WO2022268924A1

WO2022268924A1 - Endpointing by induced desorption of gases and analysis of the re-covering

Info

Publication number: WO2022268924A1
Application number: PCT/EP2022/067101
Authority: WO
Inventors: Daniel Rhinow
Original assignee: Carl Zeiss Smt Gmbh
Priority date: 2021-06-24
Filing date: 2022-06-23
Publication date: 2022-12-29
Also published as: TW202316197A; DE102021206564A1

Abstract

The present invention encompasses a method for use with a lithographic mask, comprising the following steps: (a.) directing a particle beam onto an element of the lithographic mask in an atmosphere of gas particles, (b.) inducing a desorption and/or adsorption process of at least some of the gas particles in a region of the element, and (c.) capturing a signal of secondary particles and/or backscattered particles and/or some other free-space signal generated by the particle beam during the desorption and/or adsorption process. The present invention further relates to a corresponding device for use with a lithographic mask.

Description

ENDPOINTING BY INDUCED DESORPTION OF GASES AND ANALYSIS OF

THE RE-COVERING

1. Technical field

The present invention relates to a method, a device and a computer program for determining a material on a lithographic mask and for repairing a defect of a lithographic mask by means of a particle beam.

2. Technical background

As a consequence of the constantly increasing integration density in microelectronics, lithographic masks (often just “masks” for short hereinafter) have to image ever smaller structure elements into a photoresist layer of a wafer. In order to meet these requirements, the exposure wavelength is being shifted to ever shorter wavelengths. At the present time, mainly argon fluoride (ArF) excimer lasers are being used for exposure purposes, these lasers emitting light at a wavelength of 193 nm. Lithography systems operating with light sources which emit in the extreme ultraviolet (EUV) wavelength range (10 nm to 15 nm) and corresponding EUV masks are also being used. The resolution capability of wafer exposure processes has been increased by simultaneous development of multiple variants of conventional binary lithographic masks. Examples thereof are phase masks or phase-shifting masks and masks for multiple exposure.

However, on account of the ever decreasing dimensions of the structure elements, lithographic masks cannot always be produced without defects that are printable or visible on a wafer. Owing to the costly production of masks, defective masks are repaired whenever possible.

Two important groups of defects of lithographic masks are, firstly, dark defects and, secondly, clear defects. Dark defects are locations at which absorber material and/or phase-shifting material is present, but which should be free of this material. These defects are repaired by removing the excess material preferably with the aid of a local etching process.

By contrast, clear defects are defects on the mask which, on optical exposure in a wafer stepper or wafer scanner, have greater light transmissivity than an identical defect-free reference position. In mask repair processes, such clear defects can be eliminated by depositing a material having suitable optical properties. Ideally, the optical properties of the material used for the repair should correspond to those of the absorber or phase shifting material.

A known method of removing dark defects is to use an electron beam directed directly onto the defect to be repaired (exposure). On account of the use of an electron beam, in particular, precise steering and positioning of the beam onto the defect is possible. In conjunction with a precursor gas, also called process gas, which may either be present in the atmosphere of the mask to be repaired or adsorbed on the mask itself, it is possible to induce a reaction akin to a local etching process by virtue of the incident electron beam. This induced local etching process can remove fractions of excess material (of the defect) from the mask, such that the absorber properties and/ or phase- shifting properties desired for the lithographic mask can be generated or restored.

Alternatively, it is also possible to choose the precursor gas used such that a deposition process can be induced on exposure to the beam. As a result, it is possible to deposit additional material on clear defects in order to locally reduce the light transmissivity of the mask and/or to increase the phase-shifting properties.

The masks to be repaired may generally have a multilayer structure or be composed of at least two materials typically disposed one on top of another. It is possible here for the upper material (the material facing the electron beam) to function as absorber material, as phase-shifting material or as defect material, and for the lower material to function as substrate or carrier material (or as the material of some other element arranged beneath the defect) of the lithographic mask to be repaired.

In the case of interaction of the electron beam or of another particle beam used for etching or deposition with the precursor gas or a material of the defect, there may be backscatter of electrons or of the particles. For example, backscattered electrons may be detected in parallel with the etching and/or deposition process, which leads to a signal of backscattered electrons (for example EsB signal; EsB: energy-selective backscattering). Additionally or alternatively, it is also possible to generate secondary particles, for example electrons, through the process of interaction of particle beam and the precursor gas or the material of the defect. For example, secondary electrons may lead to a secondary electron signal (SE signal) that can likewise be detected in parallel with the etching and/or deposition process. By detecting the particles mentioned or signals generated thereby during the etching process and/ or the deposition process, it is possible to monitor the progress of the repair process.

More particularly, correct and precise detection of the transition from the etching process on the material of the defect to the material of the element beneath the defect is of crucial significance for the success of the repair process. This is also referred to as endpointing. Precise endpointing can ultimately ensure that the mask to be repaired, after the etching process has ended, has the desired absorption properties and/or phase-shifting properties and, for example, the substrate material beneath the defect material is not attacked and/or removed by the etching process. On account of the high precision of demands made on a wafer structure in the semiconductor industry, correspondingly analogously stringent demands are made on the repair of a lithographic mask.

By means of the monitoring of the etching process by detecting the backscattered and/or secondary particles formed during the etching process (on the material to be etched), it is possible to obtain a kind of real-time image of the etching process. It is thus possible for a transition of the etching process between the materials to be determined by a change in signal of the particle beams mentioned. However, the contrast can be greatly attenuated in some cases, for example when the materials present in the etching process differ only very slightly (for example have a similar atomic number), such that exact determination of the endpoint (transition of the etching process from material of the defect to the material of the element beneath the defect) is impossible.

Various approaches are known for achieving precise results in spite of this problem: US 2004 / o 121069 Ai discloses a method for repairing phase-shifting photomasks by means of a charged particle beam system. Topographic data from a scanning probe microscope are used here as a substitute for endpointing. The topographic data can be utilized to adapt the dose of the charged particle beam for every point within the defect environment, based on the elevation and surface slope at the specific point.

US 6593040 B2 discloses a method and a device for correction of phase-shift defects in a photomask. This comprises scanning of the photomask and three-dimensional analysis of the defect with an AFM (atomic force microscope). Based on the three- dimensional analysis, an etch map is created and a focused ion beam (FIB) is controlled in accordance with the etch map in order to remove the defect. In order to afford higher accuracy of the repair process, test patterns of the FIB are generated and analysed three-dimensionally.

However, these approaches are time-consuming and complex. Moreover, the etch rate cannot always be predicted precisely, and so, in spite of the effort and complexity, it is by no means always possible to give optimal results.

Therefore, firstly, there is a need to further improve etching processes on defects.

Secondly, however, there is also always a need for improved diagnostics, for example in order to determine materials of elements of lithographic masks, e.g. of defects. Said diagnostics can then be used for example to tailor the repair process to specific materials.

3. Summary of the invention

The aforementioned needs are at least partly met by the various aspects of the present invention, as described below.

One embodiment can relate to a method for use with a lithographic mask. In this case, the method can comprise directing a particle beam onto an element of the lithographic mask in an atmosphere of particles. Moreover, it can comprise inducing a desorption and/or adsorption process of at least some of the particles in a region of the element. Furthermore, the method can comprise capturing a signal of secondary particles and/or backscattered particles and/ or some other free-space signal generated by the particle beam during the desorption and/or adsorption process.

The inventors of the present invention have recognized that by inducing a change in the type and/or concentration of particles on the mask, it is possible to obtain a corresponding capturable and temporally variable signal which can be generated by directing a particle beam onto the mask, e.g. a signal of secondary particles (e.g. secondary electrons (SE) and/or backscattered electrons (EsB) when an electron beam is used as particle beam). In particular, this can be done by inducing an adsorption process and/or desorption process of (e.g. physisorbed and/or chemisorbed) particles on the element, e.g. by disturbing an equilibrium of the particles (e.g. with regard to desorption and adsorption), whereupon the equilibrium is re-established in the time profile (over time), and/or by changing at least one equilibrium-determining parameter (e.g. supply of specific particles and/or (local) variation of the quantity and/or supply of a type (possibly already present) of particles), whereupon a new equilibrium is established in the time profile (over time).

