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High-κ dielectric

December 18, 2023

In the semiconductor industry, the term high-κ dielectric refers to a material with a high dielectric constant (κ, kappa), as compared to silicon dioxide. High-κ dielectrics are used in semiconductor manufacturing processes where they are usually used to replace a silicon dioxide gate dielectric or another dielectric layer of a device. The implementation of high-κ gate dielectrics is one of several strategies developed to allow further miniaturization of microelectronic components, colloquially referred to as extending Moore's Law. Sometimes these materials are called "high-k" (pronounced "high kay"), instead of "high-κ" (high kappa).

Need for high-κ materials edit

Silicon dioxide (SiO2) has been used as a gate oxide material for decades. As metal–oxide–semiconductor field-effect transistors (MOSFETs) have decreased in size, the thickness of the silicon dioxide gate dielectric has steadily decreased to increase the gate capacitance (per unit area) and thereby drive current (per device width), raising device performance. As the thickness scales below 2 nm, leakage currents due to tunneling increase drastically, leading to high power consumption and reduced device reliability. Replacing the silicon dioxide gate dielectric with a high-κ material allows increased gate capacitance without the associated leakage effects.

First principles edit

 
Conventional silicon dioxide gate dielectric structure compared to a potential high-κ dielectric structure where κ = 16
 
Cross-section of an n-channel MOSFET transistor showing the gate oxide dielectric

The gate oxide in a MOSFET can be modeled as a parallel plate capacitor. Ignoring quantum mechanical and depletion effects from the Si substrate and gate, the capacitance C of this parallel plate capacitor is given by

 

where

Since leakage limitation constrains further reduction of t, an alternative method to increase gate capacitance is to alter κ by replacing silicon dioxide with a high-κ material. In such a scenario, a thicker gate oxide layer might be used which can reduce the leakage current flowing through the structure as well as improving the gate dielectric reliability.

Gate capacitance impact on drive current edit

The drain current ID for a MOSFET can be written (using the gradual channel approximation) as

 

where

  • W is the width of the transistor channel
  • L is the channel length
  • μ is the channel carrier mobility (assumed constant here)
  • Cinv is the capacitance density associated with the gate dielectric when the underlying channel is in the inverted state
  • VG is the voltage applied to the transistor gate
  • Vth is the threshold voltage

The term VG − Vth is limited in range due to reliability and room temperature operation constraints, since a too large VG would create an undesirable, high electric field across the oxide. Furthermore, Vth cannot easily be reduced below about 200 mV, because leakage currents due to increased oxide leakage (that is, assuming high-κ dielectrics are not available) and subthreshold conduction raise stand-by power consumption to unacceptable levels. (See the industry roadmap,[1] which limits threshold to 200 mV, and Roy et al. [2]). Thus, according to this simplified list of factors, an increased ID,sat requires a reduction in the channel length or an increase in the gate dielectric capacitance.

Materials and considerations edit

Replacing the silicon dioxide gate dielectric with another material adds complexity to the manufacturing process. Silicon dioxide can be formed by oxidizing the underlying silicon, ensuring a uniform, conformal oxide and high interface quality. As a consequence, development efforts have focused on finding a material with a requisitely high dielectric constant that can be easily integrated into a manufacturing process. Other key considerations include band alignment to silicon (which may alter leakage current), film morphology, thermal stability, maintenance of a high mobility of charge carriers in the channel and minimization of electrical defects in the film/interface. Materials which have received considerable attention are hafnium silicate, zirconium silicate, hafnium dioxide and zirconium dioxide, typically deposited using atomic layer deposition.

It is expected that defect states in the high-κ dielectric can influence its electrical properties. Defect states can be measured for example by using zero-bias thermally stimulated current, zero-temperature-gradient zero-bias thermally stimulated current spectroscopy,[3][4] or inelastic electron tunneling spectroscopy (IETS).

Use in industry edit

Industry has employed oxynitride gate dielectrics since the 1990s, wherein a conventionally formed silicon oxide dielectric is infused with a small amount of nitrogen. The nitride content subtly raises the dielectric constant and is thought to offer other advantages, such as resistance against dopant diffusion through the gate dielectric.

