Upload
others
View
3
Download
0
Embed Size (px)
Citation preview
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 035
CHAPTER – 2
Experimental Techniques:
Deposition and
Characterization of thin films
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 036
Sr. No.
CONTENTS Page No.
2.1
2.2
2.3
2.4
2.5
INTRODUCTION 2.1.1 Thin Films 2.1.2 Deposition Techniques Instrument used for the Fabrication of ITO thin film
2.2.1 High Vacuum Coating Unit
I. The Vacuum Chamber
II. The Pumping System
III. Vacuum Valves
IV. Safety Devices
V. Vacuum Gauges
Characterization of Thin Films
2.3.1 Characterization techniques
Instruments used for Characterization in the present study
2.4.1 Scanning Electron Microscope (SEM) and Energy
Dispersive Analysis of X Rays (EDAX)
2.4.2 X-Ray Diffractometer
2.4.3 Spectrophotometer
2.4.4 Transmission Electron Microscope (TEM)
System used for measurement and data collection
2.5.1 Data Logger
References
037
041
047
049
056
058
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 037
2.1 Introduction
In this chapter the experimental technique and instruments used for the
deposition of ITO thin films, for the characterization of films and data
collection from the array of sensors have been described.
2.1.1 Thin films
As explained by Prof. K. L. Chopra [1] “A solid material is said to be
in thin film form when it is built up, as a thin layer on a solid
support, called substrate, ab initio by controlled condensation of
the individual atomic, molecular, or ionic species, either directly by
a physical process, or via a chemical and/or electrochemical
reaction. Since individual atomic, molecular, or ionic species of
matter may exist either in the vapour or in the liquid phase, the
techniques of thin film deposition can be broadly classified under
two main categories:
1) Vapour phase deposition
2) Liquid phase/ solution deposition
It should be emphasized here that it is not simply the small thickness
which endows thin films with special and distinctive properties, but
rather the microstructure resulting from the unique way of their
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 038
coming in to being by progressive addition of the basic building
blocks one by one, which is more important. Film prepared by direct
application of dispersion or a paste, of the material on a substrate,
and letting it dry, are called irrespective of their thickness, thick
films and have properties characteristically different from those of
thin films.
In thin films, deviations from the properties of the corresponding
bulk materials arise because of their small thickness, large surface to
volume ratio, and unique physical structure which is direct
consequence of the growth process.”
Few basic steps of the deposition of semiconductor thin films are [2]:
Materials are created and deposited by atomic layer,
molecular or particular forms prior to deposition;
Materials are transported and created to the substrate in the
form of vapours stream or spray etc.;
Materials are deposited on substrate and film growth by a
nucleation and growth process.
2.1.2 Deposition Techniques
Semiconductor thin film deposition techniques have been broadly
classified into two major categories with their sub-classifications
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 039
shown in Table 2.1.
Table 2.1 Classification of thin film deposition techniques [1-4]
Thermal evaporation of physical vapour deposition is one of the
oldest techniques, but still widely used both in laboratory and
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 040
industry. It is very simple and convenient technique [1]. The three
basic steps involved in the deposition are as:
(a) Generation of vapour from the condensed phase, solid or
liquid.
(b) Transfer of vapour from source to the substrate.
(c) Condensation of vapour on substrate surface to form the solid
film.
Merits of the Physical Vapour Deposition (PVD) Process: [5]
(1) Materials can be deposited with improved properties
compared to the substrate materials.
(2) Almost any type of inorganic material can be used as well as
some kinds of organic materials.
(3) The process is more environment friendly than process such
as electroplating.
Demerits of Physical Vapour Deposition (PVD) Process: [5].
(1) It is a line of sight technique meaning that it is extremely
difficult to coat undercuts and similar surface features.
(2) High capital cost.
(3) Some process operates at high vacuums and temperatures
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 041
requiring skilled operators.
(4) Processes requiring amounts of heat appropriate cooling
system.
(5) The rate of coating deposition is usually slow.
2.2. Instrument used for the Fabrication of ITO thin film
In the present study, the deposition of thin film was done by ITO use for
direct or thermal evaporation technique. The Hind Hi Vac make vacuum
coating unit was used for the depositions of films. For thin film deposition,
especially the physical vapour deposition technique, the evaporation
requires a good degree of vacuum. The process of deposition starts, by
creating a vacuum in the deposition chamber, usually 10-6 Torr or less. The
actual deposition is followed by this process. In the deposition procedure
the supporting devices needed include, material sources, masking
arrangements, power supplies, and thickness monitoring devices,
deposition rate controllers etc [6].
