WO2020159778A1 - Mid-infrared spectroscopy for measurement of high aspect ratio structures - Google Patents

Abstract

Methods and systems for performing high throughput spectroscopic measurements of semiconductor structures at mid-infrared wavelengths are presented herein. A Fourier Transform Infrared (FTIR) spectrometer includes one or more measurement channels spanning a wavelength range between 2.5 micrometers and 12 micrometers. The FTIR spectrometer measures a target at multiple different angles of incidence, azimuth angles, different wavelength ranges, different polarization states, or any combination thereof. In some embodiments, illumination light is provided by a laser sustained plasma (LSP) light source to achieve high brightness and small illumination spot size. In some embodiments, FTIR measurements are performed off-axis from the direction normal to the surface of the wafer. In some embodiments, a Stirling cooler extracts heat from the detector of an FTIR spectrometer. In another aspect, measurements performed by one or more spectrometer measurement channels are combined with measurements performed by a mid-infrared FTIR spectrometer channel to characterize high aspect ratio structures.

Description

MID-IN RARED SPECTROSCOPY FOR MEASUREMENT OF HIGH

ASPECT RATIO STRUCTORES

CROSS REFERENCE TO_: REEATEN REELICATION iQOOl] The present application for patent claims priority under 35 D, s . C . §119 from N.s, provisionaI patent

application serial number 62:/?97, 668, filed /January IS, 2019, the subject matter of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] The described embodiments relate to metrology syste s and methods, and more particularly to methods and systems for improved measurement of semiconductor

s ructures .

BACKGROUND INFORMATICN^;

[0003] Semiconductor devices: such as; logic and e ry devices ere typic lly fabricated by a se uence: of

processing steps applied to a s ecimen, fit© various features and multiple structural levels: of the

semiconductor devices are_: formed by these proceseihcf steps. For example, lithogr phy among otters is one semiconductor £sbrication process that involves generating a pattern on a semiconductor wafer. A ditional exa ples of semiconductor fabrication processes include, but are not limited t ;, cbe iraI-mechanical polishing, etch, deposition,_; and ion implantation, Multiple· semiconductor devices may be fabricated on a single semiconductor wafer and then

separated into individual pemiconductor devices.

10004] Metrology processes are used at various steps during a semiconductor manufacturin process to detect detects on afe s to promot hisrev yield, Optical metrolog techniques offer the potential for high throughput without the risk of sample desfraofloo , A number of optical metrology based techniques including soatieromatry and refleetometry implementations and, associated analysis algorithms are cdBMdnlf: used to characterits critical dimensions, film thicknesses, composition, overlay and other parameters of naroscale structures.

:0005] Flash memory architectures are transitioning fro two dimensional floating-gate architectures to fully three dimensional geometries:_:. In some, ex les* fil stacks and etched structyres are: very deep pe,g„,, up to six

micrometers in depth) . Such high aspect ratio structures creafe challenges for film and GD measurements,, the ability to measure the critical dimensigns tha efine the shapes of holes an trenches of these structures is

critical to achieve desired perfor ance levels and device yield,

|OOO0] Many optical techniques suffer from low signal-fo- noise ratios fSSEs > as only small fraction of the illumination light is able to reach the hotcom, of high aspect ratio features, and reflect upwards fd the detector,. Thus, many available high-throughput metrology techniques are unable to reliably perform CD and film measurements: of high aspect ratio structures, Critical dimension, small angle X-ray scattero efxy (GD-SAXS) , normal incidence reflectometry, .and seatterometry: are being explored as measurement solutions for high aspect ratio structures, but development is still on-going,

[0007] Cross-sectional scanning election microscop ISEM) is low throughput, dest uctive technique that is not suitable er inline metrology. Atomic force microscopy (RFM) is limite is its ability to measure high aspect ratio structures and: has relatively lew throughout. CD- 3&XS has hob yet been demonstrated to achieve high

throughput capabili ies recent reel by the semiconductor

industry. Model, based infrared rettectometry (MB!R) has been used for metrology: of high aspect ratio ΌR.&M

Structures but the technique lacks the resolution provided by shorter wavelengths; and the measurement spot sices are too large for semiconductor metrology. Additional

description of MBXR is provided in * easuring deep-trench structures with model-based IR,” by Goateih et al , , SolidState: chnology, col . ,49, no , 3, Mar. 1, lOQd, w ich is incorporated by reference in its entirety.

EOQOei Optical CD etrology currently la ks the ability to measure the detailed profile of structures with micron scale depths and lateral dimensions in & relatively small spot (e.g,, less than 59 microns, or even more preferably, less than 3:0 microns) at high throughput . U.S, Ratent Ho,. 8,860, 9:37, which is Incorporated by reference as if fully set forth herein, describes: infrared spectroscopic

eliipse etry techniques that are suitable for

characterisation of high aspect -ratio structures. However, the described techniques suffer from long measurement times for measurement:® spanning the ultraviolet ,and infrared wavelengths, wavelength stability limitations, and limited range of infrared wavelengths during operation.

£0003] in summary,^, ongoing reductions in feature nice and increasing depths of structural features impose difficult requirements on optical metrology aysterns. Optical

metrology systems must meet high precision and accuracy requirements for increasingly com e targets a high throughput to remain cost etfactive , In this context, speed of broadband Illumination and data collection and range of infrared wavelengths have emerged as critical, performance limiting: issues in the design of opticalmetrology systems suitable for high aspect ratio

structures. Thus,, Improved metrology systems and, methods to overcome these limitations are desired.

NUMMARY

[0010] Methods and systems for performing high: throughput spectroscopic measurements of semiconductor structures a mid-inf ared wavelengths are presented: herein. The methodsand syste s tor spentroseopie metrology ©f semicernduotor.devices described herein are applied to the measurement of high aspect ratio (BAR) structures, large lateral dimension structures, or both. The described embodiments enable optical critical dimension {CD) , film, an composition metrology for semiconductor devices.

[0011] In one aspect, a semiconductor /metrology system

1 no.Luces a: Fourier Transfor Infrared. (FITE) spectrometer suitable tor high throughput mea rements of high aspect ratio semiconductor structures. In some embodiments, anFT1 spectromete includes one or more measurement channels spanning a wavelength range between 2 rfu.eram ters and 20 micrometers:. The cue or more FTIR measurement channels; are operable in parallel ( i . e . , simultaneous measurement of the sample throughout the Wavelength range) or In sequence

sequential measuremen of the sample throughoilt the wavelength range! .

[001_:2] In a further aspect, an FTIR spectrometer measures a target at multiple different angles of incidence, azimuth angles, different wavelength ranges, different polarization states, or any combination thereof. [0013:] In

further aspect, as FIXE metrology system includes a laser sustained plasma (ISP) illu ination sours© to achieve high brightness and small illumination Spot sire,

[0014] :ln another farther aspect, the PTXR speetrosecpic measurements are performed off-axis from the irection normal to the surface oi^: the wafer to reduce the Influence pf haotatde reflections on the measurement results,

[00X5] In another further aspect, an FIIR metrology system includes a diffractive polarizer and analyzer to measure target response as a function of polarization states,

[0016] In anothe furthe aspect, an FTXR spectrometer includes a Stirling cooled sensor to mitigate the need for external liquid nitrogen supply and handling equipment,

[0017] ,ln another further aspect, measuremen s: performed by one or more spectrometer measurement channels are cbmbineh with measurements performed by a mid-infrared FTXR

spect ometer channel to characterize high aspect ratio structures_* In some embodiments, measured spectra include vacuu ultraviolet, ultraviol t, visible, near infrared and tiid-infrared wavelengths . In some of these embodiments:, measurements of a se iconduetot structure by multiplespectrometer measurement channels are performed

simultaneously at high throughput with the same alignment conciitxans _*: In this manner, machine errors, such as wavelength errors, are uniformly corrected across ail raeasured wave!engthsu These features, individually, o in combination, enable high, throughput measurements pf high aspect ratio structures (e.g., tructures having depths of me micrometer or more) with high throughput, precision, and accurac . In other embodiments,, a mid-infrared FilE spectrometer and one or jsdte additional measurement

S^: channels measure; a target seq entially . In, general , a mid- infrared FTtR: spectrometer operating in serabinatien with ,©ii@ o more additional measurement bufesystems may measure a target at multiple different angles _;©f Incidence, azimuth angles, different wavelength ranges, different poiarizafcion states_# or aby combination thereof.

1002,83 fhe foregoing is a summary and thus contains, bynecessity, slmplification * generalizations and omissions of detail; consequently_# those stilled in th art will appreciate that the summary is illustrative only and is not limiting in any way. Other aspects, inventive features,and advantages o,£ the: devices and o processes described herein will become apparent in the non-limitlag detailed description set forth herein.

BRIEF DESCRIPTION OF THE DR iTMGS

[0029] FI©. 1 depicts a plot of the extinction

coefficient of two amorphous carbon films used as hardmask materials in etch steps :of the semiconductor fabrication process ,

[0020] FIG, 2 depicts _;a plot oh the percentage of light, reflected from the two amorphous carbon: films illustrated in FIG. 1,

[0022] FIG, 3 depicts a chart 185 illustrating

simulation results predicting expected 3-sigma measure ent precision In various measurement scenarios,

[00:22] FIG,, 4 depicts an amorphous carbon layer 18€ disposed on top of a silicon substrate 187 under

measurement by an eilipsometer and a reflactometer ,

,0023^:3 FIG. 5 depicts the reflectivity of s-polarlzed i11u lnation light versus the_: p-polarized illuminationlight as a ianotion of angle of incidence. [0024] FIG. 6 depicts an exemplary metrology system 100 for performing broadband, mid-infrarad Fourier Itansiam Infrared [FUR) apeόtroscopic^: measurements of Semiconductor structures in: a ret leer ive e,

[0025:3 FIG, 7 depicts an exemplary metrology system 250 for performing broadband, Mid-infrared Fourier Transform Infrared IFTIR) speetrosooplo measurements of semiconductor struotares in a transmissive mode:.

[0026] FIG. S depicts an exemplary metrology system XOd for performing combined broadband, mid-infrared FTIR

speetroaeoplc measurements , spec reetopic ell ipsemetry measurements, and spectroscopic reflecfometry measurementsof semiconductor structures,

[60273 FIG. 9 depicts illumination incident onto a film layer disposed on a substrate at near normal incidence, but specifically avoiding normal inci ence,

[0028] FIG, 10 depicts illumination incident onto: a film layer disposed on ^:a substrate at normal incidence,

[0029] FIG. 11 depicts an infrared spectroscopic

reflec oMd er includin a Gehuaftzchild objective to avoid nor at roeid®nce,

[0630] FIG. 12 depicts an infrared spectroscopic

refiectoMeter including an off-axis, unobseured objective

1 one to achieve oblique incidence.

