APS-MAS Presentation_V2.1.2
-
Upload
mariela-georgieva -
Category
Documents
-
view
23 -
download
3
Transcript of APS-MAS Presentation_V2.1.2
UNCLASSIFIED
UNCLASSIFIED The Nation’s Premier Laboratory for Land ForcesUNCLASSIFIED The Nation’s Premier Laboratory for Land Forces
UNCLASSIFIED
Characterization of Diamond Surface Termination and Electrical Properties
Georgieva, Mariela*; Weil, James; Birdwell, A. Glen; Shah, Pankaj; Crowne, Frank J., Ivanov, TonyUS Army Research Laboratory, *University of MarylandAPS-MAS October 23-25
UNCLASSIFIED
UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces
Motivation
Following the success of other transparent semiconductors, there has been interest in diamond for high-power electronics.
The next step is to identify those critical characterization techniques that will be most effective in establishing process control through the various steps of device fabrication.
• Mobility• Surface diamond devices are limited by large surface
roughness• Decreasing the roughness from RMS ~ 1 nm to ~
0.35 nm is likely to considerably increase the mobility, from ~ 125 cm2 N-s to ~ 400 cm2 N-s.
• High power• Microwave sources kW range• mm-wave sources 100 Watt range
• High thermal stress• Less need for cooling during operation
ARL Modeling suggests higher hole mobilities can
be found by minimizing diamond surface roughness.
UNCLASSIFIED
UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces
Techniques
• Atomic Force Microscopy• Roughness• root-mean-square
roughness: based on average deviation from vibration of the probe tip
• Raman Spectroscopy• compositional & structural
data • Identifies intensities,
positions and widths of different inverse wavelength peaks
• Kelvin Probe Microscopy• electrical properties• work function: based on the contact potential
difference between the Au tip and diamond sample
Au
Kelvin Probe Sample Mount and Tip
Negative Electron Affinity
UNCLASSIFIED
UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces
Goals
• To develop a preliminary procedure for fabricating diamond FETs
• To develop diamond surfaces that exhibit better electrical properties for high-power devices
• To compare the performance of diamond substrates from two different suppliers
• To compare the performance of diamond substrates with different terminations
Top: Band scheme and electron affinity for the bare, oxidized and hydrogenated diamond (100) surface. Bottom: The atomic arrangement of the bare, oxidized and hydrogenated (100) diamond surface.
Negative Electron Affinity
UNCLASSIFIED
UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces
Characterization Procedure
Starting Materials: Diamond wafers were polished at the vendor, then shipped to ARL where they are characterized.
CVD-grown, single-crystal diamond (001)Sample 1: Vendor A, N-content (<25ppb)Sample 2: Vendor B, N-content (<3ppb)
Post-Polish Characterization|
Surface Preparation(Organic Cleans and Chemical Oxidation)
|Post Oxide Characterization
|Hydrogenation
|Post Hydrogenation Characterization
|Device Fabrication
Substrate Fabrication Process
CVD Growth Laser Cutting Polishing Substrates
ARL’s In-House Characterization
UNCLASSIFIED
UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces
Post-Polish: Raman
Sample 1
Sample 2
Characteristic Diamond Peaks:o 1332cm-1: 1st Order Peak, Characteristic of diamond quality.
- Natural Diamond FWHM: 2-2.5cm-1
- High Quality, CVD Diamond FWHM: <10cm-1
o 1350cm-1, 3120cm-1: Reveal N-V- centers
N-V-
1st Order Peak
Sample 1st Order(cm-1)
FWHM(cm-1)
N-V- Notes:
1 1333.6 4.8 Yes Other peaks indicate bulk/surface inclusions
2 1333.4 5.0 No Very clean wafer
S1 Inclusions S2 Variation in 1st Order Peak Position
2nd Order Peaks
Nitrogen below Detection Limit
= TBD
UNCLASSIFIED
UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces
AFM Data Summary
Sample 1
Sample 2
Polish Oxygenation Hydrogenation
AFM - RMS Surface Roughness (nm)Polish Oxygenation Hydrogenation
Sample 1 0.46 1.278 0.315Sample 2 0.46 1.14 0.616
Outgassing from Cassette(cleaned prior to processing)
Chemical Contamination?