In 2000, Gurtej Singh Sandhu and Trung T. Doan of Micron Technology initiated the development of atomic layer deposition high-κ films for DRAM memory devices. This helped drive cost-effective implementation of semiconductor memory, starting with 90-nm node DRAM.[5][6]

In early 2007, Intel announced the deployment of hafnium-based high-κ dielectrics in conjunction with a metallic gate for components built on 45 nanometer technologies, and has shipped it in the 2007 processor series codenamed Penryn.[7][8] At the same time, IBM announced plans to transition to high-κ materials, also hafnium-based, for some products in 2008. While not identified, the most likely dielectric used in such applications are some form of nitrided hafnium silicates (HfSiON). HfO2 and HfSiO are susceptible to crystallization during dopant activation annealing. NEC Electronics has also announced the use of a HfSiON dielectric in their 55 nm UltimateLowPower technology.[9] However, even HfSiON is susceptible to trap-related leakage currents, which tend to increase with stress over device lifetime. This leakage effect becomes more severe as hafnium concentration increases. There is no guarantee, however, that hafnium will serve as a de facto basis for future high-κ dielectrics. The 2006 ITRS roadmap predicted the implementation of high-κ materials to be commonplace in the industry by 2010.

See also edit

References edit

  1. ^ (PDF). International Technology Roadmap for Semiconductors: 2006 Update. Archived from the original (PDF) on 2007-09-27.
  2. ^ Kaushik Roy, Kiat Seng Yeo (2004). Low Voltage, Low Power VLSI Subsystems. McGraw-Hill Professional. Fig. 2.1, p. 44. ISBN 978-0-07-143786-8.
  3. ^ Lau, W. S.; Zhong, L.; Lee, Allen; See, C. H.; Han, Taejoon; Sandler, N. P.; Chong, T. C. (1997). "Detection of defect states responsible for leakage current in ultrathin tantalum pentoxide (Ta[sub 2]O[sub 5]) films by zero-bias thermally stimulated current spectroscopy". Applied Physics Letters. 71 (4): 500. Bibcode:1997ApPhL..71..500L. doi:10.1063/1.119590.
  4. ^ Lau, W. S.; Wong, K. F.; Han, Taejoon; Sandler, Nathan P. (2006). "Application of zero-temperature-gradient zero-bias thermally stimulated current spectroscopy to ultrathin high-dielectric-constant insulator film characterization". Applied Physics Letters. 88 (17): 172906. Bibcode:2006ApPhL..88q2906L. doi:10.1063/1.2199590.
  5. ^ "IEEE Andrew S. Grove Award Recipients". IEEE Andrew S. Grove Award. Institute of Electrical and Electronics Engineers. Retrieved 4 July 2019.
  6. ^ Sandhu, Gurtej; Doan, Trung T. (22 August 2001). "Atomic layer doping apparatus and method". Google Patents. Retrieved 5 July 2019.
  7. ^ "Intel 45nm High-k Silicon Technology Page". Intel.com. Retrieved 2011-11-08.
  8. ^ . Archived from the original on 2007-10-26. Retrieved 2007-10-25.
  9. ^ . Necel.com. Archived from the original on 2010-02-19. Retrieved 2011-11-08.

Further reading edit

  • Review article by Wilk et al. in the Journal of Applied Physics
  • Houssa, M. (Ed.) (2003) High-k Dielectrics Institute of Physics ISBN 0-7503-0906-7
  • Huff, H.R., Gilmer, D.C. (Ed.) (2005) High Dielectric Constant Materials : VLSI MOSFET applications Springer ISBN 3-540-21081-4
  • Demkov, A.A, Navrotsky, A., (Ed.) (2005) Materials Fundamentals of Gate Dielectrics Springer ISBN 1-4020-3077-0
  • "High dielectric constant gate oxides for metal oxide Si transistors" Robertson, J. (Rep. Prog. Phys. 69 327-396 2006) Institute Physics Publishing doi:10.1088/0034-4885/69/2/R02 High dielectric constant gate oxides]
  • Media coverage of March, 2007 Intel/IBM announcements BBC NEWS|Technology|Chips push through nano-barrier, NY Times Article (1/27/07)
  • Gusev, E. P. (Ed.) (2006) "Defects in High-k Gate Dielectric Stacks: Nano-Electronic Semiconductor Devices", Springer ISBN 1-4020-4366-X

