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20 Scanning Probe Microscopy & Lithography_3

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    Scanning probe microscopy (SPM) and lithograph

    1. Atom and particle manipulation by STM and AFM.

    2. AFM oxidation o Si or metals.!. "ip#pen nanolithography ("P$).

    %. &esist exposure by STM 'eld emitted electrons.

    . ndentation* scratching* thermal#mechanical patterning.

    +. Field e,aporation* STM -"* electrochemical deposition/etching.

    0. Scanning near 'eld optical microscope (S$M) o,er,ie.3. $anoabrication using S$M

    1

    56 Fabrication in the nanoscale6 principles* technology and applicationstor6 7o -ui* 4-4* 8ni,ersity o 9aterloo: http6//ece.uaterloo.ca/;bcui/o

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    Field emission lithography (resist exposure)e tip acts as a source o electrons to expose the resist li

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    Field emission

    4lectron emission at highelectrical 'eld

    (Foler>$ordheim theory)

    Field strength ,s. gap distancebeteen a probe tip and counter

    electrode.

    Assume tip area is (25nm)2* then at%150/cm* current?35(2515#0)2?5.!nA (typical 47@ 1nA)

    For %150/cm* gap?!nm*so resist thic

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    &esist sensiti,ity6 !5sloer than 47@

    -omparison o line patterns ,s. exposure dose6(let) -on,entional e#beam lithography (47@) at !5

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    Field emission lithography6 results in resist

    tion is 25#%5nm* limited mainly by beam lateral di,erging (since no ocusing l

    ne pass Three passes

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    Field emission lithography6 patterntranser

    ch using resist as mas< @itoD metal* then etch using metal+

    SA@ is a chemicallyampli'edphotoresist* as

    ell as 47@ resist.

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    Scanning probe microscopy (SPM) and lithograph

    1. Atom and particle manipulation by STM and AFM.

    2. AFM oxidation o Si or metals.!. "ip#pen nanolithography ("P$).

    %. &esist exposure by STM 'eld emitted electrons.

    . ndentation* scratching* thermal#mechanical patterning.

    +. Field e,aporation* STM -"* electrochemical deposition/etching.

    0. Scanning near 'eld optical microscope (S$M) o,er,ie.3. $anoabrication using S$M

    0

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    $ano#indentationsmade ith an AFM on

    a diamond#li

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    AFM lithography6 scratching

    Material is remo,ed by AFM tip scratching.

    SAM (sel#assembled mono#layer) can also be remo,ed by tip

    scratching* hich is the in,erse process o dip#pen nanolithography. As a nanoabrication method this is airly limited due to the tip ear

    and debris produced on the surace.

    Ad,antage6 precise alignment (imaging then lithography)* no additionalsteps (such as etching the substrate) needed* though the scratch is

    usually ,ery shallo. t can also be used to characteriHe micro#ear processes o materials.

    I

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    2 Jmscans

    Scratch patterns made ith an AFMon a diamond#li

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    Scratching Si using diamond tip

    "iamond is ,ery hard* no ear (tip long lie#time).

    ne grain o diamond attached to Si AFM tip.

    ery stiD cantile,er ith spring constant 325$/m (1$/m or normal tip).

    The silicon as machined using diamond tip cantile,er at a normalload o 2%5!$.

    Pitch 10nm Pitch %05nm

    11

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    n general* the probe images the surace

    'rst ith nondestructi,e imagingparameters* to 'nd an area suitable orpatterning.

    A.4limination as achie,ed by the remo,alo the SAM in proximity o the probe bymechanicalor electricalmeans.

    7.A probe coated ith a molecular Kin

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    S4M images shoing Au eatures createdthrough61. STM#based lithography on a MM4A/Au

    substrate (t?5pA: b?15: 1m/s).2. mmersing the sample into a solution o

    -1+SE or !5s.!. -yanide etching o the gold.

    A.mm suare by 152% consecuti,escanning lines.

    7.2 passes ith the tip.

    -.1 pass ith the tip.".Test grid single line patterns se,eral m#

    Fabrication using sel#assembledmono#layers by electricalKscratchingL (desorption) Mercaptomethylethanamide (MM4A*

    ES-E2

    -$E-E2

    -E!

    ) produceshomogeneous* dense* and stable mono#layers on Au substrates.

    t protects gold rom urther thiol (i.e. >SE) adsorption but did not unction as aprotecti,e layer against cyanide etch oAu.

    -1+SE protects Au against cyanide etch. till co,er here,er MM4A is KscratchedLaay.

    canning probe lithography using sel#assembled monolayersL* -hem. &e,. 15!* %!+0#%%13 (255!). (good re,ie paper*1!

    Au suare*that asprotected by-1+SE againstcyanide etch

    Au here is etched aay

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    lipede6 thermal#mechanical data storage on a poly

    1%

    Tips are brought into contact ith a thinpolymer 'lm. 4ach tip is independentlycontrolled.

