Device for measuring the power density distribution of a radiation source

Abstract

Device (1) for measuring a power density distribution of a radiation source (11), wherein the device has the following features: a radiation source designed to emit a beam of light (L) in a direction of radiation (SR); a substrate (2) located downstream of the radiation source in the direction of radiation, having an extension in an x-direction and a y-direction, wherein the substrate has a first region (3) and at least one further second region (4), and the first region comprises a diffractive structure (5) configured to separate the light beam incident on the diffractive structure (5) into a zeroth diffraction order (6) and at least one first diffraction order (7); and a detector unit (8) arranged downstream of the substrate in the direction of radiation, configured to measure the intensity of the first diffraction order transmitted through the substrate and to derive a power density distribution from it, and a device for moving the radiation source and / or the substrate, characterized in that the first region (3) is configured such that only a certain portion of the light beam is separated into the zeroth diffraction order and the at least one first diffraction order, and the substrate (2) and / or the radiation source are moved, and by the movement of the substrate (2) and / or the radiation source a plurality of portions of the light beam are separated into the zeroth diffraction order (6) and the at least one first diffraction order (7).

Description

[0001] The present invention relates to a device for measuring a power density distribution of a radiation source according to the features of claim 1.

[0002] DE 40 06 618 A1 discloses a measuring device for laser beam analysis. In order to split a measuring beam from a laser beam that reproduces the laser beam as faithfully as possible, this beam is directed at an acute angle onto a flat metal mirror whose entire surface is provided with grooves of a defined geometry and spacing such that, on the one hand, the portion of the incident beam impinging on the grooves leaves the surface of the mirror as measurement radiation, diffracted by reflection, and, on the other hand, the partial waves emanating from the grooves superimpose themselves in at least one direction, thereby forming at least one measuring beam that is detected by one or more detectors.DE 32 12 809 A1 discloses a beam splitter for detecting the ratio of differently polarized components of monochromatic radiation, wherein the radiation falls on a grating that delivers most of the intensity in the zeroth order, and polarization-selecting analyzers are arranged in angular ranges associated with higher diffraction orders. DE 10 2014 201 779 B4 discloses a beam propagation camera and a method for light beam analysis. The invention is particularly applicable to laser radiation in order to analyze the beam's focusing properties and to obtain information about both the geometric and the beam quality. DE 10 2005 038 587 A1 discloses a measuring system and a method for measuring a laser beam, wherein a deflection system is provided for deflecting the laser beam.The deflection system is a system that reflects the laser beam and whose control is configured in such a way that the laser beam can be directed in a predeterminable pattern over a detector arrangement in the measuring mode in order to be able to measure the beam properties and the position of the laser beam using simple means.

[0003] Various devices for measuring, including online measurement and control of a laser beam, are known. For example, DE 10 2007 062 825 A1 discloses a grating mirror, a monitoring device, a laser resonator, and a beam guide with which the coupling and focusing of a laser beam for online monitoring can be carried out using a single optical element. This solution is characterized by a grating mirror that has a local grating period and a local alignment of the grating lines, each of which is selected such that the grating mirror focuses a laser beam diffracted into a higher diffraction order onto at least one focal point. The raw beam is guided via a mirror to which the grating is also applied. The entire beam diameter of the laser beam is directed onto the grating.Through this grating, light is coupled out in only one diffraction order, which is additionally focused by the grating into one point, namely at the location of a detector.

[0004] The disadvantage of this arrangement is that this focusing requires a locally varying grating constant across the grating surface and the use of the raw beam. This also means that this solution is unsuitable for a lateral intensity profile, i.e., a power density distribution, as required, for example, for industrial lasers for dividing wafers or generally for laser applications with short and high radiation intensities. A reflective element for short wavelengths is disadvantageous in this case.DE 10 2007 062 825 A1 considers the use of (partially) transmissive materials such as ZnSe, GaAs, Ge, ZnS, or Si as substrates for coupling out a portion of the laser beam to be problematic because the coupled-out laser radiation passes through the substrate material, meaning that cooling of the optical element can no longer be achieved across its entire surface from the rear and must therefore take place along the circumference. Most of the materials mentioned above also have poor thermal conductivity, which, together with the altered cooling, would result in greater susceptibility to destruction if the optical element used for coupling out becomes dirty. Furthermore, focusing or imaging the coupled-out laser beam, if required, can usually only be achieved using an additional optical element.However, this is not permanently critical in the applications already mentioned above, since this is particularly true in the IR range and measurements are not required continuously.

