Cathodic sputtering is a thin film deposition technique where a target material is bombarded with energetic ions, ejecting atoms from the surface that are then deposited on a substrate. There are two main types: glow discharge sputtering and low pressure sputtering. Glow discharge sputtering uses a glow discharge to generate ions from a gas to sputter the target material and works best at pressures between 25-75 mTorr. Low pressure sputtering reduces collisions of sputtered atoms with gas to improve directionality and energy, including triode sputtering which uses an auxiliary electrode to increase ion generation efficiency.

1. UNIT III-THIN FILM DEPOSITION
TECHNIQUES
8/2/2020
DEPARTMENT OF PHYSICS, CATHOLICATE
COLLEGE, PATHANAMTHITTA
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Presented by
Dr. Dhanya I.
Department of Physics
Catholicate College
Pathanamthitta
III. CATHODIC SPUTTERING
1. OVERVIEW OF SPUTTERING PROCESS
i) GLOW DISCHARGE SPUTTERING
ii) LOW PRESSURE SPUTTERING
1) Assisted/Triode Sputtering

2. CATHODIC SPUTTERING
Sputtering Process:
Ejection of atoms from
the surface of a material
target by bombardment
with energetic particles.
Cathodic Sputtering :
Ejection is due to positive
ion bombardment
Ejected or sputtered
atoms can be condensed
on a substrate to form
thinfilm
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3. Sputtering yield : Average number of atoms
ejected from the target per incident ion
It increases with the increasing energy of ions and
mass
Yield depends on the angle of incidence of the
ions
It increases as where θ is the angle between
normal to target surface and beam direction
Depends on the atomic number of the target
materials
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Salient features for sputtering process

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Depends on the target temperature at its high value
Yield for single crystal target increases with
decreasing transparency of the crystal in the
direction of ion beam
As the yield increases, the ejected particles are
evaporated as atoms/clusters of atoms
Ejected atom leave the surface in an excited or
ionized state and show characteristic recombination
during emission

5. DIFFERENT TYPES OF SPUTTERING
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I. GLOW DISCHARGE SPUTTERING
Simple source of ions for sputtering is provided by the
phenomenon of glow discharge due to an applied electric field
between two electrodes in a gas at low pressures.
Gas break down to conduct electricity when certain minimum
voltage is reached.
Normal Glow: An attendant glow discharge maintains itself at a
constant voltage
Abnormal Glow: The region where both voltage and current
increases together
Cathode Glow: A luminous layer which covers the cathode
partially in the normal region and entirely in the abnormal glow.

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Cathode Dark Space: A fairly well defined region of
relatively low luminosity. A region where most of the
applied voltage is dropped[cathode fall]
Negative Glow region: Region followed by cathode dark
space where ions and electrons created in breakdown
region are accelerated and can collide with the gas
Positive Column: Due to collision of gas atoms in
negative glow region with energetic ions can create
secondary electrons to sustain glow and hit the anode to
give sputtering

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DEPARTMENT OF PHYSICS, CATHOLICATE
COLLEGE, PATHANAMTHITTA
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FACTORS INFLUENCING GLOW DISCHARGE
SPUTTERING
Pressure: As the gas pressure increases, voltage falls, cathode
dark space decreases and number of ions increases and favors
the sputtering process. Optimum pressure range for glow
discharge sputtering is between 25-75mTorr
Deposit distribution: Due to the collision of ions with ambient
gas atoms at high pressure, the sputtered atoms are diffusely
scattered results in a well collimated transport of material to
yield good quality of films.
Current and Voltage Dependence: Sputtering rate is
proportional to the current for a constant voltage. Glow
discharge sputtering is proportional to the product of current
and voltage. Typical voltage: 1-5KV and current density :
1-10mA/Cm2
.

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COLLEGE, PATHANAMTHITTA
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II. LOW PRESSURE SPUTTERING
Decreasing influence of gas atoms
lower concentration of trapped gas atoms
control direction
generate a high mean energy for ejected atoms.
It results in a smaller collision losses and results
in reasonable sputtering rate
4-types of Low pressure sputtering processes

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COLLEGE, PATHANAMTHITTA
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1. ASSISTED/ TRIODE SPUTTERING

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COLLEGE, PATHANAMTHITTA
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• Auxiliary electrons may be supplied thermionically
from a filament for ionization of gases
•Total ionization and efficiency are increased by
accelerating the electrons by means of third electrode
•Ejection of beams from triode to gas produce plasma
triode sputtering
•Uses: sputtering of noble metals: 20Ao
/min at
1mTorr pressure.

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