    7its are ritten by heating a resistorbuilt into the cantile,er to atemperature o %55o-. The hot tipssotens the polymer and brieNy sin

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    &esistance chang&/& Q 15#%/nm

    7M Millipede > rite and read

    ". 9outers* 8. S. Schubert* Ange. -hem. nt. 4d. 255%*1

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    Thermal bimetallic actuation

    tipexpand

    1+

    7i#metal means to metal 'lms one on top o another* here ith diDerent

    thermal expansion.Oo to http6//en.i

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    Silicon nitride probe arraysabrication

    10

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    p height6 1.0mp height homogeneity in an array6 5nmp radius6 25nm

    7M Millipede tips

    13

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    055nmAll the nanoscale pits in the array ereritten simultaneously by the millipede

    cantile,er array.Storage density G 1T7it/in2* oindentations Q 1 nm* pitch Q 2 nm.

    This is the most successul demonstrationo large scale nano#patterning using SPM

    tip#based nanoabrication.

    The Millipede data storage&ead/rite tip* radius at tipapex a e nm* tip#height

    55 # 055 nm

    1I

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    Scanning probe microscopy (SPM) and lithograph

    1. Atom and particle manipulation by STM and AFM.

    2. AFM oxidation o Si or metals.!. "ip#pen nanolithography ("P$).

    %. &esist exposure by STM 'eld emitted electrons.

    . ndentation* scratching* thermal#mechanical patterning.

    +. Field e,aporation* STM -"* electrochemical deposition/etching.

    0. Scanning near 'eld optical microscope (S$M) o,er,ie.3. $anoabrication using S$M

    25

    Fi ld ti

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    Field e,aporation Field e,aporation6 ions or atoms can be directly pulled out o material

    surace under extremely high electrical 'eld. Material deposition as easily obser,ed rom a gold tip due to its lo

    threshold 'eld or 'eld e,aporation (!./)* and gold surace is inert tochemical contamination.

    a tungsten tip as used in combination ith a gold substrate* a pit in Auas ormed* hich is because tungsten has much higher threshold in 'elde,aporation (.0/).

    Eoe,er6 Field e,aporation alone cannot completely explain the material deposition

    process6 heating by 'eld emission current may also be responsible or thedeposition.

    Field emission current occurs at much loer threshold 'eld than that o'eld e,aporation. For gold tip* the 'eld emission current becomes considerable at5.+/.

    Eigh 'eld emission current heats up tip apex* causing melting/Noing otip material.

    This can also explain hy the material deposition rom the tip issustainable despite continuous loss o material rom the tip.

    For this reason* a negati,e bias to the tip is preerable because negati,ebias is the correct con'guration or 'eld emission (o electrons that heat21

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    $ano#deposition by 'eld e,aporation

    The tip can also act as a liuid metal ion source (@MS)* hich henbrought in close proximity (155nm) to a substrate* can be used orlocal metal deposition.

    Similar to @MS or F7* except that here KocusingL is due to close 22

    ne possible mechanism6 liuid transer

    Fi ld ti

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    255nm

    15#%5nm Au dots

    Ad,antages6Small eatures6 15nm.

    "isad,antages6

    @imited to dots.@o throughput* smallarea.

    7essho* asa

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    SiHe depends on6 ,oltage pulseamplitude V duration* tip # substrate

    distance.(or 'xed current* distance increases

    ith ,oltage)

    Fe nano#particles by STM -" using Fe(-)precursor gas.

    MFM6 magnetic orce microscope.9irth* Field* Aschalom* ,on Molnar* KMagnetiHation beha,ior o nanometer#scale iron particlesL* P&7 0

    STM/AFM -" (chemical ,apordeposition)

    AFM image

    MFM image

    The process is similar to ocused electron beam induced deposition*but ith uite diDerent mechanism.

    rganometallic gas molecules are decomposed at the high 'eldaround tip apex* and a microscopic plasma (ioniHed gas) beteen tipand substrate is ormed.

    Tip is negati,ely biased (or 'eld emission o electrons)* ith current155#55pA.

    There is a threshold bias ,oltage or diDerent precursor gases6 20 oriron carbonyl gas but 1 or tungsten carbonyl.

    The deposited 'lm contains about 5W o metal* ith rest beingcarbon contamination and small amount o oxygen (this is li

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    @ocal electrochemical deposition and etchingSubstrate in solution* tip as local counter#electrode.

    Eomann* Schindler and Birschner*K4lectrodeposition o nanoscale magnetic

    L2

    -urrent>,oltage characteristics o -odeposition onto a Au STM tip rom5.2M $a2S%/1mM -oS%as recordedin the STM cell (AFM tool is used* notSTM). The potentials are uoted againsta saturated calomel electrode (S-4).

    The arros indicate the cyclingdirection o the ,oltage at a seep rate

    o 15m/s.

    Schematic illustration o the mechanism at the STM tip. ()"eposition o -o romthe electrolyte onto the unco,ered part o the tip. ()-o#co,ered STM tip. ()

    -omplete dissolution o pre,iously deposited -o causing an increase o the -o2Xconcentration near the tip according to the diDusion pro'le. () -o dissol,ed romthe ,ery end o the tip is deposited locally onto the substrate.