[0031] FIG. 13: depicts an exemplary high aspect ratio HRRB structure 400 that suffers from low light penetration Into the strnetorsfsj being measured.

[0032] FIG, 14 illnstxates a method 560 of pertarming mid-infrared FTIR spedtroscepiG measurements of one or more structures as described herein. DK iLEP DESCRXPTIOH

0033] Reference will n¾¾? be made, in detail tc .background exa ples and some embodiments of the in ention, examples of which are illustrated in the accompanying drawings.

[0034] Hathods and syste s for performing high throughput -spectroscopic meas rements of semiconductor structures at mid-infrared wavelengths ar presente herein. In one .aspect, ,a semieendaQCgr metrology system: includes a Fourier Fransform Infrared (FUR) spectrometer suitabl tor high throughput measurements of high: aspect ratio semiconductor structures . In som embodiments, ian FTIR spectrometer including one: or more: measurement channels spanning a:

wavelength range between 2 micrometers and 20 micrometers i,s employed to perform measurements of semiconductor structures. The one or more FTIR measurement channels, are :operable in parallel (:l,:e. , simultaneous measurement of the sample throughout the wavelength range) dr in sequence (i.e.,, sequential measurement of the sample throughout the wavelength range) .

[ 0035] In a further aspect, the FTIR spectroscopic

measurements are performed off-axis fro the direction normal to the: surface: of the wafer to reduce the influence_: of backside reflections on the measurement results, in another further aspect, an FTIR etrology system includes ,a laser sustained plasma :{LS^:P) illumination source to achiev© high brightness and small illumination spot size. In nnothor further _:aspeet, _:an FTIR metrology system includes a diff active polarizer and analyzer to measure target response as a_: function of polariratieh states. In another further aspect, ah FTIR spectrometer includes a Stirling cooled sensor to mitigate the need for external liquid nitrogen supplyCard handling equipmen _> In another furthe

% aspect, measurements erformed fey on® or morn spect omster measurement channels are combined with rrteasurement_:s

pertarmed by a mid-infra ed FTIE spectrometer channel to characterire high aspect ratio stractares _* In some

embodiments, easur d spectra include ultraviolet, visible, nea Infrared add mid-infrared wavelengths. In some of these embodi en s, measur ents of a semicdnauotor

structure by multiple spectrometer measurement channels: sre performed simultaneously at nigh throughput with the same alignment conditions. In this manner, machine errors, such as wavelength e ro s, are uniformly corrected across all measured wavelengths. These features, individually, or incombination, enable high throughput measurements of high aspect ratio structures (e.g. , structures having depths of One micrometer or orel with high, throughput_:, precision, and accuracy .

[ 0036] By measuring a high aspect ratio structure with :multiple spectrometer measurement channels of a single metrology syste spanning a broad range: of 1Humiliationwavelengths: (e. gl, 190 nanometers to 26 micrometers), precise characterisation of complex three dimensional structures is enabled. in general, relatively long

wavelengths penetrate deep into a structure and provide suppression of high iffraction orders when measuring structures with relatively large pitch. Relatively short wavelengths provide precise dimensional information about simetores aeeesslhls: to relatively short wavelengths

(i.e., top level_: layers) as well as relatively small CD and roughness features. In some examples, longer wavelengths enable measurement of dimensional characteristics of

targets with relatively rough surfaces or irterfaces due to dower sensitivity ©t longer wavelengths to roughness. [b 03^*7] In some e bodi ents, the ethods and syste s for spee.trosoopie metrology of semi conductor devises described feecein are applied to^; the madsur meht of high aspect ratio (H¾R) _r large lateral dimension structures, or both. These embodimen s enable optical critical dimension (CD), film, and composition metrology for semiconductor devices with BAR structures (erg., KddD, V AMD, TRAT, DRAM, tc 4 and, more generally, for complex devices that suffer from low light penetration into the structure (s) being: measured.

HAR structures often include hard mask layers to facilitateetch processes: for BARS . Ag described: herein, the term "BAR st uctu e" refers to any stru ture characterized fey an aspect ratio that exceeds ill

and may be as high as 103:1, or higher.

0038] More: spedfreally, a semiconductor metrology system including a mid-infrared FTIR: sp ctrometry based

measurement channel enables high throughput

eharaeteriza ion of several classes of: se iconductor structures that arc currently inabeoaately measured.

Measurements includes 1} Measurement of critical dimersldrs of three dimensional semiconduetor packages; 2) Measurement of epitaxial film layers with FTIR; 3) Measurement of high aspect ratio structures employed in DRAM manufacturing, in particular, the storage node; i) asure ent of thick, opaque layers such as amorphous carbon films, ana b)

Measurement of channel holes, tungsten reeess, and other critical metrolog challenges in three dimensional BARD : anufactaring .

[0039] In additiou, a semiconductor metrology system including a mid-inffared FTIR spectrometry based

measurement channel and at least one s ectposoόrίe

reflecto et y^: channel Operating in a shorter wavelength ran ©_: enables high throughput eharaotori s tion of severa1 e er ing classses bf semiconductor structures that gre currently iha bqaafoily measured, These Tsehsufeinenis include 1} Measurement or critical dimensions and shape of through silicon_: vlas; 2} Measurement of exit:!cal dimensions and shape :of DBAM capacitor structures; 3) Measurement of SlliCon/slliCon Carbide epitaxy and Co positids; 45

Measurement of films employed in three dimensional MAMD hard mast layers {e.g,, amorphous carbon layers); and 5) Measurement of three dimensional fJAHD Tungsten Recess and Channel hole profiles

[0040] FIG, i depicts a plot of the extinction coefficientof two amorphous carbon films that are used as hard ash materials in etch steps of the fabrication process for three dimensional KAMD st uctures Pietline 181 depicts the extinction coetficieni as a function of wavelength for an amorphous carbon film A, and plotline 182 depicts the extinction coefficient as ^:a function of wavelength fox an amorphous carbon film 8, The extinction coefficient of film A Riai tains a relatively high value throughout the wavelength range from 20Q nanometers to ,22_:0Q^: nano eters::. Thus, film A is strongly absorbing even: through the near IK. spectral teg1oss .

[0041] FIG, 2 depicts plotline 184 :of the percentage ei light reflected from fil A and plotline lid of the

percentage of light reflected from film B, having a

thickness ex ilySOO Angstroms a measufedfby a

refiectometer , _:The percentage of light reflected from film A remains extremely low throughout the range of wavelengths from 200 nanometers to 2200 nanometers, As illustrated in FIG, 2, the minimum wavelength required to collect

approximately^: 0, ^QS¾ of Incident light is approximately 2000 fl nanometers . Bain» approxi&afe1y 1800 nanometers the a ount of c llected signal is practically immeasurable.

[0042] FIGS _¨ 1- nd 2 illustrate th importance of employing short,--infrared light <©.,„g._:, 1400 nanometer to 3000

nanometer) and raid-infrared light (e.g, , 3000 nanometer through 20 micrometers) to perform spectroscopic

measurements of important materials employed in

semicondno e ann£actnr ,

[0043] In addition, reflactometer and ellipsometer

configurations demonstrate different ©ffedtivity when measuring high extinctIoh ratio materlaIs:. FIG. 3 depicts a chart 185 illustrating simulation, results predicting the3 --sigma measurement precision expected in various

measurement scenarios, Film thickness_: measurements of an amorphous carbon layer at two different thicknesses (I S 030 dugs rams and 20, Off hftgsiroms,) are simulated_· both in & spectroscopic reflectd eter configuratioh and a

spectroscopic ellipsometer configuration , In addltion, two different ranges of illumination wave!engoho are

considered, i one scenario SE and BR measurements are simulated with illumination wavelengths:: ranging from 9^:5D^:nanometers to 220Q nanometers. In, another scenario_/ SE, and SB measurements are simulated with illumination wavelengths ranging from 950 nanometers to 2Sh0 nanometers, ¾s

illustrated in FIG. 3_/ the SR configuration achieves significantly greater measurement precision compared to theSE measurements,. In addition, measurements performed at the extended range of illumination wavele ths also achieve greater measurement precision,

[0044] Becaus the refiectometer operates at or hear normal incidence_/ it has a ¾ath length" advantage over an

ellipsomet r when performing measurements of thick or deep structures · FIG, 4 depicts an amorphous carbon layer 186 disposed on top of a silicon substrate 187. In; an

eilipsometer eorifiguratiors, iilumunation ligh 188 is incident to film 18S at a relatively large angle {;e.g, , angle of incidence greater than id degrees} , The light refracts at the air-film interface ana propagates through film 186 a an angle of refraction that is sign! ficantly greater than zero. Similarly, light reflected from the bottom surface of film 186 propagates through film 186 at the angle of refraction* refracts at the air-^:film interface and propagates: to a detector of the SE system. In

contrast in a _:reflactometer configuration, illumingtion light 190 is incident to film 186 at a: relatively Small angle e.g, hero angle for the case of normal incidence reflecto etrf) . At normal ineideacey the light propagates through film 188 and reflects bach from the bottom surface of film 186, The reflected light 111 propagates to th SR detector, ¾s depicted in FIG, 4> the optical path length of the illumination light and the reflected light through film 186 is: longer in an SS configuration than an FR configurat ion, This additional optical path length in film 18_:6 leads to additional absorption and loss of measurement sighal. For this reason, a relatively small single SR configuration is preferable to a relatively large .angle ,SE configuration fo measurements of thiol, highly absorptive materials such as amorphous carbon layers.

10045] FIS, 5 depicts the reflectivit of s-polarited illumination light versus the p-poiarized illumination light as a function of angle of incidence, Plotline 192 depicts the reflectivity of s-pelarized light and plotline 198 depicts the reflectivity of p- polarized light. AsIllustrated in Fi G , S;, the selected polarization impacts measurement sennit ivi t y . Also, as illustrated in FIG. S, the reflectivity of p-polarite light declines

slynifleantiy in the typical angular range employed in SE measurements_: (e,,g._:, ¾OI greater than 0 degrees) . the decline -is particularly acute near the Brewster angle . As illustrated in FIS. 5, to avoid significant declines in reflectivity of p-poiarited light! a small angle

refleafo etry corfiguratiQU {e-g_^, AOl lees than 40

degtees } is preferable.

