Martin P.M. Handbook of Deposition Technologies for Films and Coatings, Third Edition: Science, Applications and Technology

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CHAPTER 1

Deposition Technologies: An Overview

1.1 The Market 1

1.2 Introduction 3

1.3 Aim and Scope 5

1.4 Deﬁnitions and Concepts 6

1.4.1 Surface Engineering 6

1.5 Physical Vapor Deposition Process Terminology 8

1.6 Classiﬁcation of Coating Processes 10

1.7 New Deposition Technologies 12

1.8 Microstructure and Properties 13

1.9 Unique Features of Deposited Materials and Gaps in Understanding 14

1.10 Current Applications 15

1.10.1 Decorative/Functional Coating 16

1.10.2 Transparent Conductive Thin Films 16

1.10.3 Thin Film Solar Cells and Batteries 17

1.10.4 Friction and Wear: Nanolaminates and Superlattices 17

1.10.5 Cutting Tools 17

1.10.6 Gas and Water Permeation Barriers on Plastic 18

1.10.7 Biomedical 18

1.10.8 Thin Film Solid Oxide Fuel Cells 18

1.10.9 Flat Panel Displays and Molecular Electronics 19

1.11 ‘Frontier Areas’ for Applications of the Products of Deposition Technology 19

1.11.1 Selection Criteria 21

1.12 Summary 23

1.1 The Market

The second edition of this handbook lists market areas for surface engineered products,

including thin ﬁlm coatings as of the mid-1990s. Since then the market for several types of

thin ﬁlm products has exploded, including photovoltaics, energy conversion, energy efﬁciency,

biomedical, pharmaceutical, and ﬂat panel displays. The demand for advanced tribological and

corrosion-resistant coatings has also increased. It is estimated that the global market for optical

thin ﬁlm coatings alone will exceed $7.5 billion by 2010. This includes optical components,

telecommunications, window glazings, large area and decorative applications, laser mirrors,

2 Chapter 1

automotive coatings (electrochromic rear view mirrors, etc.), ophthalmic applications, and

aircraft windows. The global market for solar cells will increase to $32 billion by 2012 and for

thin ﬁlm solar panels alone is estimated to be $8.3 billion by 2030. As of 2008, there are at

least 50 companies marketing thin ﬁlm photovoltaic devices and systems. And this will only

grow with increased renewable energy demands, increased efﬁciency of organic and

transparent solar cells, and low-cost solar concentrator systems. Additional energy

applications include photocatalytic coatings, thin ﬁlm fuel cells, thin ﬁlm lithium batteries,

hydrogen generation, electrochromic and thermochromic coatings, and solar control coatings.

Molecular electronics, including organic light-emitting devices (OLEDs), has changed the

entire manufacturing process for ﬂat panel displays and will continue to do so for plastic

windows. Advanced wear- and corrosion-resistant materials are being developed for medical

implants, combustion and gas turbine engines, and aircraft engines and parts.

As stated in the second edition, surface engineering will remain a growth industry well into the

next decade because surface engineered products increase and improve performance, add

functionality, reduce costs, improve materials usage efﬁciency, and provide performance not

possible with bulk materials. Thin ﬁlms thus offer enormous potential due to the following:



creation of entirely new and revolutionary products



solution of previously unsolved engineering problems



improved functionality of existing products; engineering, medical, and decorative



production of nanostructured coatings and nanocomposites



conservation of scarce materials



ecological considerations – reduction of efﬂuent output and power consumption.

Research and development (R&D) expenditures in surface engineering are very expensive.

