Table Of ContentSputtering Materials
for VLSI and Thin
Film Devices
Sputtering Materials
for VLSI and Thin
Film Devices
Jaydeep Sarkar
AMSTERDAM(cid:129)BOSTON(cid:129)HEIDELBERG(cid:129)LONDON
NEWYORK(cid:129)OXFORD(cid:129)PARIS(cid:129)SANDIEGO
SANFRANCISCO(cid:129)SINGAPORE(cid:129)SYDNEY(cid:129)TOKYO
WilliamAndrewisanimprintofElsevier
WilliamAndrewisanimprintofElsevier
225WymanStreet,Waltham,02451,USA
TheBoulevard,LangfordLane,Kidlington,OxfordOX51GB,UK
Firstedition2014
Copyrightr2014ElsevierInc.Allrightsreserved
Nopartofthispublicationmaybereproducedortransmittedinanyformorbyanymeans,electronicor
mechanical,includingphotocopying,recording,oranyinformationstorageandretrievalsystem,without
permissioninwritingfromthepublisher.Detailsonhowtoseekpermission,furtherinformationaboutthe
Publisher’spermissionspoliciesandarrangementswithorganizationssuchastheCopyrightClearanceCenter
andtheCopyrightLicensingAgency,canbefoundatourwebsite:www.elsevier.com/permissions.
ThisbookandtheindividualcontributionscontainedinitareprotectedundercopyrightbythePublisher
(otherthanasmaybenotedherein).
Notice
Knowledgeandbestpracticeinthisfieldareconstantlychanging.Asnewresearchandexperiencebroaden
ourunderstanding,changesinresearchmethods,professionalpractices,ormedicaltreatmentmaybecome
necessary.
Practitionersandresearchersmustalwaysrelyontheirownexperienceandknowledgeinevaluatingandusing
anyinformation,methods,compounds,orexperimentsdescribedherein.Inusingsuchinformationormethods
theyshouldbemindfuloftheirownsafetyandthesafetyofothers,includingpartiesforwhomtheyhavea
professionalresponsibility.
Tothefullestextentofthelaw,neitherthePublishernortheauthors,contributors,oreditors,assumeany
liabilityforanyinjuryand/ordamagetopersonsorpropertyasamatterofproductsliability,negligenceor
otherwise,orfromanyuseoperationofanymethods,products,instructions,orideascontainedinthematerial
herein.
LibraryofCongressCataloging-in-PublicationData
AcatalogrecordforthisbookisavailablefromtheLibraryofCongress
BritishLibraryCataloguinginPublicationData
AcataloguerecordforthisbookisavailablefromtheBritishLibrary
ISBN:978-0-8155-1593-7
ForinformationonallElsevierpublications
visitourwebsiteatelsevierdirect.com
PrintedandboundintheUSA
14 15 16 17 10 9 8 7 6 5 4 3 2 1
Preface
Thehighesteducationisthatwhichdoesnotmerely
giveusinformationbutmakesourlife
inharmonywithallexistence.
RabindranathTagore
Sputtering is one of the processes for depositing thin films on suitable substrates. The funda-
mentals of sputtering methods are well understood and related topics have been reviewed exten-
sively in journal articles and book chapters. The source material for sputter deposition of thin films
is called the sputtering target, which can be made using conventional metallurgical processes or
using special processing techniques depending on the requirements of a particular application.
Sputtering Materials for VLSI and Thin Film Devices is aimed at correlating the physics of sputter-
ing, the characteristics of sputtering target, chamber design and thin film properties in an integrated
manner tounderstand technologically-important manufacturingprocesses.
The idea of writing this book in such an important inter-disciplinary area was conceived during
my long and close interaction with various industry personnel (technicians, process engineers,
scientists) and university researchers from multiple disciplines who did not have access to such a
book.Some elaborationis requiredtojustifythetitleofthebookwhich mayappear unconventional
in some sense. The term sputtering materials has been used to encompass both technologically-
important materials for sputtering in the form of targets and sputter deposited thin films to keep the
title of the book short, although in practice majority of the solid materials can be sputtered under
suitable conditions. The preparation of this book involved review of not only journal articles and
textbooks, but a large number of patents, advertisement materials and reports available in the open
literature. Attempts have been made to use a large number of references for further reading and, in
particular, readers from university setting are encouraged to read patents to appreciate commer-
cially-important innovations.
