ion implantation and thermal annealing of α-al2o3-nov.19,2010
TRANSCRIPT
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H. Naramoto, C.W. White, J.M. Williams, C.J. McHargue, O.W.
Holland., M.M. Abraham, and B.R. Appleton
Solid State Division, OakRidge National Laboratory, Oak Ridge, Tennessee
Presentation by: Younes Sina
Ion implantation and thermal annealingof-Al2O3 single crystals
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Experimental
Single crystal of Al2O3 of high purity
(100 ppm total) with low dislocation
density (103-104 cm-2) from Union
Carbide Corp., and Crystal System, Inc.
Sample preparation
Disc specimens were cut perpendicular(to within 2) to the (c axis)
and (a axis) from single
crystalline rods using a diamond saw.
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Experimental
Sample preparation
These specimens were polished to a mirrorlike surface
finish with a fine diamond paste(< 1 Qm mesh) andannealed at 1200 C in air for 120 h to remove the
surface damage induced by mechanical polishing.
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280 or 300 keV
52 Cr+
1016-1017 ions/cm2
7 off
Current density : < 210-6 amp/cm2
Estimated temperature during implantation due
to beam heating : 150C
Implanted region
Unimplanted region(virgin)
musk
Experimental
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Thermal annealing in air
1 hr800C to 1600 C
RBS
Ion scattering /channeling
Using 2 MeV4
He+
Experimental
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Determine the depth profile of the implanted species
Depth distribution of damage in the lattice
Lattice location of the impurity
Using RBS to
Experimental
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Experimental
Some details about RBS
There are no strong nuclear reaction to complicate the
backscattering analysis using 2 MeV 4He+.
Random spectra were obtained while continuously rotating the
crystal to average over all crystallographic directions.
The specimens were covered with a stainless- steel plate with a
small open aperture for analysis to minimize the charge buildup.
The probing beam current was held to b10 nA ( b1 mm diameter).The scattered ion detector was cooled with Freon to b22C, which
improved the energy resolution to b14 keV.A scattering angle of 160was used for analysis.
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Lattice location measurements were carried out using
both aligned axial channeling spectra as well as detailed
angular scans across the following major axes andplanes:
, , , {0001} , {1-210} , and {10-10}
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Experimental
Angular scan measurements were taken only after
annealing to T=1300 and 1500.
After these temperatures, substantial recovery of
displacement damage in both the Al and O sublattices
occurs.
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Experimental
The valence state of the implanted impurity after
thermal annealing was determined using standard
Electron Paramagnetic Resonance (EPR) absorption
measurements.
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Experimental
EPR absorption measurement were made using a
K- band microwave spectrometer (35 GHz, 1.2 cm-1)
with the magnetic field applied perpendicular to the
axis of the crystal.
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Experimental
Changes in the hardness were measured by the useof the Knoop microhardness technique.
A force of 0.147 N was used inorder to confine the impression
depth to the near- surface region
(b0.3Q which is correspondsroughly to the full width of a typical
Gaussian distribution of theimplanted impurity ).
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Results and Discussion
Implantation damage
2- MeV He+ backscattering spectra from 52Cr(280 keV,
31016/cm2) implanted -Al2
O3
.
Random
aligned
virgin
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Results and Discussion
Implantation damage
2- MeV He+ backscattering spectra from 52Cr(280 keV,
31016/cm2) implanted -Al2
O3
.
Random
aligned
virgin
Al surface peak
O surface peak
(Random)Yield
(Aligned)Yieldmin !
%1.2(Al)min }
%6.0(O)min }
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Results and Discussion
The near-surface region was not turned
amorphous by implantation (the aligned
yield after implantation dose not reach the
random value).
We have not observed a completely disordered surface
region up to dose of 11017/cm2. This is in contrast to the
case of semiconductors such as Si, where dose of 1014-
1015/cm2 would be sufficient to turn the near- surface region
completely amorphous.
Random aligned
virgin The implanted Cr shows a small
channeling effect (the aligned yield
is b85% of the random yield)
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Results and Discussion
The fact that Al2O3 is not turned amorphous at theseimplantation energies and doses is inconsistent with the
existence of a reordering process during implantation.
The implanted Cr shows a small channeling effect (the
aligned yield is b85% of the random yield), againsuggesting a reordering process during implantation.
