TABLE OF CONTENTS The metal-oxide-semiconductor (MOS) structure is the heart of MOS technology. When this structure, commonly referred as MOS capacitor, is connected as a two terminal device, with one electrode connected to the metal and the other electrode connected to the semiconductor, a voltage dependent capacitance results. The MOS capacitor is a very useful device both for evaluating the MOS IC fabrication process and for predicting the MOS transistor characteristics. For this reason MOS capacitors are often included on the chip test sites. Note that the term MOS is still used even if the top electrode is not a metal and the insulator is not an oxide. Some-times the acronym MIS (Metal-Insulator-Semiconductor) is also used for the MOS structure.
In this chapter we first discuss the behavior of a MOS capacitor and then develop the charge-voltage (Q-V) and capacitance-voltage (C-V) relationships, which will be used later in the development of the MOS transistor model. We will conclude the chapter by discussing applications of the C-V curves in MOS technology.
The cross-section of an MOS capacitor is shown in Figure 4.1. Essentially it consist of a p- or n-type silicon substrate covered by an insulating layer of oxide. [1] The oxide is thermally grown silicon dioxide (SiO 2) with a thickness that usually lies between 100 and 1000 . On the top of the oxide is a conducting layer of metal (usually aluminum) or, more commonly, degenerately doped polysilicon or...
