JP5148945B2 - X-ray beam spot size control - Google Patents

Description

FIELD OF THE INVENTION The present invention relates generally to analyzers, and more particularly to an apparatus and method for material analysis using X-rays.

BACKGROUND OF THE INVENTION X-ray reflectometry (XRR) is a well-known technique for measuring the thickness, density, and surface quality of thin film layers deposited on a substrate. An X-ray reflectometer typically irradiates a sample with an X-ray beam at a grazing incidence angle, ie, a small angle with respect to the surface of the sample, in the vicinity of the total external reflection angle of the sample material. Operate. An x-ray detector comprising a detector array senses reflected x-rays. By measuring the intensity of the X-ray reflected from the sample as a function of angle, an interference fringe pattern is obtained, and by analyzing this pattern, the characteristics of the film layer that causes the fringe pattern are determined. Exemplary systems and methods for XRR are described in US Pat. Nos. 5,619,548, 5,923,720, 6,512,814, 6,639,968, and 6,771, 735, the disclosure of which is incorporated herein by reference.

  The spot size and angular spread of the X-ray beam incident on the sample surface affects the spatial and angular resolution of the XRR measurement result. To control these factors, for example, US Pat. No. 6,639,968 discloses a dynamic knife edge and shutter interposed in the x-ray beam. For measurements at small incident angles, the knife edge is lowered close to the surface, breaking the incident x-ray beam, thereby shortening the horizontal dimension of the spot on the surface. (In this patent application and claims, the spot dimension in a direction along the surface parallel to the projection of the beam axis on the surface is, by convention, referred to as the horizontal dimension, while the dimension in the direction perpendicular to the beam axis. Are referred to as lateral dimensions). For large angle measurements where a dynamic shutter is used, the knife edge is raised from the path and the full intensity of the x-ray beam is used. As another example, US Pat. No. 6,771,735 uses two “gates” to block certain portions of the x-ray beam.

  US Pat. No. 6,895,075, whose disclosure is incorporated herein by reference, describes a system that combines XRR with small angle X-ray scatterometry (SAXS). This system uses the dynamic knife edge and shutter of US Pat. No. 6,639,968, with a slit to limit the horizontal dimension of the beam in the horizontal direction (perpendicular to the surface of the sample). ) Control the incident beam. The minimum slit width is said to be about 100 μm.

  U.S. Patent Application Publication No. 2006/0062351, which disclosure is incorporated herein by reference, describes another multifunctional X-ray analysis system that uses XRR, SAXS and X-ray. Combined with diffraction (XRD) measurement. In one embodiment shown in FIG. 5 herein, the knife edge is made from a cylindrical, x-ray absorbing material, such as a metal wire. In this device, it is said that the lower edge of the knife can be placed close to the surface of the sample up to about 3 μm on the surface without the risk of damaging the sample. The wire can be precisely aligned with the surface, which typically creates a small gap on the surface whose effective height is uniform over the entire angular range of interest from 0 ° to 4 °. Can be provided. Based on this example, in this patent application and in the claims, the term “knife edge” is used to build this gap between the knife edge and the surface and close to the surface of the sample to prevent X-rays outside the gap. It will be understood that any type of straight edge (which is not necessarily required to be very sharp) is placed on the surface.

  Embodiments of the present invention provide an improved apparatus and method for controlling the effective spot size and angular spread of a radiation beam in a target area on the surface of a sample. As used herein, the term “effective spot size” refers to the spot size on the sample surface from which the radiation scattered (reflected or otherwise) is received by the detector.

  In one embodiment, the beam control assembly includes a beam blocker having a lower side that can be placed very close to the sample surface. The beam blocker includes front and rear slits, which are typically orthogonal to the lower side of the beam blocker. The beam blocker is installed such that the slit is located on the opposite side of the target area and defines a beam surface including the target area. In some of these embodiments, a beam limiter is installed in the beam plane to block a portion of the plane. The beam limiter has a knife edge protruding in the direction across the beam surface, typically below the lower side of the beam blocker. The beam control assembly can be used in a variety of X-ray inspection techniques, such as XRR, XRD, and SAXS, described above.

