Alignment chip for characterization devices

Abstract

The present invention relates to an alignment chip (1) for a sample characterization device, comprising: an alignment head portion (2) made of a material having an atomic weight greater than 50 and having an essentially spherical shape; and a main body (3) connected to the alignment head portion (3) and configured to be placed in a sample support.

Description

[Technical Field]

[0001] The present invention relates to an alignment chip for a sample characterization device.

[0002] The field of the invention is, but is not limited to, that of sample characterization by light, electron or ion radiation. [Background technology]

[0003] To be able to characterize a sample using a radiation beam from a metrology or characterization device such as a diffractometer, the sample must be aligned with this beam to allow accurate analysis of the measurement signal.

[0004] Alignment is typically performed using a reference object, such as a test pattern, placed in the measurement beam.

[0005] According to one example, a cross, in particular made of tungsten wire, is used to align the sample in the beam, and alignment is achieved using a goniometer, the rotation axis of which is positioned on the axis of the radiation beam, with the axes of the goniometer and the beam not being parallel.

[0006] Crosses do not allow sufficient rotation to achieve alignment in the entire angular space, as this alignment would require being able to perform and correct all the movements necessary to analyze the sample. Furthermore, because these crosses are two-dimensional structures, non-orthogonal incidence of the radiation beam causes them to appear thicker than they actually are.

[0007] In another example, Siemens test patterns or stars are used to achieve alignment within the beam with a resolution of a few nanometers, however the cost of such objects is very high.

[0008] Typically, prior art reference objects are two-dimensional objects that cannot be aligned along three rotational axes in space. Furthermore, these reference objects are not suitable for mounting to a measurement device or goniometer in the same way as the sample being characterized. As a result, alignment and measurement corrections are not very accurate.

[0009] The article "X-ray ptychographic computed tomography at 16 nm isotropic 3D resolution" by M. Holler et al., Scientific Reports, 2014, Vol. 4, p. 3857, describes ptychographic measurements using three-dimensional test objects made of porous silicon dioxide. However, these objects are very fragile, and their fabrication cannot be reproduced. Summary of the Invention

[0010] [DISCLOSURE OF THE INVENTION] It is an object of the present invention to provide an alignment chip that can be used under conditions identical to those for the characterization of the sample.

[0011] Another object of the present invention is to provide an alignment tip whose manufacturing method is easy to implement, reproducible, and low cost.

[0012] It is a further object of the present invention to provide an alignment tip that can be used for a variety of applications, in particular for characterizing metrology or characterization devices.

[0013] At least one of the above objects is to provide an alignment chip for a sample characterization device, comprising: - an alignment head made of a material having an atomic weight greater than 50 and having an essentially spherical shape; a body adapted to be connected to the alignment head and to be placed on the sample support; This is achieved with an alignment tip comprising:

[0014] The alignment chip according to the invention is for use in a characterization or measurement device, for example for the purpose of measuring or characterizing a sample, or for characterizing the measurement device itself. In use, the alignment chip can be mounted or connected to the sample support of the measurement device in the same way as the sample to be measured.

[0015] Due to its roughly spherical shape, the head of the alignment tip can be oriented in any direction in space.

[0016] When the sample to be measured needs to be aligned with the measurement beam, the alignment tip is pre-positioned so that the alignment head is on the beam axis. Because the head has a three-dimensional structure, difficulties associated with non-normal incidence of the beam are eliminated. This improves the accuracy of sample positioning in this device, thereby improving the operation of the device. The measurement time, and therefore the measurement cost, can be optimized.

[0017] In this type of metrology device, the metrology beam can be a light beam, an electron beam or an ion beam.

[0018] The alignment chip according to the present invention has a simple and solid structure that is easy to manufacture and whose dimensions can be selected to be similar to or within the same order of magnitude as the dimensions of the sample to be measured or the size of the measurement beam used in the measurement or characterization device.

[0019] Furthermore, a single alignment tip according to the present invention is reusable and can be used in a variety of different metrology devices that have a suitable sample support on which the tip can be placed, thus enabling the alignment tip to be used in a variety of applications.

[0020] The term "essentially spherical" means that the alignment head does not correspond to a perfect sphere. The sphere may in particular have a non-sphericity of up to about 10%. This means that the minimum and maximum radii of the sphere may differ from each other by up to about 10%. This non-sphericity is due to the nature of the manufacturing method of the alignment tip. However, the spherical quality of the head is sufficient for the intended application.

