METHOD AND APPARATUS FOR MASK REPAIR

Abstract

The present invention relates to methods, to an apparatus and to a computer program for processing of an object for lithography.

A method of processing an object for lithography comprises: providing a first gas comprising first molecules; providing a particle beam in a working region of the object for removal of a first material in the working region, based at least partly on the first gas. The first material may comprise chromium and nitrogen. In addition, the first material may comprise at least 5 atomic percent of nitrogen, preferably at least 10 atomic percent of nitrogen, especially preferably at least 20 atomic percent of nitrogen.

Claims

1. A method of processing an object for lithography, comprising: providing a first gas comprising first molecules; and providing a particle beam in a working region of the object for removal of a first material in the working region, based at least partly on the first gas; wherein the first material comprises chromium and nitrogen, wherein the first material comprises at least 1 atomic percent of nitrogen, and wherein a sidewall angle of the first material is 70 to 90.

2. The method according to claim 1, wherein the first material is capable of absorbing radiation associated with the object.

3. The method according to claim 1, wherein the first material corresponds to a layer material of a pattern element of the object.

4. The method according to claim 1, wherein the first material comprises a chromium nitride.

5. The method according to claim 1, wherein the first molecules comprise at least one halogen atom.

6. The method according to claim 1, wherein the first molecules comprise a halogen compound.

7. The method according to claim 6, wherein the halogen compound comprises a nitrosyl halide and/or a nitryl halide.

8. The method according to claim 7, wherein the nitrosyl halide comprises at least one of the following: nitrosyl chloride, NOCl, nitrosyl fluoride, NOF, nitrosyl bromide, NOBr; and/or wherein the nitryl halide comprises at least one of the following: nitryl chloride, ClNO.sub.2, nitryl fluoride, FNO.sub.2.

9. The method according to claim 6, wherein the halogen compound comprises a noble gas halide.

10. The method according to claim 9, wherein the noble gas halide comprises at least one of the following: xenon difluoride, XeF.sub.2, xenon dichloride, XeCl.sub.2, xenon tetrafluoride, XeF.sub.4, xenon hexafluoride, XeF.sub.6.

11. The method according to claim 6, wherein the halogen compound comprises an interhalogen compound.

12. The method according to claim 1, wherein a first dipole moment associated with the first molecules comprises at least 1 D.

13. The method according to claim 1, wherein the method further comprises: providing a second gas comprising second molecules, wherein the removing of the first material is further based at least partly on the second gas.

14. The method according to claim 13, wherein a first dipole moment associated with the first molecules and a second dipole moment associated with the second molecules differ from one another by not more than 0.1 D.

15. The method according to claim 13, wherein the second molecules comprise water, H.sub.2O, and/or heavy water, D.sub.2O.

16. The method according to claim 1, wherein the first material is removed selectively, such that a second material of the object is essentially not removed.

17. The method according to claim 16, wherein the method further comprises removing at least one intermediate material disposed between the first material and the second material.

18. The method according to claim 1, wherein the method further comprises removing at least one surface material of the object.

19. The method according to claim 1, wherein the particle beam is based at least partly on an acceleration voltage of less than 3 kV.

20. The method according to claim 1, wherein the method further comprises: determining an endpoint of the removing, based at least partly on detecting of electrons that are released from the object.

21. The method according to claim 1, wherein the particle beam comprises an electron beam.

22. The method according to claim 1, wherein the method is carried out in such a way that an opaque defect of the object is repaired.

23. The method according to claim 1, wherein the object comprises an EUV mask and/or a DUV mask.

24. An apparatus for processing an object for lithography, comprising: a first gas outlet for providing a first gas; and a particle beam source for providing a particle beam in a working region of the object, wherein the apparatus is configured to perform a method according to claim 1.

25. An object for lithography, wherein the object has been processed by a method according to claim 1.

26. A method of processing of a semiconductor-based wafer, comprising: lithographic transfer of a pattern associated with an object for lithography to the wafer, wherein the object has been processed according to claim 1.

27. A computer program comprising instructions which, when they are executed by a computer system, cause the computer system to perform a method according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0091] The following detailed description describes technical background information and working examples of the invention with reference to the figures, which show the following:

[0092] FIG. 1 gives a schematic illustration in a top view of an illustrative repair situation for an object for lithography from the prior art.