Industrial deposition systems can cost as much as $20 million. Even in the mid-1990s it was

reported that Japan spent $100–150 million on R&D in diamond and diamond-like carbon

(DLC) coatings, and this had certainly escalated by 2008 with the increased use of DLC. A

number of companies in the USA and Europe are now marketing DLC coatings for a wide

range of applications. Investments in photovoltaics worldwide have increased by a factor of 80

in the last decade. The United States Department of Energy spent approximately $24 billion on

R&D in 2007. While government support for R&D in biomedical materials in the USA has

plateaued, the market is steadily increasing, with European countries leading the way. The

same is true for many energy efﬁciency markets (thermoelectric power generation, advanced

glazings, etc.). R&D spending in China has reached $10 billion. The list continues to expand

with the need for renewable energy sources, energy efﬁciency improvements, more

sophisticated optical applications and telecommunication, advancing display technology, and

advanced medical applications with an aging population.

Deposition Technologies 3

1.2 Introduction

This is the third edition of this handbook. While many of the chapter headings are the same as

those found in the second edition, thin ﬁlm processes and technologies have advanced

signiﬁcantly in the past 14 years and descriptions in most cases are very different. New authors

have been added who focus on different and advanced aspects of this technology. Some

chapters found in the second edition present mature technologies with plateaued or

diminishing applications, and have been eliminated. The reader is referred to the second

edition of this handbook for a description of earlier technology.

Since the second edition was published in 1994, thin ﬁlm deposition technology and the

science have progressed rapidly in the direction of engineered thin ﬁlm coatings and surface

engineering. Plasmas are used more extensively. Accordingly, advanced thin ﬁlm deposition

processes have been developed and new technologies have been adapted to conventional

deposition processes. The market and applications for thin ﬁlm coatings have also increased

astronomically, particularly in the biomedical, display, and energy ﬁelds. Thin ﬁlm is the

general term used for coatings that are used to modify and increase the functionality of a bulk

surface or substrate. They are used to protect surfaces from wear, improve lubricity, improve

corrosion and chemical resistance, and provide a barrier to gas penetration. In many cases thin

ﬁlms do not affect the bulk properties of the material. They can, however, totally change the

optical, electrical transport, and thermal properties of a surface or substrate, in addition to

providing an enhanced degree of surface protection.

Thin ﬁlms have distinct advantages over bulk materials. Because most processes used to

deposit thin ﬁlms are non-equilibrium in nature, the composition of thin ﬁlms is not

constrained by metallurgical phase diagrams. Crystalline phase composition can also be varied

to a certain extent by deposition conditions and plasma enhancement. Virtually every property

of the thin ﬁlm depends on and can be modiﬁed by the deposition process and not all processes

produce materials with the same properties. Microstructure, surface morphology, tribological,

electrical, and optical properties of the thin ﬁlm are all controlled by the deposition process. A

single material can be used in several different applications and technologies, and the optimum

properties for each application may depend on the deposition process used. Since not all

deposit technologies yield the same properties or microstructures, the deposition process must

be chosen to ﬁt the required properties and application (see Chapter 12). For example, DLC

ﬁlms are used to reduce the coefﬁcient of friction (COF) of a surface and improve wear

resistance, but they are also used in infrared optical and electronic devices. Titanium dioxide

(TiO

) is probably the most important and widely used thin ﬁlm optical material and is also

used in photocatalytic devices and self-cleaning windows, and may have important

applications in hydrogen production. Zinc oxide (ZnO) has excellent piezoelectric properties

but is also used as a transparent conductive coating and in spintronics applications. Silicon

nitride (Si

) is a widely used hard optical material but also has excellent piezoelectric

4 Chapter 1

response. Aluminum oxide (Al

) is a widely used optical material and is also used in gas

barriers and tribology applications. The list goes on.

