WO2022201138A1 - Procédé de génération d'une modification de surface locale d'un élément optique utilisé dans un système lithographique - Google Patents

Procédé de génération d'une modification de surface locale d'un élément optique utilisé dans un système lithographique Download PDF

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Publication number
WO2022201138A1
WO2022201138A1 PCT/IL2021/050334 IL2021050334W WO2022201138A1 WO 2022201138 A1 WO2022201138 A1 WO 2022201138A1 IL 2021050334 W IL2021050334 W IL 2021050334W WO 2022201138 A1 WO2022201138 A1 WO 2022201138A1
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Prior art keywords
focusing
energy
energy pulse
defect
local surface
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PCT/IL2021/050334
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English (en)
Inventor
Sergey Oshemkov
Vladimir Kruglyakov
Avi Cohen
Yuval Perets
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Carl Zeiss Sms Ltd.
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Priority to PCT/IL2021/050334 priority Critical patent/WO2022201138A1/fr
Publication of WO2022201138A1 publication Critical patent/WO2022201138A1/fr

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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F1/00—Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
    • G03F1/38—Masks having auxiliary features, e.g. special coatings or marks for alignment or testing; Preparation thereof
    • G03F1/42—Alignment or registration features, e.g. alignment marks on the mask substrates
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F1/00—Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
    • G03F1/68—Preparation processes not covered by groups G03F1/20 - G03F1/50
    • G03F1/72—Repair or correction of mask defects
    • G03F1/74—Repair or correction of mask defects by charged particle beam [CPB], e.g. focused ion beam
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F1/00—Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
    • G03F1/68—Preparation processes not covered by groups G03F1/20 - G03F1/50
    • G03F1/82—Auxiliary processes, e.g. cleaning or inspecting
    • G03F1/84—Inspecting

Definitions

  • the present invention relates to the field of generating at least one local surface modifi- cation of an optical element used in a lithographic system. Further, the present inven- tion refers to a method and an apparatus for repairing at least one defect of an optical element used in a lithographic system, wherein at least one local surface modification is used for locating the at least one defect.
  • lithographic masks have to project smaller and smaller structures onto a photosen- sitive layer, i.e. a photoresist on wafers.
  • the exposure wavelength of lithographic masks has been shifted from the near ultraviolet across the mean ultraviolet into the deep ultraviolet (DUV) region of the electromagnetic spec- trum.
  • a wavelength of 193 nm is typically used for the exposure of a photore- sist arranged on wafers.
  • lithographic masks will use significantly smaller wavelengths in the extreme ultraviolet (EUV) wavelength range of the electromagnetic spectrum (approximately 10 nm to 15 nm).
  • EUV extreme ultraviolet
  • Lithographic systems using EUV radiation differ fundamentally from conventional sys- tems based on DUV radiation.
  • a DUV lithographic system usually involves transmitting optics, i.e. lenses and photomasks having an optically transparent substrate on which an absorbing or reflective pattern is deposited. All presently known materials signifi- cantly absorb EUV radiation. Therefore, EUV lithographic systems are based on optical reflection and absorption rather than on optical transmission and reflection or absorp- tion.
  • Typical EUV optics applies multilayer mirrors or multilayer (ML) reflectors that reflect electromagnetic radiation as determined by Bragg’s law. EUV masks or photo- masks are typically also reflective optical elements using multilayer reflectors.
  • Lithographic masks must be free of printable errors, since an error in the photomask reproduces on every wafer at each exposure.
  • the requirements to substrates and mask blanks used for the fabrica- tion of EUV masks are enormous, for example with respect to the flatness of these com- ponents.
  • substrates and mask blanks for EUV lithography cannot be manu- factured free of errors.
  • EUV optical elements must be repaired whenever possible.
  • the following documents exemplarily describe repair methods of EUV masks: EP 3598231 At; US 9431212 B2; US 8 674329 B2; DE 102011080 100.6; DE 102014211302.8; US 10386297 B2; DE to 2017212848.8; and DE 102020201482.5.
  • HVM high volume manufacturing
  • Xiaolei Liu, et al. “Optimal shift of pattern shifting for mitigation of mask defects in ex- treme ultraviolet lithography’, J. of Vac. Sci. and Technol. B, Vol. 33, Issue 5, 051603 (2015); Z.J. Qi and J. Rankin: “Viability of pattern shift for defect-free EUV photo- masks at the 7 nm node”, Bacus News, Vol. 32, Issue 4; US 15 / 451522 At; and US 10 295899 B2.
  • Defect mitigation by pattern shifting requires precise registration of the circuit pattern data during for example e-beam writing of an absorber pattern to the defect coordi- nates of mask blanks.
  • registration is accomplished by aligning mask blank defects to fiducial marks of mask blanks.
  • Fiducial marks for EUV photomasks are for example specified in the document: SEMI Draft Document 4580, New Standard: Speci- fication of fiducial marks on EUV mask blanks, 4/23/2010.
  • mask blank fiducials are presently generated on EUV mask blanks by using either a local etching process (subtractive process) or a local deposition process (addi- tive process).
  • a laser system can also be used for generating fiducial marks in a multilayer structure of a mask blank via local heating of the ML. This process is described in the following documents: P.V. Yan: “Strategy to implement EUVL ML blank fiducial mark”, EUVL Mask Blank Fiducial SEMI Standard Discussion, July 15, 2008; and S. Huh et al.: “Standardization of fiducial mark on EUV blankmask”, February 22, 2009, http://ieuvi.org /TWG/Mask/2009/MTGo22209/Summary_of_SPIE_Fidu- cial_Mark_sematech.pdf.
  • the fiducial mark generation on a ML of a mask blank by heating is typically a clean process. But the contrast caused by the marks and seen or detected by an e-beam writing tool is normally low. The additional mark generation on an absorber layer increases the detected contrast, however it needs a sec- ond process step which results in a more complex procedure.
  • the second process step is an etching process which involves the problems of debris generation dis- cussed above. Further, the formation of marks by means of material removal is also a local etching process which creates debris so that a cleaning step is additionally re- quired after processing a mask blank with a laser beam.
  • the above listed meth- ods are limited to a generation of marks in a ML reflector of a mask blank.
  • the document US 2018 / o 173 091 At describes the generation of fiducial marks in a metal or an absorber layer by using a laser beam. If the uppermost layer of the mask blank is a metal layer, the laser beam incidents on the front side of the mask blank to form marks in the metal layer. If a photoresist is arranged on the metal layer of the mask blank, the laser beam incidents on the rear side of the mask blank to generate the marks in the metal layer in order not to damage the photoresist layer.
  • the document EP 3598231 At describes a method for reducing reflectance of a border region surrounding a design region of an EUV mask by directing a first treatment beam having a first set of treatment parameters on the border region and di- recting a second treatment beam having a second set of treatment parameters on the border region of the EUV mask.
  • the laser spots of the first and the second treatment beam may impinge on significantly overlapping areas in the border region.
  • the local surface modifications described in the document EP 3598231 At are specifi- cally designed to reduce or to prevent reflections from the portion of the mask having the local surface modifications. Thus, these local surface modifications cannot be used for the localisation of one or more defects of an EUV mask.
  • the method of Yan and Wagner is limited to the formation of marks in a ML reflector of an EUV mask blank. Further, the trench formed in the multilayer of the blank has a width of several micrometers which limits the resolution of the generated marks, and thus the accuracy with which defects of a mask blank can be located.
  • a method according to patent claim 1 is pro- vided for solving the above problems at least partly.
  • a method ac- cording to claim 12 and an apparatus according to claim 20 are provided for using gen- erated marks for repairing defects of an optical element used in a lithographic system.
  • a method for generating at least one local surface modification in a material of an optical element used in a lithographic system comprises the steps: (a) fo- cusing a first energy pulse in the optical element; and (b) sequentially focusing at least one second energy pulse within a time interval which is shorter than a cooling time of the material, the at least one second energy pulse at least partially locally overlapping the first energy pulse so that the surface of the optical element is locally modified.
  • the time interval may be shorter than 80%, 50% or 10% of the cooling time.