[0093] FIG. 2 shows a schematic diagram of an illustrative method of the invention.

[0094] FIGS. 3A-3C give a schematic illustration, in a cross section, by way of example, of operations in a method of the invention.

DETAILED DESCRIPTION

[0095] FIG. 1 gives a schematic illustration in a top view of an illustrative repair situation for an object for lithography. The object for lithography may comprise a lithographic mask suitable for any lithography method (e.g. EUV lithography, DUV lithography, i-line lithography, nanoimprint lithography, etc.). In one example, the lithography mask may comprise an EUV mask, a DUV mask, an i-line lithography mask and/or a nanoimprinting stamp. In addition, the object for lithography may comprise a binary mask (e.g. a chromium mask, an OMOG mask), a phase mask (e.g. a chromium-free phase mask, an alternating phase mask (e.g. a rim phase mask)), a half-tone phase mask, a tritone phase mask and/or a reticle (for example with pellicle). The lithography mask may be used, for example, in a lithography method for the production of semiconductor chips.

[0096] The object for lithography may comprise (unwanted) defects. For example, a defect may be caused in the production of the object. In addition, a defect may also be caused by (lithography) processing of the object, a process deviance in the (lithography) processing, transport of the object, etc. On account of the usually costly and complex production of an object for lithography, the defects are therefore usually repaired.

[0097] In the working examples described herein, for illustrative purposes, an EUV mask is frequently employed as an example of an object for lithography. However, rather than the EUV mask, any object for lithography is conceivable (for example as described herein).

[0098] FIG. 1 can show, in schematic form, in a top view, two local states D, R of a detail 1000 of an EUV mask in the course of a repair of a defect in the mask. The detail 1000 shows part of a pattern element PE of the EUV mask. The pattern element PE may also be regarded as a pattern element of the EUV mask. The pattern element PE may be part of a designed pattern which can be transferred to a wafer, for example, via a lithography method. The local state D shows an opaque defect 1010 adjoining the pattern element PE. The opaque defect 1010 may feature, for example, excess (opaque) material that should not be present at the defect site according to the mask design. The excess (opaque) material may correspond, for example, to an opaque material of the pattern element PE, or else to any other material of a layer of the pattern element PE (as described herein). In relation to FIG. 1 (state D), a defect-free pattern element PE in the detail 1000 would have to have a square shape, it being clear that this target state does not exist as a result of the opaque defect 1010. A repair procedure RV therefore typically removes the excess (opaque) material in the region of the opaque defect 1010, such that a repaired state R of the pattern element PE can be created. Thus, it is shown in state R that no opaque effect occurs any longer in the original defect region 1020 (i.e. at the original site in the opaque defect) and there is no longer any excess (opaque) material. The removal of the defect 1010 accordingly re-establishes the target state of the rectangular shape of the pattern element PE after a repair operation.

[0099] During use in lithography apparatuses or lithography methods, a lithography mask may be subject to extreme physical and chemical environmental conditions. This is especially true of the exposure of EUV masks (and also DUV masks, or other masks as described herein) during a corresponding lithography method, in which the opaque material in particular of a pattern element PE may be subjected to these influences to a significant degree. For example, in the case of EUV exposure, a hydrogen plasma comprising free hydrogen radicals may be released, which can attack the opaque material of the pattern element PE among other materials and cause a material-altering and/or -removing effect. Further damage influences may occur in the EUV lithography process and mask cleaning processes. Damage to the mask material includes, for example, a chemical and physical alteration of the material by (EUV) radiation, temperature, and also a reaction with hydrogen or another reactive hydrogen species (e.g. free radicals, ions, plasma, etc.). The alteration of the material may also be caused by a reaction with purge gases (e.g. N.sub.2, extreme clean dry air-XCDA, noble gases, etc.), in conjunction with the exposure radiation (e.g. EUV radiation, DUV radiation). The damage to the material may likewise arise or be enhanced by downstream processes (for example a mask cleaning operation). The downstream processes may, for example, additionally attack the opaque material of the pattern element PE that has previously been damaged by chemical/physical reactions during the exposure operation, and hence worsen the damage.