Engineered materials are the future of thin ﬁlm technology. Engineered structures such as

superlattices, nanolaminates, nanotubes, nanocomposites, smart materials, photonic bandgap

materials, molecularly doped polymers, and structured materials all have the capacity to

expand and increase the functionality of thin ﬁlms and coatings used in a variety of

applications and provide new applications. New advanced deposition processes and hybrid

processes are being used and developed to deposit advanced thin ﬁlm materials and structures

not possible with conventional techniques a decade ago. Properties can now be engineered into

thin ﬁlms that achieve performance not possible when the second edition of this handbook was

published. For example, until recently it was important to deposit fully dense ﬁlms for all

applications, but now ﬁlms with engineered porosity are ﬁnding a wide range of new

applications [1]. Hybrid processes, combining unbalanced magnetron sputtering and ﬁltered

cathodic arc deposition for example, are achieving thin ﬁlm materials with record

hardness [2].

Organic materials are also playing a much more important role in many types of coating

structures and applications, including organic electronics and OLEDs. These materials have

several advantages over inorganic materials, including low cost, high deposition rates, large

area coverage, and unique physical and optical properties. It is also possible to molecularly

dope and form nanocomposites with organic materials [3]. Hybrid organic/inorganic

deposition processes increase their versatility, and applications that combine organic and

inorganic ﬁlms are increasing [4].

In addition to traditional metallizing and glass coating, large area deposition, decorative

coating and vacuum web coating have become important industrial processes. Vacuum web

coating processes employ a number of deposition technologies and hybrid processes, most

recently vacuum polymer deposition (VPD), and have new exciting applications in thin ﬁlm

photovoltaics, ﬂexible displays, large area detectors, electrochromic windows, and energy

efﬁciency.

Hybrid deposition processes are gaining new applications because a single deposition process

may not be able to achieve the optimum coating performance for multilayer and

nanocomposite thin ﬁlms. Unbalanced magnetron sputtering and electron beam evaporation

are combined with ﬁltered cathodic arc deposition to deposit ﬁlms with improved tribological

properties. Plasma-enhanced chemical vapor deposition (PECVD) is combined with

unbalanced magnetron sputtering, magnetron sputtering is combined with electron beam

evaporation, and polymer ﬂash evaporation is combined with physical vapor deposition (PVD)

processes. In addition, thin ﬁlms with new properties are deposited with new deposition

processes such as atomic layer deposition (ALD) [5], high-power pulsed magnetron sputtering

Deposition Technologies 5

(HPPMS) [6], mid-frequency/dual magnetron sputtering (MF/DMS) [7] and glancing angle of

incidence deposition (GLAD) [8].

Deposition process technology must meet the demands of advanced thin ﬁlm coating

structures, such as superlattices, nanolaminates, and nanocomposites, with advanced

processes, materials and microstructures, and control and reduce costs. Recent advanced

deposition technologies presented in this third edition, such as ALD, GLAD, HPPMS,

MF/DMS, VPD, and hybrid processes, provide materials with improved microstructure,

compositional control, properties, adhesion, and tribological properties. Opposite ends

of the spectrum are also represented; GLAD thin ﬁlms have increased porosity and low

density while HPPMS, ion beam sputtered and MF ﬁlms have increased density, all of which

lead to a new range of optical, electrical, and tribological properties. New compositions and

nanocomposites are formed by DMS and hybrid deposition processes by cosputtering,

advanced reactive sputtering techniques, cathodic arc deposition, and PECVD. Hybrid

processes combine magnetron sputtering with cathodic arc deposition, electron beam

evaporation, and PECVD. Control of plasmas and generation of highly dense plasmas has

become very important in achieving new materials and improvements in conventional

materials. High deposition rates and increased materials usage have helped industrial

processes to become more productive and economical, and to deposit a wide range of new

thin ﬁlm materials.

Advanced deposition technologies are particularly successful in furthering medical and energy

technologies, including thin ﬁlm solar cells, thin ﬁlm fuel cells (solid oxide fuel cells),

biomedical products, and tribological applications. For example, tantalum (Ta) coatings

deposited by cylindrical magnetron process have increased the lifetime and reduced the cost of

medical stents [9]. Nanocomposites, superlattices, and nanolaminates form new coating

structures with improved tribological properties.

