This document discusses the use of magnetron sputtering to deposit thin film layers for solar cell applications. Some key points: - Magnetron sputtering is widely used for vacuum thin film deposition and can coat a wide range of materials. It is used to deposit the various layers of thin film solar cells. - A typical sputtering system consists of a vacuum chamber, magnetron guns, vacuum pumps and power supplies. Magnetrons confine plasma in front of the target during sputtering. - Parameters like power, pressure and temperature can be controlled to deposit thin film layers with the desired properties. Insulating materials require RF power. - Thin film solar cells use multiple thin layers, including a sem

1. MAGNETRON SPUTTERING BASED THIN
FILMS FOR SOLAR CELLS
DEVENDRA BHALE
DBHALE@BARC.GOV.IN

2. SPUTTER DEPOSITION
• Magnetron sputtering is the most widely used method for vacuum
thin film deposition.
• Although the basic diode sputtering method (without magnetron or
magnetic enhanced) is still used in some application areas, magnetron
sputtering now serves over 90% of the market for sputter deposition.
• Magnetron sputtering can be used to coat virtually anything with a
wide range of materials - any solid metal or alloy and a variety of
compounds.

3. SPUTTERING SYSTEM
• A typical sputtering
system consists of a
vacuum chamber
with substrate
holders and
magnetron guns,
vacuum pumps and
vacuum gauges, a
gas supply system,
power supplies and
a control system.

4. THE PLASMA IN A MAGNETRON
• Plasma is called the fourth state of
matter after solid, liquid, and gas. It
is a state of matter in which an
ionized substance becomes highly
electrically conductive to the point
that long-range electric and magnetic
fields dominate its behavior.
• In many plasma coating applications
positive ions are generated by
collisions between neutral particles
and energetic electrons. The electrons
in a plasma are highly mobile,
especially compared to the larger ions
(typically argon for sputtering).
ref: www.gencoa.com

5. MICROSCOPIC VIEW OF SPUTTERING
• The impact of an atom or ion on a
surface produces sputtering from the
surface as a result of the momentum
transfer from the incoming particle.
Unlike many other vapor phase
techniques there is no melting of the
material.
• Phenomenon first described 150
years ago ...
Grove (1852) and plücker (1858) first
reported vaporization and film
formation of metal films by
sputtering.
• Other names for SPUTTERING were
SPLUTTERING and CATHODE
DESINTEGRATION.

6. THE MAGNETRON SPUTTER SOURCE
• A Magnetron is comprised is
used to confine plasma in front
of the target.
• Magnetic field
• An electrode (HV /RF)
• Target

7. PARAMETERS THAT CAN BE
CONTROLLED
• Kinetic energy of the incident ions & the sputtered
atoms
• Substrate temperature
• Deposition rate of thin film by changing either
• Input power
• Distance
• Gas scattering during transport of evaporant by
changing chamber pressure (1e-3mbar to 1e-2mbar)

8. MAGNETRON GUNS

9. WHAT IS THIN FILM
• A microscopically thin layer of material deposited on
to a metal, semiconductor, plastic or a ceramic base.
• Typical thickness of few nano meters to few microns.
• Can be conductive or nonconductive (dielectric)
• Applications include solar cell, Top metallic layer on a
chip, coating on a magnetic discs, hard coatings on
machine tools, antireflection layers on glasses etc.

10. THIN FILM SOLAR CELL
• Thin film based solar cells with relatively high
efficiency and low material usage is a promising
alternative for crystalline silicon technology.
• Easy to handle as it is flexible and can be formed on
complex shapes
• Cheaper than traditional technology, light weight easy
to move
• Thin film is better used during low light in shaded
areas

11. THE TYPICAL THIN FILM SOLAR
CELL
• Is made-up of multiple
layers
• Each layer has distinct
function and as to be
deposited with certain
key parameters
• Sputtering allows us to
deposit all these layers

12. THE ABSORBER LAYER
• The absorber layer is a semiconducting material often
considered the heart of all thin film solar cells.
• The absorber layers are like CIGS or CZTS
• The material is generally dielectric
• The thickness required is 1 to 10 microns
• The thin film should be uniform over large area
• The process should be stable and repeatable and
scalable

13. DEPOSITION OF CZTS ABSORBER
LAYER FROM A COMPOSITE TARGET
• The quaternary stoichiometric CZTS composite target is used
• The target is dielectric hence RF power supply is used
• The CZTS is deposited as tin film layer area of 25mm x 25mm
devices
• An efficiency of 5.2% has been achieved
• The process is reliable, industrially scalable
• Important process parameters pressure, stoichiometry of target,
substrate temperature, post processig

14. SPUTTERING INSULATORS AND
DIELECTRIC
• The thin film stoichiometry seen to be deviated from the ideal
stoichiometry
• The SEM images also reveal uniform thin film with grain size of
100-200nm size

15. OPTICAL TRANSMISSION SPECTRUM
• This study was done to get
effect of substrate
temperature o optical
properties
• The investigation shows a
strong effect of substrate
temperature during the
deposition on phase of the
thin film. The band gap has
reduced from 2.05 to 1.9 eV.
The band gap needs to be
~1.4eV for optimal solar cell
fabrication.

16. CO-SPUTTERING FROM MULTIPLE
TARGETS
• The CZTS precursor film
was co-sputtered using
three different targets;
copper (Cu), tin sulfide
(SnS / SnS2) and zinc
sulfide (ZnS).
• An efficiency of 6.6%
was obtiained

17. RESULTS
• The SEMM shows the
grain structure
• This route offers control
over stoichiometry and
phase of the CZTS
• The co-sputtering uses
DC power for copper
and RF power for
ZnS/SnS

18. MULTILAYER THIN FILMS AND
POST PROCESSING
• For CZTSSe solar cells
can produce flexible and
large-area modules with
homogeneous properties.
• A greater than 10%
efficiency for a cell area
larger than 2 cm2 of
certified flexible CZTSSe
solar cells

19. MULTILAYER SPUTTER DEPOSITION
• Metal precursors were deposited on the NaF layer using
99.99% pure Cu, Zn, and Sn sputtering targets with two
different stacking orders.
• The layers were deposited under sputtering powers of 150
W, 300 W, and 300W for the Cu, Zn, and Sn targets,
respectively, at a working pressure of 1 mTorr in an Ar
atmosphere
• The saples were post treatetd by sulpho-selenization using
pure Se and H2S gas

20. PREPARATION OF CZTS ABSORBER
LAYER BY REACTIVE SPUTTERING