Hot Carrier Injection (HCI)

Carriers are injected into the substrate and the gate oxide when a high depletion field (due to over-voltage or poor channel design) depletes the drain – channel junction.

Key failure components and conditions

• Drain saturation current (IDsat), Substrate Current (ISUB), Threshold Voltage and Gate induced drain leakage are all degraded
• The typical failure is a reduction in maximum measured operating frequency (slow switching) for nMOS and faster than normal switching for pMOS devices
• Damage occurs only when transistor is in saturation (switched)

Test Characteristics

• Typically test performed at the wafer level
• Tests are continuous cycling of transistor (can run 10-100 hours with constant switching)
• Interactive test instruments and probe station (semi-automatic) typical for long term tests
• High number of probe contacts typical
  • manipulator/probe holder
  • manipulator/wedge card (VersaTile™)
  • probe card
• IDSAT and ISUB are monitored so low noise and low leakage chuck is needed (fA range)
• Light and EMI shielding is recommended
• Typical voltages are in ±10 volts range
• Low temperature increases carrier mobility and accelerates failures; moisture control is often needed

Charge Pumping

Charge pumping is an "Accelerated Hot Carrier " test. As with standard hot carrier tests the carriers are accelerated by the channel electric fields and create silicon electron-hole pairs. The electron-hole pairs gain enough energy to pass through the Si-SiO₂ barrier and become trapped in the oxide damaging the insulator. Charge pumping determines the interface trapped charge density.

Test Characteristics

• Typically test performed at the wafer level
• Tests can run over a long period of time
• Interactive test instruments and probe station (semi-automatic) typical for long term tests
• Charge pumping measures the substrate current
  (picoamp or femtoamp range)
• Voltage pulses of fixed amplitude, rise time, fall time and frequency applied to the gate
• Typical voltages are in ±10 volts range
• Pulse frequency is typically in the low MHz range
• Source, drain and substrate are connected to a common/ground
• High number of probe contacts typical
  • manipulator/probe holder
  • manipulator/wedge card (VersaTile™)
  • probe card
• Light and EMI shielding is recommended

Hot Carrier Injection/Charge Pumping Test Equipment

Stations
P200-300 or 8000 series manual, motorized or semiautomatic: Feature highly stable base, low noise/low current design and integrated thermal chuck connections

Chucks: Low Noise Ambient and Thermal (to accelerate testing)
High isolation design supports low current tests and promotes stability
Thermal chuck range: -65°C to +400°C for 6 and 8" (150 and 200mm); -55° to +300°C for 12" (300mm) chucks.
Thermal chuck cast-in heating and cooling elements provide thermal ramp speed and surface uniformity.
Thermal chuck special mount and design reduces expansion of surface into the probes (minimizes contact resistance changes).
Thermal chuck base “radiator” cooled to prevent heat from getting to probe station stage causing expansion / movement and reliability issues

Light and EMI Shielding: MOS structures are light sensitive
P200-300 and 8000 series stations have a number of versions of optional integrated dark and dry enclosures

• A Light tight enclosure (LTE) for the best light, EMI and RFI shielding
• A Station base, chuck chamber and probes "Top Hat" for “local environment” dark and dry probing

Sample Contacts

• Multiple manipulators and probes can test multiple test sites at any location on the wafer and in any test site pattern. The P200-300 and 8000 series probe stations offer large platen to hold many manipulators.
• Wave Manipulators with VersaTiles™ multiple probes provide super stability, long-term contact and flexibility. Wave Manipulators feature:
• “Link Arms” provide support and force for large pin counts
• 5 Axis of motion, X,Y,Z, Planarity and Theta
• Lead-screw/lead-nut Z drive for stability and consistent contact force
• Vacuum-assisted magnetic bases are stable, moveable and won’t tip if vacuum fails
• Straight and 90° attack angles for easy positioning and multi-VersaTile™ configurations
• Low noise/low current probe card holders for 8000 and P200-300 stations which are designed to support Celadon high temperature, multi-site probe cards.

Probe Contact: Probe Holder and Probe Tip
Low noise and low leakage level triaxial probes: Model 79-T support MHz frequencies

Low contact resistance and larger probe tip are needed to handle large current densities. 7B-10G or HCT probes HCT Probe tips reduce contact resistance by up to 7X and do not develop oxide over tip!

Integrated vibration isolation tables and light tight enclosures in combination with a vibration damping station design provide the highest degree of vibration control. Vibration control is critical to insure probe contact remains constant.

Summary

• All tests require good contact with long term stability.
• Thermal chucks are needed for accelerating failures. The H1000’s unique design is ideal.
• Individual probes are needed for small devices.
• Integrated systems of manipulators, probe holder and probes for high stability and contact integrity.
• Stations which support Wave manipulators with VersaTiles™ and Multi-site probe cards.