WO2023036911A1

WO2023036911A1 - Method and apparatus for determining a beam tail of a focused particle beam

Info

Publication number: WO2023036911A1
Application number: PCT/EP2022/075070
Authority: WO
Inventors: Daniel Rhinow; Markus Bauer; David Laemmle
Original assignee: Carl Zeiss Smt Gmbh
Priority date: 2021-09-10
Filing date: 2022-09-09
Publication date: 2023-03-16
Also published as: TW202326789A; DE102021210005A1

Abstract

The present invention relates to a method (1800) and an apparatus (1700) for determining an intensity distribution of at least one beam tail (120, 125, 130, 135) of a focused particle beam (100). The method (1800) comprises the steps of: (a) irradiating (1820) a test element (300, 500, 1100, 1400, 1600) with the focused particle beam (100) such that the at least one beam tail (120, 125, 130, 135) of the focused particle beam (100) causes at least one measurable change (620, 955, 1250, 1540, 1670) of the test element (300, 500, 1100, 1400, 1600); and (b) measuring (1830) the at least one change (620, 955, 1250, 1540, 1670) of the test element (300, 500, 1100, 1400, 1600) for the purposes of determining the intensity distribution of the at least one beam tail (120, 125, 130, 135) of the focused particle beam (100).

Description

Method and apparatus for determining a beam tail of a focused particle beam

The present application claims the priority of the German patent application DE 10 2021210 005.8, entitled “Verfahren und Vorrichtung zum Bestimmen eines Strahlauslaufers eines fokussierten Teilchenstrahls” [Method and apparatus for determining a beam tail of a focused particle beam], which was filed at the German Patent and Trademark Office on 10 September 2021, and which is incorporated in its entirety in the present application by reference.

1. Technical field

The present invention relates to a method and an apparatus for determining a beam tail of a focused particle beam. In particular, the present invention relates to a method and an apparatus for determining an intensity distribution of a beam tail of a focused particle beam, for example of an electron beam.

2. Prior art

The advances in nanotechnology make it possible to produce components with ever smaller structure elements, the dimensions thereof reaching nanometer scales. To display the nanostructures, measuring tools that can image these structures are required so that a realistic image of these structures can be generated from the measurement data thereof.

Microscopes are potent tools for imaging nanostructures. In microscopes, a particle beam typically interacts with a sample to be analyzed or processed. Microscopes can be subdivided into two categories. Optical or light-optical microscopes use photons to image a sample. This microscope type is used in many different ways to image microscopic structures. With the exception of specific types, the resolution of light-optical microscopes is limited by the wavelength of the light source used to expose the sample to be examined and by the numerical aperture of the optical elements used to image the sample on account of diffraction effects. The production of light sources in the deep ultraviolet (DUV) wavelength range and, in particular, for even shorter wavelengths, for instance in the extreme ultraviolet (EUV) wavelength range, is very complicated.

Microscopes that use massive particles for imaging nanostructures, for example electron microscopes, have significant advantages in terms of the resolution over optical microscopes on account of the short de Broglie wavelength of the electrons that are used for imaging purposes. Similar to the case of optical microscopes, the diffraction limit of electron microscopes, for example, scales linearly with the de Broglie wavelength of the electrons and is inversely proportional to the aperture angle of the employed electron beam. Accordingly, the diffraction limit of electron beams can be reduced by virtue of the electrons of an electron beam being accelerated to a greater kinetic energy.

On account of their high resolution and their capability of locally initiating chemical reactions, focused particle beams are also used to repair local defects in nanostructures. By way of example, defective nanostructures may occur on wafers, photolithographic masks and/ or stamps for nanoimprint lithography. Said defective nanostructures are frequently also repaired by local particle beam-induced etching processes and/ or deposition processes. As a result of aberrations of the beam-shaping system which shapes the focused particle beam, the focused particle beam often has beam tails that extend far beyond the area of an ideal Gaussian focused particle beam. However, only the central part of the Gaussian profile of the focused particle beam is considered in conventional resolution measurements.

However, the particles which are incident on a sample in the beam tail or tails, and hence incident far away from the site to be processed, are also of importance for the local particle beam-induced repair processes. Firstly, the particles in the beam tail or tails reduce the number of particles available in the region of the sample to be processed, and secondly the particles in the beam tail may cause inadvertent particle beam-induced etching and/or deposition processes outside the region of the sample to be repaired. By way of example, the quality of the beam profile influences the number of repetitions of a repair process that are required for a best possible repair. F. Stumpf et al. describe in the article “Detailed characterization of focused ion beam induced lateral damage on silicon carbide samples by electrical scanning probe microscopy and transmission electron microscopy”, J. of Appl. Physics 123, 125104-1 to 125104-10 (2018), investigations of lateral damages induced by focused ion beams on silicon carbide. The damages were characterized using electrical scanning probe microscopy (SPM), namely, scanning spreading resistance microscopy and conductive atomic force microscopy (c-AFM).

To assess the quality of an imaging process of nanostructures and, in particular, of repair processes of nanostructures, it is therefore important to also know the intensity curve of the beam tail or tails of a focused particle beam in addition to the profile in the central region. The methods currently used to determine the beam profile of a focused particle beam often have only a very low sensitivity in relation to determining the intensity distribution of beam tails of focused particle beams. An example in this respect is the complicated preparation of samples (lamellas) for an analysis by means of a transmission electron microscope (TEM). In particular, it is currently hardly possible to carry out a quantitative analysis of the intensity distribution of a beam tail of a focused particle beam.

The present invention therefore addresses the problem of specifying a method and an apparatus that allow a determination of the intensity distribution of a beam tail of a focused particle beam.

3. Summary of the invention

In accordance with one exemplary embodiment of the present invention, this problem is at least partly solved by means of the subject matter defined by the independent claims. Exemplary embodiments are described in the dependent claims.

In an embodiment, a method for determining an intensity distribution of a particle beam on a sample comprises the steps: (a) irradiating a test element with the particle beam such that the particle beam causes at least one measurable change of the test element; and (b) measuring the at least one change of the test element for determining the intensity distribution of the particle beam on the sample.

An inventive method may translate or transform the intensity distribution of a particle beam into a permanent or persistent change of a test element. The test element may be adapted to the intensity distribution of a specific particle beam. For example, the particle beam may irradiate a precursor gas available on the test element for inducing the at least one measurable change. In another example, a monolayer of a test element may image the intensity distribution of the particle beam in a persistent modification of its structure. The permanent change of the test element can be detected, and the intensity distribution of the particle beam may be derived from the measured change of the test element. The intensity distribution may be correlated with various sources of error that may lead to a deviation of the intensity distribution from an ideal, intended intensity distribution. Hence, the influence of various sources may be identified and subsequently the influence of one or more sources may then be systematically reduced or even virtually eliminated.

The particle beam maybe a focused particle beam and determining the intensity distribution may comprise determining an intensity distribution of at least one beam tail of the focused particle beam by irradiating the test element with the focused particle beam such that the at least one beam tail of the focused particle beam causes at least one measurable change of the test element; and measuring the at least one change of the test element for determining the intensity distribution of the at least one beam tail of the focused particle beam.

An ideal Gaussian beam can easily be divided into a main beam or a central beam and a beam tail. Proceeding from the intensity maximum I_o, the main beam maybe defined as the area where the intensity is greater than a threshold that is related to the intensity maximum. By way of example, said threshold can be defined by I > I₀-e^-2. The beam tail is then formed by the area whose intensity is less than the specified relative threshold, for example I< I₀-e^-2. The beam profiles described within this application may have a significant deviation from an ideal Gaussian intensity distribution. Nevertheless, within the present application, the main or central beam is defined analogously to the ideal Gaussian beam. This means that the intensity maximum I_o of the beam is determined in the first step. Then, a drop to a certain percentage of the maximum value is specified as a threshold which marks the boundaiy between central beam and beam tail. For a real particle beam, the beam tail or tails is/ are formed by the entire intensity guided outside of the central beam. This definition does not mean that the intensity must remain below a given threshold at each point of the beam tails but said intensity may grow again with increasing distance from the intensity maximum. Moreover, in contrast to the ideal Gaussian beam, a real beam may have a beam tail whose intensity profile does not extend rotationally symmetrically about the intensity maximum I_o. Below, this circumstance is characterized by two or more beam tails. Preferably, these definitions (main beam and beam tail) relate to the focus or a region in the vicinity of the focus, in which the beam waist of the focused particle beam has increased by no more than a factor of 2 in relation to the diameter of the focal spot.

The method facilitates a quantitative analysis of the beam tail or tails of a focused particle beam by virtue of the effects of the particles contained in the beam tails being made visible by way of an interaction with a test element. This detection process may be carried out in such a way that the particles of the main beam of the focused particle beam have substantially no influence on the change of the test element. In other words, the change of the test element may essentially be determined by the beam tail(s) only.

The intensity distribution of the beam tail or tails of the focused particle beam can be determined quantitatively from the visible or measurable change of the test element. Knowledge of the intensity distribution over the entire area irradiated by the focused particle beam can be used to optimize an image generated by scanning a sample with the focused particle beam. Further, knowledge about the intensity of a focused particle beam present in the beam tails can be used to optimize a local particle beam-induced processing process of a sample. By way of example, the knowledge of the intensity distribution of the beam tails of the focused particle beam may allow minimization of the number of loop iterations required for a best possible repair of a defect. The particles of a particle beam maybe particles such as photons that have no rest mass. In this case, the intensity of the particle beam is proportional to the electrical energy density distribution. However, the particles of the particle beam may also be particles with mass, for instance electrons, atoms, ions or molecules. In these cases, the intensity is proportional to the absolute value of the square of the amplitude of the wave function of the corresponding particle type.

The particle beam may irradiate the sample through at least one precursor gas and determining the intensity distribution may comprise determining a change of the intensity distribution caused by the at least one precursor gas. The at least one precursor gas maybe on the sample.

Particles of a precursor gas may scatter particles of a particle beam when the particle beam crosses the precursor gas. The scattering of the beam particles typically results in an unwanted beam expansion on the sample. For example, a focused particle beam having a focus spot of about to nm may be expanded up to the millimeter range. The amount of scattering may depend on the concentration or density of the precursor gas.

Further, the portion of the scattered beam particles depends on the path length along which the particle beam propagates within the precursor gas. Moreover, the scattering effect of the precursor gas can be reduced by increasing the kinetic energy of the beam particles. However, a high kinetic energy of the beam particles is often undesired, since it augments the interaction volume of the particle beam with the sample. Typically, there is an optimum kinetic energy of the beam particles in a range between very low and high kinetic energies. Further, it is beneficial to minimize the precursor gas volume, the beam must cross. Moreover, reducing the precursor gas density may also help minimizing a beam expansion of the particle beam. On the other hand, the precursor gas is needed for starting and maintaining a local particle beam induced chemical reaction.

Determining the change of the intensity distribution may contribute to optimize particle beam and/or precursor gas induced etching and/or deposition processes. They may contribute to a complete characterization of possible deviations of an applied process from an ideal intended process. The change may be determined for different pressures and/or flow rates of the precursor gas.

The particle beam may irradiate the sample through a shielding element and determining the intensity distribution may comprise determining a change of the intensity distribution on the sample caused by the shielding element.

A shielding element may be used to shield a charged particle beam from an electrostatic charge generated on a sample surface due to an interaction of the charged particle beam with the sample. Residual gas particles and/or precursor gas particles may scatter beam particles on their path from the particle source to the sample. A shielding element arranged in the beam path in a small distance over a sample may also act as a barrier or as an aperture for scattered beam particles.

Determining the effect of the shielding element on the intensity distribution may also contribute to optimize particle beam and/ or precursor gas induced etching and/ or deposition processes. It may allow a complete characterization of possible deviations of an applied process from an ideal intended process. For example, the (change of the) intensity distribution may be derived from the at least one change of the test element by correlating it with a pattern of the shielding element.

The shielding element may perform at least one of: redistributing scattered particles passing the shielding element in beam direction and generating secondary particles, as for example secondary electrons.

The redistribution of scattered particles by a shielding element as well as its function as a source of secondary particles results, for example, in an augmentation of particle induced processes on a sample surface outside of the intended area defined by the spot size of the particle beam. Hence, the application of a shielding element may amplify unwanted processes on a sample surface.

In a further embodiment, a method for determining a spontaneous etching rate and/or a spontaneous deposition rate of at least one precursor gas used in a particle beam in- duced etching process and/or in a particle beam induced deposition process of a sample comprises the steps: (a) providing the at least one precursor gas with a predetermined gas flow rate on a test element for a predetermined period without irradiating the test element with a particle beam; and (b) measuring the at least one change of the test element for determining the spontaneous etching rate and/ or the spontaneous deposition rate of the at least one precursor gas on the sample.

In the context of performing local particle beam induced chemical processes, processes which are spontaneously induced by a precursor gas are typically highly unwanted as they reduce process control. A spontaneous etching of a precursor gas acting as an etching gas unintentionally removes material from a sample. Further, a spontaneous deposition of a precursor gas acting as a deposition gas accidentally deposits material on a sample. Moreover, spontaneously deposited material may not have an intended material composition.

Spontaneous processes normally act on larger sample areas, since a lateral control of a precursor gas concentration on a sample is difficult. Typically, spontaneous processes cause small sample modifications of only a few nanometers. But even these small modifications maybe detrimental for some types of samples as for example photomasks. Furthermore, the caused modifications may vary across larger areas, i.e., in a region of one or several square millimeters. The application of a specifically designed test element may allow measuring such small modifications of a sample and its variation across the sample, e.g. caused by spikes in the concentration of the precursor gas, etc. For example, local spikes may cause local peaks in the change of the test element.

Spontaneous processes may consider effects on a sample not initiated by the particle beam when performing local particle beam induced chemical processes but caused by the precursor gas used in the local particle beam induced processes. Investigations of these processes enable to separate effects of particle beam tails from effects of the applied precursor gas, und thus allow a comprehensive investigation of both effects an intensity distribution of a particle beam and the spontaneous modification of the sample caused by the precursor gas on a lateral resolution of a local particle beam induced chemical reaction. The analysis of both effects enables improving the control of local particle beam induced chemical reactions. In some examples, the gas flow rate may not be predetermined but other quantities may be controlled to obtain a controllable precursor gas environment, such as pressure, density, temperature, etc.

In another embodiment, a method for determining residual changes in a sample comprises the steps: (a) providing at least one precursor gas with a predetermined gas flow rate on a test element for a predetermined period without irradiating the test element with a particle beam; and (b) measuring the at least one change of the test element for determining a spontaneous etching rate and/or a spontaneous deposition rate of the at least one precursor gas on the sample.

Determining a spontaneous etching rate and/ or a spontaneous deposition rate may further comprise varying at least one of: the gas flow rate, a composition of the at least one precursor gas, and a temperature of the at least one precursor gas, and providing the at least one precursor gas with a predetermined gas flow rate on a test element for a predetermined period without irradiating the test element with a particle beam.

The effect of spontaneous processes can be studied by performing one or more test processes. For example, a test element is measured in a first step. Then the test element is exposed to the effect of a precursor gas under predetermined conditions. After the exposition, the persistent change of the test element is analyzed. Parameters influencing the spontaneous process are systematically varied in order to determine their effect on the spontaneous etching or deposition rate.

Another aspect of the invention that is relevant independently but also in combination with the further aspects herein is a test element. The test element may comprise a base element and at least one structure element, wherein the at least one structure element may preferably be arranged on the base element.

The at least one structure element of the test element may be specifically designed for using it with one of the methods outlined herein. The structure element for determining an intensity distribution of a particle beam or of a portion of a particle beam, e.g., for a beam tail, may differ from the one or more structure elements of a test structure used for determining the effect of spontaneous processes.

The at least one structure element may have a height in a range of 1 nm to 1000 nm, preferred 5, nm to 500 nm, more preferred 10 nm to 200 nm, and most preferred 20 nm to 100 nm.

The at least one structure element may comprise at least 2, preferred at least 5, more preferred at least 10, and most preferred at least 30 parallel lines having a spacing of 50 to 150 nm or 80 to 120 nm, preferred 30 to 70 nm or 40 to 60 nm, more preferred 20 to 40 nm or 25 to 35 nm, and most preferred 5 to 25 nm or 10 to 20 nm.

The structure element may comprise a first material and the base element may comprise a second material, wherein the first material may be different from the second material.

For example, one of the two materials may not be attacked by a spontaneous process and may therefore act as a reference, whereas the other material may be modified by the action of a precursor gas. The reference of the test structure allows a precise determination of a small modification of the test element. Furthermore, a test element having several specific structure elements enables the determination of small lateral variations of the test element caused by the exposition to a precursor gas. Moreover, by using several specific structure elements slow structural variations may be detected by discretization of the slow structural variations.