2.2.1 HIGH Vacuum Coating Unit
Fig. 2.1 shows the vacuum coating unit (Hind Hi Vac Made; Model
15F6) used for the deposition of ITO thin films. This is versatile unit
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 042
both for research as well as production. Optional accessories
increase the veracity of the unit making it suitable for a variety of
application, including optical thin film deposition, semiconductors,
and micro-electronics. A high speed vacuum pumping system fully
integrated with necessary piping and valves operated manually is
rated for high gas through-put handling and to produce clean and
high vacuum in the chamber. This vacuum coating system is wired
operated 230 V A.C., 50Hz single phase power supply / 415 V A.C. 3
phase power supply.
Fig. 2.1 Vacuum coating unit (HINDHIVAC Made; Model 15F6) actual
experimental set-up of thin film evaporation [7]
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 043
This model consisting of stainless steel cabinet mounted with
hydraulically operated cylindrical work chamber and a control panel.
This system coating units has five main parts:
I. The vacuum chamber
The vacuum chamber fabricated from well-polished stainless steel. It
consists of two glass viewing-windows for inspecting the operation of
thin films coating. The vacuum chamber is raised from the base plate
by means of hydraulic pump. When required, the chamber can be
lowered by an electromagnetically operated valve, which opens an
orifice and allows the hydraulic oil to be returned to the oil reservoir.
Cooling water pipeline is attached to the outside of the chamber to
prevent overheating.
II. The Pumping System
The vacuum chamber is evacuated by high speed pumping system
consisting of fractionating oil diffusion pump (OD 6F) with an
unbaffled speed 0f 1000 Lits/Sec., along with LN2 trap backed by a
300 Lits/Min. double stage gas ballast rotary pump, directly coupled
with 1HP motor with overload protection.
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 044
Rotary pump
Rotary pump is an oil-sealed rotary displacement pump although
they can be dry pumps as well. Rotary pumps are built in single and
double stages. Typically a two-stage pump will achieve lower
pressures than a single-stage rotary pump. Hydrogen oil is used in
rotary pump.
Diffusion pump
Diffusion pump operates quite differently than a gas displacement
pump, such as mechanical pump. These types of pumps use the
vapour of boiling fluid to capture air molecules. The fluid is then
moved to another location and cooled. The cooling forces the air
molecules to be released.
III. Vacuum Valves
The system contains following vacuum valves:
The hand operated water-cooled baffle valve to the 18 inch
diameter stainless steel base to isolate the chamber from the
pumping system.
Two numbers of 1 inch quarter swing butterfly type pipeline
valves fitted in the vacing ling line and roughing line. The
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 045
backing line valve used to isolate the diffusion pump from the
rest of the system when roughing is in progress. When high
vacuum pumping system is in progress, the roughing valve is
closed and backing valve is opened to allow the rotary pump
to back the diffusion pump.
A 1 inch diaphragm isolation valve straight-through-type fitted
in the rotary pump line for leak detection.
A quarter inch diameter air admittance valve fitted to the
chamber.
A 1 inch magnetic isolation cum air admittance valve included
in the vacuum pipe line above rotary pump. When the unit is
switched off or the power supply fails, this valve operates to
isolate the entire system and admit air to the rotary pump.
Contamination of pipeline with rotary pump oil is thus
prevented.
IV. Safety Devices
Overload protection for rotary pump motor
Thermal switch on the cooling coils of diffusion pump
Water-flow switch at the outlet of cooling water-supply
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 046
Micro-switch to isolate the power supply to the base-plate
when the chamber is raised
Vacuum switch
V. Vacuum Gauges
Pirani gauge
The unit also contains two measuring gauges along with their
displays to indicate the level of pressure. The Pirani Gauge (Hi-Tech;
Model DPG-001) is a digital vacuum measuring instrument designed
for use with the thermal conductivity type gauge-head to measure
the pressure range 0.9 mbar to 0.001 mbar.
Ionization Gauges
The Ion Gauge, (Hi-Tech; Model IG-001) is a digital high-vacuum
measuring instrument designed for use with Bayard Alpert type
gauge tube. The current measures gas number density and directly
measure pressures between 1x10-4 to 1x10-9 torr.
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 047
2.3 Characterization of Thin Films
2.3.1 Characterization techniques
To understand the behaviour and multifaceted properties of thin
films, various sophisticated characterization techniques are being
used to examine their physical, chemical and structural properties.
Table 2.2 gives the list of properties of thin films and corresponding
characterization techniques [2].
The macroscopic examination method, the X-Ray diffraction methods
used in the measurement of standard properties of the film. The
microscopic examination includes getting information about
structure of the thin films and thus involves an extensive use of
transmission electron microscope and transmission electron
diffraction techniques. Until a few years ago, information on sub-
micrometer scale length was accessible only by using indirect
techniques such electron or X-Ray diffraction or with electron or with
electron microscopes that required vacuum environment and
conductive materials [2].
