High-κ dielectric

As a high- k dielectric material is referred to in the semiconductor industry, which has a higher dielectric constant than conventional silicon ( εr = 3.9 ) or oxynitrides ( εr <6).

The term "high -k" is borrowed from the English, where the dielectric constant with often is referred to in the absence of the symbol for the Greek Kappa κ, k.

Reasons for the use of high- k dielectrics

To improve the properties of integrated circuits, for example, to reduce the power consumption of large scale integrated circuits and storage or to achieve faster switching speeds, the structures can be reduced. Due to the continuing miniaturization of microelectronic components, the semiconductor industry is reaching the physical limits and is confronted with higher leakage currents through quantum mechanical effects. Thus, the tunnel current will increase with the reduction of less than 2 nm Gatedielektrikumsdicke strongly. Especially for the production of large memory capacities ( for storing the state between refresh cycles) with low leakage currents ( power dissipation) are important. If you look, for example, a simple plate capacitor, so the capacity is calculated as follows:

Here, the distance between the plates, the area of ​​capacitor plates, the permittivity of the vacuum, and the material constant, the relative permittivity of the insulating layer.

Thus, by the use of high -k materials ( larger ) the thickness of the insulator layer in MIS structures ( often called by SiO2 MOS ) can be increased while maintaining the same capacitance, leakage currents through the thicker insulator to be drastically reduced. The ( capacitive ) For the comparison often summarized properties of such layers to a parameter, the equivalent oxide thickness (EOT, dt " equivalent oxide thickness ").

In contrast, the low-k dielectrics, which are used as insulator between the interconnects and reduce by their low dielectric constant, the resulting parasitic capacitances are.

Materials

Are investigated different material systems, such as amorphous metal oxides (eg Al2O3, Ta2O5 ), transition metals (eg, HfO2, ZrO2) and hafnium silicate and zirconium mixed oxides. A higher permittivity also supply strontium titanate, and barium titanate. A further approach provide crystalline oxides of rare earths (eg, Pr2O3, Gd2O3 and Y2O3 ) that allow the lattice matched growth and thus a perfect interface (very small number of lattice defects ) between semiconductor and insulator.

Coating

For the production of thin layers of both the physical method (PVD ) and chemical vapor deposition (CVD) can be used. For very thin layers in the thickness range of a few nanometers, the atomic layer deposition can be used for example. As with all other coating processes also, the deposition conditions (pressure, gas flows, precursor gases, etc.) are in the process of development, first by larger variation of the system parameters on the respective production system determined empirically and then optimized in a statistical experimental design for manufacturing. The process parameters determined in this way are system-specific and generally only very rarely transferable to other systems; this is due to the very high demands on the coating process or the layer often for identical assets. In the research is to process development and optimization still a so-called screening material added, in which the deposition of a layer with respect to the desired output used gases (for CVD ) is examined.

The starting material for all the above oxides and mixed oxides are known, under strictly anaerobic conditions relatively easy to produce complexes of the respective " metals ". An important condition for the use of the complexes in the production of semiconductors, a sufficient vapor pressure of the compound at a moderate temperature ( 300-600 ° C). Usually at room temperature, liquid precursors are preferred. In individual cases - HfCl4 to HfO2 deposition - but also solids come up with a sufficiently high sublimation used.

The starting materials for the oxide deposition (eg, Ziegler -Natta catalysts) produced by specialized fine chemical companies and manufacturers of catalysts for organic synthesis or production of plastics. The semiconductor industry uses its required small quantities tend beyond the laboratory chemicals trade or through collaborating with their suppliers. The price level for the compounds is high to extremely high.