Sample temperatures during implantation are estimatedto less than 150C, and if the ion beam current is
reduced by an order of magnitude, there is no significant
change in the damage distribution.
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Results and Discussion
Effect of integrated dose
Effect of integrated dose on the damage distribution produced as
a result of 300- keV implantation.
Random
Align virgin
Align (11016/cm2)
Align (11017/cm2)
The near-surface region is
relatively damage free.
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Results and Discussion
The main effect of increasing dose is to broaden the damage
profile to greater depth with little or no increase in the magnitudeof the damage level.
Higher surface peak
11017/cm2)
11016
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Results and Discussion
Plot of the dose dependence of minmeasured in the Al substrate at a depth
corresponding to the peak in the implanted
Cr distribution.
These result shows that min (Al)is essentially independent of
implantation dose, indicating a
saturation of damage along all
three crystallographic direction.
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Results and Discussion
Thermal annealing behavior of 52Cr(300 keV, 11017/cm2) implanted -Al2O3
Thermal annealing behavior No change in the damage distribution in the O or Cr
Damage recovery for Cr &O
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Results and Discussion
Thermal annealing behavior
Thermal annealing behavior of52
Cr(280 keV, 31016
/cm2
) implanted -Al2O3
Change in the damage distribution in the Al & O & Cr
Damage recovery for Cr &O
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Results and Discussion
Thermal annealing behavior
From the results presented so far, it is impossible to
determine whether Cr becomes substituonal in the Al or
O sublattice, but the angular scan results clearly show
that Cr is substitutional in the Al sublattice.
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Results and Discussion
Thermal annealing behavior
52Cr(300 keV, 11017/cm2)52Cr(280 keV, 31016/cm2)
Random
aligned
virgin
Random aligned
virgin
Aligned yield for Al and O is very close to the virgin yield.
Aligned yield for Al is very close to the virgin yield.
The dechanneling rate in the near-surface region is greater for the high-dose
crystal compared to the lower dose case.
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Results and Discussion
Thermal annealing behavior
This increased dechanneling in the near-surface region,
which is a function of the dose (or concentration) of the
impurity, may be due to either residual defects or to
lattice strain resulting from the incorporation of large
concentrations of Cr into the Al sublattice.
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Results and Discussion
Thermal annealing behavior
Comparison of total and substitutional concentration for 52Cr(300 keV,11017/cm2) in
-Al2O3 after annealing at 1500
C
%98( l)][1
(Cr)][1(%)Fractiononalsubstituti
min
min "
!
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Results and Discussion
Thermal annealing behavior
Thermal annealing behavior for 52Cr (300 keV, 11016/cm2) in -Al2O3
Random
aligned
virgin
Random
aligned
virgin
Random
aligned
virgin
Substantial redistribution of the dopant occurs in
the range of 1500-1600 C.
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Results and Discussion
Thermal annealing behavior
Concentration profile for 52Cr(300 keV, 11017/cm2) in -Al2O3 after annealing at
1500C and 1600C compared to as-implanted profile.
Substantial redistribution of the dopant occurs in
the range of 1500-1600
C.
After annealing at 1600C, Cr is
observed to be redistribution bothtoward the surface and into the crystal.
Cr diffuses by a substitutional
diffusion mechanism
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Results and Discussion
Thermal annealing behavior
Results:
Damage recovery begins selectively in the Al sublattice
at a temperature ofb800C.Damage recovery begins in the O sublattice at
b1000C.Incorporation of Cr into substitutional lattice sites
occurs predominantly in the temperature range 1200-
1500C. After 1500C annealing, Cr is 95%
substitutional in the lattice.
The onset of substitutional Cr diffusion occurs in the
temperature range 1500-1600C.
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Results and Discussion
Thermal annealing behavior
The features of Cr incorporation can be better
distinguished by separating the Cr profile into three
different segments:
(1)0.05 Qm(2)0.05-0.15 Qm
(3)0.15-0.3 Qm
Results:
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Results and Discussion
Thermal annealing behavior
Results:
(1) 0.05 Qm(2) 0.05-0.15 Qm
(3) 0.15-0.3 Qm
Where damage is the least in the as-implanted condition
The min(Cr) value increases slightly with annealing temperature
up to 1200C even though min(Al) decreases, indicating no
further incorporation of Cr at this depth into substitutional lattice
sites in this temperature range.
