Device and method for detecting and characterizing particles and other defects on semiconductor wafers, in particular gallium arsenide wafers

Abstract

The present invention relates to a device (V) for measuring surface properties of wafers, comprising: a light source (1) which is adapted to output a directed light beam; a detector arrangement (2) which is adapted to detect an azimuthal scattering characteristic (asymmetry of the scattering), an orientation of the emission characteristic in the forward direction (also backscattering) and a zenith scattering, which arise when the light beam is incident on the wafer (W); a wafer holder (3) on which a wafer can be mounted; and an evaluation unit (4). The invention also relates to a corresponding method. The device and method are used in particular to detect COPs (crystal originated pits) and particles on the wafer surface in a sufficiently sharply separated manner and to determine the size thereof.

Description

[0001] Device and method for the detection and characterization of particles and other defects on semiconductor wafers, in particular gallium arsenide wafers

[0002] The present application relates to a method and a device for detecting particles and defects on the surface of a semiconductor wafer and for determining their size or classification, in particular a gallium arsenide wafer, an indium phosphide wafer, or a gallium nitride wafer. In particular, the present invention relates to detecting and distinguishing particles and COPs (crystal originated pits), and also to being able to measure the corresponding defect sizes.

[0003] BACKGROUND OF THE INVENTION

[0004] Crystal-originated pits (COPs) are depressions in the wafer surface. In the prior art, they are sometimes also referred to as crystal-originated particles, since they can be seen or detected with a particle-detecting instrument, but are not particles themselves. They form during surface polishing, where a defect present in the crystal (precipitation, inclusion, vacancy agglomeration, etc.) is polished / etched more intensely than the undisturbed crystal. This results in a depression in the surface with a morphology characteristic of the semiconductor material.

[0005] Additionally, small particles (i.e., actual particles) can adhere to the surface of semiconductor wafers.

[0006] For subsequent epitaxy processes, it is particularly important to have homogeneous surface properties (i.e., as free from particles as possible), which is why surface defects, such as COPs and particles, must be reliably detected.

[0007] For example, prior art documentation US9645094 B2 describes a detection device for defects on a semiconductor wafer. This device uses, in particular, a silicon polymerase metal detector with an array of sensitive pixels, as well as complex optics with multiple lenses and deflection devices.

[0008] Document US7477372 B2 discloses an optical scanning system for the detection of surface anomalies on a wafer, which contains several detectors. These are arranged symmetrically around the beam that generates the scattering.

[0009] However, current measurement systems are not capable of distinguishing crystal-originated pits (COPs) from particles with sufficient accuracy across an entire wafer surface. For semiconductor wafers, especially gallium arsenide wafers, one of the quality characteristics is the lowest possible number of particles on the surface. To detect or control this, a complete measurement of the wafer surface is necessary. This is possible, for example, using the SurfScan 6220 and SurfScan 6420 light scattering devices from Tencor, which are also described in document US5864394A.

[0010] However, the optical setup of these devices is complex and large. Further particle classification is not possible due to the limited solid angle resolution. Crystal-originated pits are formed during the final polishing processes of the wafer; however, these are not considered particles because they do not affect the subsequent epitaxy process, or do so in a different way.

[0011] Nevertheless, such crystal-originated pits can exhibit light beam behavior in measuring devices that can easily be mistaken for a particle. Separating different defects, i.e., crystal-originated pits and particles, on GaAs wafers is difficult with current technology when using rotating wafers.

[0012] The frequency of crystal originated pits is approximately 1000 times greater than that of other particles; therefore, the quality of the separation must be better than 99.99% (100 ppm) for a misclassification rate of < 10%.

[0013] True particles are formed particularly below a size of 120 nm. For this reason, many state-of-the-art instruments can no longer measure such particles with sufficient accuracy and distinguish them from COPs. Such a separation leads to long measurement times and a limitation in particle size resolution with existing equipment, as the low scattering intensity of the small particles can no longer be detected and analyzed with sufficient precision.

[0014] Especially with large wafers, i.e., 6" or 8", the measurement time would be very high in existing equipment. With indium phosphide, it is also difficult with current technology to reliably separate and detect crystal-originated pits and particles of a specific size.

[0015] Given the ever-shrinking size of semiconductor structures, the detection of particles below 120 nm in size, while simultaneously separating particles from COPs, is of great importance and cannot be achieved with current state-of-the-art equipment.

[0016] It can therefore be considered a technical object of the present invention to perform a separation of COPs and particles with a separation efficiency better than 100 ppm, and to reliably detect, quantify and determine the size of particles with sizes smaller than 120 nm.

[0017] Further tasks include better classification of the particles, a reduction in maintenance costs, and the expandability of the system to indium phosphide and possibly gallium nitride wafers.

[0018] Another task could be a specific classification of defect types and sizes for other compound semiconductors such as GaN or InP.

[0019] SUMMARY OF THE INVENTION

[0020] This problem is solved by a method according to claim 1 and a device according to claim 10.

[0021] Further advantageous embodiments of the present invention are the subject of the corresponding dependent claims.

[0022] Without limiting the invention, the following points are set out to describe the main aspects, preferred embodiments and special features of the present invention: Device (V) for measuring surface properties of wafers, comprising: a light source (1) adapted to emit a directed beam of light; a detector arrangement (2) adapted to detect an azimuthal scattering characteristic (asymmetry of scattering), a forward orientation of the emission characteristic (also: backscattering) and a zenith scattering which occur when the light beam strikes the wafer (W); a wafer holder (3) on which a wafer can be stored; and an evaluation unit (4).

[0023] The light beam preferably has a small cross-section, for example 6400 pm. 2Device (V) according to point 1, wherein the detector arrangement (2) comprises several area detectors, preferably at least five area detectors (2-1, 2-2, 2-3, 2-4, 2-5). Device (V) according to point 2, wherein at least four area detectors (2-1, 2-2, 2-3, 2-4) are arranged perpendicular to the plane in which the wafer holder (3) lies, and one area detector (2-5) is arranged parallel to the plane in which the wafer holder (3) lies. Device (V) according to point 3, wherein two gaps (5) are provided between each pair of area detectors (2-1, 2-4; 2-2, 2-3), and the gaps (5) are opposite each other with respect to the point at which the beam of the light source (1) strikes the wafer (W).

[0024] This ensures that the laser can strike the wafer between two area detectors and exit on the opposite side. Thus, the entire azimuthal angle range, except for the slit, is covered by the device – meaning scattering can be detected across the entire azimuthal angle range (0°–360°) except for the slit.

[0025] 5. Device (V) according to point 3 or 4, wherein exactly four area detectors (2-1 , 2-2, 2-3, 2-4) are arranged perpendicular to the plane in which the wafer holder (3) lies, and the edges of the area detectors (2-1 , 2-2, 2-3, 2-4) which run parallel to the plane in which the wafer holder (3) lies form a rectangle, preferably a square.

