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Concept
Low-κ dielectric
Summary
In semiconductor manufacturing, a low-κ is a material with a small relative dielectric constant (κ, kappa) relative to silicon dioxide. Low-κ dielectric material implementation is one of several strategies used to allow continued scaling of microelectronic devices, colloquially referred to as extending Moore's law. In digital circuits, insulating dielectrics separate the conducting parts (wire interconnects and transistors) from one another. As components have scaled and transistors have gotten closer together, the insulating dielectrics have thinned to the point where charge build up and crosstalk adversely affect the performance of the device. Replacing the silicon dioxide with a low-κ dielectric of the same thickness reduces parasitic capacitance, enabling faster switching speeds (in case of synchronous circuits) and lower heat dissipation. In conversation such materials may be referred to as "low-k" (spoken "low-kay") rather than "low-κ" (low-kappa).
In integrated circuits, and CMOS devices, silicon dioxide can readily be formed on surfaces of Si through thermal oxidation, and can further be deposited on the surfaces of conductors using chemical vapor deposition or various other thin film fabrication methods. Due to the wide range of methods that can be used to cheaply form silicon dioxide layers, this material is used conventionally as the baseline to which other low permittivity dielectrics are compared. The relative dielectric constant of SiO2, the insulating material still used in silicon chips, is 3.9. This number is the ratio of the permittivity of SiO2 divided by permittivity of vacuum, εSiO2/ε0, where ε0 = 8.854×10−6 pF/μm. There are many materials with lower relative dielectric constants but few of them can be suitably integrated into a manufacturing process. Development efforts have focused primarily on the following classes of materials:
Fluorosilicate glass
By doping SiO2 with fluorine to produce fluorinated silica glass, the relative dielectric constant is lowered from 3.9 to 3.5.
Official source
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