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Etch Damage in Magnetic Thin Film Head Materials
Lisa Krayer (UCSD, UMD) Mentor: Brian Kirby (NIST Center for Neutron Research) Collaborating with: (Seagate Technology) Anusha Natarajarathinam Mark Kief
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<http://www.ncnr.nist.gov/instruments/dcs/>
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1956: IBM 305 RAMAC (5MB)
Hard Drives, A History
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Hard Drives, A History 1956: IBM 305 RAMAC (5MB)
<http://www.computerhistory.org/revolution/memory-storage/8/259/1044>
24 in.
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Hard Drives, A History 1956: IBM 305 RAMAC (5MB)
2013: Seagate® Enterprise Turbo SSHD (600GB)
<http://www.computerhistory.org/revolution/memory-storage/8/259/1044>
24 in.
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1956: IBM 305 RAMAC (5MB) 2013: Seagate® Enterprise
Turbo SSHD (600GB)
<http://www.computerhistory.org/revolution/memory-storage/8/259/1044>
24 in.
<http://www.seagate.com/internal-hard-drives/enterprise-hard-drives/sshd/enterprise-
turbo-sshd/>
Hard Drives, A History
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Read/Write Heads
<http://www.123rf.com/photo_10466519_parts-of-hard-drive-in-close-up-read-write-head-and-
platter.html>
• Determines speed. • Aggressive scaling to 10’s nm. • Fabrication of magnetic
materials includes etching, milling and capping. • This process damages the
interfacial region of the materials!
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CoFeB • Common read head material. ▫ Ferromagnetic
B
H
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CoFeB • Common read head material. • Etching and capping changes
electronic state at the interface.
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CoFeB • Common read head material. • Etching and capping changes
electronic state at the interface.
• Dead layers up to 3.5 nm?
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Use Polarized Neutron Reflectometry (PNR) to determine the nature of interfacial damage to magnetic materials produced by industrially relevant fabrication techniques.
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Reflectometry
2𝜋𝜋∆
2
),()(4)(: ∫= dzezkziQ
QRamplitudereflection ikzzψρπ
“Modern Techniques for Characterizing Magnetic Materials.” Ed. By Yimei Zhu. Kluwer Acad. Publishers (2005).
θλπ sin4
=Q
Δ θ θ
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Why Neutrons? • Highly penetrating with little absorption. • Sensitive to nuclear composition (scatters from
nuclei). • Magnetic ▫ Neutrons are made up of three quarks that
distribute their charge radially creating a magnetic moment with no net charge.
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Polarized Neutron Reflectometry • Non-spin flip scattering length
density:
• Spin flip scattering length density purely magnetic (M⊥H).
)(.,
,,
,
HMionmagnetizatplaneinMconstC
CMlengthscatteringbdensitynumberN
bN
magnetic
iiinuclear
magneticnuclear
==
===
=
±=
∑±
ρ
ρ
ρρρ
reflection amplitude : R(Q) =4πiQ
ρ(z)ψ(kz,z)eikzdz∫2
θλπ sin4
=Q
H
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Expected Sample Structure
1nm Magnesium Oxide (MgO)
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Etch Methods Ion Beam Etching
(IBE) Plasma Etching
(PLSM)
Reactive Ion Beam Etching
(RIE)
Ion Source
Substrate Holder Accelerated
Ions
Tilt Rotation
Substrate
Accelerated Ions
Ground
Electrode for RF Excitation
Accelerated Ions
Ground
Electrode for RF Excitation
Substrate
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Results
0.00 0.05 0.10 0.15 0.20 0.25
1E-71E-61E-51E-41E-30.010.1
1
0.00 0.05 0.10 0.15 0.20 0.250.00.51.01.52.02.53.03.54.0
Log(
Ref
lect
ivity
)
Q (1/A)
IBE Spin Up IBE Spin Down PLSM Spin Up PLSM Spin Down RIE Spin Up RIE Spin Down
Ref
lect
ivity
(100
Q)4
Q (1/A)
IBE Spin Up IBE Spin Down PLSM Spin Up PLSM Spin Down RIE Spin Up RIE Spin Down
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Step 1: Calculate what we expect
0.00 0.05 0.10 0.15 0.20 0.250
1
2
3
4
5
0.00 0.05 0.10 0.15 0.20 0.250.0
0.5
1.0
1.5
2.0
2.5
Ref
lect
ivity
(100
Q)4
Q (1/A)
IBE PLSM RIE Expected
Spin Up Comparison
Ref
lect
ivity
(100
Q)4
Q (1/A)
Spin Down Comparison
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Step 2: Modify structure