[0046] FIG. 6 depicts an exemplary_/ metrology system 1Q0for performing broadband mid- infrared FTIR,measarements of a-eiaiconductor structures fe„g,_f film thicknasA, critical dimensions, Overlay, etc, } . in some examples, tbe one or mere structures include at least one high aspect ratio ( H.rts structure or at least one targe lateral dimension s ructure_^. As depicted in FIG. 6, metrology system lot is configured as near normal incidence or near normal

incidence,, broadband FTiK spectrometer,. However, in general, metrology system 10G^: may also include: additionalmeasure en channels sacn as a spectroscopic refleetdmeter, a spectroscopic eliipscmetex, seatterometer,, or any

combination thereef .

10:047] Metrology system ltd includes an illumination source 101 that generates a beam of illumination light G09

incident on a^: wafer 115, In a further aspect, the amount of illumination light is broadband illumination light thatincludes a range of wavelengths spanning at least 9

micrometers. In one example, the- broadband illu ination light includes wavelengths below 2 ,5 micrometers an

wavelengths above 12 micrometers. In some examples, th broadband illumination ligh includes wavelengths in a range spanning at least 400 nanometers to l2, 000 nanonwters . In some e asc ies, the broadband. Illumination light includes wavelengths in a tenge spanning at least 150 :nano eters to: 20,000 nanometers_* In some embodiments, broadband illumination light including wavelengths beyond 12, D00 nanometers may be employed,. In some examples, broadband ilium!nation light includes wavelengths up to IQ, 000 nanometers ,

|004S] In some e bodiments, illumination source 101 is_: a broadband laser sustained plasma {L5P} light soars®

fa.fc.ai , laser driven plasma source) that emits

illumination light la the ultraviolet, visible, hear- IntraTed, and mid-infrared spectra_* The pump laser 102 of the LSP light source 101 may; be continuous wave dr pulsed. In the embodiment depicted in Fid, 5 a single hSF pump laser sourc 102 is employed, However, in general an LHP light source 101 may employ ore: than one LSP pump laser source to excite photons ever different wavelength ranges, thereby enhancing the brightness and power of portions of the plasma spectru or the entire plasma spectrum, A LSP light source¹ can produce signiflean iy: more radiance than an arc lamp across the entire wavelength range from 120 nanometers to 20,Q63 nanometers:. As depicted intFIG. 6, control signals 138 are commUnie fed fro computing system 130 to control LSP pump laser source 102, In response, LSP pump laser source 102 adjusts its optical output, and in turn, adjusts the output of LSP light source 101 in

accordance with command signals IM,

10049] As depicted in J’lil, t, LSP pump larer source 102 generates pump light 163 focused by focusing optics 104 to a focal point 107, The focused pump light sustains a plasma 106 contained by plasma chamber 105_* Plasma IGd, generates broadband spectrum light over a wavelength range from vacuum iXtra~vIoIet to mid-infrared. Plasma chamber: CΌ5 includes an exit part lOS through which illumination light 109 passes , In ome embodiments, plasma chamber IDS is constructed from Calcium Fluoride o Magnesium Fluoride to transmit wavelengths above 2,3: micrometers generated by plasma 106, in ^:seme other embodiments, plasma chamber 165 Includes one or more exit ports fe^g, exit port 188 , in some embodimen s , exit port 108: is constructed from diamond to trans it light spanning a wavelength range from 2

'micrometers to 20 micrometers. In some other embodiments,exit port 106 is constructed from siliboh, germanium, pi d selenide, or sine salfide to transmit in the mid infrare region. In soma other embodimenta, exit port 106 is constructed from fused silica to transmit light spanning a wavelength range from 185 nanometers tc 2.5 icrometers In some other embodiments , exit port 1⁽18 is constructed from Calcium Pi nor ids to transmit light spanning' a

wavelength range from 120 nanometers to 5 miurometers. I seme ether embodiments, plasma chamber 105 ihcludes at leas one exi port transmitting deep ultra violet to near infrared and at least one exit port transmitting id- Infrared. In some embodiments, the LSP pump laser source 102 Is a bnhilnuoiis wav laser. In some other enbobi ents, the LSF pump laser sonrce 102 is a pulsed laser.

[0050] In general, illumination source 161 is a single light source or a combination of a plurality of broadband or discrete wavelength light sources. The light generated by illumination source: 101 includes a continuous speefru or parts of a_: continuous spectrum, from ultraviolet to mid- infrared (e,g, , vacuum ultraviolet to mid Infrared) . Ingeneral, illumination light source 101 may include a LSFlight source, a superegotinuam laser source, an infrared if. supexcootinunm source, a eet of quanta cascade lasers, an infrared hellurn-neon laser source, an are lamp ie,g„, a enqri arc lamp) , a deuterium lamp, a tdermal light "s urce (e, g, , glpbax light sourcei , a quantum cascade laser source, any other suitable light SOCKS, or any combination thereof.

100513 As depicted in FIG. :b, collimating optics 121 collimate light 10$ from plasma 106 and directs: the

collimated light to FUR interferometer X2Q (e,g,, a

Michaaison interferometer) . In some other embodiments, focusing optics (hot shown) collect light from plasma 106and teens the: collected light tg an, illumination source field stop {not shewn) the illumination Source lie i.0 step defines a stable source sice and position . Light passing through the illumination source field stop is collimated by collimating optics 111 and directed to FTIR interfarometer 12c ,

[0052] FTIR interferometer 120 includes a beam splitting element that subdivides the illnrsination light into two different optical paths. In some embodimen s, a first optical path has _;a fixed optical path length, while a second optical path includes a moveable optical element that varies the optical path length of the second Optica .1 path. The two optical paths are recombined. The resulting eave interference pattern (i.e,, interFerogrant depends o the difference in optical path length {i.e, , the optical path difference) at any particular position of the moveable optical element. Thus, depending on the position of the moveable optical element, some source wavelengths are heavily (or completely) attenuated and other source

wavelengths are transmitted without attenuation. In this manner, the positio of the moveable optical element d fines the outp t spectru of the FTI interferometer at any given instant, As the position of moveable optica! element changes _f the output speutruffi of the FTIR

inferfero eter also changes_/ and measurements are performed over: a changing combination of illumination wavelengths.

[0053] ¾s depleted in /FIS,

control signals 139 are communicated from Computing system 130 to control FTIR interferometer 120. In response_/ FTIR interferometer 120 controls the position of one or more moveable optical elements_/ which in turn_/ adjusts: the spectral output of the FTIR interferometer 120 in accordance with command signals 139,

10:054] As depicted in FIS. 6, diffractice solar leer 122 collects the Illumination light transmitted by FTIR

interfero etec 120 and transmits light having a specific polarization state. In some embodiments_/ diftrac ive polarizer 122 is a wire grid polarizer, :ln some

embodi ents polarizer: 122 is a dynamic polarizer that transmits different polarizations as a function of time e.g, a rotating polarizer} . In these embodiments_/ measurements are performed, over time with different

polarization states. Although the: embodiment depicted in FIG_:, p includes a diffractive polarizer 122_/ In general_/ FTIR measurements may be performed with or without the use ef a polarizer 122 in the illumination beam path and corresponding analyzer 126 in the collection beam path. f0055] As epicted in FIG. 6, optional illumination optics 123 conditions lIght from: polarizer 12:2^:. In an example_/ optional illumination optics 123 Increases or decreases beam size. Is another example_/ optional illumination optics 123 changes the s ate of beam: eollimation. ,In another example_/ optional Illuminator optics 123 includes a second illumination field stop, (not shown) that blochs higher order diffracted light from polarizer 122.

[0056] Beam sappier 124, sa ples a portion of the lightediting the illumination field stop and directs the light to reflective objective 125, In a preferred embodiment, beam sampler 124 in a^: half mirror (e.g., a mirror

positioned to sample 5SI of the beam footprint of

Illumination light IDS) . In the preferred e bodiment, b amsampler 114 is entirely reflective., This enables the use of materials that reflect mid-inf ared light (i.e. , ligh :havlng wavelengths all the way oat to 20 diero etefed) with high efficiency (e,,g._f gold, silver, etc, } . However, in general. , bea divider 124 may be any suitable beam: samplingoptical element, & depicted in ^:F1G, H, beam sampler 12 reflects a portion IvSh of illumination light 109 anddirects illumination light 10¾¾ toward objective: 125. Th remaining portion 1Q9B of iilu ihaticn light 109 propagates to a detector 141, Defector ill generates output signals15:5 i dicative of the condition of illumination light iOfB (dig., intensity, position, intensity distribution, etc^:. ) and by prosy, the condition of illumination light iQdh directed toward the sample under measurement , in this manner, computing system Id© generates: control, signals:

fe . g. , control signals lit), to control an of ilinmination source 101, interferometer 12Q, polarirer 12^:2, and

illumination optics 123 to change the condition of

illumination light 1:09d to a desired specification.

I0057J Reflective objective 12:5 focuses the ilinmination light 1,09A over an illumination spot 117 on wafer 115.

Reflective objective 125 also collects light 12© reflected from wafer 115 in response to incident illumination light 1©9¾ and directs the collected light 129 to analyser 125. is Collected light 129 passes through baas sampler 124* atalye&r 126> and collectio optics 121. As an exa le* in the case where deem sampler 124 is a half ffiirtpr,

collection light 129 Is spatially separated from beam sampler 124 and collection light 129 is not attenuated by d^:ea ^: sampler 121, l^:n some embodiments, coilection optics 127 focuses colletted light 129 onto an active sensing serface of detector 128, In some pt-hep embodi ents*

collection optics 127 focuses collected light 129 at collection field stop (not shown) . Additional opticalelements (not shewn) collect light from the eellection field step and direc the light onto an activ sensingsurface of detector 1281

EOQS ] In some embodiments,· detector 12& do sensitive to mid-infrared light including any wavelength within a range of 2 to 12 icro eters- In some: embodiments,· etector 128 is sensitive to mid-infrared light including any wavelength within a range of 2 to 20 micrometers. In some

embodiments * detector 12:8 includes a HgddTe sensor. In some embodiments! the pho osenaitive sensor of detector 222 is cooled to the temperature of liquid nitrogen. In addition, in some embodiments> detector 128 includes a Stirling coder employed to transfer heat away from the aolive sensing elements .

[0059] Detector 128 generates detected signals 135

indicative of the optical response of the measure

structures on wafer IIS to the 11 lamination light 109.