1.3 Aim and Scope

Thin ﬁlm coating technology is rapidly advancing. The performance demands on virtually all

types of thin ﬁlm materials are continuously increasing. To meet these demands, thin ﬁlm

coatings and structures are becoming more sophisticated with engineered microstructure and

properties. Because of this, process and technology handbooks published even ten years ago

are already out of date. Deposition processes and technologies are also changing rapidly to

keep pace with advanced thin ﬁlm materials and applications. Conventional deposition

processes are also being adapted in novel coating geometries to produce thin ﬁlm structures

with improved performance and properties not achievable by conventional methods. In

addition, new deposition processes are being developed to achieve new compositions and

physical properties. Thin ﬁlms are now being engineered with electrical, optical, and

6 Chapter 1

mechanical properties not possible a decade ago. Characterization techniques are also

improving.

The aim of this handbook is to provide the reader with detailed and usable information on:



deposition processes for thin ﬁlm coatings



new and advanced deposition processes



advanced thin ﬁlm applications and structures



relationships between deposition process parameters and thin ﬁlm microstructure



nucleation and thin ﬁlm growth processes



characterization of composition, bonding, and microstructure



the role of plasmas in thin ﬁlm growth.

Because in many cases no single process can achieve ﬁlms with the required properties, hybrid

coating processes are also becoming important. Deposition processes such as ALD,

high-power impulse magnetron sputtering, ﬁltered cathodic arc, and VPD are now being used

to deposit ﬁlms with properties not possible with conventional processes. These processes are

also being combined with each other and PVD processes to deposit novel thin ﬁlm structures.

Plasmas are also being used to enhance deposition processes. Another advantage of integrating

process technologies is that manufacturing costs are being reduced.

This edition of the handbook encompasses virtually all aspects of thin ﬁlm deposition

technology with highlights on advances in thin ﬁlm deposition technology and

characterization, and emerging technologies. This book complements other handbooks by

presenting a broad range of thin ﬁlm deposition and plasma technologies and characterization

techniques written by experts in the ﬁeld. All chapters have been updated when necessary, and

some deleted, and new chapters on ALD, cathodic arc deposition, sculpted thin ﬁlms, polymer

thin ﬁlms, and emerging technologies have been added. The chapter on Plasma Assisted Vapor

Deposition Processes in the second edition has been omitted in this edition because all

information is now covered in chapters on Plasmas in Deposition Processes (Chapter 2),

Evaporation Processes (Chapter 4), Sputter Deposition Processes (Chapter 5) and

Plasma-Enhanced Chemical Vapor Deposition (Chapter 9).

1.4 Deﬁnitions and Concepts

1.4.1 Surface Engineering

The deﬁnitions of thin and thick ﬁlms referenced in the second edition of this handbook have

crossed over and are outdated. No attempt will be made to differentiate between these two

Deposition Technologies 7

types of ﬁlms in this edition. The interested reader is therefore directed to the second edition

for further details [10]. Thin ﬁlms are now absorbed into the broad subject area of Surface

Engineering. Surface engineering encompasses the modiﬁcation of a surface by application of

a thin ﬁlm, plasma enhancement, ion bombardment, self-assembly, nanomachining, chemical

treatment, or other processes. Surface engineering techniques are now being used in virtually

every area of technology, including automotive, aerospace, missile, power, electronic,

biomedical, textile, petroleum, petrochemical, chemical, steel, power, cement, machine tools,

and construction industries. They are being used to develop a wide range of advanced

functional properties, including physical, chemical, electrical, electronic, magnetic,

mechanical, wear-resistant, and corrosion-resistant properties at the required substrate

surfaces. Almost all types of materials, including metals, ceramics, polymers, and composites,

can be deposited onto similar or dissimilar materials. It is also possible to form coatings of

advanced materials (e.g. met glass, polymers, superlattices, photocatalysts), graded deposits,

metamaterials, multicomponent deposits, etc.