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    -o on Au

    a)STM image o three -o dots on a Au surace. The tip asithdran 25nm rom the Au surace during deposition: 494?#005m (946 or

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    @ocal electrochemical deposition and etching

    Simultaneous deposition (onto polymer near tip apex) and etching(the substrate) through a thin spin#coated ionically conducti,epolymer 'lm.($T in liuid solution* but the polymer acts li

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    Scanning probe microscopy (SPM) and lithograph

    1. Atom and particle manipulation by STM and AFM.

    2. AFM oxidation o Si or metals.!. "ip#pen nanolithography ("P$).

    %. &esist exposure by STM 'eld emitted electrons.

    . ndentation* scratching* thermal#mechanical patterning.

    +. Field e,aporation* STM -"* electrochemical deposition/etching.

    0. Scanning near 'eld optical microscope (S$M) o,er,ie.3. $anoabrication using S$M

    23

    F ' ld d ' ld i

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    Far#'eld and near#'eld optics Far#'eld opticso Oeometric optics based on traditional optical

    element (lens) $ear#'eld opticso Spatial con'nement o light in x* y and H.o Form o lens#less optics ith sub#a,elength

    resolution.o ndependent o the a,elength o light being

    used.

    $ear#'eld probe (5nm)

    &e,ie paper6 Tseng* K&ecentde,elopments in nanoabrication usingscanning near#'eld optical microscopelithographyL* ptics V @aser Technology*!I* 1%#2+ (2550).

    2I

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    $ear 'eld scanning optical microscope($SM)or Scanning near 'eld opticalmicroscope (S$M)

    $SM is a scanning optical microscopytechniue that enables users to or< ithstandard optical tools beyond the diDractionlimit.

    t or

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    Melt dran rom a single optical 'ber ith the core material

    Melt#dran straight $SM tip

    Fiber tip by $anonics nc.

    !1

    Tuning or< based shear orce

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    Tuning or< based shear#orcedetection

    !2

    Tip distance control6 beam deNectionmethod* shear orce measurement*pieHoelectric tuning or

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    "$A

    $ear#'eld microscope (or imaging)

    $ear 'eld illuminationFar 'eld detection

    !!$ear 'eld illumination* ar 'eld detection

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    The probe edge is coated ith Al.The metal 'lm (155nm thic

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    $ear#'eld optical techniues

    a) Apertured probe (S$M) > e,anescent a,es romtapered 'ber probe are used either to illuminatesample or couple near#'eld light rom sample into 'ber.

    b) Apertureless probe (AS$M) > small (sub#a,elength)tip scatters near#'eld ,ariations into ar 'eld.

    (or transparent substrate)

    !

    Apertureless probe (AS$M)

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    Apertureless probe (AS$M)

    Ad,antages6 Far 'eld illumination and detection allos or use o

    con,entional optics. Eigher light intensity near the tip than S$M."rabac

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    Scanning probe microscopy (SPM) and lithograph

    1. Atom and particle manipulation by STM and AFM.

    2. AFM oxidation o Si or metals.

    !. "ip#pen nanolithography ("P$).

    %. &esist exposure by STM 'eld emitted electrons.

    . ndentation* scratching* thermal#mechanical patterning.

    +. Field e,aporation* STM -"* electrochemical deposition/etching.

    0. Scanning near 'eld optical microscope (S$M) o,er,ie.3. $anoabrication using S$M.

    !0

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    $ear#'eld lithography6 direct serial riting

    Serialriting/exposure o aphoto#resist using'ber tip* li

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    -omparison o apertured and apertureless S$MApertured6lo light intensity* slo riting* tip ,ery dicult to ma

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    @ine#idth measured by AFM

    4Yin et. al., Appl. Phys. Lett. 81 3663 (2002)

    To photon near#'eld optical lithography

    Achie,e /15 resolution by ocusing emto#second laser beam

    onto Au coated AFM tip in close proximity to S8#3.To#photon polymeriHation occurs in S8#3 o,er con'ned

    regions due to local enhancement o electromagnetic 'eld bysurace plasmon on metal AFM tip.

    "iDerent rom to#photon lithography in that here the 'eld is

    KocusedL (enhanced) by the tip* not by a ocusing lens.

    Pea< poer6 5.%15129/cm2

    %5

    nm cannot expose S8#3* but 0I5/2?!Inm can.

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    S$M photo#patterning o SAM (sel assembledmonolayer)exposure in the presence o oxygen oxidiHes the SAM* ea

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    S$M material remo,al by laserablation

    $ano#lines ablated on Au substrate by aperturelessS$Mcoupled ith by ultraast laser o 3!s F9EM6a) AFM image

    b) &elationship beteen eature siHe and laser Nuence

    @aser pea< poer 12mU/3!s?5.1%15129/cm2* high enough to meltand ,aporiHe Au.

    %2

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    S$M photo#-" (chemical ,apordeposition)

    =n nano#dots deposited on glass substrate by S$M photo#dissociation6a) Shear#orce image.b) -ross#sectional pro'le ta


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