[0026] 6. Device (V) according to point 4 or 5, wherein the column (5) is provided at two corners of the rectangle or square through which a virtual diagonal of the square or rectangle passes.

[0027] 7. Device (V) according to one of points 4 to 6, wherein the slits (5) cover an angular range of ± 22.5°, preferably ± 12.5°, as viewed from the beam.

[0028] At 12.5°, the intensity of the haze scattering has dropped to a level that can also be observed in other solid angle regions. In other words, at 12.5°, the solid angle region with the most intense haze scattering is masked. At 22.5°, there is a minimum in haze scattering.

[0029] This angle is calculated as follows: angle = tan -1 ( - column width - \

[0030] Distance. Particle gap /

[0031] For larger distances, the gap width should also increase in order to exclude the same angular range.

[0032] Das folgende Dokument erklärt die Haze-Streuung genauer:

[0033] Elastic Laser Light Scattering by GaAs Surfaces

[0034] Valeriy A. Sterligov, Yuri V. Subbota, Yuri M. Shirshov, Lidia P. Pochekaylova, Eugene F. Venger, Raisa V. Konakova, and Igor Yu. Ilyi, APPLIED OPTICS y Vol. 38, No. 12, 20 April 1999.

[0035] From this document, an exponent y of 2.39 was fitted to the data from Figure 8 for a fractal PSD function 82(f) = A / T. A value of 3.0e-9 was assumed for A, and haze intensities were simulated using the Scatmech library (p. 28 of https: / / www.nist.gov / services-resources / software / scatmech-polarized-light-scattering-c-class-library https: / / pages.nist.gov / pySCATMECH / ). Device (V) according to one of the previous points, where light scattered from the wafer (W) is directly detectable by the area detectors. Device (V) according to one of the previous points, where there are no elements between the wafer (W) and the area detectors (2-1, 2-2, 2-3, 2-4, 2-5) to influence the light path. Device according to one of the preceding points, wherein the evaluation unit (4) is configured to analyze an asymmetry of the scattering in the plane, an orientation of the radiation characteristic in the forward direction and a zenith scattering perpendicular to the surface.

[0036] In spherical coordinates, the lateral angle in the plane is called the azimuthal angle and the angle towards the zenith is called the polar angle. Here, an azimuthal asymmetry of the scattering and the distribution of the scattering intensities in the polar angle are analyzed. The azimuthal angle indicates the scattering in the plane. The device according to point 10, wherein the evaluation unit (4) is configured to determine an azimuthal asymmetry of the scattering in the plane by comparing the scattering to the left and right of the beam of the light source (1), has a rotation angle. 1° from the directions 0°, 90°, 180°, and 270°, preferably at a distance > 10°. The angle of rotation <p charakterisiert die Drehung der [0-11]-Richtung des Kristalls relativ zur projizierten Einfallsrichtung des Strahls.

[0037] The azimuthal scattering angles indicate the angle between the azimuthal angle of the incident beam and the directions of the scattered intensities. Device according to one of points 10 or 11, wherein the evaluation unit (4) is configured to determine a forward-directed orientation of the emission characteristic by comparing the forward and backward scattering, each as seen from the point of impact of the beam of the light source (1) on the wafer (W).

[0038] Here is the angle difference of the rotation angle. <p zu den richtungen 90° und 270°>1°, preferably >45°, further preferably >70°, and even more preferably >80°. Device according to one of points 10 to 12, wherein the evaluation unit (4) is configured to determine zenith scattering by comparing the scattering perpendicular to the surface of the wafer and the scattering forward, backward, right and left, each as seen from the point of impact of the beam of the light source (1) on the wafer (W).

[0039] Here is the angle of rotation <p vorzugsweise im Bereich |(p-90°|<5° oder |(p-270°|<5°, weiter vorzugsweise im Bereich |(p-90°|<2.5° oder |(p-270°|<2.5°. Vorrichtung gemäß einem der vorherigen Punkte 10 bis 13, wobei die Auswerteeinheit (4) dazu angepasst ist, einen Oberflächendefekt zu detektieren und dessen Typ zu charakterisieren, wobei ein COP detektiert wird, wenn:

[0040] • the azimuthal scattering intensity in the plane to the left and right of the beam of the light source (1) is different (i.e., there is an asymmetry of the scattering - at rotation angles <p ungleich 0°, 90°, 180°, 270°),

[0041] • and / or the ratio of the scattering intensities forward and backward, each viewed from the point of impact of the light source beam (1) on the wafer (W), is greater than 1 (i.e., there is stronger forward scattering than backward scattering, at rotation angles <p ungleich 0°

[0042] • and / or the scattering intensity perpendicular to the surface of the wafer is greater than the scattering intensity forward, backward, right and left, each as seen from the point of impact of the beam of the light source (1) on the wafer (W) (zenith scattering - at a rotation angle <p von 0°).

[0043] Forward and backward here means in the direction of the light beam, in front of and behind the point of impact on the wafer. Device according to one of the preceding points 2 to 14, wherein the evaluation unit (4) is adapted to read the signals of the area detectors (2-1, 2-2, 2-3, 2-4, 2-5) and the rotation angle into a neural network and to output a defect type and / or defect size accordingly. Device according to point 1, wherein the detector arrangement (2) comprises an area detector (2-1) and at least one beam deflection device (6). Device according to point 16, wherein the beam deflection device (6) is an ellipsoidal concave mirror (6a) arranged above the wafer holder (3) and an aspherical lens (6b) arranged above the wafer holder (3).

[0044] Ellipsoidal means that a solid of revolution of an ellipse or a similar geometric shape is present.

[0045] The central axis of the ellipsoidal concave mirror passes through, or is close to, the point where the light beam ideally strikes the wafer. The ellipsoidal concave mirror completely encloses a virtual line perpendicular to the wafer surface, which passes through the point where the light beam strikes the wafer – except for two slits provided in the concave mirror to allow the light beam to enter and exit the area within the concave mirror (see point 19 below).

[0046] Here too, the entire azimuthal angle range, with the exception of two slits for the transmission of the light beam, can be detected – i.e., the azimuthal scattering characteristic. Device according to paragraph 17, wherein the ellipsoidal concave mirror (2-10) is adapted to project asymmetric scattering and backscattering onto different areas of the area detector (2-1), and wherein the aspherical lens (2-11) is adapted to project zenith scattering onto another area of ​​the area detector (2-1). Device (V) according to paragraph 17 or 18, wherein two slits (5) are provided in the concave mirror (2-10), and the slits (5) are opposite each other with respect to the point at which the beam of the light source (1) strikes the wafer (W).

