Microfabrication for Industrial Applications

295 Pages·2011·10.975 MB·English

by  Regina Luttge (Auth.)

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CHAPTER
1
Introduction
CHAPTER CONTENTS
1.1 PhilosophyofMicro/Nanofabrication ................................................ 1
1.2 TheIndustry–ScienceDualism........................................................ 5
1.3 IndustrialApplications................................................................ 8
1.4 PurposeandOrganizationofthisBook............................................... 9
References................................................................................... 11
1.1 PHILOSOPHY OF MICRO/NANOFABRICATION
Microsystemstechnology(MST)focusesontheminiaturizationofengineer-
ing systems to accommodate design specifications of small space, light
weight and enhanced portability. An additional advantage of such portable
systems is their wide-scale utility in distributed transducer networks. The
importance of MST lies, for a large part, in the economical and technical
developmentofinnovativesystemsthatitmakespossible.Thefieldofmicro-
fabrication technology has been established for approximately 50 years and
thus it is a relatively young discipline. The first object of miniaturization
wastheintegratedtransistor,theworkhorsedevicebymeansofwhichmajor
new markets were created. For example, information and communication
technology(ICT)reliesonthetechnicalprinciplesofminiaturizationbyinte-
gratingmoreandmoreelectronicfunctionalelementsintothesamerestricted
area of a silicon die, the chip. Complementing this chip with a large data
storage capacity that has fast read/write access and a high-definition display
has given rise to systems which have penetrated all layers of personal and
professional human lives. These types of devices are a smart combination
of millions of transistors on a single chip, produced on dedicated microelec-
tronic production lines. Transferring technological innovation into a robust
MicrofabricationforIndustrialApplications.DOI:10.1016/B978-0-8155-1582-1.00001-0 1
(cid:13)c 2011ElsevierInc.Allrightsreserved.
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2 CHAPTER 1 Introduction
andefficientproductionandmarketingprocessisthesecrettoprovidingmore
andmorecomputingpower.Theaccurateline-widthcontrolduringmanufac-
turing these devices, at the micrometer or subsequently the nanometer level,
is the main reason for giving this pool of associated fields concerned with
the design, fabrication, assembly and testing the names micro- and nano-
technology,respectively.Theverynatureofthesenewdisciplineswithinthe
engineering sciences originate from the principles of miniaturization, which
was based on having an increasing number of the same circuitized compo-
nents available on one die. Eventually, further and further integration allows
novel functions that were originally unforeseen by conventional machining
techniques.Oneexampleofsuchanovelmicrofabricatedproduct,combining
optical and electrical functions with a mechanical function at a small foot-
print,isanintegratedopticallightmodulator,whichwesimplycallabeamer
ineverydaylifeandwhichweconsideracommoditytoday.
Thetechnicalmethodswhichareusedtomanufacturemicroproductsare
describedcollectivelyasmicrofabricationtechniques.Theirefficiencyisdue
to the definition of patterns in a masking layer and the subsequent parallel
transfer of these accurate patterns into a functional material. During pattern
transfer,thepatternisthereforecopiedfromamask,whichcarriesthedesign
features, onto or into a work piece. This work piece can be defined within a
thinfilmorastackoffilms,orthebulkofthematerial,whichisalsousedas
thehandlingplatformduringsuchasequenceofprocesssteps.Thesetwodis-
tinctapproachesarecalledsurfaceandbulkmicromachining.Usually,pattern
transferisaprocessofatleasttwomainsteps.Thefirststepinvolvesthegen-
eration of the pattern, either directly by a serial write process, or by parallel
patterning using an exposure through a master into a layer (usually a pho-
tosensitive polymer). This layer then acts as a masking layer for the second
main step: shaping the functional material by processes such as deposition,
etching or implantation. Specialists in the field generally call this layer a
resist. Other modifications of the accessible areas of the work piece are of
coursealsopossible.
The continuous implementation and definition of novel fabrication tech-
niquesformodifyingandtransferringthepatternsiskeytoinnovationinthe
marketplace.ItisthisfieldofresearchanddevelopmentthatIwouldliketo
addressinthisbook.
