semiconductormanufacturing, a Low-κ dielectricis a material with a small dielectric constantrelative to silicon dioxide. Although the proper symbol for the dielectric constant is the Greek letter κ (kappa), in conversation such materials are referred to as being "low-k" (low-kay) rather than "low-κ" (low-kappa). 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 and closer together, the insulating dielectrics have thinned to the point where charge build up and crosstalkadversely 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 and lower heat dissipation.
The dielectric constant of SiO2, the insulating material used in
siliconchips, is 3.9. There are many materials with lower dielectric constants but few of them can be suitably integrated into a manufacturing process. Development efforts have focused primarily on three classes of materials:
Fluorine Doped Silicon Dioxide
By doping SiO2 with fluorine to produce fluorinated silica glass, the dielectric constant is lowered from 3.9 to 3.5. [ [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V0W-44MFR55-G&_user=961305&_coverDate=01%2F31%2F2002&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000049425&_version=1&_urlVersion=0&_userid=961305&md5=343451401b32a10c9c5be652692bcb0b ScienceDirect - Microelectronic Engineering] ]
Carbon Doped Silicon Dioxide
By doping SiO2 with carbon, the dielectric constant can be lowered to 3.0. Major products of carbon doped silicon dioxide include Black Diamond from
Applied Materials, [http://www.appliedmaterials.com/products/producer_black_diamond_4.html Applied Materials, Inc. - Applied Producer Black Diamond PECVD ] ] Aurora from ASM International N.V.. [http://www.reed-electronics.com/semiconductor/article/CA528453 Low-k Bursts Into the Mainstream...Incrementally - 5/1/2005 - Semiconductor International ] ] The Aurora is the low-K material used in Intel90nm, 65nm and 45nm lines, while the Black Diamond controlled about 80% of low-K material market. [ [http://www.fabtech.org/content/view/2079/74/ ASM International continues low-k dielectric relationship with Intel through 32nm node - Fabtech - The online information source for semiconductor professionals ] ] Novellus Systems' Coral also falls in this category.
Porous Silicon Dioxide
Various methods may be employed to create large voids or
pores in a silicon dioxide dielectric. Air has a dielectric constant of roughly 1.0005, thus the dielectric constant of the porous material may be reduced by increasing the porosity of the film. Dielectric constants lower than 2.0 have been reported. Integration difficulties related to porous silicon dioxide implementation include low mechanical strength and difficult integration with etch and polish processes.
Porous Carbon doped Silicon Dioxide
By UV curing, floating methyl group in carbon doped silicon dioxide can be eliminated and pores can be introduced to the carbon doped silicon dioxide low-K materials. Products in this category include Black Diamond II, Aurora 2.7 and Aurora ULK. The reported K value can be as low as 2.5.
pin-on organic polymeric dielectrics
Polymeric dielectrics are generally deposited by a spin-on approach, such as those traditionally used to deposit
photoresist, rather than chemical vapor deposition. Integration difficulties include low mechanical strength and thermal stability. SiLK from Dow Chemicalis a well known example of low-K material in this category. [ [http://www.dow.com/silk/ SiLK ] ] Other spin-on organic low-K include polyimide, polynorbornenes, Benzocyclobutene, PTFE.
By introducing pores into the SiLK resin, the dielectric constant value can be lowered to 2.2. [ [http://www.dow.com/silk/silky/feature.htm Why Porous SiLK? ] ]
pin-on silicone based polymeric dielectric
There are two kinds of silicone based polymeric dielectric materials, hydrogen silsesquioxane (HSQ) and methylsilsesquioxane (MSQ).
Relative static permittivity
* [http://nepp.nasa.gov/index_nasa.cfm/934/ Nasa on Low-k]
* [http://www.gaas.org/Digests/2002/PDF/01c.pdf The evolution of interconnect technology for silicon integrated circuitry]
Wikimedia Foundation. 2010.