  • the formation of the one or more local surface modifications according the inventive method does not generate debris. This means, the method presented in this application defines a clean process. Further, the inventive method allows to precisely control the generation of local surface modifications. Thus, the fabrication process can be adapted to the material of the optical element in which the at least one local surface modifica- tion is generated.
  • the lateral dimensions of a local surface modification are ultra-small, i.e. they are in the sub-micrometer regime.
  • the generation of one or more local surface modifi- cations allows the fabrication of a mark having a very high lateral resolution.
  • the lateral resolution can significantly be increased when generating sev- eral local surface modifications in an optical element which are combined to form a mark, a fiducial mark.
  • the generated fiducial mark can be used for determining the po- sitions of defects of mask blanks with high precision.
  • defect mitigation by pattern shifting can be based on one or more local surface modifications and/or on one or sev- eral marks created by a plurality of local surface modifications.
  • a complex defect re- pair can reliably be based on the generated mark(s).
  • the inventive method is a flexible process, as the formation of the one or more local surface modifications can be precisely controlled by setting several parameters of a la- ser system.
  • the number of energy pulses which are sequentially focussed on a same position is an important new parameter for precisely controlling the amount of energy which is locally deposited in an optical element.
  • the phenome- non of heat accumulation or the effect of a local material modification can be utilized for the generation of one or more local surface modifications.
  • one or more local surface modifications can for example be gener- ated in a mask substrate, in a multilayer of a mask blank as well as in an absorber layer of a mask blank. This enables a control of each step of the fabrication process of an op- tical element used in a lithographic system from the beginning by detecting and locat- ing defects at each manufacturing step.
  • the contrast of the one or more local surface modifications or of a mark created from the local surface modifications can be adapted to the requirements of for example an e- beam writing tool or a repair tool. Consequently, the inventive method specifies a fast and cost-effective mark formation method.
  • the at least one second energy pulse at least partially locally overlapping the first en- ergy pulse may comprise essentially locally overlapping the at least second energy pulse the first energy pulse.
  • the term “essentially locally overlapping” means that two or more energy pulses are focussed on a same position, that is a same lateral position and depth position, and the energy pulses are generated using current state of the art tech- nology. Nevertheless, the two or more energy pulses may not perfectly overlap, for ex- ample due to thermal drifts and/or vibrations of a mask blank relative to the energy pulse generation and focussing unit.
  • the two or more energy pulses may be generated by a single energy pulse source, two energy pulse sources or more energy pulse sources.
  • An optical element used in a lithographic system may comprise a substrate of a mask blank, a mask blank, a template used in a nanoimprint lithography, a photomask, and a mirror or a reflector for an extreme ultraviolet (EUV) wavelength range.
  • the mask blank may be a blank from which a photomask is fabricated for a DUV or an EUV wave- length range.
  • the photomask may be a reflective or a transmissive photomask.
  • the photomask may be any mask type, as for example, a binary or a phase-shifting photo- mask.
  • the first energy pulse and/ or the at least one second energy pulse may be generated by at least one element of the group: a photon beam, an electron beam, an atom beam, a molecular beam, and an ion beam.
  • the surface of the optical element may be locally modified at a position where the at least two energy pulses deposit their energy.
  • the first and the at least one second energy pulses may be generated by the same element or may be generated by two or more different elements of the listed group.
  • the inventive method is flexible with respect to the kind of particle which transports energy to a specific position of the optical element.
  • the energy is converted into heat in the optical element.
  • Ffocusing the first energy pulse and sequentially focusing the at least one second en- ergy pulse may comprise locally raising a temperature of the material to a predeter- mined temperature.
  • the predetermined temperature depends on the material the first energy pulse and the at least one second energy pulse incidents on.
  • the predetermined temperature may comprise a range of 400 K to 5500 K, preferably 600 K to 5000 K, more preferred 800 K to 4500 K, and most preferred 1000 K to 4000 K.
  • the time interval between the first energy pulse and the at least one second time inter- val comprises a range of: 0.05 ns to 100 ⁇ s, preferably 0.1 ns to 10 ⁇ s, more referred 0.3 ns to 3 ⁇ s, and most preferred 1 ns to 1 ⁇ s.
  • Focusing the first energy pulse and sequentially focusing the at least one second energy pulse may comprise focusing at least two energy pulses having an energy density at a focal point of: 0.01 J/cm 2 to too J/cm 2 , preferably 0.02 J/cm 2 to 50 J/ cm 2 , more pre- ferred 0.05 J/cm 2 to 20 J/cm 2 , and most preferred 0.1 J/cm 2 to 10 J/cm 2 , or having an energy density at the focal point of: 0.001 J/cm 2 to 10 J/cm 2 , preferably 0.002 J/cm 2 to 5 J/cm 2 , more preferred 0.005 J/cm 2 to 2 J/cm 2 , and most preferred 0.01 J/cm 2 to 1 J/cm 2 .
  • Different physical effects can be used for generating one or more local surface modifica- tions depending on the material composition whose surface is to be locally varied.
  • the application of different effects is best performed by using energy pulses which have different energy densities.
  • generating local surface modifications in a mask substrate requires higher energy densities (approximately 0.1 J/cm 2 to 10 J/cm 2 ) than locally modifying a multilayer (ML) of a mask blank, a ML of an EUV mir- ror, and/or a ML of an EUV photomask (approximately 0.01 J/cm 2 to 1 J/cm 2 ).
  • Modify- ing a ML mirror structure may comprise locally converting the constituents of the ML layers in a composition material, for example converting molybdenum (Mo) and the sil- icon (Si) of the ML layers into molybdenum silicide.
  • Mo molybdenum
  • Si sil- icon
  • Focusing the first energy pulse and sequentially focusing the at least one second energy pulse may comprise focusing a number of N essentially locally overlapping energy pulses, wherein N is in a range: 2 ⁇ N ⁇ 200, preferably: 2 ⁇ N ⁇ too, more preferred: 2 ⁇ N ⁇ 50, and most preferred: 2 ⁇ N ⁇ 25.
  • the number N of energy pulses may be adapted to the material or a material composi- tion of the optical element. Further, the contrast of the one or more local surface modi- fications required for example by an e-beam writing tool or a repair tool normally influ- ences the number of energy pulses which incident on a same position of the optical ele- ment. Moreover, the number of energy pulses incident on a same position of the optical element depends on the requirements to the mark which is formed of a plurality of local surface modifications.
  • Focusing the first energy pulse and sequentially focusing the at least one second energy pulse may comprise focusing at least two energy pulses having a pulse width ⁇ 1000 ps, preferably ⁇ too ps, more preferred ⁇ t ps, and most preferred ⁇ 0.2 ps.
  • the pulse width or the pulse length determines the amount of energy which is locally deposited in the optical element and thus the amount of heat which is locally generated in the optical element. This means that the three quantities are not independent from each other.
  • Focusing the first energy pulse and sequentially focusing the at least one second energy pulse comprises focusing at least two energy pulses having a pulse repetition rate > 0.1 MHz, preferably > 1 MHz, more preferred > 10 MHz, and most preferred > too MHz.
  • the pulse repetition rate is one of the parameters which can be used for controlling the local temperature raise within the optical element.
  • Focusing the first energy pulse and sequentially focusing the at least one second energy pulse comprises focusing at least two photon pulses having a wavelength within a range of 150 nm to 1500 nm.
  • a photon beam is presently the preferred source of energy for creating one or more lo- cal surface modifications of an optical element.
  • a photon beam can be controlled very precisely. Further, a photon does typically not induce any unwanted of detrimental modifications in an optical element outside of its focal spot.
  • a photon beam is generated by a laser system.
  • the wavelength range of the photon beam may reach from the DUV to the infrared (IR) range of the electromagnetic spectrum.
  • the wavelength of a photon beam dominates the focal width or the focal spot width to which the photon beam can be focussed. It is therefore beneficial to apply a photon beam having a short wavelength in order to obtain a small focal spot width which in turn creates a local surface modification that has small lateral dimensions.
  • Focusing the at least two photon pulses may comprise using an objective having a nu- merical aperture (NA) > 0.2, preferably > 0.3, more preferred > 0.4, and most pre- ferred > 0.6.