[0047] This ensures that the laser can pass through the concave mirror and strike the wafer, and that the reflected beam can exit on the opposite side. Device (V) according to any one of points 16 to 19, wherein the evaluation unit (4) is adapted to read the signals from the area detector (2-1) and the rotation angle into a neural network, and to determine a defect type and size based on historical data and output accordingly. Device (V) according to any one of the preceding points, wherein the area detector(s) (2-1, 2-2, 2-3, 2-4, 2-5) is / are designed as semiconductor detectors. Device (V) according to point 21, wherein the semiconductor detector(s) (2-1, 2-2, 2-3, 2-4, 2-5) is / are arrays of avalanche diodes. Device (V) according to any one of the preceding points, wherein the light source (1) is a laser. Device (V) according to point 23, wherein the laser has a wavelength of 400 to 500 nm.Device (V) according to one of the preceding points, wherein the wafer holder (3) is rotatable.

[0048] The wafer holder can be designed as a turntable. Device (V) according to one of the preceding points, wherein the wafer holder (3) is adapted to perform a translational movement. Device (V) according to one of points 1 to 26, wherein the angle of incidence at which the beam of the light source intersects the normal to the plane of the wafer (W) is variable between 0° and 85°.

[0049] The angle of incidence should not be too steep.

[0050] For the first embodiment (points 2-15) the angle of incidence is preferably between 35.3° and less than 85° (measured from the vertical in each case).

[0051] For the second embodiment (points 16-20) the angle of incidence is preferably between 32° and less than 85° (measured from the perpendicular).

[0052] If the laser beam strikes at a shallower angle, the scattered intensity of small particles becomes much lower, thus worsening the detection limit; Method for characterizing surface defects on a wafer, comprising the following steps: a) Irradiating a wafer (W) mounted on a wafer holder (3) with a directed light beam; b) Measuring the azimuthal scattering characteristic (asymmetry of scattering), the orientation of the emission characteristic in the forward direction (also: backscattering), and the zenith scattering that occur when the light beam strikes the wafer (W) by a detector arrangement (2); c) Evaluating the values ​​measured in step b) with an evaluation unit (4).

[0053] The azimuthal scattering characteristic determines whether the scattering to the left and right of the point of incidence of the light beam is symmetrical or asymmetrical. The procedure is as described in section 28, wherein in step b) the wafer holder (3) rotates and additionally performs a translational movement.

[0054] The translational movement is performed to scan the wafer surface. Method according to one of points 28 or 29, wherein the detector arrangement

[0055] (2) comprises several area detectors, and in step c) the evaluation unit (4)

[0056] • an asymmetry of the scattering in the plane is determined by comparing the scattering with the signals of the area detectors (2-1 , 2-2) to the left and right of the beam of the light source (1 ), using measured values ​​which were measured at rotation angles whose angular distance to the directions 0°, 90°, 180° and 270° is greater than 1°, preferably greater than 10°;

[0057] • an orientation of the radiation characteristic in the forward direction is determined by comparing the scattering forward and backward, each as seen from the point of impact of the beam of the light source (1) on the wafer (W), using measured values ​​which were measured at a rotation angle in the range of |cp-90| or |cp-270|> 1°, preferably >45°, further preferably >70°, and even more preferably >80°;

[0058] • a zenith scattering is determined by comparing the scattering perpendicular to the surface of the wafer and the scattering forward, backward, right and left, each as seen from the point of impact of the beam of the light source (1) on the wafer (W), using measured values ​​obtained at a rotation angle <p im Bereich |(p-90°|oder |cp-270°|< 5°, weiter vorzugsweise < 2,5° gemessen wurden.

[0059] For considering the asymmetry of the scattering in the plane, the following angular range applies: | cp-a | > 1°, preferably > 10° for ae {0°, 90°, 180°, 270°}.

[0060] For considering the radiation pattern in the forward direction, the following angular range applies: |cp-a|>1° or < 10° for ae {90°, 270°}

[0061] The following angular range applies for considering zenith scattering: | <p-a| <5° oder < 2,5° für a e {90°, 270°} Verfahren gemäß Punkt 30, wobei die Detektoranordnung (2) mindestens fünf Flächendetektoren umfasst. Verfahren gemäß Punkt 30 oder 31 , wobei die Auswerteeinheit (4) dazu angepasst ist, einen Oberflächendefekt zu charakterisieren, wobei ein COP detektiert wird, wenn:

[0062] • the azimuthal scattering intensity in the plane to the left and right of the beam of the light source (1) is different (i.e., there is an asymmetry of the scattering - at rotation angles <p ungleich 0°, 90°, 180°, 270°),

[0063] • and / or the ratio of the scattering intensities forward and backward, each viewed from the point of impact of the light source beam (1) on the wafer (W), is greater than 1 (i.e., there is stronger forward scattering than backward scattering, at rotation angles <p ungleich 0°), • und / oder die Streuintensität senkrecht zur Oberfläche des Wafers größer ist als die Streuintensität nach vorne, hinten, rechts und links, jeweils vom Auftreffpunkt des Strahls der Lichtquelle (1 ) auf den Wafer (W) gesehen (Zenitstreuung - bei einem Verdrehwinkel <p von 0°).

[0064] 33. Method according to one of the preceding points 30 to 32, wherein the evaluation unit (4) receives the signals from the area detectors (2-1 , 2-2, 2-3, 2-4, 2-5) as well as the rotation angle <p in ein neuronales Netz einliest, und einen Defekttyp und / oder eine Defektgröße bestimmt und entsprechend ausgibt.

[0065] 34. Method according to one of points 28 or 29, wherein the detector arrangement

[0066] (2) comprises an area detector (2-1 ) and at least one radiation deflection device (6), and in step c) the evaluation unit (4) the signals from the area detector (2-1 ) and the rotation angle <p in ein neuronales Netz einliest und einen Defekttyp und / oder eine Defektgröße entsprechend ausgibt.

[0067] The radiation deflection device captures all scattering and projects it onto the area detector.

[0068] 35. Method according to point 34, wherein an ellipsoidal concave mirror (6a) arranged above the wafer holder (3) and an aspherical lens (6b) arranged above the wafer holder (3) are provided as a radiation deflection device (6).

[0069] Ellipsoidal means that a solid of revolution of an ellipse or a similar geometric shape is present.

[0070] 36. Method according to point 35, wherein the ellipsoidal concave mirror (2-10) is adapted to project asymmetric scattering and backscattering onto different areas of the area detector (2-1 ), and wherein the aspherical lens (2-11 ) is adapted to project zenith scattering onto another area of ​​the area detector (2-1 ).

