04-07-2014, 04:50 PM
A presentation on Newest Low-k & High-k material for Fabrication
[attachment=65644]
INTRODUCTION
Silicon Industry is scaling SiO2 for the past 15 years and still continuing.
SiO2 is running out of atoms for further scaling but still scaling continues.
According to Moore Law:” Slope get double in every 18 months”.
Transistor scaling with increased performance and Reduced Power Consumption
Replacing SiO2 a challenge
Materials chosen for replacing SiO2 should be thicker (to reduce leakage power) but should have a “high-K” value
Material for interconnect two devices should have also Low –k value to speed up the device.
So to solve such a problem which arises due to device dimension scaling we need a Low-k and High-k dielectric material.
Along with it silicon is material having thickness uniformity
Low density of intersitial defects
Excellent chemical and thermal stability
Larger band gap which confers better isolation property
It has better adhesion property.
SiO2 is material with excellent electrical and thermal property
What is Dielectric
Dielectric material characterize with very low electrical conductivity (one millionth of a mho / cm), in which an electric field can be sustained with a minimal leakage.
It can store electrical energy/charge.
The electrically sensitive molecules inside dielectric material called polar molecules align by a
pattern whenever external electric voltage is applied.
What is High-K
A measure of how much charge a material can hold.
“AIR” is the reference with “K=1”."High-k" materials, such as hafnium dioxide (HfO2), zirconium dioxide (ZrO2) and titanium dioxide (TiO2) inherently have a dielectric constant or "k" above 3.9, the "k" of silicon dioxide
The improved performance related with the scaling of the device dimensions can be associated with the following equation as-
Id=UnCoxW/L(Vgs-Vth)2
Neccesity of High-k
The first problem is the leakage current. This is because when the gate dielectric is very thin, the charge carriers can flow right through the gate insulator and this is called the quantum mechanical tunneling effect.
This tunneling probability increases exponentially with the reduction in the thickness of the gate insulator. This results into an increase in the leakage current. Another issue can be the device reliability, as during the device operation carriers flow through the device, resulting in defects in the SiO2 layer and the Si-SiO2 interface.
This can result in the breakdown of the dielectric and eventual breakdown of the device.
Moreover the maximum gate voltage that can be applied to the device reduces with the thickness of the SiO2 layer . As temperature is increases some of the defect densities can increase high enough to cause a breakdown.
All these limitations have prompted research for alternate gate dielectric materials, which can compensate for the scaling effects and help in the further scaling of the devices.
The expression of C can be written in terms of xeq and kox, which are the equivalent oxide thickness and dielectric constant of the capacitor respectively. xeq is the thickness of SiO2 that would be required to achieve the same capacitance density as the dielectric.
So the physical thickness of an alternative dielectric employed to achieve the equivalent capacitive density of xeq can be obtained from the expression
Material Used for High -k
Titanium (Ti) based- TiO2 , TiSixOy.
Zirconium (Zr) based- ZrO2 .
Hafnium (Hf) based- HfO2,HfSixOy.
Aluminum (Al) based- Al2O3.
The dielectric constants for these materials range from 9 (Al2O3) to 80 (TiO2).
There is also ultra high gate dielectric SrTiO3 that has a dielectric constant 200
But it is not being investigated for the use in commercial devices.
The dielectric constant of HfSixOy is equal 8-15 depending upon the composition of Hafnium in thecompound.
Solution- Metal Gates
Metal gate electrodes are able to decrease phonon scatterings and reduce the mobility degradation problem
Challenges with Metal Gates
Requires metal gate electrodes with “CORRECT” work functions on High-K for both nMOS and pMOS transistors for high performance
Breakthroughs with Metal Gates
N-Type metal and P-Type metal with the CORRECT work functions on high-K have been engineered.
High-K\metal-gate stack achieves nMOS and pMOS channel mobility close to SiO2's.
High-K\metal-gate stack shows significantly lower gate leakage than SiO2.
