METHOD FOR OPERATING A PARTICLE BEAM MICROSCOPE, PARTICLE BEAM MICROSCOPE AND COMPUTER PROGRAM PRODUCT

Abstract

A method for operating a particle beam microscope comprises scanning an object using a particle beam and detecting electrons and x-ray radiation when scanning an object using a particle beam. Improved x-ray radiation information can be generated by combining weighted x-ray radiation information items according to the formula

[00001]$S_e\left({\stackrel{.fwdarw.}{r}}_i\right)=\underset{j}{.Math.}w\left(i,j\right).Math.S\left({\stackrel{.fwdarw.}{r}}_j\right),$

wherein S({right arrow over (r)}.sub.i) is the detected x-ray radiation intensity assigned to a location {right arrow over (r)}.sub.i. The following holds true for the weights, for example:

[00002]$w\left(i,j\right)=e^{-{\left({\stackrel{.fwdarw.}{r}}_i-{\stackrel{.fwdarw.}{r}}_j\right)}^2/{\sigma }_f^2}.Math.e^{-{\left(I\left({\stackrel{.fwdarw.}{r}}_i\right)-I\left({\stackrel{.fwdarw.}{r}}_j\right)\right)}^2/{\sigma }_g^2},$

wherein I({right arrow over (r)}) represents the intensity of the detected electrons that is assigned to the location {right arrow over (r)}, and σ.sub.f and σ.sub.g are constants.

Claims

1. A method of operating a particle beam microscope, the method comprising: directing a particle beam onto a multiplicity of locations of an object; for each given location of the multiplicity of locations: storing location information ({right arrow over (r)}) representing the given location onto which the particle beam is directed; detecting electrons generated by the particle beam directed onto the given location; storing electron radiation information representing an intensity of the detected electrons, with assignment to the location information ({right arrow over (r)}); detecting x-ray radiation generated by the particle beam directed onto the given location; and storing x-ray radiation information representing an intensity of the detected x-ray radiation, with assignment to the location information ({right arrow over (r)}); and for a plurality of given locations ({right arrow over (r)}) of the multiplicity of locations: generating improved x-ray radiation information (S.sub.e({right arrow over (r)}.sub.i); and storing the improved x-ray radiation information (S.sub.e({right arrow over (r)}.sub.i)) with assignment to the location information representing the given location ({right arrow over (r)}.sub.i) generating the improved x-ray radiation information (S.sub.e({right arrow over (r)}.sub.i)) comprising combining a plurality of weighted x-ray radiation information items (S({right arrow over (r)}.sub.j)), wherein the following holds true in each case for the weights (w(i, j)) of the x-ray radiation information items that are used in the combining: the weight (w(i, j)) decreases with a distance between the given location ( {right arrow over (r)}.sub.i) and the location ({right arrow over (r)}.sub.j) represented by the location information to which the weighted x-ray radiation information is assigned; and the weight decreases with an absolute value of a difference between the intensity represented by the electron radiation information assigned to the location information representing the given location ({right arrow over (r)}.sub.i) and the intensity represented by the electron radiation information assigned to the location information ({right arrow over (r)}.sub.j) to which the weighted x-ray radiation information is also assigned.

2. The method of claim 1, further comprising generating a representation of the improved x-ray radiation information items (S.sub.e({right arrow over (r)}.sub.i) assigned to the multiplicity of locations.

3. The method of claim 2, further comprising classifying the improved x-ray radiation information items assigned to the multiplicity of locations into a plurality of groups, wherein: pairs of x-ray radiation information items assigned to the same group are more similar to one another in accordance with a predetermined similarity criterion than pairs of x-ray radiation information items assigned to different groups; in the representation x-ray radiation information items assigned to the same group are each represented with the same representation feature; and in the representation x-ray radiation information items assigned to different groups are represented with different representation features.

4. The method of claim 3, wherein the representation features comprise a brightness, a colour and/or a colour saturation.

5. The method of claim 1, wherein the x-ray radiation information assigned to one of the location information items represents an energy spectrum.