Thin ﬁlm coatings are used to modify the physical and chemical properties and morphology of

a surface or substrate, which makes them a broad subset of surface engineering. A thin ﬁlm

can consist of one homogeneous composition, crystalline phase composition and

microstructure, or have an inhomogeneous multilayer or composite structure. The structure of

the multilayer can be periodic, have a set pattern or be entirely random. Examples of periodic

structures are optical multilayer coatings, rugate ﬁlters, superlattices, and nanolaminates.

Nanocomposites can be random or periodic in nature. Figure 1.1 shows the progression of the

dimensionality of thin ﬁlms to zero dimensions (quantum dots). The three-dimensional (3D)

ﬁlm is homogeneous in composition and crystalline structure, with thickness greater than

∼ 20 nm. Superlattices, quantum wells and nanolaminates are 2D ﬁlms consisting of hundreds

to thousands of periodic compositions with the thickness of each layer in the range 1–10 nm.

Total thickness of this structure can be as large as 20 ␮m. The quantum wire is a 1D structure

with arbitrary length and thickness between 1 and 10 nm. Nanotubes fall into this category.

The quantum dot is a 0D quantum well with width and thickness between 1 and 3 nm.

Figure 1.1: Progression of the dimensionality of thin ﬁlm structures.

8 Chapter 1

Substrate preparation is critical and the surface morphology and composition of a substrate

can also be modiﬁed by diffusion, plasma treatment, self-assembly, chemical etch, and reactive

heat treatment. The resulting surface will inﬂuence the properties, structure, adhesion, and

surface texture of a thin ﬁlm. For example, ion or gas nitriding hardens the surface of stainless

steel and signiﬁcantly improves the performance of tribological coatings deposited onto the

surface.

It is informative to list the steps in the formation of a deposit. The three basic steps are [10]:

1. synthesis or creation of the depositing species

2. transport from source to substrate

3. deposition onto the substrate and subsequent ﬁlm growth.

These steps can be completely separated from each other or can be superimposed on each

other depending on the process under consideration. It is important to note that if, in a given

process, these steps can be individually varied and controlled, a much greater degree of

ﬂexibility compared to one in which these steps are not independently variable will result. This

is analogous to the degrees of freedom in Gibbs’ phase rule. For example, consider the

deposition of tungsten by a chemical vapor deposition (CVD) process from WF

and H

. The

reaction is deﬁned as

(vapor) + 3H

(gas)

(heated substrate)

−−−−−−−−→ W(deposit) + 6HF(gas)

The rate of deposition is controlled by substrate temperature; at high substrate temperature, the

deposition rate is high and the structure consists of large columnar grains. This may not be the

desired structure. However, if tungsten is deposited by evaporation of pure tungsten, the

deposition rate is essentially independent of substrate temperature so that the process can have

a high deposition rate and a more desirable microstructure. Alternatively, a CVD process may

be chosen over evaporation because of considerations of throwing power (ability to coat

irregularly shaped objects) since high vacuum evaporation is basically a line-of-sight process.

1.5 Physical Vapor Deposition Process Terminology

PVD processes encompass a wide range of vapor-phase technologies, and is a general term

used to describe any of a variety of methods to deposit thin solid ﬁlms by the condensation of a

vaporized form of the solid material onto various surfaces. PVD involves physical ejection of

material as atoms or molecules and condensation and nucleation of these atoms onto a

substrate. The vapor-phase material can consist of ions or plasma and is often chemically

reacted with gases introduced into the vapor, called reactive deposition, to form new

compounds. PVD processes include:

Deposition Technologies 9



thermal evaporation



electron beam (e-beam) evaporation and reactive electron beam evaporation



sputtering (planar magnetron, cylindrical magnetron, dual magnetron, high-power

pulsed magnetron, unbalanced magnetron, closed ﬁeld magnetron, ion beam

sputtering, diode, triode) and reactive sputtering



ﬁltered and unﬁltered cathodic arc deposition (non-reactive and reactive)



ion plating



pulsed laser deposition.

