Ph.D. Thesis Jignesh Chapter 6 Formaldehydeshodhganga.inflibnet.ac.in/bitstream/10603/34702/9... ·...

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

Sr. No.

CONTENTS Page No.

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

Chapter 2

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

3. J. George, “Preparation of Thin Films”, Marcel Dekker, Inc., New York

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

12. http://en.wikipedia.org/wiki/data_logger

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