A spontaneous etching rate of the first material induced by the at least one precursor gas may differ from a spontaneous etching rate of the second material of the test element by at least a factor of 2, preferably by at least a factor of 5, more preferably by at least a factor of 10, and most preferably by at least a factor of 20.

The at least one structure element may have at least one of: a one-dimensional (i-D) structure, a two-dimensional (2-D) structure, and a three-dimensional (3-D) structure. The at least one structure element may comprise at least one of: a checkerboard pattern, an aperture mask having at least one opening, at least one pillar, and a randomized structure.

The randomized structure may comprise gold particles (e.g. spheres) on a carbon layer.

Measuring the at least one change of the test element may comprise at least one of: measuring a change of an edge of the test element and measuring a change across an area of the test element.

Measuring the at least one change of the test element may comprise measuring a change of an edge of at least one structure element of the test element and measuring a change across an area of the test element may comprise measuring the change across an area of the at least one structure element and/or measuring the change across an area of the base element of the test element.

Irradiating the test element may cause at least one topographic change, at least one chemical change and/or at least one physical change of the test element.

The change(s) of a test element can be measurable such that it maybe measured. Under the assumption that the change(s) caused in the test element is (are) proportional to the locally effective intensity, the dose distribution of the particles in the beam and/ or the beam tail or tails of the focused particle beam can be deduced from the measured change(s) of the test element.

(15) The test element may have at least one test structure which comprises at least one element from the group:

- at least one height step,

- at least one hard mask with at least one opening, and

- at least one monolayer.

The at least one height step defines an upper plane by the top side of the height step and a lower plane by a lower edge of the height step. The hard mask specifies a top side as the side on which the focused particle beam is incident on the hard mask and specifies a back side located opposite to the top side. The upper plane and the lower plane of the at least one height step and the top side and the back side of the hard mask can be substantially planar. Moreover, the upper and the lower plane of the at least one height step and the top side and the back side of the hard mask can form substantially parallel planes. The parallelism of the upper and the lower plane or of the top side and the back side of the hard mask can improve the accuracy with which the intensity distribution of the beam tail or tails of a focused particle beam can be determined.

The test structure may comprise at least one height step and a monolayer and/or the test structure may comprise a hard mask with at least one opening and may comprise a monolayer.

The test element may comprise a base element. The top side of the base element may form the lower plane of the at least one height step. The base element of the test element may be a substrate of a photomask. The at least one height step may be a pattern element of a photomask. The base element of the test element may be a substrate of a photomask, or a wafer and one or more height steps may be etched into the substrate of the photomask or the wafer and/ or may be produced by depositing material on the substrate of the photomask or the wafer.

The hard mask may be applied to the top side of the base element of the test element. The at least one opening of the hard mask may expose a part of the top side of the base element. The at least one opening of the hard mask maybe produced by etching.

A hard mask is a mask that can withstand irradiation by a focused particle beam for a much longer period of time than a polymer mask produced from a photoresist. Byway of example, a hard mask may comprise a metal layer, an oxide layer or a nitride layer.

Here and elsewhere in this description, the expression "substantially" denotes an indication of a measurement quantity within the measurement uncertainty if measurement equipment according to the prior art is used to measure the corresponding quantity. The at least one height step and/ or the at least one opening may have at least one edge, and/or the monolayer maybe designed to change a secondary electron contrast when irradiated with the focused particle beam.

The at least one edge of the at least one height step and/ or of the at least one opening of the hard mask may be arranged on the upper plane of the at least one height step and/or the top side of the hard mask. The at least one edge may comprise a sectionally straight edge.

The monolayer may be applied to the at least one height step, to the hard mask with at least one opening and/or to the base element of the test element. The intensity distribution of the beam tail or tails of a focused particle beam can be determined from a change of the monolayer applied to the at least one height step and/ or from a change of the monolayer applied in the at least one opening of the hard mask.

The method may further comprise: setting a height of the at least one height step and/or a thickness of the hard mask such that a beam area of the focused particle beam increases along the height by at least 2%, preferably 5%, more preferably 10%, and most preferably 30% in relation to the beam waist of the focused particle beam.

The beam waist of the focused particle beam may have a diameter of < 20 nm, preferably < 10 nm, more preferably < 5 nm, and most preferably < 2 nm.

Below, both the beam waist and the spot diameter are related to a drop in the intensity to e^-2, i.e., a drop in the intensity to 13.5% of the maximum intensity. If a main beam of a focused particle beam is based on this definition, the main beam of an ideal Gaussian beam carries approximately 93% of the particles and the beam tail carries approximately 7%. Aberrations in a real particle-optical system lead to an increase in the proportion of particles contained in the beam tails. For example, aberrations may result in beam tails having dimensions in a range of too nm.

The test element may have a number N of test structures or structure elements which comprise a range of i < N <1000, preferably of 5 < N < 500, more preferably of 10 < N < 100, and most preferably of 20 < N < 50. A test element having a number N of identical test structures can be used for N calibration measurements of the intensity distribution of the particle beam and/or the beam tails of a focused particle beam. Such a test element can be installed into an apparatus during the latter's production process. It can then be used to analyze the beam, the beam tail or tails of the focused particle beam after each service, after a modification and/ or after a repair of the apparatus over its service life. Further, the test element can be used for investigating the effect of spontaneous processes on a sample. However, it is also possible to introduce a test element into the apparatus prior to an analysis of one or more beam tails of a focused particle beam.

The test element may be an integral part of the sample, for example.

The test element may comprise at least two test structures from the group of: at least one height step, one hard mask with at least one opening, and one monolayer.

Two or three different types of test structures may be combined on a test element. As a result, it is possible to optimize the precision with which the intensity distribution of the particle bean and/ or the beam tail(s) of a focused particle beam can be determined. Moreover, a test element may also contain one or more test elements having test structure specifically designed for analyzing the effects of spontaneous processes on a sample.

Irradiating the test element may comprise: focusing the particle beam on at least one element from the group: an upper plane of the at least one height step and/ or a back side of the hard mask, a lower plane of the at least one height step and/ or a top side of the hard mask, a top side of the monolayer.

The embodiments in which the focused particle beam is focused on the lower plane of the at least one height step and/or on the top side of the hard mask are currently preferred. The best separation of the beam tails from the central part or main part of the focused particle beam can be obtained in these embodiments, and so the dose distribution of the beam tail or tails can be analyzed under the minimal influence of the main beam. In the embodiments in which the focused particle beam is focused on the upper plane of the at least one height step and/or on the lower side of the hard mask, some of the particles produced by the main beam in the height step or the hard mask may reach into the region of the beam tail and thereby change the test structure of the test element in addition to the intensity distribution of the beam tails. This can make the analysis of the dose distribution of the beam tail or tails of the focused particle beam more difficult.

The particles produced in the test element by the focused particle beam may comprise secondary electrons (SE) and/ or electrons that were scattered back by the test element (BSE).

In the upper plane or in the top side of the hard mask, the at least one sectionally straight edge of the at least one height step and/or of the at least one opening of the hard mask may comprise an angle a in the range of 6o° < a < 120°, preferably in the range of 75⁰ < a < 105°, more preferably in the range of 85° < a < 95⁰, and most preferably in the range of 89° < a < 91⁰.

The at least one height step may comprise at least two height steps which are arranged symmetrically with respect to a line of symmetry, the line of symmetry being able to be located in the lower plane. The at least one height step preferably comprises at least four height steps, the edges of which substantially have an angle of 90° with respect to one another.

The hard mask may comprise at least two openings which are arranged symmetrically with respect to a point of incidence of the focused particle beam on the hard mask, and/or which are arranged symmetrically with respect to at least one scanning direction of the focused particle beam. The at least one opening of the hard mask preferably has a rectangular shape. Slot-shaped openings of the hard mask, in particular in the form of concentric structures, for example rings, around a point of incidence of the focused particle beam on the hard mask, are likewise advantageous. In relation to the upper plane of the height step or the top side of the hard mask, the at least one edge of the at least one height step and/ or of the at least one opening of the hard mask may comprise an angle P in the range of 6o° < P < 120°, preferably in the range of 75⁰ < P < 105°, more preferably in the range of 85° < P < 95⁰, and most preferably in the range of 89° < P < 91⁰.

A height step with a right angle between the lower and the upper plane or an opening of the hard mask with a right angle between the top side and the back side increases the resolution when determining the dose distribution of the beam tail or tails of the focused particle beam.

Irradiating the test element may comprise at least one element from the group: irradiating at least one point of a lower plane of the at least one height step with the focused particle beam such that the at least one beam tail is incident on an upper plane of the at least one height step, scanning the focused particle beam along the at least one edge of the at least one height step such that the at least one beam tail of the focused particle beam is incident on the upper plane of the at least one height step, irradiating at least one point of the hard mask with the focused particle beam such that at least a part of the at least one beam tail is incident on the at least one opening of the hard mask, scanning the focused particle beam parallel to the at least one edge of the at least one opening of the hard mask such that at least one part of the at least one beam tail is incident on the at least one opening of the hard mask, irradiating at least one point of the monolayer of the test element.

Irradiating the test element may comprise at least one element from the group: choosing a distance between an intensity maximum of the focused particle beam and the at least one edge of the at least one height step such that substantially no particles that are produced by the focused particle beam in the lower plane of the at least one height step reach the upper plane of the at least one height step, choosing a distance between the intensity maximum of the focused particle beam and the at least one edge of the at least one opening of the hard mask such that substantially no particles that are produced by the focused particle beam of the hard mask reach into the at least one opening, choosing an energy of the focused particle beam such that substantially no particles of the focused particle beam reach a back side of the monolayer.

The main part of the focused particle beam may produce secondary particles, for example SE and/or BSE, in the lower plane or in the base element of the test element. These particles should not reach the upper plane of the at least one height step. These could otherwise mix with the particles of the beam tail or with the secondary particles generated by the beam tail, and thus overlay the detection of the change of the test element caused by the beam tail. The same applies to the particle beam incident on the hard mask. By virtue of spatially separating the effects of the main beam and the effects of the beam tail or tails, it is possible to analyze the dose distribution of the beam tail or tails substantially without the bothersome influence of the main beam of the focused particle beam.

When irradiating a monolayer with a focused particle beam, it is possible to set the kinetic energy of the particles such that these substantially cannot penetrate into the test element to which the monolayer has been applied, and so none of the secondary particles produced in the test element are able to change the chemical composition and/ or structure of the monolayer.

Irradiating the test element may comprise: scanning the focused particle beam along the at least one edge of at least two height steps in at least two different distances between an intensity maximum of the focused particle beam and the at least one edge of the at least two height steps.

By virtue of varying a distance between the intensity maximum of the focused particle beam and the edge of a plurality of height steps, it is possible to determine a best possible positioning of the focused particle beam for scanning along the edge of a height step. This allows the influence of the main beam on the analysis of the beam tail or tails to be minimized. Irradiating the test element may comprise: providing at least one precursor gas comprises at least one of: providing the at least one precursor gas in a region of the particle beam and providing at least one precursor gas in a region at least one beam tail of the focused particle beam. The test element experiences a topographic change by carrying out a local particle beam-induced chemical reaction. The spatial separation of main beam and the beam tail or tails of the focused particle beam renders the intensity distribution of the beam tail or tails visible, i.e., measurable, without the bothersome influence of the main beam.

The at least one precursor gas may comprise at least one element from the group: at least one etching gas, at least one deposition gas and at least one additive gas.

The at least one deposition gas may comprise at least one element from the group: a metal alkyl, a transition element alkyl, a main group alkyl, a metal carbonyl, a transition element carbonyl, a main group carbonyl, a metal alkoxide, a transition element alkoxide, a main group alkoxide, a metal complex, a transition element complex, a main group complex and an organic compound.

A metal alkyl, a transition element alkyl and a main group alkyl may comprise at least one element from the group: cyclopentadienyl (Cp) trimethyl platinum (CpPtMe₃), methylcyclopentadienyl (MeCp) trimethyl platinum (MeCpPtMe₃), tetramethyltin (SnMe₄), trimethylgallium (GaMe₃), ferrocene (Cp₂Fe) and bisaryl chromium (Ar₂Cr). A metal carbonyl, a transition element carbonyl and a main group carbonyl may comprise at least one element from the group: chromium hexacarbonyl (Cr(CO)6), molybdenum hexacarbonyl (Mo(CO)6), tungsten hexacarbonyl (W(C0)6), dicobalt octacarbonyl (CO₂(CO)8), triruthenium dodecacarbonyl (RU₃(CO)I₂) and iron pentacarbonyl (Fe(CO)₅). A metal alkoxide, a transition element alkoxide and a main group alkoxide may comprise at least one element from the group: tetraethyl orthosilicate (TEOS, Si(OC₂H₅)₄) and tetraisopropoxytitanium (Ti(OC₃H₇)₄). A metal halide, a transition element halide and a main group halide may comprise at least one element from the group: tungsten hexafluoride (WFr,), tungsten hexachloride (WCk), titanium tetrachloride (TiCl₄), boron trichloride (BC1₃) and silicon tetrachloride (SiCl₄). A metal complex, a transition element complex and a main group complex may comprise at least one ele- ment from the group: copper bis(hexafluoroacetylacetonate) (Cu(C₅F6HO₂)₂) and dimethylgold trifluoroacetylacetonate (Me2Au(C₅F₃H₄O2)). The organic compounds may comprise at least one element from the group: carbon monoxide (CO), carbon dioxide (CO2), aliphatic hydrocarbons, aromatic hydrocarbons, constituents of vacuum pump oils and volatile organic compounds.

The at least one etching gas may comprise at least one element from the group: a halogen-containing compound and an oxygen-containing compound. The halogen-contain- ing compound may comprise at least one element from the group: fluorine (F₂), chlorine (Cl₂), bromine (Br₂), iodine (I₂), xenon difluoride (XeF₂), xenon di chloride (XeCl₂), xenon tetrachloride (XeCl₄), dixenon tetrafluoride (Xe₂F₄), hydrofluoric acid (HF), hydrogen iodide (HI), hydrogen bromide (HBr), nitrosyl chloride (NOCI), phosphorus trichloride (PC1₃), phosphorus pentachloride (PC1₅) and phosphorus trifluoride (PF₃). The oxygen-containing compound may comprise at least one element from the group: oxygen (0₂), ozone (O₃), water vapour (H₂0), heavy water (D₂0), hydrogen peroxide (H₂0₂), nitrous oxide (N₂0), nitrogen oxide (NO), nitrogen dioxide (N0₂) and nitric acid (HNO₃). Further etching gases are specified in the patent application US 2012 / o 273458 Al.

The at least one additive gas may comprise at least one element from the group: an oxidizing agent, a halide and a reducing agent.

The oxidizing agent may comprise at least one element from the group: oxygen (0₂), ozone (O₃), water vapour (H₂0), hydrogen peroxide (H₂0₂), nitrous oxide (N₂0), nitrogen oxide (NO), nitrogen dioxide (N0₂) and nitric acid (HNO₃). The halide may comprise at least one element from the group: chlorine (Cl₂), hydrochloric acid (HC1), xenon difluoride (XeF₂), hydrofluoric acid (HF), iodine (I₂), hydrogen iodide (HI), bromine (Br₂), hydrogen bromide (HBr), nitrosyl chloride (NOCI), phosphorus trichloride (PC1₃), phosphorus pentachloride (PC1₅) and phosphorus trifluoride (PF₃). The reducing agent may comprise at least one element from the group: hydrogen (H₂), ammonia (NH₃) and methane (CH₄).

Irradiating the test element with the focused particle beam while simultaneously providing at least one deposition gas may locally bring about a deposition reaction on the test element. When the upper plane of the at least one height step is irradiated by a beam tail of the focused particle beam while at least one deposition gas is provided, the particles of the beam tail may induce a local chemical reaction which deposits material on the upper plane of the at least one height step. When the at least one opening of the hard mask is irradiated by a beam tail of the focused particle beam while at least one deposition gas is provided, the particles of the beam tail may induce a local chemical reaction which deposits material in the at least one opening. The material deposited in the at least one opening of the hard mask may be deposited on the top side of the base element of the test element.

Irradiating the test element with the focused particle beam while simultaneously providing at least one etching gas may locally bring about an etching reaction on the test element. When the upper plane of the at least one height step is irradiated by a beam tail of the focused particle beam while at least one etching gas is provided, the particles of the beam tail may induce a local chemical reaction which etches material from the upper plane of the at least one height step. When the at least one opening of the hard mask is irradiated by a beam tail of the focused particle beam while at least one etching gas is provided at the same time, the particles of the beam tail may induce a local chemical reaction which etches material in the at least one opening of the hard mask. The material etched in the at least one opening of the hard mask maybe etched on the top side of the base element of the test element.