Detector 128 communicafes de ected signals 135 to computing system 130, The detected signals 135 var with the

response of the wafer 115 to the known spectrum generated by FTIR interferometer 120. Computing system 130 employs the Fcurier Transform to process detected signals 135 based

30 on the known spectrum generated fey FTXR interferometer 120. in this a ner, competing s ste 130 determines the

reflectivity of the easur d target a each wavelength (i.e, , spectral response of the measured: target) , In turn, computin syste 13D determines a value gf a parameter of interest 155 associated with the measured target based on the measured spectral response,

[0060] FIS, 6 depicts an embodiment of a mid-infrared PUP based metrology system operating in a refleefive mode i.e. the illumination light is: provided to the wafer on the same side as the light collected from the wafer). In other embodiments, a mid-infrared FTIR based metrologysystem is configured to operate in a transmission mode ( i . e . , the Illumination light is provided to the wafer on the opposite side as the light collected from the wafer) .

[0061] Fid, 1 depicts an embodiment 250 of a mid-infrared FUR based metrology system operating in a transmission mode, hike numbered elements are analogous to those described with reference to FIG, 6. As depicted in FIG, 7, a beam sampler 124 is employed to direct illuminatibu light 152 to reflective objective 12SA, I:n some embodiments, beam sampler 124 is a: full aperture mirror. Reflective objective I25¾ focuses the illumination light 102 over art illumination spot 117 on wafer 115 ;as described with reference to reflective objective: 125 depicted in FIG, 5, [0062^:] As depicted in FfG. 7, reflective objective 12SB collects light 12:5 transmitted through wafer 115 in

response to incident illumination light 105 and directs the collected light 122 t© analyser 125, Collected light 125 passes through analyzer ISO and collection optics 127, In some embodiments:, collection optics 127 focuse collectedlight I2§ onto an active sensing surface o detector 128:,

31 In son·.? other embodiments, collestion optics 127 focuse collected light 129 at a collection field stop loot shown} . Sdditiooal Optical elements (sot shown) collect light front the collection field stop and direct the light onto an active sensing surface of detector 128,

CG063J :ln a further aspect, a metrology system

incorporating a mid-infrared F!IR spect ometer as described herein also includes one or more additional measurem t channels operating in one or more different wavelength ranges below mid-infrared (e.g, , less than 2 micrometers)or within mid-infraced <eg._:, between 2 and 21

micrometers} . In some embodiments, a mid-infrared FTIR:spectrometer and one ex more additional measurement

channels measure a target simultaneously, In other

embodimen s, a mid-infrared FTIR spectrometer and one or more additional measurement channels measure a target sequential ;.y . In general, a mid- infrared FTIR speotrometeroperating in combination, with one or more additional measurement subsystems: may measure a target at multiple: different angles of incidence, azimuth angles, different wavelength ranges, different polarisation, states, or any c0:mbination thereof

£00643 In some embodiments a mid-infrared FTI spectrometer cperates in combination with a hard M-ray metrology

subsystem, a soft h-tay ^metrology subsystem, a

speotioseep c ellipsometer a spectroscopic reflecto eter,

_:a hyperspectra1 imaging subsystem, a sbabteromater

subsystem, or any combination thereof.

IGO653 In some: embodiments, a mid-infrared FTIR

spectrometer operates in combination with :a broadband spect ometer channel operating in a wavelength range from ISO nanometers to rSGO nanometers, In some embodiments, a

32 mid--infra et FilR spectrometer operates in combination with both a broadband spectrometer channel operating in a wav length range fro ISO anometers to 250© nanometers and another spectrometer channel operating in a wavelength range from, 120 nanometers to 190 nanome ers.

CG066J FIS, 8 depicts a metrology system 108 Including a mid-infrared F!IR spectrometer as described with reference to FIG. 6, a spectroscopic refleetometer (SR) m asurement channel_# and a spectroscopic ellipsomete iSE) measurement channel - like numbered elements: ere analo ous to those described with reference to FIG. 6. In the efibodiment depicted in IG:, ø, the measurement spot: of the FUR, GR, and SE spectrometers are co-i©da d. in some ether

embodiments_# the measure ent spots are not cp-located,_:

0067] As depicted in FIG. 8/, 1SF ilium!nation source 101 includes additional emit ports 110 and 112, Exit port 110 transmits light to the SR measurement channel_# and exitpert 112 transmits light to the SE measurement channel.

Emit ports 110 and 112 may be constructed from a material that transmits light below the id_"-ihfrated range i©,g, _# below 2, 5 nanometers} , In some embodiments_# exit ports_: lid and 112 are constructed from fused silica_# Calcium

Fluoride_# Magnesium Fluoride_# etc. In the embodiment depicted in FIG, ;8_# exit port 112: ic const ucted from a vacuum ultraviolet light transmitting material. In some embodiments, exit port 112 transmits illumination

wavelengths ranging from 190 nanometers to 2_# 50©

nanometers. In another example_# exit por 112 transmits whole or parts of illumination wavelengths ranging from 120 nanometers to 2_# 500 nanometers. In addition_# exit port 11Q transmits the_: whole o parts of illumination wavelengths ranging from 120 nanometers to 2 , 500 nanometers. In the embodiment e icted in FIG. 8, LEP iilamination scarce 101 ge e ates illu ination light having wavelengths tanging fro vacuu ultraviolet light though mid-infrare light (i.e, t 120 nanometers to 2:0 micrometers) with high

brightness and small illumination source spot size.

[0068] As depicted in FIS. 8, optical ele ents 161 collect SR, illumination light 111 transmitted through edit port 110, and -direct $& Ilia iratign light 111 toward an

optional mirror 102, which directs SR illumination light ill to polarizing component 163. In some other

embodiments , focusin o tics (not shown) collect k

illumination light 111 transmitted through e it port 110 and focus the collected light to an illumination: source field stop (hot shown) . The illumination source field stop defines a stable source sire and position. Light passlug through the illumination source_: field stop is directed to polarizing component 163. In seine embodiments , the

polarizing component is ;a polarizer, a compensator, ox both, and ap include any -suitable commercially available_: polarizing component, The polarizing component can be^:

fixed or rotatable to different fixed positions:;. Although the SR illumina ion subsystem depicted in FIG. 8 includes one polarizing component, the SR illumination subsystem may include lagre than one polarizing component , As_: depicted in FIG. 8,_: optional illumination optics 164 collects light from polarizing component 1_:63: and conditions SR

iilumihatibh light 111 directed to beam sampler 165. In anexample, optional illumination optics 164 changes

illumination light ill beam siz or beam divergence. In anothe example, optional illu ination optres 164 focuses SR illumination light ill to an illu ination field stop

(not shown),. Beam sampler 165 samples a portion of the

34 light exiting the illumination field stop and directs the, light to reflective objective 125_* It some embodiments, bea s mpler 125 is a diehrbic_: filter. In so e other embodiments, beam sa ler 125 is a flip in mirror.

Reflective obi eatire 125 feauses the iilumination_: light 111 ever ah illumination spot 117 on Safer 1,15. Reflective objective 125 also collects SR collected light 118

reflected from wafer 115 in response to ineident

illumination light 111 and directs the collected light 118 to analyfer 167, Collected light 118 passes through bea splitter T65^: and reflects from beam sampler IS6: toward:

analyser 167, and collection optics 168_:. In an erample, beam sampler 166 is a dichroic filter. In some other embodiments, beam, sampler 1,66 is a flip in mirror. In some other embodiments, bean samplers 165 and 166 flip in to sample SR illuminatio light 111 and SR collection light XI8 and flip out of the SR illumination light ill and SR collection light, 118 for FIXE measurements, in some embodiments, collection optics 168 focuses collected light 118^: onto an active sensing su face of detector 169* In some other embodiments, collection optics 168 focuses collecte light 118 at a collection field stop fnot shown)„ hdditionai optical elements (not shown) collect light from the collection field stop and direct the light onto an active sensing surface of detector 169,

[006S] In seme embodiments, detector 161 is sensitive to vacuum ultraviolet, deep ultraviolet, ultraviolet, visible, and near~infrared light including any wavelen th within a range of 120 nanometers to 2.5 micrometers. In some embodiments, detector 162 is a charge coupled device (CtD) sensitive to ultraviolet and visible light ( e . q . , light having wavelengths between 19:0 nanometers and 8:60

35 nanometers} . However, in genera!,, other two dimensional detector technologies may toe eontempIatted |6,g., a osition sensitive detector {PSD , a photovoltaic detector, etc.} . Detector 16;9 converts the incident light into electrical signals indicative of the spectral intensity of the

i.no ident Iigh .

10070] As depicted in FIG, B, detector 169 generates detected signals lot indicative of tie optical respons of the measured structures on wafer 115 to the illumination light ill. Detector 169 communicates detected signals 136 to computing system 130 ,

[0071] As depicted in FIG, B, $&- ±Xlaminafeion light 113 Is extracted from plasma chamber 105 via exit port 112.

Optional SS source optics 149 condition and redirect illumination light 113 towards S|E i limednation optics

Entrance port 142, SE illumination light 113 passes through optional optical filters 143 polarizing component 144, field stop: 145, aperture stop 146:, and i lumination optics: 147, The one or more optical filters 143 control light level, spectra^"! output, oh tooth, from the

illumination subsystem, In some examples, one or more multi-rone filters are employed as optical filters 143, PolarIzing component 144 generates the desired polarization state exiting the illumination subsystem. In some

embodiments, the polarizing component is a polarizer, a compensator, or both, and ma include any suitable

commercially available polarizing component. The

pola izing component can be fixed or rotatable too different fixed positions. Although the illumination subsystem depicted in FIS, 8 Includes one polarizing component, the iiXumlnation subsystem may include more than one polarizing component. Field step 145 controls the field of view fffCJV) of the illumination subsystem ana may include an suitable commercially available field stop. Apex tare stop 146 controls the unifterrosl aperture {NA) of the illumination subsystem and may include any suitable commercially available aperture stop, bight from LSJ? Illumination

-source 101 is direoted through Ilia ination optics 147 to b focused on ore or more structures dn wafer 115 at awOblique angle_? a. The iliu iination subsystem ma Includeany type and arrangement of optical filter is) 143_/

polarising component 144, field stop 145, aperture stop

146, an illumination optics 147 known in the art of spectroscopic eIXipsometry -

[0072] As depicted, in FIG. 8:, the beam of illumination light 113 passes through optical filtsxis) 143, polarising component 144, field stop 1,45, aperture stop 146, and illuminat on optics 147 as the bea propagates fro the illumination source 101 to wafer US. Beam 113 illuminates a portion of wafer 113 over a measurement spot 117.

