The needle prober and its electrical measurement equipment allows for electrical characterization of individual devices directly on the wafer, which disengages us from the need to package a device before electrical measurement. We use tungsten needles with gold coating together with probe positioners equipped with micrometer screws to contact the device pads on the wafer. Our needle prober has eight individual probe positioners that allow us to contact a large number of different devices to test them electrically. The wafer lies on an eight inch chuck whose temperature can be varied between -60 °C and 205 °C. In order to prevent condensation of water and ice generation on the wafer, the whole system is flooded with dry air with a dew-point below -70 °C.
The electrical characterization equipment consists of a parameter analyzer, an impedance analyzer, a switching matrix and a high voltage unit with an appropriate voltage protection and limiter unit. The parameter analyzer has four medium-power source-measurement-units with 100 V / 100 mA maximum voltage / current ranges respectively and a high-power unit with 200 V / 1 A ranges which allow for time-resolved current measurements with a delay of about 100 µs. The parameter analyzer is further equipped with two pulse-generator-units with 40 V / 400 mA output range and a frequency range between 0.1 Hz and 33 MHz. The high voltage unit allows measurements up to 1 kV / 120 mA with 1 µs time resolution. Electrical measurements can be reliably performed down to the picoampere range. Voltage dependent capacitance measurement in the Femtofarad range between 40 Hz and 1 MHz frequency are possible.
The cryogenic probe station and its electrical measurement equipment allows for detailed electrical characterization of semiconductor devices in a very broad temperature range of 6.5 K (-267 °C) to 675 K (402 °C). The cryogenic probe station makes use of the temperature activation of point defect creation/passivation and charging/discharging mechanisms. Cooler temperatures allow characterizing processes which are too fast for electrical measurement at room temperatures. Increased temperatures accelerate degradation mechanisms which happen during normal operation within a few years to an acceptable test time of a few minutes or hours.
The Lakeshore CRX-6.5K cryogenic probe station is a closed-cycle refrigerator using liquid helium and is equipped with a high-temperature stage allowing operation above room temperature. The sample is evacuated to high vacuum of approximately 10-6 mbar pressure with a turbomolecular vacuum pump. The electrical measurement equipment consists of a digital lock-in amplifier with a transimpedance pre-amplifier and an arbitrary waveform generator. The electrical equipment allows the measurement of capacitance transients with 10 µs resolution in a bias range of +-10 V. As such, transient measurements of deep levels in semiconductors are possible and are used to identify and characterize performance and reliability limiting defects in wide band gap devices.
Alongside the cryogenic probe station KAI offers a Xenon discharge lamp emitting light in the entire visible spectrum up to the ultra violet regime. With a monochromator light of a defined wavelength and energy can be selected to excite electrons from defect levels deep in the band gap. This allows even more detailed investigation of unwanted defects in semiconductors.