Transcript Electric and Magnetic Fields

Thin Film Deposition
Prof. Dr. Ir. Djoko Hartanto MSc
Electrical Engineering Department
Faculty of Engineering University of Indonesia
February 14, 2003
Introduction
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
The need of layers of semiconductor,
dielectrics, and conductors to complete the
device
Beside the circuits have shrunk, they also
have grown in the vertical direction.
– Through increased numbers of deposit layers.
Overview
List of common deposition systems
Atmospheric Pressure (AP)
1.
2.
3.
4.
Horizontal
Vertical
Barel
Vapor phase epitaxy
List of common deposition systems
Low Pressure (LP) and
Ultra High Vacuum (UHV)
1.
2.
3.
4.
Horizontal
Vertical
Barel
Vapor phase epitaxy
Overview
There two primary techniques for layer
deposition :
1.
2.
Physical Vapor Deposition (PVD)
Chemical Vapor Deposition (CVD)
Physical Vapor Deposition (PVD)
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Physical vapor deposition (PVD) refers to a
family of processes in which a material is
converted to its vapor phase in a vacuum
chamber and condensed onto a substrate surface
as a thin film.
PVD can be used to produce coatings of a wide
variety of materials:
 metals
 ceramics
 semiconductors
 alloys
 glasses
 polymers
Physical Vapor Deposition (PVD)
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All PVD processes consist of the following
steps:
 synthesis of coating vapor,
 vapor transport to the substrate,
 condensation of vapors onto the substrate
surface to form a thin film.
These steps are carried out inside a vacuum
chamber, so evacuation of the chamber always
precedes the PVD process.
Physical Vapor Deposition (PVD)
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
Pressure Units:
 1 atm = 14.7 psia = 29.92 inches Hg
 = 760 mm Hg = 760 torr = 1.013 bar
 = 1.013 x 105 Pa
1 Pa = 1 N/m2 = 7.5 x 10-3 torr
Physical Vapor Deposition (PVD)
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The two most common PVD processes are:
 evaporation
 sputtering
We have already covered the basics of
evaporation.
For evaporation, the background pressure in the
vacuum chamber is typically ~10-6 Torr (~10-4 Pa)
or lower.
For sputtering, the background pressure in the
vacuum chamber is typically 10-3 to 10-2 Torr
(~1 Pa).
Evaporation
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
In order to evaporate a material, it must be heated
to a temperature at which its vapor pressure is 10-3
Torr or higher.
E.g., aluminum must be heated to 1000°C or more.
Evaporation
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There are two common ways to heat the source
material :
 resistive heating
 electron-beam heating.
Resistive heating uses electric current flow
through a tungsten filament to heat the source
material.
The source material can be placed directly on the
tungsten filament, or it can be put in a crucible
that is heated by the filament.
Evaporation

Evaporation from a filament-heated crucible.
Silicon Wafer
Aluminum Film
Aluminum Vapor
Evaporation
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In electron-beam (e-beam) evaporation systems,
a high intensity beam of electrons, with energy up
to 15 keV, is focused on the source material.
Electron bombardment heats the source material
to the temperature required for evaporation.
Heating can be restricted to the source material
itself .  The surroundings stay cool.
Because pressure is so low in the vacuum
chamber, in evaporation the source material
travels in a straight line from the source to the
substrate  shadowing
Physical Vapor Deposition (PVD)

The mean free path, l of atoms or molecules in
a chamber at pressure P is given by
kT
l
2
2 Pd
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T is the absolute temperature, k is Boltzmann’s
constant, and d is the diameter of the gas atoms
or molecules
The mean free path is the average distance
between collisions in the chamber.
Physical Vapor Deposition (PVD)

At room temperature and for a typical atom/molecule
diameter of 4 Å, the previous equation becomes
3
5.8  10
l
P
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
(m)
The pressure P is in pascals (Pa).
1 Pa = 1 N/m2 = 7.5  10-3 Torr
What is the mean free path for typical evaporation and
sputtering conditions?
Sputtering
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In sputtering, the source material is usually in the
form of a sheet or plate, called a target.
Sputtering is achieved by bombarding the target
with energetic ions, typically Ar+.
Atoms on the surface of the target are dislodged
by this bombardment and fly off .
These atoms then impinge on the substrate,
resulting in deposition of a thin film.
Chemical Vapor Deposition

Chemical Vapor Deposition (CVD) is the
formation of a solid material (insulator, metal, or
semiconductor) from the reaction of source gases
(or vaporized liquids).

The solid material is usually in the form of coating
(a “thin film”) 20-5000nm thick (200-50,000Å or
0.02-5mm).
CVD of Zinc Oxide (ZnO)

A simple Chemical Vapor Deposition system for
the preparation of thin film coatings of ZnO on a
substrate (e.g., a Si or GaAs wafer) is shown:
Air
N2 + H2O +
Zn(OOCCH3)2
Wafer
Furnace
Exhaust
Chemical Vapor Deposition
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Materials deposited by CVD are usually
amorphous or polycrystalline.

If a “clean” crystalline substrate is used, it can
sometimes act as a seed, resulting in a single
crystal deposited layer.

A crystalline layer deposited on a crystalline
substrate is called an epitaxial layer.
Chemical Vapor Deposition
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Examples in microelectronics -- insulators
(dielectrics)

Silica (SiO2) deposition (400-500ºC)
SiH4 + O2  SiO2 + 2H2

Silicon Nitride (Si3N4) deposition (700-800ºC)
3SiH4 + 4NH3  Si3N4 + 12H2
LPCVD Systems