Since the (old or new) equilibrium can be established differently in the time profile, depending on material (at the surface) of the element (e.g. on account of different adsorption or desorption rates or different diffusion rates on the surface), the temporal profile of the signal can be specifically different, depending on material (at the surface) of the element.

The (time-dependent) signal captured during the adsorption and/or desorption process, e.g. during the restoration of equilibrium, can therefore be material-specific and thus be used for a large number of useful purposes. As described in detail herein, a specific material of an element (e.g. of a defect) can thus be ascertained, for example, such that the subsequent repair of the element can then be tailored (e.g. suitable selection of repair parameters, e.g. type or concentration of a process gas, etc.). Moreover, the captured signal can be used directly for endpointing during an etching process in association with a defect, since it can be manifested differently, for example, depending on whether the defect has not yet been completely removed (i.e. the temporal profile of the signal is still determined by a material of the defect) or has already been removed (i.e. the temporal profile is determined by material of an element arranged beneath the defect). The particles of the atmosphere of particles can generally be gas particles, e.g. gas atoms or gas molecules. The particles can partly be adsorbed or desorb on the element, such that an equilibrium can be established between the particles situated in the atmosphere and particles adsorbed on the element. An equilibrium can be understood e.g. as a state of the system under consideration in which the average number of particles that are freely mobile in the atmosphere and/ or the average number of particles adsorbed on the element are/is constant. In particular, an equilibrium state can relate to both desorption and absorption processes. Particles situated on the element can also move byway of surface diffusion on the element, e.g. from a region of the element to locations outside this region, and vice versa. Hereinafter, to facilitate understanding, instead of the term particles the term gas particles is often used as well for simplification, without the respective aspects being intended to be restricted thereto. The term gas particles here is intended explicitly also to relate to particles that have adsorbed on the element from the atmosphere (e.g. as a result of adsorption) or to particles that move on the surface of the element into the region of the element (e.g. by way of surface diffusion).

The particles of the particle beam can be particles having mass, e.g. electrons, protons, ions, atoms, molecules, but also just energetic particles, e.g. photons, etc.

Inducing a desorption and/ or adsorption process can be effected here by external action on the coating or occupancy (German: “Belegung”) of physisorbed and/or chemisorbed particles (at least on the element) (the coating could be understood e.g. as an average number of particles adsorbed per unit time). Acting on the coating can be understood here as disturbing an equilibrium coating (which is established e.g. at a specific temperature and a specific (partial) gas pressure of the particles). This can mean, for example, that after the equilibrium coating has been disturbed, at least in the region of the element, the number of gas molecules (or of some other type of particles) is different from the number of gas molecules in this region before the equilibrium coating is disturbed. Afterwards, e.g. the disturbance can be ended, such that the equilibrium coating is established again in the time profile. Additionally or alternatively, it is also possible to act on the coating by setting a new equilibrium coating. This can mean, for example, that after the new equilibrium coating has been set, at least in the region of the element, the number of gas molecules is different from the number of gas molecules in this region before the setting. In the time profile, the coating can correspondingly change from a first equilibrium coating to a second equilibrium coating.

Besides the explained endpointing and material determination, the aspects described herein in particular also afford the possibility of ascertaining whether undesired changes to the surface occur in the vicinity e.g. of a repaired defect. In the case of lithographic masks for EUV lithography, a capping layer can be situated between an absorber and an MoSi multilayer serving as a Bragg mirror. Said capping layer can comprise or consist of Ru, for example. Damage to the Ru layer in the vicinity of the defect during the repair should be avoided in this case. This can be ascertained in situ, for example, by way of the aspects presented herein. In particular, it is possible to ascertain whether there is a capping layer, e.g. an Ru capping layer, at a predetermined position and/or whether some other material is present there at least in part (e.g. because the capping layer has been damaged at least in part). This can be used either during a defect repair or else e.g. during the development of repair processes (when carrying out corresponding etching series). The parameters of a repair could be optimized such damage to the capping layer is minimized.

The method can furthermore comprise selecting the element such that it comprises a predetermined material. This makes it possible, in particular, to assign the captured signal to the predetermined material. Attaining an assignment of the signals respectively captured to different, predetermined materials is thus made possible. A calibration or reference measurement in respect of the signal with regard to different materials and/ or material compositions of the element can thus be made possible.

The method can furthermore comprise storing at least one parameter of the signal. The parameter of the signal can be stored e.g. with at least one parameter associated with the material as reference data. For example, at least one physical and/or chemical property of the material upon interaction with the particle beam can be reflected in the at least one parameter of the signal. Said property can then be stored in the reference data. It is also possible to use a designation of the respective material as a parameter associated with the material.

The at least one parameter of the signal can relate e.g. to a rate of change of the captured signal, a gradient of the signal, a shape (e.g. intensity profile vs. time profile) of the signal, a maximum of the signal, a signal-to-noise ratio, etc. However, it is also possible to store (a portion of the) raw data of the signal as at least one parameter of the signal, optionally even all the raw data. Furthermore, it is possible to provide e.g. the time after which a (re-)adsorption of a predetermined percentage of gas particles in the region of the element has occurred (e.g. after inducing the desorption and/or adsorption process has ended), e.g. in order to to capture the time dynamics of the re adsorption in this way. For instance, it is possible to determine the time after which a re-adsorption corresponding to a specific percentage (e.g. 90%) of an adsorption in an equilibrium state has been achieved, e.g. after the gas particles have substantially been removed. This can be done for example by capturing the signal in the form of a saturation curve and checking when the curve has reached a specific percentage of its saturation value.

The method can further comprise determining a material of the element on the basis of comparing at least one parameter of the signal with at least one corresponding parameter of stored reference data. The parameter can generally comprise any of the parameters mentioned above or mentioned in some other way herein, or else other suitable parameters.

The reference data can be ascertained e.g. as described herein. The corresponding parameter of stored reference data can be stored directly in the reference data.

However, it is also possible for the corresponding parameter used for the comparison only to be derived from the stored reference data. For example, the parameters “gradient”, “maximum”, etc., mentioned by way of example above can be contained in the reference data. However, it is also possible to store (only) less abstract data in the reference data, in the extreme case e.g. the raw data of a signal obtained e.g. during a calibration measurement (with an element of known material). From these it is then possible to derive required parameters as necessaiy.

It is likewise possible to apply the steps described herein to elements constructed from a plurality of material components.

The element can comprise a defect of the lithographic mask. A defect of the lithographic mask can comprise in this case e.g. excess material on a substrate of the lithographic mask. In this case, said excess material can influence the functionality of the lithographic mask. The method can furthermore comprise directing the particle beam onto the defect, such that a local etching process takes place at the defect. Further, the method can comprise determining, at least partly on the basis of the signal captured during the desorption and/or adsorption process, e.g. during the restoration of equilibrium, whether the local etching process at the defect has already transitioned to a local etching process at an element of the mask that is arranged beneath the defect.

It may be possible, for example, for the expected temporal signal profile to change as soon as the etching process has transitioned from a material of the defect to a material of the mask that is arranged beneath the defect. On the basis of the captured signal and in particular one or more parameters obtained therefrom (as described herein), it can therefore be deduced whether the etching process for removing the defect has already ended. For example, an induced desorption and/or adsorption process can lead to a signal developing more rapidly (or more slowly) over time if the material of the defect is still arranged at the surface of the mask (i.e. the etching process has not yet ended), while a signal developing more slowly (or more rapidly) over time is expected when the desorption and/or adsorption process is induced if the defect has already been (at least partly) removed, such that material of an element arranged beneath the defect is situated at the surface of the mask. By way of example, the material of the defect and respectively of the element arranged beneath the defect can cause different adsorption, desorption and/or surface diffusion rates that lead to a different temporal profile (e.g. progressing at different speeds) of the captured signal.

The method can further comprise selecting at least one type of gas particles having an adsorption and/or desorption rate at a predetermined material of the defect, which differs from an adsorption and/ or desorption rate at a material of an element of the mask that is arranged beneath the defect by at least one predetermined threshold value. That can be preceded in particular by predetermining the materials involved. For example, the material of the defect can be determined as described herein.

