Equivalent oxide thickness

The English term equivalent oxide thickness (EOT, dt " equivalent oxide thickness " ) referred to in the semiconductor industry a comparative size of a thin layer mainly of layers of novel high-k dielectrics with silicon dioxide, the Standardgatedielektrika in metal - oxide - semiconductor field-effect transistors ( MOSFETs).

Background

The electrical characteristics of a MOSFET is determined in part by the gate dielectric, the gate electrode separated from the conductive channel in the semiconductor. The physical properties (thickness, band gap, Dielektrizitäszahl ), for example, influence the threshold voltage of the transistor. Since the inception of microelectronics in the 1960s (thermal ) silica was used mainly as a gate dielectric. Analogous to the continuous reduction of the structures and the dielectric thickness was reduced, so this mid-2000s only lay in the range of 1 to 2 nanometers. At these thicknesses, the influence of leakage currents through the dielectric by the so-called tunnel effect is no longer negligible. For a further miniaturization of integrated circuits, therefore, the reduction of these leakage currents is required. However, a simple increase of the layer thickness is not acceptable, since thereby the threshold voltage of the transistors (and therefore the operating voltage) to increase and decrease the maximum switching speed would be.

For the solution of the problem, the use of materials with a higher dielectric constant applies ( high-k dielectric) than silica (). A layer of high-k dielectric with dielectric constant of 39 can be ten times as thick as a silicon oxide layer. The term EOT has been introduced in order to have a simple comparative measure of the new layers with respect to silica. This is all the more significant when one considers that the dielectric constant of a very thin layer is not necessarily the same as a bulk layer, depending on the production method and may change with the film thickness.

Definition

The EOT of a dielectric layer specifies how thick would be an electrically comparable silicon dioxide layer. Electrically similar in this context if it has the same capacitance -voltage characteristics and the same capacity per unit area.

Capacitance per unit area:

Calculation of EOT:

With

  • The dielectric constant of thermal silicon dioxide ...
  • The dielectric constant ... the high- k layer
  • ... The thickness of the high-k layer
  • The equivalent thickness of a ... layer of thermal silicon dioxide
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