[0100] In general, therefore, the material properties of an EUV mask, especially the opaque material of the EUV mask (or of the pattern element PE), are therefore designed to be resistant to the aggressive physical/chemical conditions in lithography, in order to specifically counteract the material-removing effects. The specific opaque material used here in a pattern element PE may be a chemically resistant material. In particular, it is possible to employ chromium nitride-containing materials, and also chromium-containing materials having a high nitrogen content (as described herein), on account of their very high chemical stability, as resistant material in an EUV mask. The chromium nitride-containing materials may take the form, for example, of Cr.sub.aN.sub.bZ.sub.c (a, b>0, c0, Z: one or more further elements). Z here may comprise a metal, nonmetal, semimetal, alkali metal (e.g. Li, Na, K, Rb, Cs). In addition, Z may comprise an alkaline earth metal (e.g. Be, Mg, Ca, Sr, Ba), a 3rd main group element (e.g. B, Al, Ga, In, Tl), a 4th main group element (e.g. C, Si, Ge, Sn, Pb), a 5th main group element (e.g. N, P, As, Sb, Bi). In addition, Z may comprise a chalcogenide (e.g. O, S, Se, Te), a halogen (e.g. F, Cl, Br, I) a noble gas (atom) (e.g. He, Ne, Ar, Kr, Xe), a transition group element (e.g. Ti, Hr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg).

[0101] However, this type of resistant (opaque) material of a pattern element PE or of an EUV mask can make the repair operation RV of an opaque defect 1010 significantly more difficult since the repair operation is to specifically remove the resistant (opaque) material. In particular, this circumstance can make it more difficult to repair masks by use of electron beam-induced etching processes.

[0102] FIG. 2 shows a schematic diagram of an illustrative method 200 of the invention. The method 200 may be employed in order to remove material from an EUV mask. In particular, the method 200 may be employed in order to remove material from an opaque defect 1010 in the course of a repair operation.

[0103] The method 200 may comprise providing a first gas including first molecules. The first gas may comprise, for example, NOCl and/or XeF.sub.2 as first molecules. In addition, other gases are also conceivable as first gas, as described herein.

[0104] Other molecules are also suitable as first molecules of the first gas for the method 200. For example, the first molecules may comprise molecules that may be regarded as acid halides of nitrogen-containing (e.g. inorganic) acids. The first molecules may likewise comprise molecules that can be split into chlorine radicals and nitrogen oxides under suitable reaction conditions and/or additionally, for example, a further nonpolar species. In addition, the first molecules may comprise molecules which, in aqueous solution, afford at least one of the following molecules: NO, HCl, HNO.sub.2, HNO.sub.3.

[0105] In addition, the method 200 may comprise providing 220 of a particle beam in a working region of the object for removal of a first material in the working region, based at least partly on the first gas. The first material here may comprise chromium and nitrogen. It may also be a characteristic 230 of the method 200 that the first material comprises at least 5 atomic percent of nitrogen, preferably at least 10 atomic percent of nitrogen, especially preferably at least 20 atomic percent of nitrogen. The method 200 may also comprise an electron beam as particle beam, such that electron beam-induced etching of the first material by the method 200 may be enabled.

[0106] The first material here may especially correspond to the resistant (opaque) material of the EUV mask (as described herein), which is to be removed in the course of the repair of an opaque defect.

[0107] The method 200 may also comprise providing a second gas as additive gas that assists the etching process (for example with regard to etch selectivity, etch rate, anisotropy factor, etc.). In particular, in the case of electron beam-induced etching, the first gas used in the method 200 may be NOCl and the additive gas H.sub.2O (i.e. water (vapor)). It is likewise conceivable that, in the case of electron beam-induced etching, the first gas used in the method 200 may be XeF.sub.2 and the additive gas H.sub.2O (i.e. water (vapor)). In addition, the second molecules may comprise a dipole moment between 1.6 D and 2.1 D, preferably between 1.7 D and 2 D, more preferably between 1.8 D and 1.95 D, most preferably between 1.82 D and 1.9 D. It is likewise conceivable that the second molecules comprise at least one oxygen atom, but no nitrogen atom. In addition, the second molecules may comprise molecules which, on reaction with NOCl, afford at least one of the following molecules: NO, HCl, HNO.sub.2, HNO.sub.3.