Conclusion of High-k material
Intel achieved 20 percent improvement in transistor switching speed
Reduced transistor gate leakage by over 10 fold.
Integration of more than 400 million transistors for dual-core processors and more than 800 million for quad-core in Intel® 45nm high-k metal gate silicon technology.
What is Dielectric
Dielectric material characterize with very low electrical conductivity (one millionth of a mho / cm), in
which an electric field can be sustained with a minimal leakage. It can store electrical
energy/charge.
The electrically sensitive molecules inside dielectric material called polar molecules align by a
pattern whenever external electric voltage is applied.
The polar molecules align with the field so that
the positive charges accumulate on one face of the dielectric and the negative charges on the other face.
Dielectric strength may be defined as the maximum potential gradient to which a material can be
subjected without insulating breakdown
SEMICONDUCTOR Applications
Due to improvement in dielectric material characteristics used in semiconductor devices, the
performance of semiconductor device such as power consumption, speed, and size are improved.
Also semiconductor chips can integrate high capacitance capacitors inside the chip to save the
circuit from using external decoupling capacitors between the power and the ground planes.
These decoupling capacitors will reduce the transient voltage on the voltage supply, which are
caused by the current spikes that occur when the transistors on the semiconductor circuit switch on
or off.
Since in the mid-1990s, the microelectronics industry has innovated high- and low-k dielectrics (k isthe dielectric constant of a material) for continuing reduction of both horizontal and vertical
dimensions of integrated circuits (ICs). Due to use of low K material the gate leakage current and
heat dissipation can be brought down. Low K materials offer lower propagation delay, and lower
cross talk enabling devices to operate at higher frequencies i.e in the range of giga hertz
Low K dielectric materials
In both the vertical and horizontal dimensions the reduction in spacing of metal interconnects has
created the need for low-k materials that serve as interlevel dielectrics to offset the increase in
signal propagation time between transistors, known as RC delay (R is metal wire resistance and C
is interlevel dielectric capacitance). To fulfill these requirements at 32nm and lesser IC fabrication
nodes, innovation in dielectric materials is must if the device density of ICs has to continue at
Moore's Law rate. Low K materials are used in multi level interconnects, interlayer dielectrics, and
for passivation layers.
Some of the examples of low K dielectric material are, Nanopourous Silica,
Hydrogensilsesquioxanes (HSQ), Teflon-AF (Polytetrafluoethylene or PTFE), Silicon Oxyflouride
(FSG). The present trend now is using dielectric with K of less than 2.
High K dielectric materials
The High K dielectric materials are needed for the storage capacitors, and nonvolatile static
memory devices. Wherever high capacitance is required the high-K material is used.
High K dielectric material is used between gate and the silicon in CMOS transistors to increase the
capacitance of the metal and silicon.
http://yuekuo.tamu.edu/Hkgd.htm
Conventional materials such as thermal and chemical vapour deposition (CVD) SiO2 are being
replaced with new materials such as high k gate dielectrics, and carbon doped SiO2 for low k
interlevel dielectrics.
Some of the latest high k dielectric materials include:
--- SiNx with 4 < k < 10
--- Ta2O5, Al2O3, ZrO2, and HfO2 with 10 < k < 100
--- PZT with k<100
To find dielectric constant for thousands of chemical compounds and elements visit the site
Disadvantages of Porous Materials
Weakens mechanical properties
Lower thermal conductivity
Narrow pore distribution to ensure dielectric constant is homogeneous and isotropic
Pores need to be closed cells to prevent crack propagation and moisture absorption
Need to add silica to seal surface pores
Air Gaps and Bridges (k = 1.0)
Low breakdown voltage
Low thermal conductivity
Low strength
Deposition method unknown
Conclusions of Low –k material
Introduction of low-k dielectric is needed in order to continue to downscale technology
Several CVD or Spin-on deposited materials look promising for the near-future generations
Spin-on porous materials appear to be the only option for future generations
Air gaps need more research in order to be considered for future low-k dielectrics
[attachment=65644]
INTRODUCTION
Silicon Industry is scaling SiO2 for the past 15 years and still continuing.