December 18, 2023
high, dielectric, semiconductor, industry, term, high, dielectric, refers, material, with, high, dielectric, constant, kappa, compared, silicon, dioxide, used, semiconductor, manufacturing, processes, where, they, usually, used, replace, silicon, dioxide, gate. In the semiconductor industry the term high k dielectric refers to a material with a high dielectric constant k kappa as compared to silicon dioxide High k dielectrics are used in semiconductor manufacturing processes where they are usually used to replace a silicon dioxide gate dielectric or another dielectric layer of a device The implementation of high k gate dielectrics is one of several strategies developed to allow further miniaturization of microelectronic components colloquially referred to as extending Moore s Law Sometimes these materials are called high k pronounced high kay instead of high k high kappa Contents 1 Need for high k materials 1 1 First principles 1 2 Gate capacitance impact on drive current 2 Materials and considerations 3 Use in industry 4 See also 5 References 6 Further readingNeed for high k materials editSilicon dioxide SiO2 has been used as a gate oxide material for decades As metal oxide semiconductor field effect transistors MOSFETs have decreased in size the thickness of the silicon dioxide gate dielectric has steadily decreased to increase the gate capacitance per unit area and thereby drive current per device width raising device performance As the thickness scales below 2 nm leakage currents due to tunneling increase drastically leading to high power consumption and reduced device reliability Replacing the silicon dioxide gate dielectric with a high k material allows increased gate capacitance without the associated leakage effects First principles edit nbsp Conventional silicon dioxide gate dielectric structure compared to a potential high k dielectric structure where k 16 nbsp Cross section of an n channel MOSFET transistor showing the gate oxide dielectricThe gate oxide in a MOSFET can be modeled as a parallel plate capacitor Ignoring quantum mechanical and depletion effects from the Si substrate and gate the capacitance C of this parallel plate capacitor is given by C k e 0 A t displaystyle C frac kappa varepsilon 0 A t nbsp where A is the capacitor area k is the relative dielectric constant of the material 3 9 for silicon dioxide e0 is the permittivity of free space t is the thickness of the capacitor oxide insulatorSince leakage limitation constrains further reduction of t an alternative method to increase gate capacitance is to alter k by replacing silicon dioxide with a high k material In such a scenario a thicker gate oxide layer might be used which can reduce the leakage current flowing through the structure as well as improving the gate dielectric reliability Gate capacitance impact on drive current edit The drain current ID for a MOSFET can be written using the gradual channel approximation as I D Sat W L m C inv V G V th 2 2 displaystyle I D text Sat frac W L mu C text inv frac V G V text th 2 2 nbsp where W is the width of the transistor channel L is the channel length m is the channel carrier mobility assumed constant here Cinv is the capacitance density associated with the gate dielectric when the underlying channel is in the inverted state VG is the voltage applied to the transistor gate Vth is the threshold voltageThe term VG Vth is limited in range due to reliability and room temperature operation constraints since a too large VG would create an undesirable high electric field across the oxide Furthermore Vth cannot easily be reduced below about 200 mV because leakage currents due to increased oxide leakage that is assuming high k dielectrics are not available and subthreshold conduction raise stand by power consumption to unacceptable levels See the industry roadmap 1 which limits threshold to 200 mV and Roy et al 2 Thus according to this simplified list of factors an increased ID sat requires a reduction in the channel length or an increase in the gate dielectric capacitance Materials and considerations editReplacing the silicon dioxide gate dielectric with another material adds complexity to the manufacturing process Silicon dioxide can be formed by oxidizing the underlying silicon ensuring a uniform conformal oxide and high interface quality As a consequence development efforts have focused on finding a material with a requisitely high dielectric constant that can be easily integrated into a manufacturing process Other key considerations include band alignment to silicon which may alter leakage current film morphology thermal stability maintenance of a high mobility of charge carriers in the channel and minimization of electrical defects in the film interface Materials which have received