  In a typical XRR, for example, the assembly is such that the beam plane is aligned with the x-ray beam incident on the sample and the knife edge is positioned adjacent to the target area and parallel to the surface of the sample without contact. Installed. In this configuration, the lateral dimension of the X-ray spot formed on the surface and the angular spread of the beam in the lateral direction are limited by the width of the slit. The horizontal dimension of the spot is limited by the knife edge. (Or, the beam blocker can be used to limit the lateral dimension of the spot by itself, without a knife edge, and / or by other means of limiting the horizontal spot dimension).

  The spot size can thus be very small with a size of several microns or less in the lateral direction. Furthermore, the beam blocker can be made sufficiently wide and the underside of the beam blocker can be placed close enough to the surface of the sample, so that the sample outside the area of the slit at an angle above a certain minimum angle. All X-rays incident on the surface hit the beam blocker and can thus be prevented from reaching the XRR detector. (X-rays below this minimum angle can also be blocked otherwise by dynamic shutters, as described in "Background of the invention"). Thus, the use of the beam control assembly facilitates X-ray analysis of the sample surface with finer spatial and angular resolution than can otherwise be achieved.

  In other embodiments, the lateral spread of the beam is controlled without necessarily using a beam blocker of the type described above. These embodiments are generally characterized by the lateral offset of the focal spot on the sample that our system for converging energetic radiation such as X-rays varies as a function of elevation. Is based on the discovery that This offset results in a substantial increase in spot size when the sample is illuminated over a range of angles, similar to the XRR system known in the prior art.

  To overcome this problem, in some embodiments of the invention, the beam is continuous in each of a number of different elevation angles (or in different partial angular ranges in the vicinity of each of these different elevation angles). ) And controlled to hit the target area. The lateral offset of each of the beams is determined for each different angle, and a lateral correction is applied to either the beam, the sample, or both to compensate for the respective offset. Thus, by maximizing the overlap between irradiated spots on the sample at different elevation angles, the effective lateral spread of the spots is minimized.

  Thus, according to one embodiment of the present invention, an apparatus for analyzing a sample comprising a radiation source configured to direct a radiation beam along a beam axis and impinge on a target area on a surface of the sample; A detector assembly configured to sense radiation scattered from the sample, and a beam control assembly having a lower side adjacent to the surface of the sample, orthogonal to the lower side, and having a beam axis A beam control assembly including a beam blocker including a front and a rear slit defining a beam plane passing through the target area, the front slit being located between the radiation source and the target area, the rear slit being a target An apparatus is provided that is located between the region and the detector assembly.

  In the disclosed embodiment, the radiation source is configured to generate a beam for the radiation to converge to a target region over a range of elevations with respect to the surface of the sample, and the detector assembly is configured to scatter Configured to decompose the emitted radiation as a function of elevation angle. Typically, the radiation includes x-rays and the detector assembly is configured to detect an x-ray reflection spectrum that is characteristic of a thin film on the surface of the sample in the target area.

Typically, the beam blocker has a width between the front and rear slits, and the lower side is positioned so that it is separated from the surface of the sample by a gap of a predetermined height, the width and height are The radiation emitted from the radiation source at an elevation angle greater than a predetermined angle with respect to the surface of the sample is selected to prevent it from passing through the gap and striking the detector assembly. In one embodiment, the width and height are selected to satisfy the relation α _min ≈2 h / W, where α _min is a predetermined angle, h is the height, and W is the width. Additionally or alternatively, the apparatus comprises a shutter positioned between the radiation source and the sample and positioned to block radiation emitted from the radiation source below a predetermined angle.