In region (1):In region (1):
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Results and Discussion
Thermal annealing behavior
Results: (1) 0.05 Qm
(2) 0.05-0.15 Qm(3) 0.15-0.3 Qm
Surface side of the damage distribution, min(Cr) change very
little with annealing to 1200C
In region (2):In region (2):
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Results and Discussion
Thermal annealing behavior
Results: (1) 0.05 Qm
(2) 0.05-0.15 Qm(3) 0.15-0.3 Qm
Saturation of damage occurred in the as-implanted state,
min(Cr) decreased with annealing up to b1200C.
In region (3):In region (3):
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Results and Discussion
Thermal annealing behavior
Results:
(1) 0.05 Qm
(2) 0.05-0.15 Qm
(3) 0.15-0.3 Qm
These results suggest that up to 1200C, damage
recovery in Al sublattice competes with Cr
incorporation.With annealing to 1500C, min(Cr)
decreases substantially in region (2) and (3), whilethe aligned yield in the oxygen sublattice increases
slightly. These results suggest that Cr incorporation
in region (2) and (3) may be accompanied by oxygen
indiffusion from the surface during annealing at thehigher temperatures.
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Results and Discussion
Results:
Thermal annealing behavior
Summary of thermal annealing result for52Cr(300 keV, 11017/cm2) in -Al2O3
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
4a
4c
4b
4d 7b
7c7a
5a5b
5c
Results presented in previous Figs. suggest that implanted Cr is
substitutional in -Al2
O3
after thermal annealing to temperatures
in the range of 1300-1500 C, because the implanted Cr exhibits
a pronounced channeling effect. However these measurements
alone are not sufficient to determine weather Cr is substitutional
in the Al or O sublattice.
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
To determine whether Cr is substitutional in the Al or Osublattice, angular scans across the major axis and
planes are necessary.
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
Axial angular scans for 2-MeV He+ incident on virgin -Al2O3(depth range=0.05-0.35)
Yield of particles scattered from Al and O atoms in depth interval 0.05-0.35 Qmnormalized to the random value plotted as a function of tilt angle away from the major
axis or plane
2 1/2: full width at half maximum of the channeling dip
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
Planar angular scans for 2-MeV He+ incident on virgin -Al2O3(depth range=0.05-0.35)
2 1/2: full width at half maximum of the channeling dip
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
"! 1021cutx"! 0001cutz
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
Calculated and measured planar channeling critical half angles
(1/2) for 2-MeV He+ scattering from Al, O, and Cr atoms in virgin
and Cr-implanted -Al2O3.
Uncertainties in the experimental critical half angles are estimated to be 10% of the measured
value.
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
Calculated and measured axial channeling critical half angles(1/2) for 2-MeV He
+ scattering from Al, O, and Cr atoms in virgin
and Cr-implanted -Al2O3.
Uncertainties in the experimental critical half angles are estimated to be 10% of the measured
value.
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
Critical angles for both axis and planar were calculatedusing Barrett method:
2/112/1 )]/)([ EmVk Q] !
Adjustable parameters
k=0.76, m=1.6 (for planar critical angles)k=0.83, m=1.2 (for axial critical angles)
Mean one- dimensional vibrational amplitude( for planes)
Mean two- dimensional vibrational amplitude( for axis)
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
The potential was calculated using a model given by :
0VVV il ji !Contribution to the continuum potential due to
the jth atomic species in the ith plane
A constant to make the minimum potential energy equal to zero
Such a model assumes that mixed atomic sheets such
as the Al2 + O sheet in the {10-10} planar channel can
be treated as a superposition of atomic sheets each
with a unique atomic species.
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
Thermal vibrational amplitudes were determined usinga Debye model of the solid with a Debye temperature
of 1034K.
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
Static continuum potential for the various major planes in Al2O3. The atomic
constituent is indicated for each plane in a given configuration by the atomic
symbol, and a superscript which indicates relative atomic abundance.
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
O3
Al
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
(Al green, O red)
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
There is a good agreement between experiment andtheory data of channeling critical half angles.
Therefore all assumptions during calculated angles
can be justified.
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
Angular scans on implanted crystals were obtained using
crystals implanted to dose of 1 and 31016/cm2 after thermal
annealing at temperatures of 1300 and 1500 C.
Angular scan across the axis for 52Cr (300 keV, 11016/cm2) in Al2O3 after
1300C annealing.