Measuring the at least one change of the test element may comprise at least one element from the group: scanning at least the area of the test element covered by the particle beam using a measuring probe of a scanning probe microscope, scanning at least the area of the test element covered by the at least one beam tail of the focused particle beam using a measuring probe of a scanning probe microscope, scanning at least the area of the test element covered by the particle beam using a detection beam and analyzing the particles produced by the detection beam, scanning at least the area of the test element covered by the at least one beam tail of the focused particle beam using a detection beam and analyzing the particles produced by the detection beam, imaging at least the area of the test element covered by the particle beam using an optical system, imaging at least the area of the test element covered by the at least one beam tail of the focused particle beam using an optical system, preparing at least a part of the area of the test element covered by the particle bean or the at least one beam tail of the focused particle beam and imaging the prepared part of the test element using an electron beam of a transmission electron microscope.

Measuring the at least one change of the test element may comprise at least one element from the group: scanning an area of o.oi cm², preferred o.i cm², more preferred i cm², and most preferred 5 cm² of the test element covered by 2 x 2, preferred 5 x 5, more preferred 10 x 10, and most preferred 20 x 20 measuring points using a measuring probe of a scanning probe microscope, scanning an area of 0.01 cm², preferred 0.1 cm², more preferred 1 cm², and most preferred 5 cm² of the test element covered by 2 x 2, preferred 5 x 5, more preferred 10 x 10, and most preferred 20 x 20 measuring points using a detection beam, imaging an area of 0.01 cm², preferred 0.1 cm², more preferred 1 cm², and most preferred 5 cm² of the test element covered by 2 x 2, preferred 5 x 5, more preferred 10 x 10, and most preferred 20 x 20 measuring points using an optical system.

A correspondingly designed test element may be provided as part of the methods outlined herein but also independently therefrom. For example, the test element may comprise an area of at least 0.01 cm², preferred at least 0.1 cm², more preferred at least 1 cm², and most preferred at least 5 cm² of the test element covered by 2 x 2, preferred 5 x 5, more preferred 10 x 10, and most preferred 20 x 20 measuring points, e.g. in the form of pillars, apertures, checkerboard pattern fields, and/or structure elements as outlined herein, etc. This may allow, e.g. determining residual changes by spontaneous etching/ deposition processes and/or etching or deposition rates of such processes over a larger scale, for example. When irradiating a test element using a stationary focused particle beam, a part of the entire three-dimensional (3-D) intensity profile of the beam tail is imaged into or onto the test element. As a result, it is possible to detect a part of the 3-D beam tail. However, a possible disadvantage of this process regime may be a poor signal-to-noise ratio, which may limit the accuracy of the determination of the beam tail.

By contrast, if the focused particle beam is scanned along an edge of the test structure, the 3-D intensity profile of the beam tail is reduced along the edge to a two-dimensional (2-D) intensity profile, that is to say it is averaged parallel to the scanning direction. A 2-D profile containing an image representation of the beam tail in or on the test structure with an improved signal-to-noise ratio is produced in this way. Or expressed differently: The effect of a beam tail is distributed over an area when scanning a focused particle beam along the edge. Averaging over the modified area yields a profile of the beam tail with an improved signal-to-noise ratio.

A scanning probe microscope may comprise at least one element from the group: an atomic force microscope (AFM), a magnetic force microscope (MFM), a scanning tunnelling microscope (STM), a scanning near-field optical microscope (SNOM) and a scanning near-field acoustic microscope (SNAM). A scanning probe microscope may comprise one or more measuring probes operating in parallel.

The scanning probe microscope is able to measure a topographic change of the test element which was caused by irradiating the test element with at least one beam tail of the focused particle beam in combination with at least one etching gas. In conjunction with at least one etching gas, the at least one beam tail can change the topography of the upper plane or of the lower plane of the at least one height step by etching or depositing material. Changing the upper plane of the at least one height step is currently preferred. In combination with at least one precursor gas, the at least one beam tail can change the topography of the hard mask and/ or of the at least one opening of the hard mask by etching or depositing material. Changing the at least one opening of the hard mask is currently preferred.

Should the hard mask be applied to a base element of the test element, the at least one beam tail of the focused particle beam changes the base element of the test element in combination with at least one precursor gas. Prior to scanning the at least one opening of the hard mask using a measuring probe of a scanning probe microscope, it may be advantageous to remove the hard mask from the test element. The hard mask can be removed by carrying out an etching process. The etching process can be a particle beam- induced etching process. Adapting the etching gas for removing the hard mask from the test element to the material of the hard mask is advantageous.

The detection beam may be the focused particle beam. However, that detection beam and the focused particle beam may also use different particle types. By way of example, the detection beam may use electrons and the focused particle beam may use ions. The particles produced in the irradiated test element by the detection beam can be SE and/or BSE. Further, photons can be used to measure the change of the test element initiated by the at least one beam tail of the focused particle beam and said photons maybe subjected to an x-ray analysis. Moreover, it is possible to analyze the Auger electrons generated by the detection beam.

The optical system may comprise at least one element from the group: a confocal laser scanning microscope (CLSM), a scanning near-field optical microscope (SNOM), an aerial image-generating microscope, and an interferometer.

Measuring the at least one change of the test structure may comprise: scanning at least the area of the monolayer covered by at least one of: the particle beam, the beam tail of the focused particle beam and the at least one precursor gas using a detection beam and detecting a secondary electron contrast in at least the covered area.

Like in the embodiment explained above, the detection beam may use the same particle type as the focused particle beam. This embodiment is advantageous, but the same particle beam source can be used both for changing the monolayer and for analyzing the change caused. Should the detection beam and the focused particle beam use particles with mass, the kinetic energy with which the particles are incident on the monolayer is a parameter in terms of which these beams differ. The detection beam preferably uses electrons for scanning the monolayer irradiated by the focused particle beam. Already small changes of the monolayer can be rendered visible in the image of the monolayer produced by SE electrons. However, the detection beam and the focused particle beam may also use different particle types.

The at least one monolayer may comprise a self-assembled organic compound.

A self-assembled organic compound (SAM, self-assembled monolayer) may form spontaneously when immersing a substrate in a solution or a suspension of surface-active or organic substances. The thickness of a self-assembled organic compound may comprise a range of 0.1 nm to 50 nm, preferably of 0.5 nm to 20 nm, more preferably of 0.8 nm to 10 nm and most preferably of 1 nm to 5 nm.

By way of example, self-assembled compounds form alkanethiols or alkyltrichlorosilanes. By way of example, alkanethiols with an alkane or carbon chain length of eight (CsHiySH) to fifteen carbon atoms (C15H31SH) can form monolayers with a thickness suitable for imaging the beam tail or tails. The primary electrons of the beam tail and the SE generated by the primary electrons can interact with the monolayer. As a result, electron beam-induced reactions may occur in the monolayer. The interaction is accompanied by an energy transfer from the primary electrons and/ or the SEs to the carbon atoms of the carbon chains of the monolayer. The electrons, in general the particles, of the beam tail can change the chain length of the alkanes, that is to say shorten this byway of particle beam-induced breaking of the alkane chain. Further, the particles of the beam tail of a focused particle beam may change the thiol group or the terminal functional groups located at the end of the alkyl chain distance from the surface of the monolayer. The change(s) of the monolayer can be analyzed using a detection beam, for example by way of the caused variation in the SE contrast.

The test element may comprise at least one layer comprising at least one element of: gold (Au), silver (Ag), platinum (Pt), copper (Cu), graphite (C) and silicon (Si).

Hence a test element produced from a silicon wafer is directly suitable, that is to say suitable without the deposition of a further layer, to form a test structure in the form of a monolayer. By contrast, producing a test element from a substrate of a photomask requires the deposition of a thin metal layer made of one of the aforementioned elements so that a stable self-assembled monolayer can be formed on the test element as a test structure.

A monolayer can be applied to one of the above-described test structures. The change in the monolayer caused by the beam tail of the focused particle beam, which change is substantially not influenced by the main beam as a result of the spatial separation between main beam and beam tail, can be used to determine the intensity profile of the beam tail.

The base element maybe adapted such that a particle beam induced etching process does essentially not etch the base element of the test structure and the at least one structure element of the test structure may comprise at least one pillar to be etched in the particle beam induced etching process.

The structure element may comprise at least two pillars adapted such that a particle beam induced etching process does essentially not etch the at least two pillars and the base element comprises a material to be etched in the particle beam induced etching process.

The at least one structure element may comprise at least one aperture mask adapted such that a particle beam induced etching process does essentially not etch the at least one aperture mask and the base element may be adapted such that the particle beam induced etching process may etch the base element.

The aperture mask may comprise at least two openings for determining a variation of the base element.

A computer program can contain instructions that prompt a computer system to perform the steps of one of the methods described herein when the computer program is executed by the computer system.

In a further embodiment, an apparatus for determining an intensity distribution of a particle beam on a sample comprises: (a) means for irradiating a test element with the particle beam such that the particle beam causes at least one measurable change of the test element; and (b) means for measuring the at least one change of the test element for determining the intensity distribution of the particle beam on the sample.

The apparatus for determining an intensity distribution may further comprise means for focusing the particle beam.

The apparatus for determining an intensity distribution may further comprise means for providing at least one precursor gas on the sample and/or the test element.

The means for providing the at least one precursor gas may comprise means for setting a gas flow rate, a temperature, a pressure, and/or a density of the at least one precursor gas.

The apparatus for determining an intensity distribution may further comprise means for measuring the at least one change of the test element.

The apparatus for determining an intensity distribution may further comprise means for determining the intensity distribution of the particle beam from the at least one measured change of the test element.

In another embodiment, an apparatus for determining an intensity distribution of at least one beam tail of a focused particle beam comprises: (a) a setting unit configured to set at least one parameter of the focused particle beam such that when a test element is irradiated by the focused particle beam the focused particle beam causes a measurable change of the test element; and (b) a measuring unit configured to measure the change of the test element for determining the intensity distribution of the at least one beam tail of the focused particle beam.

The setting unit can set various parameters of a particle beam source and/ or of an imaging system of the particle beam. The parameters adjustable by the setting unit may comprise: a kinetic energy of a beam of particles with mass, a beam waist of the focused particle beam, a position of the beam waist in the beam direction, a beam current, a scanning scheme, an aperture angle of the focused particle beam, and a stigmator setting. A scanning scheme describes the movement of a focused particle beam on a plane. Further, the setting unit can be configured to set parameters of a detection beam. The parameters of the detection beam may comprise the parameters of the focused particle beam. Moreover, the setting unit can be configured to set various parameter settings of a detection apparatus of the detection beam. The parameters of the detection apparatus may comprise: an acceleration voltage of a detector, an energy filter of a detector and a detector type.

The apparatus may further comprise a holding apparatus for the test element. The holding apparatus for the test element can be a unit that is separate from the sample holder.

The test element may comprise a number of test structures. As a result, it becomes possible where necessaiy to repeatedly use a single test element for analyzing the at least one beam tail of the focused particle beam of the apparatus, over the service life of the apparatus. However, it is also possible to use a dedicated test element for each individual analysis procedure of the at least one beam tail. Moreover, it is possible to use the apparatus for producing a test element.

The holding apparatus may comprise a positioning unit configured to position the test element under the focused particle beam and/or under the measuring unit.

The positioning unit may comprise one or more micro-manipulators which are able to move the test element in one, two or three spatial directions.

Further, the apparatus may comprise a computing unit configured to determine the intensity distribution of the at least one beam tail of the focused particle beam from the measured change of the test element.

In accordance with still another exemplary embodiment of the present invention, this problem is at least partly solved by means of the subjects of the independent embodiments 1 and 17 of the present application. Further exemplary embodiments are described in the dependent claims. In embodiment 1, a method for determining an intensity distribution of at least one beam tail of a focused particle beam comprises the steps: (a) irradiating a test element with the focused particle beam such that the at least one beam tail of the focused particle beam causes at least one measurable change of the test element; and (b) measuring the at least one change of the test element for the purposes of determining the intensity distribution of the at least one beam tail of the focused particle beam.

An ideal Gaussian beam can easily be divided into a main beam or a central beam and a beam tail. Proceeding from the intensity maximum I_o, the main beam is defined as the area where the intensity is greater than a threshold that is related to the intensity maximum. Byway of example, said threshold can be defined by I > I₀-e^-2. The beam tail is then formed by the area whose intensity is less than the specified relative threshold, for example I< I₀-e^-2.

The beam profiles described within this application may have a significant deviation from an ideal Gaussian intensity distribution. Nevertheless, within the present application, the main or central beam is defined analogously to the ideal Gaussian beam. This means that the intensity maximum I_o of the beam is determined in the first step. Then, a drop to a certain percentage of the maximum value is specified as a threshold which marks the boundary between central beam and beam tail. For a real particle beam, the beam tail or tails is/are formed by the entire intensity guided outside of the central beam. This definition does not mean that the intensity must remain below a given threshold at each point of the beam tails but said intensity may grow again with increasing distance from the intensity maximum. Moreover, in contrast to the ideal Gaussian beam, a real beam may have a beam tail whose intensity profile does not extend rotationally symmetrically about the intensity maximum I_o. Below, this circumstance is characterized by two or more beam tails. Preferably, these definitions (main beam and beam tail) relate to the focus or a region in the vicinity of the focus, in which the beam waist of the focused particle beam has increased by no more than a factor of 2 in relation to the diameter of the focal spot.

The method facilitates a quantitative analysis of the beam tail or tails of a focused particle beam by virtue of the effects of the particles contained in the beam tails being made visible by way of an interaction with a test element. This detection process is carried out in such a way that the particles of the main beam of the focused particle beam have substantially no influence on the change of the test element.

The intensity distribution of the beam tail or tails of the focused particle beam can be determined quantitatively from the visible or measurable change of the test element. Knowledge of the intensity distribution over the entire area irradiated by the focused particle beam can be used to optimize an image generated by scanning a sample with the focused particle beam. Further, knowledge about the intensity of a focused particle beam present in the beam tails can be used to optimize a local particle beam-induced processing process of a sample. By way of example, the knowledge of the intensity distribution of the beam tails of the focused particle beam may allow minimization of the number of loop iterations required for a best possible repair of a defect.

The particles of a particle beam maybe particles such as photons that have no rest mass. In this case, the intensity of the particle beam is proportional to the electrical energy density distribution. However, the particles of the particle beam may also be particles with mass, for instance electrons, atoms, ions or molecules. In these cases, the intensity is proportional to the absolute value of the square of the amplitude of the wave function of the corresponding particle type.

The change(s) of a test element can be measured. Under the assumption that the change(s) caused in the test element is (are) proportional to the locally effective intensity, the dose distribution of the particles in the beam tail or tails of the focused particle beam can be deduced from the measured change(s) of the test element.

The test element may have at least one test structure which comprises at least one element from the group:

- at least one height step,

- at least one hard mask with at least one opening, and

- at least one monolayer. The at least one height step defines an upper plane by the top side of the height step and a lower plane by a lower edge of the height step. The hard mask specifies a top side as the side on which the focused particle beam is incident on the hard mask and specifies a back side located opposite to the top side. The upper plane and the lower plane of the at least one height step and the top side and the back side of the hard mask can be substantially planar. Moreover, the upper and the lower plane of the at least one height step and the top side and the back side of the hard mask can form substantially parallel planes. The parallelism of the upper and the lower plane or of the top side and the back side of the hard mask can improve the accuracy with which the intensity distribution of the beam tail or tails of a focused particle beam can be determined.

The test structure may comprise at least one height step and a monolayer and/or the test structure may comprise a hard mask with at least one opening and comprise a monolayer.

The at least one edge of the at least one height step and/or of the at least one opening of the hard mask may be arranged on the upper plane of the at least one height step and/or the top side of the hard mask. The at least one edge may comprise a sectionally straight edge.

The monolayer may be applied to the at least one height step, to the hard mask with at least one opening and/or to the base element of the test element. The intensity distribution of the beam tail or tails of a focused particle beam can be determined from a change of the monolayer applied to the at least one height step and/or from a change of the monolayer applied in the at least one opening of the hard mask.

The method can further comprise: setting a height of the at least one height step and/or a thickness of the hard mask such that a beam area of the focused particle beam increases along the height by at least 2%, preferably 5%, more preferably 10%, and most preferably 30% in relation to the beam waist of the focused particle beam.

Below, both the beam waist and the spot diameter are related to a drop in the intensity to e^-2, i.e., a drop in the intensity to 13.5% of the maximum intensity. If a main beam of a focused particle beam is based on this definition, the main beam of an ideal Gaussian beam carries approximately 93% of the particles and the beam tail carries approximately 7%. Aberrations in a real particle-optical system lead to an increase in the proportion of particles contained in the beam tails.

The test element may have a number N of test structures which comprise a range of 1 < N <1000, preferably of 5 < N < 500, more preferably of 10 < N < too, and most preferably of 20 < N < 50. A test element having a number N of identical test structures can be used for N calibration measurements of the intensity distribution of the beam tails of a focused particle beam. Such a test element can be installed into an apparatus during the latter's production process. It can then be used to analyze the beam tail or tails of the focused particle beam after each service, after a modification and/or after a repair of the apparatus over its service life. However, it is also possible to introduce a test element into the apparatus prior to an analysis of one or more beam tails of a focused particle beam.