[0071] 37. Procedure according to one of points 34 to 36, wherein the neural network is trained before step a).

[0072] For this purpose, for example, well-defined spheres can be measured.

[0073] 38. Procedure according to point 37, wherein the training includes calibration with polystyrene latex balls.

[0074] 39. Use of the method according to one of points 28 to 38 for characterizing surface defects on a wafer.

[0075] Surface defects can be COPs and particles, but also linear defects (e.g. scratches), surface defects, etc.

[0076] 40. Use of the method according to one of points 28 to 39 for characterizing surface defects on a GaAs wafer, a GaN wafer or an InP wafer.

[0077] 41. Use of the method according to any of points 28 to 41 for distinguishing particles and COPs on a GaAs wafer, a GaN wafer or an InP wafer.

[0078] 42. Use of the method according to any of points 28 to 41 to determine the size of particles and COPs on a GaAs wafer, a GaN wafer or an InP wafer.

[0079] Preferred embodiments of the present invention are described in more detail below with reference to the accompanying figures. Fig. 1 shows a detector arrangement according to a first embodiment of the present invention.

[0080] Fig. 2 shows angular ranges (azimuthal angles) of the individual area detectors of the detector arrangement in polar coordinates, idealized by a cube.

[0081] Fig. 3 shows a curve of the integrated scattering cross-sections of all area detectors according to the first embodiment for PSL spheres, for p-polarized light of wavelength 480 nm and grazing incidence of less than 20°.

[0082] Fig. 4 shows a progression of the integrated scattering cross-sections of the detectors of the various area detectors according to a first embodiment of the present invention for COPs.

[0083] Fig. 5 shows a comparison of relative intensities of PSL spheres and COPs of the detectors of the detector arrangement in a first embodiment from simulations.

[0084] Fig. 6 shows the general dispersion measured by different detectors of the area detector arrangement.

[0085] Fig. 7 shows an example of a neural network for evaluating the detector signals according to a first embodiment of the present invention.

[0086] Fig. 8 shows the distribution of the cross-sections of the light scattered by the roughness of the surface as a function of various quantities, in particular the polar angle and the azimuthal angle.

[0087] Fig. 9 shows a detector arrangement according to a second embodiment of the present invention.

[0088] Fig. 10 shows a schematic view of the scattering with a detector arrangement according to a second embodiment of the present invention.

[0089] Fig. 11 shows solid angle regions (azimuthal angles) that are mapped onto a planar detector arrangement according to a second embodiment of the present invention. Fig. 12 schematically shows a complete device for measuring surface properties of wafers.

[0090] Fig. 1 shows a basic device for measuring the surface properties of wafers.

[0091] Fig. 1 a) shows a front view.

[0092] A light source 1 is arranged here, designed to shine directed light onto a wafer W (as precisely as possible). Around the point of impact of the light beam on the wafer W, area detectors 2-1 and 2-2 (not shown here), as well as 2-3, 2-4, and 2-5, are arranged in the shape of a cube. Figure 1b shows a different, rotated view, again showing area detectors 2-3, 2-4, and 2-5. Area detectors 2-3 and 2-4 are arranged laterally, while area detector 2-5 is arranged parallel to the plane in which the wafer (W) lies. It can be seen that there is a gap 5 between area detectors 2-3 and 2-4, through which the light beam can exit.

[0093] Fig. 1c) shows another top view of the entire detector arrangement 2. The area detectors 2-1, 2-2, 2-3, and 2-4 are perpendicular to the plane in which the wafer W is located. The area detector 2-5 rests on top of the area detectors 2-1, 2-2, 2-3, and 2-4 and is arranged in a plane parallel to the plane of the wafer W. The slit 5 is also visible here. Thus, several area detectors are arranged near the laser's base point in such a way that the largest possible solid angle can be captured, eliminating the need for complex collector optics. Differences in the scattering characteristics of COPs and particles can therefore be detected on rotating wafers, enabling both the classification of defects and the measurement of their dimensions.

[0094] In the present example, five area detectors are arranged around the laser's base point, and the scattered intensity can be evaluated as being narrow (detector 2-5) or wide (detectors 2-1, 2-2, 2-3, and 2-4) and as being influenced by their azimuthal asymmetry. Due to its small size, the system can be easily parallelized, either by using multiple measurement systems in a single device, or by simultaneously measuring a wafer with multiple detector arrays. Fig. 2 shows the angular ranges (azimuthal angles) of the area detectors in polar coordinates, idealized by a cube. A slit 5 (not shown here) is inserted between area detectors 2-2 and 2-3, and between area detectors 2-1 and 2-4, to allow the incident and reflected laser beams to pass through unimpeded. On rough surfaces, the light scattered by the surface (also called haze) is predominantly scattered within an angular range (azimuthal angle) of 0 to 5° around the reflected beam.The size of the gap 5 (not shown here) between the area detectors 2-1 and 2-4 can be varied accordingly to reduce interference from haze light, or to analyze the haze light in addition to the defects. Haze scattering is scattering at the surface roughness, i.e., a type of background scattering. Haze is the ratio of scattered light to incident light relative to the detector.

[0095] Here, the azimuth range is primarily shown - the area detector 2-1 covers the azimuthal angle range between 0° and 90°, the area detector 2-2 covers the azimuthal angle range between 90° and 180°, the area detector 2-3 covers the azimuthal angle range between 180° and 270°, the area detector 2-4 covers the azimuthal angle range between 270° and 360°, and the area detector 2-5 covers the polar angle range from 0° to approximately 40°.

[0096] Figure 3 shows that each solid angle region can be captured by a detector, which is necessary for precise measurement. Figure 3 analyzes the reflectance as a function of diameter. PSL spheres and p-polarized light with an incidence angle of 70° were used. The curves of detectors 2-1 and 2-4 represent forward scattering, while the curves of area detectors 2-2 and 2-3 represent back scattering. The curves of detectors 2-2 and 2-4, as well as those of detectors 2-2 and 2-3, overlap because the scattering characteristics of spheres are mirror-symmetric with respect to the direction of the incident light. Below a particle size of approximately 200 nm, in the Rayleigh scattering range, a dependence proportional to the sixth power of the diameter can be observed.This is also described in the following document: Pedro Lilienfeld (1986) Optical Detection of Particle Contamination on Surfaces: A Review, Aerosol Science and Technology, 5:2, 145-165. Fig. 4 shows a curve of the reflectance expected from detectors 2-1, 2-3, 2-4, and 2-5 for COPs. The curves of the individual detectors no longer coincide because the variation in the rotation angle results in very different scattering intensities for a given defect size.