[0073] In some xa ples , the beam sire of the amount ofIllumination light 113 projected onto the surface_: of wafer 115 is emailer than a site of §c measurement target that is measured on the surface of the specimen. Exemplary beam shaping techniques are described in detail In Oh S, latentApplication Publication NO. 2013/0114085 by Wang et al,, the contents of which are incor orated herein by referencein their entirety, In one aspect, the use of a 313Pillumination source enables wery small illumination spot sice on all measurement channels of metrology system 10b,

In some embodimenta , a L$P iliuminaiion source generates plasma: haring: a sice of approximately I0Q micrometers.

This small sired illumination source is, in turn, projected onto the wafer with a magnification of approximately ID times. Ihus_:, in principle, in some embodiments, an, illuminatio sp t sine of a proximately It micrometers is achieved, This can fee farther reduced in size fey passing the illumination light through an illumination pertura.

For example, a 100 micrometer source size may fee reduced to50 micrometers using am 11 laminatier aperture, which is, in turn, proj cted onto tfee wafer with a magnificat ion, ofapproximately If limes_:. Thus, in principle, in some e bodi ents_/ an illumination spot cine of approximately 5 micrometers is achieved. In some embodiments_/ beam

apodization optics are_: used to reduce the illumination spot size at the wafer. How ver, attenuation by use of th illumination aperture Gomes at a cost of lost photons . In seme embodiments, illumination light is projected from anfeSF light source onto the wafer with an i.llumlnation spot size of SO micrometers, or less, without signi£leant beam apobication (e, g, , less than 10¾ photon loss due to

:apodiration} ,, In some embodiments, illumination light is projected from an hSF light source onto th water with an illumination spot size of 25 micrometers, or less, without signifleant beam apodization (e . q . , leas than lt% photon less due to apodization) . As described herein, the spotsize is defined fey the distance along the longest direction of extent pf the ifrumination spot , For example, the size of a circular illumination spot is defined fey the diameter of the circle. In another example, the size of a

elliptical 1Idurn1nation spot is defined by the distance across the ellipse along the .major axis,

[0074] In Contrast, the minimum spot size of a thermal illumination source such as a lobar light source is approximately 2 000 micrometers which is, in turn,

projected Onto the wafer with a magnification of

2B approxi ately 10 times. Thus, in principl an illumination spat sine of approximately 230 micromotors is achieved by a giobar light source. Further reductions in spot sine may be_: achieved by use of an illumination

aperture:, bat to achieve a spot size comparable to a LSJ? light source reguires a severe loss of photons. For this reason , it Is preferable to employ a LSP^: light source fo semieon uo metrology based on FTIR spectroscopy ,

[0075] tietrology syste 100 also includes a collection optics subsystem configured to collect light generated by the interacti on between the one or more siruetunes and: the incident illsemination beam 113_» A beam oi collected light 114 is_: collected fro measurement spot LIT by collec ionoptics 118. Collected light 114 pastes through collection aperture stop^: 140, polarising element 150 an field sto 151 of the collection optics subsystem.

[00761 Collection optics 141 includes any suitable optical elements to collect light from the one or more structures formed on wafer 115. Collection aperture stop 148 controls the NA of the correction optics subsystem. Polarizing:

element 15b analyzes the desired polar! ration state, The polarizing element ISD is an analyzer or a compensator,.

The polarizing element ISO can be fired or rotatable to different fired positions. Although the collection

subsystem depleted in FI©. 8 includes one: polarising element, the collection subsystem may include more than one polarizing element. Collection field stop 151 controls the ^:F©¥ of^: the oolieotion subsystem. The collection subsystem takes light from wafer 115 and directs the light through collection optics 148 and polarizing element ISO to be focused: on collection field stop 151 in some embodiments, colldot ion field stop^: 151 is used as a spectrometer slit

39 for the spectromet rs of the detection subsystem. However,c llection field stop 151 may fee located at or near a spectro eter slit 152 of ^:tne^: spectrometers of the detection subsystem.

[007 3 the collection subsystem may include any type and arrangement fef collection optics 148, aperture stop 1 5, polarizing element 150,_: and field stop 151 known in the art p£ spectreacop;1c eIIipsometry,

[:007b] In the embodiment depicted in FI©, 8, the collection optics subsystem direct Light to spectrometer of the detection eufosysfem, The detection subsystem genefatea output responsive to light collected from the one_: or morestructures illuminated by th illumination subsystem. In the embodiment depicted; in FIG, 8, collected light 114 passes through: spectrometer slit 152 and is incident on biffraetl e elemen 153, Diffractive element 153 is configured to spatially separate wavelengths of the

incident light at the light sensitive surface of detector154, In one example, detecto ISi is a charge: coupled device (CGD) sensitive to vacuum ultraviolet and

ultraviolet fe.g. light having; wavelengths between 120nanometers and 40Q nanometers} , In another example, detector 154 is a charge coupled device (CCD sensitive to deep ultraviolet to near infrared (e,g, , light having wavelengths between ltd nanometers and ISO nanometers,) , In another example, detector 154 is a near infrared sensor ie.gv, sensitive to light having wavelengths between 858 nanometers and 2,S0D^: nanometers)

[0079] Metrology system 10® also includes computing system 130 configured to receive detected signals IBS, 136, and 133, Including; the spectral, response of wafer 115 to 5TGn> DBVy visible, near-infrared,, and mid-infrared illumination. Furthermere computing system 130 determines an estimate 155 of a vnlee of a parameter- of interest of the measuredstructurefs) based bn detected signals 135 136 and 137.

By simultaneously collecting measurement signals 133, 136, and 137, measurement times are reduced and all spectra are measured with the same alignment cofoditions . This allowswarelength errors ho foe corrected ore easily because a common correction can foe applied to all spectral data sets, [0080] In another aspect, the mid-infrared FTIB

spectrometers described herein employ off-arid

illumination, collection, or both, to regent basureiKentsignals generated by reflec ions from the bottom of the under1ying substrate:.

[0081] Fid, 9; depicts Illumination 188: incident onto film layer 186, which is disposed on substrate 1871 As depleted in FI<3:_* 9, the iiiuminatidn is arranged at near normal incidence, but specifically ayciding normal incidence (BOX = zero degrees) , A portion of incident light reflects from tbs surface of film 186, another portion 111 reflects from the interface between film 186 and substrate 187 , These reflections are desirable and must foe collected t© estimate the thickness of film 186 based on a reflectometxy

technique, Mowecer, in addition, a portion IBS of the Incident light 188 penetrates the substrate 187. A portion 190 of light 188 reflects from the bottom of the substrate te.g. the backside of a wafer) , propagates through

substrate 187 and film 186. Light 180 is undesirable and; contaminates the measurement of; film iSt, As depicted inFIG. 1, a collection aperture 193 it successfully employed to block the undesirable light 198 reflected fro the bach surface of the substrate 187. Tills is possibl because the son-zero angle: of incidence of the illumination creates a spatial se ar tion between light reflected from the top and bottom surfaces of film 18¾ and light 190 reflected from tie bottom b,f^: substrate M,

[00823 In contrast FIS, 10 depicts illumination 1:94 incident onto film, layer G88, which is disposed or

substrate 187_* As depicted in FIG. 10* the iliumnation is arranged at normal incidence. A portion of incident light reflects from the surface of film 188* anothe portion reflects from the interface between fil 186 and substrate 187_:. In addition* a portion 195 of the incident light 194 penetrates thc_: substrats 187. A portion 196 of light 195 reflects from: the bottom of the substrate_: (e,g. * the

backside of a wafer), propagates through substrate 187 and film 188, Light lib is undesirable and contaminates themeasurement; of film 186- As depicted in FIG. 10, a

Collection aperture 193 is unable to block the un sirable light: 196 reflected from the bask surface of the substrate 187 because the zero angle of incidence of the illumination does not generate spatial separation between light

reflected from the top and bottom surfdoes of film: :186 and light XS7 reflected from the bo tom of substrate 187,

[0083] Thus, in some embodiments, it is referable to perform mid-infrared FTIR measurements: and spectrosoopie refieebsmetry measurements as described herein at non-zero angles of incidence. In this, manner, light generated f ees backside reflections can be effectively ^blocked from the measurement , In soma embodiments, oblique 11 laminafish isemployed to reduce measurement sensitivity to backside reflections as described with reference to FIG, 9, and alsoillustrated in embodiments of FIG. 1^,1. In some other embodiments, normal, illumination is employed, but an obscuration mask 123 in the collection path at or near the. 3_:2 collection aperture atop: or its conin a as, is employed to block the central rays over the numerical aperture sneh that the back side refheelidu is net admitted into the measurement optica as illustrated in e bodiment of IG. 12. This approach enables normal illumination incidence,_: bar suffers from possible¹ disadvantages shoh as a; centrally obscured pupil, ligh loss, and algorith ic Complexity. la come other embodi ents, obscuration 223 is located in the: iilumination path .

[0084] FIG, II depicts an infrared spectrosco ic

reflectemeter including o e or more Measuremeht channelsspanning a wavelen th rang between 750, nanometers an 2500 nanometers in another embodiment. In one aspect, infrared spectroscopic refleetometer 280 includes a Schwartschild Objeetive to avoid normal incidence. A S hwartzo_:hiId objective as described herein may^: be employed as an

objective in an FUR Measurement channel as described with reference to FIGS, 6 and, S, As depicted In FIG. 11,infrared spectroscopic reflactometer 200 includes polarizer 201, objective SSI, analyser 210, and spectrometer 212. As depicted in FIG. XI, a^: light beam is generated by the illumination source 282 in response to command signals received from computing system 130. Light from

illumination source 202 is conditioned by optional beam forming optics 203 to generate an illumination light beam 220. Ilinmination light beam 220 is directed to polarizer 281, Although, _:as depieted, iilimb nation light directed to olarizer 20;4 comes from, illumination source 202, in general, light from any of the illumination sources o^:f system 1Q8 may be combined to generate a illumination light beam directed to polarizer 2d4. In this manner, the spectral components of the illnmina:tiOh light can be configured as a combination of light emitted from mul-fipie i1.1wihstisa aources ,

[0085] la, soma embodiments, polar!ter 204 is corfi ured to selectively rotate a polarizing element about the optical axis of the Illuminatic _: light beam 220. Xn general,, polarizer 204 m p include any polarising element and system to rotate the polarising element known in he art! For example, the polarizer 204 ap include a polarising element mechanically coupled to a rotational actuator. Xn one example, the polarising; element may^: fee a Pochon prism. In another example, the polarising element may include a beamdisplacer , Polarizer 204 is configured to operate withinsystem 200 in either a rotationally active or r tat,tonallyinactive state. In one instance, :a rotatiohal actuator of polarizer 204 ma be inactive sued that the polarizing element remains rotafionaily fixed about the optical axis of i lamination light: 220. Xn another instance, the rotational actuator ay rotate the polarizing element at a selected angular frequency, br, about the optical axis of the illumination light.