Lithographicprocesseshavebeendescribedmanytimes.Inbrief,thecare-
ful definition of process steps brought about the initial success of industrial
lithography, specifically photolithography utilizing a mercury lamp with an
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1.1 Philosophy of Micro/Nanofabrication 3
intensitypeakatawavelengthof365nm(UV-light)fortransferringtheinfor-
mation contained in the master into the resist. An average process sequence
for a single device may contain 20–30 individual steps, some of which are
consideredtobethemainstepsoftheprocess.Thismainstepreceivesgreater
attentionduringthedevelopmentofaprocessdocument.However,anysetor
combinationofthesestepsmayleadtoanewtechnology.
MSTisconsideredaslessconservativethanintegratedcircuittechnology
(microelectronics), because MST processes are reshaped by prototyping or
thefabricationofdemonstrationdevicesinsteadoffocussingonhigh-volume
production. For microelectronics it is important that each process step is
optimizedforthrough-putandrobustness(achievingahighyield).Costsare
reducedinmicroelectronicsmanufactureduetotheabilitytocopyacomplex
design in parallel from a special information carrier (photomask) hundreds
andthousandsoftimes,withthesamehighpatternfidelity,bysimpleshadow
optics(exposurethroughamask).Thismanufacturingstrategyiscalledbatch
processing and is also an essential aspect of the philosophy of micro- and
nanofabrication. An overview of the procedure which establishes a societal
need, develops the technology and realizes an MST device is depicted in
Figure1.1.
1. Business intelligence / identification of need 3. Front-end process technology
Mask-set (one mask per process layer)
Multiple cycles using one mask per layer
Substrate Thin-film, Lithography Pattern transfer
resist, etc.
deposition
2. Modeling and design 4. Back-end process technology
• Concept device
(cid:129) Analysis
(cid:129) Process Wafer-level inspection Dicing Individual die Die-level packaging
Documentation Hybrid assembly Device-level Final test
packaging
FIGURE1.1
Schematicoftheprocessfromtheindentificationofaneedtothedevelopmentof
batch-processtechnology.
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4 CHAPTER 1 Introduction
Nanofabricationisalogicalsteptothefurtherdownscalingofthephysical
sizeofcomponentsandfunctionalelements,oftenusingthesamemachinery
as microfabrication. Nanotechnology as a new discipline, however, should
not be considered as simply an extension of existing techniques to smaller
dimensions,butastheintegrationofnovelfunctionsbasedonanunderstand-
ing of interactions at a scale of less than 100 nm. Alongside this, bottom-up
manufacturing has been introduced. This approach or the previously used
top-down method can be chosen, depending on the nature of the engineer-
ing problem at hand. Selection of appropriate methodology should also take
intoaccount:
(i) performance-basedcriteriarelatedtothefunctioningofthesystem,
(ii) affordabilityoffabricationduringthedemonstrationphase,
(iii) cost-to-performance criteria for efficient manufacture and sustainable
resourcesduringaproduct’smanufacturingcycle.
Thisisnotatrivialtaskforscientistsandproductdevelopers,particularly
sinceallthreeofthesegroupsofcriterianeedtobesatisfiedsimultaneously.
Anotheraspectofthephilosophyofmicro-andnanofabricationisthecon-
cept of integration levels. The terms hybrid and monolithic integration are
used, with fully monolithically manufactured systems being the most inte-
grated.Fromanindustrialpointofview,however,thelatterisnotnecessarily
the most favourable. It is the requirements of a specific product in a market
placethatdeterminetheoptimalapproach.
Oneofthekeyinnovationsduringthelastfivedecadeshasbeenthecon-
trolled deposition of thin films. Solvent-based liquid, vapour or gas phase
depositionprocessesarenowreadilyavailableinthemicroelectronicsindus-
try. Thin-film technology is also an important driver for the definition of
materials at the nanoscale. Tuning a material’s properties allows the cre-
ation of novel applications. An introduction to nanofabrication is presented
in Chapter 4 of this book. Presenting emerging nanofabrication techniques
in the context of this book will allow us to draw additional attention to the
paradigm shift that is now occurring in the world of production processes.
Chapter4drawsspecificattentiontothechallengesofthepositionalassembly
ofnanoscalebuildingblocks.
Unfortunately, at this moment it is difficult to give a clear definition of
either micro- or nanotechnology. Thin-film technologies, for example, are
already difficult to put into one category or the other, so it is important to
clarify what one means when using the terms micro- or nanofabrication. In
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1.2 The Industry–Science Dualism 5
thiscontextwedistinguishnanofabricationfrommicrofabricationtechniques
ifthecontroloflateraldimensionscanberealizedpreciselyenoughtoresult
infeaturesatthesub-micrometerscale.Withinthisframework,thestructure
height-to-linewidthratio(aspectratio)becomesaspecialmeasureofprocess
performanceinmicrosystems’productdevelopment.
