XPS/UPS and EFM - University of Florida · XPS/UPS and EFM Brent Gila XPS/UPS – Ryan Davies EFM...
Transcript of XPS/UPS and EFM - University of Florida · XPS/UPS and EFM Brent Gila XPS/UPS – Ryan Davies EFM...
XPS/UPS and EFM
Brent GilaXPS/UPS – Ryan Davies
EFM – Andy Gerger
A 21st Century Approach to Reliability
XPS/ESCA
X-ray photoelectron spectroscopy (XPS) also called ElectronSpectroscopy for Chemical Analysis (ESCA) is a chemical surface analysismethod. XPS measures the chemical composition of the outermost 100 Å of a sample.Measurements can be made at greater depths by ion sputter etching to remove surfacelayers. All elements (except for H and He) can be detected at concentrations above 1.0atom %. In addition, chemical bonding information can be determined from detailedanalysis.
30 25 20 15Binding Energy (eV)
Ga(GaOX)
Ga(GaN) A Ga 3d peak with 2 curves fitted.Can determine relativeconcentration of Ga-O and Ga-N
A 21st Century Approach to Reliability
XPS/UPS
XPS/ESCA Perkin-Elmer PHI 5100 ESCA System - MAIC
1. X-ray source – Mg or Al anode2. Sample3. Lens and aperture4. Hemisphere energy analyzer5. Position Sensitive Detector6. Data Collection - Computer
A 21st Century Approach to Reliability
0 5 10 15
co
un
ts
sputter cycles
as-rec 12.5 min ozone 25 min ozone
Oxygen concentration vs.ozone exposure time
(depth)
Used XPS to determine the surfacecomposition/contamination and nature ofthe chemical bonding.
Oxygen surface conc. increases with ozoneexposure time, however, oxygen depthdoes not. Surface converted to anoxynitride. (sample temperature~50°C)
Surface carbon concentration reduced 50%by conversion to CO and CO2.
Optimize the ex-situ cleaning recipe
Past XPS use on HEMT passivation optimization
A 21st Century Approach to Reliability
540 536 532 528
Binding Energy (eV)
OxynitrideonAlGaN(23%)cappedHEMT
80 76 72 68
Binding Energy (eV)
O1sAl2p
30 25 20 15
Binding Energy (eV)
as received 2 min sputter
Ga3d
80 76 72 68
Binding Energy (eV)24 20 16
Binding Energy (eV)540 536 532 528
Binding Energy (eV)
as-rec1st sputter
Native Oxide(0.7eV surface charge)
UV-ozone Oxide(0.6eV surface charge)
as-rec1st sputter2nd sputter3rd sputter4th sputter
Past XPS use on HEMT passivation optimization
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OxynitrideonGaNcappedHEMT
24 20 16
Counts
Binding Energy (eV)536 532 528
Counts
Binding Energy (eV)
540 536 532 C
ou
nts
Binding Energy (eV)
O 1sGa 3d
28 24 20 16 12
Counts
Binding Energy (eV)
as-rec1st sputter
Native Oxide(0.6eV surface charge)
UV-ozone Oxide(4.8eV surface charge)
as-rec1st sputter2nd sputter3rd sputter4th sputter
Past XPS use on HEMT passivation optimization
A 21st Century Approach to Reliability
30 25 20 15Binding Energy (eV)
Ga3dfromGaNcappedHEMTAs-ReceivedGaNSurface
Ga(GaOX)
Ga(GaN)
NoticethedecreaseintheGaOXportion(correspondingwithsputtertime)andtheshiftintheGa3dsignalassurfacechargeisreduced.
Past XPS use on HEMT passivation optimizationSPU
TTER TIM
E
0min
2min
4min
6min
8min
Ga 3d
GaOx
GaN
30 25 20 15Binding Energy (eV)
A 21st Century Approach to Reliability
GaN
X-RAY
e
e
XPS signal
GaON
As x-rays enter the material,photo-electrons are generatedfrom different depths.Thick (2nm) ozone GaON isnot conductive;
Large surface charge (4.8eV) isindicated from XPS spectra shift.
28 24 20 16 12
Cou
nts
Binding Energy (eV)
Ga 3d
electrons leavingthe surface are not replenishedfrom the bulk.
