Copper Interconnect (Via) Reliability

Copper metal technology uses barrier metals to “encapsulate” the copper line and prevent diffusion.

Copper is subject to electromigration especially at:

• The dielectric interface where it bonds more weakly than aluminum
• At via points mostly due to incomplete dielectric etch;
  the Via stress point produces an area of high electromigration flux.

As the void grows (past 20%), current flows through the barrier metal, producing a hot spot and thermal failure. This hot spot may be detected through emission microscopy.
Note: Copper Low K dielectric interconnects are sensitive to light. Illumination produces leakages currents (femtoAmp Levels). Thus copper interconnect reliability tests require light/EMI shielding.

With the addition of light/EMI shielding electromigration test systems, conditions and tests apply to copper interconnect reliability tests.

Copper Interconnect (Via) Reliability Test Equipment

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

Chucks: Low Noise 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: Low K dielectric interconnects 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 9000 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 provide shielding for high voltage and high amperage tests

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 enclosure 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.