SiO2 is running out of atoms for further scaling but still scaling continues.
According to Moore Law:” Slope get double in every 18 months”.
Transistor scaling with increased performance and Reduced Power Consumption
Replacing SiO2 a challenge
Materials chosen for replacing SiO2 should be thicker (to reduce leakage power) but should have a “high-K” value
Material for interconnect two devices should have also Low –k value to speed up the device.
So to solve such a problem which arises due to device dimension scaling we need a Low-k and High-k dielectric material.
Along with it silicon is material having thickness uniformity
Low density of intersitial defects
Excellent chemical and thermal stability
Larger band gap which confers better isolation property
It has better adhesion property.
SiO2 is material with excellent electrical and thermal property
What is Dielectric
Dielectric material characterize with very low electrical conductivity (one millionth of a mho / cm), in which an electric field can be sustained with a minimal leakage.
It can store electrical energy/charge.
The electrically sensitive molecules inside dielectric material called polar molecules align by a
pattern whenever external electric voltage is applied.
What is High-K
A measure of how much charge a material can hold.
“AIR” is the reference with “K=1”."High-k" materials, such as hafnium dioxide (HfO2), zirconium dioxide (ZrO2) and titanium dioxide (TiO2) inherently have a dielectric constant or "k" above 3.9, the "k" of silicon dioxide
The improved performance related with the scaling of the device dimensions can be associated with the following equation as-
Id=UnCoxW/L(Vgs-Vth)2
Neccesity of High-k
The first problem is the leakage current. This is because when the gate dielectric is very thin, the charge carriers can flow right through the gate insulator and this is called the quantum mechanical tunneling effect.
This tunneling probability increases exponentially with the reduction in the thickness of the gate insulator. This results into an increase in the leakage current. Another issue can be the device reliability, as during the device operation carriers flow through the device, resulting in defects in the SiO2 layer and the Si-SiO2 interface.
This can result in the breakdown of the dielectric and eventual breakdown of the device.
Moreover the maximum gate voltage that can be applied to the device reduces with the thickness of the SiO2 layer . As temperature is increases some of the defect densities can increase high enough to cause a breakdown.
All these limitations have prompted research for alternate gate dielectric materials, which can compensate for the scaling effects and help in the further scaling of the devices.
The expression of C can be written in terms of xeq and kox, which are the equivalent oxide thickness and dielectric constant of the capacitor respectively. xeq is the thickness of SiO2 that would be required to achieve the same capacitance density as the dielectric.
So the physical thickness of an alternative dielectric employed to achieve the equivalent capacitive density of xeq can be obtained from the expression
Material Used for High -k
Titanium (Ti) based- TiO2 , TiSixOy.
Zirconium (Zr) based- ZrO2 .
Hafnium (Hf) based- HfO2,HfSixOy.
Aluminum (Al) based- Al2O3.
The dielectric constants for these materials range from 9 (Al2O3) to 80 (TiO2).
There is also ultra high gate dielectric SrTiO3 that has a dielectric constant 200
But it is not being investigated for the use in commercial devices.
The dielectric constant of HfSixOy is equal 8-15 depending upon the composition of Hafnium in thecompound.
Solution- Metal Gates
Metal gate electrodes are able to decrease phonon scatterings and reduce the mobility degradation problem
Challenges with Metal Gates
Requires metal gate electrodes with “CORRECT” work functions on High-K for both nMOS and pMOS transistors for high performance
Breakthroughs with Metal Gates
N-Type metal and P-Type metal with the CORRECT work functions on high-K have been engineered.
High-K\metal-gate stack achieves nMOS and pMOS channel mobility close to SiO2's.
High-K\metal-gate stack shows significantly lower gate leakage than SiO2.