The test element may comprise at least two test structures from the group: at least one height step, one hard mask with at least one opening, and one monolayer.

Two or three different types of test structures may be combined on a test element. As a result, it is possible to optimize the precision with which the intensity distribution of the beam tail of a focused particle beam can be determined.

Irradiating the test element may comprise: focusing the particle beam on at least one element from the group: an upper plane of the at least one height step and/ or a back side of the hard mask, a lower plane of the at least one height step and/or a top side of the hard mask, a top side of the monolayer.

The embodiments in which the focused particle beam is focused on the lower plane of the at least one height step and/or on the top side of the hard mask are currently preferred. The best separation of the beam tails from the central part or main part of the focused particle beam can be obtained in these embodiments, and so the dose distribution of the beam tail or tails can be analyzed under the minimal influence of the main beam.

In the embodiments in which the focused particle beam is focused on the upper plane of the at least one height step and/or on the lower side of the hard mask, some of the particles produced by the main beam in the height step or the hard mask may reach into the region of the beam tail and thereby change the test structure of the test element in addition to the intensity distribution of the beam tails. This can make the analysis of the dose distribution of the beam tail or tails of the focused particle beam more difficult.

The hard mask may comprise at least two openings which are arranged symmetrically with respect to a point of incidence of the focused particle beam on the hard mask, and/or which are arranged symmetrically with respect to at least one scanning direction of the focused particle beam. The at least one opening of the hard mask preferably has a rectangular shape. Slot-shaped openings of the hard mask, in particular in the form of concentric structures, for example rings, around a point of incidence of the focused particle beam on the hard mask, are likewise advantageous.

In relation to the upper plane of the height step or the top side of the hard mask, the at least one edge of the at least one height step and/ or of the at least one opening of the hard mask may comprise an angle P in the range of 6o° < P < 120°, preferably in the range of 75⁰ < P < 105°, more preferably in the range of 85° < P < 95⁰, and most preferably in the range of 89° < P < 91⁰. A height step with a right angle between the lower and the upper plane or an opening of the hard mask with a right angle between the top side and the back side increases the resolution when determining the dose distribution of the beam tail or tails of the focused particle beam.

The main part of the focused particle beam produces secondary particles, for example SE and/or BSE, in the lower plane or in the base element of the test element. These particles should not reach the upper plane of the at least one height step. These could otherwise mix with the particles of the beam tail or with the secondary particles generated by the beam tail, and thus overlay the detection of the change of the test element caused by the beam tail. The same applies to the particle beam incident on the hard mask. By virtue of spatially separating the effects of the main beam and the effects of the beam tail or tails, it is possible to analyze the dose distribution of the beam tail or tails substantially without the bothersome influence of the main beam of the focused particle beam.

By virtue of varying a distance between the intensity maximum of the focused particle beam and the edge of a plurality of height steps, it is possible to determine a best possible positioning of the focused particle beam for scanning along the edge of a height step. This allows the influence of the main beam on the analysis of the beam tail or tails to be minimized.

Irradiating the test element may comprise: providing at least one precursor gas in a region of the at least one beam tail of the focused particle beam. The test element experiences a topographic change by carrying out a local particle beam-induced chemical reaction. The spatial separation of main beam and the beam tail or tails of the focused particle beam renders the intensity distribution of the beam tail or tails visible, i.e., measurable, without the bothersome influence of the main beam. The at least one precursor gas may comprise at least one element from the group: at least one etching gas, at least one deposition gas and at least one additive gas.

A metal alkyl, a transition element alkyl and a main group alkyl may comprise at least one element from the group: cyclopentadienyl (Cp) trimethyl platinum (CpPtMe₃), methylcyclopentadienyl (MeCp) trimethyl platinum (MeCpPtMe₃), tetramethyltin (SnMe₄), trimethylgallium (GaMe₃), ferrocene (Cp₂Fe) and bisaryl chromium (Ar₂Cr). A metal carbonyl, a transition element carbonyl and a main group carbonyl may comprise at least one element from the group: chromium hexacarbonyl (Cr(CO)6), molybdenum hexacarbonyl (Mo(CO)6), tungsten hexacarbonyl (W(C0)6), dicobalt octacarbonyl (CO₂(CO)8), triruthenium dodecacarbonyl (RU₃(CO)I₂) and iron pentacarbonyl (Fe(CO)₅). A metal alkoxide, a transition element alkoxide and a main group alkoxide may comprise at least one element from the group: tetraethyl orthosilicate (TEOS, Si(OC₂H₅)₄) and tetraisopropoxytitanium (Ti(OC₃H₇)₄). A metal halide, a transition element halide and a main group halide may comprise at least one element from the group: tungsten hexafluoride (WFr,), tungsten hexachloride (WCk), titanium tetrachloride (TiCl₄), boron trichloride (BC1₃) and silicon tetrachloride (SiCl₄). A metal complex, a transition element complex and a main group complex may comprise at least one element from the group: copper bis(hexafluoroacetylacetonate) (Cu(C₅F6HO₂)₂) and dimethylgold trifluoroacetylacetonate (Me₂Au(C₅F₃H₄O₂)). The organic compounds may comprise at least one element from the group: carbon monoxide (CO), carbon dioxide (C0₂), aliphatic hydrocarbons, aromatic hydrocarbons, constituents of vacuum pump oils and volatile organic compounds.

The at least one etching gas may comprise one element from the group: a halogen-con- taining compound and an oxygen-containing compound. The halogen-containing compound may comprise at least one element from the group: fluorine (F₂), chlorine (Cl₂), bromine (Br₂), iodine (I₂), xenon difluoride (XeF₂), xenon dichloride (XeCl₂), xenon tetrachloride (XeCl₄), dixenon tetrafluoride (Xe₂F₄), hydrofluoric acid (HF), hydrogen iodide (HI), hydrogen bromide (HBr), nitrosyl chloride (NOCI), phosphorus trichloride (PC1₃), phosphorus pentachloride (PC1₅) and phosphorus trifluoride (PF₃). The oxygencontaining compound may comprise at least one element from the group: oxygen (0₂), ozone (O₃), water vapour (H₂0), heavy water (D₂0), hydrogen peroxide (H₂0₂), nitrous oxide (N₂0), nitrogen oxide (NO), nitrogen dioxide (N0₂) and nitric acid (HNO₃). Further etching gases are specified in the patent application US 2012 / o 273458 Al.

Irradiating the test element with the focused particle beam while simultaneously providing at least one deposition gas may locally bring about a deposition reaction on the test element. When the upper plane of the at least one height step is irradiated by a beam tail of the focused particle beam while at least one deposition gas is provided, the particles of the beam tail may induce a local chemical reaction which deposits material on the upper plane of the at least one height step. When the at least one opening of the hard mask is irradiated by a beam tail of the focused particle beam while at least one deposition gas is provided, the particles of the beam tail may induce a local chemical reaction which deposits material in the at least one opening. The material deposited in the at least one opening of the hard mask may be deposited on the top side of the base element of the test element. Irradiating the test element with the focused particle beam while simultaneously providing at least one etching gas may locally bring about an etching reaction on the test element. When the upper plane of the at least one height step is irradiated by a beam tail of the focused particle beam while at least one etching gas is provided, the particles of the beam tail may induce a local chemical reaction which etches material from the upper plane of the at least one height step. When the at least one opening of the hard mask is irradiated by a beam tail of the focused particle beam while at least one etching gas is provided at the same time, the particles of the beam tail may induce a local chemical reaction which etches material in the at least one opening of the hard mask. The material etched in the at least one opening of the hard mask maybe etched on the top side of the base element of the test element.

Measuring the at least one change of the test element may comprise at least one element from the group: scanning at least the area of the test element covered by the at least one beam tail of the focused particle beam using a measuring probe of a scanning probe microscope, scanning at least the area of the test element covered by the at least one beam tail of the focused particle beam using a detection beam and analyzing the particles produced by the detection beam, imaging at least the area of the test element covered by the at least one beam tail of the focused particle beam using an optical system, preparing at least a part of the area of the test element covered by the at least one beam tail of the focused particle beam and imaging the prepared part of the test element using an electron beam of a transmission electron microscope.

When irradiating a test element using a stationary focused particle beam, a part of the entire three-dimensional (3-D) intensity profile of the beam tail is imaged into or onto the test element. As a result, it is possible to detect a part of the 3-D beam tail. However, a possible disadvantage of this process regime may be a poor signal-to-noise ratio, which may limit the accuracy of the determination of the beam tail.

The scanning probe microscope is able to measure a topographic change of the test element which was caused by irradiating the test element with at least one beam tail of the focused particle beam in combination with at least one etching gas. In conjunction with at least one etching gas, the at least one beam tail can change the topography of the upper plane or of the lower plane of the at least one height step by etching or depositing material. Changing the upper plane of the at least one height step is currently preferred. In combination with at least one precursor gas, the at least one beam tail can change the topography of the hard mask and/or of the at least one opening of the hard mask by etching or depositing material. Changing the at least one opening of the hard mask is currently preferred.

Should the hard mask be applied to a base element of the test element, the at least one beam tail of the focused particle beam changes the base element of the test element in combination with at least one precursor gas. Prior to scanning the at least one opening of the hard mask using a measuring probe of a scanning probe microscope, it may be advantageous to remove the hard mask from the test element. The hard mask can be removed by carrying out an etching process. The etching process can be a particle beam- induced etching process. Adapting the etching gas for removing the hard mask from the test element to the material of the hard mask is advantageous. The detection beam may be the focused particle beam. However, that detection beam and the focused particle beam may also use different particle types. By way of example, the detection beam may use electrons and the focused particle beam may use ions. The particles produced in the irradiated test element by the detection beam can be SE and/or BSE. Further, photons can be used to measure the change of the test element initiated by the at least one beam tail of the focused particle beam and said photons maybe subjected to an x-ray analysis. Moreover, it is possible to analyze the Auger electrons generated by the detection beam.

Measuring the at least one change of the test element may comprise: scanning at least the area of the monolayer covered by the beam tail of the focused particle beam using a detection beam.

Like in the embodiment explained above, the detection beam may use the same particle type as the focused particle beam. This embodiment is advantageous, but the same particle beam source can be used both for changing the monolayer and for analyzing the change caused. Should the detection beam and the focused particle beam use particles with mass, the kinetic energy with which the particles are incident on the monolayer is a parameter in terms of which these beams differ. The detection beam preferably uses electrons for scanning the monolayer irradiated by the focused particle beam. Already small changes of the monolayer can be rendered visible in the image of the monolayer produced by SE electrons.

However, that detection beam and the focused particle beam may also use different particle types.

The at least one monolayer may comprise a self-assembled organic compound.

The test element may comprise at least one layer made of an element from: gold (Au), silver (Ag), platinum (Pt), copper (Cu), graphite (C) and silicon (Si).

A monolayer can be applied to one of the above-described test structures. The change in the monolayer caused by the beam tail of the focused particle beam, which change is substantially not influenced by the main beam as a result of the spatial separation between main beam and beam tail, can be used to determine the intensity profile of the beam tail. A computer program can contain instructions that prompt a computer system to perform the steps of one of the above-described methods when the computer program is executed by the computer system.

In embodiment 17, an apparatus for determining an intensity distribution of at least one beam tail of a focused particle beam comprises: (a) a setting unit configured to set at least one parameter of the focused particle beam such that when a test element is irradiated by the focused particle beam the focused particle beam causes a measurable change of the test element; and (b) a measuring unit configured to measure the change of the test element for the purposes of determining the intensity distribution of the at least one beam tail of the focused particle beam.

The setting unit can set various parameters of a particle beam source and/ or of an imaging system of the particle beam. The parameters adjustable by the setting unit may comprise: a kinetic energy of a beam of particles with mass, a beam waist of the focused particle beam, a position of the beam waist in the beam direction, a beam current, a scanning scheme, an aperture angle of the focused particle beam, and a stigmator setting. A scanning scheme describes the movement of a focused particle beam on a plane.

Further, the setting unit can be configured to set parameters of a detection beam. The parameters of the detection beam may comprise the parameters of the focused particle beam. Moreover, the setting unit can be configured to set various parameter settings of a detection apparatus of the detection beam. The parameters of the detection apparatus may comprise: an acceleration voltage of a detector, an energy filter of a detector and a detector type.

The test element may comprise a number of test structures. As a result, it becomes possible where necessary to repeatedly use a single test element for analyzing the at least one beam tail of the focused particle beam of the apparatus, over the service life of the apparatus. However, it is also possible to use a dedicated test element for each individual analysis procedure of the at least one beam tail. Moreover, it is possible to use the apparatus for producing a test element.

4. Description of the drawings

The detailed description that follows describes currently preferred exemplaiy embodiments of the invention with reference to the drawings, wherein:

Fig. la illustrates a schematic section of a beam profile of a focused particle beam with two different beam tails;

Fig. ib reproduces a plan view of a sample which is irradiated by the focused particle beam from Figure la;

Fig. 2 schematically represents the area irradiated by a focused particle beam with non-centrosymmetric beam tails;

Fig. 3 reproduces, in the upper partial image, a schematic plan view of a test element whose test structure comprises two pattern elements of a photomask and represents, in the lower partial image, a cross section through the test element of the upper partial image; Fig. 4 elucidates, in the upper partial image, the irradiation of the test element from Figure 3 by a focused particle beam with beam tails and illustrates, in the lower part, the position of the focus of the particle beam in relation to the test structure of the test element from Figure 3;

Fig. 5 shows a schematic plan view of a second example of a test structure of a test element;

Fig. 6 schematically elucidates the scanning of the focused particle beam from Figure 1 along the edges of the height steps of the test element from Figure 3, with the distance between the intensity maximum of the focused particle beam and the distance from the edge of the height step being changed;

Fig. 7 reproduces Figure 6, with the areas whose topographic changes are measured for determining the beam tails of the focused particle beam additionally being marked;

Fig. 8 reproduces Figure 7, with the determination of the one-dimensional profiles for calculating the beam profile of the beam tails additionally being elucidated;

Fig. 9 schematically presents the scanning of the focused particle beam from Figure 1 along the four edges of the test structure of the test element from Figure 5;

Fig. 10 repeats Figure 9, with the areas whose topographical changes caused by the combined effect of the beam tails and at least one precursor gas are measured for determining the intensity distribution of the beam tails of the focused particle beam from Figure 1 additionally being marked;

Fig. 11 shows, in the upper partial image, a schematic plan view of a third example of a test element and, in the lower partial image, a cross section therethrough, with the test structure of the test element comprising a base element with a hard mask with an opening deposited thereon; Fig. 12 illustrates, in the upper partial image, the irradiation of the test structure of the test element from Figure n with the focused particle beam from Figure i and the lower partial image illustrates the topographic change of the test element caused by the combined effect of a beam tail and an etching gas;

Fig. 13 reproduces, in the upper partial image, a plan view of the modified base element of the test element from Figure 11 following the removal of the hard mask and presents, in the lower partial image, a cross section through the modified base element following the removal of the hard mask;

Fig. 14 reproduces, in the upper partial image, a schematic plan view of a fourth example of a test element, the test structure of which has a hard mask with eight openings arranged symmetrically about a longitudinal axis and which is irradiated by scanning a focused particle beam in the y-direction, and shows, in the lower partial image, a cross section through the test element;

Fig. 15 reproduces, in the upper partial image, a plan view of the modified base element of the test element from Figure 14 following the removal of the hard mask and presents, in the lower partial image, a cross section through the modified base element following the removal of the hard mask;

Fig. 16 represents, in the upper partial image, a plan view of a fifth example of a test element in the form of a self-assembled monolayer following an irradiation with the focused particle beam from Figure 1, and the lower partial image reproduces a cross section through the test element and the focused particle beam;

Fig. 17 reproduces a schematic section through a few components of an apparatus which facilitates the irradiation of a test element with a beam tail of a focused particle beam or with a focused particle beam and a precursor gas and which allows the measurement of the caused change of the test element; and

Fig. 18 specifies a flowchart of the method for determining an intensity distribution of a beam tail of a focused particle beam. 5. Detailed description of preferred exemplary embodiments

Currently preferred embodiments of a method according to the invention and of an apparatus according to the invention are explained below. The apparatus according to the invention is explained using the example of a scanning electron microscope (SEM) in combination with a scanning probe microscope (SPM). However, the method according to the invention and the apparatus according to the invention are not restricted to the determination of the beam tails of a beam of particles with mass in the form of an electron beam. Rather, these can be used for analyzing a beam tail of any particle beam whose particles comprise bosons or fermions. Should the particle beam comprise a photon beam, the method according to the invention can be used for short wavelength photons in particular, that is to say photons with wavelengths in the deep ultraviolet (DUV) wavelength range or in the range of even shorter wavelengths.

