synchrotron x-ray beam monitoring / etching diamond for super-thin membranes, adamas workshop,...
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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
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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1. Synchrotrons and X-ray beam monitoring needs
2. diamond quadrant devices
3. CVD bulk and surface defects
4. diamond etching
Outline
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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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
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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• 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
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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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
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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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:
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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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)
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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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)
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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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
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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MASKING TECHNIQUES
Vitreous carbon diamond holder
Laser machined polycrystalline diamond masks for plasma etching
4.5m
m
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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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
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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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.
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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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
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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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
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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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.
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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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.