The content of the book can be divided into two sections. The first section (Chapters 1 to 3) has
been prepared for the readers from a range of disciplines (e.g. electrical, chemical, chemistry, phys-
ics)foraninsightintouseofsputteredfilmsinvariousdevices(e.g.semiconductors,displays,photo-
voltaic, data storage), the basics of sputtering and performance of sputtering targets in relation to
productivity. The second section (Chapters 4 to 8) has been prepared for readers who already have
backgroundknowledgeofsputterdepositionofthinfilms,materialsscienceprinciples,andareinter-
ested in the details of sputtering target manufacturing methods, sputtering behavior and thin film
propertiesspecifictosemiconductors,liquidcrystaldisplays,photovoltaicandmagneticdatastorage
applications. In Chapters 5 to 8, a general structure has been used, i.e. a description of the applica-
tions of sputtered thin films, sputtering target manufacturing methods (including flow charts),
sputteringbehavioroftargets(e.g.current(cid:1)voltagerelationship,depositionrate)andthinfilmprop-
erties (e.g. microstructure, stresses, electrical properties, in-film particles). While discussing these
topics, attemptshave beenmadetoinclude examplesfromtheactualcommercialprocessestohigh-
lighttheincreasedcomplexityoftheprocesseswiththegrowthofadvancedtechnologies.Inaddition
x Preface
topersonnelworkinginindustrysetting,universityresearcherswithadvancedknowledgeofsputter-
ing will also find discussion of such topics (e.g. attributes of target design, chamber design, target
microstructure,sputtersurfacecharacteristics,varioustroubleshootingissues)useful.
It is worthwhile to mention that the discussions of semiconductor and insulator materials in
Chapter 1 is not aimed at teaching the physics of it, but to emphasize the more common sputtering
of conducting materials in the light of less common sputter deposition of semiconductor and insu-
latingthinfilms.Also,thediscussionofdevicephysics,fundamentalsofthinfilmgrowthandcharac-
terization techniques are beyond the scope of this book. However, appendices on Thin film
properties, Crystallographic texture and Metallography of samples have been made available in this
book’scompanionwebsitefoundatbooksite.elsevier.com/9780815515937.Everybookhasitsweak-
ness and in this case limitations have to do with (a) more examples presented from cases involving
DC magnetron sputtering and semiconductor industry processes and (b) occasional use of results
fromtheworkofasingleresearcher (cid:1)eitherbecauseofthegoodqualityofthedataormorerecent
work or unavailability of enough literature on a specific topic. I hope that all attempts of reducing
errors, omissions and inconsistencies in a book of this nature (600 pages with 566 illustrations) was
successful.Iwelcomeconstructivecommentsandsuggestiononthecontentofthebook.
I am indebted to my friends, colleagues and also to the management team of Praxair Inc. for
their encouragement and support during the preparation of the book. In particular, I would like to
thank Chi-Fung Lo, Professor Bikramjit Basu, Biswajit Choudhury and Samit Chakrabarty for their
help with literature survey. Thanks are due to Peter McDonald and John Portanova for sharing their
knowledge of commercial sputter tool operation and maintenance. I am grateful to Rajan Mathew
and Paul Gilman for reading the manuscript and making valuable suggestions. I would also like to
thank the publishing team, in particular Senior Publisher Matthew Deans of Elsevier and Melissa
Read, who have been constant source ofencouragement and assistance.
This book is dedicated to all my teachers and late Professor Sanjay K. Biswas, former Dean of
Engineering at the Indian Institute of Science, Bangalore for their contributions to my development
asa MaterialsScientist.
CHAPTER
1
Sputtering Targets and Sputtered
Films for the Microelectronic
Industry
1.1 Materials for microelectronics
1.1.1 Introduction
Themicroelectronicindustryarguablyusesawidevarietyofmaterialsintheformofsolid,liquid,gas
and gas plasma in microelectronic device components and for the processing of devices. Figure 1.1
showstheseelementsintheperiodictable.Choicesformaterialselectionaremadebasedontheappli-
cations [1]. With the exception of actinides (the bottom-most row) and a few other unstable and less
commonelements,mostoftheelementsareusedinmicroelectronicsindustry.Alargenumberofsuch
elements and their alloys are used in microelectronics devices in the form of thin films [2(cid:1)20].
Sputtering is one of the techniques for depositing such thin films in which atoms are ejected from a
sourcematerialbyusingenergeticparticlesinsideachamber[4,6,14].Inprinciple,themajorityofsolid
materialscanbesputteredundersuitableconditionstoformthinfilms.Chapter2reviewsvarioussput-
tering methods for depositing thin films and device technology driven evolution of sputtering equip-
ment (also known as sputtering tools). Sputtering can also be used to remove a thin layer of material
fromasubstrateandthisapplicationofsputteringisoutofthescopeofthisbook.