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 048
Table 2.2 Characterization techniques for analysis of thin films
Thin Film
Semiconductor
Properties
Characterization Techniques
Topography A. Stylus Techniques
B. Scanning Electron Microscope (SEM)
C. Transmission Electron Microscope in Replica
Mode (TEM)
D. Scanning Tunnelling Microscope (STM)
E. Magnetic Force Microscope (MFM)
Bulk Structure A. X-Ray Diffraction (XRD)
B. Transmission Electron Microscopy (TEM)
Surface
Structure
A. Low Energy Electron Diffraction (LEED)
B. Reflection High Energy Electron Diffraction
(RHEED)
C. Field Emission Microscope (FEM)
D. Field Ion Microscope (FIM)
E. Atom Probe Field Ion Microscope (APFIM)
F. Atomic Force Microscope (AFM)
Chemical
Analysis
A. Electron Probe Micro Analyser (EPM)
B. Auger Electron Spectroscopy
C. Scanning Auger Microprobe
D. Electron Spectroscopy for Chemical Analysis
(ESCA)
E. Ion Scattering Spectroscopy (ISS)
F. Secondary Ion Mass Spectrometry (SIMS)
G. Rutherford Back Scattering (RBS)
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 049
2.4 Instruments Using for Characterization in the present study
In the present study, the ITO thin film were examined by the SEM attached
with EDAX, X-Ray Diffractometer and TEM attached with EDAX, for
Structural and Chemical Analysis and UV-VIS-NIR Spectrophotometer for
optical analysis. A brief description of the instruments used is given here.
2.4.1 Scanning Electron Microscope (SEM) and Energy
Dispersive Analysis of X- Rays ( EDAX)
The Scanning Electron Microscope (SEM) is a microscope that uses
electrons rather than light from the image. The SEM has a large
depth of field, which allows a large amount of the sample to be in
focus at one time. The SEM also produces images of high resolution,
which means that closely spaced features can be examined at high
magnification. Preparation of the samples is relatively easy since
most SEMs require the sample to be conductive. The combination of
higher magnification, larger depth of focus, greater resolution, and
ease of sample observation makes SEM one of the most heavily used
instruments in research area today. EDAX provides qualitative
elemental, chemical analysis and element localization on samples
being analyzed [8].
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 050
Fig. 2.2 shows the picture of the instrument for SEM/EDAX, Make:
JEOL JSM-5610LV, used in the present study.
Fig. 2.2 Scanning Electron Microscope (Make: JEOL JSM-5610LV)
2.4.2 X-RAY Diffractometer (XRD)
X-ray Scattering Technique is a family of non-destructive
analytical techniques which reveals information about
the crystallographic structure, chemical composition, and physical
properties of materials and thin films. These techniques are based
on observing the scattered intensity of an X-ray beam hitting a
sample as a function of incident and scattered angle, polarization,
and wavelength or energy. The intensities are recorded in
computer/strip charts. An important feature of the Diffractometer is
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 051
its ability to focus into sharp diffraction line, the radiation which is
Bragg-reflected from extended specimen area.
X-RAY Diffractometer (Philips make: Model – XPERT MPD), shown in
Figure 2.3 is Philips’s latest revolutionary concept in multi-purpose X-
Ray Diffractometer. The XRD is very useful tool for researcher’s work
and analysis or identifications of various types of materials like
powder, texture, stress, single crystal and high resolution analysis,
forensic material, zeolites, explosive materials, super conducting,
inorganic materials, organic materials, minerals, metal + alloy
material, cement materials, correction product polymer, material
detergent product pigments, pharmaceutical product, ceramic
materials and kidney stones [9].
Fig. 2.3 X-RAY Diffractometer (Philips make: Model – XPERT MPD) [9]
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 052
X-ray diffraction is widely used to identify crystalline phases,
measure crystallite sizes, lattice parameters, orientation and provide
quantitative phase analysis and atomic coordinates. This information
is important for relating the production of a material to its structure
and hence its properties. As well as in academic interest, X-ray
results are used in patent disputes, forensic study and for quality
control.
Specifications
Source: Cu target X-Ray tube
X-Ray Operating Power of the tube: 2 KW
Detector: Xe-filled Counter or Proportional detector Software:
JCPDF database for powder Diffractometer
Goniometer
Operation Modes: Vertical & Horizontal
Accuracy: ± 0.0025, 2θ Measurement range: 3˚ to 136˚
Diffractometer radius: 130mm to 230 mm.