[0097] Fig. 5 shows a comparison of the relative intensities of polystyrene-latex spheres (PSL spheres) (bottom) and COPs (top) of detectors 2-1, 2-2, 2-3, 2-4, 2-5, calculated here from simulations. A background noise level was added to the scattering cross-sections using Poisson-distributed random numbers, resulting in a resolution limit corresponding to a scattering cross-section of 3 x 10⁻¹⁰. 4 pm 2 This corresponds to the scattering cross-section of a 100 nm PSL sphere. The discrete point distribution in Fig. 5 corresponds to the detection of individual photons. Plotting the signals of area detectors 2-2 against 2-1 shows the ratio of forward and backward scattering. Plotting the signals of area detectors 2-4 against 2-1 shows the asymmetry to the right and left in the forward direction. Plotting the signals of area detectors 2-5 against 2-1 shows the ratio of perpendicular emission to emission at shallow angles. Here it can be clearly seen that there is a distinct difference between COPs, which are pits, and PSLs, which are intended to simulate particles (since PSL spheres were used), and thus, based on the scattering patterns, corresponding conclusions can be drawn about defect types and sizes. With PSL spheres, relatively linear curves can be seen except in a few scattering intensity ranges (the detector signals 2-1 and 2-5, respectively, are approximately 100 nm).2-2, 2-3, 2-4, and 2-5 are quite similar, but there are significant variations with COPs. This is because the rotation of the wafer plays no role with spheres, but it does with COPs.

[0098] Fig. 6 shows results of simulated scattering characteristics of certain detectors.

[0099] Fig. 6 a) shows again the general arrangement of the area detectors 2-1 , 2-2, 2-3, 2-4 and 2-5 viewed from above in a sectional view.

[0100] Fig. 6 b) shows an asymmetry in the orientation of COPs. It is shown that the ratios of the signals of the detectors 2-3 / 2-2 and 2-4 / 2-1 are only equal to 1 for the PSL spheres, but not for the COPs. At an angle <p (Verdrehwinkel), welcher nahe bei 90° ist, ist allerdings der Quotient ungefähr 1 , weswegen hier eine Unterscheidung zwischen COP und PSL-Kugeln (stellvertretend für einen Partikel) nicht möglich sind. Bei PSL-Kugeln sind bis auf wenige Streustärkebereiche relativ gleichmäßige Verläufe im logarithmischen Auftrag zu sehen (die Detektorsignale 2-2 und 2-3 sowie 2-1 und 2-4 sind recht ähnlich), bei COPs gibt es allerdings deutliche Streuungen.

[0101] Fig. 6 c) shows a test for forward scattering; the ratios of the signals from detectors 2-1 / 2-2 and the ratios of the signals from detectors 2-4 / 2-3 represent a measure of the orientation of the radiation pattern in the forward direction. A ratio comparable to that of the PSL spheres is only observed at COP rotation angles around 90°. At angles near 0°, COPs and PSL spheres, representing particles, exhibit very different scattering behavior in the longitudinal direction.

[0102] With PSL spheres, relatively uniform profiles can be seen in the logarithmic plot, except for a few scattering ranges (the detector signals 2-1 and 2-2 as well as 2-3 and 2-4 are quite similar), but with COPs there are significant scatterings, especially at rotation angles that differ significantly from 0° and 90°.

[0103] In the combination of the tests in Fig. 6 b) and 6 c), COPs and PSL spheres are only indistinguishable from each other in the area around 90°.

[0104] In Fig. 6d, only the signal ratios of detectors 2-5 / 2-1, 2-5 / 2-2, 2-5Z2-3, and 2-5 / 2-4 are shown. In the remaining COP orientation of approximately 90° from Figs. 6b) and 6c), the signals of the PSL spheres, representing particles, and the COP scattering differ significantly from the portion scattered perpendicular to the surface and detected by detector 2-5. For PSL spheres, relatively uniform profiles are visible in the logarithmic plot, except for a few rotation angle ranges (the detector signals 2-1 and 2-5, 2-2 and 2-5, 2-3 and 2-5, and 2-4 and 2-5 are quite similar). However, for COPs, there are clear variations and intensity differences (deviations from the uniform behavior in Fig. 6d).

[0105] Overall, the following conditions for distinguishing between COP and PSL spheres can be derived from Fig. 6:

[0106] The £ values ​​are constants. The s values ​​are parameters that are selected after calibration to achieve sufficient discrimination between COPs and particles. A value of 0.5 for all £ values ​​sufficiently distinguishes COPs from PSL spheres.

[0107] The combination of these three conditions enables a test to differentiate between COP and PSL spheres. Signals 2-1 to 2-5 for PSL are derived from calibration measurements of PSL spheres.

[0108] Fig. 7 shows one possibility for a neural network, which can be used as an alternative to the evaluation in Fig. 6. Here, a neural network 7 is shown, accordingly with an input 7a, a hidden layer 7b, and an output 7c. The signals from the area detectors, i.e., the signals from detectors 2-1 to 2-5, as well as the angle <p als Orientierung des Wafers stehen als Eingangsdaten zur Verfügung und werden entsprechend in den Eingang 7a eingegeben. Die Logarithmen der Zählraten werden verwendet, um den Quotienten der Zählraten als Summe in dem Netzwerk zu verarbeiten, und den sehr dynamischem Wertebereich abbilden zu können. Ein Ausgang 7c ist vorhanden zur Klassifizierung des Defekttyps (in diesem Fall PSL stellvertretend für Partikel und COPs), sowie der Defektgröße.

[0109] Fig. 8 shows the angular dependence of the light scattered by the surface roughness in selected directions of the solid angle – represented here as a bidirectional reflectance distribution function (BRDF) for an angle of incidence of 70°. In particular, Fig. 8a) shows that in the azimuthal direction of the incident ray, below a certain polar angle of reflection (labeled here as the polar angle) of approximately 70°, the backscattering increases dramatically, then decreases again. At 70°, the reflected ray is located in this case. Thus, the polar angle is varied here, while the azimuthal angle remains constant. <p =0. In der Abb. 8 b) ist die Verteilung des Streulichts in Abhängigkeit des azimutalen Streuwinkels <p für einen Ausfallwinkel von 70° gezeigt. Hier wird der Azimutalwinkels <p variiert, bei einem festen Polarwinkel 70°. Die hohen Streuquerschnitte sind auf einen engen Winkelbereich und einen reflektierten Strahl begrenzt.

[0110] In addition to scattering by particles or COPs, scattering intensities due to scattering from surface roughness (also called haze) are present. The simulated spatial distribution of these intensities at an incidence angle of 70° is shown in Figures 8a) and 8b). A concentration of scattering is observed in the vicinity of the reflected beam, which can be isolated in the detection optics to separate scattering from particles and scattering from surface roughness (haze). This allows the position and width of the slit to be optimized accordingly. By optimizing the position and width of the slit in the detection optics, a large portion of the haze light can be separated from the scattered light from the particles and measured, for example, by a separate detector. This enables the characterization of the surface roughness and reduces the background noise in particle characterization.

