Low-k dielectric
As a low -k dielectric, a material is referred to in the semiconductor industry, which has a lower dielectric constant than SiO2, ie εr < 3.9. The objectives are nowadays so-called ultra - low-k materials with dielectric constant is less than 2.4.
The term " low-k " is borrowed from the English, where the dielectric constant (relative permittivity) is often denoted by (kappa ), sometimes only with k is in contrast to the high-k dielectrics used as gate insulator be due to their high dielectric constant and allow a thicker insulation layer and thus contribute to the reduction of leakage currents.
Background
To improve the properties of integrated circuits, for example to reduce power consumption of the large scale integrated circuit, or to achieve higher switching speeds, the structures can be reduced. Due to the continuing miniaturization of microelectronic components, the semiconductor industry is reaching the physical limits. An effect of the miniaturization, the reduction of the spacing metallization ( wiring layers for wiring the devices ) on the chip. The downsizing of the insulator thickness between two meridians of the influence of the parasitic capacitance increases. They interfere with the function of the circuit and reduce example, the maximum switching speed.
Parasitic capacitances arise, for example, when two conductor paths intersect at different levels or when two conductive lines run parallel to each other. The road junction and the adjacent interconnects enables us to match a simple plate capacitor. The capacitance of a plate capacitor is calculated by:
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.
It can be seen that the reduction of the distance d, the capacitance C increases. To compensate for this, it is necessary, the board surface A ( resulting from the track width, to interconnect or parallel tracks ) or the dielectric constant to decrease. The Leiterbahnquerschitt and thus the plate surface of the parasitic capacitances are hardly reduced. Since the current density in the conductor tracks should not rise and small cross-sections to increase the electrical resistance through stronger influence of the interface scattering of the electrons. It therefore remains only the development of new insulating layers with low dielectric constant, low- k dielectrics.
In principle there are two ways to reduce the dielectric constant:
- Carbon-carbon ( C-C)
- Carbon-hydrogen (C -H)
- Silicon - fluorine (Si -F)
- Silicon-carbon (Si -C), for example, Applied Materials, " Black Diamond I"
Materials
Currently used in the semiconductor industry for low -k materials are identifiable by CVD or spin-on process (so-called spin-on dielectrics, SOD) deposited microporous SiO and SiOC layers. As base materials are organosilicon compounds ( silicones) which are also used among other things in the building materials and coating sector in a large scale. Typical low-k precursors tetraethyl orthosilicate ( TEOS) ... a large organosilicon compound engineered, which melts at -77 ° C and boils at 168.5 ° C and the methyl-substituted silanes ..., tetramethylsilane and trimethylsilane.
Silane and functionalized silanes are particularly by the German company Evonik Industries ( Chemicals Business Area, formerly Degussa) and Wacker-Chemie and manufactured by the American Dow Corning Inc. on an industrial scale. Specialty silanes with demanding organic substituents is for example here, the American company Silar. In addition, silanes can be obtained from the laboratory and chemicals wholesale.
Microporous low-k layers ... example here are the well-known since the 1930s silicon aerogels ... can be generated for low-k precursor, for example by mixing oxidizing agents and emulsifiers.
Other low-k materials include plastics, although not always have the required for use in semiconductor technology mechanical strength.
In the whole area of the low-k materials is currently being researched and developed intensively. The spectrum of the discussed low-k materials widens thereby quickly. However, the materials as a thin layer of the current industrial requirements with respect to leakage current density (< 10-9 A / cm ) and break-through field strength (EBD > 3 MV / cm ) must satisfy.
History
Low-k dielectrics were first used around 2002 with the introduction of the 130 - nm technology node in industrial production, such as AMD Athlon 64 and Opteron. Since then, low-k and ultra-low -k materials, at least for products in 65 - nm technology and below, becoming the Standarddielektrikum for the first metallization were.