Introduction for PECVD Plasma Enhanced Chemical Vapor Deposition

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Introduction for PECVDPlasma Enhanced Chemical
Vapor Deposition
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Vacuum level
Under standard atmospheric pressure Pressure 1
atm 760 mmHg 760 torr 1.013 x 105 Pa
(?kg/cm2) 1013 mbar
14.7 psi 7.6 x 105 micron

• According to the different behavior of the size
  of the gas pressure and gas movement, vacuum
  divided into five levels

Pa torr
Rough vacuum Airflow morphologyViscous flow 1atm102 Pa 7601 torr
Medium vacuum Airflow morphologyTransition flow 10210-1 Pa 110-3torr
High vacuum Airflow morphologyMolecular flow 10-110-5 Pa 10-310-7 torr
Ultra-high vacuum Airflow morphologySingle-molecule movement 10-510-8 Pa 10-710-10 torr
Ultra-high vacuum Airflow morphologySingle-molecule movement less 10-8 Pa less 10-10 torr
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Mean free path

• Gas molecules in the movement, each molecule
  before the collision to other molecules, the
  average walking distance is called the gas mean
  free path, usually represented by the symbol ???
  , unit is cm. at room temperature 20 C (The
  higher the temperature, molecular motion faster)

Pressure Mean free path
1 x 10-3 torr 5cm
1 x 10-4 torr 50cm
1 x 10-5 torr 5m
1 x 10-6 torr 50m
1 x 10-7 torr 500m
1 x 10-8 torr 5km
1 x 10-9 torr 50km
1 x 10-10 torr 500km
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Vacuum pump operating range
Medium vacuum
High vacuum
Rough vacuum
Ultra-high vacuum
Pressure (mbar)
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Classification of the vacuum gauge

• (?) Divided according to the measuring method
• 1. DirectThe size of the direct measurement of
  the gas molecules acting on the wall or membrane
  of the sensing element force, reading is usually
  nothing to do with the gas species, a rough
  vacuum regardless of the often used this way.
• 2. IndirectCharacteristics of the measuring gas
  in a vacuum, such as thermal conductivity,
  viscosity, etc., to be converted into pressure,
  high vacuum regardless of this approach is
  commonly used in reading and gas type.
• (?) Divided on the basis of the work principle
• 1. MechanicalWall or membrane of the sensing
  element to the force acting on a size to
  determine the size of the pressure.
• 2. ElectronicNumber of different vacuum gas
  molecules caused by the thermal conductivity,
  viscosity, ionizing the measured strength of
  electronic signals converted into the size of the
  pressure.
• (?) Divided according to the measurement range
• 1. Rough vacuum 1 atm 102 Pa, Gauge
  U-tube?Gauges Bourdon ?
• 2. Medium vacuum 10210-1 Pa, Gauge
  thermocouple?Gauges capacitance manometer
• 3. High? Ultra-high vacuum 10-1 10-10 Pa Gauges
  cold cathode?Gauge ionization

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PVD thin film growth mechanism

• First of all, the atoms reach the substrate must
  have a vertical movement, atoms in order to
  adsorption on a substrate. these atoms in a
  chemical reaction to form a thin film substrate.
  thin film composition atoms in the surface of the
  substrate diffusion movement, this phenomenon is
  known as the adatom Surface Migration. when the
  atoms collide with each other combination of the
  trip atoms, Known as nucleation.
• Atoms must reach a certain size, the continuous
  stable growth. therefore, the small clusters will
  be inclined to each other polymerization,
  formation of a larger atoms, to cut overall
  energy. Atoms continue to grow will form the
  island. gaps between the nuclear island need
  to fill in order of atomic island junction and
  the formation of the entire continuous film.
  unable to bonding of atoms and the substrate,
  will be taken from the substrate surface
  detachment, to formation of free atoms, this step
  is called the atomic desorption.

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Sputter (PVD)
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PVD-Sputtering
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PVD-Sputtering

• The frequency of using magnets to scan the film
  thickness can be controlled, scanningmore the
  number of film thickness and the thicker.
• In general, more suitable for thin film
  deposition conditions high substrate
  temperature, low pressure, clean, smooth and
  non-reaction with the deposited film and the
  lattice size similar substrate.

