synchrotron x-ray beam monitoring / etching diamond for super-thin membranes, adamas workshop,...

Synchrotron X-ray beam monitoring / Etching diamond for super-thin membranes, ADAMAS Workshop, Trento 18-20 Dec 2014, J Morse, C. Burman

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i. Synchrotron X-ray beam monitoring and ii. Etching diamond

John MorseS ESRF Charlotte Burman, ESRF & University of Bath


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1. Synchrotrons and X-ray beam monitoring needs

2. diamond quadrant devices

3. CVD bulk and surface defects

4. diamond etching

Outline


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3

Third generation light sourceLocation: Grenoble, FranceCooperation: 20 countriesAnnual budget: ~100M€Staff: 600

6.04Gev electron storage ring

844m circumference 32 straight sections

42 beamlines operating simultaneously some with 2 or 3 experimental stations

X-ray beam energies ~1keV ...1MeV

The European Synchrotron Radiation Facility

10 Hz Booster Synchrotron

200 MeV Electron Linac

User Availability: >98% of 250days/yearMean Time Between Failures: ~80 hours

~6000 annual user visits of duration ~few days~2000 journal publications/year


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• high purity diamond plate ~5…100µm thick, size ~10mm2

• low-Z metal 'blocking' contacts 20 ~ 100nm thick • externally applied bias field 0.5 ~ 5 Vµm-1 → full charge collection

diamond X-ray beam monitors: quadrant devices

photo-ionization current readout → simple, compact devices

surface contact

bea

m

DIAMOND

• absorption of small fraction of incident X-ray beam, diamond acts as solid state ‘ionization chamber’ photo-electron thermalization range a few µm for <20keV X-rays • charge cloud drifts for ~ nanosecond in applied E field transverse lateral thermal diffusion ~10µm during drift beam 'center of gravity' determined by signal interpolation -- difference/sum algorithm

• signal currents can be measured with 'pulse averaging ' electrometers, or by narrow bandwidth synchronized RF techniques different signal measurement methods give different position response functions


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550V

217V

138V

SAME device measured at DESY-DORIS F1 (white bending magnet, Al filtered beam)with Libera RF readout system

-500 -400 -300 -200 -100 0 100 200 300 400 500

0.1

1

10

100

1000

e6 ELSC sample S361-1(390um thick, , 50µm quadrant isolation gap, TiW electrodes)

beam on other quadrants(signal from beam halo?)cu

rren

t qua

d 2

(m

odul

us n

A)

bias (volts)scan at 4V/sec

beam on quadrant B

beam off ceramic package leakage 17pA at +350V

Quadrant device with Keithley 485 electrometers (100msec integration), monochromatic beam ESRF ID09

signal variation with readout method

Libera RF readout measures signal power in bandwidth ~5MHz at 500MHz synchrotron radiofrequency → only ‘fast' e, h charge drift induction signal (Ramo) within RF passband is measured→ signal increases with bias as e, h carriers have not reached saturation drift velocity ( E fields ≤ 1.4Vµm-1)

electrode ground bounce crosstalk


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J. Keister and J. Smedley, NIM A 606, (2009), 7

scCVD diamond responsivity with X-ray energy; linearity vs. X-ray flux

responsivity fit

J Morse et al, J. Synch. Rad 16 (2007)

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E-07 1.E-05 1.E-03 1.E-01 1.E+01

power Absorbed by Diamond (W)

Gas ion chamber calibration

Calorimetric calibration

Fit, w = 13.4 +/- 0.2 eV

diam

ond

sign

al (A

mps

)J. Bohon et al, J. Synch. Rad 17, (2010)

105 106 107 108

-5

0

5

Re

sid

ual (

%)

beam flux (photon/s)

→ linear current response demonstrated over 10 orders of magnitude !

data from e6 ELSC material

Platinum electrodes M edge features:


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M.P. Gaukroger et al., Diam Relat. Mat. 2008

threading dislocations → crystal strainvisible with X-ray diffraction topography

HPHT grown substrate crystal

high purity CVD overgrowthovergrowth with threading dislocations

laser cut

Surface damage from thinning/polishing

CVD bulk, surface defects

or by polarized optical light transmission(birefringence)


