metal Mirrors X2. Solid Refractive lenses X3. Binary Zone Plates X4. Multilayer Mirrors

5. Multilayer Lens

6. Kinoform


1.Single Bounce Solid Metal Mirrors

Technology Theoretical limits

Spot size (FWHM)

Experimental spot sizes FWHM (nm)

Facility

Fixed profile mirrors

Metal coating

25 nm 15keV SP8 (1Km BL)

68X80 nm (white)

APS (BL34)

)(.

PtnmC

2131

Table courtesy of O.Hignette

Single Bounce Solid Metal Mirrors: Best case is for the most dense material Pt.

* Multiple bounce mirrors can improve the situation.


2.Binary Zone Plates

Equation for fresnel boundaries

222( mmfym

• The spot size is of order the smallest zoneWork at harmonics, reduces efficiency

• As photon energy increases, the zone plate thickness T increases

• To get smallest spot sizes at hard x-ray energies requires Large aspect ratios that are difficult to

manufacture

• E-beam lithography tools have tolerances of order 2nm


3.Refractive

1. Absorption

Incident Beamt=y2/(2F)

Transmission ~ exp( -4t/)

Lens

T

rans

mis

sion

EffectiveLensAperture

Solid Refractive Lens

2e

Optic Axis

Resolution ~ 1/f

To get 1nm , we can have f = 1μm, aperture 100nm ! Aperture too small!

Courtesy of Schroer


Paths to 1nm

Optic Type Comment

1. Single bounce Solid Metal Mirrors

X

2. Binary Zone Plates X3. Solid Refractive lenses X4. Multilayer Mirrors Pursued by ESRF,Spring8

5. Multilayer Lens Proposed NSLS-II R&D

6. Kinoform Proposed NSLS-II R&D


4. Multilayer Mirror (MLM)

O. Hignette Optics group- ESRF

L

fΛ1.7

maxNA

λ0.44FWHM diffraction limited

full width half maximum

d-spacing Wavelengthf focal lengthL mirror lengthNA numerical apertureApproach being followed by ESRF and Spring8

45nm ESRF


5. Novel Approach : Multilayer Laue Lenses

substrate

Varied line-spacing grating

Depth-graded multilayers on flat Si substrate

Multilayer Linear Zone Plate

• Deposit varied line-spacing grating on flat substrate (thinnest structures first!)

• Section to 5-20 m thickness (high aspect ratio structure)

• Assemble into a multilayer linear zone plate (MLZP)

• Assemble two MLZP’s into a single device (MLL)

Crossed Linear Zone Plate : 1-D focusing opticsDeposition + Sectioning + Assembling

From CNM,APS group


Fabrication of MLLGrowth

Si substrate

Dicing ~ 1mm Polishing ~ 5-25 m

Assembling by face to face lens configuration

Central stop

Tilting

WSi2/Si, 12.4 m

r~58 nm

r~10 nm


-150 -100 -50 0 50 100 150

0.0

0.2

0.4

0.6

0.8

1.0

Sample A Sample B Sample C Gaussian fit

Inte

nsity

(no

rmal

ized

)

X (nm)Incident beam size : 12.4 m (H) X 50 m (V)

Focal spot size : ~ 30 nm (H)

Measured Focal Spot @ 19.5 keV X-rays

-5000 0 5000 10000 15000 20000

X (nm)

Focal spot

Incident beam

FWHM :

72.7 nm (sample A)

57.4 nm (sample B)

30.6 nm (sample C)

Sample C, rout =10 nm

Latest unpublished ~ 19nm


MLL issues

Need to fabricate wedged MLL to get below 5nmWedged deposition is novel technology.

Works better at higher energies > 20keV

Metrology?


Why we need “wedges”


Our Proposed MLL approach

1. Use single crystal lattice matched oxides that can be grown atomically smooth.

2. High density (BaBiO3) and low density films (MgO) with z lattice spacings 0.42 and 0.43 respectively.

3. Bozovic will be a resource for the growth effort.


Single Crystal MLL Issues

Discrete Lattice OK; like interface roughnessDensity contrast OK; larger contrast is better

•Interfacial roughness

OK; reduced intensity into spot

•Growth rate errors Very important

•Apodization OK.

