1. A
Seminar
on
HIGH-K DEVICES
Name: Subash John
Roll number: CGB0911005
Course: M.Sc. [Engg.] VLSI System Design
Module Code: VSD527
Module Title: Integrated Circuit Analysis and Design
Module Leader: Prof. Cyril Prasanna Raj P.
24/10/2011 1
M.S.Ramaiah School of Advanced Studies, Bangalore

2. Contents
• Introduction
• Problem with SiO2
• What is high-k?
• Why high-k dielectric?
• High-k and polysilicon interface
• Use of metal gates
• The high-k – metal gate solution
• Future scope
• References
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M.S.Ramaiah School of Advanced Studies, Bangalore

3. Introduction
• Since the 1960‟s semiconductor industry has used poly-Silicon gate with a Silicon dioxide
gate dielectric layer.
• As transistor sizes are shrinking, the gate dielectric and Silicon dioxide are only a few atomic
layers thick.
• Further scaling would increase the already-problematic gate current leakage (IG) and lead to
power loss, increased power consumption, and generate excess heat.
• Intel has achieved a significant breakthrough in transistor technology by developing high-k +
metal gate transistors for its 45 nm node codenamed Penryn processor that significantly
reduces leakage power, deliver higher performance and greater energy efficiency
• Use of HfO2 (k=20), ZrO2 (23), and Ta2O5 (26) as high-k gate-dielectrics.
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4. Problem with SiO2
• SiO2 layer thickness has shrunk to 1.2nm (5 atoms) for 90nm node
• Due to excessive tunneling current, it would stop playing role of an insulator
C
• The capacitance of the gate can be modeled as a parallel-plate capacitor
• Since the t is greater for the new dielectric gate material, it requires an even larger dielectric
constant k to increase the overall capacitance – that‟s where the new high-k dielectric
materials come into play.
Figure 1 Oxide thickness vs. Gate leakage
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M.S.Ramaiah School of Advanced Studies, Bangalore

5. What is High-K?
• The dielectric constant, k, is a parameter defining ability of material to store energy/charge.
• “AIR” is the reference with “K=1”.
• Silicon dioxide has k=3.9. Dielectrics featuring k>3.9 are referred to as “high”-k dielectrics.
• A higher k value means a greater capacitance at greater thicknesses.
Figure 2 SiO2 vs. HK
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6. Why High-k dielectric?
Figure 3 Capacitance vs. Dielectric thickness plot Figure 4 Leakage current vs. Vg plot
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M.S.Ramaiah School of Advanced Studies, Bangalore

7. High-K and PolySilicon Interface
Figure 5 HK and PolySi interface
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M.S.Ramaiah School of Advanced Studies, Bangalore

8. Mobility degradation and Phonon
scattering at High-kPolySilicon interface
Figure 6 Mobility vs. Electric field Figure 7 Phonon scattering
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M.S.Ramaiah School of Advanced Studies, Bangalore

9. When SiO2 is replaced with a high-k material it was found that PolySi and High-k material
were not compatible so PolySi is being replaced by a Metal to make it compatible with the
high-k material.
Figure 8 Conventional vs. HK based transistor
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M.S.Ramaiah School of Advanced Studies, Bangalore

10. Use of Metal Gates
• As a conductor, metal can pack in hundreds of times more electrons than poly silicon
• Metal gate electrodes (Co, Ni, Mo, W) are able to decrease phonon scatterings and reduce the
mobility degradation problem.
• The key property - Work Function of metal.
Figure 9 Scattering in Poly vs. Metal gate
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M.S.Ramaiah School of Advanced Studies, Bangalore

11. Metal Gate
• Metal gate screens surface phonon scattering and improves channel mobility in high-k
transistors
• Furthermore, a thicker Hafnium-based dielectric gate with a metal gate increases
resistance and reduces the unwanted gate leakage current.
Figure 10 Surface mobility vs. Electric field plot
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M.S.Ramaiah School of Advanced Studies, Bangalore

12. The High-k – Metal gate solution
Figure 11 HK + Metal gate solution
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M.S.Ramaiah School of Advanced Studies, Bangalore

13. The High-k – Metal gate solution
Metal Gate
• Increases the gate field effect
High-k Dielectric
• Increases the gate field effect
• Allows use of thicker dielectric layer to
reduce gate leakage Figure 12 Gate leakage vs. Vgs plot
HK + MG Combined
• Drive current increased >20% (>20%
higher performance)
• Or source-drain leakage reduced >5x
• Gate oxide leakage reduced >10x
Figure 13 E-field vs. Technology node plot
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M.S.Ramaiah School of Advanced Studies, Bangalore

14. Future scope
• High-k dielectrics are vital for next-generation low power-consumption, low leakage, high
performance logic devices
• Formation and compatibility of high-k dielectrics better with non-silicon materials (non SiO2-
based). Use of Germanium substrate with a high-k dielectric and a metal gate increases the
total capacitance.
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M.S.Ramaiah School of Advanced Studies, Bangalore

15. References
[1] Chao, L. (2008) „Intel‟s 45nm CMOS Technology‟ Intel Technology Journal [online] 12(3).
available from <http://www.intel.com/technology/itj/2008/v12i2/index.htm> [23 Oct 2011]
[2] Intel 45nm high-k metal gate press release (2007), Intel Demonstrates High-k + Metal Gate
Transistor Breakthrough on 45nm Microprocessor [online] available from
<http://www.intel.com/pressroom/kits/45nm> [21 Oct 2011]
[3] Mark T. Bohr (2007), The High-k Solution [online] available from
<http://spectrum.ieee.org/semiconductors/design/the-highk-solution> [16 Oct 2011]
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16. THANK YOU
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M.S.Ramaiah School of Advanced Studies, Bangalore