considerable attention are hafnium silicate zirconium silicate hafnium dioxide and zirconium dioxide typically deposited using atomic layer deposition It is expected that defect states in the high k dielectric can influence its electrical properties Defect states can be measured for example by using zero bias thermally stimulated current zero temperature gradient zero bias thermally stimulated current spectroscopy 3 4 or inelastic electron tunneling spectroscopy IETS Use in industry editIndustry has employed oxynitride gate dielectrics since the 1990s wherein a conventionally formed silicon oxide dielectric is infused with a small amount of nitrogen The nitride content subtly raises the dielectric constant and is thought to offer other advantages such as resistance against dopant diffusion through the gate dielectric In 2000 Gurtej Singh Sandhu and Trung T Doan of Micron Technology initiated the development of atomic layer deposition high k films for DRAM memory devices This helped drive cost effective implementation of semiconductor memory starting with 90 nm node DRAM 5 6 In early 2007 Intel announced the deployment of hafnium based high k dielectrics in conjunction with a metallic gate for components built on 45 nanometer technologies and has shipped it in the 2007 processor series codenamed Penryn 7 8 At the same time IBM announced plans to transition to high k materials also hafnium based for some products in 2008 While not identified the most likely dielectric used in such applications are some form of nitrided hafnium silicates HfSiON HfO2 and HfSiO are susceptible to crystallization during dopant activation annealing NEC Electronics has also announced the use of a HfSiON dielectric in their 55 nm UltimateLowPower technology 9 However even HfSiON is susceptible to trap related leakage currents which tend to increase with stress over device lifetime This leakage effect becomes more severe as hafnium concentration increases There is no guarantee however that hafnium will serve as a de facto basis for future high k dielectrics The 2006 ITRS roadmap predicted the implementation of high k materials to be commonplace in the industry by 2010 See also edit nbsp Electronics portalLow k dielectric Silicon germanium Silicon on insulatorReferences edit Process Integration Devices and Structures PDF International Technology Roadmap for Semiconductors 2006 Update Archived from the original PDF on 2007 09 27 Kaushik Roy Kiat Seng Yeo 2004 Low Voltage Low Power VLSI Subsystems McGraw Hill Professional Fig 2 1 p 44 ISBN 978 0 07 143786 8 Lau W S Zhong L Lee Allen See C H Han Taejoon Sandler N P Chong T C 1997 Detection of defect states responsible for leakage current in ultrathin tantalum pentoxide Ta sub 2 O sub 5 films by zero bias thermally stimulated current spectroscopy Applied Physics Letters 71 4 500 Bibcode 1997ApPhL 71 500L doi 10 1063 1 119590 Lau W S Wong K F Han Taejoon Sandler Nathan P 2006 Application of zero temperature gradient zero bias thermally stimulated current spectroscopy to ultrathin high dielectric constant insulator film characterization Applied Physics Letters 88 17 172906 Bibcode 2006ApPhL 88q2906L doi 10 1063 1 2199590 IEEE Andrew S Grove Award Recipients IEEE Andrew S Grove Award Institute of Electrical and Electronics Engineers Retrieved 4 July 2019 Sandhu Gurtej Doan Trung T 22 August 2001 Atomic layer doping apparatus and method Google Patents Retrieved 5 July 2019 Intel 45nm High k Silicon Technology Page Intel com Retrieved 2011 11 08 IEEE Spectrum The High k Solution Archived from the original on 2007 10 26 Retrieved 2007 10 25 UltimateLowPower Technology Advanced Process Technology Technology NEC Electronics Necel com Archived from the original on 2010 02 19 Retrieved 2011 11 08 Further reading editReview article by Wilk et al in the Journal of Applied Physics Houssa M Ed 2003 High k Dielectrics Institute of Physics ISBN 0 7503 0906 7 CRC Press Online Huff H R Gilmer D C Ed 2005 High Dielectric Constant Materials VLSI MOSFET applications Springer ISBN 3 540 21081 4 Demkov A A Navrotsky A Ed 2005 Materials Fundamentals of Gate Dielectrics Springer ISBN 1 4020 3077 0 High dielectric constant gate oxides for metal oxide Si transistors Robertson J Rep Prog Phys 69 327 396 2006 Institute Physics Publishing doi 10 1088 0034 4885 69 2 R02 High dielectric constant gate oxides Media coverage of March 2007 Intel IBM announcements BBC NEWS Technology Chips push through nano barrier NY Times Article 1 27 07 Gusev E P Ed 2006 Defects in High k Gate Dielectric Stacks Nano Electronic Semiconductor Devices Springer ISBN 1 4020 4366 X Retrieved from https en wikipedia org w index php title High k dielectric amp oldid 1167586450, wikipedia, wiki, book, books, library,

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