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Vacuum evaporation, sputtering and ion deposition
three kinds of PVD method of characteristics.
PVD Evaporation Vacuum evaporation Sputtering Ion deposition
Ions generated heat kinetic heat
Thin film growth rate Can improve ( lt 75 µm/min) Pure metal other than low (Cu1µm/min) Can improve( lt 25 µm/min)
Particle Atoms, ions Atoms, ions Atoms, ions
Deposition uniformity if no gas mix in , and it will be worse good,but the film thickness uneven good,but the film thickness uneven
Deposition of metal YES YES YES
Evaporation alloy YES YES YES
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Vacuum evaporation, sputtering and ion deposition
three kinds of PVD method of characteristics.
PVD Evaporation Vacuum evaporation Sputtering Ion deposition
Evaporation heat-resistant compounds YES YES YES
Particle energy 0.10.5eV 1100eV 1100eV
The impact of the inert gas ion usually not Yes,or not because of its shape YES
Mixing between the surface and layer usually not YES YES
Heating (external heating) YES usually not Yes and No
Deposition rate 10-9 m/sec 1.671250 0.1716.7 0.5833
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Vapor deposition, molecular beam epitaxy and sput
tering PVDcharacteristics comparison
Nature of the  method Deposition rate Large-size control Precise composition control Can be deposited materials Manufacturing cost
???? (Evaporation) Slow Poor Less Poor Poor
??????? (MBE) Slow Poor Excellent Poor Poor
??(Sputter) Best Best Best many Excellent
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Thin Film Deposition
CVD (Chemical Vapor Deposition)
PVD ( Physical Vapor Deposition)
By Pressure APCVD 760 torr LPCVD 10-1
torr PECVD 500 mtorr
By Energy Resistance Heat Re induction Glow
Discharge Photons
By Reactor Type Hot/Cool wall
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????????????CVD 5 mechanisms

• (1) Import the main airstream of the reactants
  (laminar flow (?))
• (2) internal diffusion of reactants
• (3) Atomic adsorption
• (4) Surface chemical reaction
• (5) Resultant outer diffusion and remove

Boundary layer
(6)Chemical reaction
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Atmospheric pressure chemical vapor
deposition(APCVD)
The so-called atmospheric pressure chemical vapor
deposition method,  as the name implies, is the pr
essure to tap into the atmospheric pressure  CVD
reactor of a deposition, the deposition
rate of this method is very fast (high deposition 
rate),approximately 600-1000 nm / min. Close
to atmospheric pressure(1 atm) the APCVD the opera
ting pressure,  the pressure of
molecular collisions between the high frequency
of  homogeneous nucleation "gas phase
reactions likely to occur, and easy to
produce particles (easily generate particles). APC
VD use in industrial applications are
concentrated in the larger particle
endure the process,  such as the
protection layer (just for to passivation).
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APCVD Reactor
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Low-pressure chemical vapor deposition(LPCVD)
Low-pressure chemical vapor deposition during thin
film deposition,  the gas pressure inside the rea
ctor lowered to below about 100 torr. A
chemical vapor deposition reaction. Reaction at
low pressure, the film deposited by
LPCVD method has better step coverage,
but the lower  the frequency of collisions
between gas molecules makes the LPCVD  deposition 
rate is slow compared to APCVD. The deposition rat
e is lower.
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LPCVD System
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Plasma enhanced chemical vapor deposition(PECVD)

• In the CVD reaction, the decomposition of gas
  molecules need to have sufficient excitation
  energy .Plasma enhanced chemical vapor
  deposition 
• method, the reaction gas in an
  electromagnetic field energy, and a variety
•   of chemical reactions in the plasma body
  quickly, resulting in a short 
• period of time to complete the chemical vapor
  deposition.

• Belongs to the non-equilibrium plasma in the PECVD
  .In the body of such a plasma, the free
  electrons of the absolute temperature is usually
  higher than the average gas temperature of 1-2 cla
  ss times, these high-energy
•  electron impact gas molecules of the
  reactants, excitation and ionization,
• resulting in very lively chemical
  properties of free radicals group. Addition ,
• the ions hit the substrate surface,
  resulting in a more lively surface structure,
• there by speeding up the chemical
  reaction. In order to reduce the reaction
• temperature required to reach the lowered
  energy consumption for heating, in
• PECVD share of the weight in the
  CVD process to gradually become a
• major thin film deposition tools in
  Taiwan, especially for IC wafer BEOL
•   metal and dielectric deposition of the plasma
  membrane.