Moreover, the method described in this application and the associated apparatus can be used in microscopes which use a scanning focused particle beam for recording an image. Below, a particle beam comprises a beam of particles with mass and a particle beam containing particles without rest mass.

Figure la schematically shows the profile of a focused particle beam too. The exemplary particle beam too comprises a focused electron beam too. The focused electron beam too contains a main beam 110, which comprises a main part of the electrons, and two beam tails 120 and 130. The definition of the main beam 110 used in this application is specified above. The focused electron beam too has an intensity maximum I_o 190. As elucidated schematically in Figure la, the profile of the focused particle beam too - unlike that of an ideal Gaussian beam - does not decrease monotonically starting from the centre or intensity maximum I_o 190 and the beam profile is not centrosymmetric. This means that the beam tail or tails 120, 130 of the focused particle beam too are likewise not centrosymmetric; rather, in the plane of the paper, the focused particle beam too has two beam tails 120 and 130 that differ in terms of their intensity distribution. As already explained in the third part, the main or central beam no is defined in this application as the area within which the intensity has dropped to a specified percentage of the maximum intensity proceeding from a maximum value I_o. By way of example, this may be a drop to I₀-e^-2. The areas of non-vanishing intensity outside the main beam no form the beam tails 120 and 130.

Figure 2 elucidates the area of a sample exposed by a focused particle beam 100 with a narrow peak and asymmetric beam tails 120, 130. The narrow peak of the focused particle beam 100 is concentrated in the small area 200. The next larger area presents a pixel 150 of a defective region of the sample, which should be processed by the focused particle beam 100 in combination with one or more precursor gases. The areas 210, 220, 230 and 240 symbolize various parts of the beam tails 120, 130 of the focused particle beam 100. In the example reproduced in Figure 2, the beam tails have an asymmetric beam profile in the x-direction (in the horizontal direction), but the beam tails are symmetric with respect to the intensity maximum in the y-direction (in the vertical direction).

Even though the intensity levels of the beam tails 120, 130 in the areas 210, 220, 230 and 240 are small in comparison with the intensity maximum of the main beam 110, the beam tails 120, 130 may carry a significant portion of the entire intensity of the focused particle beam too on account of their sheer size. In the case of corresponding aberrations of the optical system that focuses the particle beam too, up to half of the entire beam intensity maybe present in the beam tails in an extreme case.

Referring back to Figure 1, the focused electron beam too is directed at a sample 140. In the portion reproduced in Figure la, the sample too has a defect not depicted in Figure la. The defect of the sample 140 should be repaired by carrying out a particle beam- induced local chemical process. In the example illustrated in Figure la, the focused electron beam too can carry out a local electron beam-induced etching (EBIE) process and/or a local electron beam-induced deposition (EBID) process.

To carry out the repair process, the defective area of the sample 140 is divided into pixels 150, which the focused electron beam too scans sequentially. In combination with a corresponding precursor gas, the focused electron beam 100 locally removes material from the sample 140 or locally deposits material on the sample 140.

Figure la shows a pixel 150 of a region of the sample 140 to be processed by the focused electron beam 100. On account of the beam tails 120 and 130, irradiating the pixel 150 with the focused electron beam 100 inadvertently also leads to particle beam-induced local chemical reactions in the areas 160, 170, 210-240 outside of the pixel 150. As may be gathered from Figure 2 and Figure ib - the latter likewise reproducing a plan view of the focused particle beam 100 on the pixel 150 of the sample 140 - the beam tails 120 and 130 lead to a processing area 180 of the focused particle beam 100 that is many times larger than the area of the pixel 150 to be processed.

To control and, more particularly, optimize a particle beam-induced local processing process of a sample 140, it is therefore necessary to also know the distribution of the radiation dose present in the beam tails 120 and 130, in addition to the beam profile of the main beam 110. This likewise applies if the focused particle beam too is used to image a sample 140.

Various exemplary embodiments that facilitate a quantitative analysis of the intensity distribution of the beam tails 120, 130 of the focused particle beam too are described below in detail.

Figure 3 shows a schematic plan view of a first exemplary embodiment of a test element 300 in the upper partial image and the lower partial image shows a schematic section through the test element 300. The test element 300 comprises a base element 310 and a structure element 390. As base element 310, the exemplary test element 300 from Figure 3 comprises a substrate 310 of a photolithographic mask. Two rectangular pattern elements 320 and 360 have been applied as structure element 390 to the base element 310 of the test element 300. The rectangular pattern elements 320 and 360 can be any pattern elements of a photomask, for instance absorbing and/or phase-shifting pattern elements. The two pattern elements form at least two height steps 320 and 360. Their height 380 may range from 50 nm to 2000 nm. The upper plane 340 of the height step 320, 360 forms the surface of the pattern elements 320, 360. The lower plane 350 of the two height steps 320, 360 forms the surface 370 of the base element 310 of the test element 300.

The edge 330 of the two height steps 320, 360 denotes the transition from the upper plane 340 to the lower plane 350. In the exemplary test element 300 presented in Figure 3, the edge 330 has an angle a of substantially 90°. This angle is advantageous for the function of the test element explained below. In Figure 3, the edge 330 has a sectionally straight profile. The angle P within the upper plane 340 likewise substantially has an angle of 90°.

Figure 4 presents a first schematic example of a use of the test element 300 for analyzing the beam tails 120, 130 of a focused particle beam too. In the first step, the focus of the particle beam too is set to the upper plane 340 of the height step 320, 360. This is illustrated schematically by the beam waist 400 in the lower partial image in Figure 4. In the next step, the beam waist 400 or the intensity maximum is positioned in relation to the edge 330 of the height step 320, 360 such that the main beam 110 of the focused particle beam too radiates past the edge 330 of the height step on the lower plane 350 of the height step 320, 360 and the beam tail 120 is focused on the upper plane 340 of the height step 320, 360. The optimal positioning of the focused particle beam too in relation to the edge 330 can be determined experimentally by varying the distance between the intensity maximum I_o of the focused particle beam too and the edge 330.

A precursor gas is provided in the region of the beam tail 120 following this alignment and said precursor gas is irradiated for a predetermined duration by the particle beam too which has been aligned optimally with respect to the edge 330. A precursor gas in the form of an etching gas locally removes material from the upper plane 340 of the height step 320, 360, initiated by the combined effect of the particles of the beam tail 120 and of the etching gas. By way of example, a halogen-containing etching gas, for instance xenon difluoride (XeF₂), can be used as an etching gas. Should a deposition gas be provided in the region of the beam tail 120, the intensity distribution of the beam tail 120 induces the deposition of material on the upper plane 340 of the height step 320, 360. Byway of example, a metal carbonyl, for instance chromium hexacarbonyl (Cr(CO)6), can be used as a deposition gas. Changing the upper plane 340 of the height step 320, 360, either by the etching or deposition of material, persistently maps the intensity profile of the beam tail 120 into the upper plane 340 of the height step 320, 360 of the test element 300.

The visible or measurable reproduction of the intensity distribution of the beam tail 120 is facilitated by the spatial separation of the effect of the main beam 110 of the focused particle beam 100 from the effect of the beam tail or tails 120. The provision of a precursor gas cannot be spatially concentrated to such an extent that gas molecules of the precursor gas are only present on the upper plane 340 of the height step 320, 360. This means that the main beam 110 of the focused particle beam 100 also modifies the lower plane 350 of the height step 320, 360 just like - to a lesser extent - the beam tail 130 of the focused particle beam too. However, the change of the lower plane 350 is implemented in a manner spatially separated from the local chemical reaction which is triggered by the beam tail 120 in the upper plane 340 of the height step 320, 360 of the test structure 390 of the test element 300. Therefore, the effect of the main beam 110 substantially does not influence the persistent mapping of the intensity distribution of the beam tail 120 in or on the upper plane 340 of the height step 320, 360.

The beam tail 130 of the focused particle beam too can be rendered visible with the aid of one or more precursor gases using the left edge 330 of the height step 320. Alternatively, it is also possible to use the right edge 330 of the height step 360 of the test structure 390 of the test element 300 to permanently map the beam tail 130 of the focused particle beam too.

The height step 320, 360 of the test structure 390 of the test element 300 facilitates the spatial separation of the effect of the main beam 110 and of the beam tail 130 on the lower plane 350 and the effect of the beam tail 120 on the upper plane 340 of the test structure 390. When changing a plane sample 140 by irradiation with the focused particle beam too, the effect of the far higher intensity of the main beam 110 would conceal the effect of the beam tails 120, 130 and hence render the analysis of the intensity distribution of the beam tails 120, 130 impossible. As a result of the incidence of the main beam 110 and of the beam tail or tails 120, 130 on different planes along the beam propagation, SEs and BSEs of the main beam 110 can substantially no longer reach into the detection region 340 of the beam tail or tails S120, 130. In principle, it is also possible to carry out the described procedure in reverse. This means the focus 400 of the particle beam 100 is set on the lower plane 350 and the main part 110 of the particle beam 100 is directed at the upper plane 340 of the test structure 390 in such a way that the beam tail 120 or 130 is focused on the lower plane 350. However, in this embodiment, the main beam 110 produces particles in the height step 320, 360, some of which emerge from the height step 320, 360 below the edge 330 and may be incident on the lower plane 350. As a result, some of the effect of the main beam 110 can be transferred into the area exposed by the beam tail 120 or 130. This can render the analysis of the intensity distribution of the beam tails 120 and 130 more difficult. Therefore, this embodiment is not preferred.

Figure 5 presents a schematic plan view of a test element 500 with a test structure 590. The exemplary test structure 590 of the test element 500 from Figure 5 is applied to a base element 510. By way of example, the base element can be a substrate of a photomask, into which a rectangular or a square depression has been etched. However, the test structure 590 of the test element 500 may also be a contact hole of a wafer. It is also possible to produce the test structure 590 by way of depositing material on a base element 510.

The exemplary test structure 590 from Figure 5 comprises a square height step 520. The height step 520 has an upper plane 540 and a lower plane 550. The lower plane 550 is the surface 570 of the base element 510. The upper plane 540 of the height step 520 has an edge 530 all around, with four right angles in the upper plane 540. Moreover, the edge 530 has a right angle with respect to the lower plane 550, that is to say a = 90°. The edge 530 of the height step 520 can be used - analogously to the description of Figure 4 - for analyzing the beam tails 120, 130 of the focused particle beam too. This means that the focus 400 of the particle beam too is located in the upper plane 540 of the height step 520. By virtue of the beam tails 120, 130 being imaged from four different sides, the profile of the beam tails can be determined with great precision.

However, the number of exposures for determining the intensity distribution of the beam tails 120, 130 is not restricted to two or four. Rather, the beam tails 120, 130 can be exposed any number of times where necessary in order to obtain an image that is as comprehensive as possible about the intensity distribution in the beam tails 120, 130. By way of example, the test element 300, 500 can be rotated about the beam axis of the focused particle beam 100 through defined angles to this end. Alternatively, or in addition, the particle beam 100 can be rotated about a stationary test element 300, 500.

The beam tails 120, 130 of the focused particle beam 100, which are persistently imaged into the upper plane 340, 540 of the height step 320, 360, 520, can be detected by scanning with a measuring probe of a scanning probe microscope (SPM), for example an atomic force microscope (AFM). Alternatively, and/or cumulatively, it is also possible to image the modified regions of the upper plane 340, 540 with the aid of an optical system in order to analyze the change of the test structure 390, 590 of the test element 300, 500. Moreover, the modified region of the upper plane 340, 540 of the height step 320, 360, 520 can be scanned using a detection beam. By way of example, the topographic change of the test structure 390, 590 can be analyzed with the aid of a CLSM (confocal laser scanning microscope). Moreover, the change caused by the chemical reaction of the test structure 390, 590 can be analyzed with the aid of a detection beam in the form of an electron beam, for example by virtue of the modified region being scanned using electrons with different kinetic energy. Further, it is possible to examine the material composition of the deposited material, for example by means of a SIMS (secondary ion mass spectrometry) apparatus.

Figure 6 illustrates a second exemplary embodiment for analyzing the beam tails 120, 130 of the focused particle beam too. The analysis of the beam tails 120, 130 is carried out on the basis of the test structure 390 of the test element 300. Unlike what was explained in the context of Figure 4, however, the focused particle beam too is not set on a fixed point with respect to the edge 330 of the test structure 390 but instead is scanned parallel to the edge 330. A precursor gas suitable for changing at least the upper plane 340 of the height step 320, 360 is provided while the focused particle beam too is scanned along the edge 330. By scanning the particle beam too, the area of the test structure 390 modified by the former is increased multiple times. Moreover, the topographic change of the upper plane 340 of the test structure 390 of the test element 300 caused by the combined effect of the beam tails 120 or 130 and the precursor gas can be amplified by the design of the scanning process. This simplifies the metrological detection of the topographic changes of the test structure 390. Scanning the focused particle beam 100 along the edge 330 is symbolized by the double-headed arrow 600 in Figure 6. As a result of scanning the focused particle beam 100, the main beam 110 thereof irradiates the rectangular area 610 which extends along the edge 330, either along the height step 320 or the height step 360 on the lower plane 350 of the height step 320, 360. When scanning along the edge 330 of the height step 320, the beam tail 120 is imaged in focus on the upper plane 340 of the height step 320 and the beam tail 120 irradiates the area 620. In combination with one or more precursor gases, the beam tail 120 modifies the area 620 of the upper plane 340 of the height step 320 of the test structure 390 when the focus 400 is scanned along the edge 330. The test structure 390 images the beam tail 130 of the focused particle beam 100 onto the lower plane 350 of the height step 320 away from the focus.

The areas 650, 660 and 670 in Figure 6 show scans 600 of the focused particle beam 100 along the edge 330 of the left height step 320. These scans 600 differ in terms of the distance of the intensity maximum I_o of the focused particle beam too from the edge 330 of the height step 320. Varying this distance allows the best possible separation of the effect of the main beam 110 from the effect of the beam tail 120 when carrying out a particle beam-induced etching or deposition process. The modification of the area 620 of the upper plane 340 of the height step 320 is analyzed for the purposes of determining the intensity distribution of the beam tail 120.

The areas 655, 665 and 675 in Figure 6 show scans 600 of the focused particle beam too along the edge 330 of the right height step 360. The intensity distribution of the beam tail 130 of the focused particle beam too can be determined from the modified areas 655, 665 and 665. These scans 600 differ in terms of the distance of the intensity maximum of the focused particle beam too from the edge 330 of the height step 360. Changing this distance allows the best possible separation of the effect of the main beam 110 from the effect of the beam tail 130 when carrying out a particle beam-induced etching or deposition process. Only the modification of the area 630 of the upper plane 340 of the height step 360 is analyzed for the purposes of determining the intensity distribution of the beam tail 130. Figure 7 presents the areas 750, 760 and 770, the changes of which are detected for the purposes of determining the intensity profile of the beam tail 120 of the focused particle beam 100. As may be gathered from Figure 7, parts of the upper plane 340 over which the beam tails 120, 130 did not sweep while the focused particle beam 100 was scanned are also measured in addition to the areas 620 and 630 of the upper plane 340 that were irradiated by the beam tails 120, 130. The measurement of said non-swept regions can be used to calibrate the measurement process. Moreover, the modification of the irradiated area 610 produced by the main beam 110 can likewise be used for calibration purposes. By way of example, detecting can be implemented by scanning the areas 750, 760 and 770 using a measuring probe of an AFM. The particle beam-induced changes of the surfaces 755, 765 and 775 can be detected for the purposes of determining the intensity distribution of the beam tail 130. It is self-evident that the above-described detection methods can likewise be used to this end.

Figure 8 schematically presents an evaluation method for the topographic changes in the areas 750, 755, 760, 765, 770, 775 of the upper plane 340 of the test structure 390 caused by the beam tails 120, 130. In this method, one-dimensional (i-D) profiles of the areas 620, 630 are summated along the edge 330, that is to say in the y-direction. The i-D profiles are elucidated in Figure 8 by the dotted lines 810, 840 and 870. For the scans 810 and 840, the parts 820 and 850 extend within the modified area 620, 630 of the upper plane 340 of the test structure 390. The changes of the test structure 390 are averaged over these parts. This is symbolized by the rectangle 800 in Figure 8. i-D scans are likewise averaged in the regions 830 and 860 of the scans 810 and 840 which are located outside of the modified area 620, 630. These mean values serve as a reference to which the mean values of the i-D scans 820 and 850 can be related. A further reference emerges from the averaged i-D scan 870, which extends completely outside of the modified area 620, 630 of the structure element 390. The intensity profile of the beam tails 120, 130 of the focused particle beam too can be reconstructed from the averaged i-D profiles 820, 850. The averaged i-D profiles 820, 850 can also be considered to be a convolution of the edge 330 with the point spread function (PSF) of the focused particle beam too.