[0005] Solutions are also known in which the light distribution is either imaged onto a CCD camera using an optical setup or determined using absorbing apertures, and the resulting intensity behind the aperture is recorded using a total integrating detector (photodiode, calorimetric detector, etc.). Aperture-based measurement systems sometimes use different apertures, such as those used for cutting (oblique and straight) and / or slits. The profile is then calculated from the data obtained in this way (decovolution / unfolding). These apertures are usually made of metal or an absorbing metal layer on a transparent carrier substrate. The minimum aperture sizes are in the range of 2 to 5µm.

[0006] This, in turn, has the disadvantage that, on the one hand, CCD-based measurement systems can only withstand low intensities. If the intensity increases, the laser beam must be attenuated to avoid damaging the CCD camera. This attenuation is usually achieved using neutral density filters. However, surface irregularities or the formation of thermal lenses can lead to distortions in the laser beam image. This can sometimes seriously distort the measurement.

[0007] At high intensities, aperture or cutting systems are used. However, the disadvantage is that at very high intensities, especially with pulsed lasers, the absorbing aperture material is also removed, causing the aperture to degrade rapidly.

[0008] It is therefore an object of the invention to provide a device for measuring a power density distribution of a radiation source that is improved over the prior art and can be used particularly at high power densities, for example, in the VUV range. This object is achieved by the features of patent claim 1. Advantageous embodiments emerge from the respective subclaims and the following description.

[0009] A device for measuring a power density distribution of a radiation source is presented, the device having the following features: a radiation source configured to emit a light beam in a radiation direction; a substrate arranged downstream of the radiation source in the radiation direction and having an extension in an x-direction and a y-direction, wherein the substrate has a first region and at least one further second region, and the first region comprises a diffractive structure designed to separate the light beam incident on the substrate into a zeroth diffraction order and at least one first diffraction order; and a detector unit arranged downstream of the substrate in the radiation direction, which is designed to measure the intensity of the first diffraction order transmitted through the substrate and to derive a power density distribution therefrom.

[0010] The invention takes advantage of the finding that with a diffractive structure the degree of degradation is significantly lower because the light beam is not absorbed but only deflected or transmitted. The invention therefore uses only the transmitted radiation. The device therefore has a significantly longer service life and can also be used at intensities at which an absorbing aperture according to the prior art would fail. The increased service life thus enables more cost-efficient operation of the device. The technical feature "diffractive structure" is understood according to the invention to mean any optical element for shaping a light beam. For example, the structure can be an area of ​​a glass carrier onto which microstructures are applied by photolithography.In them, phase modulations occur due to different optical path lengths of the partial beams, which creates interference patterns.

[0011] It may also be provided that a higher diffraction order is optionally used instead of the first diffraction order if an even greater attenuation of the intensity is required, since higher diffraction orders generally have a lower diffraction efficiency and thus a lower intensity. Thus, according to the invention, the first diffraction order is also understood to mean a higher diffraction order.

[0012] In a preferred embodiment, the entire light beam can impinge on the diffractive structure. Thus, the entire light beam is diffracted and can be measured by the detector unit.

[0013] According to the invention, the first region is designed such that only a specific portion of the light beam is separated into a zeroth diffraction order and at least a first diffraction order, and the substrate and / or the radiation source are designed to be movable, and by moving the substrate and / or the radiation source, a plurality of portions of the light beam can be separated into a zeroth diffraction order and at least a first diffraction order, which means that the use of a higher diffraction order should not be excluded. The diffractive structure can therefore be implemented on a very small, limited area, which only needs to be a few square micrometers. With this arrangement, a specific portion, preferably a single point of the light beam, can be evaluated. By moving or scanning the substrate, a two-dimensional image of the power density distribution can then be recorded.Preferably, the substrate also has a plurality of first regions, each of which is configured to separate at least a specific portion of the light beam into a zeroth diffraction order and at least one first diffraction order. Thus, the overall measurement speed can be increased.

[0014] Furthermore, in a further preferred embodiment, the radiation source can be designed as a laser radiation source, in particular with a wavelength of 343 nm. Such a laser radiation source is particularly suitable for material processing, for which the device according to the invention can be used.

[0015] In a further preferred embodiment, the diffractive structure is designed as a binary grating, wherein the grating lines of the binary grating are aligned in the x and / or y directions. Particularly preferably, an embodiment could be designed such that the diffractive structure of a first region and the diffractive structure of an immediately adjacent, further first region are aligned in the x and y directions, respectively. Thus, in addition to spatially resolved information about the power density distribution, information about the local polarization could also be obtained.

[0016] According to a further preferred embodiment, the binary grating has a grating period, wherein the grating period varies within the grating. Such an embodiment allows for the generation of different deflection angles of the first diffraction order. Thus, a spatially resolved measurement of the power density distribution is possible.