[0021] According to one embodiment, the diameter of the head portion can be 5 μm to 100 μm.

[0022] The above dimensions correspond to typical dimensions of samples that may be measured or characterized, in particular with a device that implements an alignment chip according to the invention.

[0023] The above dimensions also correspond to the dimensions of the measurement beam used in the metrology device.

[0024] According to an advantageous embodiment, the collar region of the body immediately adjacent to the alignment head has a diameter that is significantly smaller than the diameter of the head.

[0025] A collar region forming part of the body of the alignment tip is located in close proximity to the sphere of the head, where the dimensions of the body are such that the head is securely supported by the body, but are significantly smaller and incomparable to the diameter of the head.

[0026] When the alignment tip is mounted on a measurement or characterization device, alignment, measurement, or characterization is performed using a roughly spherical head. When the tip is placed in the measurement beam, it is important that the collar area does not interfere with the use of the tip. Therefore, the diameter of the collar area should be as small as possible. Specifically, the collar area should obscure the measurement beam as little as possible to obtain a satisfactory contrast image, especially when the beam is at non-orthogonal incidence.

[0027] According to an embodiment, the diameter of the collar region can be between 2 μm and 80 μm.

[0028] Advantageously, the ratio between the length of the tapered portion of the body and the diameter of the rod-shaped portion of the body is greater than or equal to 0.5.

[0029] This minimum ratio has been found to be advantageous in order to avoid disturbances caused by excessively wide bodies, for example in the case of non-orthogonal incidence of the measurement beam, and in particular to obtain usable contrast images.

[0030] Advantageously, the body may comprise a rod-shaped portion and a tapered portion adjacent the alignment head.

[0031] The diameter of the body thus increases between the head and the other end of the body.

[0032] According to an embodiment, the diameter of the body may be between 80 μm and 300 μm.

[0033] According to an advantageous embodiment, the head and the body may form a single unit.

[0034] The head and rod of the tip thus form one piece. There are no bond points or similar that could weaken the bond between the head and body. The single unit withstands difficult measurement conditions, such as cryogenic conditions.

[0035] The chip material is selected for its robustness, its radiation resistance, but also for its cost.

[0036] Advantageously, the head is made of a material with a high atomic mass (greater than 50). The alignment head can in particular be made of tungsten.

[0037] Indeed, to align the alignment tip with the metrology beam, it is important that the tip's head casts a shadow when placed in the beam so that its precise positioning can be assessed. In the case of electron or X-ray beams, the material used for the alignment head must have a sufficiently large atomic mass so that the beam is partially or completely blocked by the head, producing contrast.

[0038] According to one embodiment, the alignment tip according to the present invention can include a detachable base.

[0039] The detachable base is particularly suitable for mounting on a sample support of a metrology or characterization device.

[0040] According to a first implementation example, the alignment chip according to the present invention can be used as a two-dimensional or three-dimensional reference object to align a sample in a sample characterization device under the projection of a measurement beam, or to characterize a measurement device as a reference sample.

[0041] The alignment tip can be used for centering the goniometer, in particular to align the alignment tip with respect to the radiation beam or metrology beam of the sample characterization device.

[0042] Thus, the alignment tip can be used as follows: - placing the alignment tip according to the invention on the sample support of a goniometer, - recording the position, displacement and dimensional parameters of the alignment tip in the control module; - centering the alignment tip with respect to the measurement beam using the dimensional parameters, and - Replace the alignment chip with the sample to be characterized.

[0043] According to a second implementation example, the alignment chip according to the invention can be used as a three-dimensional reference object.

[0044] In fact, the alignment head can feature three-dimensional structures such as hollow spaces or gaps, which are found especially in the volume of the alignment head, but also on the surface. These generally irregular 3D structures are significantly more resistant to metrology beams implemented in devices in which the alignment tip is intended to be used.

[0045] The microstructured alignment tip can be used to measure the volume resolution of metrology or characterization devices, especially in tomography or ptychography.

[0046] Durable nanostructures are generally very difficult to obtain and their fabrication (using focused ion beams) is very expensive. The alignment tip according to the invention constitutes a 3D structured object that is highly resistant to difficult mounting conditions such as high doses of ionizing radiation or cryogenic conditions. It is suitable for permanent use, i.e., at least 100 uses.