[0111] Fig. 9 shows a device for measuring surface properties of wafers according to a second embodiment of the present invention.

[0112] Fig. 9 a) shows a schematic arrangement of the second embodiment of a device for measuring surface properties of wafers according to the present invention.

[0113] Here, a light source 1 is again present. A corresponding light beam is directed onto a wafer W, where it is reflected and backscattered. To capture the scattered light, a beam deflection device 6 is provided, which here consists of an ellipsoidal concave mirror 6a (this can be considered a solid of revolution of an ellipse or a similar geometric figure) and an aspherical lens 6b. The aspherical concave mirror 6a is shown here in a cross-sectional view and is arranged around the point of incidence of the light beam on the wafer. The aspherical lens 6b is arranged inside the ellipsoidal concave mirror 6a and directly above the point of incidence of the light beam on the wafer. Above the ellipsoidal concave mirror 6a, the area detector 2-1 is arranged; this receives the backscattered light from the ellipsoidal concave mirror 6a and the aspherical lens 6b.In this way, a large solid angle range can be projected onto an array, i.e., the area detector 2-1. The aspherical lens 6b is selected such that the light scattered by a particle at the focal point of the lens is diffracted parallel out of the detector, and the imaging function of the mirror is chosen in this case such that the relative proportion of the differential solid angle range 2%-sin(0)-d0 to the half-solid angle 2K is equal to the relative area proportion of a circular ring 2%r-dr to the area of ​​a circle with diameter K of the detector array.

[0114] From this, a mapping function is derived: r(0) = - V1 - cos 0

[0115] This determines the shape of the mirror. In this way, the intensity distribution of the scattered particle can be mapped very homogeneously and in the correct sequence onto a circular area of ​​the detector array.

[0116] Fig. 9b) shows the ellipsoidal concave mirror 6a in more detail. It can be seen that it has two opposing slits 5 – for the entry and exit of the light beam. It also shows how the aspherical lens 6b is attached to the concave mirror 6a by means of a holding device 6c. The aspherical lens 6b is positioned in the lower third within the concave mirror 6a, with the axes of rotation of the concave mirror 6a and the aspherical lens 6b being identical.

[0117] Fig. 10 again shows the scattering of the light beam by a particle P. The light reflected by the ellipsoidal concave mirror 6a is captured radially at the outer edge of the planar detector 2-1, while the light diffracted directly by the lens strikes the central region of the planar detector 2-1. This allows for appropriate differentiation, and only a planar planar detector array 2-1 is required. Zenith scattering is mapped onto the inner segments, and wide-angle scattering onto the outer segments of the planar detector. The azimuthal distribution is resolved by the two-dimensional arrangement of the segments. The angle 0 describes the scattering relative to the normal of the incident light beam.

[0118] Figure 11 shows the solid angles (azimuthal angles) that can be imaged by a detector array 2-1. The figure thus illustrates the subdivision of the solid angle into the regions that can be imaged by the collector optics onto a detector array 2-1, for example, a square 8x8 detector array.

[0119] Fig. 12 shows a general setup of a complete device V for measuring the surface properties of wafers. A wafer W rests on the wafer holder 3, which is designed as a turntable. A light source 1 emits a light beam onto the wafer W, where it is scattered. A detector device 2 captures the scattering and forwards it to an evaluation device 4.

[0120] An inventive device for measuring surface properties of wafers comprises: a light source adapted to emit a directed beam of light; a detector arrangement adapted to detect an azimuthal scattering characteristic (i.e., asymmetry of scattering), a forward orientation of the emission characteristic (also: backscattering), and zenith scattering, which occur when the light beam strikes the wafer; a wafer holder on which a wafer can be stored; and an evaluation unit.

[0121] The orientation of the radiation pattern in the forward direction is the ratio of the scattering forward and backward from the point where the light beam hits the wafer - forward here means in the direction of the beam, i.e. from the point where the light beam hits the wafer forward in the direction of the beam, and backward here means opposite to the direction of the beam, i.e. from the point where the light beam hits the wafer backward in the direction of the radiation source).

[0122] This is a simple design that is particularly suitable for measuring GaAs wafers. The described detector configuration makes it possible to distinguish between gallium arsenide COPs and other particles on a rotating wafer with sufficient accuracy, especially below 100 ppm. Even at very low particle concentrations (e.g., 10,000 COPs with only 10 particles), sufficiently high resolution is possible, and particles smaller than 120 nm can also be reliably detected.

[0123] Preferably, the detector arrangement comprises several area detectors, and more preferably at least five area detectors. Area detectors are inexpensive components that can be easily arranged in a cube shape, enabling precise measurement. Preferably, at least four area detectors are arranged perpendicular to the plane in which the wafer holder lies, and one area detector is arranged parallel to the plane in which the wafer holder lies.

[0124] Scattering can thus be detected in all solid angle ranges and can be used to separate COPs from particles and to determine their size.

[0125] Preferably, two slits are provided between each pair of area detectors, and these slits are located opposite the point where the light source beam strikes the wafer. This ensures that the light beam can pass between the area detectors, but the main light beam can also exit the area detectors again, so that only the scattering is detected by them, and this can be differentiated with sufficient accuracy.

[0126] Furthermore, this can suppress haze dispersion.

[0127] Preferably, the evaluation unit is configured to analyze an asymmetry of the scattering in the plane, an orientation of the radiation characteristic in the forward direction, and a zenith scattering perpendicular to the surface.

[0128] Further preferably, the evaluation unit is configured to determine an azimuthal asymmetry of the scattering in the plane by comparing the scattering to the left and right of the light source beam, and / or the evaluation unit is configured to determine an orientation of the radiation characteristic in the forward direction by comparing the scattering forward and backward, in each case viewed from the point of impact of the light source beam on the wafer, and / or the evaluation unit is configured to determine a zenith scattering by comparing the scattering perpendicular to the surface of the wafer and the scattering forward, backward, right and left, in each case viewed from the point of impact of the light source beam on the wafer.

[0129] Since the wafer rotates with the turntable, three different ratios of scattering intensities are measured, and conclusions can be drawn about the defect type (distinction between COPs and particles) or the size of the defect based on these scattering characteristics using defined criteria or a neural network.

[0130] Measuring these three types of scattering is relatively easy to implement, and the signals provide sufficiently reliable criteria for differentiating between particles and COPs.