Conclusion of High-k material
Intel achieved 20 percent improvement in transistor switching speed
Reduced transistor gate leakage by over 10 fold.
Integration of more than 400 million transistors for dual-core processors and more than 800 million for quad-core in Intel® 45nm high-k metal gate silicon technology.
What is Dielectric
Dielectric material characterize with very low electrical conductivity (one millionth of a mho / cm), in
which an electric field can be sustained with a minimal leakage. It can store electrical
energy/charge.
The electrically sensitive molecules inside dielectric material called polar molecules align by a
pattern whenever external electric voltage is applied.
The polar molecules align with the field so that
the positive charges accumulate on one face of the dielectric and the negative charges on the other face.
Dielectric strength may be defined as the maximum potential gradient to which a material can be
subjected without insulating breakdown
SEMICONDUCTOR Applications
Due to improvement in dielectric material characteristics used in semiconductor devices, the
performance of semiconductor device such as power consumption, speed, and size are improved.
Also semiconductor chips can integrate high capacitance capacitors inside the chip to save the
circuit from using external decoupling capacitors between the power and the ground planes.
These decoupling capacitors will reduce the transient voltage on the voltage supply, which are
caused by the current spikes that occur when the transistors on the semiconductor circuit switch on
or off.
Since in the mid-1990s, the microelectronics industry has innovated high- and low-k dielectrics (k isthe dielectric constant of a material) for continuing reduction of both horizontal and vertical
dimensions of integrated circuits (ICs). Due to use of low K material the gate leakage current and
heat dissipation can be brought down. Low K materials offer lower propagation delay, and lower
cross talk enabling devices to operate at higher frequencies i.e in the range of giga hertz
Low K dielectric materials
In both the vertical and horizontal dimensions the reduction in spacing of metal interconnects has
created the need for low-k materials that serve as interlevel dielectrics to offset the increase in
signal propagation time between transistors, known as RC delay (R is metal wire resistance and C
is interlevel dielectric capacitance). To fulfill these requirements at 32nm and lesser IC fabrication
nodes, innovation in dielectric materials is must if the device density of ICs has to continue at
Moore's Law rate. Low K materials are used in multi level interconnects, interlayer dielectrics, and
for passivation layers.
Some of the examples of low K dielectric material are, Nanopourous Silica,
Hydrogensilsesquioxanes (HSQ), Teflon-AF (Polytetrafluoethylene or PTFE), Silicon Oxyflouride
(FSG). The present trend now is using dielectric with K of less than 2.
High K dielectric materials
The High K dielectric materials are needed for the storage capacitors, and nonvolatile static
memory devices. Wherever high capacitance is required the high-K material is used.
High K dielectric material is used between gate and the silicon in CMOS transistors to increase the
capacitance of the metal and silicon.
http://yuekuo.tamu.edu/Hkgd.htm
Conventional materials such as thermal and chemical vapour deposition (CVD) SiO2 are being
replaced with new materials such as high k gate dielectrics, and carbon doped SiO2 for low k
interlevel dielectrics.
Some of the latest high k dielectric materials include:
--- SiNx with 4 < k < 10
--- Ta2O5, Al2O3, ZrO2, and HfO2 with 10 < k < 100
--- PZT with k<100
To find dielectric constant for thousands of chemical compounds and elements visit the site
Disadvantages of Porous Materials
Weakens mechanical properties
Lower thermal conductivity
Narrow pore distribution to ensure dielectric constant is homogeneous and isotropic
Pores need to be closed cells to prevent crack propagation and moisture absorption
Need to add silica to seal surface pores
Air Gaps and Bridges (k = 1.0)
Low breakdown voltage
Low thermal conductivity
Low strength
Deposition method unknown
Conclusions of Low –k material
Introduction of low-k dielectric is needed in order to continue to downscale technology
Several CVD or Spin-on deposited materials look promising for the near-future generations
Spin-on porous materials appear to be the only option for future generations
Air gaps need more research in order to be considered for future low-k dielectrics