6. The method of claim 5, wherein detecting the x-ray radiation comprises reading an energy-dispersive x-ray detector (29).

7. The method of claim 1, wherein detecting the electrons comprises reading an electron detector.

8. The method of claim 7, wherein the electron detector is a backscattered electron detector.

9. The method of claim 1, wherein combining the plurality of weighted x-ray radiation information items comprises adding weighted intensity values of detected x-ray radiation intensities.

10. The method of claim 1, wherein: the improved x-ray radiation information is determined according to the following equation: $S_e\left({\stackrel{.fwdarw.}{r}}_i\right)=\underset{j}{.Math.}w\left(i,j\right).Math.S\left({\stackrel{.fwdarw.}{r}}_j\right);$ S.sub.e({right arrow over (r)}.sub.i) represents the improved x-ray radiation intensity assigned to the given location {right arrow over (r)}.sub.i; S({right arrow over (r)}.sub.j) represents the x-ray radiation intensity assigned to the location ({right arrow over (r)}.sub.j) and w(i, j) represents the weight.

11. The method of claim 10, wherein:
w(i, j)=f(|{right arrow over (r)}.sub.i−{right arrow over (r)}.sub.j|).Math.g(|I({right arrow over (r)}.sub.i)−I({right arrow over (r)}.sub.j)|); I({right arrow over (r)}) represents the intensity of the detected electrons that is assigned to the location {right arrow over (r)}; f(|{right arrow over (r)}.sub.i−{right arrow over (r)}.sub.j|) is a function which decreases with the distance between the locations {right arrow over (r)}.sub.iand {right arrow over (r)}.sub.j; and g(|I({right arrow over (r)}.sub.i)−I({right arrow over (r)}.sub.j)|) is a function which decreases with the absolute value of the difference between the intensities of the detected electrons.

12. The method of claim 11, wherein $f\left(.Math.{\stackrel{.fwdarw.}{r}}_i-{\stackrel{.fwdarw.}{r}}_j.Math.\right)=\frac{1}{C_f}{e}^{-{\left({\stackrel{.fwdarw.}{r}}_i-{\stackrel{.fwdarw.}{r}}_j\right)}^2/{\sigma }_f^2},$ and C.sub.f and σ.sub.f are parameters.

13. The method of claim 12, wherein $g\left(.Math.I\left({\stackrel{.fwdarw.}{r}}_i\right)-I\left({\stackrel{.fwdarw.}{r}}_j\right).Math.\right)=\frac{1}{C_g}{e}^{-{\left(I\left({\stackrel{.fwdarw.}{r}}_i\right)-I\left({\stackrel{.fwdarw.}{r}}_j\right)\right)}^2/{\sigma }_g^2},$ and C.sub.g and σ.sub.g are parameters.

14. The method of claim 13, further comprising generating a representation of the improved x-ray radiation information items (S.sub.e({right arrow over (r)}.sub.i)) assigned to the multiplicity of locations.

15. The method of claim 14, further comprising classifying the improved x-ray radiation information items assigned to the multiplicity of locations into a plurality of groups, wherein: pairs of x-ray radiation information items assigned to the same group are more similar to one another in accordance with a predetermined similarity criterion than pairs of x-ray radiation information items assigned to different groups; in the representation x-ray radiation information items assigned to the same group are each represented with the same representation feature; and in the representation x-ray radiation information items assigned to different groups are represented with different representation features.

16. The method of claim 15, wherein the representation features comprise a brightness, a colour and/or a colour saturation.

17. The method of claim 11, wherein $g\left(.Math.I\left({\stackrel{.fwdarw.}{r}}_i\right)-I\left({\stackrel{.fwdarw.}{r}}_j\right).Math.\right)=\frac{1}{C_g}{e}^{-{\left(I\left({\stackrel{.fwdarw.}{r}}_i\right)-I\left({\stackrel{.fwdarw.}{r}}_j\right)\right)}^2/{\sigma }_g^2},$ and C.sub.g and σ.sub.g are parameters.