[0131] According to a further embodiment, the detector arrangement comprises a segmented area detector (preferably a segmented area detector having, for example, 8 x 8 segments that can be read separately) and at least one beam deflection device, wherein the beam deflection device further preferably comprises an ellipsoidal concave mirror arranged above the wafer arrangement and an aspherical lens arranged above the wafer holder. More preferably, two slits are provided in the concave mirror, and the slits are located opposite the point at which the light source beam strikes the wafer. The central axis of the concave mirror passes through or is close to the point at which the light beam strikes the wafer.The ellipsoidal concave mirror completely encloses a virtual line perpendicular to the wafer surface, passing through the point where the light beam strikes the wafer – except for the two slits provided in the concave mirror. This embodiment requires only one collector (in this case, a detector array), and by using the beam deflection device, all types of scattering can be projected onto a single area detector, enabling a simple and cost-effective design.

[0132] Preferably, the area detector(s) are formed from semiconductor detectors, preferably as arrays of avalanche diodes. Semiconductor elements have reliable detection properties; they have a rectangular cross-section ranging from several millimeters to several centimeters. This allows different scattering regions to be imaged and detected with sufficient clarity on the semiconductor detector.

[0133] Preferably, the wafer holder is rotatable and further adapted to perform a translational movement. The rotation of the wafer holder allows for the measurement of various rotation angles, which is particularly important for defects with a large aspect ratio of width to length. The translational movement enables the entire wafer to be scanned and thus allows particles or COPs to be detected and quantified across the entire wafer surface.

[0134] Preferably, the evaluation unit is adapted to read signals from the area detector(s) and the rotation angle into a neural network. A calculation is then performed in the neural network, and a defect and / or defect size can be determined accordingly. Particularly in the second embodiment, a neural network can be trained by calibration with different materials (e.g., polystyrene spheres), and the more measurements are performed, the more accurate the neural network's analyses become with regard to defect type and / or defect size.

[0135] A method for characterizing surface defects on a wafer comprises the following steps: a) Irradiating a wafer, which is attached to a wafer holder, with a directed light beam; optionally: rotating the wafer holder; b) Measuring the azimuthal scattering characteristic, a forward orientation of the emission characteristic (also: backscattering), and zenith scattering, which occur when the light beam strikes the wafer, using a detector arrangement; c) Evaluating the values ​​measured in step b) with an evaluation unit.

[0136] By measuring and evaluating the three scattering characteristics, COPs and particles can be distinguished with sufficient precision. According to a first embodiment, the detector arrangement comprises several area detectors; in step c), the evaluation unit performs the following steps:

[0137] • Measurement of the asymmetry of the scattering in the plane by comparing the scattering, determined using the signals of the area detectors to the left and right of the beam of the light source, using measured values ​​which were measured at rotation angles whose angular distance to the directions 0°, 90°, 180° and 270° is greater than 1°, preferably greater than 10°;

[0138] • Measurement of the orientation of the radiation pattern in the forward direction by comparing the scattering forward and backward, each as seen from the point of impact of the light source beam on the wafer, using measured values ​​which were measured at a rotation angle in the range of | cp-90°| or |(p-270°| > 1°, preferably > 45°, further preferably > 70°, and even more preferably > 80°;

[0139] • Measurement of zenith scattering by comparing the scattering perpendicular to the surface of the wafer and the scattering forward, backward, right and left, each as seen from the point of impact of the beam of the light source (1) on the wafer (W), using measured values ​​obtained at a rotation angle <p im Bereich |cp-90°| oder |cp-270°| < 5°, weiter vorzugsweise < 2,5° gemessen wurden.

[0140] The zero point of the angle of rotation <p ist ausgerichtet an der Längsachse der COPs (also der länglichen Ausdehnung der COPs).

[0141] According to a second embodiment, the detector arrangement comprises a segmented area detector and at least one radiation deflection device, and in step c) the evaluation unit then reads the signals from the area detector into a neural network. This determines a defect type and / or a defect size accordingly. The radiation deflection device preferably has an ellipsoidal concave mirror arranged around the wafer holder and an aspherical lens arranged above the wafer holder.

[0142] Preferably, the method according to the invention is used to characterize

[0143] Surface defects on a wafer, particularly a GaAs wafer, a GaN wafer, or an InP wafer, are used, and more preferably, particles and COPs are distinguished and characterized. Thus, it is possible to differentiate between particles and COPs, and the size of these surface defects can also be determined. Certain patterns can also be recognized for other surface defects, such as scratches or surface defects.

[0144] The aim is to resolve the scattering behavior in the wide-angle and narrow-angle ranges between COPs and particles to such an extent that sufficient separation of the two defects is possible. This is particularly important for gallium arsenide, since, unlike silicon wafers, for example, an azimuthal partition of the solid angle range is necessary to separate COPs from particles. Reference is made in particular to Fig. 11.

[0145] The present application is not limited to the embodiments mentioned above.

[0146] For example, it is possible to place filters in front of the detector, such as a bandpass filter or analyzer filter. A bandpass filter can be used to analyze inelastically scattered light, e.g., photoluminescence. The sensor's sensitivity may then not be optimal; however, by filtering only a portion of the detector elements, particle measurement and photoluminescence measurement could be combined in a single step.

[0147] Furthermore, scattering cross-sections are highly dependent on polarization. Analyzer filters can thus be used to vary the scattering cross-sections, providing additional information about defects.

[0148] Furthermore, the power supply to each segment of the detector array could be individually configured, allowing the gain to be varied segment by segment. This enables an expansion of the dynamic range, in which detector segments with low scattering intensities can be operated with higher gain, and segments with high measured scattering intensities with lower gain. Since the reflected beam leaves the collector optics undisturbed, it can be used for other simultaneous measurements (haze, depolarization).

[0149] For measuring particle sizes in light scattering, a standard measurement of polystyrene latex spheres (PSL) deposited on silicon wafers was performed. This allows the correlation between particle size and measured intensity of scattered light to be calibrated in different solid angle ranges.

[0150] Differential scattering cross sections, which describe which proportions of the light are scattered into a solid angle region, were determined for the PSL spheres using the SCATMECH library:

[0151] : / / www.nist.qov / services-resources / software / scatmech-polarized-liqht-scatterinq-c-

[0152] The simulation is verified to reproduce the results from the following publication (especially Fig. 6): Wafer Inspection Technology Challenges for ULSI Manufacturing, Stan Stokowski and Mehdi Vaez-Iravani, CP449, Characterization and Metrology for ULSI Technology: 1998 International Conference edited by DG Seiler, AC Diebold, WM Bullis, TJ Shaffner, R. McDonald, and EJ Walters, The American Institute of Physics 1-56396-753-7, 1998, https: / / aip.scitation.org / doi / abs / 10.1063 / 1.56824

[0153] To estimate the differential scattering cross-sections of COPs in gallium arsenide, the electronic dipole approximation method was chosen. The following literature derives an analytical solution for the light scattering intensity of cuboid particles or COPs on or in surfaces whose geometry is aligned parallel to the incident light:

[0154] Light Scattering by Small Particles and Small Defects on the Silicon Wafer Surface - Calculations of Scattering Light Intensity and Optical Image through a Lens -, Toshihiko Kataoka et al., Zeitschrift der Japanischen Gesellschaft für Feinmechanik, 2000 Vol. 66 No. 11 pp. 1716-1722, https: / / doi.org / 10.2493 / jjspe.66.1716

[0155] After reproducing the results, the integral in equation 35 is solved numerically by replacing the integral over the volume with the sum over many volume elements with an edge length "X". This allows the estimation of the scattered intensities even for defects rotated relative to the incident beam.