Critical angles for scattering from Al and Cr have approximately the same width.
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
Critical angles for scattering from Al and Cr haveapproximately the same width but different from O.
Most of Cr atoms are substitutional in the Al sublattice
There are some Cr and O atoms in interstitial lattice
sites after annealing at 1300C. Interstitial Cr can
trap O atoms and diffuses in from surface during
annealing.
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
Al & O critical angle after Cr implantation and annealing
Al O
1300C
Al & O critical angle for the virgin sample
Al critical angle is considerably wider on the
implanted crystal compared to the virgin,
indicating that damage recovery is not complete
after annealing at this temperature.
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
Axial angular scan for 52Cr(280keV, 31016/cm2) in -Al2O3
1500 C thermal annealing
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
Planar angular scan for 52Cr(280keV, 31016/cm2) in -Al2O3
1500 C thermal annealing
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
Axial angular scan for52Cr(280keV, 31016/cm2) in
-Al2O3
1500 C thermal annealing
Al & O critical angle for the
virgin sample
Axial angular scan for52Cr(300keV,
31016/cm2) in -Al2O3
1300 C thermal annealing
Comparison of axial/planar angular scans for different cases shows that critical angle
in higher annealing temperature is closer to the virgin case.
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Results and Discussion
Lattice location of implanted 52Cr in Al2O3 after thermal annealing
Conclusion: Near-surface region is not turn completely
amorphous with Cr implantation on sapphire at
doses less than 1017/cm2.
Upon annealing, damage recovery beginsselectively in the Al sublattice at T~800 C.
Recovery in the oxygen sublattice begins at
T~1000 C for Cr.
After Cr implantation followed by thermalannealing at ~1500 C, the implanted impurity is
observed to be >95% substitutional in the Al
sublattice.
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Valence state of implanted 52Cr
The valence state of the implanted impurity can bedetermined usingElectron Paramagnetic Resonance
absorption (EPR) techniques.
The EPR spectrum of substitutional trivalent chromium
ions (Cr3+) in Al2O3 may be described by the followingspin Hamiltonian:
]3/)1([)(2
! B SSSDSHSHgSHgH zyyxxBzzB QQ
1cm0.382D1.987,g1.984,g3/2,S B
!!!!
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EPR spectroscopy is the measurement and interpretation of the
energy differences between the atomic or molecular states.
These measurements are obtained because the relationship
between the energy differences and the absorption of electro-
magnetic radiation.
To acquire a spectrum, the frequency of the electromagnetic
radiation is changed and the amount of radiation which passesthrough the sample with a detector is measured to observe the
spectroscopic absorptions.
EPR Spectroscopy
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EP
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EP
R
Like a proton, an electron has a spin, which gives it a magnetic
property known as a magnetic moment.
When an external magnetic field is supplied, the paramagneticelectrons can either orient in a direction parallel or antiparallel to
the direction of the magnetic field .
This creates two distinct energy levels for the unpaired electrons
and measurements are taken as they are driven between the two
levels.
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-Al2O3 with trace Cr3+ impurity
Valence state of implanted 52Cr
52Cr(300keV, 11016/cm2) in -Al2O3
EPR line shape of high
field Cr3+ absorption line
(Ms=-1/2Ms=-3/2)
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Microhardness change of Al2O3 with52Cr implantation followed by thermal annealing
HARDNESS CHANGES DUE TO ANNEALINGFor implanted Cr(1017/cm2) and Zr (41019/cm2) in - Al2O3
Annealing temperature(C)
Th k
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Kurdish rug with hexagonal grid
Thank you
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EPR spectroscopy is the measurement and interpretation of the
energy differences between the atomic or molecular states.
These measurements are obtained because the relationship
between the energy differences and the absorption of electro-
magnetic radiation.
To acquire a spectrum, the frequency of the electromagnetic
radiation is changed and the amount of radiation which passesthrough the sample with a detector is measured to observe the
spectroscopic absorptions.
EPR Spectroscopy
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EP
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R
Like a proton, an electron has a spin, which gives it a magnetic
property known as a magnetic moment.
When an external magnetic field is supplied, the paramagneticelectrons can either orient in a direction parallel or antiparallel to
the direction of the magnetic field .
This creates two distinct energy levels for the unpaired electrons
and measurements are taken as they are driven between the two
levels.