[0017] In a further preferred embodiment, the substrate can be tilted by a specific angle and / or a surface normal of the substrate can be tilted relative to a preferred orientation of the grating. By tilting or tilting, more light can be directed into one of the first two diffraction orders. This procedure can be used to tune the detector unit.

[0018] In a further preferred embodiment, an evaluation and control unit can also be provided, which evaluates the data measured by the detector unit and is configured to transmit control signals to the radiation source. Thus, the intensity of the radiation source can be influenced by feedback control.

[0019] Since the output signal intensity could still be very high, depending on the power of the radiation source used, it is possible that the detector unit could be damaged during the measurement. The diffractive structure makes it possible to very easily control the intensity of the diffracted light by adjusting the grating depth and the aspect ratio between the groove and the ridge within a grating period.

[0020] Furthermore, a method for measuring a power density distribution of a radiation source is presented, wherein the method can be carried out according to an embodiment of the device presented above, wherein the method comprises the following steps: Providing a radiation source configured to emit a light beam in a radiation direction; Providing a substrate arranged downstream of the radiation source in the radiation direction and having an extension in an x-direction and a y-direction, wherein the substrate has a first region and at least one further second region and the first region comprises a diffractive structure which is designed to separate the light beam incident on the substrate into a zeroth diffraction order and at least one first diffraction order; Providing a detector unit downstream of the substrate in the radiation direction; Measuring an intensity of the first diffraction order transmitted through the substrate by means of the detector unit; and Deriving a power density distribution from the measured intensity.

[0021] In a further embodiment of the method, the zeroth diffraction order can be used to machine a workpiece, and the beam source can be readjusted if the derived power density distribution does not correspond to a predetermined power density distribution. The readjustment step can be carried out, for example, by the evaluation and control unit evaluating the data measured by the detector unit and transmitting control signals to the radiation source. The device can therefore also be suitable for monitoring and controlling during a work process, e.g., the cutting process for wafers, in order to achieve the highest degree of uniformity on and in the machined workpieces and the desired shapes.

[0022] The invention is explained in more detail below with reference to the accompanying figures. They show: Fig. 1 is a schematic diagram of a device for measuring a power density distribution according to a first embodiment of the present invention; Fig. 2 is a schematic diagram of a device for measuring a power density distribution according to a second embodiment of the present invention; Fig. 3 shows a further schematic representation of an apparatus for measuring a power density distribution according to the second embodiment of the present invention; Fig. 4-6 various embodiments of a first region according to the invention, which is designed as a diffractive structure; Fig. 7 is a schematic diagram of a power density distribution measuring apparatus according to a third embodiment of the present invention; Fig. 8 is a schematic diagram of a device for measuring a power density distribution according to a fourth embodiment of the present invention; and Fig. 9 Procedure of a method according to the invention.

[0023] Fig. 1 shows a schematic representation of a device 1 for measuring a power density distribution according to a first exemplary embodiment of the present invention. The device is designed to measure a power density distribution of a radiation source (not shown in detail) that emits a light beam L in a radiation direction SR. The radiation source can be, for example, a laser radiation source designed to process a workpiece (not shown in detail). This device is provided to determine the quality of the radiation, i.e., its power density distribution.

[0024] The device 1 comprises a substrate 2 formed from a transparent material. The substrate comprises a first region 3 and a second region 4. The first region 3 is formed as a diffractive structure 5. This structure is suitable for separating the light beam into a zeroth diffraction order 6 and a first diffraction order 7 as well as higher diffraction orders, wherein Fig. For the sake of clarity, only the beam path of a first diffraction order is shown in Figure 1. The first diffraction order is focused onto a detector unit 8 by means of a focusing lens F, and its intensity is measured, resulting in a power density distribution.

[0025] Fig. Figure 2 shows a schematic representation of a device 1 for measuring a power density distribution according to a second embodiment of the present invention. The difference between this embodiment and the embodiment according to Fig. 1 consists in the fact that only a certain portion of the light beam is split into a zeroth diffraction order 6 or a first diffraction order 7. In order to measure the entire light beam, this embodiment provides for the substrate 2 to be movable by a device not shown in detail. Any movement of the substrate 2 is clearly indicated by an arrow M. Fig. 3 shows a further schematic representation of a device 1 according to Fig. 2. The Fig. 3 shows that the first region is smaller in area than the second region 4. For an analyzing area of ​​2 to 5 µm, for example, 5 to 15 grating periods of a binary grating can be used.