[0156] REFERENCE MARK LIST

[0157] V Device for measuring surface properties of wafers

[0158] 1 light source

[0159] 2 Detector arrangement

[0160] 2-1 Area Detector

[0161] 2-2 Area Detector

[0162] 2-3 area detector

[0163] 2-4 area detector

[0164] 2-5 Area Detector

[0165] 3 wafer holder

[0166] 4 evaluation units

[0167] 5 columns

[0168] 6 Radiation deflection device

[0169] 6a Concave mirror

[0170] 6b lens

[0171] 6c Holding device

[0172] W Wafer

[0173] P particles

Claims

PATENT CLAIMS 1. Device (V) for measuring surface properties of wafers, comprising: a light source (1) adapted to emit a directed beam of light; a detector arrangement (2) adapted to detect an azimuthal scattering characteristic, a forward orientation of the emission characteristic and zenith scattering which occur when the light beam hits the wafer (W), a wafer holder (3) on which a wafer can be stored, and an evaluation unit (4).

2. Device (V) according to claim 1, wherein the detector arrangement (2) comprises several area detectors, preferably at least five area detectors (2-1 , 2-2, 2-3, 2-4, 2-5).

3. Device (V) according to claim 2, wherein at least four area detectors (2-1 , 2-2, 2-3, 2-4) are arranged perpendicular to the plane in which the wafer holder (3) lies, and one area detector (2-5) is arranged parallel to the plane in which the wafer holder (3) lies, wherein two gaps (5) are provided between each pair of area detectors (2-1 , 2-4; 2-2, 2-3), and the gaps (5) are opposite each other with respect to the point at which the beam of the light source (1 ) strikes the wafer (W).

4. Device according to one of the preceding claims, wherein the evaluation unit (4) is configured to analyze an azimuthal scattering characteristic (asymmetry of scattering in the plane), an orientation of the radiation characteristic in the forward direction, and a zenith scattering perpendicular to the surface.

5. Device according to claim 4, wherein the evaluation unit (4) is configured to determine an azimuthal asymmetry of the scattering in the plane by comparing the scattering to the left and right of the beam of the light source (1), and / or wherein the evaluation unit (4) is configured to determine a forward direction of the radiation characteristic by comparing the scattering forward and backward, each as seen from the point of impact of the beam of the light source (1) on the wafer (W), and / or wherein the evaluation unit (4) is configured to determine a zenith scattering by comparing the scattering perpendicular to the surface of the wafer and the scattering forward, backward, right and left, each as seen from the point of impact of the beam of the light source (1) on the wafer (W).

6. Device according to claim 1, wherein the detector arrangement (2) comprises an area detector (2-1 ) and at least one beam deflection device (6), wherein the beam deflection device (6) preferably comprises an ellipsoidal concave mirror (6a) arranged above the wafer holder (3) and an aspherical lens (6b) arranged above the wafer holder (3), wherein two slits (5) are further preferably provided in the concave mirror (6a), and the slits (5) are opposite each other with respect to the point at which the beam of the light source (1 ) strikes the wafer (W).

7. Device (V) according to one of the preceding claims, wherein the area detector(s) (2-1 , 2-2, 2-3, 2-4, 2-5) is / are designed as semiconductor detector(s), preferably as array(s) of avalanche diodes.

8. Device (V) according to one of the preceding claims, wherein the wafer holder (3) is rotatable and / or the wafer holder (3) is adapted to perform a translational movement.

9. Device (V) according to one of the preceding claims, wherein the evaluation unit (4) is adapted to read the signals of the area detector(s) (2-1 , 2-2, 2-3, 2-4, 2-5) and the rotation angle into a neural network, and to output a defect type and / or a defect size accordingly.

10. Method for characterizing surface defects on a wafer, comprising the following steps: a) Irradiating a wafer (W) attached to a wafer holder (3) with a directed light beam; optionally: rotating the wafer holder; b) Measuring the azimuthal scattering characteristic, the orientation of the emission characteristic in the forward direction, and zenith scattering, which occur when the light beam strikes the wafer (W), using a detector arrangement (2); c) Evaluating the values ​​measured in step b) with an evaluation unit (4).

11. Method according to claim 10, wherein the detector arrangement (2) comprises several area detectors, and in step c) the evaluation unit (4) • an asymmetry of the scattering in the plane is determined by comparing the scattering with the signals of the area detectors (2-1 , 2-2) to the left and right of the beam of the light source (1 ), using measured values ​​which were measured at rotation angles whose angular distance to the directions 0°, 90°, 180° and 270° is greater than 1°, preferably greater than 10°; • an orientation of the radiation characteristic in the forward direction is determined by comparing the scattering forward and backward, each viewed from the point of impact of the beam of the light source (1) on the wafer (W), using measured values ​​obtained at a rotation angle in the range of |(p-90°| or |(p-270°| > 1°, preferably > 45°, further preferably > 70°, and even further preferably > 80° were measured; • a zenith scattering is determined by comparing the scattering perpendicular to the surface of the wafer and the scattering forward, backward, right and left, each as seen from the point of impact of the beam of the light source (1) on the wafer (W), using measured values ​​obtained at a rotation angle <p im Bereich |(p-90°| oder |(p-270°| < 5°, weiter vorzugsweise < 2,5° gemessen wurden.

12. Method according to claim 10, wherein the detector arrangement (2) comprises an area detector (2-1 ) and at least one radiation deflection device (6), and in step c) the evaluation unit (4) reads the signals of the area detector (2-1 ) into a neural network and determines and outputs a defect type and / or a defect size accordingly, wherein the radiation deflection device (6) is preferably a An ellipsoidal concave mirror (6a), which is arranged above the wafer holder (3), and an aspherical lens (6b), which is arranged above the wafer holder (3), are provided.

13. Use of the method according to one of claims 10 to 12 for Characterization of surface defects on a wafer, in particular on a GaAs wafer, a GaN wafer or an InP wafer, preferably for distinguishing particles and COPs.

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