Integrated Circuit Vulnerability to EBeam Decontamination Process

1
Integrated Circuit Vulnerability to E-Beam
Decontamination Process

• Fred W. Sexton, Paul E. Dodd
• Marty R. Shaneyfelt, and Jim R. Schwank
• Sandia National Laboratories
• Albuquerque, NM

This work was supported by the United States
Department of Energy. Sandia is a multi-program
laboratory operated by Sandia Corporation, a
Lockheed Martin Company, for the United States
Department of Energy under Contract
DE-AC04-94AL85000.
2
Purpose

• Following the post 9/11 anthrax attacks, the
  United States Postal Service has taken steps to
  decontaminate mail items using high-energy e-beam
  irradiation.
• Driven by a need for radiation tolerant
  electronics in defense and space applications,
  the effects of radiation on electronics have been
  studied for more than 40 years by the radiation
  effects community.
• Commercial electronics, because of their high
  performance and lower cost relative to radiation
  hardened ICs, have also been studied.
• This information is relevant to electronics
  vendors in assessing the impact of the USPS
  sanitizing process

3
Outline

• Bacterial spore survival curves terminology
• Total dose mechanisms
• Total dose response of CMOS technologies
• USPS mail sanitization procedure
• Summary

4
Survival curves for bacterial spores

• Factors Affecting Sensitivity
• Species of microorganism,
• Number of microorganisms
• Medium
• Temperature
• Gas Phase
• Water Activity
• Sensitizing compounds

Dry spores are least susceptible to radiation!
S. A. Goldblinth, The Inhibition and Destruction
of the Microbial Cell by Radiations, in
Inhibition and Destruction of the Microbial Cell,
ed W. B. Hugo, Academic Press, 1971.
5
Decontamination Terms

• D10 value the dose required to reduce the
  initial spore population by 90 (to 10
  remaining)
• DI Inactivation Dose the minimum dose at which
  spores are sterile in an incubating medium
• DS Sterilizing Dose the dose that causes a
  12-log reduction in spore survival, used in food
  industry (equivalent to D10x12, or IF1012)

6
Sterilizing Dose Derived from Survival Curve
Lethal exposure of anthrax in 21-year old healthy
male is 8000 spores
D10810 krad Implies DS 9.7 Mrad
7
US Postal Service Sanitizing MailUsing E-Beam
Irradiations

• Radiation source 10 MeV electrons from a pulsed
  linear accelerator
• Beam aperture is 2x4 foot
• Mail is boxed to ease handling
• Minimum dose is determined by dose depth curves
  for electrons in typical materials plus a safety
  factor

USPS is using a dose of 5 Mrad OR GREATER to
sanitize mail items!
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Total Dose Basic Mechanisms
-

Not hole trapping (E)
radiation





Nit interface trap formation (Pb)

gate
proton transport
H
proton release
hole transport

e/h pair generation and field-dependent
recombination
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Total-Dose Radiation Effectsin MOS Structures
10
IC Effects

• DVth DVit DVot
• Large DVot leads to increases in static supply
  leakage current
• Large DVit leads to degradation in timing
  parameters through reduced carrier mobility

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DVot and DVit Decrease WithDecreasing Oxide
Thickness
12
Edge Leakage Dominates Todays Thin-Gate-Oxide
Technologies
Leakage Path
LOCOS Field Oxide
Source
Gate
Source
Drain
Gate
Drain
Positive Trapped Charge
P-type Substrate
Bird's Beak
Source
Gate
Drain
Shallow Trench Field Oxide
Positive Trapped Charge
13
SOI Transistors Are Affected By Total-Dose
Charge Buildup in the Buried Oxide

• Partially-depleted transistors
• Charge buildup can invert the back surface
  causing a source-to-drain (back-channel) leakage
  current
• Leakage current relatively unaffected by gate
  bias
• Fully-depleted transistors
• Much more sensitive to radiation-induced oxide
  and interface-trap charge buildup
• Positive oxide charge buildup tends to deplete
  the back-channel interface causing a decrease in
  the threshold voltage of the front-channel gate
  oxide and increased back-channel leakage current
• Threshold voltage instabilities can result

Fully-depleted transistor
14
Sidewall And Buried Oxide Leakage Add To
Transistor Leakage Current
After R. A. Kjar and J. Peel, IEEE Trans. Nucl.
Sci. NS-21, 2081 (1974)
15
Base Oxide Defects Lead to Recombination

• Radiation increases
• base recombination
• net positive oxide trapped charge spreads
  emitter-base depletion region
• Si-SiO2 interface traps increase surface
  recombination velocity

16
Total Dose Reduces Bipolar Current Gain
Gain reduction is due to increased base
recombination current
17
Radiation Performance of COTS Rad-Hard
18
Rad Hardness Varies Widely for Commercial ICs
0
19
Total Dose Hardness of Commercial MOS ICs Varies
Significantlyfor 16 Mbit DRAMs from 15 Different
Manufacturers
Dose
Irradiation Details  Dynamic Bias (Only one set
of operating conditions) Co60 Exposure _at_ 0.4-1.0
rad(Si)/s, tested to functional failure (1024
errors)
Manufacturer Key FUJ Fujitsu HIT Hitachi MIC
Micron SAM Samsung TEX Texas
Instruments TOS Toshiba
R. Harboe-Sorenson et al., IEEE Radiation Effects
Data Workshop Record, 1995, p. 42 and R. L.
Pease, IEEE Trans. Nucl. Sci. Vol. 43, No. 2, P.
442 (1996)
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Commercial FG EEPROMS ShowLarge Variations in
Hardness

• WRITE FAILURES
• UNPOWERED

• WRITE FAILURES
• UNPOWERED

• WRITE FAILURES
• UNPOWERED

• WRITE FAILURES
• UNPOWERED

After Shaneyfelt et al., IEEE TNS 41, 2536 (1994)
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Current USPS Anthrax Sanitizing Process

• Anthrax spores are particularly difficult to
  kill. Requires 5 Mrad OR GREATER total dose.
• This is sufficient to destroy virtually all Si
  MOS and BJT integrated circuits.
• All mail going to the US Capitol (zip codes
  202-205) is being irradiated
• All quarantined material from Oct 01 was
  irradiated at two facilities, located in Ohio and
  New Jersey
• There are plans to expand the irradiation
  program, depending on need and funding.

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Alternative to Irradiation

• Develop Identified Mailer process to separate
  risk from non-risk items
• Certification of known originators and carriers
• Requires a verification process
• Identifying sensitive items film, electronics,
  credit cards, pharmaceuticals .
• Process must be adaptive to threat
• USPS is seeking input from affected industries,
  electronics, shippers, etc.
• What type of items go thru the mail?

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Conclusions

• USPS anthrax sanitization process will kill most
  microelectronic devices
• Alternatives to irradiation are essential
• Shipping using certified originators and carriers
  is the preferred approach
• USPS is coordinating its mail sanitization
  process with affected industrial groups
  throughout the US