[0108] FIGS. 3A-3B give a schematic illustration, in a cross section, by way of example, of procedures in the method 200 that can take place in the course of repair of a defect in a lithography object.

[0109] FIG. 3A presents, in schematic form, an illustrative characteristic layer structure of a reflective lithography mask for the EUV wavelength region (i.e. an EUV mask). The illustrative EUV mask may be designed, for example, for an exposure wavelength in the region of 13.5 nm. The EUV mask may include a substrate S made of a material with a low coefficient of thermal expansion, for example quartz. Other dielectrics, glass materials or semiconducting materials likewise can be used as substrates for EUV masks.

[0110] The substrate S may be adjoined by a deposited multilayer film or a reflective layer stack ML including, for example, 20 to 80 pairs of alternating molybdenum (Mo) and silicon (Si) layers, which are also referred to as MoSi layers. The individual layers of the multilayer film ML may differ in refractive index, giving rise to a Bragg mirror that can reflect incident radiation (e.g. EUV radiation).

[0111] In order to protect the reflective layer stack ML, a cap layer D may be applied, for example, atop the uppermost layer of the reflective layer stack ML. The cap layer D may protect the reflective layer stack ML from damage by chemical processes during the production and/or during the use of the EUV mask (for example during a lithography method). The cap layer D may comprise ruthenium, and also elements or compounds of elements that increase reflectivity at wavelength 13.5 nm by not more than 3%. In addition, the cap layer D may comprise Rh, Si, Mo, Ti, TiO, TiO.sub.2, ruthenium oxide, niobium oxide, RuW, RuMo, RuNb, Cr, Ta, nitrides, and also compounds and combinations of the aforementioned materials.

[0112] Atop the cap layer D there may be several layers that may include, for example, the layers of the pattern element (i.e. pattern element layers). The pattern element layers may comprise a buffer layer P, an absorption layer A and/or a surface layer O. The properties of the pattern element layers (for example an intrinsic material property of a pattern element layer, a layer thickness of a pattern element layer, etc.) and the geometry of the pattern element PE shaped therefrom may be designed to cause an opaque effect in relation to the exposure wavelength of the EUV mask. For example, the pattern element PE may be designed such that it is opaque (i.e. non-transparent to light or highly light-absorbing) with respect to light radiation having a wavelength of 13.5 nm. The pattern element layers may correspond to the layers of the opaque defect 1010, although the opaque defect 1010 need not necessarily have all the pattern element layers. For example, the opaque defect 1010 may have merely the buffer layer P and the absorption layer A.

[0113] The buffer layer P may be present atop the cap layer D. In addition, the absorption layer A may be present atop the buffer layer P. The absorption layer A may be designed to be effective in absorbing the radiation of lithography wavelengths (as described herein). Accordingly, the absorption layer A may make the main contribution to an opaque effect of the pattern element (or of the opaque defect 1010). The optical properties of the absorption layer A can be described, for example, by a complex refractive index that may include a phase shift contribution (i.e. n) and the absorption contribution (i.e. k). For example, n and k may be regarded as intrinsic material properties of the absorption layer. Only particular chemical elements and/or compounds of chemical elements have advantageous phase-shifting and/or absorptive properties for the corresponding lithography method (e.g. an EUV lithography method). FIG. 3A indicates, by way of example, the layer thickness d of the absorption layer A. The layer thickness d of the absorption layer A (and also a layer thickness of another layer of the mask) is ascertained, for example, along a normal vector in relation to the plane of the mask. In addition, the surface layer O may be present atop the absorption layer A. The surface layer O may comprise an anti-reflection layer, oxidation layer and/or passivation layer. As well as the absorption layer A, it is also possible for the buffer layer P and/or the surface layer O to contribute to the absorption and to the opaque effect of the pattern element PE or of the opaque defect 1010.