  • NA nu- merical aperture
  • the NA of the focusing objective determines the minimum focal spot width which can be achieved: the higher the NA the lower the focal spot width. Illuminating a mask blank from a backside may limit the NA of the objective used to focus the energy pulses of the photon beam.
  • Focusing the first energy pulse and sequentially focusing the at least one second energy pulse may comprise focusing at least two energy pulses in at least one element of the group: a template for a nanoimprint lithography, a substrate of a mask blank, a sub- strate of an EUV mirror, a substrate of a photomask, a multilayer of a mask blank, a multilayer of an EUV mirror, a multilayer of a photomask, and an absorber layer of a photomask.
  • the inventive method also allows the generation of local surface modifica- tions on a backside or a rear side of the optical element.
  • the optical element may have a backside or a rear side coating.
  • the backside coating may be an electrically conductive and may be an at least partially optically transmissive coating.
  • the backside of the mask blank, the EUV mirror and the photomask is the side which is opposite to the side having the patterned structure and/or a ML reflector.
  • the front side of a mask blank is defined as the side which will later-on carry the patterned structure.
  • the front side of an EUV mirror de- notes the side which has a multilayer reflector.
  • Focusing the first energy pulse and sequentially focusing the at least one second energy pulse may comprise at least one of: focusing at least two energy pulses through a back- side of a substrate of a mask blank, focusing at least two energy pulses through a back- side of a mask blank, focusing at least two energy pulses through a backside of an EUV mirror, and focussing at least two energy pulses through a backside of a photomask.
  • Fo- cussing the at least two energy pulses through the backside of the mask blank may com- prise focusing the at least two energy pulses into the substrate or focusing the at least two energy pulses into the ML mirror structure of the mask blank.
  • Focusing the first energy pulse and sequentially focusing the at least one second energy pulse may comprise focusing the energy pulses in a depth D of the optical element be- low a surface to be locally modified, wherein D is ⁇ 20 , p ⁇ mreferably ⁇ 10 , m ⁇ omre preferred ⁇ 3 ⁇ m, and most preferred ⁇ 1 ⁇ .m
  • the inventive method is very flexible with respect to the material in which the local sur- face modifications are created.
  • the one or more local surface modifications can be gen- erated by locally providing the energy via a front side or a backside of the optical ele- ment used in a lithographic system.
  • focusing the energy pulses through the backside of the mask blank may limit the NA of the focusing objective and thus the minimum focal spot width.
  • a method for repairing at least one defect of an optical element used in a lithographic system comprises: (a) generating at least one local surface modi- fication of the optical element using at least one focussed photon beam; (b) aligning at least one massive particle beam to the at least one defect based on the at least one local surface modification; and (c) repairing the at least one defect using the at least one massive particle beam and at least one precursor gas.
  • Generating the at least one local surface modification may comprise generating a plu- rality of local surface modifications in form of a geometric structure.
  • the geometric structure may form a mark or a fiducial mark.
  • Fiducial marks or mask fiducials are structures on optical elements (mask blanks or photomasks) typically used for alignment on wafer steppers. Generally, each brand and model of wafer stepper requires specific fiducials. Fiducial marks are usually located outside of a patterned area.
  • the plurality of the local surface modifications for forming a mark may comprise 2 to 200 local surface modifications, preferably 3 to too local surface modifications, more preferred 4 to 50 local surface modifications, and most preferred 5 to 25 local surface modifications.
  • the geometric structure may be at least one element of: a line, a cross, a circle, a rec- tangle, a square, a triangle, a free-form shape, a code, a bar code, a logo, and text.
  • the at least one defect may comprise at least one element of the group: a substrate de- fect of mask blank, a substrate defect of an EUV mirror, a substrate defect of a photo- mask, a clear defect and/or a black defect of a template for a nanoimprint lithography, a multilayer defect of a mask blank, a multilayer defect of an EUV mirror, a multilayer defect of an EUV photomask, an absorber defect of a photomask, and a defect of a phase shifting photomask.
  • a continuous photon beam can be used for generating the at least one local surface modification.
  • the photon beam may have a wavelength within a range of 150 nm to 1500 nm.
  • the at least one local surface modification can be generated by focus- sing a single photon pulse to a position of the photon beam in the optical element.
  • the parameters of the photon pulse(s) may be one or more of the parameters indicated above.
  • the one or more local surface modifications may be generated by focussing a first laser pulse and sequentially focussing at least one second energy pulse essentially locally overlapping the first energy pulse so that the surface of the optical element is lo- cally modified, e.g., as indicated above.
  • the massive particle beam may comprise particles having a rest mass which is larger than zero (m 0 > o kg).
  • Presently preferred massive particles are electrons.
  • Repairing the at least one defect may comprise: inducing a local chemical reaction by the at least one massive particle beam.
  • the massive particle beam may comprise at least one particle type of the group: electrons, ions, atoms, and molecules.
  • Repairing the at least one defect may comprise: inducing a local chemical reaction initi- ated by the at least one massive particle beam.
  • the local chemical reaction may be a local etching process and the at least one precur- sor gas may be at least one etching gas.
  • the local chemical reaction may be a local dep- osition process and the at least one precursor gas may be at least one deposition gas.
  • the at least one precursor gas may further comprise at least one additive gas.
  • the at least one deposition gas may comprise at least one of a metal alkyl, a transition element alkyl and a main group element alkyl, for example cyclopentadienyl (Cp) tri- methylplatinum (CpPtMe 3 ), methylcyclopentadienyl (MeCp) trimethylplatinum (MeCpPtMe 3 ), tetramethyltin (SnMe 4 ), trimethylgallium (GaMe 3 ), ferrocene cyclopen- tadienyl (Cp 2 Fe), andbis-aryl chromium (Ar 2 Cr).
  • Cp cyclopentadienyl
  • CpPtMe 3 cyclopentadienyl
  • MeCp methylcyclopentadienyl
  • SnMe 4 tetramethyltin
  • GaMe 3 ferrocene cyclopen- tadienyl
  • Ar 2 Cr
  • the deposition gas may com- prise a metal carbonyl, for example chromium hexacarbonyl (Cr(CO) 6 ), molybdenum hexacarbonyl (Mo(CO) 6 ), and triruthenium dodecarbonyl (RU 3 (CO) 12 ).
  • the deposition gas may comprise a metal alkoxide, for example, tetraethyl orthosilicate (Si(OC 2 H 5 ) 4 ) and titanium isopropoxide (Ti(OCH(CH 3 ) 2 ) 4 ).
  • the etching gas may comprise at least one element of the group: a halogen (F 2 , Cl 2 , Br 2 , J 2 ), oxygen (O 2 ), ozone (O 3 ), hydrochloric acid (FI Cl), hydrogen fluoride (HF), xenon difluoride (XeF 2 ), xenon tetrafluoride (XeF 4 ), xenon hexafluoride (XeF 6 ), xenon chlo- ride (XeCl), argon fluoride (ArF), sulphur difluoride (SF 2 ), sulphur tetrafluoride (SF 4 ), sulphur hexafluoride (SF 6 ), nitrosyl chloride (NOCl), phosphor trichloride (PCl 3 ), phos- phor pentachloride (PCl 5 ), phosphor trifluoride (PF 3 ), nitrogen trifluoride (NF 3
  • the additive gas may comprise at least one element of the group: oxygen (O 2 ), ozone (O 3 ), water (H 2 O), hydrogen peroxide (H 2 O 2 ), nitrous oxide (N 2 O), nitrogen oxide (NO), nitrogen dioxide (NO 2 ), nitric acid (HNO 3 ), chlorine (Cl 2 ), hydrochloric acid (HCl), hydrofluoric acid (HF), iodine (I 2 ), hydrogen iodide (HI), bromine (Br 2 ), hydro- gen bromide (HBr), nitrosyl oxide chloride (NOCl), phosphorus trichloride (PCl 3 ), phosphorus pentachloride (PCl 5 ), phosphorus trifluoride (PF 3 ), nitrogen trifluoride (NF 3 ), hydrogen (H 2 ), ammonia (NH 3 ), and methane (CH 4 ).
  • the at least one local surface modification may be detected by at least one element of the group: an electron beam writing tool, a defect review tool, a defect inspection tool, a mask blank inspection tool, and a repair tool.