[0086] In some other embodiments, polarizer 204 is

configured, with a, fixed polarization angle about the optical axis of the illumination light beam ZZΰ.

[0:087] As depicted in FIG. 11, illumination light bea 220 passes through polarizer 204 while the rotational actuator rotates the polarising ele ent at the selected angular frequency, op . In this anner, polarizer 204 generates a polarized light beam 221 directed toward beam sampler 216. Beam sampler 206 directs a portion 221B of the polarized light beam, 2:21 towards ofeyecfiye 2^:01 , The remaining portlaa 22IB of the polarize light beam 2:21 is directed towards a beam dump (hot sfeowh) or a detec.tor (not shown) to procide feedback to computing :system 130 regarding beam condition as described: with reference to FIG, 6.

[0088] In, the embodiment depicted in FIG, 11 objective 201 is a SchwartzschiId type objective including reflective optical elements only. The SehwactEsehiXd objective depicted in FIG. 11 includes a: conc ve mirror 208 with an opening (erg. hole) aligned with the optical axis, Oh, toallow ligh to pass in and out of the objective 2(11.

Incoming light passea through the opening, and reflects off convex mirror 207 toward concave: mirro 208. The reflected light is focused on the surface of wafer 212 b concave irror 2:00, The polarized light: beam 221 is focuse onto the surface of wafer 212 over a range of angles of

incidence by objective 2,01, but not at a Eero angle of Incidence (i.e., normal to the surface of wafer 2120. In so e exampl s, polar! zed .light bea 2;2^:1 is focused onto the surface of wafer dll within a range Of angles of incidence between 5 and ID degrees. In some other examples,

polarized light beam 221 is focused onto the surface ©fwafer 212 within a range of angles of incidence between 5 and 22 degrees, In some examples, a portion of polarized light: beam 221 is focuse onto the surface_: cf wafer 2i2⁽ at ah angle of incidence less than 20 degrees. In some other examples, a portion cf polarized light beam 221 is focused onto the surface of wafer 212 at an angle: of incidence less than 15 degrees. In some examples, the polarized light beam 221 is focused onto the surface of wafer 2,12 at small angles of incidence results in a small illumination spot. In come exantples, the resulting

illumination spot is less than 20 micrometers in diameter, In seme other examples, the resulting illumination spot size is less t an Id micrometers in diameter. [0089] The Interactio of the focused, polarized light tea 221 with wafer 212 modifies the polarleafloo of the

radiation ^:hy any of reflection, scattering, difftaction, trapamisstop, or other types_: of processes. Afte

interaction with the wafer 212, modified light 222 is collected by objectire 221 and directed to beam sampler IQS:. Light from wafer 2i2 is collected by concave mirror 2QS and focused onto convex mirror 207 where it exits the: SchwartzschiId objective through the same hole as the incoming light toward beam sampler 206, Seam sampler 206 is eonfigured to transmit modified light 222 toward

analyser 210. In the: embodiment depicted in FIG, XI,analyzer 210 includes a polarizer element that remains retationally fixed about the optical axis of modified light beam 222 while the modified light bea 222 passes through, the analyzer 210 and optional beam focusing optics 211 to spectrometer 2X2, In spectrometer 212,· the beam components having different, wavelengths are refracted, (e,g. in a prism spectrometer or diffracted {e . g. _t in a grating spectrometei in different directions to different

detectors , The detectors may be a linear array of

photodiodes, with each photodiode measuring radiation in ,a different wavelength range. The radiation received b the spechrometer 212 is anal zed with regard to polarizatio abate_# allowing ter spectral analysis by the spectrometer of radiation passed by the polarizer 212, These spectra 226 are passed te competing system 130 for analysis of the structural characteristics £ wafer 212,

[0090] FIG, 12 depicts an infrared spectroscopic

refiectometer including ¾ne or mote measurement channels spanning a wavelength range between 75D nanometers and 2600nanometers in: another embodiment. In one aspect, infrared spectroscopic refXe toiseter 3:00 includes an, off-axis unobseared objective lens 301 to chieve oblique incidence. An off-axis uucbsoured objective lens as deteribeci herei may be employed as at objective in an FT1R measurement channel as described with, reference to PIGS, 0 and Si

[0091 ] As depicted in :FTS. 12, infrated spectroscopic reflactometer 300 is analogous to infrared spectroscopic refleet©meter 20:0 described with reference to Fit!. 11_» How ver_/ instead of a Schwartschild objective, an off-amis unebseare objective lens 301 in employed, incoming light reflects off convey mirror 307 toward concave mirror 3Q .The reflected Light Is focused on the surface of wafer 3X2 by concave mirror 308. The polariced light beam 221 is focused; onto the surface of wafe 312 over a range of angles of incidence by objective 301. In some examples, polarised light beam 2:21 is focused onto the surface of wafer 33,3 within a range of angles of incidence between 5 and 40 degrees » In some other examples,, polarised, light beam 221 is focused onto the surface of wafer 312 within a range of angles of incidence¹ between 5 and 2S^: degrees. in some examples, a portion of polarised light beam 231 is_: focused onto the surface of wafe 312 at ,ah angle of incidenoo leas than 20 degrees. In some other examples,, a portion pf polariced light beam 221 is focused onto the surface of wafer 312 at an angle of incidence less than 15 degrees, solarized light beam 221 is focused onto the su face of wafer 312, at small angles of incidence results In a_: small 11 lamination spot,, in some examples, the resulting illumination spot is less than 2^:Q micrometers in diameter. I some other examples, the resulting

ilium!nation spot sice is lean than 13 micrometers in diameter. In some examples, an illumination mask with a central obscaratios_# such as_: as 223 depicted ip FIG. 12_i: s located at or near an illumination pupil .

[0092] The interaction of the focused, polarized light toam 221 with_: water 312 modifies the polarisation of the

radiation bp any of reflection, scattering, diffraction, transmission, or other types of prosesses. After

inferact!on with the wafer 312, modified light 222 Is

OQileeted bp objective 361 and directed to bea sampler

206. Light fro wafer 312 is collected by concave mirror 31)8 and_: focused_: onto convex mirror 307 where it is

colli ated and emits objective 301 towar beam sampler 206 , In some other examples, a collection mask having a centralobscuration, such as SiasJc 223 depicted in FIG. 12, is located; at or bear the collection pupil.

[00:93] Exemplary imp1ernentations of off-axis anobscnred objective lenses are described in detail in ll.il. Patent Application publication do. 2016/01:39032 by Rampoidi et al., the contents of which are incorporated herein bp reference in their entirety.

[ 0094] In general, the reflective objectives described with reference to FIGS. II and 12 are exemplary embodiments of reflective objective 125 depicted in FIGS. 6 and 8 when: off-axis ilinmination, collection, or both, is implemented for pid~infrared FTIR measurements SR measurements,, or both .

[0095] As depicted in FIGS. 6, 8> II, and 12, the

11 lustrated Measurement channels include a polarizer oh the illumination side and an analyzer on the collection side.

However, in general, it is contemplated that any

measurement channel map include, or not include, an

illumination_: polarizer, a collection analyzer, an

11,1a inatio comp nsator, a collection compensator, In any combination, to perform m aseremeats of the polarised reflectivity of the sample, unpcdarised reflectivity of the sample or tote ,

[0096] In some embodiments, one or more measurement channels of the metrology systems described herein are configured to measure¹ the wafer at different eri irth angles, In addition to different ranges of wavelength and angle of incidence · in some embodime ts, a metrologysystem including a mid~infrared FTIR spectrometer as described herein i eonfigured to perform measurements of the wafer at azimuth angles of aero and ninety degrees relative to the metrology target:, In so e embodim nts, the metrology system is configured_: to measure wafer

efleotlvity over one or more wavelength ranges, one or more ,AQI ranges, and one or more azimuth angles

simu11aneoas1 y

[0097] In another further aspect, the dimensions of an illumination field stop: projected on wafer plane area justed to optimise the resulting measurement accuracy and speed based on the nature of target under measurement.

[Od90] In another further aspect, the dimensions of illumination field stop are adjusted to achieve the desired spectral resolution for each measurement application .

[0099] In some examples, s ,g . , if the sample Is a very thich film or grating structure, the illumination field stop projected on wafer plane in the direction

perpendicular to he plane of Incidence is adjusted to reduce: the field sire to achieve increase: spectral

resolution, In some examples, e.g,, If the sample i a thin film, the illumination field stop projected on wafer piano In the direction perpend cular to the plane ofincid nce_: is adjusted to increase the field sice to achieve a shortened measurement time without losing spectral resolution .

[OO10O| In so e e bodi ents_:? c mputing: system 130 is coniigured te^: receive signa1s (e g . _t signais 13S^: 136 , 137 , or any combination thereof) indicative of the spectral respbnae of the measured structure (s:) . Computing system 130 is further configured to determine control signals that e e communicated to a programmable illumination field atop (e.g,, illaminat ion field stop 145) A programmable illumination field stop receives: the control signals and adjusts the sice of the illumination aperture to achieve the desired iiluminafion field sire,

[QdlOlJ In some tramples, the iliu lnafelon field stop is adjusted to optimise measurement accuracy end speed as described hereinb fore. In another example, the

illumination field stop is adjusted to prevent image clipping by the spectrometer silt and corresponding

degradation of measurement results, In this manner, theillumination field size is adjusted such that the image: of the measurement target underfills the spectrometer slit. In one example, the iilamination field stop is adjusted such that the projection of the polariPer slit of the

ί11-fi ination optics Underfills the spectrometer slut of the metr©logy :system .

1:001021 As depicted in FIS, 5, a single: ASP source having ^multiple ports provides illumination light for SB, SR and FTIR measurements · In .another embodiment, separate

illumination source are employed to provide illumination light to AS, SR and Flxfi measurement channels .