[0047] According to a third implementation example, the alignment chip according to the invention can be used as a functional reference object for fluorescence measurements.

[0048] For this purpose, the head of the tip can be provided with a fluorescent material, which can in particular be introduced into hollow spaces present in the alignment head.

[0049] The alignment chip thus functions as a 3D marker, allowing for parameterization and calibration of detection, for example in X-ray fluorescence analysis.

[0050] According to a fourth implementation example, the alignment chip according to the invention can be used as a refractive optical element.

[0051] In fact, the head of the tip can feature curved crystalline zones that can act as focusing lenses for electromagnetic radiation. [Brief explanation of the drawings]

[0052] Other advantages and features will become apparent upon review of the detailed description of the fully non-limiting embodiments and from the accompanying drawings. [Figure 1] 1 is a schematic diagram of an alignment chip according to one embodiment of the present invention inserted into a support. [Figure 2] 1 is an optical microscope image showing details of an alignment tip according to one embodiment of the present invention. [Figure 3] Image produced with an alignment tip according to the invention inserted into a hard x-ray beam. DETAILED DESCRIPTION OF THE INVENTION

[0053] It is clearly understood that the embodiments described below are in no way limiting. In particular, all of the described variations and embodiments can be combined with each other if there are no technical obstacles to the combination.

[0054] In the drawings, the same reference numbers may be used for features that are common to several drawings.

[0055] An embodiment of an alignment chip according to the present invention will now be described with reference to FIGS.

[0056] As shown in FIG. 1, the chip 1 includes an alignment head portion 2 and a main body 3 connected to the head portion 2 .

[0057] The head 2 is essentially spherical in shape. An image of an example embodiment is shown in Figure 2, which shows the alignment head 2 and a portion of the body 3 connected to the head 2, as viewed under an optical microscope. In this example, the head 2 and body 3 are formed as a single piece.

[0058] The joint 4 between the head 2 and the body 3 has a diameter, or a transverse dimension if the cross section of the joint is not circular, that is much smaller than the diameter of the head 2. The diameter of the head is between 5 μm and 100 μm. The diameter, or a transverse dimension, of the joint 4 between the head and the body 3 is preferably between 2 μm and 80 μm.

[0059] As an example, referring to FIG. 2, the diameter of the head portion is about 30 μm, and the diameter of the joint 4 immediately adjacent to the head portion is about 10 μm.

[0060] The body 3 of the tip 1 comprises a rod-shaped portion 8 and a conical or tapered portion 7. The conical portion 7 corresponds to the narrowed region of the body 3. However, in the embodiment shown in Figure 2, the generatrices of the "cone" outer casing are not straight, but describe an approximately circular line.

[0061] As an example, the length of the diameter-reduced region 7 can be set to 100 μm to 1 mm.

[0062] Of course, the narrowing region of the body can have other shapes: it may in particular be shaped like a true cone or a rod.

[0063] The alignment tip 1 can be placed on a sample support of a measurement or characterization device. In the embodiment shown in Figure 1, the sample support consists of a base 6 and a cannula 5. The cannula 5 receives the body 3 of the alignment tip, and the inner diameter of the cannula 5 is approximately the same as the outer diameter of the end of the body 3. The cannula 5 can be considered a removable base for the tip 1. The base 6 is suitable for installation on a standardized measurement or characterization device.

[0064] Thus, when such an alignment tip is inserted into the measurement beam of a metrology device and the alignment head is centered in the beam, an image such as that shown in FIG. 3 is observed. Here, the measurement beam is a hard X-ray beam. To generate the image shown in FIG. 3, the alignment tip is oriented horizontally along the X-axis with the head pointing to the right in the drawing. The head and the body of the collar region partially block the beam, resulting in a contrast image due to the so-called "corona" effect, i.e., partial obscuration of the beam. A toroidal-shaped spot 10 is generated on the observation surface, with a circular shadow 11 in the center and a slit-shaped shadow 12 to the left of spot 10. These shadows correspond to the locations of the tip's head and body, respectively, in the path of the beam.

[0065] Ideally, the observed contrast image should have a perfect "doughnut" shape with no lateral slits. In this case, the alignment or centering of the sample in the measurement beam can be performed more efficiently. Therefore, it is very important that the transverse dimension of the body collar area, near the head of the alignment tip, is as small as possible so as to obscure the measurement beam as little as possible.

