Presentation on Antireflection coatings

EPL - 211

Presented by –

Ajay Singh 2010ph10821

ANTIREFLECTION COATINGS

REFLECTION

coating

What is antireflective coating ?

Where does blue light disappear ?

Antireflective  or  anti-reflection  (AR)  coating  is a type of

optical coating applied to the surface of lenses and other

optical devices to reduce reflection.This improves the

efficiency of the system since less light is lost.

Antireflection is achieved by destructive interference

between……

coating

For destructive interference Δ =

(2m+1) λ/2

2nd = (2m+1) λ/2 => d = λ/4nc

= λ’/4

d = minimum required thickness of

coating

λ’ = wavelength in coating medium

’

Formation of antireflection coating

Layer deposition involves chemical reactions

Large density films

Good stoichiometry & uniformity over large surface area.

SiO2 SiN, SiON, SiOC , and TiO2 with proper thickness are

the common AR material deposited chemically. Required high temp to produce high quality material and

for

many application the substrate cannot tolerate being

heated

so not useful in that case .

CHEMICAL VAPOUR DEPOSITION :

LIMITITATION :

PHYSICAL VAPOUR DEPOSITION

A variety of vacuum deposition

Purely physical process , no

chemical reaction involved.

Process involved three steps: •        Evaporation •        Transportation •        Deposition

multiple coating layers possible

MgF2 coating on glass

    Almost any type of inorganic material can be

used as well as some kinds of organic materials.

The process is more environmentally friendly

than processes such CVD.

Advantages of PVD

Disadvantages

  High capital cost

Equipment size large because vacuum required

Processes requiring large amounts of heat require

appropriate cooling systems

  The rate of coating deposition is usually quite slow

Combined process of both CVD and PVD

a process used to deposit thin films from a gas

state (vapour)

to a solid state on a substrate.

Chemical reactions are involved in the process,

which occur after creation of a plasma of the

reacting gases

The plasma is generally created by RF (AC)

frequency or DC discharge between two

electrodes, the space between which is filled

with the reacting gases.

Processing plasmas are typically operated at

pressures

PLASMA ENHANSED CHEMICAL VAPOUR DEPOSITION

of a few millitorr to a few torr , although arc

discharges and

inductive plasmas can be ignited at atmospheric

pressure

Plasma enhanced CVD is most useful because it can deposit layers

on fragile

substrates that cannot withstand the high temperatures of other

CVD methods

Plasma enhanced CVD systems allow for greater control of the film

composition, density, and film stress.

Higher deposition rate at low temperature relatively

Plasma can cause damage to the substrate surface when either

secondary

electrons collide with the wafer surface or the energy of the ion

bombard-

ment becomes too high.

High cost.

Advantages of PECVD

Disadvantages

How much reflection while using AR coating ?

Can be reduced up to ~ 0.2%

APPLICATION OF ANTIREFLECTION COATING

Anti-reflection coated optical windows

Reflex free sight glasses

Laser scanner windows

Contrast enhancement

Anti glare coated instrument windows

Sensor technology

Low reflection camera windows

Holography components

Antireflection coated glass for displays

In microelectronic photolithography to

reduce image (substrate) distortions .solar cell with SiO coating

Glass with MgF2 coating

http://en.wikipedia.org/wiki/anti-reflectivecoating

http://

www.pgoonline.com/intl/katalog/antireflection.html

http://

hyperphysics.phy-astr.gsu.edu/hbase/phyopt/antire

f.html

http://www.rp-photonics.com/anti_reflection_coatin

gs.html

http://

www.guardian.com/oracleprd/groups/guardiandotco

m

http://

www.pveducation.org/pvcdrom/design/anti-reflectio

n-coatings

http://www.eere.energy.gov/basics/renewable_ener

gy/pv_contacts_coatings.html

Reference links :