Low-K
Encyclopedia
In semiconductor
manufacturing, a low-κ dielectric is a material with a small dielectric constant
relative 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 transistor
s) from one another. As components have scaled and transistors have got 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 and lower heat dissipation.
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 dielectric constants but few of them can be suitably integrated into a manufacturing process. Development efforts have focused primarily on three classes of materials:
, Aurora from ASM International N.V. The Aurora is the low-κ material used in Intel 90 nm, 65 nm and 45 nm lines, while the Black Diamond controlled about 80% of low-κ material market. Novellus Systems
' Coral also falls in this category.
' Black Diamond II technology and ASM International
's Aurora 2.7 and Aurora ULK process.
, rather than chemical vapor deposition. Integration difficulties include low mechanical strength and thermal stability. SiLK from Dow Chemical is a well known example of low-κ material in this category. Other spin-on organic low-κ include polyimide
, polynorbornenes, Benzocyclobutene
, PTFE, SU-8 2000.
(HSQ) and methylsilsesquioxane (MSQ).
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
manufacturing, a low-κ dielectric is a material with a small dielectric constant
Dielectric constant
The relative permittivity of a material under given conditions reflects the extent to which it concentrates electrostatic lines of flux. In technical terms, it is the ratio of the amount of electrical energy stored in a material by an applied voltage, relative to that stored in a vacuum...
relative to silicon dioxide. Although the proper symbol for the dielectric constant is the Greek
Greece
Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....
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
Moore's Law
Moore's law describes a long-term trend in the history of computing hardware: the number of transistors that can be placed inexpensively on an integrated circuit doubles approximately every two years....
. In digital circuits
Electrical network
An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources and switches. An electrical circuit is a special type of network, one that has a closed loop giving a return path for the current...
, insulating dielectrics separate the conducting parts (wire interconnects and transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
s) from one another. As components have scaled and transistors have got 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
Parasitic capacitance
In electrical circuits, parasitic capacitance, stray capacitance or, when relevant, self-capacitance , is an unavoidable and usually unwanted capacitance that exists between the parts of an electronic component or circuit simply because of their proximity to each other...
, enabling faster switching speeds and lower heat dissipation.
Low-κ materials
The dielectric constant of SiO2, the insulating material used in siliconSilicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
chips, is 3.9. This number is the ratio of the permittivity
Permittivity
In electromagnetism, absolute permittivity is the measure of the resistance that is encountered when forming an electric field in a medium. In other words, permittivity is a measure of how an electric field affects, and is affected by, a dielectric medium. The permittivity of a medium describes how...
of SiO2 divided by permittivity of vacuum, εSiO2/ε0,where ε0 = 8.854×10−6 pF/μm. 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.Carbon-doped silicon dioxide
By doping SiO2 with carbon, one can lower the dielectric constant to 3.0. Major products of carbon doped silicon dioxide include Black Diamond from Applied MaterialsApplied Materials
Applied Materials, Inc. is a capital equipment producer serving the semiconductor, TFT LCD display, Glass, WEB and solar manufacturing industries....
, Aurora from ASM International N.V. The Aurora is the low-κ material used in Intel 90 nm, 65 nm and 45 nm lines, while the Black Diamond controlled about 80% of low-κ material market. Novellus Systems
Novellus Systems
Novellus Systems Inc. develops, manufactures, sells, and services semiconductor equipment used in the fabrication of integrated circuits. It is a leading supplier of chemical vapor deposition , plasma-enhanced chemical vapor deposition , physical vapor deposition , electrochemical deposition ,...
' 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 groups in carbon doped silicon dioxide can be eliminated and pores can be introduced to the carbon doped silicon dioxide low-κ materials. The technology for producing porous dielectric layers with very low dielectric constants was developed by A. Grill, V.V. Patel, S.M. Gates in the late 1990s at IBM (US6312793-International Business Machines]. Virtually identical technology was patented under US2004096593 in 2003. While all materials used for the deposition of low-k dielectric layers are in the public domain and therefore not patentable, the technique of making such layers was rapidly adopted by the semiconductor manufacturing equipment industry and commercialised as an essential application supplied with the equipment. Examples include Applied MaterialsApplied Materials
Applied Materials, Inc. is a capital equipment producer serving the semiconductor, TFT LCD display, Glass, WEB and solar manufacturing industries....
' Black Diamond II technology and ASM International
ASM International (company)
ASM International is a Dutch company active in the semiconductor industry.The company was founded by Arthur del Prado in 1968. ASMi has been the co-founder with Philips Electronics of the company ASML. The shares of the company are listed on the Nasdaq and Euronext Amsterdam. Since 2008 the son of...
's Aurora 2.7 and Aurora ULK process.
Spin-on organic polymeric dielectrics
Polymeric dielectrics are generally deposited by a spin-on approach, such as those traditionally used to deposit photoresistPhotoresist
A photoresist is a light-sensitive material used in several industrial processes, such as photolithography and photoengraving to form a patterned coating on a surface.-Tone:Photoresists are classified into two groups: positive resists and negative resists....
, rather than chemical vapor deposition. Integration difficulties include low mechanical strength and thermal stability. SiLK from Dow Chemical is a well known example of low-κ material in this category. Other spin-on organic low-κ include polyimide
Polyimide
Polyimide is a polymer of imide monomers. The structure of imide is as shown. Polyimides have been in mass production since 1955...
, polynorbornenes, Benzocyclobutene
Benzocyclobutene
Benzocyclobutene is a benzene ring fused to a cyclobutane ring. It has chemical formula 88.BCB is frequently used to create photosensitive polymers. BCB-based polymer dielectrics may be spun on or applied to various substrates for use in Micro Electro-Mechanical Systems and microelectronics...
, PTFE, SU-8 2000.
Porous SiLK
By introducing pores into the SiLK resin, the dielectric constant value can be lowered to 2.2.Spin-on silicone based polymeric dielectric
There are two kinds of silicone based polymeric dielectric materials, hydrogen silsesquioxaneHydrogen silsesquioxane
Hydrogen silsesquioxane is a negative tone electron-beam resist. The Hydrogen silsesquioxane monomer is a cubical-shaped molecule having one Si atom at each corner, with corners being linked via oxygen atoms. Additionally, a hydrogen group is attached to each Si. The formula of the HSQ monomer is...
(HSQ) and methylsilsesquioxane (MSQ).