  • these tools have different requirements with respect to the contrast ratio one or more local surface modifications, a mark and/or a fiducial mark have to fulfil.
  • the at least one local surface modification may have a lateral dimension ⁇ 2 ⁇ m, prefer- ably ⁇ 1 ⁇ m, more preferred ⁇ 0.5 ⁇ m, and most preferred ⁇ 0.2 ⁇ m.
  • the minimum focal spot width of the energy pulses determines the minimum lateral di- mensions obtainable for the local surface modifications. If a photon beam transports or carries the energy to the optical elements, the wavelength and the NA of the focussing objective essentially define the focal spot width and thus the minimum lateral dimen- sions of the one or more local surface modifications.
  • the at least one local surface modification may have a height variation of > 5 nm, pref- erably > 10 nm, more preferred > 20 nm, and most preferred > 50 nm.
  • the height vari- ation of the at least one local surface modification comprises o local deviation of the surface with respect to an undisturbed surface of the optical element. This means that the height variation also comprises a depth variation.
  • a mark or a fiducial mark fabricated from a plurality of local surface modifications may have a standard deviation of a lateral positioning which is ⁇ 500 nm, preferably ⁇ too nm, more preferred ⁇ 30 nm, and most preferred ⁇ 10 nm.
  • a single local surface modification of an optical element can be used as a mark.
  • a local surface modification can be created having lateral dimen- sions in the sub-micrometer regime.
  • a mark or a fiducial mark can be generated.
  • a mark formed of a plurality of local surface modifi- cations has a higher lateral resolution than a single local surface modification.
  • the at least one local surface modification may comprise a local depression and/or a needle like structure.
  • the depression may comprise a bump-like or a pit-like structure.
  • An optical element for use in a lithographic system may be treated with a method ac- cording to one of the preceding aspects.
  • a computer program may comprise instructions which perform the method steps of any one of the preceding aspects when the instructions are executed by a computer sys- tem.
  • an apparatus for repairing at least one defect of an optical element used in a lithographic system comprises: (a) means for providing at least one focused photon beam operable to generate at least one local surface modification of the optical element; (b) a control unit operable to align at least one massive particle beam to the at least one defect based on the at least one local surface modification; and (c) at least one gas provision system providing at least one precursor gas, wherein the control unit is further operable to control a gas flow rate of at least one precursor gas and to scan the at least one massive particle beam across the at least one defect to repair the at least one defect.
  • the apparatus may be adapted to implement any of the methods steps as described herein.
  • the control unit may be further operable to controlling the at least one focused photon beam.
  • the alignment of the at least one precursor gas to the at least one defect may be based on the at least one local surface modification.
  • the means for providing the at least one focused photon beam and a source for generating the at least one massive par- ticle beam may be arranged in a single housing.
  • Fig. 1 schematically shows in cross-section through an ideal flat mirror or reflector for extreme ultraviolet (EUV) radiation
  • Fig. 2a schematically shows in cross-section through a defect-free EUV mask blank
  • Fig. 2b schematically presents EUV mask blank structures having a buffer layer and without having a buffer layer
  • Fig. 3 schematically depicts a cross-sectional view of a perfect EUV photomask
  • Fig. 4a schematically illustrates a top view of an EUV photomask having four fiducial marks
  • Fig. 4b schematically presents an enlarged top view of one fiducial mark of Fig. 4a
  • Fig. 5 schematically presents a block diagram of an apparatus for generating local surface modifications of a mask blank, an EUV mirror and/or a photomask
  • Fig. 6 schematically shows focusing of an energy pulse into a mask blank in the left upper partial image, illustrates the local spread of the heat in the mask blank in the right upper partial image, and depicts the time diagram of the heat accu- mulation in the mask blank of eight energy pulses sequentially focussed on a same position in the lower partial image;
  • Fig. 7 presents a microscope image of a top view on a multilayer (ML) mirror struc- ture having rows of local surface modifications which are created as a function of the pulse energy and the number of sequentially essentially overlapping en- ergy pulses;
  • ML multilayer
  • Fig. 8 shows in the diagram 805 local surface modifications generated in various depths in a substrate of an optical element which are detected by an optical microscope; presents in the diagram 835 a local surface modification in form of a local bump for a focusing depth of 2.25 ⁇ mmeasured by AFM (Atomic Force Microscope) scans; and depicts in the diagram 865 profiles obtained in two perpendicular directions from the bump of the diagram 835;
  • AFM Anamic Force Microscope
  • Fig. 10 depicts a flow diagram of a method for generating one or more local surface modifications of an optical element used in a lithographic system
  • Fig. 11 reproduces the EUV photomask of Fig. 3 having a defect
  • Fig. 12 schematically illustrates a cross-section of an apparatus for repairing a defect of a mask blank, an EUV mirror and/or a photomask
  • Fig. 13 schematically represents a second example of an apparatus for repairing a de- fect of a mask blank, an EUV mirror and/or a photomask
  • Fig. 14 schematically shows a portion of the repair apparatus of the Figures 12 and 13;
  • Fig. 15 presents a flow chart of a method for repairing a defect of an optical element used in a lithographic system.
  • optical elements used in lithographic systems.
  • These optical elements comprise mask blanks at various stages of their manufacturing, i.e. a mask blank also comprises a substrate of an optical element.
  • Optical elements as referred in this application comprise transmissive and re- flective masks or photomasks.
  • optical elements include all kind of photo- masks, as for example binary and phase-shifting masks.
  • optical elements also comprise mirrors or reflectors used in the extreme ultraviolet (EUV) wavelength range.
  • EUV extreme ultraviolet
  • the defined methods are not restricted to the generation of marks on mask blanks or photomasks and/or us- ing the generated mark(s) for correcting defective blanks or lithographic masks. Rather, the inventive methods can also be used for generating marks in templates to be used in the nanoimprint lithography and applying these marks for correcting defective tem- plates.
  • energy pulses are provided to optical elements in the form of photon pulses.
  • inventive methods are not restricted to this specific kind of energy provision. Rather, other kind of particles, as for example, electrons, atoms, molecules, and/or ions can be applied for focusing energy pulses in an optical element in order to produce local surface modifications.
  • Fig. l shows a schematic cross-sectional view of a flat EUV mirror too for an exposure wavelength of 13.5 nm.
  • Beam forming EUV mirrors too are used to direct EUV radia- tion from an EUV source to an EUV mask and from the EUV photomask into a photore- sist which is arranged on a wafer.
  • An EUV mirror too comprises a substrate 110.
  • the substrate 110 may comprise a fused silica substrate.
  • Other transparent dielectrics, glass materials or semiconducting materials may also be applied as substrates 110 of EUV mirrors too or EUV reflectors too, as for example ZERODUR ® , ULE ® or CLEAR- CERAM®.
  • a multilayer (ML) mirror system 160 is deposited on a front surface 115 of the substrate 110.
  • the multilayer mirror system 160 typically comprises 20 to 80 pairs of alternating molybdenum (Mo) 130 and silicon (Si) layers 140 (referred to in the following as MoSi layers).
  • Mo molybdenum
  • Si silicon
  • the normal thickness of each Mo layer 130 is 4.0 nm and that of the Si layer 140 amounts to 2.9 nm.
  • the Mo layers 130 act as scattering layers, whereas the silicon layers 140 function as separation layers.
  • other elements with a high Z number may utilized, such as cobalt (Co), nickel (Ni), tungsten (W), rhe- nium (Re) and iridium (Ir) instead of Mo.
  • the ML 160 on the substrate 110 acts as a mirror or a reflector for EUV electromagnetic radiation. This is illustrated in Fig. 1 by the arrows 180 which symbolize the EUV beam incident on the EUV mirror too and the arrows 190 which indicate the EUV radiation reflected by the ML mirror structure 160 of the EUV mirror too.
  • a ML 160 can reflect approximately 70% of the incident EUV photons180.
  • a capping layer 150 of silicon with a native oxide of 7 nm depth is typically arranged on top of the ML 160.
  • Fig. 2a presents a schematic cross-sectional view of a mask blank 200. Further, Fig. 2b shows two further cross-sectional views of mask blanks 210 and 220.
  • a buffer layer 230 and an absorbing layer 240 are additionally deposited on the capping layer 150 of the EUV mirror too.