[0066] The alignment tip according to the present invention can be manufactured according to an electrochemical manufacturing method, the steps of which are detailed below. As an example, the manufacture of a tungsten alignment tip is presented.

[0067] Tungsten rods can be obtained from simple tungsten wire. The wire diameter can be approximately 250 μm. A portion of the rod is subjected to chemical erosion by electrolysis in a sodium hydroxide bath. As a result, the immersed portion of the rod thins and is eventually severed by a chemical reaction at its thinnest point. The electrolysis is immediately stopped to maintain the thinnest portion of the immersed portion of the rod. The rod is removed from the sodium hydroxide and immersed in an acid bath of the same concentration as the sodium hydroxide bath to stop the chemical reaction on the rod. The resulting rod has a sharp end with dimensions on the order of tens of nanometers.

[0068] At this stage, the sharp end of the rod can be inspected using any suitable means to verify the previous manufacturing steps: for this purpose, optical microscopy, scanning electron microscopy or X-rays can be used.

[0069] The sharpened end of the rod is then subjected to pulsed laser irradiation. To achieve this, the tip is centered on the axis of the pulsed laser beam. Between each pulse, the sharpened end is gradually inserted into the laser beam until a physical alteration of the tip occurs. The sharpened end undergoes partial local melting, resulting in a spherical shape. The size of the resulting sphere varies depending on the length of the rod irradiated by the laser.

[0070] As can be seen in Figure 2, the thinned region 7 of the rod 3 between the sphere 2 and the non-immersed part of the rod 3 is roughly conical in shape, however the generatrix of the outer casing of this "cone" is not a straight line in the illustrated embodiment, but describes a roughly circular line.

[0071] The sphere 2 obtained by irradiation with a laser can be further characterized using an optical microscope, a scanning electron microscope, or X-rays. The diameter of the sphere 2 and the dimensions of the rod 3 supporting it can be measured in this way. The dimensions of the rod 3 include the diameter D of the rod's base and the diameter of the junction 4, the approximate length L of the tapered portion, and the radius corresponding to the circular line of the narrowed region 7 of the rod 3. An example of a spherical head portion 2 and a tungsten rod portion 3 is shown in FIG. 2.

[0072] As an example, the sodium hydroxide bath (electrolyte) used to initially immerse the rods is a 2M NaOH bath used with stainless steel electrodes. Electrolysis is carried out at a voltage of about 12 V and a current of, for example, 50 mA, which can vary from 10 μA to 1 A.

[0073] The laser used may be, for example, a Nd:YAG laser delivering pulses of energy between 10 mJ and 20 J, in particular 1 ms pulses with an energy of 1.5 J.

[0074] The rod and its sphere at the end thus constitute the body and head of an alignment tip according to the invention, which can then be inserted into a suitable support for use in a measuring or characterization device.

[0075] Examples of implementations of alignment chips according to the present invention are described below.

[0076] According to a first implementation example, the alignment chip according to the invention can be used as a two-dimensional or three-dimensional reference object under the projection of a metrology beam in a sample characterization device.

[0077] The tip can be used in particular to align the sample with respect to this measurement beam.

[0078] This alignment can be performed, for example, using a goniometer, in which case the alignment tip is positioned using the sample support as shown in Figure 1. Ideally, this is the same sample support that will be used for the sample that will subsequently be measured. The alignment tip's alignment is then adjusted with respect to the measurement beam using the goniometer. An image such as that shown in Figure 3 can then be observed. The parameters related to the tip's alignment, displacement (e.g., rotation), and dimensions are stored in a look-up table. The alignment tip is then removed from the sample support and the sample to be measured is placed on the same support.

[0079] The alignment chip according to the present invention can also be used to test and characterize metrology devices. In this case, the alignment chip is used as a reference sample for the sequential improvement of devices such as optical lines and off-synchrotron X-ray microscope stations. Measurements from these different devices can then be compared.

[0080] According to a second implementation example, the alignment chip according to the invention can be used as a three-dimensional reference object.