As far as MST is concerned, it is easier to give a definition of the field
ofworkinsteadofdefiningwhatactuallymicro-ornanotechnologyis.MST
leadstosystems-on-chipdevices,includingtheirperipheralsystems,contain-
ingelectronic,sensingandactuatingfunctionalitypackagedwithinavolume
of a few cubic centimeters. Hence, specifically in the USA, this field is his-
torically referred to by the name microelectromechanical systems (MEMS)
technology. Sometimes the integrated electronic circuits, sensors and actu-
ators are referred to as the brains, eyes and arms of artificial systems, an
expression that has been used by Huff in his tutorial report on MEMS tech-
nology [1]. Optical switching and attenuation components are another large
group of devices which benefit from the research and development into
micro- and nanofabrication principles. The manufacture of microsystems
involves a variety of precision engineering techniques, combined with sili-
con surface micromachining techniques. The first group of techniques (e.g.,
dicing, laser cutting, lamination, thermal compression bonding) enables the
separationorassemblyofcomponents,whilemicromachiningisdedicatedto
theintegrationofthethreesub-functionsfromtheelectrical,mechanicaland
opticaldomainatthemicroscale.
With respect to the choice of materials, silicon is the most abundantly
used material in miniaturization, although fabrication techniques should be
evaluatedforsubstratematerialsotherthansilicon.Asystematicoverviewof
basicmicrofabricationtechniquesisgiveninChapter2.
Thenextthreesectionswillgiveanoverviewofthecontentofthisbook.
I also wish to present some guidelines on how this book may be used edu-
cationally as part of a course concerned with micro- and nanofabrication
technologyanditsimpactonindustrialapplications.
1.2 THE INDUSTRY–SCIENCE DUALISM
It is interesting that today, in the year 2011, we talk about knowledge
societies. It was not long ago that productivity and industrialization were
considered to be the key to a better health and education system, and hence
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6 CHAPTER 1 Introduction
a better life. In this section, we would like to discuss briefly the process
behindtheaccumulationofknowledge,whichisimportantforfeedingexist-
ing industries such as raw materials industries (e.g., mining and farming),
manufacturing,orservicesindustries(dealingwithlaw,medicineorthedistri-
butionofgoods).Recentlyanewtypeofindustryhasbeenaddedtothethree
existing sectors: the knowledge industry, which deals with research, design
and development. Knowledge creation is a skill one can teach. Children,
teenagers and young adults all around the world are taught that knowledge
is a driving force for building their careers. Adults are the workforce for the
many successful businesses, including multinational corporations and gov-
ernments. Industrial organizations cannot exist without mining accumulated
knowledgeortheapplicationofbusinessintelligence.
Incontrastwithanacademic(pre-competitive)knowledgecreation,how-
ever, industry points towards the economic valuation of knowledge: knowl-
edge had to become a marketable product. Hence, it became a common
practicetoapplyforpatents.
A patent grants the owner the exclusive right to commercialize products
or services. The idea or process being protected by a patent must contain an
innovativestep,andthedisclosedinformationmustbeindustriallyapplicable
whenthepatentapplicationisfiled.Ofcourse,ifsuchanideaisdiscloseditis
already branded as intellectual property (IP), but a patent or trademark must
befirstregisteredandgrantedbeforetheknowledgecanbeeffectivelytraded
on the market. This is a concept inherently different from science as an aca-
demicoccupation.Therightthatonereceivestocommercializethedisclosed
knowledgeisanon-tangibleassetofabusiness,whichcanbeveryvaluable.
Withrespecttothedevelopmentofmicro-andnanofabricationtechniques
for industrial applications, it is important that we understand how IP is first
generatedandsecondlytraded.Thelatterisimportantifonewantstosellthe
accumulatedknowledgethroughtechnologytransfer.Not-for-profitorganiza-
tionssuchasuniversitiescanbeimportanttradingpartnersinthisknowledge
industry. This approach may be easier understood if one realizes that a mar-
ketable, tangible product does not normally consist of only one invention.
