Space Qualification for Semiconductor Devices

Sammy Kayali Jet Propulsion Laboratory California Institute of Technology

sammy.a.kayali@jpl.nasa.gov

(818) 354-6830

May 14, 2007

Acknowledgment: The work described in the paper was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Tutorial Objectives

Describe the environmental, reliability and operational challenges for space applications. Provide a description of space qualification requirements and associated product testing and evaluation. In addition, semiconductor device processing, test and characterization requirements along with supporting data and application support will also be presented. Lastly, practical considerations for development of qualification plans for space applications will also be presented.

Outline

Space application Challenges

The application of microelectronics in space systems faces a number of challenges

Space environment
Reliability and Lifetime
Lack of accessibility

Consideration must be given to the impact of:

Lot non-uniformity & traceability
Temperature range of component
Availability of test data

It is critical that all aspects of reliability and relevant known failure modes and mechanisms be addressed prior to the insertion of the component in the application

Environmental Challenges for Space Applications

Reliability Challenge

Challenges We Face Now

Industry Trends

Parts Temperature Application Range

Temperature (C)

The Relative Cost of IC Failure

Relative Cost of a Integrated Circuit Failure (Rule of Thumb)

1X 10X > 100X

At Chip In the Manufacturer Field

Low Impact to Catastrophic Impact System Reliability To System Reliability

Space Qualification

Process Qualification

Acceptance of starting materials
Documentation of procedures
Implementation of handling procedures
Establishment of Lifetime and failure data
Test Structures
Process Monitors
Technology Characterization Vehicles
Etc.

Utilize the manufacturer existing and defined process with established reliability and qualification procedures and practices

Product Qualification

Verification that a component will satisfy the design and application requirements under specific conditions.

Product Acceptance

Utilization of standard MIL-STD type tests without consideration to material and design limitations may be detrimental

17

Special Environments

Characterization of radiation tolerance under the intended application

Definitions:

Reliability: “The Probability that an item Will Perform a Required Function Under Stated Conditions for a Stated Period of Time

Quality: “A measure of the variance of a product from the desired state”

deviations in oxide thickness from the target value

Failure Classification

Failures Can be Classified into two Groups:

An Important Parameter Drifts so For From It’s Original Value That The Component No Longer Functions Properly

Quantifying Reliability

R = A exp (-Ea/KT)

R = Rate of the Process
A = Proportional Multiplier
Ea = Activation Energy, a Constant
K = Boltzman’s Constant (8.6x10-5 eV/K)

Common Reliability Effects

Die

•...

Package

•...

Reliability Considerations Drive Technology Changes

Lightly Doped Drains

Hot Carrier Injection

(LDD)

Electromigration

Cu in Al Interconnect

Junction

Si in Al

Spiking

Interconnect

The Risk of Reliability Failures Has Increased As a Function of Device Scaling

2012

11M transistors

1,400M transistors

.050 micron features

0.25 micron features

± 60 mvolts allowable

Reliability Sensitivity to Processing Conditions

    • Oxide Reliability
    • starting material, oxide thickness, poly doping, plasma etching
    • Hot Carrier Injection
    • epi thickness, poly doping, channel length, LDD, S/D anneal
    • Electromigration and Stress Voiding
    • metalization, interlevel dielectrics, passivation
  • Power Slump

doping Profile, surface states, Source/Drain Ledge

Reliability / Performance Trade

    • End-of-life margins are often traded off against increased performance
    • e.g., thinner gate dielectrics increase the speed of transistors which also increasing the risk of electrical breakdown
    • The high volume, high turnover markets the industry focuses on have short lifetimes
    • typically <5 years
  • End-of-life wear-out is generally not seen in Integrated Circuits

large end-of-life reliability safety margins

Yield and Reliability

Early Constant End-of-Life Failures Failure (Intrinsic (Defects) Rate Failures)

Failure Rate

Time

Radiation Effects

Space Radiation Environments

Environments of Earth-Orbiting Spacecraft

Geosynchronous Orbit (35.8 km)

Located in outer electron belt Primary concerns are electrons from the belt and heavy ions

Total dose ~ 50 krad (5-year mission)

Total dose values are approximate, and depend on shielding

32

Charge Generation by Heavy Ions and Protons

A few protons cause nuclear reactions

p-substrate

Short-range recoil produces ionization

a) Heavy Ions (ionization Protons (nuclear reaction by each particle) needed to produce recoil) Most protons pass through the device with little effect

Military Environments

Approximate Total Dose Hardness Levels

HBTs

MESFETs

Digital logic

Memories

Linear amplifiers

Laser diodes

Light-emitting diodes (Only occurs with proton damage) (Only occurs with proton damage)

1 1000

10 100 Total Dose [krad] 35

Total Dose Effects in Silicon Devices

  • Primary Effects:
    • MOSFETs (including CMOS)
        • Negative threshold shift in gate voltage
          • Worse when positive voltage is applied to gate
          • Depends on square of oxide thickness (less important for parts with small feature size)
      • Increased leakage in field oxide
    • Bipolar Devices (particular linear circuits)
      • Gain is reduced
      • Radiation damage can be far less under the low dose rate conditions in space compared to high dose-rate test conditions

Total Dose Damage in a Linear Circuit

This figure shows that very large changes can occur in a linear integrated circuit when it is tested at low dose rate compared to results at high dose rate.