[0081] In fact, depending on the materials used and the manufacturing method of the chip, the alignment head can exhibit three-dimensional structures such as hollow zones or gaps, which are found especially in the volume of the alignment head, but also on its surface. These 3D structures, which may be irregular, cannot be altered and are resistant to the metrology beams (electrons, ions, X-rays) implemented in the device in which the alignment chip is intended to be used. The dimensions of the structures are typically several tens of nanometers.

[0082] Such structured alignment tips can also be used to test and characterize metrology devices, for example to measure the volume resolution or contrast of a metrology or characterization device, where the alignment tip is used as a reference sample for the sequential improvement of devices such as tomography or ptychography devices.

[0083] According to a third implementation example, the alignment chip according to the invention can be used as a functional reference object for fluorescence measurements.

[0084] In practice, it is possible to introduce fluorescent material into the alignment head, for example into the aforementioned hollow zone present in the alignment head.

[0085] To fill the hollow zone with fluorescent material, several techniques can be implemented: 1. The alignment head can be immersed in a solution containing nanobeads and / or fluorescent molecules, followed by laser irradiation to form spheres. Upon partial melting, the fluorescent material is at least partially incorporated into the volume of the sphere. 2. The formed spheres can also be immersed in a solution containing fluorescent nanobeads and / or fluorescent molecules.

[0086] The two techniques can of course be combined. Furthermore, to improve the incorporation of fluorescent agents, an additional galvanic force can be applied between the tip and the solution containing fluorescent nanobeads or fluorescent molecules.

[0087] Such an alignment tip thus allows for parameterization and calibration of detection values ​​in, for example, X-ray fluorescence analysis.

[0088] In practice, the sphere can be subjected to a focused ion beam (FIB) to cut away a portion of the sphere and thus reach one or more of the cavities filled with fluorescent material, which can then be used to measure its diameter by scanning a fluorescence-induced measurement beam.

[0089] According to a fourth implementation example, the alignment chip according to the invention can be used as a refractive optical element.

[0090] In practice, the head of the alignment tip may feature one or more crystalline zones already present on its surface or may be modified to expose the crystalline zones. It is also possible to modify the head to expose or expose such crystalline zones. These zones result from the fabrication of the tip, particularly from subjecting the tip to pulsed laser irradiation. The crystalline zones are generally curved and can therefore be used as focusing lenses for electromagnetic radiation. For example, such a tip can be used to characterize microlenses for X-rays.

[0091] Naturally, the invention is not limited to the examples described above, and many adjustments can be made to these examples without departing from the scope of the invention.

Claims

1. An alignment chip (1) aligned with a measurement beam in a sample characterization device, comprising: an alignment head (2) made of a material with an atomic mass greater than 50 and having an essentially spherical shape; a body (3) connected to the alignment head (2) and adapted to be placed on a sample support; An alignment tip comprising:

2. 2. An alignment tip (1) according to claim 1, characterized in that the collar area (9) of the body (3) immediately adjacent to the alignment head (2) has a diameter that is significantly smaller than the diameter of the head.

3. 3. The alignment tip (1) according to claim 1 or 2, characterized in that the body (3) comprises a rod-shaped portion (8) and a tapered portion (7), the tapered portion (7) being located near the alignment head (2).

4. The alignment tip (1) according to any one of claims 1 to 3, characterized in that the diameter of the head part (2) is between 5 μm and 100 μm.

5. 5. The alignment tip (1) according to claim 3 or 4, characterized in that the ratio between the length of the tapered portion (7) of the body (3) and the diameter of the rod-shaped portion (8) of the body (3) is 0.5 or more.

6. Alignment tip (1) according to any one of claims 1 to 5, characterized in that the head part (2) is made of tungsten.

7. Alignment tip (1) according to any one of claims 1 to 6, characterized in that the head (2) and the body (3) form one piece.

8. Use of an alignment chip (1) according to any one of claims 1 to 7 as a two-dimensional or three-dimensional reference object in a sample characterization device.

9. Use of an alignment chip (1) according to any one of claims 1 to 7 as a three-dimensional reference object in a sample characterization device, wherein the alignment head part (2) comprises a microstructure.

10. Use of an alignment chip (1) according to any one of claims 1 to 7 as a functional reference object in a device for sample characterization by fluorescence, wherein the alignment head part (2) comprises a fluorescent material.

11. Use of an alignment tip (1) according to any one of claims 1 to 7 as a refractive optical element, wherein the alignment head (2) comprises at least one refractive crystal zone.

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