high k dielectric
DESCRIPTION
Need and challenges of high k dielectricTRANSCRIPT
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
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….!
Gate Leakage Current
Quantum mechanical tunneling
Tunneling current increases exponentially
with decrease in oxide thickness
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
The Challenges for High-K
Dielectric Development
High-K and Poly-Si Incompatibility due
to Fermi Level PinningDefect 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
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
Surface phonon scattering
The Metal Gate Solution
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
Types of Metal Gates
Requires metal gate electrodes with “CORRECT” work functions on High-K for both nMOS and pMOS transistors for high performance.
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.
Mobility Improvement by using TiN
High-K/Metal-gate reduces leakage
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
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.