[0114] In principle, any of the pattern element layers described herein may include the resistant material mentioned (i.e. chromium nitride or chromium having a high nitrogen content). Typically, for example, the absorption layer A includes the (high) chromium nitride content or chromium with a high nitrogen content. In addition, however, it is alternatively possible, for example, for the buffer layer to have the (high) chromium nitride content or chromium with a high nitrogen content.

[0115] The first material in the method 200 may accordingly comprise a material of any pattern element layer. In particular, the first material in the method 200 may comprise the material of the absorption layer A.

[0116] FIG. 3B shows a result of an illustrative method 200 for removal of part of the absorption layer A. The absorption layer A is designed as the first material in the method 200. Initially, part of the surface layer O may first be removed. For example, this can be carried out analogously to the method 200 via electron beam-induced etching in a separate step. The surface layer need not necessarily be removed with the first and/or second gas (as described herein). It is also conceivable that the electron beam-induced etching is designed exclusively for the removing of the surface layer (for example with an etching gas matched to the material of the surface layer). After the surface layer O has been removed, it is then possible to remove part of the absorption layer A as the first material in the method 200 (for example to repair an opaque defect). FIG. 3B illustrates selective electron beam-induced etching of the absorption layer A with respect to the buffer layer P. Accordingly, the method 200 may be adjusted such that the etch rate of the absorption layer A is elevated compared to the etch rate of the buffer layer P. For example, the etching selectivity can be adjusted via the properties of the second gas in the method 200 (for example via a suitable choice of the second gas (e.g. water), or the gas flow rate of the second gas). In addition, the etch selectivity can also be adjusted by the properties of the first gas (for example via the choice of first gas) (e.g. NOCl or XeF.sub.2), or via the gas flow rate of the first gas). In this example, the buffer layer P accordingly functions as etch stop via the etch selectivity chosen.

[0117] FIG. 3C shows a further result of an illustrative method 200 for removal of part of the absorption layer A. Initially, it is possible here (as described herein) to remove a portion of the surface layer O. After the surface layer O has been removed, it is then possible to remove part of the absorption layer A as the first material in the method 200. It is also possible here to etch a portion of the buffer layer P as intermediate material. Accordingly, the method 200 may be adjusted such that the etch rate of the absorption layer A, and also the etch rate of the buffer layer P, are elevated compared to the etch rate of the cap layer D. The etch rate of the absorption layer A may be in the same order of magnitude as the etch rate of the buffer layer P. The etch selectivity may be adjusted as described herein. As shown in FIG. 3C, this can achieve selective electron beam-induced etching of the absorption layer A and of the buffer layer P with respect to the cap layer D. In this example, the cap layer D therefore functions as etch stop via the etch selectivity chosen.

[0118] In one example, the surface layer O is not removed separately, but via the same process which is employed for the local removing of the absorption layer A (or of the absorption layer A and the buffer layer P) in a method 200.

[0119] In an example, the characteristic layer structure may comprise a ruthenium-based cap layer D and a tantalum-based buffer layer P (as described herein). In this example the characteristic layer structure may further comprise the absorption layer A (as described herein), wherein the absorption layer A may comprise the (herein described) first material. In such an example, the absorption layer A may comprise, for example, chromium and at least one atomic percent nitrogen (e.g., chromium nitride), the buffer layer P may comprise tantalum, the cap layer D may comprise ruthenium.

[0120] This exemplary characteristic layer structure may, for example, be processed sequentially with the herein described method (e.g., via two or more sub-processes).

[0121] For example, in a first step the absorption layer A may be locally removed with an electron beam induced process wherein NOCl is provided as a main etching gas and H.sub.2O is provided as an additive gas. For example, the etching rate of this sub-process may be adapted such that the absorption layer A is etched with a higher etching rate than the buffer layer P. The buffer layer P may thus function as an etching stop for this sub-process wherein the buffer layer P may not be (substantially) removed during the first sub-process. Subsequently, the buffer layer P (comprising tantalum) may be locally removed with an electron beam induced process wherein XeF.sub.2 is provided as a main etching gas and NO.sub.2 and H.sub.2O is provided (together) as an additive gas. For example, the etching rate of this sub-process may be adapted such that the buffer layer P is etched with a higher etching rate than the cap layer D. The cap layer D may thus function as an etching stop for this sub-process wherein the cap layer D may not be (substantially) removed during this sub-process.