The requirements to be made of the threshold value (i.e. the quantitative characteristic form of the threshold value) can be determined here in particular by the capturing accuracy in respect of the signal. This can mean, for example, that the respective material-dependent re-adsorption rates, for the at least one type of gas molecules, should differ from one another to a greater extent if the capturing accuracy of the signal is rather low. By contrast, given a comparatively high capturing accuracy, it can be sufficient for the re-adsorption rates to differ from one another only comparatively slightly. For example, one adsorption and/or desorption rate (e.g. at the defect material or at the material of the element arranged beneath the defect) can be greater than another respective adsorption and/or desorption rate (e.g. at the material of the element arranged beneath the defect or at the defect material) by at least 10%, 20%, 50%, 100%, 200%, 500%.

In the previous paragraph, as also repeatedly hereinafter, mention was made only of a (re-)adsorption (e.g. by way of an adsorption from the gas phase and/ or by way of surface diffusion), for reasons of clarity. However, the examples correspondingly explained should be understood to be merely by way of example and equally also relate to desorption processes (e.g. into the gas phase or by way of surface diffusion).

A further aspect during the restoration of equilibrium during re-covering or generally during adsorption and/or desorption processes is as follows: The adhesion coefficient for the particles, e.g. molecules, is generally inversely proportional to the temperature. If the materials of e.g. defect and underlying element (e.g. substrate) differ significantly in their thermal conductivity and/or specific heat capacity, the decay curve of the temperature after laser-induced desorption of the molecules is also different for the two materials. This effect can also be utilized in order to obtain a different temporal profile (e.g. progressing at different speeds) of the captured signal, irrespective of whether the two materials possibly do not differ otherwise in their surface properties.

Moreover, it is possible to actively cool the substrate. This can contribute to reducing the rate of surface diffusion of the molecules. The capture of the time-dependent signal during re-covering or generally of the adsorption and/ or desorption processes can be simplified in this way.

The atmosphere can contain at least one precursor gas and/ or one contrast gas. In particular, the contrast gas and/or the precursor gas can be selected in a material- dependent and / or application-related manner. It can be advantageous, for example, to induce a desorption and/or adsorption process of gas particles of a contrast gas. A temporally variable signal can then be captured, e.g. without changing the ratios in relation to the precursor gas, such that e.g. the etching process remains unaffected.

This can be done e.g. by selective desorption of gas particles of the contrast gas, as will be described in even greater detail herein. For example, the contrast gas can be selected such that an adsorption rate of the contrast gas on a material of the element arranged beneath the defect (often also called mask material hereinafter) (at least on average over time) is higher (lower) than an adsorption rate of the contrast gas on a material of the defect (defect material). This can be accompanied by the desired requirement that the contrast material adsorbs preferably and/ or more rapidly (or to a lesser extent and/ or more slowly) on the material of the material arranged beneath the element or the defect. This can have various reasons here. For instance, it is possible that the contrast gas exhibits a higher (lower) adsorption rate on the mask material through physisorption than on the defect material. It is equally and alternatively possible that the contrast gas has a longer (shorter) dwell time on account of chemisorption on the mask material than on the defect material. These different adsorption properties can lead to a variation of at least one parameter of the (time-dependent) signal and can be used for determining the etching progress (or for material analysis).

Alternatively or additionally, it is also possible that a contrast gas is chosen such that it has a lower affinity (coating, adsorption rate and/ or dwell time) for the defect material than a precursor gas used for the etching process. Alternatively or additionally, it is also possible that the contrast gas is chosen such that it has a higher affinity (coating, adsorption rate and/ or dwell time) for the mask material than a precursor gas used for the etching process. This can provide support here for making the endpointing more reliable, even if e.g. the precursor gas adsorbs on defect material and mask material to the same extent and/or at the same rate.

Furthermore, the selection of the contrast gas can be based at least partly on diffusion rates of the selected contrast gas on the defect material and respectively the mask material being as different as possible. This can have the effect that the capture of secondary particles and/ or backscattered particles and/ or some other free-space signal generated by the particle beam, during the desorption and/or adsorption process, follows different temporal dynamics (for example, the contrast gas can be chosen such that the adsorption and/or desorption process takes place more rapidly on the material of the element, e.g. after local removal of the contrast gas at the element or in a vicinity of the element, than on the material arranged beneath the element). It is possible here for at least one precursor gas and/or contrast gas already to be contained in the atmosphere of gas particles at the beginning of the method. Alternatively or additionally, it is also possible for at least one precursor gas and/or contrast gas only to be supplied during the method and/ or for the supply of the gas to be changed in each case in order to induce an adsorption and/or desorption process.

A useful contrast gas here can be one or more oxidants, for example 0₂, 0₃, H₂0, H₂0₂, N₂0, NO, N0₂, HNO3 and/or other oxygenous gases. It is likewise possible to use one or more halides, for example Cl₂, HC1, XeF₂, HF, I₂, HI, Br₂, HBr, NOC1, NF₃, PC1₃, PC1₅, PF₃ and/or other halogen-containing gases. Useful contrast gases can likewise include gases having reducing action, for example H₂, NH₃, CH₄, H₂S, H₂Se, H₂Te and other hydrogen-containing gases. Useful contrast gases can include gases having low chemical reactivity, for example N₂, He, Ne, Ar, Xe. It should furthermore be pointed out that the contrast gases mentioned can also be used as precursor gases.

Useful precursor gases here can be one or more (metal, transition element, main group) alkyls, for example cyclopentadienyl (Cp)- or methylcyclopentadienyl (MeCp)- trimethylplatinum (CpPtMe₃ and/or MeCpPtMe₃), tetramethyltin SnMe₄, trimethylgallium GaMe₃, ferrocene Cp₂Fe, bisarylchromium Ar₂Cr, dicyclopentadienylruthenium Ru(C₅H₅)₂ and other compounds of this kind. It is likewise possible to use one or more (metal, transition element, main group) carbonyls, for example chromium hexacarbonyl Cr(CO)6, molybdenum hexacarbonyl Mo(CO)6, tungsten hexacarbonyl W(CO)6, dicobalt octacarbonyl Co₂(CO)s, triruthenium dodecacarbonyl Ru₃(CO)_i2, iron pentacarbonyl Fe(CO)₅ and/or other compounds of this kind. It is likewise possible to use one or more (metal, transition element, main group) alkoxides, for example tetraethoxysilane Si(OC₂H₅)₄, tetraisopropoxytitanium Ti(OC₃H₇)₄ and other compounds of this kind. Moreover, it is also possible to use one or more (metal, transition element, main group) halides, for example WF6, WCk, TiCk, BC1₃, SiCl₄ and/or other compounds of this kind. It is furthermore likewise possible to use one or more (metal, transition element, main group) complexes, for example, copper bis(hexafluoroacetylacetonate) Cu(C₅F₆H0₂)₂, dimethylgold trifluoroacetylacetonate Me₂Au(C₅F₃H₄0₂) and/or other compounds of this kind. In addition, it is possible to use organic compounds such as CO, C0₂, aliphatic or aromatic hydrocarbons, constituents of vacuum pump oils, volatile organic compounds and/or other compounds of this kind. It should furthermore be pointed out that it is also conceivable to use the precursor gases listed as contrast gases. The person skilled in the art is able to recognize here that the above lists are not exhaustive, and that any desired combinations of the selection of possible contrast gases and precursor gases cited here merely by way of example are possible, including beyond the selection cited.

An adsorption and/or desorption process denotes herein any process accompanied by a change in the coating of the surface of the element with gas particles. This can occur e.g. by way of exchange of gas particles with the atmosphere and/ or by way of exchange with parts of the surface of the mask that are arranged around the element (e.g. by means of surface diffusion).

Inducing can comprise for example (locally) removing gas particles in a region of the element. Following the corresponding desorption, e.g. the complete removal of the gas particles from the element, a corresponding adsorption can then occur, e.g. by way of re-adsorption of the gas particles from the atmosphere and/ or by way of surface diffusion of gas particles from sections of the mask from which the gas particles were not removed.

Alternatively or additionally, inducing can comprise changing a supply of gas particles. Changing can comprise e.g. altering a volumetric flow guided into the atmosphere (e.g. increasing, decreasing or closing) in regard to the supply of gas particles. In the case where the gas supply is closed, gas particles can subsequently be delivered substantially only on the basis of surface diffusion effects, e.g. after gas particles have been removed in at least one region of the element (defect) as a result of the inducing. This can likewise lead to a capturable, time-dependent signal.