18. One or more machine-readable hardware storage devices comprising instructions that are executable by one or more processing devices to perform operations comprising the method of claim 1.

19. A system comprising: one or more processing devices; and one or more machine-readable hardware storage devices comprising instructions that are executable by the one or more processing devices to perform operations comprising the method of claim 1.

20. The system of claim 19, further comprising: a particle source configured to generate a particle beam; an electron detector; and an x-ray radiation detector.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Embodiments of the disclosure are explained in greater detail below with reference to figures, in which:

[0024] FIG. 1 shows a schematic illustration of a particle beam microscope in accordance with one embodiment;

[0025] FIG. 2 shows a flow diagram for elucidating a method for operating the particle beam microscope from FIG. 1 in accordance with one embodiment;

[0026] FIG. 3 shows a schematic illustration of an image generated on the basis of electron radiation information items obtained from an object via the particle beam microscope from FIG. 1;

[0027] FIG. 4 shows a schematic illustration of an image generated on the basis of improved x-ray radiation information items obtained from the object from FIG. 3 via the particle beam microscope from FIG. 1; and

[0028] FIG. 5A and FIG. 5B show exemplary x-ray radiation information items assigned to different regions of the images in FIGS. 3 and 4.

DETAILED DESCRIPTION

[0029] FIG. 1 is a schematic illustration of a particle beam microscope 1. The particle beam microscope 1 comprises a particle source 3, which emits particles that are accelerated towards an electrode 5 in order to generate a beam 7 of particles. The particles can be electrons or ions. The particle beam 7 can be collimated by a collimation lens 9. The particle beam 7 passes through an objective lens 11 in order to be focused at a surface 13 of an object 15. A beam deflector 17 is controlled by a controller 19, comprising a computer, in order to deflect the particle beam 7 in such a way that the particle beam is incident on the surface 13 of the object 15 at a desired adjustable location 23 within a two-dimensional region 21.

[0030] The particle beam 7 incident on a given location 23 at the surface 13 of the object 15 generates interaction products on account of the interaction of the particles of the particle beam 7 with the material of the object 15 at the location 23, said interaction products being detectable. The particle beam microscope comprises a backscattered electron detector 25 for detecting backscattered electrons. An exemplary trajectory of a backscattered electron is provided with the reference sign 27 in FIG. 1. The particle beam microscope furthermore comprises an x-ray detector 29 for detecting x-ray quanta. An exemplary trajectory of an x-ray quantum is provided with the reference sign 31 in FIG. 1.

[0031] One example of a method for operating the particle beam microscope 1 is explained below with reference to the flow diagram in FIG. 2.

[0032] Firstly, the object 15 is positioned relative to the particle beam microscope 1 in such a way that the particle beam microscope 1 can scan a region 21 of interest at the surface 13 of the object 15 using the particle beam 7. Then, in a step 101, the region 21 of the surface 13 of the object 15 is scanned systematically via the partial beam 7. This means that the particle beam 7 is scanned line by line over the surface 13. In this case, as a result of the actuation of the beam deflector 17, the incidence location 23 of the beam 7 at the surface is displaced to a next location within the line and left there for a predetermined time (“dwell time”). During this time the detectors 25 and 29 collect electron radiation information and x-ray radiation information, respectively, which is read in by the controller 19 and stored in a manner assigned to the location 23 onto which the particle beam 7 is directed. The storage can be effected for example in the data structure of a two-dimensional array, as is illustrated by way of example in FIG. 2 with an array 103 for the electron radiation information items and an array 105 for the x-ray radiation information items. The storage contents of the data structures 103 and 105 are addressable in each case by way of two indices x and y, the values of which are between 0 and N, and 0 and M, respectively. The individual storage contents of the data structure 103 of the electron beam radiation information items can each be for example a numerical value representing the number of electrons which were detected by the detector 25 during the predetermined time duration. The individual storage contents of the data structure 105 of the x-ray radiation information items can each be for example an energy spectrum representing the x-ray spectrum which was detected by the detector 29 during the predetermined time duration. Each x-ray spectrum can be represented by a specific number of numerical values each representing the number of x-ray quanta which were detected in a specific energy interval.

