News

February 10, 2023

An analysis of the state of a semiconductor – from start wafer until final device – is considered a job for specialists and there are very few analysis tools that can be used as a “decision maker” for good and/or bad material quality directly in the production.

The new Freiberg Instruments high-resolution surface photovoltage spectroscopy (HR-SPS) tool is a true production tool in the sense that it does its job without influencing the workflow speed. The HR-SPS checks critical-to-yield parameters in the material used in the production – be it silicon, silicon carbide or other semiconductors or photoactive materials.

The HR-SPS tool measures the time-resolved surface photovoltage response of the material when excited by one or more light sources. The light source(s) are chosen according to the material electronic properties and to known imperfections in the material that can be associated with yield loss. As an example, in silicon monocrystalline wafers, there can be a number of imperfections that can lead to yield losses during device processing. Silicon monocrystalline wafers can have high concentrations of nitrogen originating from the boule growth cycle or from the different device processing steps. The nitrogen atoms can form a substitutional pair in the otherwise perfect silicon crystal and this pair can heavily impact the performance of MOS gate structures, because the pair form unfortunate electronic states in the silicon wafer. The HR-SPS tool can not only measure the presence of such defects, but also their approximate density. In this way, variations within wafer batches and between wafer batches can be monitored and reported over the equipment/tool-to-host interface protocol and used for SPC purposes.

The HR-SPS is a very versatile tool that can be configured in a number of ways. It can be used for almost any photoactive material – the only limitation currently is the bandgap energy, which is limited to 5.0 eV. The basic measurement is a nanosecond time-resolved surface photovoltage signal with an excellent signal-to-noise ratio and 5-6 orders magnitude scale. One measurement takes approximately 15–30 seconds, including the signal analysis loop. The output can be anything from a good/no-good criterion to a full measurement report on the state of the tested material(s). Needless to say, but any mechanical adaption to automated material handling systems (AMHS) compliant to SEMI standards can of course be made.

• Application example 1: Defects in 4H-SiC investigated by surface photovoltage spectroscopy – power semiconductors

• Application example 2: Defects and charge dynamics in 3C- and 4H-SiC investigated by surface photovoltage spectroscopy – photoelectrochemical/photocatalytic water splitting

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