[0026] In the Fig. 4 to Fig. 6 shows various embodiments of a diffractive structure 5 according to the invention, or the orientation of the grating lines forming the structure. The person skilled in the art will recognize from the figures that the grating lines can be oriented along an x- or y-direction or in another direction. Several diffractive structures can also be arranged on the substrate, with the grating lines of different diffractive structures having the same (see, for example, Fig. 6b) or can have a different orientation (see e.g. Fig. 6a).

[0027] According to the embodiments described in the Fig. 7 and Fig. 8, the device 1 additionally has an evaluation and control unit 9. This unit 9 serves to evaluate the data measured by the detector unit 8 and to transmit corresponding control signals to the radiation source 11. Thus, the radiation source 11 could be controlled during the processing of a workpiece 12. Optionally, the device 1 could be Fig. 7 may comprise a further optical control unit 10.

[0028] Fig. 9 shows a flowchart of a method 400 for measuring a power density distribution of a radiation source according to an embodiment of the present invention. The method 400 for measuring a power density distribution is in connection with or using the device from the Fig. 1, Fig. 2 or Fig. 7 and Fig. 8 can be carried out advantageously.

[0029] The method 400 comprises a step 401 of providing a radiation source configured to emit a light beam L in a radiation direction SR. The method 400 also comprises a step 402 following the providing step 401 of providing a substrate 2 arranged downstream of the radiation source in the radiation direction and extending in an x-direction and a y-direction, wherein the substrate has a first region 3 and at least one further second region 4, and the first region comprises a diffractive structure 5 configured to separate the light beam incident on the substrate into a zeroth diffraction order 6 and at least a first diffraction order 7. Furthermore, the method 400 comprises a step 403 following the providing step 402 of providing a detector unit 7 arranged downstream of the substrate 2 in the radiation direction.Furthermore, the method 400 comprises a step 404 following the providing step 403, of measuring an intensity of the first diffraction order transmitted through the substrate using the detector unit. Furthermore, the method 400 comprises a step 405 following the measuring step 404, of deriving a power density distribution from the measured intensity.

[0030] In the following description of advantageous embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the various figures and having a similar effect, whereby a repeated description of these elements is omitted.

[0031] The exemplary embodiments described and shown in the figures are selected only as examples. Different exemplary embodiments can be combined with one another in their entirety or with regard to individual features. Furthermore, one exemplary embodiment can be supplemented by features of another exemplary embodiment.

[0032] If an embodiment includes an “and / or” link between a first feature and a second feature, this should be read as meaning that the embodiment according to one embodiment includes both the first feature and the second feature and according to another embodiment includes either only the first feature or only the second feature.

Claims

[1] Device (1) for measuring a power density distribution of a radiation source (11), the device having the following features: a radiation source configured to emit a light beam (L) in a radiation direction (SR); a substrate (2) arranged downstream of the radiation source in the radiation direction and having an extension in an x-direction and a y-direction, wherein the substrate has a first region (3) and at least one further second region (4), and the first region comprises a diffractive structure (5) which is designed to separate the light beam incident on the diffractive structure (5) into a zeroth diffraction order (6) and at least one first diffraction order (7); and a detector unit (8) arranged downstream of the substrate in the radiation direction, which is designed to measure the intensity of the first diffraction order transmitted through the substrate and to derive a power density distribution therefrom, and a device for moving the radiation source and / or the substrate, characterized by that the first region (3) is designed such that only a certain portion of the light beam is separated into the zeroth diffraction order and the at least one first diffraction order and the substrate (2) and / or the radiation source are moved and by the movement of the substrate (2) and / or the radiation source a plurality of portions of the light beam are separated into the zeroth diffraction order (6) and the at least one first diffraction order (7). [2] Device according to claim 1, characterized bythat the substrate has a plurality of first regions, each of which is designed to separate at least a certain portion of the light beam into a zeroth diffraction order and at least one first diffraction order. [3] Device according to claim 1 or 2, characterized by that the radiation source is designed as a laser radiation source, in particular with a wavelength of 343 nm. [4] Device according to one of the preceding claims, characterized by that the diffractive structure is designed as a binary grating and the grating lines of the binary grating are aligned in the x and / or y direction. [5] Device according to claim 4, characterized by that the binary grating has a grating period and the grating period varies within the grating. [6] Device according to one of the preceding claims, characterized bythat the substrate (2) can be inclined by a certain angle and / or a surface normal of the substrate (2) has an inclination relative to a preferred orientation of the grating. [7] Device according to one of the preceding claims, characterized by that an evaluation and control unit (9) is further provided which evaluates the data measured by the detector unit (8) and is designed to transmit control signals to the radiation source.

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