Lucideon Investigates Electrical Drift in MOSFET Devices

In the Semiconductor Industry, metal-oxide-semiconductor field-effect transistor (MOSFET) technology provides the most common form of transistors for switching of electrical signals and amplification purposes. A metal-oxide-semiconductor structure is obtained by growing a layer of silicon dioxide (gate oxide) onto a silicon substrate and subsequently depositing a layer of metal (gate electrode) on the SiO2.

The Challenge

A batch of semiconductor device wafers undergoing long-term electrical stability testing were identified as failed due to excessive electrical drift. The cause of the problem was suspected to be ionic contamination of the gate oxide region of the MOSFET structure. The wafer manufacturer commissioned Lucideon (then Ceram) to investigate the problem and to provide a possible solution.

What We Delivered

Lucideon used Secondary Ion Mass Spectrometry (SIMS) in mass spectral and depth profiling modes to identify contaminant species (Na, Mg, Ca) and monitor their depth distribution within the aluminium gate and gate oxide regions.

Figure 1 - SIMS depth profiles of control device - no drift (left) and device with electrical drift (right)

The depth profile of the device exhibiting electrical drift revealed an approximately ten-fold higher level of ionic contamination in the form of Na, Mg and Ca within the gate oxide region of the device. This was deemed sufficient to cause the drift characteristics - the cause of the problem was identified as poor quality rinsing water at a critical point in the production cycle.

Value to the Client

On Lucideon's recommendation a quality audit of the fabrication plant's water system was carried out and further filtering and cleaning of the distribution system implemented.

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