Effect of Proton Damage on a High-Frequency SiGe HBT

Some degradation occurs at low collector currents There is essentially no degradation at the normal operating current level, even at such high total dose levels.

10-7 10-5 10-3 10-1 10 IC (mA)

38

Effect of Total Dose Damage on an InP Heterojunction Bipolar Transistor

III-V HBTs have very thin base regions, and are usually highly resistant to ionization damage.

0.1 1 10

IC (mA)

Radiation Testing for Total Dose

    • Cobalt-60 gamma rays are usually used
      • Convenient, low cost irradiator
      • Does not simulate displacement damage effects, only ionization
  • Total dose damage is affected by bias conditions applied during irradiation
  • The usual approach is to irradiate devices at several levels, making measurements between successive irradiations

Radiation Testing for Displacement Damage

  • This diagram shows an array of light-emitting diodes that are placed at the exit port of a proton accelerator
    • The tests are expensive, because
    • several people are required to operate the facility.
  • Measurements are automated to reduce testing time.

a) Irradiation

b) Measurements

Effect of Proton Damage on Optocouplers

Optocouplers can be extremely sensitive to radiation damage Damage in the light-emitting diode is the cause

Equivalent Total Dose [krad (Si)] for Protons & Gamma Rays

Qualification Issues: Device Variability

  • Many parts used in space are commercial devices, not specifically designed for radiation or for long-duration missions
  • Data bases provide a guide for overall susceptibility, but radiation tests of specific lots may be required to ensure satisfactory performance

109 1010 1011 Proton Fluence (p/cm2)

Single-Event Upset Testing

Devices are placed at the exit port of a cyclotron The cyclotron produces charged heavy ions The range of the ions is limited (they have much lower energies than

ions in space) Usually the part lid must be removed to allow the ions to reach the active chip Some facilities require that the tests are done in a vacuum chamber

Single-Event Upset Testing

Pulses from the output of an optocoupler during tests at a heavy-ion facility. Special line drivers were used to allow the signals to be transmitted to an oscilloscope, located 30 feet away from the test devices.

6

0.004

5

Cross Section (cm2)

0.003

Output Voltage (V)

4 3

2

1

0.002

Diode

area

0.001

0 -1

0 0

Time (ns)

LET (MeV-cm2/mg)

SEU Mitigation

  • Several mitigation approaches can be used for SEU, including errordetection-and-correction (EDAC)
  • Older 4-Mb DRAMs were used on the Cassini spacecraft

Galactic cosmic rays produced about 307 errors per day in a 2.4 Gbit arra)

The EDAC method could correct for all single-bit 101 errors, and detect double-bit 100 errors

10-1

10-2 10-3 10-4 10-5

10-6

Cross section for correctable and hard (uncorrectable errors) in a 64-Mb SDRAM

Single-Event Effects Comparison for Silicon and Compound Semiconductors

    • Silicon Technology
    • Very large scale circuits are used
      • Circuits may upset in simple, correctable ways
      • Complex upsets can also occur that “crash” parts, requiring reset
    • Compound Semiconductors
      • Large scale circuits are rarely used
      • Low hole mobility limits use of complementary logic
        • Several specialized areas of importance:
          • High-speed, high power devices (MESFETs and HFETs)
          • Optoelectronics, particularly LEDs and laser diodes

Effects of Latchup on a CMOS Circuit

Break in metallization caused by very

Melting of silicon in highly localized

high current from latchup

region of current flow during latchup

Catastrophic Damage in High-Voltage SiC Diodes after Exposure to Heavy Ions

This figure shows how the breakdown voltage in a 600-V SiC diode is affected when it is exposed to a low fluence of heavy ions. Extensive derating is necessary if this part is used in a radiation environment.