(N.Bozovic NSLS-II)

Use of single crystal lattice would raise some issues. We have carried out some initial simulations to gain some insight into these:


Timelines for MLL

FY07 • Explore materials for single crystal MLL approach.• Explore techniques to deposit multi-layers in wedged MLL geometry.• Carry out coupled wave (vector) calculations of MLL to determine sensitivity to errors.• Develop positioning techniques to mount and manipulate up to 4 MLL sectionsFY08• Develop techniques to deposit multi-layers for wedge MLL geometry• Develop metrology capable of determining zone width and placement to ~2nm resolution.• Develop techniques to slice an MLL section from graded multilayerFY09• Design a prototype MLL device (optics and mechanics) with 2nm limit FY10• Construct 2nm prototype device


Proposed Strategies for MLL

• Initially grow flat MLL, but in parallel will design chambers for wedged growth (I. Bozovic). (Possibly adapt the KB mirror fabrication techniques from APS.)

• Develop Metrology for layers


Instead of solid refractive optic:

Use a kinoform:

One can view the kinoform equivalently as

a) A blazed zone plate

b) An array of coherently interfering micro-lenses.

7.Kinoform


Normalized focal lengthIn

tens

ity

c)

b)

a)

2FF2F

1. Kinoform transmission function is almost uniform as a function of lens aperture, and so

=> NA of the lens is not limited by absorption.

2. Kinoform does not have to be fabricated with structures as small as the resolution of the lens.

3. A compound lens gets around the small , which limits the focusing power of a single lens, and would otherwise limit the spatial resolution to 0.61/c.

N.A.= Mc

M lenses

Summary of the Kinoform Case


Multiple kinoform lenses can go beyond critical angle limit

D

Single refractive lens has deflection angle D= C, => resolution limit is /C

We have fabricated a 4 lens compound lens with f =25mm, total aperture =0.3mm, D= 2C

Imperfect lens: Actual result for lens array is 1.1 C . Need to improve fabrication.

2C


Kinoform issues

While Kinoform is further behind at present (600nm at NSLS), no new technology is needed. Investments here have been small to date.

• We need to improve etch quality

• Etch depth is 100μm; need to improve.

• Reduce roughness of etched sidewall

• Test lens designs for n>4. (n=24 needed for Si)


Timelines for Kinoform

T=6m Develop Deep Vertical Si etching

T=12m Optimized E-beam Si process to allow many lens writesDevelop Etches for InSb, C, Si.Test Compound Si lens sub 40nm

T=18m Develop E-beam for alternate materials

T=24m Test Alternate materials lens in xrayTest sub 20nm lens in xray

T=36m Test sub 10nm lens


Other Components of Proposed R&D plan

MLL

Kinoform

Measurements and metrology

Simulations/theory/Computational Benefits all optics


Testing and Metrics

Need to develop testing facilities.

Diagnostics at NSLS

Diagnostics at APS

Numerical support, and investigation of new methods (Souvorov)


Computational Research

Going beyond Fresnel Kirchhoff thin lens approximation

Develop a simulation code that one can drop in density matrices representing real optics.

Help in diagnostics simulations.


dsr

ikrPU

iPU

cos)exp(

)(1

)(01

01

),(

10

22201 )()( yxzr ])(

2

1)(

2

11[( 22

01 z

y

z

xzr

2223 )()(4

yxz

Can crossed optics get down to 1nm?

showing the replacement of the spherical wave by a pair of orthogonal parabolic terms.

For 100 micron aperture, focal length 1cm, we can use crossed lenses down to at least 10nm, but how far can we go?

Using the Fresnel Kirchhoff Integral

Limit of the approximation:


Can crossed optics get down to 1nm?

Answer: Yes, but with increased background

Small NA, crossed lens indistinguishable from two independent lenses

Large NA ~0.1, crossed lens ok but:Central spot still sharp but weaker,More intensity outside the spot=> Lower signal to noise ratio


Summary

1nm optics are possible, but will require a targeted R&D effort

NSLS-II is proposing to pursue 2 of the possible paths.• MLL: Develop wedged structures• Kinoforms: Improve etch quality and increase lens count

1 BROOKHAVEN SCIENCE ASSOCIATES 1nm R&D plan K. Evans-Lutterodt Contributions from: C. Jacobsen, N....

Documents

Transcript of 1 BROOKHAVEN SCIENCE ASSOCIATES 1nm R&D plan K. Evans-Lutterodt Contributions from: C. Jacobsen, N....