The primary focus of this book is to discuss metallurgy and material science of sputtering mate-
rials that are technologically important. These include both: (a) bulk source materials, known as
sputtering targets, and (b) deposited thin films for microelectronic applications. Sputtering target
can be a conductor, semiconductor or an insulator. Conductivity is one of the key parameters that
contrast these three types of solids. As one would expect, a small section of a chapter of this nature
has limited scope to cover this subject. Hence, the following sections will only summarize the gen-
eral characteristics of conduction in conductors, semiconductors and insulators. Afterwards, discus-
sion has been shaped in such a way that readers eventually arrive at those technologically
important materials that are sputtered to form thin films for making commercial device such as
integrated circuits (ICs), displays, magnetic and optical data storage systems, photovoltaic solar cell
and so forth [2(cid:1)20]. As discussion progresses, readers will note that sputtering is primarily used to
deposit metal-based conductors and not so much for semiconductor and insulators (with some excep-
tions).Itisimportantforreaderstonotethat,inmanycases,bythetimethinfilmsaresputterdeposited
onasubstrate,asignificantamountofinvestmenthasalreadybeendoneforsubstratepreparation.Asa
result, any failure at the sputter deposition stage will reduce the overall yield and productivity of the
J.Sarkar:SputteringMaterialsforVLSIandThinFilmDevices.DOI:http://dx.doi.org/10.1016/B978-0-8155-1593-7.00001-1 1
©2014ElsevierInc.Allrightsreserved.
2 CHAPTER 1 Sputtering Targets and Sputtered Films for Microelectronics
IA VIIIA
Dopant Data storage Superconductors
H IIA IIIA IVA VA VIA VIIA He
Semiconductor Processing
Li Be B C N O F Ne
Contact Insulators
Na Mg IIIB IVB VB VIB VIIB VIII VIII VIII IB IIB Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra Ac
Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Lanthanide
Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lw
Actinide
FIGURE1.1
Periodictableshowingelementsandtheirapplicationsinmicroelectronicindustry[1].
process. For example, in a complementary metal oxide semiconductor (CMOS) chip manufacturing
process, by the time a cobalt or nickel film is sputter deposited prior to the silicide formation, active
regionshavealreadybeenformedonthesiliconwaferwithsignificantinvestment.
1.1.1.1 Electrical conductivity
The most common approach to distinguishing conductors, semiconductors and insulators for micro-
electronic applications is based on their electrical conductivity (reciprocal of resistivity) values.
Electrical conductivity (σ)of amaterialis given bythe equation
σ5n:q:μ (1.1)
where n is the number of carriers, q is the charge and μ is the mobility of the carriers. While con-
ductorshavehighelectricalconductivity(104(cid:1)106ohm21cm21)insulatorshavelowelectricalcon-
ductivity (#10215ohm21cm21) and semiconductors have intermediate electrical conductivity
(1026(cid:1)103ohm21cm21).These boundariesare notrigid and acertain degreeofoverlap ispossible
between these sets of values. In general, the electrical conductivity of the conductors shows a slight
but gradual drop with increasing temperature. This is because n is large for conductors and essen-
tially remains unchanged with temperature. Similarly, q remains constant but the mobility term μ
decreases slightly with increasing temperature. The mobility of the carriers decreases because of
the collision between moving electrons and the phonons (lattice vibrations). Silver, copper and gold
are among the best electrical conductors. Transition metals such as iron and nickel are not as good
conductors as above metals. However, for semiconductors and the insulators, n increases dramati-
cally with temperature unlike conductors which outweighs the slight decrease in the mobility term.
As a result, electrical conductivity ofsemiconductors increases rapidly with temperature.
1.1 Materials for microelectronics 3
Table1.1 ElectricalConductivityofSelectedBulkMaterials
Materials Conductivity(Ohm21cm21)
Metals
Silver(Ag) 6.803105
Copper(Cu) 5.983105
Gold(Au) 4.263105
Aluminum(Al) 3.773105
Nickel(Ni) 1.463105
Iron(Fe) 1.003105
Semiconductors
Silicon(Si) 5.0031026
Germanium(Ge) 2.0031022
Insulators
Silicaglass 10217
Alumina(Al O ) 10214
2 3
Siliconcarbide(SiC) 1021to1022
Boronnitride(BN) 10213
Table 1.1liststhe electrical conductivityofsomeofthe commonmaterialsat roomtemperature.
