1. Thin films are layers of material ranging from fractions of a nanometer to several micrometers thick. 2. Common methods for applying thin films include physical vapor deposition, chemical vapor deposition, electrodeposition, and sol-gel. 3. Physical vapor deposition works by controllably transferring atoms from a source to a substrate, with important methods being evaporation and sputtering.

1. THIN FILMS
DEFINITION
A thin film is a layer of material ranging from fractions of
a nanometer (monolayer) to several micrometers in
thickness.

2. METHODS OF APPLYING THIN FILMS
• Physical vapor deposition
• Chemical vapor deposition
• Electrodeposition
• Langmuir-Blodgett
• Sol-gel method

3. PHYSICAL VAPOUR DEPOSITION
The objective of these deposition processes is to controllably transfer atoms from
a source to a substrate where film formation and growth proceed atomistically.
IMPORTANT METHODS :
EVAPORATION
SPUTTERING
LASER DEPOSITION

4. EVAPORATION
In evaporation method , atoms are removed from the source by thermal means.
Until the late 1960s, evaporation clearly surpassed sputtering as the preferred film deposition technique.
Higher deposition rates, better vacuum, and, thus, cleaner environments for film formation and growth, and
general applicability to all classes of materials were some of the reasons for the ascendancy of evaporation
methods.
Two modes of evaporation can be distinguished in practice, depending on whether the vapor effectively
emanates from a liquid or solid source. As a rule of thumb, a melt will be required if the element in question
does not achieve a vapor pressure greater than lop3 torr at its melting point. Most metals fall into
this category, and effective film deposition is attained only when the source is heated into the liquid phase.
On the other hand, elements such as Cr, Ti, Mo, Fe, and Si reach sufficiently high vapor pressures below the
melting point and, therefore, sublime.
The vapour composition is usually different from that of the original solid or liquid source.

5. Reaction Type Chemical Reaction Examples Comments
Evaporation without
MX(s or I) -+ MX( g) SiO, B,O,
dissociation
GeO, SnO, A1N
CaFz, MgFz
Compound
stoichiometry
maintained in
deposit
Decomposition MX(s) ⟶t M(I) + (l/n)X,(g) III-V
semiconductors
Separate
sources are
required to
deposit these
compounds
Evaporation
with dissociation
a. Chalcogenides
X = S, Se, Te
MX(s) + M(g) + (1/2)Xz(g) CdS, CdSe
CdTe
Deposits are
metal-rich;
separate
sources are
required to
deposit these
compounds
b. Oxides
MO2 푠 ⟶ MO g + (1/2)O(g) SiO2,GeO2,TiO2,
SnO2,
ZrO2
Metal-rich
discolored
deposits;
dioxides are
best deposited
in 0, partial
pressure
(reactive
evaporation)

6. SPUTTERING
When the ion impact establishes a train of collision events in the
target leading to the ejection of a matrix atom.
DIFFERENT TYPES OF SPUTTERING:
DC Sputtering
RF Sputtering
Reactive Sputtering
Magnetron Sputtering
Bias Sputtering

7. 1. Thermal evaporation mechanism
2. Low kinetic energy of evaporant
atoms (at 1200 K, E = 0.1 eV)
4. Directional evaporation according to cosine law
5. Fractionation of multicomponent alloys,
decomposition, and dissociation of compounds
6. Availability of high evaporation source purities
1. Ion bombardment and collisional
2. High kinetic energy of sputtered
4. Directional sputtering according to cosine law at
high sputter rates
5. Generally good maintenance of target stoichiometry,
but some dissociation of compounds.
6. Sputter targets of all materials are available; purity
varies with material
1. Evaporant atoms travel in high or ultrahightorr
2. 2. Thermal velocity of evaporant io5 cm/sec.
3. Mean-free path is larger than evaporant - substrate
spacing.
Evaporant atoms undergo no collisions in vacuum discharge
pressure discharge region
1. Sputtered atoms encounter high) ambient (- 100 mtorr)
2. 2. Neutral atom velocity - 5 x lo4
3. Mean-free path is less than targetsubstrate spacing.
Sputtered atoms undergo many collisions in the
1 . Condensing atoms have relatively
2. Low gas incorporation
3. Grain size generally larger than
4. Few grain orientations (textured low energy
for sputtered film).
1. Condensing atoms have high energy
2. Some gas incorporation
3. Good adhesion to substrate
4. Many grain orientations

8. CHEMICAL VAPOUR DEPOSITION
Chemical vapor deposition (CVD) is the process of chemically
reacting a volatile compound of a material to be deposited, with
other gases, to produce a nonvolatile solid that deposits
atomistically on a suitably placed substrate.
low-pressure (LPCVD),
plasma-enhanced (PECVD), and
laser-enhanced
(LECVD) chemical vapor deposition

9. SOL-GEL METHOD
”Formation of an oxide network through polycondensation reactions of a
molecular precursor in a liquid.”
A sol is a stable dispersion of colloidal particles or polymers in a solvent.
The particles may be amorphous or crystalline. An aerosol is particles in a gas
phase, while a sol is particles in a liquid,
A gel consists of a three dimensional continuous network, which encloses a
liquid phase, In a colloidal gel, the network is built from agglomeration of
colloidal particles. In a polymer gel the particles have a polymeric sub-structure
made by aggregates of sub-colloidal particles. Generally, the sol particles may
interact by van der Waals forces or hydrogen bonds. A gel may also be formed
from linking polymer chains. In most gel systems used for materials synthesis,
the interactions are of a covalent nature and the gel process is irreversible. The
gelation process may be reversible if other interactions are involved.

10. •The idea behind sol-gel synthesis is to “dissolve” the compound in a
liquid in order to bring it back as a solid in a controlled manner.
•Multi component compounds may be prepared with a controlled
stoichiometry by mixing sols of different compounds.
•The sol-gel method prevents the problems with co-precipitation, which
may be inhomogeneous, be a gelation reaction.
•Enables mixing at an atomic level.
•Results in small particles, which are easily sinterable

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