  • the buffer layer 230 may be deposited to protect the ML 160 during processing, for example, when etching or repairing the absorbing layer 240.
  • Possible buffer layer materials are, for example, fused silica (SiO 2 ), silicon-oxygen-ni- tride (SiON), ruthenium (Ru), chromium (Cr), and/or chromium nitride (CrN).
  • the mask blank 200 of Fig. 2a has both, a capping layer 150 and a buffer layer 230.
  • Fig. 2b shows two EUV mask blanks 210, 220 having either a capping layer 150 or a buffer layer 230.
  • the upper left partial image of Fig. 2b presents an EUV mask blank 210 hav- ing a CrN buffer layer 230.
  • the upper right partial image of Fig. 2b depicts an EUV mask blank having a Ru capping layer 150 but not a buffer layer 230.
  • the capping layer has a thickness of 2.5 nm.
  • the thickness of the cap- ping layer may depend on whether the mask blank has a buffer layer 230 or not.
  • the absorbing layer 240 may comprise a material having a large absorption coefficient for photons 180 in the EUV wavelength range. Examples of these materials are chro- mium (Cr) and/or tantalum boride (TaB). A thickness of about 50 nm is typically enough to absorb essentially all EUV photons 180 incident on the absorbing layer 240. In order to reduce scattered EUV and/or DUV light, the absorbing layer 240 may have an anti-reflective (AR) layer 250. Tantal oxynitride (TaON) may be used for fabricating an AR layer 250. As indicated in Fig.
  • an absorbing structure 260 deposited on the capping layer 150 of the ML 160 may comprise a buffer layer 230, an absorbing layer 240 and an AR-layer 250.
  • the absorbing structure 260 may comprise an absorbing layer 240 and an AR layer 250 but no buffer layer 230.
  • a mask blank 200, 210, 220 as defined in this application does not include a photore- sist layer (not indicated in Figs. 2a and 2b).
  • the substrate 110 of a mask blank 200, 210, 220 normally has lateral dimensions of 152 mm x 152 mm and a thickness or height of essentially 6.35 mm.
  • the rear surface or backside 105 of the substrate 110 normally has a thin conductive coating 230.
  • the coating 230 may comprise films of CrN, TaB or other suitable materials.
  • the thickness of the conductive coating layer 230 is typically in a range of 20 nm to 400 nm.
  • the metallic coating 230 is used for fixing the mask blank 200, 210, 220 and later- on a photomask to an EUV scanner by using an electrostatic chuck.
  • the con- ductive backside coating 230 is semi-transparent for laser light, for example, a CrN coating with a thickness of about 20 nm or a TaB coating with a thickness of approxi- mately 70 nm allows to penetrate enough light to the substrate 110 of an EUV mirror too or an EUV blank 200, 210, 220 in order to generate local surface modifications of these optical elements.
  • a transparent or semi-transparent conductive coating 240 may for example also com- prise indium tin oxide (ITO).
  • Alternative materials for optically semi-transparent and electrically conductive coatings 240 are, for example, fluorine tin oxide (FTO) and/or aluminium zinc oxide (AZO), and/or antimony tin oxide (ATO). These materials can easily be applied to the rear substrate surface 105 of a fused silica substrate 110 and have an electrical conductivity which is high enough for electrostatically chucking a photomask to an EUV scanner.
  • the optically semi-transparent and electrically conduc- tive coating 240 enables to irradiate a completely manufactured mask blank 200 or a photomask with light pulses of a laser beam through the rear substrate surface 105.
  • the absorb- ing structure 260 is structured or patterned as predetermined by the design of the mask 300. This is schematically illustrated in Fig. 3.
  • the pattern 360 can be generated from the absorbing structure 260 by e-beam writing.
  • the ab- sorbing pattern 360 When forming the ab- sorbing pattern 360 to generate the photomask 300 from the mask blank 200210, 220, there is a certain level of flexibility to shift, rotate and/or scale the pattern elements 360 of a die with respect to the design specifications, as a wafer stepper can compen- sate small shift, rotation and/or scale errors of a photomask. It is advantageous to use this flexibility for defect mitigation of mask blanks 200, 210, 220. This means, it is an objective of defect mitigation to position the pattern elements 360 such that they cover the largest possible number of printable defects. For this purpose, the printable defects and their location has to be known when writing the pattern 360 with a pattern writing tool.
  • Fig. 3 illustrates that EUV photons 180 incident on an absorbing pattern element 360 are absorbed, whereas EUV photons 180 which incident on the capping layer 150 or the buffer layer 235 deposited on the ML 160 are reflected by the ML 160 to a large extent. This is symbolized by the arrows 190 in Fig. 3.
  • Diagram 405 of Fig. 4a presents a top view to the front surface 430 of the EUV mask 300 of Fig. 3.
  • the EUV mask 300 has two major portions 410 and 420.
  • the active por- tion 410 or the array 410 is the area made up of rows and column of dice having pattern elements 360 for structuring a photoresist layer arranged on a wafer (not shown in Fig. 4a).
  • the active area 410 or active portion 410 is reserved for lithography.
  • the not acti- vated portions 420 of the mask surface 430 are reserved for various purposes. For ex- ample, code can be written into the area 420 which identifies the mask 300.
  • the area of the not activated portions 420 which is not used is covered by the absorbing structure 260 shown in Fig. 2a in order to reduce stray light.
  • the not activated portions 420 of the mask surface 430 are areas where marks or fiducial marks can be generated.
  • Fig. 4a shows four marks 450 which have been written in the not activated portions 420 of the mask 300.
  • the marks 450 have a form of a cross.
  • a mark 450 is not restricted in its shape. Marks 450 can be created having any form.
  • all four marks 450 have an identical shape. This is not necessary. Rather, each mark 450 can have a unique shape.
  • the example of Fig. 4a depicts four marks 450 which are arranged at the corners of the EUV mask 300.
  • One single mark 450 may be enough as a reference point for a pattern writing tool, an inspection tool, a review tool, and/or a repair tool.
  • the single mark 450 may be posi- tioned at an arbitrary position within the not activated portions 420 of the mask sur- face 430.
  • the mask blank 200, 210, 220 has an absorbing structure 260 which extends across the overall mask surface 430. This means that the mark(s) 450 are created in the absorbing structure 260. It is also possible to write one or several marks 450 or fiducial marks 450 in a ML mirror structure 160. This can, for example, be done by writing marks 450 in a mask blank having the processing state of an EUV mirror too.
  • one or several marks 450 can also directly be generated in a substrate 110 of a mask blank too, 200, 210, 220.
  • the ML 160 may not be deposited on the not activated regions 420 of the mask surface 430.
  • energy pulses incident on the backside 105 of the substrate 110 of the EUV mirror too, the mask blank 200, 210, 220, and/or the photomask 300 can generate marks 450 in the ML mirror structure 160 deposited on the front side 115 of the sub- strate 110.
  • marks 450 can be created in the substrate 110 and/or in the ML mirror 160 by radiating the energy pulses through the coating 240.
  • the diagram 455 of Fig. 4b shows a mark 450 or a fiducial mark 450 of Fig. 4a greatly enlarged.
  • the mark 450 is formed of a number of small indi- vidual local surface modifications 480 illustrated in form of black dots.
  • a reference point can be determined for the cross 450 which has a significantly higher accuracy than a reference point determined from a single local surface modification 480.
  • Fig. 5 depicts a schematic block diagram of an apparatus 500 which can be used for generating local surface modifications 480.
  • the local surface modifications 480 can be creating in a specific geometric structure forming a mark 450 or a fiducial mark 450 which can be used for positioning various tools during processing of a mask blank 200, 210, 220 and/or for repairing defects.
  • the apparatus 500 comprises a sample holder 520 which may be movable in two or three dimensions. The movement of the sample holder 520 in two dimensions in the plane of the sample holder 520 is indicated in Fig. 5 by crossed arrows.
  • the sample 510 may be fixed to the sample holder 520 by using various techniques, as for example, clamping or electrostatic chucking (not indicated in Fig. 5).