+ + + + + + + + +Surface charge forms
Past XPS use on HEMT passivation optimization
A 21st Century Approach to Reliability
CurrentCollapseMeasurements
GaNcappedHEMTsshowbetterpassivationthatAlGaNcappedHEMTs
IncreaseinAl%=increaseinsurfacereactivity=lesspassivation
HEMT structure As-received UV-Ozone
treatment Sc2O3
passivation
AlGaN cap20-23%
50% of DC 35% of DC 80% of DC
GaN cap3nm 40% of DC 40% of DC 95% of DC
Past XPS use on HEMT passivation optimization
A 21st Century Approach to Reliability
Effects on Isolation Currentmesa to mesa leakage measurements
0 10 20 30 4010
-10
10-9
10-8
10-7
10-6
Before UV Ozone 25 mins UV Ozone UV Ozone + 3Days Effect
Isola
tion
Cu
rren
t (A
)
Voltage (V)
1 2 3 4 5 610
-9
10-8
10-7
10-6
1x10-5
1. Unpassivated2. O
3 + Sc
2O
3
3. O3 + MgO
4. O3 + SiN
X
5. O3 + NH
4OH + SiN
X
6. Ashing + NH4OH + SiN
X
Iso
lati
on
Cu
rren
t (A
)Passivation Method
Must have isolation for realization of HEMT circuits.
Large scale features to aid in optimization
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Passivation Reliability
0 10 20 30 40 50 60 70
1.4
1.5
1.6
1.7
200°C age100°C agepassivateas-rec
Sheet C
arr
ier
Conc. (x
10
13
cm-2
)
Day
control HEMT (no age) aged HEMT (RT) aged HEMT (ele.temp.)
Hall effect samples (5mm x 5mm) areprocessed to determine the passivationeffect of the dielectric films. Samplesare aged at elevated temperatures todetermine effectiveness.
5mm Hall Effect sample
5mm
Hall samples are large enough for furtheranalysis (AFM, AES, XPS) for post agingstudies.
Hall sample w/ 10nm MgO passivation, a 15%increases in sheet carrier density post passivation
Large scale features to aid in optimization
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Small spot XPS/UPS
Custom XPS/UPS on Nitride MBE system allows for sampletransfer without exposure to atmosphere, 3” wafer capable.Intermediate chamber available for additional processing or testing.
System based on a PHI 5400 XPS - Area resolution is <500µm,2500mm2 viewing area.
Aging of samples by both thermal stress (800°C sample heater)and bias stress (electrical feedthru to sample). Surface chemicaldesorption experiments and real-time diffusion data possiblewith sample heater.
Ultraviolet He arc discharge source installed for UPS
A 21st Century Approach to Reliability
What UPS adds to the package
Mainly used for studies of the valence electron density of states. TheVUV (10-200nm) discharge covers a useful range from 10 to 50 eVphoton energy. The line width of excitation is generally a few meV,excellent for resolving molecular vibrational structures.
UV excited photoelectron spectra could be used for a comparison withband structure calculations and (in comparison with XPS) providing someadditional fingerprint information in surface chemical analysis.(ex. Determine Al2O3, AlPO4, Al4(P4O12)3 on a sample)
Provides a high resolution valance band spectra compared to XPS fordetermining valance band on surfaces.
A 21st Century Approach to Reliability
Reliability of dielectrics
Reliability (aging) of the dielectric can be determined through boththermal stress and bias stress to determine method of failure. (largearea features)
The two regions for dielectric coverage have significantly differentsurface chemistries and structure.
Identify key interface species/reactions that lead to stablepassivation, isolation or field plates dielectric.
AlGaN
GaN
AlGaNRegion 2
Region 1
dielectric
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Metal contact failure mechanism
0 40 80 1200.0
5.0k
10.0k
15.0k
20.0k
25.0k
Al
N
Ga
Au
O
Ni
Co
un
ts
Sputter cycles
Ni/Au gate on HEMT after thermal failure
-2 -1 0 1 2
-100.0n
-50.0n
0.0
50.0n
100.0n
Cu
rre
nt
Voltage
Using AES (area = micron to submicron) onecan easily determine certain metal contactfailure mechanisms.