Figure 9 once again shows the test element 500 with the test structure 590 from Figure

5. In a manner analogous to the description of Figure 6, the focused particle beam 100 is scanned along the four edges 530 of the test structure 590. In this case, the areas 950, 960, 970 and 980 are topographically modified by the combined effect of a precursor gas and the focused particle beam. The beam tails 120, 130 of the focused particle beam 100 are imaged in focus on the portions 955 and 975 of the irradiated areas 950, 975 of the upper plane 540. The two beam tails 125, 135 of the focused particle beam 100, which are perpendicular to the plane of the paper in Figure 1, are imaged by scanning along the horizontal edges 530 of the height step 520 on the portions 965 and 985 of the irradiated areas 960, 980 of the upper plane 540 of the height step 520. In correspondence with the beam tails 120, 130, the beam tails 125, 135 of the focused particle beam 100 which extend perpendicular to the plane of the paper may likewise be non- centrosymmetric. It is also possible for the beam tails 125, 135 to be symmetric with respect to the intensity maximum of the main beam 110.

Figure 10 reproduces Figure 9 with additional labelling of the areas 1050, 1060, 1070 and 1080 within which the changes are detected, for example by scanning with the measuring probe of a scanning probe microscope, in order to determine the changes in the areas 1050, 1060, 1070, 1080 of the upper plane 540 of the test structure 590 caused by irradiation with the beam tails 120, 125, 130, 135 in combination with a precursor gas. As already explained above, the areas 1050, 1060, 1070, 1080 comprise regions which were not irradiated by the beam tails 120, 125, 130, 135 during the scanning procedures along the edge. These regions 530 are used for calibration purposes. Then, the intensity distributions of the beam tails 120, 125, 130, 135 of the focused particle beam too are determined quantitatively from the measured changes of the areas 1050, 1060, 1070, 1080, as explained above in the context of Figure 8.

Figure 11 presents a schematic plan view of a third example of a test element in the upper partial image and the lower partial image shows a cross section through said test element. The test element 1100 from Figure 11 comprises a base element 1110 and a test structure 1190. The exemplary test element 1100 from Figure 11 comprises a substrate of a photomask, for instance a quartz substrate, as a base element 1110. A hard mask 1120 has been applied to the surface 1170 of the base element 1110. Byway of example, the hard mask 1120 can be deposited by way of a planar deposition of a chromium layer on the quartz substrate 1110. The thickness of the chromium layer, and hence the thickness of the hard mask 1120, may range between 1 nm and 500 nm. The hard mask 1120 has a top side 1115 and a back side 1125. Further, the hard mask 1120 has an opening 1180. The opening 1180 has an edge 1130, which surrounds the rectangular opening 1180 of the hard mask 1120, in the plane of the top side 1115, that is to say the upper plane 1140. Just like for the above-described test elements 300 and 500, it is advantageous for the test element 1100 if the edge 1130 forms an angle of 90° with the plane of the top side 1115 and the opening 1180. The opening 1180 of the hard mask 1120 can be implemented by etching the chromium layer. By way of example, ni- trosyl chloride (NOCI), optionally by way of the addition of an additive gas, can be used as etching gas. Etching is implemented through the entire thickness of the hard mask 1120. Hence, the opening 1180 of the hard mask 1100 defines a height step 1160 with an upper plane 1140, which is equivalent to the top side 1115 of the hard mask 1120, and a lower plane 1150, which corresponds to the back side 1125 of the hard mask 1120 or the top side 1170 of the base element 1110.

In the upper partial image, Figure 12 elucidates the exposure of the test element 1100 from Figure 11 with the focused particle beam 100 and the lower partial image elucidates the change of the test element 1100 caused by a beam tail 120, 130 of the focused particle beam too in the opening 1180 of the hard mask 1120 of the test element 1100 when an etching gas is provided at the same time. The particle beam too is directed at the top side 1115 of the hard mask 1120. This is illustrated by the beam waist 1200 in the lower partial image in Figure 12. Should the hard mask 1120 have only a small layer thickness which is smaller than the depth of field of the focused particle beam too, the focus of the latter can be related to both the top side 1115 and the lower side 1125 of the hard mask 1120. Preferably, the focus of the focused particle beam too is related to the top side 1170 of the substrate 1110 so that the beam tails 120, 125, 130, 135 thereof modify the substrate 1110 maximally.

In the xy-plane, that is to say in the plane of the paper, the focused particle beam too is directed at the hard mask 1120 in such a way that at least a part of a beam tail 120, 130 falls into the opening 1180 in said hard mask. A precursor gas in the form of an etching gas is provided in the region of the opening 1180 of the hard mask 1120 simultaneously with the particle beam too. Byway of example, xenon difluoride (XeF₂) can be used for etching the base element 1110 of the test element 1100. The lower partial image in Figure 12 shows the depression 1250 etched into the base element 1110 by the beam tail 120, 130 of the focused particle beam 100 in combination with the etching gas in the region of the opening 1180 of the hard mask 1120.

In the upper partial image, Figure 13 presents a plan view of the modified base element 1300 of the test element 1100 from Figure 11 following the removal of the hard mask 1120. The etching gas NOCI can be used, in combination with an additive gas, when necessary, for the purposes of removing the hard mask 1120 from the modified base element 1300 of the test element 1100. The base element 1110 has a depression 1250 in the region of the opening 1180 of the hard mask 1120. This depression 1250 can be measured, for instance by scanning with a measuring probe of a scanning probe microscope. The measurement data obtained can be used for quantitative determination of the intensity profile of the beam tail 120, 130 of the focused particle beam 100.

Analysis of the depression 1250 that arose by the local etching process in the opening 1180 can also be carried out without the prior removal of the hard mask 1120. By way of example, this maybe the case for very thin hard masks 1120. However, the metrological challenges are significantly larger in the case of thick hard masks 11200. Further, it is possible to remove only a small region of the hard mask 1120 around the opening 1180 by etching, said region being just so large that the measurement of the depression 1250 is not impaired by the hard mask 1120.

Figure 14 schematically illustrates a fourth exemplary embodiment of a test element 1400. The upper partial image reproduces a plan view of the test element 1400 and the lower partial image reproduces a cross section through the test element 1400. The base element 1410 corresponds to the base element 1110 of the test element 1100 from Figure 11. It is formed by a quartz substrate of a photomask. A hard mask 1420 has been attached to the base element 1410. Production, processing and removal of a hard mask 1420 have been explained above in the context of Figures 11 to 13. The hard mask 1420 from Figure 14 differs from the hard mask 1120 byway of eight openings 1480 in place of one opening 1180. The eight openings 1480 of the hard mask 1420 form the test structure 1490 of the test element 1400. Each of the eight openings 1480 of the hard mask 1420 has an edge 1430. On account of the larger area of the eight openings 1480 from Figure 14 in comparison with a single opening 1180 of the hard mask 1120 as in Figure 12, a significantly larger portion of the beam tails 120, 130 of the focused particle beam 100 can be imaged persistently into the base element 1410 of the test element 1400 with the aid of the hard mask 1420. Similar to Figure 12, the particle beam 100 is focused on the back side 1425 of the hard mask 1420 when the test element 1400 is irradiated.

Moreover - and unlike in Figure 12 - the focused particle beam 100 is scanned in the vertical direction along the line of symmetry of the hard mask 1420, as symbolized by the double-headed arrow 1450. As a result, the changes caused on the test element 1400 can be amplified, which may improve the accuracy in the detection thereof. However, it is also possible to direct the focused particle beam 100 on the average of the line of symmetry with fixed positioning.

The upper partial image in Figure 15 shows a plan view of the modified base element 1500 of the test element 1400 following the removal of the hard mask 1420 and the lower partial image reproduces the depressions 1510, 1520, 1530, 1540 which the beam tail 120 of the focused particle beam too has generated in the base element 1410 of the test element 1400 in conjunction with the etching gas XeF₂. The depressions 1550, 1560, 1570, 1580 represent the changes of the combined action of the beam tail 130 of the focused particle beam too with the etching gas XeF₂. The etching depths which decrease with increasing distance from the intensity maximum of the main beam 110 represent the intensity levels in the beam tails 120, 130 that become lower with increasing distance from the intensity peak I_o. The intensity distribution of the beam tails 120, 130 of the focused particle beam too can be determined on the basis of the measurement data obtained.

For more precise analysis of the beam tails 125, 135 of the focused particle beam too, the test structure 1400 can be rotated through 90° for the purposes of carrying out a scan of the focused particle beam too in the horizontal direction. From the measurement of the modified base element 1300 of the test element 1100, it is possible to determine the intensity profiles of the beam tails 125, 135 of the focused particle beam too. A further improvement in obtaining measurement data can be achieved by virtue of the openings of the hard mask 1420 being adapted to the symmetry of a particle beam. This means that maximally large parts of the beam tails 120, 125, 130, 135 can be imaged into a corresponding test element through openings of the hard mask 1420 in the form of concentric rings. However, a test element with a test structure in the form of concentric rings does not allow scanning of the focused particle beam. As a result, the degrees of freedom arising thereby for the purposes of increasing the changes of the test element 1100 cannot be rendered usable.

In the upper partial image, Figure 16 reproduces a plan view of a fifth test element 1600 and the lower partial image reproduces a cross section through the test element 1600 following the irradiation thereof by a focused particle beam too. The base element 1610 of the test element 1600 comprises a silicon wafer. A test structure 1690 in the form of a monolayer 1620 has been applied to the base element 1610. The monolayer 1620 has a top side 1615 and a back side 1625. The monolayer 1620 may comprise a self-assembled monolayer (SAM). A self-assembled monolayer 1620 has a layer of molecules which are arranged on the surface of the base element 1610 with a thickness or a layer height of one molecule.

The self-assembled monolayer 1620 may comprise a self-assembled organic compound. Examples of self-assembled organic compounds are alkanethiols or alkyltrichlorosilanes. The chain length of the molecules of the monolayer and the chemical functionalization of the chains are chosen in such a way that a particle beam-induced change of the molecules of the monolayer is achieved by the interaction with the SEs. The extent of the change caused in the monolayer is proportional to the acting electron dose. By way of example, the caused change of the molecules can be rendered visible using a scanning electron microscope as a change in the SE signal. The particle beam- induced change in the molecules of the monolayer is accompanied by a change in the work function for SEs from the surface of the monolayer. Alternatively, and/or cumulatively, the modified work function can be used for detecting the change in the mono- layer.

The molecules of the monolayer may have functional groups, for example a hydroxyl group, a carbonyl group, a carboxyl group, an amino group or a combination of these 6o functional groups. Alkanethiols with an alkane or carbon chain length of eight (CsHiySH) to fifteen carbon atoms (C15H31SH) are currently preferred. Monolayers with these chain lengths are particularly suitable for the analysis of the beam tails 120, 125, 130, 135 of focused electron beams 100. Further, this can be used to analyze the beam tails 120, 125, 130, 135 of photon beams from the DUV and EUV wavelength range of the electromagnetic spectrum.

The self-assembled layer 1620 forms spontaneously when the base element 1610 is immersed in a solution or a suspension. Should the base element 1610 of the test structure 1600 comprise a material which does not permit a spontaneous formation of self-assembled monolayers 1620, the base element 1610, for example a quartz substrate of a photomask, can be prepared by depositing a thin gold layer for the purposes of a spontaneous formation of a self-assembled monolayer 1620. Moreover, silicon dioxide can be functionalized with the aid of alkyltrichlorosilanes.

The upper partial image in Figure 16 illustrates the changes which are produced by a focused electron beam too in the self-assembled monolayer 1620. In the beam centre or in the main beam 110, the large number of electrons incident on the self-assembled monolayer 1620 generate damage in the self-assembled monolayer 1620 by breaking the molecule chains, for example the alkane chains. Additionally, the functional groups of the self-assembled monolayer 1620 may be chemically altered by irradiation with a focused particle beam too. This is elucidated in Figure 16 by the dark hue 1660. There are far fewer electrons in the region of the beam tails 120, 125, 130, 135 than in the main beam 110. However, the number of electrons in the beam tails 120, 125, 130, 135 is significantly greater than zero. Electrons of the beam tails 120, 125, 130, 135 generate a visible change or a change that can be rendered visible. The changes caused by the beam tails 120, 125, 130, 135 are elucidated by the greys 1670, 1675, 1680, 1685 in the upper partial image in Figure 16. The lower partial image in Figure 16 reproduces a cross section of the test element 1600 along the x-axis.

In a modification, the self-assembled layer 1620 is augmented with a structure which reduces or shields the intensive effect of the main beam 110 on the monolayer 1620. By way of example, the main beam 110 could be directed at a central absorbing layer, for instance a metal layer, for example a chromium layer, which is surrounded by a self-assembled layer 1620 on which the beam tails 120, 125, 130, 135 are incident. Alternatively, or in addition, the base element 1610 of the test structure 1600 could have a depression into which the main beam 110 falls, said depression substantially preventing the main beam 110 or the SEs of the main beam 110 from being able to modify the monolayer 1620. Moreover, it is possible to provide the test structures 300, 500, 1100, 1400 with a monolayer 1620 and to use the change of the monolayer 1620 caused by the beam tails 120, 125, 130, 135 for the purposes of determining the intensity profile of the beam tails 120, 125, 130, 135.

The changes generated by the focused electron beam too in the self-assembled mono- layer 1620 react sensitively to the SE contrast when imaging the damaged, self-assembled monolayer 1630 in a scanning electron beam. By scanning the modified or damaged areas 1660, 1670, 1675, 1680, 1685 of the self-assembled monolayer 1620 using a detection beam in the form of an electron beam, it is possible to render the local damage to the self-assembled monolayer 1620 visible. The extent of the local change of the self-organising monolayer 1620 is proportional to the beam intensity of the focused particle beam too acting locally on the monolayer 1620. Therefore, the intensity distribution in the beam tails 120, 125, 130, 135 can be determined quantitatively from the reproduction of the modified monolayer.

Figure 17 shows a schematic section through some important components of an example of an apparatus 1700, which can be used to determine an intensity distribution of one or more beam tails 120, 125, 130, 135 of a focused particle beam too. A sample 1705, for example in the form of a photolithographic mask, can be arranged on the sample stage 1702. The photomask can have one or more defects in the form of excess material (“dark defects”) and/or missing material (“clear defects”). The defect or defects of the photolithographic mask are not reproduced in Figure 17. The defect or generally defects of excess or missing material can be scanned and thus analyzed with the aid of a particle beam and/or with the aid of a measuring probe of a scanning probe microscope 1780. Further, defects can be corrected by means of a particle beam-induced processing process. For this purpose, the apparatus 1700 comprises a modified scanning particle microscope 1710 in the form of a scanning electron microscope (SEM) 1710. In the SEM 1710 from Figure 17, an electron gun 1712 produces an electron beam 1715 which is directed as a focused electron beam 1715 to the sample 1705 by the imaging elements, not illustrated in Figure 17, arranged in the electron column 1717. The sample 1705 is arranged on a sample stage 1702 or a sample mount 1702. A sample stage 1702 is also known as a "stage" in the art. As symbolized by the arrows in Figure 17, a positioning device 1707 can move the sample stage 1702 about six axes relative to the column 1717 of the SEM 1710. The movement of the sample stage 1702 by the positioning device 1707 can be effected with the aid of micro-manipulators, for example, which are not shown in Figure 17. Hence, the positioning system 1707 facilitates the analysis of defects of the sample 1702 by way of producing an image of the defect. For this purpose, the imaging elements of the column 1717 of the SEM 1710 can scan the electron beam 1715 over the sample 1705. By tilting and/or rotating the six- axis sample stage 1702, the latter makes it possible to examine one or more defects from different angles or perspectives. The respective position of the various axes of the sample stage 1702 can be measured by interferometry (not reproduced in Figure 17). The positioning system 1707 is controlled by signals of a setting unit 1725. The setting unit 1735 can be part of a computer system 1730 of the apparatus 1700.

Moreover, displacing the sample stage 1702 in the beam direction allows lowering of the sample stage 1702 such that a test element 1725 can be positioned under the electron beam 1715 and the measuring probe of the SPM 1780.

The apparatus 1700 can further comprise sensors that make it possible to characterize both a current state of the SEM 1710 and the process environment in which the SEM 1710 is used (for instance a vacuum environment).

The electron beam 1715 can further be used for inducing a particle beam-induced processing process for correcting identified defects for example in the context of an electron beam-induced etching EBIE process for removing dark defects and/or an electron beam-induced deposition EBID process for correcting clear defects. Moreover, the electron beam 1715 for analyzing a repaired site of the sample 1702 can be used in the apparatus 1700 in Figure 17. The apparatus 1700 comprises a holding apparatus 1722 for holding a test element 1725. The test element 1725 can comprise one of the above-described test elements 300, 500, 1100, 1400, 160. Further, the holding apparatus 1722 comprises a positioning unit 1727. The positioning unit 1727 facilitates the positioning of the test element 1725 under the electron beam 1715 and/or under the measuring probe of the SPM 1780. The electron beam 1715 can be the electron beam 100 that is used to irradiate the test element 1725 and whose beam tails 120, 125, 130, 135 are intended to be analyzed using the test element 1725. Further, the electron beam 1715 can be the electron beam 100 used to irradiate the test structure 1690 of the test element 1600. Moreover, the electron beam 1715 can be the detection beam used to analyze the changes of the test structure 1690 of the test element 1600.

