Modulation of the conductance of a thin layer by surface charges, a concept that goes back to 1930, was revived for semiconductors in 1948.233 Practical devices did not ensue until about 1960, when diffusion and oxide technologies for Si were developed. MOSFET structures manufactured during the next few years are illustrated in Fig. 7.1. The current flows by majority carrier movement from the source to drain and is controlled by the voltage on the insulated metal gate which determines the channel charge. In the n-channel enhancement type structure [see Fig. 7.1(a)] the channel is not initially present and must be induced by a positive gate voltage V GS . A threshold voltage V T is needed before any usable characteristic is obtained. In the n-channel depletion type structure [see Fig. 7.1(b)] the channel is already present (as a result of a shallow n-type diffusion or implant or as a result of interface conditions). This channel can be partially depleted by a negative gate voltage or enhanced by a positive gate voltage.

Insulated Gate Field-Effect-Transistors: MOSFETs, IGFETs and Related Devices

A simple method for the determination of parameters of ion implanted doping profiles by means of threshold voltage measurements of MOSFET's

The impurity redistribution in silicon substrates of MOSFET's is estimated from the measurement of dc voltage-current characteristics using the exact theory of the effect of substrate bias. The usefulness of the present method depends upon the acceptability of substituting the Fermi potential before thermal treatments for that after thermal treatments, which then allows for the direct calculation of the impurity concentration. The accuracy of the present method is given theoretically by the discussion of relative errors.

A. Wada

Papers

Estimation of the impurity redistribution in silicon substrates from MOSFET characteristics