Example: Ni/Au gate contactThe Ni diffuses to the surface,
leaving Au in contact with the AlGaN.
Fairly straight forward.
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Metal contact failure mechanism
0 1000 2000 30000
10
20
30
40
50
60
70
80
90
100
Sputter Depth (Å)
N
Ato
mic
Co
nc
en
tra
tio
n (
%)
Au Ir
GaTi
Al
O
Ir-Control
0 1000 2000 3000 40000
10
20
30
40
50
60
70
80
90
100
Sputter Depth (Å)
N
Ato
mic
Co
nc
en
tra
tio
n (
%)
Au
Ir
Ga
Ti
Al
O
Ir-900oC
Good Ohmic Contact (Ir based)
Failure of Ohmic contacts not as easilyunderstood using AES.
Using AES one cannot determine thebonding state of the element, only theamount and depth position.
Example: A low resistivity ohmic contact isa blending of the different metals. Cannotdetermine if TiN interface formed.
Must use XPS.
A 21st Century Approach to Reliability
280 285 290 295
Counts
/sec
Binding energy (eV)
acetone ipa copolymer mibk ipa
Identification of contamination
525 530 535 5400
5000
10000
15000
20000
25000
30000
Counts
/sec
Binding energy (eV)
acetone ipa copolymer mibk ipa
C 1s
O 1s
Use of XPS can identify differentsources of carbon contamination thatare left behind from deviceprocessing.
Characterization enhanced with UPS
AES can only determine that C andO are present, but not the species orsource.
A 21st Century Approach to Reliability
XPS/UPSProjected MilestonesYear 1- Characterize operational and failed devices in the mesa isolationregion. Determine changes in surface chemistry and work function.Correlate chemical/electrical changes.
Year 2- Design test structures to be placed in the die cut lines. Apply teststructures to the cut lines and investigate variations in surface chemistryfrom post field stressing.
Year 3- Design in-situ bias stressing fixture for XPS-UPS. Characterize cutline test structures under bias stress using XPS-UPS. Identify degradationmechanism. Investigate reactions of semiconductor/passivation interface.
Year 4- Real-time observation of near-surface changes during biasstressing.
Year 5- Small spot size XPS capability for direct analysis on die
A 21st Century Approach to Reliability
Electrostatic force microscopy - EFM
- - --- --- --
- -- + + ++ +
-- -
--
----
-
sample
tip
EMF trace
Image of high aspect ratio EFM tipavailable from Veeco.
Scan area in AFM Tappingmode, then apply a bias to the tipand scan in EFM mode.
Veeco Dimension 3100 with Nanoscope V controller iscurrently installed in the MAIC facility
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Electrostatic force microscopy - EFM
Applied to pre and post aged devices to scanfor variations of the electric field on the devicesurface.
Examine defects propagating to the surfaceduring testing, electromigration of gate metalin the gate-drain region, and increases in thesurface potential from UV illuminationemptying traps.
Identify area for TEM/LEAP.
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Projected MilestonesYear 1 – Map the device surface of operational devices varying substratebias and tip bias. Establish scan parameters for various compoundsemiconductor surfaces.
Year 2 – Map the device surface of failed devices and establish trends offailure in this region. Design probe cards for device biasing during scanning.
Year 3 – Correlate the failure mode to evolution of defects observed byTEM/LEAP. Incorporate defect generation and field profile into simulators.
Year 4- Real-time imaging of devices during stressing
Year 5-Establish limits of predictive forecast of reliability using short bais-aging cycles.
Electrostatic force microscopy - EFM
A 21st Century Approach to Reliability
xtra
A 21st Century Approach to Reliability
High resolution XPS/UPS
State of the art tools have <9um spot size and can build chemicalmaps of the surface – Physical Electronics & Omicron
High intensity monochromatic x-ray sourcesscan the surface.
Sphera – 60µm NanoESCA – 650nm
A 21st Century Approach to Reliability
Imaging Mode XPS/UPS
Imaging at high kinetic electron energies.Ag evaporated on Cu, 35 µm field of view,20 min acquisition time on Ag 3d5/2.
A 21st Century Approach to Reliability