The electrons backscattered from the electron beam 1715 by the sample 1705 or the test element 1725 and the secondary electrons produced by the electron beam 1715 in the sample 1705 or the test element 1725 are registered by the detector 1720. Should the test element 1725 comprises a portion of a photomask 110, the detector 1720 identifies secondary electrons (SEs) emitted when scanning the absorbing upper plane 340, 540 of the test element 300, 500. The detector 1720 arranged in the electron column 1717 is referred to as an "in lens detector". The detector 1720 can be installed in the column 1717 in various embodiments. The detector 420 is controlled by the setting unit 1735 of the computer system 1730 of the apparatus 1700.

The apparatus 1700 may contain a second detector 1721. The second detector 1721 is designed to detect electromagnetic radiation, particularly in the x-ray range. As a result, the second detector 1721 facilitates the analysis of the material composition of both the test element 1725 and the sample 1705. The detector 1721 is likewise controlled by the setting unit 1735.

The setting unit 1735 of the computer system 1730 can set the parameters of the electron beam 1715 for inducing a deposition process and an etching process on the test element 1725.

Further, the computer system 1730 of the apparatus 1700 may comprise a computing unit 1740. The computing unit 1740 receives the measurement data of the detector or detectors 1720, 1721. The computing unit 1740 can generate from the measurement data, for example from SE contrast data, images in a greyscale representation or a greyscale value representation, which can be represented on a monitor 1732. Moreover, the computer system 1730 comprises an interface 1737, by means of which the computer system 1730 or the computing unit 1740 is able to receive data in respect of the changes of the test element 1725 from further external detectors. Further, the computer system 1730 can transfer the measurement data from the detectors 1720 and/or 1721 to an external evaluation apparatus via the interface 1737. Moreover, the computer system 1730 of the apparatus 1700 can receive one or more processed or evaluated images and/or one or more overlaid images of the test element 1725 from the external evaluation apparatus.

As already explained above, the electron beam 1715 of the modified SEM 1710 of the apparatus 1700 can be used for inducing an electron beam-induced processing process. As likewise already explained above, the test element 1725 can be permanently modified from a topographic and/ or chemical point of view by means of an electron beam-induced exposure process. In order to carry out these processes, the exemplary scanning electron microscope 1710 of the apparatus 1700 in Figure 17 has three different supply containers 1750, 1760 and 1770.

The first supply container 1750 stores a first precursor gas in the form of a deposition gas, for example a metal carbonyl, for instance chromium hexacarbonyl (Cr(CO)6), or a carbon-containing precursor gas, such as pyrene, for instance. With the aid of the precursor gas stored in the first supply container 1750, material can be deposited on the sample 1705 or the test element 1725 in a local chemical reaction, with the electron beam 1715 of the SEM 1710 acting as an energy supplier in order to split the precursor gas stored in the first supply container 1750 preferably into chromium atoms and carbon monoxide molecules at the location at which material is intended to be deposited, i.e., on the upper plane 340, 540 of the test structure 390, 590 of the test element 1725. This means that an EBID process for permanently changing the test element 1725 is carried out by the combined provision of an electron beam 1715 and a precursor gas.

In the apparatus 1700 illustrated in Figure 17, the second supply container 1760 stores a precursor gas in the form of an etching gas, which makes it possible to perform a local electron beam-induced etching (EBIE) process. Depressions can be etched into the upper plane 340, 540 of the test element 1725 and/ or to the base element 1110, 1410 of the test element 1725 with the aid of an electron beam-induced etching process. A precursor gas in the form of an etching gas can comprise for example xenon difluoride (XeF₂), chlorine (Cl₂), oxygen (0₂), ozone (O₃), water vapour (H₂0), hydrogen peroxide (H₂0₂), dinitrogen monoxide (N₂0), nitrogen monoxide (NO), nitrogen dioxide (N0₂), nitric acid (HN0₃), nitrosyl chloride (NOCI), ammonia (NH₃) or sulfur hexafluoride (SF_(|) or a combination thereof.

An additive gas can be stored in the third supply container 1570, said additive gas, where necessary, being able to be added to the etching gas kept available in the second supply container 1760 or to the deposition gas stored in the first supply container 1750. Alternatively, the third supply container 1770 can store a precursor gas in the form of a second deposition gas or a second etching gas.

In the scanning electron microscope 1710 illustrated in Figure 17, each of the supply containers 1750, 1740 and 1770 has its own control valve 1752, 1762 and 1772 for monitoring or controlling the amount of the corresponding gas that is provided per unit time, i.e., the gas volumetric flow at the site of the incidence of the electron beam 1715 on the sample 1705 or the test element 1725. The control valves 1752, 1762 and 1772 are controlled and monitored by the setting unit 1735. By this means, it is possible to set the partial pressure conditions of the gas or gases provided at the processing location for carrying out an EBID and/or EBIE process in a wide range.

Furthermore, in the exemplary SEM 1710 from Figure 17, each supply container 1750, 1760 and 1770 has its own gas feedline system 1754, 1764 and 1774, which ends with a nozzle 1756, 1766 and 1776 in the vicinity of the point of incidence of the electron beam 1715 on the sample 1705 or the test element 1725.

The supply containers 1750, 1760 and 1770 can have their own temperature setting element and/ or control element, which allows both cooling and heating of the corresponding supply containers 1750, 1760 and 1770. This makes it possible to store and in particular provide the precursor gases of the deposition gas and/or the etching gas at the respectively optimum temperature (not shown in Figure 17). The setting unit 1735 can control the temperature setting elements and the temperature control elements of the supply containers 1750, 1760 and 1770. During the EBID and the EBIE processing processes, the temperature setting elements of the supply containers 1750, 1760 and 1770 can furthermore be used to set the vapour pressure of the process gas(es) stored therein byway of the selection of an appropriate temperature.

The apparatus 1700 can comprise more than one supply container 1750 in order to store precursor gases of two or more deposition gases. Furthermore, the apparatus 1700 can comprise more than one supply container 1760 for storing precursor gases of two or more etching gases.

The scanning electron microscope 1710 illustrated in Figure 17 can be operated under ambient conditions or in a vacuum chamber 1742. Implementing the EBID and EBIE processes necessitates a negative pressure in the vacuum chamber 1742 relative to the ambient pressure. For this purpose, the SEM 1710 in Figure 17 comprises a pump system 1744 for generating and for maintaining a negative pressure required in the vacuum chamber 1742. With closed control valves 1752, 1762 and 1772, a residual gas pressure of <io ⁴ Pa is achieved in the vacuum chamber 1742. The pump system 1744 can comprise separate pump systems for the upper part of the vacuum chamber 1742 for providing the electron beam 1715 of the SEM 1710 and for the lower part 1748 or the reaction chamber 1748 (not shown in Figure 17).

The SEM 1710 presented in the apparatus 1700 in Figure 17 has a single electron beam 1715. However, it is also possible for the SEM 1710 to have a source of a second particle beam. The second particle beam can comprise a photon beam and/or an ion beam (not shown in Figure 17). Furthermore, the SEM 1710 can have two or more electron beams 1715 in order to be able to carry out in parallel two or more particle beam-induced processing processes or two or more measuring processes.

Additionally, the exemplary apparatus 1700 illustrated in Figure 17 comprises a scanning probe microscope (SPM) 1780 which, in the apparatus 1700, is embodied in the form of a scanning force microscope (SFM) 1780 or an atomic force microscope (AFM) 480. The SPM 1780 can be used to scan a permanently modified test element 1725. Moreover, the SPM 1780 can be used for repairing the sample 1705. To this end, the SPM 1780 may comprise a first measuring probe for analyzing the test element 1725 and/or the sample 1706, and a second measuring probe for processing the sample 1705.

Only the measuring head 1785 of the SPM 1780 is illustrated in the apparatus 1700 in Figure 17. In the example in Figure 17, the measuring head 1785 comprises a holding unit 1787. The measuring head 1785 is fastened to the frame of the apparatus 1700 by means of the holding unit 1787 (not shown in Figure 17). A piezo-actuator 1790 which enables a movement of the free end of the piezo-actuator in three spatial directions (not illustrated in Figure 17) is attached to the holding unit 1787 of the measuring head 1785. A probe 1795 or a measuring probe 1795 comprising a cantilever 1794 or lever arm 1794 and a measuring tip 1792 is secured to the free end of the piezo-actuator 1790. The free end of the cantilever 1794 of the measuring probe 1795 has the measuring tip 1792. The SPM 1780 consequently realizes a measuring unit 1780 designed to measure a change, more particularly a topographic change, of a test element 1725.

The setting unit 1735 of the computer system 1730 can move the holding unit 1787 of the measuring head 1785 of the AFM 1780. It is furthermore possible for the setting unit 1735 to perform a coarse positioning of the sample 1705 or the test element 1725 in height (z-direction) and for the piezo-actuator 1790 of the measuring head 1785 to perform a precise height setting of the AFM 1780.

In the apparatus 1700, the SPM 1780 can alternatively or additionally be used for scanning the sample 1705. The apparatus 1700 can use two or more SPMs 1780. The SPMs 1780 can be of the same type or can be realized as different types of SPM.

In the example illustrated in Figure 17, the SPM 1780 is integrated into the apparatus 1700 and is controlled by the computer system 1730 of the apparatus 1700. It is also possible for the SPM 1780 to be embodied as an independent unit (not shown in Figure 17).

The computing unit 1740 of the computer system 1730 of the apparatus 1700 may have algorithms designed to determine the intensity profile of the beam tails 120, 125, 130, 135 of the focused particle beam 1715 from the measurement data of the SPM 1780. The algorithms can be realized as hardware, software, firmware or a combination thereof. Finally, the flowchart 1800 of Figure 18 summarizes once again essential steps of the described method for determining an intensity distribution of one or more beam tails 120, 125, 130, 135 of a focused particle beam 100. The method begins in step 1810. In the next step 1820, a test element 300, 500, 1100, 1400, 1600 is irradiated with the focused particle beam 100 such that the at least one beam tail 120, 125, 130, 135 of the focused particle beam 100 causes a measurable change 620, 955, 1250, 1540 of the test element 300, 500, 1100, 1400, 1600.

In step 1830, the change 620, 955, 1250, 1540 of the test element 300, 500, 1100, 1400, 1600 is measured for the purposes of determining the intensity distribution of the at least one beam tail 120, 125, 130, 135 of the focused particle beam 100. The method ends in step 1840.

In the following further embodiments are described to facilitate the understanding of the invention:

1. A method (1800) for determining an intensity distribution of at least one beam tail (120, 125, 130, 135) of a focused particle beam (100), the method (1800) comprising the steps of: a. irradiating (1820) a test element (300, 500, 1100, 1400, 1600) with the focused particle beam (100) such that the at least one beam tail (120,

125. 130. 135) of the focused particle beam (100) causes at least one measurable change (620, 955, 1250, 1540, 1670) of the test element (300, 500, 1100, 1400, 1600); and b. measuring (1830) the at least one change (620, 955, 1250, 1540, 1670) of the test element (300, 500, 1100, 1400, 1600) for the purposes of determining the intensity distribution of the at least one beam tail (120, 125,

130. 135) of the focused particle beam (100).

2. The method (1800) of embodiment 1, wherein the irradiation of the test element (300, 500, 1100, 1400, 1600) causes at least one topographic change (620, 955, 1250, 1540), at least one chemical change (1660, 1670, 1675, 1680, 1685) and/or at least one physical change of the test element (300, 500, 1100, 1400, 1600).

3. A method (1800) of embodiment 1 or 2, wherein the test element (300, 500, 1100, 1400, 1600) comprises at least one test structure (390, 590, 1190, 1490, 1690) which comprises at least one element from the group: at least one height step (320, 360, 520), at least one hard mask (1120, 1420) with at least one opening (1180, 1480), and at least one monolayer (1620). The method (1800) of embodiment 3, wherein the at least one height step (320, 360, 520) and/or the at least one opening (1180, 1480) comprises at least one edge (330, 530, 1130, 1430), and/or wherein the monolayer (1620) is designed to change a secondary electron contrast when irradiated with the focused particle beam (100). The method (1800) of embodiment 3 or 4, further comprising: setting a height (380) of the at least one height step (320, 360, 520) and/or a thickness of the hard mask (1120, 1420) such that a beam area of the focused particle beam (100) increases along the height (380) by at least 2%, preferably 5%, more preferably 10%, and most preferably 30% in relation to the beam waist (400) of the focused particle beam (100). The method (1800) of embodiments 3-5, wherein irradiating the test element (300, 500, 1100, 1400, 1600) comprises: focusing the particle beam (100) on at least one element from the group: an upper plane (340, 540) of the at least one height step (320, 360, 520) and/or a back side (1125) of the hard mask (1120, 1420), a lower plane (350, 550) of the at least one height step (320, 360, 520) and/or a top side (1115) of the hard mask (1120, 1420), a top side (1615) of the monolayer (1620). The method (1800) of any of embodiments 3-6, wherein irradiating the test element (300, 500, 1100, 1400, 1600) comprises at least one element from the group: irradiating at least one point of a lower plane (350, 550) of the at least one height step (320, 360, 520) with the focused particle beam (too) such that the at least one beam tail (120, 125, 130, 135) is incident on an upper plane (350, 550) of the at least one height step (320, 360, 520), scanning the focused particle beam (too) along the at least one edge (330, 530, 1130, 1430) of the at least one height step (320, 360, 520) such that the at least one beam tail (120, 125, 130, 135) of the focused particle beam (too) is incident on the upper plane (350, 550) of the at least one height step (320, 360, 520), irradiating at least one point of the hard mask (1120, 1420) with the focused particle beam (100) such that at least a part of the at least one beam tail (120, 125, 130, 135) is incident on the at least one opening (1180, 1480) of the hard mask (1120, 1420), scanning the focused particle beam (100) parallel to the at least one edge (330, 530, 1130, 1430) of the at least one opening (1180, 1480) of the hard mask (1120, 1420) such that at least one part of the at least one beam tail (120, 125, 130, 135) is incident on the at least one opening (1180, 1480) of the hard mask (1120, 1420), irradiating at least one point of the monolayer (1620). The method (1800) of any of embodiments 3-7, wherein irradiating the test element (300, 500, 1100, 1400, 1600) comprises at least one element from the group: choosing a distance between an intensity maximum of the focused particle beam (100) and the at least one edge (330, 530; 1130, 1430) of the at least one height step (320, 360, 520) such that substantially no particles that are produced by the focused particle beam (too) in the lower plane (350, 550) of the at least one height step (320, 350, 520) reach the upper plane (350, 550) of the at least one height step (320, 260, 520), choosing a distance between the intensity maximum of the focused particle beam (too) and the at least one edge (330, 530, 1130, 1430) of the at least one opening (1180, 1480) of the hard mask (1120, 1420) such that substantially no particles that are produced by the focused particle beam (too) of the hard mask (1120, 1420) reach into the at least one opening (1180, 1480), choosing an energy of the focused particle beam (too) such that substantially no particles of the focused particle beam (too) reach a back side (1625) of the monolayer (1620). The method (1800) of any of embodiments, wherein irradiating the test element (300, 500, 1100, 1400, 1600) comprises: scanning the focused particle beam (too) along the at least one edge (330, 530, 1130, 1430) of at least two height steps (320, 360, 520) in at least two different distances between an intensity maximum of the focused particle beam (100) and the at least one edge (330, 530, 1130, 1430) of the at least two height steps (320, 360, 520). The method (1800) of any of embodiments 1-9, wherein irradiating the test element (300, 500, 1100, 1400, 1600) comprises: providing at least one precursor gas in a region of the at least one beam tail (120, 125, 130, 135) of the focused particle beam (100). The method (1800) of embodiment 10, wherein the at least one precursor gas comprises at least one element from the group: at least one etching gas, at least one deposition gas and at least one additive gas. The method (1800) of any of embodiments 1-11, wherein measuring the at least one change of the test element (300, 500, 1100, 1400, 1600) comprises at least one element from the group: scanning at least the area (620, 955) of the test element (300, 500, 1100,

1400, 1600) covered by the at least one beam tail (120, 125, 130, 135) of the focused particle beam (100) using a measuring probe (1795) of a scanning probe microscope (1780), scanning at least the area (520, 955) of the test element (300, 500, 1100,

1400, 1600) covered by the at least one beam tail (120, 125, 130, 135) of the focused particle beam (too) using a detection beam and analyzing the particles produced by the detection beam, imaging at least the area (620, 955) of the test element (300, 500, 1100,