Locally can be understood here such that gas particles are removed only in a partial region which is small in comparison with the total size of the lithographic mask, e.g. in a region ranging from l cm² to l mm², from l cm² or l mm² to too pm², below too pm², e.g. from too pm² to l pm², from l pm² to too nm², or from too nm² to l nm². Alternatively, however, it can also be possible for the removing not to be effected locally, but rather to involve removing the entire lithographic mask.

The method can furthermore comprise the fact that (at least locally) removing gas particles is effected by means of a second particle beam and/ or by means of electric and/or magnetic fields applied to the element. In particular, locally removing gas particles can be effected by means of the second particle beam.

The supply of energy by the second particle beam can lead to (local) heating of the substrate (i.e. of the material of the lithographic mask and/or the material of the element). In this case, heating of the substrate can result in gas particles being removed. For example, the binding energy between the gas molecules and the substrate can be exceeded, as a result of which the binding can be dissociated. Additionally or alternatively, it is possible for the supply of energy to lead to a selective excitation of the gas molecules. A selective excitation is understood here to mean that the energy of the particles of the particle beam is coordinated with an excitation spectrum of the gas particles. For example, a larger number of gas particles can be removed as a result. Moreover, if a plurality of types (i.e. different gases) of gas molecules are present, e.g. only a selected type of gas molecules can then be excited, e.g. only a contrast gas can be removed, but the precursor gas cannot be removed, and so e.g. an etching process remains substantially unimpaired by the inducing. More generally, the second particle beam can be selected such that the wavelength assignable to the particle beam is in resonance only with a specific excitation energy of one type from the different types of gas molecules (e.g. with at least one portion of the gas molecules present as process gas and/or as contrast gas). The excitation of gas molecules can have the effect, for example, that they transition to more highly energetic vibration, translation and/or rotation modes, which can ultimately likewise lead to a dissociation of the binding of the gas molecules to the substrate. It can likewise be possible for the wavelength of the particle beam to be coordinated with the absorption spectrum of the substrate in order thus e.g. to enable optimized and rapid heating of the substrate.

For a given second particle beam, it can furthermore generally be possible to select the contrast gas such that the absorption spectrum of the selected contrast gas can be excited by means of e.g. the second particle beam (as described further below) in order thus to facilitate the inducing of the desorption process. In other words, the gas particles (e.g. of the contrast gas) and the second particle beam can be coordinated with one another.

In order to increase the absorption of a particle beam by the material of the element (or of the defect) and/or of the material (e.g. substrate) arranged beneath the element, provision can be made for altering (in a targeted manner) the composition of the material of the element and/or of the material arranged beneath the element. This can be done e.g. by doping, producing colour centres, etc. It can likewise be possible to alter a material composition in a targeted manner during the production process by mixing with molecules to the effect that preferred absorption windows for light beams are attained in the material to be produced (e.g. in wavelength ranges for which particle sources can be realized technically with an outlay that tends to be low). In a similar manner, it is possible - independently of the use of a second particle beam - to modify the materials involved such that different physisorption and/or chemisorption properties arise and/or the diffusion rate of the gas molecules at the materials is made differentiable. It is preferred here to have as little adverse effect as possible on the optical and mechanical properties of the photomask with regard to the lithographic process.

It is possible, in particular, to implement the second particle beam as a photon beam, e.g. as a light beam, e.g. as laser.

The second particle beam can generally be coherent or incoherent and can be embodied as either monochromatic or polychromatic. In this case, the particle beam can be pulsed (duty cycle < 1) or alternatively non-pulsed (e.g. CW, continuous wave).

The use of a pulsed particle beam affords the advantage, in particular, of ensuring a temporal resolution of the individual particle beam pulses (i.e. it is possible for a particle beam to be switched on for a duration of to ms, for example, and to be switched off for 50 ms and then to be switched on again for 10 ms, whereby gas particles can be removed in a pulsed manner). Furthermore, pulsed particle beams afford the advantage that they can be provided with a higher beam (or pulse) energy. What can be made possible in this way is that, in comparison with CW particle beams, a higher energy per unit time can be transmitted in the particle beam. This makes it possible, example, to remove a larger number of gas particles using a single pulse.

Furthermore, in each case the same beam and scanning parameters can be employed for the (first) particle beam and the second particle beam. For example, for both particle beams it is possible to provide identical acceleration voltages, an identical beam current (each in the case of charged particle beams), an identical dwell time of the beam at a specific position, an identical line step of the beam (between two positions to be scanned), etc. Alternatively, however, it is possible for only some of the beam parameters to match. It can likewise be possible for the beam parameters to be chosen completely differently from one another.

It can alternatively also be provided that the same (first) particle beam is used for inducing and capturing the signal (independently of its implementation). This can mean that the first particle beam (which can be directed onto an element of the lithographic mask) can also be used for inducing the desorption and/or adsorption process. In such a scenario, provision can be made for temporarily and/ or locally increasing e.g. the intensity (e.g. expressed by the number of particles per unit time and/or the energy per particle) of the particle beam in order to enable inducing (e.g. by removing gas particles). After inducing, provision can be made for altering the intensity of the (first) particle beam to the original value again. It is conceivable, for example, to use a beam of charged particles. Charged particles are understood here to mean particles which carry an electric charge such as, for example, electrons, protons, ions, charged molecules, etc. Additionally or alternatively, it is also possible to use a beam of neutral particles, such as e.g. a beam of atoms, molecules, photons, etc.

Additionally or alternatively, provision can be made for removing gas particles by applying an (optionally local) electric (or electromagnetic) field. An electric field can be understood here to mean a field which is caused by the separation of two opposite electric charges. The effect of an electric field on the gas molecules can take place here directly and or indirectly, e.g. by way of heating of the mask with the aid of the electric field. A direct effect can be achieved e.g. in such a way that, as a result of an electrostatic interaction with the gas molecules, the electric field removes said gas molecules from their binding to the substrate. In other words, if the gas molecules have a negative charge, for example, then an electric field caused by a positive charge, inter alia, can make it possible to draw away the negatively charged gas molecules towards the positive charge of the electric field. By applying e.g. a gradient field, this can be accomplished e.g. for uncharged particles as well.

Alternatively or additionally, it can be possible to remove gas molecules by applying an (optionally local) magnetic (or electromagnetic) field. A magnetic field is understood here to mean the resultant field which can result from charge transport (e.g. from a current flow). The use of magnetic fields can make it possible to generate a temporally variable magnetic field and to achieve a dissociation of the binding of the gas molecules to the substrate by way of e.g. radio-frequency-based heating (of the substrate) of the mask and/or of the gas molecules. The use of a magnetic field makes it possible to control the drawing away of the gas molecules by means of using the magnetic field (e.g. by utilizing a resultant Lorenz force). Furthermore, it can be possible, if the gas molecules have a magnetic dipole character, by applying a magnetic gradient (in one or more spatial directions), to remove these gas molecules by way of the resultant force on the magnetic dipole.

Capturing the signal can further comprise capturing at at least two successive points in time during the desorption and/or adsorption process.

The method can further comprise determining a rate of change of the signal during the desorption and/or adsorption process. It can be possible e.g. on the basis of capturing the signal at least twice (e.g. at at least two successive points in time) to determine the rate of change of the signal that occurred or the re-adsorption rate of the gas molecules in the region of the element (or defect). The time-dependent re-adsorption process or the rate of change can be understood as a determination of a mathematical gradient of the (time-dependent) re-adsorption process between the two chosen points in time.

The re-adsorption process in this case can follow e.g. a saturation function.

Determining can further comprise comparing the determined rate of change with at least one predetermined rate of change. As a result, a precise determination of the progress of the etching process at the lithographic mask can be made possible since, for example, the time-dependent gradient (i.e. the second derivative of the time-dependent signal, e.g. at a predetermined point in time after the respective inducing) can change upon the transition of the etching process to the gradient of the material beneath the defect. On the basis of the determined rate of change or gradient of the time-dependent signal, deducing the progress of the etching process can be possible, by way of comparing with a predetermined rate of change of the signal. If the gradient falls below or exceeds a predetermined threshold value, then this can be interpreted e.g. as the etching process approaching a termination criterion (e.g. associated with a transition of the etching process at a defect material to a mask material). Provided that, for example, the rate of change lies above (below) a predefined threshold value for the rate of change, the etching process is continued further. By contrast, if the rate of change of the signal lies below (above) a predefined threshold value for the rate of change, then this can be used as a criterion for terminating the etching process. For clarification, it should be pointed out that during an etching process, for example, an adsorption and/or desorption process can be repeatedly induced in the same way (e.g. by applying a laser pulse and/or other means explained herein) and in each case the change in the corresponding captured signal over time is observed which results therefrom (and can change upon a transition of the etching process). Similarly, generally a material of an element can be determined in this way, without a defect and/or an etching process necessarily having to be present. It is also possible in this case to average the change in the signal over time during a repeatedly induced adsorption and/or desorption process, in order to improve the signal-to-noise ratio. For example, at least two, at least five or at least ten signal profiles can be used in each case for averaging.