[001031 As depicted in FIG, G, the SB, SR and FTIR measurement channels have collocated focus at the wafer. In son·.? other embodiments, the SS :SR ana FTIR measurement channels are not collocated at the wafer_*

£OQ104| FIG. 14 11lostsafes a ethod 500 of pe forming spectroscopic measure ents in; at least one novel aspect. Method 500 is suitable for implementation by a metrologsystem such as metrology systems 100,, 2Gii, ana 300

illustrated in FIGS . ø, 9, and, 10, respectively, of the present invention. In one aspect, It is recognized that, data processing blocks of method 5Off may be carried cut via a pre-programmed algorithm execut d by one or more

processors of computing system 130, or any other general purpose computing system, If is recognized herein that the particular Structural aspects of metrology systems Iff,

_:200 and 300 do not represent limitations and should be interpreted as illustrative only,

[001053 I» block, 501, a first amount of broadband

illumination light ineluding wavelengths spanning a range from 2,5 micrometers to 12 micrometers is generated by one or more illumination sources,

[001061 In block 502, an amount of FTIR iliuminatioh light having time varying spectrum is_: generated from, the first: amount of broadband illumination light,

[001071 Ih block 503, the amount of FTIR illuminationlight is directed to a PT P measurement spot on a surface of a specimen under measurement at one or more angles oh incidence, one or more azimuth an les^ or a combination thereof. The sloe of the FTIR measurement spot on the surface of the specimen is less than 50 micrometers,

[001083 In block 5©i, an amount of FTIR collected light is collected from the FTIR measurement spot on the surface of the specimen in response to the amount of FTIR

11,1u iuation 11ght . [001091 In Mack 505, the amount of FTIR collected. light is detected and FTIR output signals indicative <¾£ the e ected FUR collected light ar generated,

[001101 In Mock 506, an estimated value of a first parameter of interest of the specimen under measurement isdetermined haded on the FTIR output signals and the time varying spectrum of the amount of FTIR illumination light, fOOlllJ In a further embodiment, systems 100, 200, and300 include one or more computing syste s 130 employed: to: perfor ^'measurements of actual device structures: based on- speetroseoplio measurement data collected in accordance with the methods described herein . Th on on mor computingsystems 130 may be communicatively coupled to the

spectrometer. In one aspect, the one or more comp ting systems X3^:G are configured to reo;ei:ve measurement data associated with measurements cf the structure od the

Specimen under measurement ,

[001121 It should be recognised that one or more steps described throughout the present disclosure may fee carried cu by a single computer system 130 dr, alternatively, a multiple computer syste 131. Moreover; different

subsystems of system 100 may include a computer systemsuitable for carrying out at least a port ion of the steps described herein. Therefore, the -aforementioned

description should ne be interpreted as a limitation an the present invention but merely an illustration,

[00113! in addition, the computer system 130 may be communiontrycry coupled to tbe spect omet rs in any manner known in the art. for /example, the one am more computing systems C3Ό may be coupled to computing systems associated with the spectrometers . In another example, the spectrometers may be controlled directly by a single co puter system coupled to co pu er system 130_*

[00114 Thie· computer syste 130 of metrology system 100 may be copfi u ed tg receive and/or aeguire data or

information from the subsystems of the system (e.g.,

-spectrometers and ltd like by a transmission: medium that may include wireline and/or wireless portions_* to this manner, the transmission ediu may serve as a^: data link between: the computer system 130 and other subsystems of syste 100.

[00115J Computer system 13D of metrology system G0O may be configured to receive and/or acquire data or information, e.g. measurement results, modeling inputs,, modelingresults, reference measurement results,, etc,} front othe systems by a: fcranamission medium that may include wireline and/or wirelfoss portions. In this anner, he transmission medium may serve as a data lint between the computer system 130 and other systems {e . g . , memory on-board metrology system 100, external memory, or other external systems).

For example, the computing system 130 may be configured to receive measurement data from a storage medium (ice., memory 1:32 or an external memory via a data link. For instance, spectral results obtained Using the spectrometers described herein may be stored in a p rmanent or semi^¬ permanent memory device [e.g., memory 132 dr an external memory) . In this regard, the spectral results may beimported from qn-bcard memory or from an external memory system, Moreover;, the computer system 130 ma send data to other systems via a transmission medium. For instance, a measurement model pr an estimated parameter value 171determined by computer system 130 may foe communicated and sto ed in an external memory, In this regard, measurement results may be exported to another aystem.

[00116J Computing system 130 Sidy include, but is not limited to, a_: personal computer system, mainframe computer system, workstation, image computer, parallel processor, or any Other denice kroon in the art. In general, the term "Computing sys em:'' may be broadly defined to encompass any evice having one or mor processors, which execute

instructions from a memory medium.

[001171 Program instructions 134 implementing methods such as those described herein may he transmitted ove a transmission medium such as a wire, cable, or wireless transmission link. For example, as iLlustrated in Fid. I, program instructions 134 stored in memory 132; are

t ansmitted to processor 131 over bus 133. P ogram

instructions 134 are stored in & computer readable mediu : Ce.y , memory 132}. Exemplary computer-readable media include read-only memory, a random access memory, a

magnetic or optical disk, or a magnetic tape.

[001181 In some examples, the measurement models are implemented as an element of a SpectraSbaped optical critical—dimension metrology system available from RLA- Tencor Corporation, Milpitas, California, USA. In this manner, the model Is created and ready for use immediately after the spectra are collected by the system.

[001191 In some other examples, the measurement models are implemented off-line, for example, by a computing system: implementing AcaShapeb software available from KLA— Teneor Corporation, Milpitas, California, USA. The

resulting, trained model may be incorporated as an element of an AeaShapea library that is accessible by a metrology system performing measurements. [001201 Ίr another aspect_# the methods and systems forspectroscopic metrology of semi cor nctor devices described herein are applied to^; the meds remeht of high aspect ratio (HAM) structures_# large lateral dimension structures_# or both. The described embodiments enable o tical criticaldimension (CEQ fxlftp an composition metrology for

semiconductor devices including three dimehsibnal KAMD structures_# such as vertical-hAMD {V-MAf!D) structpres, dynamic random access memory structures (DEAM) , etc., manufactured by various semiconductor manufacturers such as Samsung Inc. (South Korea!_# SK Hynlx Inon ihonfh Korea¹) _# Toshiba Corporation (Japan) , and Micron Technology_# Inc. (United States) _# etc. These complex devices suffer from log light penetration into the structure (s) being measu ed. Fib,, 13 depicts an exemplary high aspect ratio HAND

structure 41)0 that suffers fro low light penetration into the structure (g) being measured. A spectroscopic

ellipsc eter with broadband capability and, wide ranges of ACM_# arimuth angle_# or both_# havin simultaneous: spectral band detection as escribe herein is suitable¹ for

measurements of these high-aspect ratio structures EAR structure® often include hard ash layer® to facilitate etch processes for HAMS, AS described: herein_# the term "HAM structure” refers to any structure characte ise by anaspect ratio that exceeds 2fl or 10 1, and may be: as high as 10011_# o higher ,

[001211 Ip yet another aspect_# the mensarerneht results described herein can _:be used to provide active feedback to a process tool (e.g, _# lithography food, etch tool_#

deposition tool_# etc,} , Fgr example_# values of measured parameters defermined based on measurement methods

described herdin can be communicat d to a lithography tool to adjust the lithography system to achieve a desired

outpu . In a similar way etch parameters ,g, etch time, diffueivity, etc_:,} O deposition parameters {e,g. time, concentration:, etc,,:} may fee included In a measurement model to provide active feedback to etch tools or deposition tools, respectively_:, in some exam le, corr ct ions tfe

process pa ame ers determined based pit measured device parameter values and a trained measurement model may fee communicated to a lithography tool, etch tool, or

depos 1tion tool,

100122} ¾s described herein, the terms "critical

dimension" includes auy^: critical dimension of a structure }e,g., bottoms critical dimension, middle critical

dimension, top critical dimension, Sidewall angle, prating height, etc,), a critical dimension between any two or more structures (e,g, , distance between two structures}, and a displacement between two or more structures (e,g, , overlaydisplacement between overlaying grating structures, etc.} . Structures may include throe dimensional structures, patterned structures, overlay structures, etc.

[001231 ¾s described herein,, the term "critical dimension applica ion" or "critical dimension measurement

application’'' includes any critical dimension; measurement, [00124} hs described herein, the term "metrology syste " includes any system employed at least in part to

characterize a: specimen in any aspect_:, including

measurement applications such as critical dimension

metrology, overlay metrology, foeus /dosage; metrology, and composition metrology. However, such terms e^:f art do^: not limit the scope ^::of the term "metrology system" as described herein. In addition, the metrology system 100 may fee configured tor measurement of patterned waters an /or

4f, unpatturned wafers . The metrology system may be configured as a LSD inspection tool, edge inspention tool, bacfeside inspection tool, acro inspection toot, or iftulfci-modb inspection tool (involving data team one or more pl tforms simultaneously] , and any other metrolog or inspection tool that benefits from the calibration of system parameters based on critical dimension ata,

[00125] Various embodiments are: desoribed herein for a se icohdbot©r measurement sy tem that may be nsec fox measuring a specimen within any semiconductor processing tool. (e.g. an inspection system or a lithography system). _:The term ” specimen” is used herein to refer to a wafer:, a reticle, or any other sample that may be processed (e.g. , printe or inspected for defects) by means known in the art.

[0012:6J As used herein, the term ‘’waf r*' generally refers to substrates formed of a semiconductor or non- semiconductor material . Examples include, but are no limited to, monocrystalLine silicon, gallium arsenide, and indium phosphide. Such substrate may ^"fee co monly found and/or processed in semiconductor fabrication facilities, in some cases, a wafer may include_: onl the substrate

(ire., bare wafer). Alternatively, a wafer ma inelide one or more layers of different materials formed upon a

substrate. One or more layers termed on a wafer may be "patterned" or "unpatterned, " For example, a wafer mayinclude _:a plurality of dies having repeatable pattern features ,

[00:1271 A "reticle" may he a reticle at any stage of a reticle fabrication process, o a completed reticle thatmay or may not be released for use in a semiconductor fabrication fadifty , A reticle , or a '’mask,*' is generally d fined as a substantially transparent substrate baaingsubstantially opagne regions formed thereon and configured irs a pattern. The substrate may include, for example, a glass material such as amorphous SiOi, A reticle may be disposed above a resist-covered wafer during an exposure step of a lithography process such that the pattern on the reticle may be transferred to the resist_:,

[00128] On or more layers formed on a later may be patterned or unpattexned, For example, a wafer may include a plurality of dies, each having repeatable pattern

features, Formation and processing of such layers of material may ultimately result In completed devices, Many different types of devices may be formed on a wafer:, and the term wafer as used herein is infended to encdrapabs_: a wafer on which any type of device known in the art is feeing fabricated.