1400, 1600) covered by the at least one beam tail (120, 125, 130, 135) of the focused particle beam (too) using an optical system, preparing at least a part of the area (620, 955, 1250, 1540) of the test element (300, 500, 1100, 1400, 1600) covered by the at least one beam tail (120, 125, 130, 135) of the focused particle beam (too) and imaging the prepared part of the test element (300, 500, 1100, 1400, 1600) using an electron beam of a transmission electron microscope. The method (1800) of any of embodiments 1-12, wherein measuring the at least one change (620, 955) of the test structure (300, 500, 1100, 1400, 1600) comprises: scanning at least the area of the monolayer (1620) covered by the beam tail (120, 125, 130, 135, 135) of the focused particle beam (100) using a detection beam and detecting a secondary electron contrast in at least the area covered by the focused particle beam (100). The method (1800) of any of embodiments 3-13, wherein the at least one mono- layer (1620) comprises a self-assembled organic compound. The method (1800) of embodiment 14, wherein the test element (300, 500, 1100, 1400, 1600) comprises at least one layer made of an element from the group: gold (Au), silver (Ag), platinum (Pt), copper (Cu), graphite (C) and silicon (Si). A computer program containing instructions that prompt a computer system to carry out the method steps of any of embodiments 1 to 15 when the computer program is executed by the computer system. An apparatus (1700) for determining an intensity distribution of at least one beam tail (120, 125, 130, 135) of a focused particle beam (100), comprising: a. a setting unit (1735) configured to set at least one parameter of the focused particle beam (too) such that when a test element (300, 500, 1100, 1400, 1600) is irradiated by the focused particle beam (too) the focused particle beam (too) causes at least one measurable change (620, 955, 1250, 1540, 1670) of the test element (300, 500, 1100, 1400, 1600); and b. a measuring unit (1780) configured to measure the at least one change (620, 955, 1250, 1540, 1670) of the test element (300, 500, 1100, 1400, 1600) for the purposes of determining the intensity distribution of the at least one beam tail (120, 125, 130, 135) of the focused particle beam (too). The apparatus (1700) of embodiment 17, further comprising a holding apparatus (1722) for the test element (300, 500, 1100, 1400, 1600). The apparatus (1700) of embodiment 18, wherein the holding apparatus (1722) comprises a positioning unit (1727) configured to position the test element (300, 500, 1100, 1400, 1600) under the focused particle beam (100) and/or under the measuring unit (1780). The apparatus (1700) of any of embodiments 17-19, further comprising a computing unit (1740) configured to determine the intensity distribution of the at least one beam tail (120, 125, 130, 135) of the focused particle beam (100) from the measured change (620, 955, 1250, 1540, 1670) of the test element (300, 500, 1100, 1400, 1600).

Claims

75

Claims A method for determining an intensity distribution of a particle beam on a sample, the method comprising the steps: a. irradiating a test element with the particle beam such that the particle beam causes at least one measurable change of the test element; and b. measuring the at least one change of the test element for determining the intensity distribution of the particle beam on the sample. The method of claim 1, wherein the particle beam is a focused particle beam and determining the intensity distribution comprises determining an intensity distribution of at least one beam tail of the focused particle beam by irradiating (1820) the test element (300, 500, 1100, 1400, 1600) with the focused particle beam (100) such that the at least one beam tail (120, 125, 130, 135) of the focused particle beam (100) causes at least one measurable change (620, 955, 1250, 1540, 1670) of the test element (300, 500, 1100, 1400, 1600); and measuring (1830) the at least one change (620, 955, 1250, 1540, 1670) of the test element (300, 500, 1100, 1400, 1600) for determining the intensity distribution of the at least one beam tail (120, 125, 130, 135) of the focused particle beam (too). The method of claim 1, wherein the particle beam irradiates the sample through at least one precursor gas and determining the intensity distribution comprises determining a change of the intensity distribution caused by the at least one precursor gas on the sample. 76 The method of any of claims 1-3, wherein the particle beam irradiates the sample through a shielding element and determining the intensity distribution comprises determining a change of the intensity distribution on the sample caused by the shielding element. The method of claim 4, wherein the shielding element performs at least one of: redistributing scattered beam particles passing the shielding element in beam direction and generating secondary particles. A method for determining a spontaneous etching rate and/or a spontaneous deposition rate of at least one precursor gas used in a particle beam induced etching process and/or in a particle beam induced deposition process of a sample, the method comprises the steps: a. providing the at least one precursor gas with a predetermined gas flow rate on a test element for a predetermined period without irradiating the test element with a particle beam; and b. measuring the at least one change of the test element for determining the spontaneous etching rate and/or the spontaneous deposition rate of the at least one precursor gas on the sample. The method of claim 6, further comprising varying at least one of: the gas flow rate, a composition of the at least one precursor gas, and a temperature of the at least one precursor gas; and repeating step a. The method according to any of claims 1-7, wherein the test element comprises a base element and at least one structure element, wherein the at least one structure element is preferably arranged on the base element. The method of the preceding claim, wherein the structure element comprises a first material and the base element comprises a second material, wherein the first material is different from the second material. 77 The method of the preceding claim, wherein a spontaneous etching rate of the first material induced by the at least one precursor gas differs from a spontaneous etching rate of the second material of the test element by at least a factor of 2, preferably by at least a factor of 5, more preferably by at least a factor of 10, and most preferably by at least a factor of 20. The method of any of claims 1-10, wherein the at least one structure element comprises at least one of: a checkerboard pattern, an aperture mask having at least one opening, at least one pillar, and a randomized structure. The method of the preceding claim, wherein the randomized structure comprises gold particles on a carbon layer. The method of any of claims 1-12, wherein measuring the at least one change of the test element comprises at least one of: measuring a change of an edge of the test element and measuring a change across an area of the test element. The method (1800) according to any of claims 1-5 or 8-13, directly or indirectly referred back to claim 1, wherein the irradiation of the test element (300, 500, 1100, 1400, 1600) causes at least one topographic change (620, 955? 1250, 1540), at least one chemical change (1660, 1670, 1675, 1680, 1685) and/or at least one physical change of the test element (300, 500, 1100, 1400, 1600). The method (1800) according to any of claims 1-14, wherein the test element (300, 500, 1100, 1400, 1600) has at least one test structure (390, 590, 1190, 1490, 1690) which comprises at least one element from the group: at least one height step (320, 360, 520), at least one hard mask (1120, 1420) with at least one opening (1180, 1480), and at least one monolayer (1620). 78 The method (1800) according to the preceding claim, wherein the at least one height step (320, 360, 520) and/or the at least one opening (1180, 1480) has at least one edge (330, 530, 1130, 1430), and/or wherein the monolayer (1620) is designed to change a secondary electron contrast when irradiated with the focused particle beam (100). The method (1800) according to claim 15 or 16, further including: setting a height (380) of the at least one height step (320, 360, 520) and/or a thickness of the hard mask (1120, 1420) such that a beam area of the focused particle beam (100) increases along the height (380) by at least 2%, preferably 5%, more preferably 10%, and most preferably 30% in relation to the beam waist (400) of the focused particle beam (100). The method (1800) according to any of claims 15-17, wherein irradiating the test element (300, 500, 1100, 1400, 1600) comprises: focusing the particle beam (100) on at least one element from the group: an upper plane (340, 540) of the at least one height step (320, 360, 520) and/or a back side (1125) of the hard mask (1120, 1420), a lower plane (350, 550) of the at least one height step (320, 360, 520) and/or a top side (1115) of the hard mask (1120, 1420), a top side (1615) of the monolayer (1620). The method (1800) according to any of claims 15-18, wherein irradiating the test element (300, 500, 1100, 1400, 1600) comprises at least one element from the group: irradiating at least one point of a lower plane (350, 550) of the at least one height step (320, 360, 520) with the focused particle beam (100) such that the at least one beam tail (120, 125, 130, 135) is incident on an upper plane (350, 550) of the at least one height step (320, 360, 520), scanning the focused particle beam (100) along the at least one edge (330, 530, 1130, 1430) of the at least one height step (320, 360, 520) such that the at least one beam tail (120, 125, 130, 135) of the focused 79 particle beam (100) is incident on the upper plane (350, 550) of the at least one height step (320, 360, 520), irradiating at least one point of the hard mask (1120, 1420) with the focused particle beam (100) such that at least a part of the at least one beam tail (120, 125, 130, 135) is incident on the at least one opening (1180, 1480) in the hard mask (1120, 1420), scanning the focused particle beam (100) parallel to the at least one edge (330, 530, 1130, 1430) of the at least one opening (1180, 1480) in the hard mask (1120, 1420) such that at least one part of the at least one beam tail (120, 125, 130, 135) is incident on the at least one opening (1180, 1480) in the hard mask (1120, 1420), irradiating at least one point of the monolayer (1620). The method (1800) according to any of claims 15-19, wherein irradiating the test element (300, 500, 1100, 1400, 1600) comprises at least one element from the group: choosing a distance between an intensity maximum of the focused particle beam (100) and the at least one edge (330, 530, 1130, 1430) of the at least one height step (320, 360, 520) such that substantially no particles that are produced by the focused particle beam (100) in the lower plane (350, 550) of the at least one height step (320, 350, 520) reach the upper plane (350, 550) of the at least one height step (320, 260, 520), choosing a distance between the intensity maximum of the focused particle beam (100) and the at least one edge (330, 530, 1130, 1430) of the at least one opening (1180, 1480) in the hard mask (1120, 1420) such that substantially no particles that are produced by the focused particle beam (100) in the hard mask (1120, 1420) reach into the at least one opening (1180, 1480), choosing an energy of the focused particle beam (100) such that substantially no particles of the focused particle beam (100) reach a back side (1625) of the monolayer (1620). 80 The method (1800) according to any of claims 15-20, wherein irradiating the test element (300, 500, 1100, 1400, 1600) comprises: scanning the focused particle beam (100) along the at least one edge (330, 530, 1130, 1430) of at least two height steps (320, 360, 520) in at least two different distances between an intensity maximum of the focused particle beam (100) and the at least one edge (330, 530, 1130, 1430) of the at least two height steps (320, 360, 520). The method (1800) according to claim 2 or any of claims 3-5 or 8-21, directly or indirectly referred back to claim 2, wherein irradiating the test element (300, 500, 1100, 1400, 1600) comprises at least one of: providing at least one precursor gas in a region of the particle beam and providing at least one precursor gas in a region of the at least one beam tail (120, 125, 130, 135) of the focused particle beam (100). The method (1800) according to the preceding claim, wherein the at least one precursor gas comprises at least one element from the group: at least one etching gas, at least one deposition gas and at least one additive gas. The method (1800) according to any of claims 1-23, wherein measuring the at least one change of the test element (300, 500, 1100, 1400, 1600) comprises at least one element from the group: scanning at least the area of the test element covered by the particle beam using a measuring probe (1795) of a scanning probe microscope (1780), scanning at least the area (620, 955) of the test element (300, 500, 1100, 1400, 1600) covered by the at least one beam tail (120, 125, 130, 135) of the focused particle beam (too) using a measuring probe (1795) of a scanning probe microscope (1780), scanning at least the area of the test element covered by the particle beam using a detection beam and analyzing the particles produced by the detection beam, scanning at least the area (520, 955) of the test element (300, 500, 1100, 1400, 1600) covered by the at least one beam tail (120, 125, 130, 81

135) of the focused particle beam (100) using a detection beam and analyzing the particles produced by the detection beam, imaging at least the area of the test element covered by the particle beam using an optical system, imaging at least the area (620, 955) of the test element (300, 500, 1100,

1400. 1600) covered by the at least one beam tail (120, 125, 130, 135) of the focused particle beam (100) using an optical system, preparing at least a part of the area (620, 955, 1250, 1540) of the test element (300, 500, 1100, 1400, 1600) covered by the particle beam or the at least one beam tail (120, 125, 130, 135) of the focused particle beam (100) and imaging the prepared part of the test element (300,

500. 1100. 1400. 1600) using an electron beam of a transmission electron microscope. The method according to any of claims 1-24, wherein measuring the at least one change of the test element comprises at least one element from the group: scanning an area of 0.01 cm², preferred 0.1 cm², more preferred 1 cm², and most preferred 5 cm² of the test element covered by 2 x 2, preferred 5 x 5, more preferred 10 x 10, and most preferred 20 x 20 measuring points using a measuring probe (2795) of a scanning probe microscope (1780), scanning an area of 0.01 cm², preferred 0.1 cm², more preferred 1 cm², and most preferred 5 cm² of the test element covered by 2 x 2, preferred 5 x 5, more preferred 10 x 10, and most preferred 20 x 20 measuring points using a detection beam, imaging an area of 0.01 cm², preferred 0.1 cm², more preferred 1 cm², and most preferred 5 cm² of the test element covered by 2 x 2, preferred 5 x 5, more preferred 10 x 10, and most preferred 20 x 20 measuring points using an optical system. The method (1800) according to any of claims 1-25, wherein measuring the at least one change (620, 955) of the test structure (300, 500, 1100, 1400, 1600) comprises: scanning at least the area of the monolayer (1620) covered by at least one of: the particle beam, the beam tail (120, 125, 130, 135) of the focused particle beam (100) and the at least one precursor gas using a detection beam and detecting a secondary electron contrast in at least the covered area. The method (1800) according to any of claims 15-20, or claims 21-26 directly or indirectly referred back to claim 15, wherein the at least one mono- layer (1620) comprises a self-assembled organic compound. The method (1800) according to the preceding claim, wherein the test element (300, 500, 1100, 1400, 1600) comprises at least one layer comprising at least one element of the group of: gold (Au), silver (Ag), platinum (Pt), copper (Cu), graphite (C) and silicon (Si). The method of any of claims 8-10, or 11-28 directly or indirectly referred back to claim 8, wherein the base element is adapted such that a particle beam induced etching process does essentially not etch the base element of the test structure and the at least one structure element of the test structure comprises at least one pillar to be etched in the particle beam induced etching process. The method of any of claims 8-10, or 11-29 directly or indirectly referred back to claim 8, wherein the structure element comprises at least two pillars adapted such that a particle beam induced etching process does essentially not etch the at least two pillars and the base element comprises a material to be etched in the particle beam induced etching process. The method of any of claims 8-10, or 11-29 directly or indirectly referred back to claim 8, wherein the at least one structure element comprises at least one aperture mask adapted such that a particle beam induced etching process does essentially not etch the at least one aperture mask and the base element is adapted such that the particle beam induced etching process etches the base element. The method of the preceding claim, wherein the aperture mask comprises at least two openings for determining a variation of the base element. Computer program containing instructions that prompt a computer system to carry out the method steps of any one of claims 1 to 32 when the computer program is executed by the computer system. An apparatus for determining an intensity distribution of a particle beam on a sample, comprising: a. means for irradiating a test element with the particle beam such that the particle beam causes at least one measurable change of the test element; and b. means for measuring the at least one change of the test element for determining the intensity distribution of the particle beam on the sample. The apparatus of claim 34, further comprising means for focusing the particle beam. The apparatus of claim 34 or 35, further comprising means for providing at least one precursor gas on the sample and/ or the test element. The apparatus of claim 36, wherein the means for providing the at least one precursor gas comprises means for setting a gas flow rate of the at least one precursor gas. The apparatus of any of claims 34-37, further comprising means for measuring the at least one change of the test element. 84 The apparatus of any of claims 34-38, further comprising means for determining the intensity distribution of the particle beam from the at least one measured change of the test element. An apparatus (1700) for determining an intensity distribution of at least one beam tail (120, 125, 130, 135) of a focused particle beam (100), comprising: a. a setting unit (1735) configured to set at least one parameter of the focused particle beam (100) such that when a test element (300,

500. 1100. 1400. 1600) is irradiated by the focused particle beam (100) the focused particle beam (100) causes at least one measurable change (620, 955, 1250, 1540, 1670) of the test element (300,

500. 1100. 1400. 1600); and b. a measuring unit (1780) configured to measure the at least one change (620, 955, 1250, 1540, 1670) of the test element (300, 500,

1100. 1400. 1600) for determining the intensity distribution of the at least one beam tail (120, 125, 130, 135) of the focused particle beam (100). The apparatus (1700) according to the preceding claim, further comprising a holding apparatus (1722) for the test element (300, 500, 1100, 1400, 1600). The apparatus (1700) according to the preceding claim, wherein the holding apparatus (1722) comprises a positioning unit (1727) configured to position the test element (300, 500, 1100, 1400, 1600) under the focused particle beam (too) and/or under the measuring unit (1780). The apparatus (1700) according to any of claims 40-42, further comprising a computing unit (1740) configured to determine the intensity distribution of the at least one beam tail (120, 125, 130, 135) of the focused particle 85 beam (100) from the measured change (620, 955, 1250, 1540, 1670) of the test element (300, 500, 1100, 1400, 1600).