[0033] A pair of the indices (x.sub.i,y.sub.i) thus indicates the location information {right arrow over (r)}.sub.irepresenting the i-th location 23 at the surface 13 of the object 15 onto which the particle beam 7 was directed during the process of obtaining the electron beam information assigned to this location and the x-ray radiation information assigned to this location. The storage in the data structure of the two-dimensional arrays 103 and 105 is just one example, however, and other data structures can be used in order to store the location information items {right arrow over (r)}.sub.i and the electron beam information and x-ray radiation information respectively assigned to said location information items.

[0034] The contents of the data structures 103 and 105 can be represented as images on a representation medium, such as a screen or paper, for instance, by representation features, such as brightness, colour or colour saturation, for instance, being assigned to the contents, i.e. the individual electron radiation information items and x-ray radiation information items, and these representation features being used in the generation of the representation.

[0035] The situation in practice is such that the values stored in the individual elements of the data structure 105 for the x-ray radiation information items may have a comparatively large proportion of noise and small signal proportion in comparison with those in the elements of the data structure 103 for the electron radiation information items, on account of deficient statistics. Therefore, after the scanning of the surface 13 of the object 15 in step 101, the x-ray radiation information items of the data structure 105 are improved.

[0036] For this purpose, a processing 107 including a plurality of steps is carried out for each location (x.sub.i, y.sub.i). Therefore, a given location (x.sub.i, y.sub.i) is set to the value (0, 0) in a step 109, the processing 107 is executed for this given location, and then a step 111 involves querying whether all the given locations (x.sub.i, y.sub.i) have been processed. If this is not the case, the given location (x.sub.i, y.sub.i) is set to a next location in a step 113, and the processing 107 and also the query 111 are executed again.

[0037] The processing 107 comprises a step 119, in which the improved x-ray radiation information S.sub.e assigned to the given location (x.sub.i, y.sub.i) is set to zero.

[0038] A calculation in which all locations (x, y) are taken into consideration is then carried out for the given location (x.sub.i, y.sub.i). For this purpose, a considered location (x.sub.i, y.sub.i) is set to the value (0, 0) in a step 121, a processing is executed for this considered location in a step 123, and then a step 125 involves querying whether all the considered locations (x.sub.j, y.sub.j) have been processed. If this is not the case, the considered location (x.sub.j, y.sub.j) is set to a next location in a step 127, and step 123 and also the query 125 are executed again.

[0039] In step 123, the x-ray radiation information assigned to the considered location (x.sub.i, y.sub.i) is weighted with the weight W(i, j) and added to the improved x-ray radiation information assigned to the given location (x.sub.i, y.sub.i). The processing 107 thus realizes a calculation in accordance with the following equation:

[00003]$\begin{array}{cc}{S}_e\left({\stackrel{.fwdarw.}{r}}_i\right)=\underset{j}{.Math.}w\left(i,j\right).Math.S\left({\stackrel{.fwdarw.}{r}}_j\right)& \left(1\right)\end{array}$

[0040] The weight w used here depends on the two locations, that is to say the given location (x.sub.i, y.sub.i) and the considered location (x.sub.j, y.sub.j). The weight decreases with the distance between the given location (x.sub.i, y.sub.i) and the considered location (x.sub.j, y.sub.j). The weight furthermore decreases with the absolute value of the difference between the intensity represented by the electron radiation information assigned to the given location (x.sub.i, y.sub.i) and the intensity represented by the electron radiation information assigned to the considered location (x.sub.j, y.sub.j).

[0041] For example, the weight can be calculated for example as a product of two terms, of which one is dependent on the distance between the given location (x.sub.i, y.sub.i) and the considered location (x.sub.j, y.sub.j) and the other is dependent on the difference between the electron radiation intensity at the given location (x.sub.i, y.sub.i) and the electron radiation intensity at the considered location (x.sub.j, y.sub.j).

