Radiation Effects in Strained MOSFET

1
Radiation Effects in Strained MOSFET

• Scott Thompson, Hyunwoo Park, Mark Law
• University of Florida
• June 14, 2007

2007 Vanderbilt MURI Annual Review
thompson_at_ece.ufl.edu
2
Outline

• Motivation
• Strained Si Jig/Band Calculations
• Single Event Effects
• Total Ionization Effects
• Conclusions/Plans

3
90/65nm Node Uniaxial Strain Everywhere!
4
Uniaxial Stress Used ALL Markets
Consumer
Computer
Wireless / handheld
Source Chipworks
5
Roadmap FLOOPs Channel Stress
Stress (GPa)
Ge 30
2.0
Ge gt25
1.5
Gate
1.0
Ge gt20
SiGe
SiGe
0.5
SiGe under gate
SiGe
Ge 17
90
130
45
32
22
65
Node (nm)
Time
pMOSFET channel SiN and SiGe
6
Outline

• Motivation
• Strained Si Jig/Band Calculations
• Single Event Effects
• Total Ionization Effects
• Conclusions/Plans

7
gt 1GPa Mechanical Stress Wafer

Flexure based design
Wafer
Pressure sensor
Highest to date wafer bending achieved of 1.5GPa
8
Stress Calibration Strain gauge, wafer
curvature, pressure sensor
Metal strain gauge
Wafer
Pressure sensor
Three Technique lt 5 error at 1GPa
9
Jig Strain Calibration
10
Industrial MOSFET/ bulk R Samples
11
High stress Hole mobility enhancement
Full Band Simulation
Hole mobility enhancement
Experimental data
Piezo
12
Self-consistent Procedure

• kp self-consistent solution to Poisson and
  Schrödingers equation

13
6 Band k p With Confinement
Subband structures obtained using the
Finite-Difference Method
14
Theory Developed to Extract Si and Ge Deformation
Potentials
15
Same Physics for holes in IV, III-V Materials
Si
Ge
GaAs
1GPa Uniaxial
1GPa Biaxial
Unstressed
16
Outline

• Motivation
• Strained Si Jig/Band Calculations
• Single Event Effects
• Total Ionization Effects
• Conclusions/Plans

17
Measurement Set Up Concept
Plan - Jig Design ( July , 2007) - Measurement (
September, 2007)
lt High frequency Probe station in Vanderbilt
University gt
18
Single Event Effect in MOSFET
MeV Heavy ions, proton, and alpha particle
e
h

• Single Event Effect (transient pulse) occurs in
  MOSFET
• The transient pulse can make data in memory
  circuits change Single Event Upset

19
SEE Plan (Measurement Concept)
4 5 V
connector
Delay line
Signal Splitter
Bias Tee
Signal
Trigger
Digital Real time Oscilloscope 12GHz Analog
Bandwidth Tr(0.35/12GHz) 29ps
Bending jig
Time (mA)
20
SEE in Strained Si MOSFETs
Biaxial stress
No Stress
Current
Longitudinal Uniaxial stress
e
h
µ
SS
Time

• Vertical electron mobility will be reduced.
• (Effective mass of out-of-plane electrons will
  increase in MOSFET in tensile stress)
• Rise and fall time is expected to be slower in
  tensile stress case.

21
Outline

• Motivation
• Strained Si Jig/Band Calculations
• Single Event Effects
• Total Ionization Effects
• Conclusions/Plans

22
Set up in Aracor Machine
Mechanical jig is used to apply stress to samples.
X-ray gun
Mechanical bending jig
23
TID Experiment Matrix
24
TID effect in MOSFET (100 MPa)
6 7 decrease
VG 0.6
VG 0.3
10 decrease
The decrease of drain current is observed after
irradiating devices, because impurity scattering
increase according generation of interface traps
25
TID effect in MOSFET (100 MPa)
The decrease of on current and increase of off
current indicate that the number of traps
increase due to radiation.
26
Total Ionization Dose effect in MOSFET
27
Total Ionization Dose effect in MOSFET(How does
stress change TID effect?)
Vg gt 0
keV x-ray
lt No Stress gt
B
B
1) Bond angle (?) and length (d) are related to
binding energy of bond 2) These terms are
affected by mechanical stress
lt Stress gt
O
?
d

Si02

Si

Si
Yu Wang and T.P. Ma, 1989
The number and activation energy of traps will
be changed under stress.
28
Non-Volitile SONOS Flash Memory
1 Bit
Trapped Electrons
s
D
29
Effect of Strain on Electron Traps
30E-6
25E-6
Unprogrammed
20E-6
post bake
Id (A)
15E-6
no strain
10E-6
programmed
5E-6
Vt shift
0
0
2
4
6
8
Vg (V)
Id vs. Vgs for unstressed memory cell in D1
W/L0.16/0.22 before and after programming and
data retention baking at 187C for 24hrs
30
Strain Significantly Alters Trap Energy Level
31
TID effect in MOSFET (No stress)
Off drain current after 200Krad irradiation is
determined by Body current
32
Broken Devices (Damage of Gate Oxide)
Damage of gate oxides are observed in I-V
characteristics
Possible cause Voltage spike pulse while
switching X-ray equipments (For example,
turning x-ray start button or turning on or off
equipments) Our group had similar experience
for turning on and off light.
33
Total Ionization Dose Experiment
Samples are irradiated under bias (Vg0.5V,
VsVdVb0) according to stress.
X-ray (31.5 krad/min)
Sample Tox 1.1nm 45nm Technology
0.5V
0V
0V
0V
Si Wafer
Mechanical jig
34
Simulation Result
DUT
35
Outline

• Motivation
• Strained Si Jig/Band Calculations
• Total Ionization Effects
• Single Event Effects
• Conclusions/Plans

36
Conclusions

• Strained Si channels being used in ALL markets
  for sub 90nm logic technologies
• Measure deformation potentials to give highly
  accurate semi empirical strained Si band
  structure for arbitrary types of strain
• Measured data shows strain alters trapping and
  activation for TID. Tensile strain increases
  trap energy level
• Band calculations suggest strain will increase or
  decrease single even transient

37
Reference

• 1 Viktor Zekeriya and T.-P Ma, Effect of
  stress relaxation on the generation of
  radiation-induced interface traps in
  post-metal-annealed Al-SiO2-Si devices, Applied
  Physics Letters, Volume 45, Issue 3, August 1,
  1984, pp.249-251
• 2 Ivan Sanchez Esqueda, Hugh J. Barnaby, and
  Michael L. Alles Two-Dimensional Methodology for
  Modeling Radiation-Induced Off-State Leakage in
  CMOS Technologies, IEEE TRANSACTIONS ON NUCLEAR
  SCIENCE, VOL. 52, NO. 6, DECEMBER 2005
• 3 Bongim Jun et al Temperature-Dependence of
  Off-State Drain Leakage in X-Ray Irradiated 130
  nm CMOS Devices, IEEE TRANSACTIONS ON NUCLEAR
  SCIENCE, VOL. 53, NO. 6, DECEMBER 2006
• 4 Ji-Song Lim, Xiaodong Yang, Toshikazu Nishida
  and Scott E. Thompson, "Measurement of conduction
  band deformation potential constants using gate
  direct tunneling current in n-type metal oxide
  semiconductor field effect tansistors under
  mechanical stress," Applied Physics Letters, 89,
  073509, 1-3, August 14, 2006.
• 5 Akemi Hamada and Eiji Takeda, Hot-Electron
  Trapping Activation Energy in PMOSFETs Under
  Mechanical Stress, IEEE ELECTRON DEVICE LETTERS,
  VOL. 15, January 1994.