600

The damage mechanism may

500

be related to the high defect density of silicon carbide

400

300

0.001 0.01 0.1 1 10 100 LET (SiC) [MeV-cm2/mg]

Average breakdown voltage [V]

Approximate Testing Costs

    • Facility costs
      • Total dose (~ $100 per hour)
      • Proton accelerator (~ $700 per hour + travel time for experimenters)
    • Overall test cost
      • Total dose (~ $15 to $20k)
      • Proton test (~$20 to $30k)
      • Costs may be higher for parts that require elaborate measurements, or extensive analysis of results

Testing for Military Environments

    • Neutrons
      • Similar in concept to proton tests
      • Protons and neutrons produce similar results for most devices, and are sometimes considered interchangeable
    • Gamma Rays
      • Tests are usually done at a flash X-ray
      • The facility produces very intense, short-duration pulses
      • The part(s) to be tested must be biased, usually with special instrumentation to measure currents and voltages
      • A great deal of noise is introduced by the X-ray pulse
      • Gamma ray test costs are higher, ~ $40 to $60k

The Evolution

1947: Ge transistor 2007: 90nm Pentium M Processor

J. Bardeen, W. Brattain, W. Shockley on 300 mm silicon wafer

Common Failure Mechanisms in Silicon

Gate Electrode Band bending Ultra-B penetration (p channel)

Ultra-thin Gate

Shallow

Insulator

Junctions

Direct

Resistive

tunneling gate

currents Surface

contacts

Junction

defects

spiking

Stress induced leakage

Sub-threshold Drain induced

currents

leakage barrier lowering Punch through Vth control

54

Common Failure Mechanisms in GaAs

Surface States

Ohmic Contact Degradation

Channel Degradation

Failure Mechanism Classifications

  • Material-Interaction Induced Mechanisms
  • Stress Induced Mechanisms
  • Mechanically Induced Mechanisms
  • Environmentally Induced Mechanisms

Material Interaction Induced Mechanisms

Gate

  • Gate Metal Sinking
  • Contact Degradation
  • Channel Degradation
  • Surface State Effects
Source Au Drain
Pt
Ti
GaAs
Semi-insulating GaAs

Gate Metal Sinking

FIB Cross-sections of Control and Two Degraded Gate Locations Gate Sinking Caused by 4380 hours at 260ºC

Base Defects

TEM/FIB cross section of 2m emitter AlGaAs/GaAs HBT after beta degradation of ~30%

Surface States Effects

Schematic cross section of a MESFET with Different surface charges. The gate-drain bias is the same for the two cases: (a) with low density of surface states Ds and

(b) with high density of Ds.

Stress Induced Failure Mechanisms

  • Electromigration
  • Electrical Stress
  • Hot Electron Trapping

Electromigration

  • The movement of metal atoms along a metallic strip due to momentum exchange with electrons
  • Depends on the temperature and the number of electrons
  • Generally seen in narrow gates and in power devices where the current density is greater than 2x105 A/cm2
  • Effect is observed both perpendicular to and along the source and drain contact edges and also at the interconnect of multilevel metallization.

Electrical Stress

Airbridge Metal Deformation Caused By High Current >4 million A/cm2, 175ºC, 1000 hours

ESD Damage

On-Chip Damage as a result of Electro-Static Discharge

Electrical Overstress

Electrostatic induced damage

Electrical Stress

HBM ESD Damage in Capacitor (~300Volts) 50um x 50 um MIM Capacitor, 2000 Å Nitride

Hot Electron Trapping

Under RF Overdrive, hot electrons are generated near the drain end of the channel where the electrical field is the highest.

Electrons can accumulate sufficient energy to tunnel into Si3N4 passivation to form permanent traps.

The traps can result in lower open-channel drain current and transconductance, and higher knee voltage, leakage current, and breakdown voltage.

Mechanically Induced Mechanisms

  • Die Fracture
  • Die Attach Voids
  • Surface Defects
  • Metal Voids

Die Fracture

Die Crack Discovered After IR Reflow Simulation

Die Attach Voids

Infra-red Image Showing Poor Die Attach

Surface Defects

Surface Defects have become a Very Critical Discriminator of Yield

Detrimental Particle Size has Shrunk in response to Reduction of Feature Size

Air Bridge Voids

Via Metal Voids

Incomplete Metal in Via

Fabrication Defects

reduced Al thickness (70%)

Lead Delamination

Infra-red Image Showing lead Delamination and Poor Contact

Environmentally Induced Mechanisms

  • Humidity Effects
  • Hydrogen Effects
  • Ionic Contamination

Humidity Effects

MetalFament Gthas a result of ilrowexposure to Humidity

Hydrogen Effects in GaAs & InP

Changes in peak transconductance,gm, and drain current at zero bias, Idss, of (a) InP HEMT and (b) GaAs PHEMT under nitrogen and 4% hydrogen treatment at 270°C

Hydrogen Effects -Example

Summary

  • The environmental, reliability and operational challenges present a challenge to the application of commercially available microelectronics.
  • Qualification of microelectronics for space application requires an understanding and consideration of the space environmental effects and relies on process qualification, products qualification and test under the intended use conditions.
  • Prediction of end-of-life of a product requires an understanding of relationship between product yield and reliability.
  • Space radiation effects are a major driver of acceptability of a product for reliable space application.
  • All aspects of reliability and relevant known failure modes and mechanisms should be addressed prior to the insertion of the component in the application.