1. i. Synchrotron X-ray beam monitoring
and
ii. Etching diamond
John MorseS ESRF
Charlotte Burman, ESRF & University of Bath

2. Outline 1. Synchrotrons and X-ray beam monitoring needs
2. diamond quadrant devices
3. CVD bulk and surface defects
4. diamond etching 2

3. 10 Hz Booster Synchrotron
The European Synchrotron Radiation Facility
Third generation light source
Location: Grenoble, France
Cooperation: 20 countries
Annual budget: ~100M€
Staff: 600
10 Hz Booster Synchrotron
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
200 MeV Electron Linac
User Availability: >98% of 250days/year
Mean Time Between Failures: ~80 hours
~6000 annual user visits of duration ~few days
~2000 journal publications/year 3

4. diamond X-ray beam monitors: quadrant devices
photo-ionization current readout → simple, compact devices
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
surface
contact
beam
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

5. signal variation with readout method
SAME device measured at DESY-DORIS F1
(white bending magnet, Al filtered beam)
with Libera RF readout system
-500
-400
-300
-200
-100
100
200
300
400
500
0.1 1 10
1000
e6 ELSC sample S361-1
(390um thick, , 50µm quadrant
isolation gap, TiW electrodes)
beam on other quadrants
(signal from beam halo?)
current quad 2
(modulus nA)
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
electrode ground bounce crosstalk
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)

6. scCVD diamond responsivity with X-ray energy; linearity vs. X-ray flux
J Morse et al, J. Synch. Rad 16 (2007)
1.E - 08 07 06 05 04 03 02 01
1.E+00
1.E+01
power Absorbed by Diamond (W)
Gas ion chamber calibration
Calorimetric calibration
Fit, w = /
0.2 eV
diamond signal (Amps)
J. Bohon et al,
J. Synch. Rad 17, (2010)
→ linear current response demonstrated over 10 orders of magnitude !
data from e6 ELSC material
responsivity fit
Platinum electrodes
M edge features:
J. Keister and J. Smedley, NIM A 606, (2009), 7

7. CVD bulk, surface defects
M.P. Gaukroger et al., Diam Relat. Mat. 2008
threading dislocations → crystal strain
visible with X-ray diffraction topography
or by polarized optical light transmission
(birefringence)
Surface damage
from thinning/polishing
laser cut
high purity CVD overgrowth
overgrowth with threading dislocations
HPHT grown substrate crystal

8. 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)
→ need to remove polish-damaged sub-surface layer (several microns depth)
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
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

9. 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.
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, (2013
Consider/test different masking methods to delimit membrane area.

10. Masking techniques
Laser machined polycrystalline diamond masks for plasma etching
4.5mm
Vitreous carbon diamond holder

11. 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.
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, (2013
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.

12. Plasma Etching techniques
Electron cyclotron resonance plasma etching machine – Centre de Recherche Plasmas-Matériaux-Nanostructures, Grenoble, with Alexandre Bes.
Inductively coupled plasma etching machine - PTA-Minatech, Grenoble, with Thierry Chevolleau and Thomas Charvolin.
Plasma
Diamond sample

13. 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

14. Argon/Oxygen etch result
Electron cyclotron resonance plasma etching
Courtesy of
Etienne Bustarret,
Insitut Néel,
CNRS, Grenoble
Etch time: 60 minutes.
Argon flow:
24sccm
Oxygen flow:
4sccm
Pressure: 7.0mT
Coil power:
2 x 600W
Platen power: 120W
Bias: ~ -140V

15. Argon/Chlorine Etch Results
Inductively coupled plasma etching machine - PTA-Minatech, Grenoble, with Thierry Chevolleau and Thomas Charvolin.
Pre-etch surface
RMS: 3.85nm
Post-etch surface
Etch time: 60 minutes, Argon flow: 25sccm, Chlorine flow: 40sccm.
Lee, C.L et al. (2008) Diamond and Related Materials, 17 (7-10). pp
RMS: 1.84nm

16. Conclusions
Thank you.
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.
Argon/Oxygen
~ 12µm/hour
Preferential etching of pre-existing damage pits along crystal planes.
ICP
Argon/Chlorine
~ 4µm/hour
Surface roughness improved