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Situation

After diffusion (standard or one-sided), there is usually a parasitic emitter present on the rear side of the cell, which is interconnected with the front across the edges. Application of cell contacts without accounting for the parasitic emitter leads to low parallel resistances, often completely shunted cells. For edge isolation, plasma etching as well as wet chemical etching directly after diffusion is applied.

As an alternative, the cells front and rear surface are isolated after the processing is finished by cutting a laser groove around the cell. The ISO-TEST is specially designed for testing the edge isolation directly after the wet chemical or plasma-based process to improve the stability of the isolation process and increase the process yield.

Description

The ISO-TEST is a reliable contacting tool for testing of wafer edge isolation resistance. The tool features two plastic plates with levelled metal contact tips for monitoring the edge isolation directly after diffusion, with the top contacts integrated into the swinging closing lid. Measurement electronics, control buttons, and a graphical display are integrated in the unit. All functions are configurable in a guided setup mode.

For characterisation the wafers are placed into the ISO-TEST in a position defined by mechanical position bars. By closing the lid, the contact tips come in contact with the wafer surface, and the measurement starts automatically. A constant current is applied to the tips, and the edge resistances for all four edges separately and interconnected in parallel are measured and displayed. By configuring limit values for measured values, the sample classification based on these limits can be indicated with coloured LED and acoustic signal.

All tool functions can be controlled by PC via RS232 interface with an open protocol.