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High k dielectric


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Need and challenges of high k dielectric

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High k dielectric

  1. 1. A Term Paper on Achievements & Challenges of MOSFET’s with High-K Gate Dielectrics Course instructor : Dr.Dipanjan Basu Presented by :Anubhav Srivastava Bandarupalli Jayadeepthi Noor Mohamed EV
  2. 2. Why this is required…….?  Scaling of transistor to drive Moore’s Law  SiO₂ is running out of atoms for further scaling but still scaling continues. Thickness of SiO₂ layer required in 45nm technology is about 1.2nm (4 atomic layers deep!!)  Quantum Mechanical phenomenon of electron tunneling results in Gate Leakage Current….!
  3. 3. Gate Leakage Current Quantum mechanical tunneling  Tunneling current increases exponentially with decrease in oxide thickness
  4. 4. Choice of High-K oxide High-K oxide should satisfy the following properties: 1. High Dielectric constant and Barrier Height 2. Thermodynamic stability 3. Interface Quality  Volume expansion caused by cubic to tetragonal to monoclinic transformation induces large stress in ZrO2
  5. 5. The Challenges for High-K Dielectric Development
  6. 6. High-K and Poly-Si Incompatibility due to Fermi Level Pinning Defect formation at the polySi and high-K interface is most likely the cause of the Fermi level pinning in the upper part of the band gap which causes high threshold voltages in MOSFET (M=Zr or Hf) Results in: 1. High threshold voltage 2. Low drive current So the need to replace poly-Si gate by a suitable metal
  7. 7.  Mobility Degradation Coulombic scattering :  Dominant at low field  Caused due to high interface trapped charge  Higher trap density near conduction band  More severe for nMOSFET
  8. 8. Surface phonon scattering
  9. 9. The Metal Gate Solution
  10. 10. Use of Metal Gates As a conductor metal can pack in hundred of times more electrons than poly-Si Metal gate electrodes (Co,Ni,Mo,W) are able to decrease scattering and reduce the mobility degradation problem
  11. 11. Types of Metal Gates Requires metal gate electrodes with “CORRECT” work functions on High-K for both nMOS and pMOS transistors for high performance.
  12. 12. Metal Gate/High-K Transistor When SiO2 is replaced with High-K material it was found that poly-Si and High –K material were not compatible. So poly-Si is being replaced by a metal to make it compatible with High-k material.
  13. 13. Mobility Improvement by using TiN High-K/Metal-gate reduces leakage
  14. 14. Yeah…Nobody knows for sure……….!!!  Intel achieved 20 percent improvement in transistor switching speed by using metal Gate /high-K transistor with HfO2 as dielectric. Intel 45nm Transistor – performance compared to 65nm 2x improvement in transistor density 30% reduction in switching power 20% improvement in switching speed 10x reduction in gate oxide leakage power
  15. 15. Reference Achievements and Challenges for the Electrical Performance Of MOSFET’s with High-k Gate Dielectrics by G. Groeseneken , L. Pantisano and M. Heyns 0-7803-8454-7/04/$20.00 2004 IEEE.