Materials

ISFH offers to measure the dopant profile of phosphorus or boron in silicon. We use the electrochemical capacitance-voltage (ECV) technique, which measures the electrically active concentration of acceptors and donors as a function of depth.

The ECV profiler covers the entire range of interest of dopant concentrations, i.e. from 1015 to 1021 cm-3. The step size for depth resolution can be varied as well, usually from 2 to 20 nm. The setup can handle samples with an edge length between 20 and 156 mm.

Lifetime measurements can be used to investigate material properties, such as the presence of defects, as well as interface properties, such as surface passivation.

ISFH offers a variety of different lifetime measurement techniques that are suited for different requirements. We have different tools of the Sinton Lifetime Tester (WCT-100 and WCT-120) which uses an area-averaged measurement of the photoconductivity to determine injection-dependent charge carrier lifetimes. One setup also allows variation of the sample temperature between room temperature and 140 °C, which allows temperature- and injection-dependent lifetime spectroscopy for characterization of defects. Apart from this area-averaged (across roughly 250 mm²) method ISFH also hosts three different lifetime measurement setups that yield spatially-resolved information.

A microwave-based setup from Semilab (WT-2000) can measure lifetimes between 1 μs and 10 ms at different bias light intensities without detailed knowledge of the investigated sample. The measurement itself is done on a small spot, which can be scanned across the entire wafer, thus yielding a lifetime map of the sample.

A much faster way to generate such mappings is to use a camera to gain spatially resolved information. At ISFH, two different camera-based systems have been developed which either detect the photoluminescence signal (PCPLI – Photoconductance-Calibrated Photoluminescence Imaging) or the infrared emission (ILM – Infrared Lifetime Mapping) of the sample. An advantage of photoluminescence-based measurement techniques is the detection of radiative recombination which avoids measurement artefacts often observed in photoconductivity-based methods. This enables correct lifetime measurements even in low-injection in defect-rich materials.

In order to get sufficient infrared emission for a good signal-to-noise ratio, samples are heated to 70 °C for ILM measurements. By using a periodic optical generation, the infrared emission is varied accordingly and the carrier lifetime can be determined through a suitable analysis routine. A specific advantage of the ILM method compared to photoconductance-based techniques is its capability to investigate partially metallized samples, such as solar cell precursors.