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Belongs to the non-equilibrium plasma in the
PECVD. In the body of such a plasma, free
electrons of the absolute temperature is usually
higher than the average gas temperature 1-2 class
times,Free Electrons have high temperature
(energy). They will bomb the reactants and gases.
The gases will be ionized. The ionics will be
active to react with other ionics. These
high-energy electron impact reactant gas
molecules, so that excitation and ionization, and
chemical properties of very lively radicals.
Addition, ion bombardment to the substrate
surface, The ionics will also bomb on the
substrate surface. Sometime it help deposition,
but Sometime it is a damage. More lively surface
structure, thereby speeding up the chemical
reaction. In order to reduce the reaction
temperature required to reach the lowered energy
consumption for heating, in PECVD share of the
weight in the CVD process to gradually become a
major thin film deposition tools in Taiwan,
especially for IC wafer BEOL metal and dielectric
deposition of the plasma membrane.
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Plasma Enhanced CVD System
13.56 MHz/ 60MHz 50-1000W
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Various comparative advantages and disadvantages
of CVD
Process Advantage Shortcoming Application
APCVD Simple structure of the reactor Fast deposition rate Low temperature process Step coverage of the poor particle pollution Low temperature oxide
LPCVD High-purity Step coverage excellent Can be deposited on large area chips High-temperature process Low deposition rate High-temperature oxide Polysilicon Tungsten, silicide tungsten
PECVD Low temperature process High deposition rate Step coverage Chemical pollution Particle pollution Low-temperature insulator Passivation layer
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CVD System
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CVD System
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Thin Film - PECVD
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PECVD?Solar Cell ???? a-SiH
PECVD way to the deposition of thin films,
generally have a high hydrogen content in the
case of Hydrogen amount is very a high, because
the Plasma in the H atoms with unsaturated bonds,
not when the deposition statement of Si and N to
form the Si-H and NHkey results. Since H is
easily affected by temperature has been released
(H will be released at a high temperature),
resulting in the instability of the TFT device
characteristics. H in plasma will connected with
unsaturated Si and N to become Si-H and N-H
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Hydrogen treat for SiNx layer
After the g-of SiNx do an H2, Plasma, change the
surface structure of g-of SiNx, to fill some of
the Dangling Bond, in order to avoid the Channel
with a-Si Defect trap caused by Cell Mobility
lower
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Preparation and Properties of amorphous silicon

• Thin film deposition method
• a-Si and its alloys is the plasma CVD, the heat
  of CVD, reactive sputtering or optical CVD
  method, vapor-phase synthesis method to prepare
  thin films.The use of a-Si solar cell, to the
  plasma of CVD method prepared, it is the first
  production method described, followed by optical
  CVD method, Doping.

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Plasma CVD method
Materials and gases to stimulate dissociation film
As shown the generated SiHx (x ? 3) response
(neutral and ionic).These reactions are diffusion
to reach 100 to 300.C substrate, on which a
variety of reactions (adsorption, detachment,
pulled out, insert and surface diffusion
process), the formation of a-Si film.
Excitation, Decomposition
Transport
Surface reaction
Film
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Commercialization of solar cells using the plasma
technology applications
Effect Passivation Antireflection Abosrbers Contacts
Material SiNxH SiO2 SiO2, TiO2, Si3N4 a-SiH, Cu, In, Ga, Se, S,CdTe Al, Ag, NiV, Mo, SbTe, ITO, Ti, Pd, ZnOAl, i-ZnO
Equipment and technology PECVD Sputtering PECVD Sputtering
Equipment and technology Sputtering PECVD Evaporation Evaporation
Equipment and technology Sputtering
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Applied by different generations of solar cells,
plasma equipment
Solar cell classification Applications of plasma devices Plasma coating membranes 2004 2020
The first generation Silicon type PECVD?Etcher Antireflection film batch coated 93 50
Second-generation Film-type(Silicon?II-VI?III-V) PECVD?PVD Transparent conductive film, the metal electrode, the silicon thin film 7 42
Third-generation Nano, organic, dye PVD?PECVD SiNx/SiOx film?Transparent conductive filmTiO2/Ta2O5?Metal electrodes 0 8
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Thin film growth

• Chip film, the initial covered on the wafer
  surface, many gas molecules or other
  child, such as atoms and ions. These
  particles may be because the 
• chemical reaction, the solid particles, and
  then deposited on the wafer surface or lose
  part of the kinetic energy through a surface
  diffusion 
• campaign, the wafer surface adsorbed (absorbed) we
  re deposited. According to the order of
  occurrence can be divided into the following
  five steps (a) crystal growth (b) the grain
  growth and (c) grain coalescence 
• (d) seam Road to fill the (e) The deposition
  film growth.