UNCLASSIFIED
UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces
Kelvin Probe Data Summary
Post-Polish Post-Oxygenation Post-Hydrogenation
Sample 2 Sister Sample
Expected Values:
~4.8 – 5.2 eV
(Hydrogenation)
~5.8 – 6.2 eV
(Oxygenation)
Chemical Contamination?
UNCLASSIFIED
UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces
Findings
• There is a significant difference between the measurements taken using samples from the two manufacturers as-received
• Large variation in work function values indicate likely chemical contamination issues during the oxidation step• Supported by AFM data
• Hydrogen plasma treatment may “decorate” inclusion sites and other surface defects
• Need to be careful with sample handling with respect to metal tweezers, etc…metals can diffuse into diamond during high-temperature processes
Laser confocal microscopy image of hydrogenated diamond surface
UNCLASSIFIED
UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces
Conclusions
• Consequences of the wafer manufacturing and device processing must be addressed• Example: Better cleaning between process steps
• Need to study additional samples from each manufacturer
• Overall, data is generally in-line with predictions based on literature• Sample 1 shows the most correspondence to expected
behavior
• Techniques utilized appear adequate to evaluate the quality of diamond
UNCLASSIFIED
UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces
Future Plans
• Environmental chamber for Kelvin probe measurements
– Temperature and environmental control
– UHV-Scanning capbility– Illumination
• Polishing study– Intended to review different
polishing processes’ effects on the quality of the material surface
• Test device manufacture– The development of Hall bar
structures to measure the electrical performance for different polishes
UHV-Kelvin Probe
Photons
Electrons
Photoemission
Temperature Ramping (77-875 K)
In-house Capability BuildUHV-Scanning Kelvin Probe and
Photoemission Spectroscopy
UHV-Optical Chamber
w/ x,y,z scanning!
UV Light Source
UNCLASSIFIED
UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces
Sample CPD (mV)
CPD Stdev (mV) WF (eV) Comments
S1 111.8 5.8 5.2518N2 ambient (20 SCFH overnight, 5 SCFH during measurement);
Temp=26.1; RH=2%; no illumination
S1 112.2 6.3 5.2522N2 ambient (20 SCFH overnight, 5 SCFH during measurement);
Temp=25.1; RH=2%; no illuminationAl
Standard
-1060.0 2.3
WF (tip) = 5.140
N2 ambient (20 SCFH overnight, 5 SCFH during measurement); Temp=25.6; RH=2%; no illumination
S2 683.0 3.9 5.7531N2 ambient (20 SCFH overnight, 5 SCFH during measurement); no
illumination; after cleaningAl
Standard 990.1 4.6
WF (tip) = 5.07 normal room ambient
NOTES Used 4.080eV as the WF for Al; Tip size = 2mm; Gradient = ~300.
Post-Polish: Kelvin Probe
UNCLASSIFIED
UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces
Post-Oxygenation: Kelvin Probe
Sample CPD (mV)
CPD Stdev (mV) WF (eV) Comments
S2 -429.1 118.46 4.675N2 ambient (20 SCFH overnight, 5 SCFH during
measurement); no illumination
Al Standard -1024.1 3.6 WF (tip) = 5.104 normal room ambient
S1 1022.2 3.3 6.142N2 ambient (20 SCFH overnight, 5 SCFH during
measurement); no illumination
Al Standard -1039.8 3.8WF (tip) =
5.1198 normal room ambient
NOTES Used 4.080eV as the WF for Al; Tip size = 2mm; Gradient =
~300.
UNCLASSIFIED
UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces
Post-Hydrogenation: Kelvin Probe
SampleCPD (mV)
CPD Stdev (mV) WF (eV) Comments
S1 -193.7 3.05 4.8504N2 ambient (20 SCFH overnight, 5 SCFH during measurement);
no illumination
Al Std -964.1 4.21 WF (tip) = 5.0441N2 ambient (20 SCFH overnight, 5 SCFH during measurement);
no illumination
S2 7.098 2.7 5.0577N2 ambient (20 SCFH overnight, 5 SCFH during measurement);
no illumination
Al Std -970.6 4.08 WF (tip) = 5.0506N2 ambient (20 SCFH overnight, 5 SCFH during measurement);
no illumination