The process of Sputtering and the different types of sputtering. DC, RF, Magnetron, Reactive, Bias.

1. SPUTTERING
Lalrinfeli Ralte
ECE/20/08

2. CONTENTS
• Introduction
• Sputtering Mechanism
• Sputter Yield
• Different Techniques of Sputtering
DC Sputtering
RF Sputtering
Magnetron Sputtering
Reactive Sputtering
Bias Sputtering
• Advantages and Disadvantages
• Conclusion

3. INTRODUCTION 3
Sputtering is a mechanism by which atoms are dislodged
from the surface of a material as a result of collision with high
energy particles.
It is a type of Physical Vapor Deposition (PVD).
It can be described as a sequence of these steps:
1) Ions are generated and directed at target material.
2) The ions sputter atoms from the target
3) Sputtered atoms get transported to the substrate through a
region of reduced pressure
4) The sputtered atoms get condensed on the substrate,
forming a thin film.

4. SPUTTERING MECHANISM
• An electrical circuit where the Target is connected
to the cathode and the Substrate is connected to
the anode around a pressurised inert gas like
Argon is created.
• This creates a glow discharge which is a self-
sustaining type of plasma created by the
breakdown of the inert gas (Argon). The plasma
gets ionised as high electrical bias is created
within the electrodes around the plasma & the ions
travel at high velocity towards the cathode i.e., the
Target.
• When the ions hit the Target, they dislodge or eject
some of the atoms sitting on the surface of the
Target.
• These Target atoms then get deposited on the
surface of the substrate forming a layer of the
Target atoms over it.

5. SPUTTER YIELD 5
Sputter yield is the ratio of number of sputtered atoms to
number of incident ions.
𝑆 =
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑝𝑢𝑡𝑡𝑒𝑟𝑒𝑑 𝑎𝑡𝑜𝑚𝑠
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑖𝑛𝑐𝑖𝑑𝑒𝑛𝑡 𝑎𝑡𝑜𝑚𝑠
Sputter Yield depends on :
• 𝑆 ∝
1
𝑏𝑖𝑛𝑑𝑖𝑛𝑔 𝑒𝑛𝑒𝑟𝑔𝑦
• 𝑆 ∝ 𝐸𝑛𝑒𝑟𝑔𝑦 𝑜𝑓 𝑖𝑜𝑛𝑠
• 𝑆 ∝ 𝐼𝑛𝑐𝑖𝑑𝑒𝑛𝑡 𝑎𝑛𝑔𝑙𝑒 𝑜𝑓 𝑖𝑜𝑛𝑠
• Reduction in deposition of pressure gives better yield.

6. DC SPUTTERING
6
 Here a D.C electric field is impressed across the
electrodes which are located in the inert gas.
 The deposition rate depends on the pressure of the inert
gas and the DC voltage.
 As pressure is increased at fixed voltage, the mean free
path is decreased & more ions are generated. If pressure
is too high, the sputtered atoms undergo increased
collisional scattering and are not efficiently deposited.
 Energy is gained via elastic collisions until E > 15 eV for
ionisation.
 𝐴𝑟 + 𝑒− → 𝐴𝑟+ + 2𝑒−
The Optimum condition is shown in the shaded region of the
graph.
This range of pressure is suitable for DC Sputtering.

7. RF SPUTTERING
• The RF Sputtering helps to deposit insulating thin
films (resistivity > 106 Ω-cm).
• It is usually carried out with 1 to 3 kV peak-to-peak
RF potential.
• At AC signal above 50 kHz, electrons oscillating in
the glow region acquire enough energy to cause
ionising collisions, reducing the need for 2°
electrons to sustain the discharge.
• Also, RF voltages can be coupled through any kind
of impedance so that the electrodes need not be
conductors. So it is possible to sputter any material
irrespective of its resistivity.
• Typical RF frequencies employed is 13.56 MHz.

8. MAGNETRON SPUTTERING
8
• This technology uses powerful magnets to confine the
"glow discharge" plasma to the region closest to the target
plate.
• That vastly improves the deposition rate by maintaining a
higher density of ions, which makes the electron/gas
molecule collision process much more efficient.
• Uses either DC or RF power.
• A magnetic field of 100-200 gauss is used, resulting in
field lines which confine electrons to the region embraced
by them
• The discharge region is in the shape of a torroid or
elongated ring, with extensive sputtering of the target in
these regions.
• Substrates are usually placed on a rotating anode in order
to obtain uniform film deposition.

9. REACTIVE SPUTTERING 9
• In Reactive Sputtering, thin films of compounds are deposited on
substrates using metallic targets in the presence of a reactive gas in a
chamber, usually mixed with the inert gas to tune atrial pressure.
• The most common compounds reactively sputtered (and the reactive
gases employed) are:
Oxides: Al2O3, SiO2
Nitrides: TaN, TiN, AlN
Carbides: TiC, SiC
Oxycarbides and Oxynitrides of Ti, Ts, Al and Si
• Irrespective of which of these materials is considered, during reactive
sputtering the resulting film is either a solid solution alloy of the target
metal doped with the reactive element, a compound or some mixture of
the two.

10. BIAS SPUTTERING
• In Bias sputtering, electric fields near the substrate are modified in order to
vary the flux and the energy of the incident charged species and is achieved
by applying either a negative RF or DC bias to the substrate.
• A target voltage of -1000V to -3000V, bias voltage of -50V to -300 V are
typically used.
• This technique is use in all sputtering configurations (DC, RF, Magnetron
and Reactive) to tune resistivity, stress, dielectric properties, optical
properties, etc rate, density and adhesion of the deposited film.

11. ADVANTAGES &
DISADVANTAGES
11
ADVANTAGES
• Large size targets thus
simplifying the deposition
with uniform thickness over
large wafers.
• Film thickness is easily
controlled by fixing operating
parameters and simply
adjusting the deposition time.
• Device damage from X-rays
generated by electron beam
is avoided.
• In-situ cleaning is easily
done with sputter etch.
• Adhesion is excellent.
DISADVANTAGE
• High capital expense are
required
• Rate of deposition of some
materials (such as SiO2 are
relatively low.
• Ionic bombardment damage
occurs in organic solids
• Possibility of incorporating
impurities due to low-medium
vacuum range as compared
to Evaporation

12. CONCLUSION
Sputtering is a Physical Vapor Deposition technique
and it is widely used for depositing thin metal layers
on semiconductor wafers.
In Sputtering, ions are generated by a plasma
discharge usually within an inert gas (Ar).
It is also possible to bombard the substrate with an
ion beam from an external ion source. This allows
to vary energy and intensity of ions reaching.

13. THANK YOU