Device makers have a critical need to measure sheet resistance. Knowing it as a function of position (mapping) allows for optimization of epi reactors to maximize yield.
The Semilab LEI-1510 family allows for non-destructive measurement of sheet resistance. These instruments are optimized for compound semiconductor applications with ranges of operation that dovetail nicely with customer applications. The LEI technology became the process of record in the RF device area with many people asking to see the “LEI” map.
Figure 1. The “Semilab LEI” Maps - the process of record for sheet resitance
The 1510 Non-destructive Sheet Resistance Measurement System uses eddy current to measure sheet resistance.
Theory of resistivity measurement is based on alternating current in a coil (or pair of coils) inducing alternating Eddy current in a conducting material. The Eddy current measurement is actually the measurement of the electrical loss in the material.
The measured signal depends on:
The Eddy current is higher in good conducting material compared to less conductive ones.
Figure 2. Diagram of Eddy current - upper coil shown only