Variants on these processes are:



bias sputtering



ion-assisted deposition



GLAD



hybrid processes.

Hybrid processes combine the best attributes of each PVD and/or CVD process. Among the

combinations are



magnetron sputtering and e-beam evaporation



magnetron sputtering and ﬁltered cathodic arc deposition



e-beam evaporation and ﬁltered cathodic arc deposition



VPD, polymer ﬂash evaporation and magnetron sputtering/evaporation.

The basic PVD processes are evaporation, sputtering and ion plating. Materials are physically

created in the vapor phase by energetic bombardment of a source (e.g. sputtering target) and

subsequent ejection of material. A number of specialized PVD processes have been derived

from these processes and extensively used, including reactive ion plating, reactive sputtering,

unbalanced magnetron sputtering, HPPMS, and ﬁltered cathodic arc deposition. There is also

the possibility of confusion since many of these processes can be covered by more than one

name. For example, if the activated reactive evaporation (ARE) process is used with a

negative bias on the substrate, it is very often called reactive ion plating. Simple evaporation

using a radio-frequency (RF) heated crucible is often called gasless ion plating. There is even

more confusion over the ion plating process (Chapter 6), where the material is converted from

a solid phase to the vapor phase using a number of processes involving thermal energy

(evaporation), momentum transfer (sputtering), and electrical energy (cathodic arc), or

10 Chapter 1

supplied as vapor (similar to CVD processes). Logically, one could deﬁne all PVD processes

as ion plating, but this ignores the most important aspect of ion plating: modiﬁcation of the

microstructure and composition of the deposit caused by ion bombardment of the deposit

resulting from bias applied to the substrate.

To resolve this dilemma, it is proposed that we consider all of these basic processes and their

variants as PVD processes and describe them in terms of three steps in the formation of a

deposit as described in the previous section. Every PVD process can therefore be deﬁned by

three basic steps:

1. Creation of vapor-phase species. Material can be converted to a vapor phase by

evaporation, sputtering, or chemical vapors and gases.

2. Transport from source to substrate. Transport of vapor species from the source to the

substrate can occur under line-of-sight, thermal scattering, or molecular ﬂow conditions

(i.e. without collisions between atoms and molecules). Alternatively, if the partial pressure

of the metal vapor and/or gas species in the vapor state is high enough for some of these

species to be ionized (by creating a plasma), there will be a large number of collisions in

the vapor phase during transport to the substrate.

3. Film growth on the substrate. Once the atoms or molecules are deposited, the ﬁlm

nucleates on the substrate and grows by a number of processes. Microstructure and

composition of the ﬁlm can be modiﬁed by bombardment of the growing ﬁlm by ions from

the vapor phase, resulting in sputtering and recondensation of the ﬁlm atoms and enhanced

surface mobility of the atoms in the near surface and surface of the ﬁlm.

Every PVD process can be usefully described and understood in term of these three steps. The

reader is referred to Chapter 11 for a more comprehensive treatment.

1.6 Classiﬁcation of Coating Processes

Because of the overlap in process mechanisms and the formation of hybrid deposition

processes, no one scheme can accurately deﬁne and classify all coating processes. While

several attempts have been made to classify deposition process, including the second edition of

this handbook, we take a much simpler and basic classiﬁcation scheme. Refer to Appendix 1.1

for a full treatment of classiﬁcation schemes described in the second edition. Four general

categories of thin ﬁlm deposition have emerged over the past few decades: atomistic growth,

particulate deposition, bulk coating, and surface modiﬁcation. The best summary to date is still

given by Bunshaw and Mattox [11], with the addition of advanced techniques, shown in

Table 1.1.

In atomistic processes, atoms form a ﬁlm by condensing onto a substrate and migrating to

nucleation and growth sites. Adatoms often do not occupy their lowest possible energy