[0042] By way of example, the weight can be calculated according to the formula:

w(i, j)=w({right arrow over (r)}.sub.i,{right arrow over (r)}.sub.j)=f(|{right arrow over (r)}.sub.i−{right arrow over (r)}.sub.j|).Math.g(|I({right arrow over (r)}.sub.i)−I({right arrow over (r)}.sub.j)|)   (2)

[0043] wherein

[0044] {right arrow over (r)} represents the location (x, y),

[0045] I({right arrow over (r)}) represents the intensity of the detected electrons that is assigned to the location (x, y),

[0046] f(|{right arrow over (r)}.sub.i−{right arrow over (r)}.sub.j|) is a function which decreases with the distance between the given location {right arrow over (r)}.sub.i and the considered location {right arrow over (r)}.sub.j, and

[0047] g(|I({right arrow over (r)}.sub.i)−I({right arrow over (r)}.sub.j)|) is a function which decreases with the absolute value of the difference between the intensities of the detected electrons.

[0048] The function f can be represented by the following formula, for example:

[00004]$\begin{array}{cc}f\left(.Math.{\stackrel{.fwdarw.}{r}}_i-{\stackrel{.fwdarw.}{r}}_j.Math.\right)=\frac{1}{C_f}{e}^{-{\left({\stackrel{.fwdarw.}{r}}_i-{\stackrel{.fwdarw.}{r}}_j\right)}^2/{\sigma }_f^2}& \left(3\right)\end{array}$

[0049] wherein σ.sub.f and C.sub.f are parameters that can be chosen in a suitable manner.

[0050] The function g can be represented by the following formula, for example:

[00005]$\begin{array}{cc}g\left(.Math.I\left({\stackrel{.fwdarw.}{r}}_i\right)-I\left({\hat{r}}_j\right).Math.\right)=\frac{1}{C_g}{e}^{-{\left(I\left({\stackrel{.fwdarw.}{r}}_i\right)-I\left({\stackrel{.fwdarw.}{r}}_j\right)\right)}^2/{\sigma }_g^2}& \left(4\right)\end{array}$

wherein σ.sub.g and C.sub.g are parameters that can be chosen in a suitable manner.

[0051] If it is found in step 125 that all locations have been used as considered locations (x.sub.j, y.sub.j) in step 123, the processing is continued at step 111.

[0052] If it is found in step 111 that all locations have been used as given locations (x.sub.i, y.sub.i) in the processing 107, the improved x-ray radiation information items S.sub.e({right arrow over (r)}) are classified into groups in a step 131. In a step 133, different representation features are assigned to each of the plurality of groups. In a step 135, the x-ray radiation information items are then represented on a representation medium using the representation features.

[0053] FIG. 3 shows a schematic illustration of an image 51 which was generated on the basis of the contents of the storage structure 103, i.e. the electron radiation information items obtained from an object 15 via the particle beam microscope 1. FIG. 3 thus shows an image 51 of the surface 13 of the object 15, in which two smaller regions 53 and 55 are discernible, which are spaced apart from one another and embedded in a larger region 57.

[0054] The regions 53 and 55 have identical greyscale values in the image 51, while the greyscale value of the region 57 surrounding the regions 53 and 55 is different therefrom. On the basis of the analysis of the image 51 of the electron radiation information, it can be deduced that the material in the regions 53 and 55 is different from the material in the region 57. However, it cannot necessarily be deduced that the material in the region 55 is identical to the material in the region 53, since it is possible for different materials to result in identical greyscale values in the electron beam image.

[0055] This last is the case in the example explained here. FIG. 5A shows an exemplary x-ray spectrum 61 obtained by combining the x-ray spectra assigned to the locations within the region 53 of the image 51. FIG. 5B shows an exemplary x-ray spectrum 63 obtained by combining the x-ray spectra assigned to the locations within the region 55 of the image 51. It is evident that the x-ray spectra 61 and 63 in FIG. 5A and FIG. 5B, respectively, differ significantly from one another, for which reason it can be deduced that the regions 53 and 55 are formed by different materials.