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thin film deposition steps
(a) crystal growth (b) grain growth and
(c) grain coalescence (get together) (d) The seam
Road to fill the gap (e) The deposition film growt
h(1) physical adsorption on the wafer
surface adatom(2) adatom back to the gas
phase by absorption of the solution
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Thin film structure

• island structure
• In the deposition, when the atoms or molecules
  are mutually binding capacity than the substrate
  strong island structure, such as metal insulator,
  graphite and other substrates.
• layer structure
• As the atoms and the substrate bonding is
  stronger than the others. The first layer
  of coverage completed with the second
  layer of bonding will be weak, such as
  semiconductor thin film of single crystal growth.
• Stranski-Krastanov(S.K.) structure
• Do the aforementioned model of an intermediate
  process, the current study such behavior is
  not fully understood, there may
  be disturbance to the growth of layered
  structure due to the binding energy.

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Residual stress

• Within the film and the substrate must have the
  existence of residual stress (thermal expansion
  coeff.), residual stress according to
  their form to distinguish can be divided
  into two, divided into the two kinds of tensile
  stress and compressive stress.
• The film tensile stress of the role, then the film
   - substrate will show a concaveshape
• Film by the compressive stress of
  the role, then the film - substrate will
  show aconvex shape

(a) Tensile stress
(b) Compressive stress
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VHF-CVD reactor electrode structure
Its structure for the strip-type electrodes, Howev
er, due to the spacing of theelectrode
structure is very narrow, and therefore will
produce a standing wave effect,
affecting the quality of thin film
growth, the left side of the SignalModulator gener
ated waves phase, the elimination of standing
wave effect, in order to improve the filmdepositio
n quality.
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Applications of PECVD in TFPV

• a-SiH film quality related to the experimental
  parameters
• (1) Substrate temperature (2)SiH4/H2 ratio
  (3)Total gas flow rate (4)RF power density
  (5)Electrode to substrate distance (6) growth
  pressure,
• To increase the growth rate of a-SiH
  films , some possible problems
• Increase the power density of the plasma
  power increase free radical production rate,
  but will also enhance the pears bombarded
  by an increase in film stress.
• Increase the gas pressure the homogenous reaction
  generates more, the powder easily occur, the
  plasma will easily generate porous film.
• Increase viscosity coefficient of free
  Radicals cause free radical surface
  diffusion will decrease to reduce the decline
  in film quality.

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Applications of PECVD in TFPV

• a-SiH thin film deposited by PECVD has lower
  defect density than by sputter due passivation of
  dangling bonds by H atoms

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Applications of PECVD in TFPV

• Doped a-SiH thin film
• Doped a-SiH can be fabricated by mixing PH3 and
  mixing B2H6 or into SiH4/H2 gas in plasma
  deposition process.
• Conductivity of a-SiH may be varied more than a
  factor of108
• But doping in a-SiH inevitable leads to
  creation of dangling bonds, higher defects
  density and shorter diffusion length of carriers.

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Microcrystalline Xicheng film agencies

• As raw material, SiH4, SiH3 of SiH4 reaction and
  very stable, is generally considered the
  main precursor for the SiH4 there
  is a proportion of about1/1000.
• Hydrogen atoms from SiH4 and H2, but with SiH4 to
  produce the binding reaction.
• Of SiH4  H ? H2  SiH3 extinguished, there is
  no hydrogen dilution system,the hydrogen atom is
  almost impossible to reach the substrate surface. 
  To growthe crystal structure must be about
  10 times more hydrogen dilution.

Crystalline deposition of microcrystalline
silicon thin film changes with thethickness
and hydrogen dilution schematic
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grain boundary
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Grain size and shape