It is conceivable for the intensity of the captured signal to be captured (only) at a first point in time during a desorption process and additionally (only) at a second point in time during the desorption process. It is likewise possible for the signal to be captured at a first point in time during an adsorption process and additionally at a second point in time during the adsorption process. Furthermore, it can be possible for the signal to be captured firstly at a first point in time during a desorption process and subsequently at a second point in time during an adsorption process.

It can furthermore be possible for capturing the signal to comprise capturing a temporal profile of the signal during the desorption and/or adsorption process. This can be done e.g. within a predetermined (time) interval. It is furthermore also possible to determine at least two disjoint time profiles of the time-dependent signal during the same induced adsorption and/or desorption process and to combine the at least two time profiles with one another. The captured time profile(s) can be compared with at least one stored time profile of the signal (e.g. for material analysis and/or for endpointing).

It can be possible for the captured signal to have initially (i.e. in temporal proximity to the inducing, e.g. the removing of gas molecules; e.g. l ms, 5 ms or 10 ms after the inducing) a higher gradient than at a point in time which is temporally further away from the inducing (e.g. 50 ms after the inducing). This can mean that the signal becomes flatter as time increases, i.e. the gradient of the time-dependent re-adsorption process decreases, e.g. in accordance with a saturation curve. The captured signal profile can also be stored (together with existing information about the material of the element), such that it can be used as a reference for future measurements, as described herein with regard to reference data. In such an application scenario, provision can be made for ascertaining and optionally storing the time-dependent profile of the signal for different materials of the element and/or of the material arranged beneath the element.

A captured temporal profile of the signal can be compared with at least one stored (predetermined) temporal profile, e.g. in order to deduce the etching progress and/or a material determination.

Capturing a time profile can be understood in this context such that the capturable, time-dependent signal is represented at least by three data points. For example, said signal can be captured repeatedly per unit time (e.g. at a rate of too Hz, 1000 Hz, etc.), such that at least one portion (e.g. a temporal segment, such as e.g. 1 ms, to ms, etc.) of the induced transition from the disturbed equilibrium back to the original equilibrium or to a further equilibrium can be represented. In principle, it is preferred for the signal profile to be represented by means of a multiplicity of data points.

However, storing the signal profile can for example also make it possible that at a later point in time (for endpointing and/or for material analysis) it can be sufficient to capture a corresponding signal only at a predetermined point in time or in a predetermined short time window (after inducing the desorption and/or adsorption process), wherein this can then be compared with a corresponding value of the stored signal profile at this point in time or in this time window. Alternatively, it is also possible for example to ascertain a parameter of the signal at a predetermined point in time or in a predetermined time window (e.g. the gradient) and to compare it with a corresponding value of the stored signal profile at this point in time or in this time window.

In this case, provision can be made for capturing the signal (only) during a determined, e.g. short, time window during the transition from the original equilibrium disturbed by the inducing back to the original equilibrium or to a further equilibrium. In this case, the time window can be designed such that e.g. 1%, 5%, 10%, 20%, 50%, etc., of the total time required for an equilibrium state to be re-formed is captured (this time can be approximated e.g. by the time after which removed gas particles substantially re- adsorb, which can be specified e.g. by t = i/adsorption rate). It is also possible to capture the signal during two or more time windows of this type. Consequently, the time duration of the measurement of the captured signal can be kept comparatively short in comparison with capturing the entire formation (of the original equilibrium or of a further equilibrium).

Capturing can furthermore comprise capturing the signal at (only) at least one predetermined point in time after inducing the desorption and/or adsorption process. In this case, the point in time can correspond to a sampling window for a data point. In this case, the method can be carried out in such a way that capturing the signal is effected e.g. 5 ms (or at any other suitable point in time) after inducing the desorption and/or adsorption process. Consequently, e.g. the amount of data arising as a result of the capturing can be reduced and the capturing can be restricted to such a point in time and/or a subsequent (temporal) region of the desorption and/or adsorption process which is potentially meaningful (i.e. on the basis of which a statement about the etching progress and/or the material can be made). For example, a suitable point in time can be given for instance by the time after which removed gas particles re-adsorb to a relatively great extent, which can be approximated for example by t = (0.5/adsorption rate of the element). If, at this point in time, the expected coating has not (yet) occurred or has (already) occurred to a relatively great extent, it can be deduced e.g. that the material (and thus the adsorption rate) has changed, which can be used for the endpointing.

For example, it can be possible to determine the intensity of the signal at a predetermined point in time after the inducing (or after ending the inducing) and to compare this with at least one value of the intensity at the same point in time, which emerges e.g. from stored reference data (e.g. for the material analysis and/or for the endpointing).

The method can furthermore comprise synchronizing the capturing with the inducing. This can make it possible to establish a fixed temporal relationship between the capturing and the inducing. What can be made possible in this case is that the capturing begins (automatically) at the same time as the inducing. Alternatively, on the other hand, it can be possible for a temporal offset to be provided between the inducing and the beginning of the capturing (e.g. it can be possible for the capturing to begin 10 ms (or at any other suitable point in time) after the inducing). It is also possible for the capturing already to begin at a point in time before the beginning of the inducing, in order for example to concomitantly capture the induction dynamics. It is thus possible for example to carry out an automatic routine which, e.g. byway of pressing a button once, yields a captured signal which is for example material-specific (such that corresponding reference data can be stored or a material determination is made possible and/or which allows endpointing).

It is furthermore possible for (at least) the method steps of inducing a desorption and/or adsorption process, capturing a signal, and determining whether an at least local etching process at a defect has already transitioned to an element arranged beneath the defect, to be carried out repeatedly, preferably periodically. This affords the advantage, in particular, that repeatedly carrying out the steps enables an iterative (and more precise) monitoring of the etching process from the defect through to an element of the mask that is arranged beneath the defect. In this case, periodically carrying out the steps can be understood to mean repeatedly carrying out the steps, at equidistant time intervals. In other words, it is thus possible, for example, to carry out the steps l time per second, l time per minute, l time per hour, etc. Furthermore, it is also possible to carry out the steps at a high frequency, i.e. a number of times per second (e.g. to times per second, 100 times per second, etc.). High-frequency measurement can be advantageous in order to keep the time for the endpointing short relative to the duration of a repair process that is carried out, if appropriate.

It can also be possible to carry out the steps directly in succession or virtually continuously, that is to say that after the last (process) step has ended, the first (process) step of the subsequent iteration of the method can be carried out directly.

In this case, the preferred periodicity for carrying out the steps can depend at least on the process speed of the etching process and/or the desorption and/or adsorption process, that is to say that when there is a higher process speed, preference can be given to carrying out the steps more often than when there is a process speed that is lower in comparison therewith.

The present disclosure furthermore encompasses a device for use with a lithographic mask. The device can comprise means for directing a particle beam onto an element of the lithographic mask in an atmosphere of gas particles, and means for inducing a desorption and/or adsorption process of at least some of the gas particles in a region of the element. Furthermore, the device can comprise means for capturing a signal of secondary particles and/ or backscattered particles and/ or some other free-space signal generated by the particle beam during the desorption and/or adsorption process.

The device can be configured to carry out the methods described herein automatically, e.g. upon single pressing of a button.

In this case, the means for directing a particle beam can comprise inter alia a focusing means, e.g. a focusing optical unit. In this case, a means for capturing a signal can be various detector arrangements which are sensitive to the type of backscattered and/or secondary particles and/ or to any other free-space signal induced by the particle beam. Furthermore, the means for capturing can comprise corresponding data recording and further processing devices. These can be understood to be e.g. DAQ cards, signal amplifiers, filters, computers, servers, databases, software (for controlling the device and/or for data analysis), etc.