  • the sample 510 maybe a template used in nanolithography, a substrate 110, an EUV mirror too, a mask blank 200, 210, 220 or a photomask 300, i.e. an optical ele- ment too, 300
  • the apparatus 500 includes a pulse laser source 530 which can produce a beam or a photon beam 535 of energy pulses or photon pulses.
  • the laser source 530 generates light pulses or photon pulses of variable duration.
  • the pulse duration may be as low as 10 fs but may also be increased up to 1000 ps.
  • the pulse energy density of the photon pulses at the focal point can also be adjusted across a huge range reaching from 0.001 J/cm 2 per pulse up to too J/cm 2 per pulse.
  • the repetition rate of the photon pulses comprises the range from 1 Hz to 1 GHz.
  • the photon pulses maybe generated by a Ti:Sapphire laser operating at a wavelength of 800 nm.
  • each laser type producing photons in a wavelength range from 150 nm to 1500 nm and which are able to generate pulses with durations in the femto-second range may be used.
  • Nd-YAG laser systems or dye laser systems may also be applied for generating local surface modifications.
  • the steering mirror 540 directs the pulsed laser beam 535 into the focusing objective 550.
  • the objective 550 focuses the pulsed laser beam 535 into the EUV mirror too, the mask blank 200 or the photomask 300.
  • the NA (numerical aperture) of the applied ob- jective 550 depends on a predetermined spot size at the focal point and the position of the focal point with respect to the mask surface 430.
  • the NA of the objective 550 may be up to 0.9 which results in a focal point spot diameter of essentially 1 ⁇ m.
  • the apparatus 500 also includes a controller 570 and a computer 575 which manage the translations of the two-axis positioning stage of the sample holder 520 in the plane of the sample (x and y directions).
  • the controller 570 and the computer 575 also control the translation of the objective 550 perpendicular to the plane of the sample holder 520 (z direction) via the one-axis positioning stage 555 to which the objective 550 is fixed.
  • the sample holder 520 may be equipped with a three-axis positioning system in order to move the sample 510 to a target location 560 and the objective 550 may be fixed, or the sample holder 520 may be fixed and the objective 550 may be moveable in three dimensions.
  • Alt- hough not economical, it is also conceivable to equip both the objective 550 and the sample holder 520 with three-axis positioning systems.
  • the computer 575 may be a microprocessor, a general-purpose processor, a special purpose processor, a CPU (central processing unit), a GPU (graphic processing unit) or the like. It maybe arranged in the controller 570, or maybe a separate unit such as a PC (personal computer), a workstation, etc.
  • the computer 575 may further comprise I/O (input/output) units like a keyboard, a touchpad, a mouse, a video/graphic display, a printer, etc.
  • the computer 575 may also comprise a volatile and/or a non- volatile memory.
  • the computer 575 may be realized in hardware, software, firmware or any combination thereof.
  • the computer 575 may control the laser source 530 (not indicated in Fig. 5).
  • the computer system 575 may comprise an interface 580.
  • the computer 575 may exchange data with another apparatus or with a computer system of another apparatus via the interface 580.
  • the apparatus 500 may also provide a viewing system including a CCD (charge-coupled device) camera 565 which receives light from an illumination source arranged to the sample holder 520 via the dichroic mirror 545.
  • the viewing system fa- cilitates navigation of the sample 510 to the target position 560.
  • the viewing system may also be used to observe the formation of a local surface modification 480 of an optical element too, 200, 300 generated by the pulse laser beam 535 of the light source 530.
  • Fig. 6 schematically illustrates the formation of a local surface modification 480 in an optically transmissive or transparent substrate 110 of an EUV mirror too, a mask blank 200, 210, 220 and/or a photomask 300.
  • the upper left partial image 605 presents fo- cusing of energy pulses 610 to 645 in form of photon pulses 610 to 645 through the ob- jective 550 of the apparatus 500 of Fig. 5 into a sample 510 which is a fused silica sub- strate 110 and/or an ML mirror structure 160 of an optical element too, 300 or of a mask blank 200, 210, 220.
  • the objective 550 has an NA of 0.9 in Fig. 6. Further, in the example depicted in Fig.
  • the pulses 610 to 645 incident through the front side surface 115 of the substrate 110 As already indicated, it is also possible that the energy pulses 610 to 645 incident through the rear side surface 105 and are focussed in a distance 665 below the front side surface 115 (not indicated in Fig. 6).
  • the distance 665 may vary from about 0.3 ⁇ m to too ⁇ m.
  • the upper right partial image 655 of Fig. 6 shows that the energy pulses 610 to 645 are focussed at a distance z 665 below the front side surface 115.
  • the temperature raises within the volume 650 of the substrate 110 if the cooling time of the material of the ra- diated volume 650 is larger than a time interval between the two or more sequential en- ergy pulses 610, 615, 620, 625, 630, 635, 640, 645.
  • the heat spreading is governed by the heat transfer coefficient which is typically a ma- terial-specific constant.
  • the heat conduction typically leads to an exponential decay of the temperature at the position the energy pulses locally deposit energy.
  • the cooling time may be defined as the time period the temperature difference between the maxi- mum temperature at the focal point of the laser pulses 610 to 645 and a portion of the optical element having an ambient temperature is halved.
  • the local temperature raises in the material of the optical element at the focal position, if the time period between two consecutive energy pulses 610 to 645 is smaller than the cooling time of the material the two or more energy pulses 610 to 645 are incident on.
  • the method of heat accumulation also works, if the time period between two consecu- tive energy pulses 610 to 645 is two-times or three-times the cooling time, but its effi- ciency decreases.
  • the first energy pulse 610 and the second energy pulses 615, 620, 625, 630, 635, 640, 645 have a pulse width of 200 fs (femto-seconds) and a repeti- tion rate of 5 MHz, i.e. the time period between two sequential laser pulses 610, 615, 620, 625, 630, 635, 640, 645 is 200 ns as denoted by the double-headed arrow 680 in Fig. 6.
  • the temperature almost linearly raises in the volume 650 based on the energy provision by the consecu- tive energy pulses 610 to 645.
  • the energy density needed for the formation of local sur- face modifications 480 depends on the pulse repetition rate and the energy density of the energy pulses 610 to 645.
  • the energy density of the energy pulses 610 to 645 is within a range of 0.1 J/cm 2 and 1 J/cm 2 .
  • the time interval indicated by the double-headed arrow 685 corresponds to about three-times the cool- ing time.
  • a bump-type local surface modification 480 is formed on the surface530 of the substrate 110 of the optical element too, 300 and/or the mask blank 200, 210, 220.
  • the predetermined temperature for forming a local surface modification 480 is in a range of 1700 K to 5300 K. The generation of lo- cal surface modification 480 does not produce any debris.
  • Local surface modifications 480 can also be generated in a multilayer (ML) mirror structure 160 of an EUV mirror too and/or an EUV mask blank 200, 210, 220.
  • the MoSi layers 130, 140 of an ML 160 can locally be converted in molybdenum silicide when locally heating the ML 160 with energy pulses 610 to 645.
  • the formation of molybdenum silicide leads to a local compaction of the ML 160 of about 20% compared to the width or height of a MoSi layer.
  • the compaction of the MoSi layers into molybdenum silicide starts at a temperature of approximately 520 K.
  • the compaction of the ML 160 causes a local depression or pit which results in a local decrease of the ML reflectivity. This means that all local surface modifications 480 gen- erated on the ML 160 are clearly visible when an actinic mask inspection tool uses EUV radiation in the range of the actinic wavelength.
  • the number N of energy pulses 610 to 645 focussed on a same position and the NA of the focusing objective 550, small pits which may additionally have a nano-needle structure in their center can be formed on an ML surface 430 without any modification of the ML 160 outside of the la- ser focus. This is discussed in detail in the context of Figures 9a to 9c. Further, the pro- cess of molybdenum silicide formation does not produce any debris.
  • the diagram 700 of Fig. 7 presents a top view of a microscope image on a surface 430 of a multilayer 160 on which local surface modifications 480 have been generated as a function of the energy locally deposited per energy pulse (indicated on the left side) and the number N of energy pulses 610, 615, 620, 625, 630, 635, 640, 645 incident on a same position of the ML surface 730 (indicated on the right side of the microscope im- age).