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Deep etching of diamond

quadrant position monitors use signal interpolation, requires s/n ~103… 104

→ need high uniformity of response across device active area ~10mm2

beam position and intensity monitoring measurement 'bandwidth' required is from zero …~1kHz→ drift from polarization effects, and/or signal 'lag' cannot be tolerated (use of bias reversal very undesirable in this application)

practical challenges: - etching processes are not inherently planarizing-need to avoid local etch pit formation at pre-existing bulk or surface defects-surface roughening related to existing polish damage of surface

… and need process with ≥microns/hour etch rate

plasma and ion beam etching techniques : ` planar removal of diamond surface with ~nanometer residual damage offers local area, masked etching to create robust, 'superthinned' (few µm) devices

central area ArO etched to ~3µm

diamond polished plate ~50µm metal

electrodes~50nm

~3um thick device tested at Soleil Synchrotron

K Desjardins et al,J. Synchrotron Rad. (2014) 21

→ need to remove polish-damaged sub-surface layer (several microns depth)


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DEEP ETCHING - PROJECT AIMS

•To obtain adequate X-ray transparency for low energy X-ray beams (2~5 keV), diamonds must be ‘super-thinned’ to 5~20 µm.

•Consider/test different masking methods to delimit membrane area.

• High risk of plate edge chipping and breakage when processing to <50µm using scaife ‘abrasive’ polishing method.

Ion Beam Milling Inc.Argon etched

•Masked plasma etching can give robust ‘window-framed’ membrane devices. See M.Pomorski, Appl. Phys. Lett. 103, 112106 (2013


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MASKING TECHNIQUES

Vitreous carbon diamond holder

Laser machined polycrystalline diamond masks for plasma etching

4.5m

m


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DEEP ETCHING - PROJECT AIMS

•To obtain adequate X-ray transparency for low energy X-ray beams (2~5 keV), diamonds must be ‘super-thinned’ to 5~20 µm.

•Consider/test different masking methods to delimit membrane area.

•Compare different etchant gases and machine set-ups.

•Determine how initial surface polish affects etch rates and final surface.

• High risk of plate edge chipping and breakage when processing to <50µm using scaife ‘abrasive’ polishing method.

Ion Beam Milling Inc.Argon etched

•Masked plasma etching can give robust ‘window-framed’ membrane devices. See M.Pomorski, Appl. Phys. Lett. 103, 112106 (2013


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PLASMA ETCHING TECHNIQUES

Plasma

Diamond sample

Inductively coupled plasma etching machine - PTA-Minatech, Grenoble, with Thierry Chevolleau and Thomas Charvolin.

Electron cyclotron resonance plasma etching machine – Centre de Recherche Plasmas-Matériaux-Nanostructures, Grenoble, with Alexandre Bes.


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PURE OXYGEN ETCH RESULT

•Electron cyclotron resonance plasma etching

Etch time: 120 minutes.

Oxygen flow: 40sccm

Pressure: 4.0mT

Coil power: 2 x 600W

Platen power:150W

Bias: ~ -142V


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ARGON/OXYGEN ETCH RESULT

•Electron cyclotron resonance plasma etching

Etch time: 60 minutes.

Argon flow:24sccm

Oxygen flow:4sccm

Pressure: 7.0mT

Coil power: 2 x 600W

Platen power: 120W

Bias: ~ -140V

Courtesy of Etienne Bustarret,

Insitut Néel, CNRS, Grenoble


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ARGON/CHLORINE ETCH RESULTS

Inductively coupled plasma etching machine - PTA-Minatech, Grenoble, with Thierry Chevolleau and Thomas Charvolin.

Pre-etch surface

Post-etch surface

RMS: 1.84nm

RMS: 3.85nm

Etch time: 60 minutes, Argon flow: 25sccm, Chlorine flow: 40sccm.Lee, C.L et al. (2008) Diamond and Related Materials, 17 (7-10). pp. 1292-1296.


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CONCLUSIONS

•Initial trials: surface quality (presence of damage pits on 'standard' e6 CVD samples) has major impact on final surface roughness and topology.

•Pursuing trials with fine scaife polished HPHT 1b and CVD samples.

Machine type

Gas used Etch rate achieved

Comments

ECR Oxygen ~ 6µm/hour Fast etch but surface roughness increased.

ECR Argon/Oxygen ~ 12µm/hour Preferential etching of pre-existing damage pits along crystal planes.

ICP Argon/Chlorine ~ 4µm/hour Surface roughness improved

Thank you.

synchrotron x-ray beam monitoring / etching diamond for super-thin membranes, adamas workshop,...

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