The device can furthermore comprise means for determining a material of the element on the basis of comparing at least one parameter of the signal with at least one corresponding parameter of stored reference data.

The device can furthermore comprise means for directing the particle beam onto the element, such that a local etching process takes place at the element. In this example, the element can comprise a defect, for example, such that a local etching process takes place at the defect. Furthermore, the device can comprise means for determining, at least partly on the basis of the signal captured during the desorption or adsorption process, whether the local etching process at the defect has already transitioned to a local etching process at a (further) element of the mask that is arranged beneath the defect. The means for determining can furthermore comprises a database. In this case, the database can hold one or more stored signals (e.g. temporal profiles of the captured signal), which can be compared with the (currently) captured signal by the means for determining, in order thus to be able to draw a conclusion about the etching progress.

The means for inducing can furthermore comprise a means for (locally) removing gas particles in a region of the element. Possible implementations for the means for (locally) removing gas particles have already been described further above. The device can furthermore comprise a means for generating a second particle beam for at least locally removing gas particles and/or for generating an electric and/or magnetic field for at least locally removing gas particles. The means for generating a second particle beam can comprise e.g. an electron beam source. Moreover, the means can comprise a laser beam source, that is to say that the second particle beam can be e.g. a laser beam. Furthermore, it is possible for the means for generating a second particle beam to comprise a means for generating an ion beam or a beam of uncharged atoms or molecules.

In this case, the means for generating electric fields can comprise e.g. a capacitor. In this case, the means for generating magnetic fields can comprise at least one conductor through which current flows. In this case, the conductor through which current flows can be wound to form at least one coil (e.g. Helmholtz coil, Maxwell coil, Barker coil, etc.). The means for generating magnetic fields can furthermore comprise means for generating constant currents, as a result of which homogeneity fluctuations and temporal drifting of the magnetic fields within the coils can be minimized.

Furthermore, both for the electric fields and for the magnetic fields (additional) oscillators can be provided in order to be able to generate in each case temporally variable electric and/or magnetic fields, e.g. in the RF range.

The means for capturing the signal can furthermore be configured for capturing the signal (only) within one or more predetermined time windows or points in time in association with inducing the desorption or adsorption process. These time windows or points in time can be embodied in particular as explained herein in regard to a method.

The means for capturing can furthermore comprises means for synchronizing the capturing with the inducing. In this case, the means for synchronizing (if implemented in hardware) can comprise at least one oscillator or clock generator in order to enable the capturing to be synchronized with the inducing.

The present disclosure can furthermore be implemented as a computer program comprising computer-executable code which, when executed, causes a computer to carry out a method according to any of the features described herein. The present disclosure furthermore relates to a device which can be configured as described herein and comprises a computer. The computer program can be stored and/or executed thereon. The computer program can be configured such that it causes the device to carry out (automatically) the method steps set out herein, e.g. upon the pressing of a button, in order to analyse a material, or e.g. (fully automatically) for accompanying an etching process.

Irrespective of whether the aspects of the present application are explicitly described as method steps, computer program and/or means, they can be embodied in each case as method step, computer program (or part thereof) or means of a corresponding device.

Moreover, the features described herein can generally be embodied as hardware, software, firmware and/or a combination thereof. If they are implemented in software/firmware, the features can be implemented on or as one or more instructions or code on a computer-readable medium. Computer-readable media encompass both computer storage media and communication media, including all media which enable a computer program to be transferred from one location to another. A storage medium can be any available medium which can be accessed by a computer. Examples can comprise RAM, ROM, EEPROM, FPGA, CD/DVD or other optical disc storage devices, magnetic disc storage devices or other magnetic storage devices, or any other medium.

It is furthermore pointed out that the present invention is not restricted to the specific combinations of features expressly presented here. Combinations expressly presented here should be understood merely as examples. Other features and/or combinations of features are likewise conceivable.

4. Brief description of the figures

The following detailed description describes possible embodiments of the invention, with reference being made to the following figures:

Figure 1 shows a schematic illustration of endpointing by way of induced desorption of gas molecules during particle beam-induced etching on a lithographic mask; Figure 2 shows a schematic illustration of inducing by way of supplying an external energy;

Figure 3 shows a schematic illustration of inducing by way of altering an external gas supply.

5. Detailed description of possible embodiments

Embodiments of the present invention are described below primarily with reference to (a repair of) a lithographic mask. However, the invention is not restricted thereto and it can also be used for other kinds of mask processing, or even more generally for surface processing or examination in general, for example of objects used in the field of microelectronics, for example for examination, modification and/or repair of structured wafer surfaces or of surfaces of microchips, etc. By way of example, it is possible to repair the defect that is arranged generally at a surface or above an element of a surface. Even if reference is therefore made hereinafter primarily to the application of processing a mask surface, in order to keep the description clear and more easily understandable, the person skilled in the art will nevertheless keep the other possible uses of the teaching disclosed in mind.

In particular, in the context of the embodiments described in detail below, it can also be possible to carry out a determination of a material of an element (e.g. of a defect).

It is furthermore pointed out that only individual embodiments of the invention can be described in detail hereinafter. However, a person skilled in the art will understand that the features and modification options described in association with these embodiments can also be modified even further and/or can be combined with one another in other combinations or sub-combinations, without this leading away from the scope of the present invention. Moreover, individual features or sub-features can also be omitted provided that they are dispensable in respect of achieving the intended result. In order to avoid unnecessary repetition, reference is therefore made to the remarks and explanations in the preceding sections, which also retain their validity for the detailed description which now follows below. Figure l shows various schematic illustrations of endpointing by way of induced desorption of gas molecules during electron beam-induced etching on a lithographic mask.

The top left section of Figure 1 (designated by A in Figure 1) shows a first (substrate) layer 1, on which a second layer 2 is arranged. Situated on the second layer 2 is a region of a defect 3, which in the present example consists of an excess of material that is arranged on the first layer 1. This excess of material (i.e. the region of the defect 3) is intended to be removed as far as the first layer 1 in order to repair the defect. In this case, the removal can be effected by particle beam-induced etching, i.e. by directing a first particle beam 4 (e.g. an electron beam; see the right-hand part of Figure 1 A) onto the region of the defect 3 in the presence of an atmosphere of gas molecules (e.g. of a precursor gas and/or of a contrast gas).

In this case, monitoring the progress of the etching process is of particular importance, in order to prevent the first layer 1 from being etched unintentionally. This can be achieved e.g. by the endpointing - described in this disclosure - byway of induced desorption of particles, e.g. molecules, and analysis of the adsorption or re-adsorption of the particles, e.g. molecules.

In an undisturbed state, the gas molecules of the atmosphere are in an equilibrium state with regard to desorption and adsorption in the region of the defect 3 and at the first layer 1. By at least locally disturbing the equilibrium, it is possible to remove a portion of the (gas) molecules adsorbed on the defect 3. Preferably, this disturbing can be induced by a second particle beam 5. Figure 1 shows that the second particle beam 5 (e.g. a laser) can be directed onto the region of the defect 3.

By directing the second particle beam 5 onto the region of the defect 3, it is possible to remove gas particles from the region of the defect 3. This can be achieved e.g. by way of local heating 6 of the location to be repaired (i.e. of the region of the defect 3). As a consequence of the local heating of the region of a defect 3, desorption of the gas molecules adsorbed in the region of the defect 3 can be initiated, which gas molecules, as a consequence thereof, leave their original adsorption location in the region of the defect 3. However, other mechanisms for removing the gas particles are also possible, as described herein. Moreover, it is possible to remove the particles in the region of the defect 3 without directing the second particle beam onto the region of the defect 3, e.g. by directing it onto an adjacent region.

The removal of gas particles can be understood as disturbing 7 the original equilibrium of desorbed and adsorbed gas molecules. As a consequence of disturbing 7 the equilibrium, after the second particle beam 5 has been switched off it is possible for the gas molecules to revert to the original equilibrium (e.g. byway of adsorption) or to transition to a new equilibrium (provided that e.g. the gas supply is changed as well). This reverting to the original equilibrium state or to a new equilibrium state can be material-dependent in this case (as described herein). This reverting is illustrated at the top right in Figure 1.