  • the NA used for focusing the energy pulses 610 to 645 was 0.6. As can be seen in Fig.
  • the optical microscope clearly detects the generated local surface modification 480 when using energy pulses 610, 615, 620, 625, 630, 635, 640, 645 which have an en- ergy of 0.12 nJ or a higher energy.
  • Fig. 8 shows in the upper partial image 805 local surface modifications 480 having the shape of bumps 801, 804, 807, 810, 813, 816, 819, 822, 825, and 828.
  • the local surface modifications 480 are generated in a substrate 110 of an optical element too, 300 which comprises fused silica.
  • the pulse energy is 21 nJ for all pulses 610 to 645.
  • the parameter in the diagram 805 is the depth ⁇ z 665 into which the energy pulses 610 to 645 are focused.
  • the depth Dz is referred to the surface 430 of the substrate 110 or al- ternatively of the ML mirror structure 160.
  • the local surface modifications 480 are measured with an optical microscope in the diagram 805 of Fig. 8.
  • the local surface modifications 480 can be detected with the optical microscope for focusing depths 665 within a range 0.75 ⁇ m ⁇ ⁇ z ⁇ 7.5 ⁇ m.
  • the lower partial image 865 or the diagram 865 shows the profiles 870 and 875 of the bump 810 obtained in two perpendicular directions determined from the AFM image presented in the diagram 835 of Fig. 8.
  • the bump 810 has a height of 56 nm and a width (FWHM, Full Width Half Maximum) of 0.45 ⁇ m.
  • Fig. 9a presents in the upper partial image 905 more details of the local surface modifi- cations 480 of Fig. 7 generated in the ML mirror structure 160.
  • the number N of en- ergy pulses 610 to 645 focused on the same position for generating the local surface modifications 480 varies for the various rows of local surface modifications 480.
  • the local surface modifications are pits.
  • Each pulse has an energy of 0.3 nJ.
  • the local surface modifications 480 are measured with an AFM.
  • FIGa shows the profiles of the local surface modifications 480 along the line 1-1 in the diagram 905.
  • the profiles of the diagram 925 reveal that the energy pulses 610 to 645 of the diagram 905 generate depressions 910 or pits whose depth increases as a function of the number of energy pulses focused on the same posi- tion.
  • the local surface modifications 480 have a needle-like structure 915 in the center of the depression 910 for pulses having an energy of 0.3 nJ. For 40 overlapping energy pulses, the height of the needle-like structure 915 reaches the height of the un- disturbed surface 430 of the ML mirror structure 160.
  • the diagram 935 of Fig. 9b presents the local surface depression 480 generated by fo- cusing 40 energy pulses having a pulse energy of 0.3 nJ on the same position. This means the diagram 935 reproduces the local surface modification 480 of the diagram 905 of Fig. 9a in more detail.
  • the depression 910 has a needle-like structure 915 as al- ready discussed in the context of Fig. 9a.
  • the diagram 955 depicts the profiles 940 and 950 of the depression 910 obtained along the perpendicular directions 920 and 925, re- spectively.
  • the energy of the two overlapping pulses is 0.12 nJ.
  • the diagram 995 represents the profiles 970 and 980 again obtained along the direc- tions 920 and 925, respectively.
  • the width of the depression 960 is similar to that of the depression 910 of Fig. 9b, but the depth is only about 25% of that of the depression 910. Further, the depression 960 does not show a needle-like structure 915 in the cen- ter of the depression 960. This reveals that the energy of the energy pulses is decisive whether the generated depression additionally has a needle-like structure 915.
  • both the local surface modifications 480 in the form of bumps 801 to 828 or the ones having the shape of depressions 910, 960 with or without a nano-needle structure 915 in the center of the depression 910, 960 have sharp edges. Hence, they are clearly visible for example in an e-beam writing tool.
  • marks 450 and/or fiducial marks 450 can be generated from the bump-like 801 to 828 and/or the pit-like 910, 960 local surface modifications 480 which can reliably be detected, for example, by a pattern writing tool and/or a repair tool.
  • Fig. io depicts a flow diagram 1000 of one of the inventive methods.
  • the method for generating at least one local surface modification 480 of an optical element too, 300 used in a lithographic system begins at 1010.
  • a first energy pulse 610 is fo- cussed in the optical element too, 300.
  • At step 1030 at least one second energy pulse 615, 620, 625, 630, 635, 640, 645 is sequentially focussed in the optical element too, 300 which at least partially locally overlaps the first energy pulse 610 so that the surface 430 of the optical element too, 300 is locally modified. It is also possible that the at least one second energy pulse 615, 620, 625, 630, 635, 640, 645 is sequentially focussed in the optical element too, 300 which essentially locally overlaps the first en- ergy pulse 610 so that the surface 430 of the optical element too, 300 is locally modi- fied.
  • the method ends at 1040.
  • Fig. 11 reproduces the EUV photomask 300 of Fig. 3, but in contrast to Fig. 3 the EUV photomask 1100 of Fig. 11 has a black defect 1150.
  • the defect 1150 essentially absorbs the EUV photons 180 hitting its surface. This results in a local reduction the reflected EUV intensity.
  • the defect 1150 can be removed from the capping layer 150 or the buffer layer 230 of the photomask 1100. This can be done by performing a local etching pro- cess providing an etching gas at the defect position and using a massive particle beam in order to induce a local etch reaction at the defective position of the mask 1100.
  • the particle beam has to be aligned to the defect 1150 of the mask 1100 in order to secure that the local etching process does not etch a pattern element 360 and/or does not attack the capping layer 150 and/or the buffer layer 230 protecting the ML 160 of the EUV photomask 1100.
  • the alignment of the particle beam with respect to the defect 1150 can be performed by means of one or more local surface modifications 480, marks 450 or fiducial marks 450.
  • the generation of one or more local surface modifications 480 has been discussed above in the context of the Figures 4 to 10.
  • the position or location of the defect 1150 with respect to the one or more local surface modifications 480 and/or one or several marks 450 can for example be determined by a defect review tool. Based on this data, the massive particle beam of a repair tool can precisely be aligned to the defect 1150.
  • the defect 1150 can then be removed from the EUV mask 1100 by performing a local etching process. Fig.
  • the apparatus 1200 may comprise the apparatus 500 which is designed for generating one or more local surface modifications 480. Further, the ap- paratus 1200 may also include a repair tool 1400 which is in the following explaining in the context of the discussion of Fig. 14. Moreover, the apparatus 1200 may comprise a computer system 1250 which is connected via the connections 1210 and 1220 to the ap- paratus 500 and the apparatus 1400. The computer system 1250 of the apparatus 1200 may have a control unit 1230 which controls both, the apparatus 500 generating the lo- cal surface modification(s) 480 and the repair tool 1400. The apparatus 500, the appa- ratus 1400 and the computer system 1250 maybe contained in the housing of the appa- ratus 1200.
  • an apparatus 1300 connects the apparatus 500 and the apparatus 1400 via a connection 1310.
  • Fig. 13 schematically presents the apparatus 1300.
  • the apparatus 500 and the apparatus 1400 have their own computer system 575, 1480 as is described at the discussion of the Figures 5 and 14.
  • the apparatus 1300 is more expensive as the apparatus 1200 but of- fers more flexibility with respect to the process management of a defect repair process.
  • Fig. 14 schematically shows a section through a few components of a repair tool 1400 that can be used for the repair of the defect 1150 of the EUV photomask 1100. Further, the apparatus 1400 can be used for repairing a clear defect of missing material, for ex- ample, missing absorber material and/or missing phase-shifting material of a photo- mask 1100.
  • the repair tool 1400 may obtain position data of the defect 1150, for exam- ple, from a defect review tool.
  • the example illustrated in Figure 14 presents a scanning particle microscope 1400 in the form of a scanning electron microscope (SEM) 1400.
  • a massive particle beam 1405 in the form of an electron beam 1405 for repairing the black defect 1150 (or a clear de- fect) is advantageous in that the electrons 1405 substantially cannot damage the EUV mask 1100 or it can only damage the EUV photomask 1100 to a small extent.
  • other massive particle beams are also possible, for example an ion beam of a FIB (Fo- cused Ion Beam) system (not illustrated in Figure 14).