[001291 in one Or more exemplary embodiments , the

functions described may be Implemented in hardware, software:, firmware, or any combination: thereof, I

implemented in software, time functions may be stored on or transmitted over as one or more instructions or code on a compu er-readable_: medium. Computer-readable media includes both computer storage media and eommunication media

_:including an medium that facilitates transfer o a

computer program from: one place to another, A storage media may fee any available media that can be accessed b a general purpose or special purpose computer. By way ofexample, and not limitation, such computer-readable media can comprise RaM, ROM, EEPROM, CD-ROM or othe optical dish storage, magnetic disc storage or other magnetic storagedevices, or any other medium that can be used to carry or store esire ogram node means in the form of instructions or data structures and tha car fee accessed fey ,a general-purpose or special-purpose computer, or a

genets1-purpose or specia1-purpose processcr. Also, any connection is properly termed: a computer-readable

medium. For exa ple. If the software is transmitted fro a website, server, or Other remote source using a coaxial cable, fiber optic cable, "twiste pair, digital subscriber line (:D8L) o wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSD, or wireless technologies such: as infrared, radio, an microwave are included lb the

definition of edium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD) , floppy disk and biu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of com ute -readabie edia.

CQ913QJ hlthough certain specific embodiments are

described above for instructional purposes, the teachings ©f this patent document nave general applicability and are not limited to the specific embodiments: described above. Accordingly, various modifications, adaptations, and combinations of various features of the described

embodiments can be practiced without departing from th scope of the invention as set forth in the claims.

Claims

CLAIMS What is claimed is:

1. A metrology system comprising:

a mid-infrared Fourier Transform Infrared (FTIR) spectrometer including:

at least one illumination source generating a first amount of broadband illumination light including wavelengths spanning a range from 2.5 micrometers to 12 micrometers;

an interferometer receiving the first amount of broadband illumination light and generating an amount of FTIR illumination light having a time varying spectrum;

an FTIR illumination optics subsystem directing the amount of FTIR illumination light from the

interferometer to a FTIR measurement spot on a surface of a specimen under measurement at one or more angles of incidence, one or more azimuth angles, or a

combination thereof, wherein a size of the FTIR measurement spot on the surface of the specimen is less than 50 micrometers;

a FTIR collection optics subsystem collecting an amount of FTIR collected light from the FTIR

measurement spot on the surface of the specimen in response to the amount of FTIR illumination light; at least one FTIR detector having a surface sensitive to incident light, the at least one FTIR detector detecting the amount of FTIR collected light and generating FTIR output signeils indicative of the detected FTIR collected light; and a computing system configured to generate an estimated- value of a first parameter of interest of the specimen under measurement based on the FTIR output signals and the time varying spectrum of the amount of FTIR illumination light .

2. The metrology system of Claim 1, the at least one illumination source generating illumination light

spanning a wavelength range from 2 micrometers to 20 micrometers .

3. The metrology system of Claim 1, wherein the mid- infrared FTIR spectrometer includes a polarizing element in an optical path between the at least one illumination source and the speciment under measurement, a polarizing element in an optical path between the specimen under measurement and the FTIR detector, or both.

4. The metrology system of Claim 1, wherein the at least one illumination source includes a laser sustained plasma (LSP) light source generating the first amount of broadband illumination light.

5. The metrology system of Claim 1, wherein the at least one illumination source includes an infrared

supercontinuum laser source generating the first amount of broadband illumination light.

6. The metrology system of Claim 1, wherein the at least one illumination source includes a set of quantum cascade laser sources generating the first amount of broadband i11umination 1ight .

7. The metrology system of Claim 1, wherein the at least one illumination source includes a thermal

illumination source or a globar illumination source

generating the first amount of broadband illumination light ,

8. The metrology system of Claim 1, the mid-infrared FTIR spectrometer including a reflective objective focusing the amount of FTIR illumination light onto the FTIR

measurement spot and collecting the amount of FTIR

collected light from the FTIR measurement spot, wherein the amount of FTIR illumination light covers a first portion of a pupil of the reflective objective and the amount of FTIR collected light covers a second portion of the pupil of the reflective objective that is spatially separate from the first portion.

9. The metrology system of Claim 1, wherein the one or more angles of incidence does not include a normal angle of incidence.

10. The metrology system of Claim 1 , wherein the one or more angles of incidence are within a range of angles of incidence from 5 degrees to 40 degrees.

11. The metrology⁷ system of Claim 1, wherein the at least one FTIR detector is cooled by/ a Stirling cooler.

12. The metrology⁷ system of Cleiim 1, further

comprising :

a second metrology subsystem including: an illumination optics subsystem directing an amount of illumination light from the at least one illumination source to a measurement spot on the surface of the specimen under measurement at one or more angles of incidence, one or more azimuth angles, or a combination thereof;

a collection optics subsystem collecting an amount of collected light from the measurement spot on the surface of the specimen in response to the amount of illumination light;

at least one detector having a surface sensitive to incident light, the at least one detector detecting the amount of collected light and generating output signals indicative of the detected collected light, wherein the computing system is further configured to generate an estimated value of a second parameter of interest of the specimen under measurement based on the output signals.

13. The metrology system of Claim 12, wherein the first and second parameters of interest are the same parameter of interest.

14. The metrology system of Claim 12, wherein the amount of illumination light includes wavelengths different from the amount of FTIR illumination light.

15. The metrology system of Claim 12, wherein the FTIR measurement spot and the measurement spot are

colocated .

16. The metrology system of Claim 12, wherein the detecting of the amount of collected light and the

detecting of the amount of FTIR collected light occurs simultaneously .

17. The metrology system of Claim 12, wherein an optical path of the mid-infrared FTIR spectrometer and an optical path of the second metrology subsystem include a reflective objective.

18. The metrology system of Claim 12, wherein the second metrology subsystem is any of a spectroscopic ellipsometer, a spectroscopic reflectometer, a

scatterometer, an X-ray based metrology subsystem, or a hyperspectral imaging based metrology system.

19. A method comprising:

generating a first amount of broadband illumination light including wavelengths spanning a range from 2.5 micrometers to 12 micrometers ;

generating an amount of FTIR illumination light having a time varying spectrum from the first amount of broadband illumination light;

directing the amount of FTIR illumination light to a FTIR measurement spot on a surface of a specimen under measurement at one or more angles of incidence, one or more azimuth angles, or combination thereof, wherein a size of the FTIR measurement spot on the surface of the specimen is less than 50 micrometers;

collecting an amount of FTIR collected light from the FTIR measurement spot on the surface of the specimen in response to the amount of FTIR illumination light; detecting the amount of FTIR collected light and generating FTIR output signals indicative of the detected FTIR collected light; and

determining an estimated value of a first parameter of interest of the specimen under measurement based on the FTIR output signals and the time varying spectrum of the amount of FTIR illumination light.

20. The method of Claim 19, wherein the at least one illumination source includes a laser sustained plasma (LSP) light source generating the first amount of broadband illumination light .

21. The method of Claim 19, wherein the one or more angles of incidence does not include a normal angle of incidence .

22. The method of Claim 19, further comprising:

polarizing the amount of FTIR illumination light, the amount of FTIR collected light, or both.

23. The method of Claim 19, wherein the specimen under measurement includes a three dimensional HAND

structure or a dynamic random access memory structure.

24. The method of Claim 19, further comprising:

directing an amount of illumination light from the at least one illumination source to a measurement spot on the surface of the specimen under measurement at one or more angles of incidence, one or more azimuth angles, or ai corobination thereof; collecting an amount of collected light from the measurement spot on the surface of the specimen in response to the amount of illumination light;

detecting the amount of collected light and generating output signals indicative of the detected collected light; and

determining an estimated value of a second parameter of interest of the specimen under measurement based on the output signals.

25. The method of Claim 24, wherein the first and second parameters of interest are the same parameter of interest .

26. The method of Claim 24, wherein the amount of illumination light includes wavelengths different from the amount of FTIR illumination light.

27. The method of Claim 24, wherein the FTIR

measurement spot and the measurement spot are colocated.

28. The method of Claim 24, wherein the

detecting of the amount of collected light and the

detecting of the amount of FTIR collected light occurs simultaneously.

29. A metrology syste comprising:

a mid-infrared Fourier Transform Infrared (FTIR) spectrometer including:

one or more illumination sources including a laser sustained plasma (LSP) light source generating a first amount of broadband illumination light including wavelengths spanning a range from 2.5 micrometers to 12 micrometers;

an interferometer receiving the first amount of broadband illumination light and generating an amount of FTIR illumination light having a time varying spectrum;

an FTIR illumination optics subsystem directing the amount of FTIR illumination light from the

interferometer to a FTIR measurement spot on a surface of a specimen under measurement at one or more angles of incidence, one or more azimuth angles, or a

combination thereof, wherein a size of the FTIR measurement spot on the surface of the specimen is less than 50 micrometers;

a FTIR collection optics subsystem collecting an amount of FTIR collected light from the FTIR

measurement spot on the surface of the specimen in response to the amount of FTIR illumination light; at least one FTIR detector having a surface sensitive to incident light, the at least one FTIR detector detecting the amount of FTIR collected light and generating FTIR output signals indicative of the detected FTIR collected light; and

a computing syste configured to generate an estimated value of a first parameter of interest of the specimen under measurement based on the FTIR output signals and the time varying spectruin of the amount of FTIR illumination light .

30. The metrology system of Cleiim 29, wherein the one or more angles of incidence does not include a normal angle of incidence.

31. The metrology system of Claim 29, wherein a measurement channel of the mid-infrared FTIR spectrometer includes a polarizing element in an illumination path, a collection path,_: or both, of the mid-infrared FTIR

spectrometer .

32. The metrology system of Claim 29, further comprising :

a second metrology subsystem including:

an illumination optics subsystem directing an amount of illumination light from the one or more illumination sources to a measurement spot on the surface of the specimen under measurement at one or more angles of incidence, one or more azimuth angles, or a combination thereof;

a collection optics subsystem collecting an amount of collected light from the measurement spot on the surface of the specimen in response to the amount of illumination light;

at least one detector having a surface sensitive to incident light, the at least one detector detecting the amount of collected light and generating output signals indicative of the detected collected light, wherein the computing system is further configured to generate sin estimated value of a second parameter of interest of the specimen under measurement based on the output signals.

33. The metrology system of Claim 32, wherein the amount of illumination light is generated by the LSP light source .

34. The metrology system of Claim 32, wherein the first and second parameters of interest are the same parameter of interest.

35. The metrology system of Claim 32, wherein the amount of illumination light includes wavelengths different from the amount of FTIR illumination light.

36. The metrology system of Claim 32, wherein the FTIR measurement spot and the measurement spot are

colocated .

37, The metrology system of Claim 32, wherein the detecting of the amount of collected light and the

detecting of the amount of FTIR collected light occur simultaneously.