[0056] FIG. 4 shows a schematic illustration of an image 65 which was generated on the basis of the improved x-ray radiation information items S.sub.e({right arrow over (r)}) obtained on the basis of the electron radiation information items and the x-ray radiation information items obtained from an object 15 via the particle beam microscope 1. In FIG. 4, the regions 53, 55 and 57 are represented by representation features that are pairwise distinct from one another, such as brightness or colour, for instance, such that the observer of the image can directly perceive that the regions 53 and 55 differ from one another with regard to their material.

[0057] The implementation of the method explained with reference to FIG. 2 reveals that the improved x-ray radiation information items S.sub.e({right arrow over (r)}) for the regions 53 and 55 differ from one another. This is owing to the fact that a plurality of weighted x-ray radiation information items are combined in order to determine the improved x-ray radiation information items S.sub.e({right arrow over (r)}), the weights used decreasing with the distance between the considered locations. Therefore, in the determination of the improved x-ray radiation information items S.sub.e({right arrow over (r)}) for example within the region 55 x-ray radiation information items from the region 55 contribute to a greater extent than x-ray radiation information items from the region 53 arranged at a distance from the region 55. Accordingly, in the determination of the improved x-ray radiation information items, the locations in the two different regions 53 and 55 are not treated identically on account of their corresponding electron radiation information items, i.e. corresponding greyscale values, which would make them indistinguishable to the observer's eye in the image generated from the improved x-ray radiation information. According to the method described here, regions which are arranged at a distance from one another and which are very similar on the basis of the electron radiation information items assigned to them can be detected and correspondingly also represented as regions that are indeed different with regard to the material forming the regions.

[0058] In this case, the method can be adapted to a specifically present problem in practice by the setting of parameters. One of these parameters is the parameter σ.sub.f in formula (3) above, which can be considered as a lateral filter width, which sets how the contribution of x-ray radiation information at a considered location (x.sub.j, y.sub.j) to the improved x-ray radiation information at the given location (x.sub.j, y.sub.j) decreases with the distance between the considered location and the given location. The parameter C.sub.f in formula (3) above can be considered as a normalization parameter and be set accordingly. The parameters can be chosen suitably for example for each object examined. By way of example, the user can set the value of the parameter σ.sub.f and change it until the user approves of the resulting image of the improved x-ray radiation information after consideration. It is also conceivable for the values of the parameters σ.sub.f and C.sub.f to be set in an automated manner, specifically for example on the basis of an analysis of the electron radiation information, the x-ray radiation information and/or the improved x-ray radiation information with regard to, for example, contrast, image noise, characteristic variables of image constituents and the like. A similar procedure can be adopted with the parameters σ.sub.g and C.sub.f in formula (4). If formulae other than formulae (1) to (4) mentioned in association with the embodiment explained with reference to FIG. 2 are used in the method, then such other methods also contain parameters which are correspondingly settable, thus establishing a result which is suitable for the user.

[0059] The method explained above can be carried out by the controller 19 of the particle beam microscope 1. For this purpose, the controller 19 has the functions of a computer in order to execute the desired image processing. These functions are provided by hardware having components which comprise one or more processors, main memory for the processor, storage media for programs and data and communication interfaces. These components can be arranged close to the particle-optical components such as the particle source 3 and the objective lens 11, but they can also, in part or in their entirety, be arranged remotely therefrom and, in this case, can be connected for example via a remote data connection, such as the Internet, for instance, to a part of the controller 19, which is arranged close to particle-optical components in order to control the latter. The method is carried out by the controller, for example, by virtue of the latter accessing a computer program product comprising computer-readable instructions. These instructions implement the method as a program which comprises instructions for processors of the controller 19, is loaded from a storage medium into the main memory of the processors and is processed by the processors. Using the program, the location information items and the electron radiation information items and x-ray radiation information items assigned to the locations are likewise loaded into the main memory and analysed as described above in order that the improved x-ray radiation information items are generated, stored in storage media and optionally represented on a display medium.