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Capturing Ion-Soild Interactions
with MOS structures
Radhey Shyam, Daniel Field, Steven
Chambers, W.R. Harrell, James E.
Harriss, C.E. Sosolik
“Devices” to Study Ion-Solid Physics
• Our goal?
– To use standard electronic devices (diodes,
capacitors, tunnel junctions)
• Physics of operation is known
• Can be fabricated in-house (or even in-situ)
– To modify those devices with an ion beam and use
the “new” device characteristics to determine the
beam-solid interaction
Metal-Oxide-Semiconductor(MOS)
Metal
Oxide
Semiconductor
The goal is to establish that MOS devices can be used
to probe ion-modified oxides.
Metal-Oxide-Semiconductor(MOS)
Ion Beam
Oxide
Semiconductor
Metal-Oxide-Semiconductor(MOS)
Ion Beam
Oxide
Metal
Oxide
Semiconductor
Semiconductor
Encapsulation of the ion irradiation
effects in a finished device
The Experiment
• Device fabrication
– Si wafer: P-type; <100>; resistivity 1-10 Ω-cm.
–Grow an oxide (1900 Ǻ of SiO2) on the front side.
–Make Ohmic contacts on wafer back side.
– Deposit top metal contact on one of the control devices.
• Irradiate the oxide
– alkalis ions: Na+ ; 100 eV - 10 keV (kinetic energy).
– HCIs (at CUEBIT).
• Deposit top metal contact (capture irradiation effects)
• Characterize the device (Capacitance-Voltage measurements)
Beam Line & Manipulator
Standardized Terminology for Oxide Charges
Associated with Thermally Oxidized Silicon
Bruce E. Deal*
Energy-band diagram at thermal equilibrium for
an ideal MOS system.
Fig.[2]
Energy-band diagram of the MOS system under
flat-band conditions
V’FB= MS = M – S
This FB voltage does not include oxide charges.
Fig. [2]
S depends on the semiconductor doping.
S =  + (EC – EF)FB
The Effects of fixed charge oxide charge density
on the MOS system
VFB  x1  ox   x1 
Qox
 ox
Qox  x1

Cox  xox
for an arbitrary charge distribution,
VFB
Qf
1


Cox Cox
xox

0
x
  ( x)dx
xox
Capacitance(F)
Capacitance of Exposed Devices
Capacitance(F)
C-V(MOS # 8)
2 10
-10
1.8 10
-10
1.6 10
-10
1.4 10
-10
1.2 10
-10
1 10
-10
8 10
-11
-40
-30
-20
-10
Gate Voltage(V)
0
10
Capacitance(F)
Capacitance of Irradiated Devices(F)
Capacitance(F)
C-V(MOS #9)
8 10
-11
7 10
-11
6 10
-11
5 10
-11
4 10
-11
3 10
-11
-40
-30
-20
-10
Gate Voltage(V)
0
10
20
Getting at “Ion Beam Physics” with C-V
• ΔVFB – the shift in flat band voltage
– Calculate using typical doses (beam currents and
times)
– Dosing the oxide with 5.917*1012 ions /cm2 (15.80 nA
for 60 seconds)
– Calculated Dosage from ΔVFB =2.08*1013 ions/ cm2
– Linked to the probability of implantation of Ions into
the oxide. We found this probability to be 0.2845
– Vary this probability as a function of ion species and
energy of the ions (follow it with ΔVFB)
– C-V plot characteristics may also give information on
irradiation damage of the oxide (to be determined).
References:
1.Goodstein D.M.,Dahl E.B.,Dirubio C.A., and B.H. Cooper,”
Trapping of Ions at Metal Surfaces “,Physical Review Letters,
Vol. 78,pp 3213-3216.
2. Device Electronics for Integrated Circuits Muller & Kamins
,Third Edition.
3. Kohn M, Solid State Electronics,1971,pp 966-970, “Ionic
Contamination and Transport of Mobile Ions in MOS
Structures.”
4. Heatwave Standard Ø.250" Na source with coaxial heater
5. Keithley Semiconductor Characterization System
6. Agiliant E4980 A
7. Micromanipulator Probe Station