Several, often at different developmental stages, have to be combined to
be able to form one product. Obviously, higher complexity will increase
the number of components required, which means that the involvement of
other market players becomes increasingly important for the effective real-
ization of the product. For this type of development, a relatively new term
has been introduced to business models: the concept of open innovation.
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1.2 The Industry–Science Dualism 7
Althoughmanycompanieswillstillbeabletodrawgoodprofitsfromclosed
innovation, the complexity of systems in the modern world asks for more
flexibility.
If you are not familiar with IP rights and their generation, the website of
theWorldIntellectualPropertyOrganization(WIPO)isagoodstartingpoint
for finding out, and also for continuous updates on the procedures [2]. For
details of the patent application process, and the legal rights attached to a
patent, other sources are better, e.g., for Europe it may be helpful to check
specific guidelines concerned with European patents [3, 4]. There are also
guidelinesonthistopicforothercountriesandregions.Rememberthatordi-
nary people, as well as large organizations can apply for a patent, and many
inventorsusethisinstrumenttopassontheirknowledgetoavoidtheneedfor
large investments. Large investments of the order of millions of US Dollars
are very common for the initial steps of product development and scientific
publicationofthefindingmaycompromisetheinventor’scommercialrights
toit,butapatentcanbeappliedforandmaintainedthroughvariousstagesof
this development process without significant costs. Also, inventors in small
and medium-sized enterprises as well as researchers in the academic com-
munity can create businesses in this knowledge industry, by making use of
patent protection as a business instrument by first attaining the commercial
rightstotheirIPandthensellingittocreatetheirownknowledge-generating
businesses.Iffinanciallysustainedwiththeappropriateauthorities,apatentis
grantedfor20years,whichintoday’sfastlife-styleisprobablyareasonable
headstartoverpossiblecompetitors.
How is IP initially generated? Of course, one immediately wishes to say:
IP is generated by good ideas! However, that is not sufficient according to
the description above, which suggests a patent is only granted if there is an
inventive and an innovative step as well as an industrial application, which
means, that quickly the inventor finds him- or herself in the area of technol-
ogy. In the field of technology, the design plays a major role. Replacing the
word technique in the field of technology with design, we can also formu-
lateaguidelineforexercisingtheknowledgepresentedinthisbookbyafree
translationofaDutchquotetakenfromvandenKroonenberglecturenotesin
1998:
“Designistheprocess,whichisdirectedtocombinetheknowledgeoftheexisting
lawsofnatureinsuchawaythatitincreasestheefficacyofcollectionofknowledge
in relation to another matter on the reason of need, demands and wishes of a
humanbeing.”[6]
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8 CHAPTER 1 Introduction
How is a human being, an inventor, actually collecting natural laws to
realize the process of knowledge generation, and how is an inventor making
useofitinadesignprocess?Theguideline,unfortunately,doesnotgivedirect
answerstothesequestions.Thisbookisdedicatedtothecomplexityofsuch
designprocessesintheuseofmicrofabricationtechniquesinindustry.
1.3 INDUSTRIAL APPLICATIONS
Sinceknowledgefromtechnologymayhavemultipleapplicationsacrosssev-
eral different working fields the term “industrial applications” is specifically
chosentounderlinethepotentialofmicrofabricationforuseinotherresearch
fieldsandmarketablesolutions.Fromabusinesspointofviewthesemultiple
applicationswouldbefurtheredbylicensingagreements,whichwouldallow
the technology to be used commercially for a specific purpose by different
industrialplayers.
To be able to clarify the definition of industrial players one needs to
have a closer look at the creation of markets. Based on a simple definition
in marketing we can call the total population “a market”, but the “poten-
tial market” is the portion of the total population who have an interest in
acquiring the product or service under consideration. In this definition the
availablemarketcoversthesub-populationthathassufficientmoneytoafford
theproduct.Thelattermayshrinktoaqualifiedmarket,whichrepresentsthe
sub-sub-populationthatiseligibletobuytheproduct.Thisqualifiedavailable
market may subsequently be reduced to the target market, which is the mar-
ketsharethatthecompanyhasdecidedtoservewithitsproduct(sub-sub-sub
population). Finally, the penetrated market remains, which is the sub-sub-
sub-sub-population of those in the market who have actually purchased the
product. This final sub-sub-sub-sub-population is difficult to capture at the
veryearlystagesofaproductdevelopmentcycle,particularlyforanoveland
complex technology, which has yet to prove its worth. This is often referred
toasthetechnologygapbetweenscienceandindustry.Onewaytoapproach
thisisthereductionofrisksbydevelopingaproductoverseveralstagesthat
deliveraproof-of-conceptforeachstage.Earlystageinvestmentsintoarising
technologystar,obviously,maypromiseveryattractiveprofits.