  • the modified SEM 1400 comprises as essential components a particle gun 1402 and a column 1410, in which the electron optics or beam optics 1412 is arranged.
  • the electron gun 1402 produces an electron beam 1405 and the electron or beam optics 1412 focuses the electron beam 1405 and directs it at the output of the column 1415 onto a sample 1425 which maybe identical to the EUV mask 1100 of Fig. 11.
  • the sample 1425 for example the EUV mask 1100, is arranged on a specimen stage 1425. As symbolized in Figure 14 by the arrows, the specimen stage 1425 can be moved in three spatial directions in relation to the electron beam 1405 of the SEM 1400.
  • the apparatus 1400 or the repair tool 1400 contains a detector 1417 for detecting the secondary electrons or backscattered electrons produced at the measurement point 1422 by the incident electron beam 1405.
  • the detector 1417 is controlled by a computer system 1480 which may comprise a control device 1485 for controlling the detector 1417.
  • the computer system 1480 of the apparatus 1400 may receive meas- urement data of the detector 1417.
  • the apparatus 1400 may include a second detector 1435 which can detect electromagnetic radiation emitted by the electron beam 1405 in- Jerusalem local chemical reaction.
  • the control device 1485 and/or the computer system 1480 can generate images from the measurement data which may be presented on a monitor 1490.
  • the apparatus 1400 may comprise an ion source which may provide low-en- ergy ions in the region of the measurement point 1422, wherein the low-energy ions prevent the EUV mask 1100 or the surface thereof from having a negative surface charge (not illustrated in Figure 14).
  • an ion source With the aid of an ion source, it is possible to re- prise a negative charge of the EUV mask 1100 in a local and controlled fashion, and hence it is possible to prevent a reduction in the lateral spatial resolution of the electron beam 1405 during a local chemical reaction.
  • the electron beam 1405 of the apparatus 1400 can additionally be used to analyze the defect 1150 and, in particular, to scan the repaired position in order to determine whether a repairing process has been successful or not.
  • the computer system 1480 may comprise an interface 1487. By way of this interface, it is possible to connect the computer system 1480 to the apparatus 500 of Fig. 5 (not il- lustrated in Figure 14).
  • the computer system 1480 can receive position data via the in- terface 1487.
  • the computer system 1480 can obtain measurement data of the black defect 1150 via the interface 1487, the position data have for example been recorded by means of a defect review tool. It is also possible that the computer system 1480 obtains for the one or more local surface modifications 480 and/or the defect 1150 from the apparatus 500.
  • the computer system 1480 or the control unit 1485 further comprises a scanning unit which scans the electron beam 1405 over the EUV mask 1150.
  • the scanning unit con- trols deflection elements in the column 1410 of the SEM 1400, which are not illustrated in Fig. 14.
  • the computer system 1480 or the control unit 1485 may comprise a setting unit, in order to set and control the various parameters of the SEM 1400. Pa- rameters that can be set by the setting unit may be for example: the magnification, the focus of the electron beam 1405, one or more settings of the stigmator, the beam dis- placement, the position of the electron source 1402 and/or one or more stops (not illus- trated in Figure 14).
  • the apparatus 1400 for correcting defects, for example the defect 1150, and for ascer- taining a best-possible repair concept for an examined defect 1150 preferably comprises several different storage containers for various gases or precursor gases. Three storage containers 1440, 1450 and 1460 are illustrated in the exemplary apparatus 1400 of Fig. 14. However, an apparatus 1400 may also have more than three storage containers for processing an EUV mirror too, an EUV mask blank 200, 210, 220 and/or an EUV pho- tomask 1100.
  • the first storage container 1440 stores a precursor gas or a first deposition gas, which can be used in cooperation with the electron beam 1405 of the SEM 1400 for depositing material for example to correct or repair a clear defect or a defect of missing material.
  • the missing material may for example be material of a phase-shifting mask or a binary mask.
  • the first storage container 1440 may have a precursor gas in the form of a metal carbonyl, for example molybdenum hexacarbonyl (Mo(CO) 6 ).
  • the second storage container 1450 contains an etching gas, with the aid of which the dark defect 1150 can be etched from the surface of the capping layer 150 protecting the multilayer structure 160 of the EUV mask 1100.
  • the second storage container 1450 may comprise xenon difluoride (XeF 2 ).
  • etching gases which can be stored in the storage container 1450 are e.g. a halogen, for example fluorine (F 2 ) or chlorine (Cl 2 ) or a compound containing a halogen.
  • the third storage container 1460 stores an additive gas which can be mixed to either a deposition gas stored in the container 1440 or an etching gas stored in the container 1450.
  • the additive gas may for example comprise oxygen (O 2 ) or ammonia (NH 3 ).
  • the third storage container 1460 may contain a second deposition gas or a second etching gas.
  • Each storage container 1440, 1450, 1460 is equipped with its own valve 1442, 1452,
  • the three storage containers 1440, 1450, 1460 have dedi- cated gas feeds 1445, 1455 and 1465, which end with a nozzle 1447, 1457 and 1467 near the point of incidence 1422 of the electron beam 1405 on the EUV mask 1150.
  • the valves 1442, 1452, 1462 are installed in the vicinity of the storage containers 1440, 1450, 1460.
  • valves 1442, 1452, 1462 may be arranged in the vicinity of the corresponding nozzle 1447, 1457, 1467 (not shown in Figure 14).
  • Each storage container 1440, 1450, 1460 may have a dedicated element for the individual temperature setting and control. The temperature setting facilitates both cooling and heating for each gas.
  • gas feeds 1445, 1455, 1465 may likewise respectively have a dedicated element for setting and monitoring the temperature at which the gases are provided at the reaction location 1422.
  • the apparatus 1400 of Figure 14 may have a pump system 1470 to produce and main- tain the required vacuum.
  • the apparatus 1400 may include a suction ex- traction device (not illustrated in Figure 14).
  • the suction extraction device in combina- tion with the pump system 1470 makes it possible that the fragments or constituents that are produced during the decomposition of a precursor gas, i.e. a deposition gas or an etching gas, and are not required for the local chemical reaction can substantially be extracted from the vacuum chamber 1475 of the apparatus 1400 at the point of origin.
  • a focused electron beam 1405 is exclusively used in the apparatus 1400 that is given by way of ex- ample in Figure 14. However, additionally or alternatively, it is also conceivable to initi- ate the local reaction(s) with the aid of a photon beam, for example, the focused photon beam 535 of the apparatus 500.
  • Fig. 15 shows a flow chart 1500 of method for repairing at least one defect of an optical element too, 300, 1100 used in a lithographic system.
  • the method begins at 1510.
  • At step 1520 at least one local surface modification 480 of the optical element too, 300, 1100 is generated using at least one focussed photon beam 535. This step may be performed by the apparatus 500 of Fig. 5 which is designed for generating one or more local surface modifications 480 which can be formed in form of a mark 450 or a fiducial mark 450.
  • at least one massive particle beam 1405 is aligned to the at least one defect 1150 based on the at least one local surface modification 480.
  • the at least one defect 1150 is repaired using the at least one mas- sive particle beam 1405 and at least one precursor gas. Then the method ends at 1550.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Preparing Plates And Mask In Photomechanical Process (AREA)

Abstract

La présente invention concerne un procédé (1000) pour générer au moins une modification de surface locale (480) d'un matériau d'un élément optique (100, 300) utilisé dans un système lithographique. Le procédé (1000) comprend les étapes consistant à : (a) focaliser une première impulsion d'énergie (610) dans l'élément optique (100, 300) ; et (b) focaliser de manière séquentielle au moins une seconde impulsion d'énergie (615, 620, 625, 630, 635, 640, 645) dans un intervalle de temps qui est plus court qu'un temps de refroidissement du matériau, la ou les secondes impulsions d'énergie (615, 620, 625, 630, 635, 640, 645) chevauchant au moins partiellement la première impulsion d'énergie (610) de sorte que la surface de l'élément optique (100, 300) est localement modifiée (480).
PCT/IL2021/050334 2021-03-24 2021-03-24 Procédé de génération d'une modification de surface locale d'un élément optique utilisé dans un système lithographique WO2022201138A1 (fr)

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