Transcript Document 7146360

太陽能工程-太陽能電池篇
National Formosa University
Introduction for PECVD
Plasma 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
1atm~102
Pa
760~1 torr
Medium vacuum
Airflow morphology：Transition flow
102~10-1 Pa
1~10-3torr
High vacuum
Airflow morphology：Molecular flow
10-1~10-5 Pa
10-3~10-7 torr
Ultra-high vacuum
Airflow morphology：Single-molecule movement
10-5~10-8 Pa
10-7~10-10 torr
Rough vacuum
Airflow morphology：Viscous flow
Ultra-high vacuum
less 10-8 Pa
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Airflow morphology：Single-molecule
movement
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 「λ」 , 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
Rough vacuum
Medium vacuum
High vacuum
Ultra-high vacuum
Pressure (mbar)
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Classification of the vacuum gauge
(一) Divided according to the measuring method:：
1. Direct：The 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. Indirect：Characteristics 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.
(二) Divided on the basis of the work principle ：
1. Mechanical：Wall or membrane of the sensing element to the force acting on
a size to determine the size of the pressure.
2. Electronic：Number 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.
(三) Divided according to the measurement range：
1. Rough vacuum: 1 atm ~ 102 Pa, Gauge U-tube、Gauges Bourdon 。
2. Medium vacuum: 102~10-1 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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Thin Film Deposition
PVD
CVD
( Physical Vapor Deposition)
(Chemical Vapor Deposition)
Evaporation
DC Sputter
Sputter
AC Sputter
Reactive Sputter
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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”.
Adsorption
Chemical Surface
reaction Migration
Desorption
nucleation
Substrate
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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
Sputtering
Ion deposition
heat
kinetic
heat
Thin film growth rate
Can improve ( < 75
μm/min)
Pure metal other
than low (Cu：
1μm/min)
Can improve( < 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
YES
YES
YES
YES
YES
YES
evaporation
Ions generated
Deposition of metal
Evaporation alloy
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Vacuum evaporation, sputtering and ion deposition
three kinds of PVD method of characteristics.
PVD Evaporation
Vacuum
Sputtering
Ion deposition
YES
YES
YES
0.1~0.5eV
1~100eV
1~100eV
usually not
Yes，or not because
of its shape
YES
usually not
YES
YES
YES
usually not
Yes and No
1.67~1250
0.17~16.7
0.5~833
evaporation
Evaporation heatresistant compounds
Particle energy
The impact of the inert
gas ion
Mixing between
the surface and layer
Heating (external
heating)
Deposition rate
m/sec
10-9
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Vapor deposition, molecular beam epitaxy and
sputtering PVDcharacteristics comparison
Nature of the
method
Deposition rate
Large-size control
Precise composition control
真空蒸鍍
(Evaporation)
Slow
Poor
Less
Poor
Poor
分子束磊晶成長
(MBE)
Slow
Poor
Excellent
Poor
Poor
濺鍍(Sputter)
Best
Best
Best
many
Excellent
Can be Manufacturi
ng cost
deposited
materials
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Thin Film Deposition
PVD
CVD
( Physical Vapor Deposition)
(Chemical Vapor Deposition)
By Pressure
APCVD
Hot/Cool wall
760 torr
LPCVD
10-1 torr
PECVD
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500 mtorr
By Reactor Type
By Energy
Resistance Heat
Re induction
Glow Discharge
Photons
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化學氣相沉積五個主要機制：
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
(1)Reactant
(4)main airstream
SiH4, H2
High concent
Boundary layer
(5) outer diffusion
(2)internal diffusion
Low concent
(3) Adsorption
基板
At High temperature
(200-500C))
(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 pressure 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 operating 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). APCVD 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
Shower head
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Low-pressure chemical vapor deposition
(LPCVD)
Low-pressure chemical vapor deposition during thin film deposition,
the gas pressure inside the reactor 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 rate 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 class 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
Shower head
13.56 MHz/ 60MHz
50-1000W
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Various
comparative
advantages
and
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disadvantages of CVD
Process
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-temperature process
Low deposition rate
Hightemperature
oxide
Polysilicon
Tungsten, silicide
tungsten
PECVD
Advantage
High-purity
Step coverage
excellent
Can be deposited
on large area chips
Low temperature
Chemical pollution
Low-temperature
process
insulator
Particle pollution
High deposition
Passivation layer
rate
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Step coverage
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CVD System
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CVD System
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Thin Film - PECVD
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PECVD
way
to the University
deposition of thin films, generally have a high
National
Formosa
hydrogen content in the case of Hydrogen amount is very a high,
PECVD在Solar
Cell
上的應用
a-Si:H
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 α-Si Defect trap caused by Cell Mobility lower
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Preparation and Properties of
amorphous silicon
1. 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
Excitation, Decomposition
Transport
Surface
reaction
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.
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Commercialization of solar cells using
the plasma technology applications
Effect
Passivation Antireflection
Abosrbers
Contacts
Material
SiNx:H
SiO2
SiO2, TiO2,
Si3N4
a-Si:H, Cu,
In, Ga, Se,
S,CdTe
Al, Ag, NiV,
Mo, SbTe,
ITO, Ti, Pd,
ZnO:Al, i-ZnO
Equipment
and
technology
PECVD
Sputtering
PECVD
Sputtering
Sputtering
PECVD
Evaporation
Evaporation
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%
Secondgeneration
PECVD、PVD
Filmtype(Silicon、
II-VI、III-V)
Transparent
conductive film,
the metal
electrode, the
silicon thin film
7%
42%
Thirdgeneration
Nano, organic, PVD、PECVD
dye
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) were 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 growth
(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, However, 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 generated waves phase, the elimination of standing wave effect, in
order to improve the filmdeposition quality.
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Applications of PECVD in TFPV
• a-Si:H 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-Si:H films , some possible
problems:
(1)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.
(2)Increase the gas pressure :the homogenous reaction generates
more, the powder easily occur, the plasma will easily
generate porous film.
(3)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-Si：H 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-Si：H thin film
• Doped a-Si：H can be fabricated by
mixing PH3 and mixing B2H6 or into
SiH4/H2 gas in plasma deposition process.
• Conductivity of a-Si：H may be varied
more than a factor of108
• But doping in a-Si：H 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
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