Figure1.2 conceptuallypresentsthethree possiblemarketdrivers, which
divide the market population into three sub-populations (markets) that are
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1.4 Purpose and Organization of this Book 9
Need
Market 1 No competing products
Wish Competing products but
Market 2
with complementary functions
Desire Market 3 Competing products with
identical functionality
FIGURE1.2
Driversforgainingmarketshares.
driven by their specific needs, wishes and desires. At a very early stage of
business it is difficult to propose that these markets could mix and merge.
Currently, few publications exist that enlighten us on the mechanism of
successful business development in a knowledge society [5]. I would like
tosuggestthatatthisinitialstageofconsideringatechnology–productmatch
itmaybepossibletoanalyzethesethreedriversindividually.Withhigh-tech
products, the three areas may merge eventually if a real need has been iden-
tified, and making products to satisfy this need is more likely to produce a
satisfyingreturn-of-investmentthanifaspecificneedisnotidentified.
1.4 PURPOSE AND ORGANIZATION OF THIS BOOK
This book is a study book. A study book should not only make you buy the
book based on an interesting title but should also satisfy your needs; in this
case,aneedtolearnmoreaboutmicrofabricationforindustrialapplications.
This book is not a thesis on the definition of the economical value of micro-
fabrication nor a dedicated technology handbook for specialists. The focus
is micro-nanofabrication in innovative industrial areas, such as the field of
(bio)medicalapplications.
Chapter 2 presents an overview of the basic process technologies of con-
temporary microfabrication. Chapter 3 extends this to broaden the range of
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10 CHAPTER 1 Introduction
materials being used, and considers processes that specifically aim at three-
dimensionalmicrostructures.Chapter4isanintroductiontotheterminology
ofnanotechnology,andanoverviewofthedevelopmentofnanolithographic
techniques that can pattern features less than 100 nm in width. Those which
can produce large-scale, highly ordered pattern arrangements are of especial
interest.Thelatterareoftenreferredtoasmeta-materials.
Chapter 5 briefly reflects on the components and techniques of microme-
chanicaltransducers.Chapters6and7giveanintroductiontotheapplication
of microfabrication in the field of bio-chemical sensors and microfluidic
Lab-on-a-Chiptechnologies,respectively.Chapter8providesthereaderwith
a case study of microfabrication research dedicated to the drug delivery
market.Thisexampleofdeskresearchguidesthereaderthroughacommonly
applied approach in the engineering sciences: knowledge accumulation and
reduction of risk by applying a systematic design analysis. Finally, Chapter
9 gives some reflective comments and conclusions concerning the safety of
micro- and nanotechnology and nanoparticles in particular. This last chapter
alsoprovidesthereaderwithanoverallconclusiontothebook.
We will discuss fields of applications and introduce specific cases, which
may have already entered the market, in the various chapters. Many exam-
ples of science-based innovation utilizing microfabrication can be found in
the health sectors and a specific example is discussed in Chapter 8. Product
developmentcyclesare particularlylong(>10years)in themedicaldevices
industryduetothenecessityfordevicesthatfunctionrobustly,toahighsafety
standard, because they are to be used in close vicinity to the body or inside
it. Due to my personal research interest in the medical devices’ sector, par-
ticular attention will be paid in the book to the opportunities for micro- and
nanofabricationtoplayapartinthemanufactureofnovelimplants,diagnos-
ticandtherapeuticsystems.Nevertheless,somemicrofabricationapplications
willbealsopresentedacrossothermarketstoindicatethevarietyofindustrial
perspectiveswhicharepossible.
The book contains case studies for students in the engineering sciences
andfornon-engineeringspecialistsinterestedinthisspecificfieldofengineer-
ing. They reflect the current state-of-the-art of microfabrication in industrial
applications, and seek to interest the student in the more advanced literature
that is beyond the scope of this book. The book also provides an introduc-
tion for technology managers who are possibly experienced in business but
less so with the terminology in the emerging field of micro- and nanofab-
ricated industrial applications. For a specialist, e.g., a starting PhD student