By directing the first particle beam 4 onto the region of the defect 3, it is possible to generate a signal composed of backscattered electrons 8 (EsB signal) and/or secondary electrons 9 (SE signal) and/or some other free-space signal 10 generated by the etching beam, which signal can be captured. Since this signal can be dependent on the coating of the defect 3 with gas particles, the captured signal can reflect the dynamics of the re coating with gas particles.

The result of disturbing 7 the equilibrium is that the generated and capturable signal, during the transition of the system back to the original equilibrium or the further equilibrium, across various points in time t ,...,t_n, can also be subject to time dynamics which can be manifested in the number of backscattered electrons (EsB signal 8) and/or secondary electrons (SE signal 9) that is capturable (in the time profile). This (these) signal(s) can be dependent here on the current adsorption of gas molecules in the region of the defect 3. This can make it possible to track or monitor the reverting to the original or a further equilibrium state.

In one exemplary embodiment, the EsB signal 8, with (once again) increasing adsorption of the gas molecules at the region of the defect 3, proceeding from the point in time at which the second particle beam 5 is switched off, can increase across the points in time h and t₂ (that is to say that it is possible to capture e.g. more backscattered electrons per unit time). This is illustrated at the top middle in Figure 1. During the same time interval under consideration, it is possible, for example, for the SE signal 9 to decrease across the points in time h and t₂ (that is to say that it is possible to capture e.g. fewer secondary electrons per unit time). This is likewise illustrated at the top middle in Figure 1.

In the context of the present disclosure, it is possible here to capture this (these) time- dependent signal(s) and to use same for determining an etching progress on the lithographic mask. Since the re-coating with gas particles can be material-dependent, the time dynamics of the signals can thus likewise be material-dependent. The time profile of the signals can thus change during the transition of the etching process from etching the defect 3 to etching the underlying substrate 1. In this case, reliable endpointing is also possible, in particular, if the signals do not differ measurably in the respective equilibrium states during etching at the defect 3 and respectively at the substrate 1.

This is explained below with reference to the lower region in Figure 1 (designated by B in Figure 1). It is emphasized that, in a further embodiment, with an experimental set up similar to that described with reference to Figure 1, the EsB signal 8 and/ or the SE signal 9 can be used for determining a material of the region of the defect 3 by the time- dependent reverting of the gas molecules to the original equilibrium state or to a further equilibrium state being captured and compared with reference data (which represent the same time dynamics). An etching process need not necessarily be present for this purpose.

The lower region of Figure 1 (section B) shows one possible, exemplary state at a further advanced point in time of the repair process on the lithographic mask. It is assumed here that, at this point in time, the excess material which initially was arranged above the first layer 1 and led to the formation of the region of the defect 3 has already been removed and the etching process is at a transition to an etching process at the first layer 1 of the lithographic mask.

As described above, by directing the second particle beam 5 onto the region of the defect 3, it is possible once again to attain a determination of the progress of the etching process in the region of the defect 3. As already explained above, once again disturbing 7 the equilibrium of the desorbed and adsorbed gas molecules in the region of the defect 3 can be effected, by way of local heating 6, which is followed by the gas molecules reverting to the original equilibrium state or to a further equilibrium state. Once again, after disturbing the equilibrium, it is possible for an EsB signal 8 and/or an SE signal 9 and/ or a further free-space signal 10 to be brought about by the first particle beam 4. By capturing the signal(s), it is possible, as already described above, to observe or to monitor the (time-dependent) transition of the gas molecules from the disturbed equilibrium state. In this case, it is possible, as already described above, for the signal intensity of the EsB signal 8 to increase in the time profile, while it can be possible at the same time for the signal intensity of the SE signal 9 to decrease in the time profile. However, other configurations are also conceivable.

The increasing removal of the material of the defect 3 (i.e. with increasing etching progress) can result in the adsorbed gas molecules approaching the first layer 1 more closely. This can generally alter the binding strength of the gas molecules in the time profile (i.e. with increasing etching progress) (e.g. strengthen or weaken the binding strength, depending on the selection of the gas molecules (as described above) and the materials of which the first layer 1 and the defect 3 consist). In tandem with this it is possible for the capturable time-dependent signal during the etching of the defect 3 (Figure 1, top) to differ from that in the case of the transition to etching of the first layer 1 (Figure 1, bottom). Even if the signals do not differ at the respective starting points (e.g. in the equilibrium state before the inducing or directly after the removing of the gas particles), it can be possible for said signals to exhibit a different temporal profile. For example, upon the transition of the etching process to etching of the first layer 1, the captured signals can revert to an equilibrium (increasingly) more slowly or more rapidly (e.g. because the gas particles adsorb on the layer 1 more slowly or more rapidly than on the defect 3). In this regard, e.g. signal intensities similar to those during the etching at the defect can be detected at other times t3 and t4, as illustrated at the bottom middle in Figure 1. For example, by comparing the respective times, it is thus possible to reliably detect a transition of the etching process.

In this case, it is possible to carry out the above-described method steps periodically (as described herein). It is likewise conceivable to carry out the method steps only at suitable points in time, e.g. at points in time at which drawing close to the transition of the etching process is expected. It is likewise conceivable to carry out the method steps initially occasionally (e.g. once, twice, etc.) and, if drawing close to the transition is expected, to carry out the method steps periodically. It can likewise be conceivable to carry out the method steps only after explicit actuation of a button (e.g. a physical button, a GUI button, etc.), e.g. by an operator of the etching device. Figure 2 shows a schematic illustration of the steps of a method for disturbing an equilibrium state while an external energy is supplied, and for capturing a time- dependent signal upon reverting to an equilibrium.

In the possible embodiment according to Figure 2, it is conceivable here for an original equilibrium state n to be disturbed by desorption and adsorption of gas molecules in e.g. a region of an element (e.g. the region of the defect 3 from Figure 1) by way of the supply of energy 12, e.g. in the form of a particle beam (e.g. a light beam or a laser). As already explained above, the disturbing can be caused e.g. by at least locally heating the region of the element. As has likewise already been explained above, this can lead to an at least locally altered state 13 of the number of adsorbed gas molecules (or of at least one species of gas molecules) in the region of the element.

As a consequence of the locally altered state 13, after the energy supply has been switched off, a time-dependent process of the reverting of the gas molecules to the original equilibrium state or a further equilibrium state 14 can ensue. In this case, it can be possible to capture a time-dependent signal, e.g. a time-dependent intensity of backscattered electrons (EsB signal) and/ or secondary electrons (SE signal), here expressed by ISEOO, at various points in time t ,...t_n. In this case, the capturable signal can represent, at least partly, the re-covering of the region of the element with gas molecules (or at least one species of gas molecules). The captured time-dependent signal ISEOO can thus make it possible to be able to deduce progress of an etching process (as described above) and/ or to enable a material of the element to be determined.

Figure 3 shows a schematic illustration of the steps of a method for disturbing an equilibrium state while supply of gas molecules is altered, and for capturing the time- dependent signal upon transition to an equilibrium.

In a further embodiment (which can also be combinable with the embodiment according to Figure 2), provision can be made for disturbing an equilibrium state 11 of desorbed and adsorbed gas molecules in a region of an element (e.g. the region of the defect 3 from Figure 1) by altering an external gas supply 15 for at least one species of the gas molecules. This can comprise e.g. reducing or turning off (or increasing) an external gas supply, e.g. of a precursor gas. As a consequence thereof, balance-related drifting away or desorbing (or adsorbing) of the gas molecules (or at least one species thereof) adsorbed in the region of the element can ensue since no (more) gas molecules are subsequently delivered as a result of the reduced (increased) external gas supply. Consequently, a state with reduced (increased) covering 16 of the region of the element can be established.

This can change in the time profile, across the points in time t ,...,t_n, towards e.g. a state of almost completely desorbed gas molecules 17 in the region of the element. Particularly the transition towards the state of almost completely desorbed gas molecules 17 can be manifested here in a capturable, temporally variable signal ISEOO.

In this case, the temporally variable signal I_SEOO can represent the time dynamics of the desorbing, which can be dependent inter alia on the material-dependent binding or an affinity of the gas molecules (or at least one species thereof) with respect to the material in the region of the element. This can make it possible to monitor an etching process (as has been described above) or to effect a determination of a material in the region of the element.