[0122] In principle, it may also be necessary in a mask repair to produce or to deposit material (as repair material). In the case of mask repair by use of electron beam-induced deposition of chromium nitride (for example in the form of Cr.sub.aN.sub.bZ.sub.c, as described herein), chromium oxides or other chromium-containing deposits may also result in unwanted material deposition. Unwanted material deposition may be caused, for example, by off-target strands of the electron beam and secondary electrons generated thereby. In addition, unwanted deposition (of the repair material) may be caused by secondary electrons produced at sites adjacent to the repaired defect, and also by secondary electrons that escape at vertical edges of the processed material and propagate to sites adjacent to the repaired defect.

[0123] It is likewise possible for forwardscattered electrons (FSE) that escape from the flanks of existing material and backscattered electrons (BSE) that escape from the surface in the environment of the repaired site to contribute to unwanted material deposition.

[0124] A further application of the method 200 is therefore the removal of material that has been deposited by these mechanisms mentioned on areas adjacent to the repaired defect. In one example, the method 200 therefore also comprises the producing of a repair material.

[0125] In the course of production of the repair material, it is possible to use a deposition gas in the electron beam-induced deposition. It is possible here for at least one of the following to be included as deposition gas in the invention: (metal, transition element, main group) alkyls such as cyclopentadienyl (Cp) or methylcyclopentadienyl (MeCp) trimethylplatinum (CpPtMe.sub.3 or MeCpPtMe.sub.3), tetramethyltin SnMe.sub.4, trimethylgallium GaMe.sub.3, ferrocene Cp.sub.2Fe, bisarylchromium Ar.sub.2Cr and other compounds of this kind. In addition, at least one of the following may be included in the invention as first gas: (metal, transition element, main group) carbonyls such as chromium hexacarbonyl Cr(CO).sub.6, molybdenum hexacarbonyl Mo(CO).sub.6, tungsten hexacarbonyl W(CO).sub.6, dicobalt octacarbonyl Co.sub.2(CO).sub.8, triruthenium dodecacarbonyl Ru.sub.3(CO).sub.12, iron pentacarbonyl Fe(CO).sub.5 and other compounds of this kind. In addition, one of the following may be included in the invention as first gas:(metal, transition element, main group) alkoxides such as tetraethoxysilane Si(OC.sub.2H.sub.5).sub.4, tetraisopropoxytitanium Ti(OC.sub.3H.sub.7).sub.4 and other compounds of this kind.

[0126] It is also possible for at least one of the following to be included as deposition gas in the invention: (metal, transition element, main group) halides such as WF.sub.6, WCl.sub.6, TiCl.sub.6, BCl.sub.3, SiCl.sub.4 and other compounds of this kind. In addition, at least one of the following may be included in the invention as deposition gas: (metal, transition element, main group) complexes such as copper bis(hexafluoroacetylacetonate) Cu(C.sub.5F.sub.6HO.sub.2).sub.2, dimethylgold trifluoroacetylacetonate Me.sub.2Au(C.sub.5F.sub.3H.sub.4O.sub.2) and other compounds of this kind. It is also possible for one of the following to be included as deposition gas in the invention: organic compounds such as CO, CO.sub.2, aliphatic or aromatic hydrocarbons, constituents of vacuum pump oils, volatile organic compounds and further such compounds.

[0127] The method 200 (or the method in the first aspect) may be executed via the apparatus of the invention described herein. In one example, the apparatus comprises a mask repair apparatus for repair or processing of lithography masks. The apparatus may be used to localize and to repair or remedy mask defects. The apparatus may comprise parts such as the apparatus described in US 2020/0103751 A1 (see the corresponding FIG. 3A therein). The apparatus may comprise, for example, a control unit which may, for example, be part of a computer system. The apparatus, in one example, may be configured such that the computer system and/or the control unit controls the process parameters of the method in the first aspect as disclosed herein. This configuration can enable controlled, and also automated, implementation of the method according to the invention as specified herein, for example without manual interventions. This configuration of the apparatus can be achieved or enabled, for example, via the computer program according to the invention as described herein.