Si Wafer | Major Effects of Wafer Crystal Defects on Electrical Devices


July 17, 2019

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If a Si Wafer contains crystallographic defects, then it’s likely that the electrical efficiency of the device built into this wafer is faulty. And in extreme cases, these defects can even result in device failures. Here are the major effects of wafer crystal defects on electrical devices:

Minority Carrier Lifetimes

This indicates the standard time interval between the recombination and generation of electrons in p-type silicon and holes in n-type silicon in a semiconductor crystal. The defect affects the efficiency of the device by decreasing the minority carrier lifetime. The defects and contaminants tend to create recombination centers inside the crystal that ambush active carriers.

Leakage Currents in P-N Junctions

As much as possible, there should be little to no leakage in reverse-biased p-n junctions because they’re non-conducting. But the presence of defects in wafer crystals creates too much leakage. The excessive leakage causes power loss, degradation of DRAM storage stability, and shifting of device current or voltage characteristics.

Collector-Emitter Leakage Currents in Bipolar Transistors

The collector-base and base-emitter leakage currents stay at minimum levels, even while there is an escalation in collector-emitter leakage. This means that current flows from collector to emitter even if there is no current entering into the base. The presence of defects can permit appreciable current to enter between the collector and emitter even if the ground current is zero. Diffusion is another effect during emitter formation, which contributes to excessive collector-emitter leakage current.

MOS Gate Oxide Quality and MOS Threshold Voltages

Stacking faults in a Si Wafer boosts gate oxide current leakage and lowers the gate oxide’s disintegration voltage. The presence of oxygen precipitates on an Si wafer’s surface can reduce the oxide’s disintegration voltage. Maintaining the threshold voltages within the necessary requirement is also important for appropriate device operation.

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