It is also possible for at least one species of the gas molecules to be “consumed” at different rates by electron beam-induced processes when the gas supply is turned off during the etching process on the different materials. In this way, too, a correspondingly temporally variable signal would permit conclusions to be drawn about the respective material, e.g. for endpointing, for material determination and/or for checking a capping layer.

In both embodiments depicted by Figures 2 and 3, provision can further be made for at least one further material to be situated beneath the region of the element (or defect)

(as shown in Figure 1). In such a scenario, it can be desirable to select the gas molecules, or a species thereof, such that the latter has a different affinity for the materials involved. This can lead to a differentiability of the time-dependent signal ISEOO if the gas molecules adsorb on the two materials in a manner characteristically manifested at different rates.

In this case, it is particularly desirable for the atmosphere of gas particles, as described above, to be selected such that said atmosphere results in a change in the signal of secondary particles and/ or backscattered particles and/ or some other free-space signal generated by the particle beam when the etching process on the lithographic mask approaches a transition, from the material of the element/defect to a material of the mask that is arranged beneath the defect.

Furthermore, provision can be made for combining the method steps for determining a material of an element (e.g. of a defect) and the endpointing according to the invention. It is conceivable for firstly the method steps for determining a material of the region of the defect 3 to be carried out. On the basis thereof, at least one species of the gas atmosphere can be selected, such that the preferred criteria (as described above) for a differentiability of the desorption and/or adsorption at the material of the region of the defect 3 and/or at the first layer 1 can be achieved. On the basis thereof, the particle beam-induced etching process (optionally adapted to the specific defect material) can then be added (as described above) in order to be able to apply the endpointing according to the invention and tailored to the materials actually present.

In all embodiments, the capturing can be implemented in diverse ways here. For example, it is possible to divide the region of the element (e.g. of the defect) into at least one group of pixels. In this case, one pixel can comprise a (square) subregion of the region, such as e.g. a 10% areal proportion of the region (although any other areal proportion is also possible). In this case, the capturing can be configured such that it comprises “scanning” the at least one group of pixels of the region using an electron beam (or any other particle beam desired). Alternatively, it is also possible to capture just a single pixel or individual (selected) pixels of the region or of the location to be repaired.

In a further embodiment (not illustrated in the figures), provision can be made for the material of the defect to be determined before the beginning of the etching process (as described above). In this case, provision can be made for determining the material of the defect by applying a method as described herein. Knowledge of this material of the defect can make it possible to select a type of gas particles which can be situated in an atmosphere around the defect such that an adsorption and/ or desorption rate of the gas particles at the defect differs from an adsorption and/or desorption rate of the gas particles at a material of an element of the mask that is arranged beneath the defect.

In this case, the requirements made in respect of a difference can be dependent e.g. on the measuring arrangement used. If the measurement is subject to e.g. the influence of disturbance variables (e.g. electronic noise, a low capturing accuracy of backscattered particles) which decrease the signal-to-noise ratio, it can be regarded as advantageous to select the type of gas particles such that the adsorption and/ or desorption rates of the two materials involved differ from one another to the greatest possible extent. This (desired or required) difference can be specified in particular by the definition of a threshold value. In this regard, it can be provided, for example, that an adsorption and/or desorption rate at the materials involved ought to differ from one another by at least 10%, 20%, 50%, 100%, 200%, 500%, etc. What can be made possible in this regard is that possible losses of accuracy during the detection of a transition of an etching process (as described above) are detected as accurately as possible, even in the case of comparatively disadvantageous measurement parameters (e.g. when a disturbance variable is present).

In contrast thereto, in the case of comparatively high measurement accuracy, it can be provided that, in comparison with a measurement in the case of lower measurement accuracy, less stringent requirements are made in respect of the desired difference in an adsorption and/or desorption rate of the materials involved. In this case, it can be provided, for example, that an adsorption and/or desorption rate of the materials involved ought to differ from one another by only 10% in order e.g. to enable cost- efficient monitoring of an etching process, since it is possible, if appropriate, to have recourse to a more cost-effective type of gas particles.

Claims

CLAIMS (l to 24)

1. Method for use with a lithographic mask, comprising: a. directing a particle beam (4) onto an element (3) of the lithographic mask in an atmosphere of particles, b. inducing a desorption and/ or adsorption process (7) of at least some of the particles in a region of the element (3), c. capturing a signal of secondary particles (9) and/ or backscattered particles (8) and/or some other free-space signal (10) generated by the particle beam during the desorption and/or adsorption process.

2. Method according to Claim 1, wherein capturing the signal comprises capturing at least two successive points in time during the desorption and/or adsorption process.

3. Method according to Claim 2, furthermore comprising determining a rate of change of the signal during the desorption and/or adsorption process.

4. Method according to any of the preceding claims, wherein capturing the signal comprises capturing a temporal profile of the signal during the desorption and/or adsorption process.

5. Method according to Claim 4, wherein capturing the signal during the desorption and/or adsorption process comprises capturing a transition from a disturbed equilibrium to an original equilibrium or a further equilibrium.

6. Method according to any of the preceding claims, furthermore comprising selecting the element (3) such that it comprises a predetermined material.

7. Method according to Claim 6, furthermore comprising storing at least one parameter of the signal with at least one parameter associated with the material as reference data.

8. Method according to any of Claims 1-5, further comprising: determining a material of the element (3) on the basis of comparing at least one parameter of the signal with at least one corresponding parameter of stored reference data.

9. Method according to any of the preceding claims, wherein the element (3) comprises a defect (3) of the lithographic mask.

10. Method according to Claim 9, further comprising: directing the particle beam (4) onto the defect (3), such that a local etching process takes place at the defect (3), and determining, at least partly on the basis of the signal captured during the desorption and/or adsorption process (7), whether the local etching process at the defect (3) has already transitioned to a local etching process at an element (1) of the mask that is arranged beneath the defect.

11. Method according to either of Claims 9 and 10, furthermore comprising selecting at least one type of particles having an adsorption and/or desorption rate at a predetermined material of the defect (3) which differs from an adsorption and/ or desorption rate at a material of an element (1) of the mask that is arranged beneath the defect by at least one predetermined threshold value.

12. Method according to any of the preceding claims, wherein the atmosphere contains at least one precursor gas and/or one contrast gas.

13. Method according to any of the preceding claims, wherein inducing comprises locally removing particles in a region of the element (3) and/or changing a supply of particles.

14. Method according to the preceding claim, wherein removing particles is effected by means of a second particle beam (5) and/ or by means of electric and/ or magnetic fields applied to the element.

15. Method according to any of the preceding claims, wherein capturing comprises capturing the signal at least one predetermined point in time after inducing the desorption and/or adsorption process.

16. Method according to any of the preceding claims, furthermore comprising synchronizing the capturing with the inducing.

17. Device for use with a lithographic mask, comprising: a. means for directing a particle beam (4) onto an element (3) of the lithographic mask in an atmosphere of particles, b. means for inducing (5) a desorption and/ or adsorption process (7) of at least some of the particles in a region of the element (3), c. means for capturing a signal of secondary particles (9) and/or backscattered particles (8) and/or some other free-space signal (10) generated by the particle beam during the desorption and/or adsorption process.

18. Device according to Claim 17, furthermore comprising a means for determining a material of the element (3) on the basis of comparing at least one parameter of the signal with at least one corresponding parameter of stored reference data.

19. Device according to either of Claims 17 and 18, further comprising: means for directing the particle beam (4) onto the element (3), such that a local etching process takes place at the element (3), and means for determining, at least partly on the basis of the signal captured during the desorption or adsorption process (7), whether the local etching process at the element (3) has already transitioned to a local etching process at a further element (1) of the mask that is arranged beneath the element (3).

20. Device according to any of Claims 17-19, wherein the means for inducing (5) comprises a means for locally removing particles in a region of the element (3).

21. Device according to Claim 20, wherein the means for removing comprises a means for generating a second particle beam (5) for removing particles and/or for generating an electric and/or magnetic field for removing particles.

22. Device according to any of Claims 17-21, wherein the means for capturing the signal is configured for capturing within one or more predetermined time windows or points in time in association with inducing the desorption or adsorption process.

23. Device according to any of Claims 17-22, furthermore comprising a means for synchronizing the capturing with the inducing.

24. Computer program comprising computer-executable code which, when executed, causes a computer to carry out a method according to any of Claims 1-16.