2.4.3 Spectrophotometer
Spectrophotometry is a process where we measured absorption and
transmittance of monochromatic light in terms of ratio or a function
of the ratio, of the radiant power of the two beams as a functional of
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 053
spectral wave length. The ray of light to be absorbed by some
material simply passes through others without being affected. When
a molecule absorbs light, energy is transferred from the ray of light
to the molecule. If the frequency of the electronic and magnetic
fields of a ray of light match the frequency at which molecules will
vibrate, then light will be absorbed, if the frequency does not match,
then the light will pass straight through unaltered [10]. Fig.2.4 shows
the Systronics 656 Model 105 Spectrophotometer used for the
present study.
Fig. 2.4 Spectrometer (Systronics 656 Model 105)
2.4.4 Transmission Electron Microscope (TEM)
The Transmission Electron Microscope (Make: Philips, Model: Tecnai
20 Twin) shown in Fig.2.5 is a highly advanced state of the art
instrument. The fundamental understanding of material’s properties
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 054
starts with a thorough characterization of the materials. Morphology,
Crystal Structure, Chemical Composition, Interface Structure,
Surfaces and defects all have their influence on the properties of
materials. TEM has proven to be a very powerful technique for
studying a range of general and advanced materials down to the
Angstrom level. It’s generates a wide range of signals carrying out
different types of valuable information’s. Tecnai 20 has been
especially designed to acquire and process these signals efficiently
and effectively. The combination of high-resolution imaging, bright
field, dark field imaging, electron diffraction and detailed micro
analysis are the important features of TEM.
Fig. 2.5 Transmission Electron Microscopes
(Make: Philips, Model: Tecnai 20 Twin) [11]
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 055
TEM Specification
Electron Source:- W emitter and LaB6
Accelerating Voltage:- 200 kV
Objective lens:- S- TWIN
Point Resolution: 0.27 nm or better
Line Resolution : 2.0 nm or better
Magnification : 25x to 750000x or higher
Single tilt holder with CCD Camera
TEM Applications:
Morphology, crystal structure, interface structure, crystal
defects can be studied
Study of biological micro organisms.
Particle Size measurement
Liposomes
Single crystal diffraction
Virus & Bacterial study
Materials Science/Metallurgy
Biological Science Nano Technology
Ceramics
Pharmaceuticals
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 056
Semiconductors
TEMs images are formed using transmitted electrons (instead of the
visible light) which can produce magnifications detail up to 25x to
750000x or higher. The images can be resolved over fluorescent
screen or a photographic film. Furthermore the analysis of the X-Ray
produced by the interaction between the accelerated electrons with
the samples allows determining the elemental composition of the
sample allows determining the electrical composition of the sample
with high spatial resolution. Since, the first TEM was built; much
progress has been made to improve instruments and methods for
exploring the micro- and nano-world.
2.5 System used for measurement and data collection
2.5.1 Data Logger
Fig. 2.6 Data Logger Onset, Hobo 4 channel U 12
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 057
A data logger (also data recorder) is an electronic device that
records data over time or in relation to location either with a built in
instrument sensor or via external instruments and sensors.
Increasingly, but not entirely, they are based on a digital processor
(or computer). They generally are small, battery powered, portable,
and equipped with a microprocessor, internal memory for data
storage, and sensors. Some data loggers interface with a personal
computer and utilize software to activate the data logger and view
and analyze the collected data, while others have a local interface
device (keypad, LCD) and can be used as a stand-alone device [12].
In the present study, a 4 channel external channel Data Logger (Make:
Onset: Hobo Data Logger U 12), as shown in Fig.2.6 was used for
recording the output from the array of three sensors kept in a
measurement system.
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 058
References
1. Kasturi Lal Chopra and Inderjeet Kaur, “Thin Film Device
Applications” Plenum Press, New York and London, 1983
2. Kasturi Lal Chopra and Lalit K Malhotra, Thin Film Technology and
Applications Tata McGraw-Hill Publishing Company Ltd., New Delhi
1985
3. J. George, “Preparation of Thin Films”, Marcel Dekker, Inc., New York
1992
4. A. R. West, John Willy & Sons, Singapore, 2003
5. http://www.azom.com/article.aspx?ArticleID=1558, Physical Vapour
Deposition
6. S. Dushman, Scientific Foundation of Vacuum Technique (J. M.
Lafferty ed.) 2nd Edition, Wiley, New York (1962)
7. Hind Hi Vac Operating Instruction Manual for Vacuum coating unit,
Model: 15F6 [1M-017]
8. Philips, The SEM with EDAX, Model: XL 30 ESEM, Operating Manual.
9. Philips, XRD, Model: Xpert MPD, Operating Manual
10. http://www.rmsc.nic.in/RHSDP%20Training%20Modules/SPECTROP
HOTOMETER.pdf
11. TEM Philips, Model: Tecnai 20 TWIN, Operating Manual
Chapter 2
Jignesh N. Panchal / Ph.D. (Electronics) Thesis/ Sardar Patel University /2014 059
12. http://en.wikipedia.org/wiki/data_logger