1nm Magnesium Oxide (MgO)
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PLSM
1nm Magnesium Oxide (MgO)
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IBE
0.00 0.05 0.10 0.15 0.20 0.250.00.51.01.52.02.53.03.5
0 500 1000 1500 2000 2500 3000
0123456
Ref
lect
ivity
(100
Q)4
Q (1/A)
Data Spin Down Theory Spin Down Data Spin Up Theory Spin Up
Cr2O3
Cr
CoFeBMgOTaSiO2
ρ(1E
-6/A
2 )
Thickness (A)
ρ(z) ρM(z)
𝜒𝜒2=3.06421
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IBE
0.00 0.05 0.10 0.15 0.20 0.250.00.51.01.52.02.53.03.5
2750 2800 2850 2900 2950 3000 3050 3100 3150 3200
0123456
Ref
lect
ivity
(100
Q)4
Q (1/A)
Data Spin Down Theory Spin Down Data Spin Up Theory Spin Up
ρ(1E
-6/A
2 )
Thickness (A)
ρ(z) ρM(z)
SiO2Ta
MgO CoFeB
CrCr2O3
𝜒𝜒2=3.06421
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RIE
0.00 0.05 0.10 0.15 0.20 0.250
1
2
3
4
2850 2900 2950 3000 3050 3100 3150 3200
0123456
Ref
lect
ivity
(100
Q)4
Q (1/A)
Data Spin Down Theory Spin Down Data Spin Up Theory Spin Up
ρ(1E
-6/A
2 )
Thickness (A)
ρ(z) ρM(z)
SiO2
Ta
MgO CoFeB
CrCr2O3
𝜒𝜒2=2.64126
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PLSM
0.00 0.05 0.10 0.15 0.20 0.250
1
2
3
4
2850 2900 2950 3000 3050 3100 3150 3200 3250
0123456
Ref
lect
ivity
(100
Q)4
Q (1/A)
Data Spin Down Theory Spin Down Data Spin Up Theory Spin Up
ρ(1E
-6/A
2 )
Thickness (A)
ρ(z) ρΜ(z)
SiO2Ta
MgOCoFeB
CrCr2O3
Unknown Oxide
𝜒𝜒2=3.2559
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-250 -200 -150 -100 -50 0 50 100 150
0
1
2
3
4
5
6
-225 -150 -75 0 75 150
0
1
2
3
4
5
-225 -150 -75 0 75 150
0
1
2
3
4
5
6
7
8
Cr2O3
CrCr
Unknown Oxide
CoFeB
MgOTaSiO2
ρ(1E
-6/A
2 )
Thickness (A)
IBE ρ(z) IBE ρΜ(z) RIE ρ(z) RIE ρΜ(z) PLSM ρ(z) PLSM ρΜ(z)
Normalized Profileρ(
1E-6
/A2 )
Thickness (A)
IBE RIE PLSM
Magnetic Profile
ρ(1E
-6/A
2 )
Thickness (A)
IBE RIE PLSM
Nuclear Profile
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-250 -200 -150 -100 -50 0 50 100 150
0123456
-30 -20 -10 0 10
0123456
Cr2O3
CrCr
Unknown Oxide
CoFeBMgO
TaSiO2
ρ(1E
-6/A
2 )
Thickness (A)
IBE ρ(z) IBE ρΜ(z) RIE ρ(z) RIE ρΜ(z) PLSM ρ(z) PLSM ρΜ(z)
Normalized Profileρ(
1E-6
/A2 )
Thickness (A)
Etch Method
• IBE • RIE • PLSM
Dead Layer
• 8.97129 A • 6.378326 A • 4.153826 A
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Step 3: Verify model • Are we sure the differences are magnetic and not
structural? ▫ Constant dead layer. ▫ No dead layer.
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IBE
0.00 0.05 0.10 0.15 0.20 0.250.00.51.01.52.02.53.03.5
0.00 0.05 0.10 0.15 0.20 0.250.00.51.01.52.02.53.03.5
0.00 0.05 0.10 0.15 0.20 0.250.00.51.01.52.02.53.03.5
Data Spin Down Theory Spin Down Data Spin Up Theory Spin Up
Unique Dead Layer
Ref
lect
ivity
(100
Q)4
Constant Dead Layer
Q (1/A)
No Dead Layer
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RIE
0.00 0.05 0.10 0.15 0.20 0.250
1
2
3
4
0.00 0.05 0.10 0.15 0.20 0.250
1
2
3
4
0.00 0.05 0.10 0.15 0.20 0.250
1
2
3
4
Data Spin Down Theory Spin Down Data Spin Up Theory Spin Up
Unique Dead Layer
Ref
lect
ivity
(100
Q)4
Constant Dead Layer
Q (1/A)
No Dead Layer
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PLSM
0.00 0.05 0.10 0.15 0.20 0.250
1
2
3
4
0.00 0.05 0.10 0.15 0.20 0.250
1
2
3
4
0.00 0.05 0.10 0.15 0.20 0.250
1
2
3
4
Data Spin Down Theory Spin Down Data Spin Up Theory Spin Up
Unique Dead Layer
Constant Dead Layer
Ref
lect
ivity
(100
Q)4
Q (1/A)
No Dead Layer
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Trend • Dead layer does not match expected • Comparison of integrated magnetization with
magnetic flux.
B
H
456789
23
24
25
2.3
2.4
2.5
PLSMRIEDea
d La
yer (
A)IBE
gM
agne
tizat
ion
(nW
b)
IBE RIE PLSM
Flux
(nW
b)
SampleIBE RIE PLSM
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In Conclusion • Fit is sensitive to dead layer, not just structural
differences. • Ion Beam Etching appears to have the most damage
while Plasma Etching has the least. • Magnetization consistent with Seagate data.
Future Considerations • X-Ray Reflectometry to verify nuclear structure. • TEM for a better image of the depth profile
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Acknowledgements • Brian Kirby • Seagate Collaborators: ▫ Anusha Natarajarathinam ▫ Mark Kief
• NIST/CHRNS • Julie A. Borchers, Robert D. Shull and Terrell A.
Vanderah (Directors, MML/NCNR Materials Science SURF Program)
• Dan Neumann, Rob Dimeo