Figure1.2showsthevariationofelectricalconductivityinaluminumandgermaniumwithtempera-
ture. In fact, insulators are extreme state semiconductors when n is small at normal temperature. In
the following sections, a cursory review of the principles of conduction in solids (conductors, semi-
conductors and insulators) has been presented prior to the discussion of various devices that inte-
grate such materials. Finally, the discussion leads to those conductors, semiconductors and
insulators that are sputtered toform films for device fabrication.
The electronic behavior of solids can be described in terms of band theory or zone theory. The
band theory of solids is well supported by the spectroscopic data and the two independent theoreti-
cal approaches, namely the chemical approach and physical approach. In the chemical approach to
band theory, molecular orbital theory is applied to small and finite molecules and this treatment is
extended to infinite and three-dimensional structures. The physical approach to band theory consid-
ers the energy and the wavelength of electrons in a solid. From either theory, one obtains a model
with bands of energy levels for the valence band (the outermost energy band of an atom that is
fully or partially filled) electrons and conduction band (the band that is above the valence band and
is emptyat 0K) electrons.
Figure 1.3 shows such bands and forbidden energy regions known asband gap. Metals are good
examplesof conductorsthat have partially filled energy bands. As showninFigure1.3(a), inacon-
ductor, conduction and valence bands overlap. A small electric field is adequate to induce conduc-
tion or current flow. Semiconductors typically have small band gap (,3.0eV). As shown in
Figure 1.3(b), the most popular semiconductor silicon has band gap energy of 1.11eV at 300(cid:3)K.
4 CHAPTER 1 Sputtering Targets and Sputtered Films for Microelectronics
106
Aluminum
–1) 105 Reducing
m
c mobility
1.
–
m 100
h
O
y (
ctivit 10.0 Germanium
u
d
n
o
al c 1.00 Increasing charge
c carriers
ctri
Ele 0.10
0.01
0 100 200 300 400
Temperature (°C)
FIGURE1.2
Variationofelectricalconductivityinaluminum(Al)andgermanium(Ge)withtemperature.
FIGURE1.3
Characterizationofconductor,semiconductorandinsulatingmaterialsusingbandgap.Solidswithbandgap
between0.5and3.0eVareknownassemiconductors.HereSiisshownasarepresentativesemiconductor.
Materialswithmorethan2eVbandgapareknownasinsulators.
1.1 Materials for microelectronics 5
This is 1.21eV at 0(cid:3)K. Energies ofthis magnitude cannot usually beachieved from applied electric
field to induce conduction. Table 1.2 lists band gap energy values of various industrially important
semiconductors. Insulators have very wide band gap (.3.0eV), as shown in Figure 1.3(c). Energy
of this magnitude cannot be obtained from an external electric field. In-depth discussions of this
subject can be found in books devoted to solid state physics [21,22]. In the following sections,
some important properties of conductors, semiconductors and insulators and methods of thin film
depositionfor microelectronic applicationsare summarized.
Table1.2 BandGapWidthandtheNatureofSemiconductorMaterialsat300K
Semiconductor BandGap(eV) Type
Element
Silicon(Si) 1.11 Indirect
Germanium(Ge) 0.66
III-VCompounds
Galliumarsenide(GaAs) 1.43 Direct
Galliumphosphide(GaP) 2.26 Indirect
GaSb 0.72 Direct
InAs 0.36 Direct
Indiumphosphide(InP) 1.35 Direct
InSb 0.17 Direct
AlAs 2.16 Indirect
AlSb 1.58 Indirect
II-VICompounds
Cadmiumsulfide(CdS) 2.42 Direct
Cadmiumselenide 1.7 Direct
Cadmiumtelluride(CdTe) 1.49 Direct
ZnS 3.68 Direct
ZnSe 2.7 Direct
ZnTe 2.2 Direct
Copperindiumdiselenide 1.01 Direct
(CuInSe ,CIS)
2
Copperindiumgalliumdiselenide 1.0(cid:1)1.7 Direct
(CuIn Ga xSe ,x:0(cid:1)1,CIGS)
x 1- 2
IV-VICompounds
PbS 0.41 Direct
PbSe 0.27 Direct
PbTe 0.31 Direct
SnTe 0.18 Direct
Amorphousmaterial
Amorphoussilicon(a-Si) 1.6 Direct