  In one embodiment, the beam control assembly includes a beam limiter positioned between the front and rear slits across the beam surface, the beam limiter between the underside of the beam blocker and the sample. A knife edge is provided adjacent to and parallel to the surface of the sample in the region, the knife edge defining a gap between the sample surface and the knife edge, and blocking the portion of the beam that does not pass through the gap. In one embodiment, the lower side of the knife edge adjacent to the target area is rounded and the gap is 3 μm or less. Additionally or alternatively, the beam limiter has a center, the center delimits the beam surface, has a knife edge, is adjacent to the surface of the sample outside the center and tilts upward away from the knife edge With external edges.

  In one embodiment, the beam blocker comprises a single block of material having a longitudinal slit formed therethrough, the longitudinal slit being at the front And a rear slit. In another embodiment, the beam blocker comprises separate front and rear blocker units, each including a front and rear slit. In yet another embodiment, at least one of the front and rear slits has a non-uniform width profile in a direction across the beam surface.

  In the disclosed embodiment, the front and rear slits have a dimension across the beam axis that is 50 μm or less, and the dimension may be 10 μm or less.

  According to an embodiment of the present invention, there is provided a method for analyzing a sample, in which a radiation beam is guided along a beam axis and applied to a target area on the surface of the sample, a beam blocker is interposed in the beam, The beam blocker includes a beam axis and includes front and rear slits that define a beam plane that passes through the target region, with the beam blocker interposed so that the underside of the beam blocker is adjacent to the surface of the sample and the radiation beam is The radiation scattered from the sample in the beam plane through the front slit before hitting the target area is allowed to pass through the rear slit, and the radiation is scattered from the sample after passing through the rear slit. A method is provided that includes sensing radiation.

  In accordance with an embodiment of the present invention, an apparatus for analyzing a sample comprising a radiation source configured to direct a radiation beam along a beam axis and impinge on a target area on a surface of the sample, and to scatter from the sample A detector assembly configured to sense the emitted radiation, and a beam interposed between the radiation source and the sample, thereby limiting the size of the beam impinging on the sample to 50 μm or less in a direction transverse to the beam axis Further provided is an apparatus comprising a control assembly.

  In some embodiments, the dimension is 10 μm or less.

  In accordance with an embodiment of the present invention, a method for analyzing a sample comprising directing a radiation beam along a beam axis to impinge on a target area on a surface of the sample and applying a beam control assembly to Further provided is a method comprising limiting the size of the beam impinging to 50 μm or less in a direction transverse to the beam axis and sensing radiation scattered from the sample.

  In accordance with an embodiment of the present invention, a method for analyzing a sample, wherein a radiation beam is directed onto a target area on the surface of the sample at each of a plurality of different elevation angles along the beam axis. And determining the respective offset of the beam in the direction across the beam axis for each of the different angles and directing the radiation beam to strike the target area at each of the different elevation angles Applying a lateral correction to at least one of the beam and sample to compensate for each offset, and the beam undergoes a lateral correction while irradiating the target area at each of the different elevation angles Further provided is a method comprising sensing radiation scattered from a sample.

  In the disclosed embodiment, directing the beam includes directing the radiation and converging the radiation onto the target area over each of the successive angular ranges in the vicinity of each of the different elevation angles. Sensing includes resolving scattered radiation as a function of elevation within each range. Typically, the radiation includes x-rays, and decomposing the scattered radiation includes detecting an x-ray reflection spectrum that is characteristic of the thin film on the surface of the sample in the target area.

  In some embodiments, directing the beam includes positioning the beam limiter between the radiation source and the sample and adjusting the beam limiter to pass the radiation at each successive different elevation angle, while , Including blocking radiation emitted from a radiation source at another elevation angle. In one embodiment, positioning the beam limiter positions the shutter for each predetermined elevation angle to block radiation emitted from the radiation source at any elevation angle less than the predetermined elevation angle. And positioning the beam clipper to block radiation emitted from the radiation source at any elevation angle greater than a predetermined elevation angle.

  Typically, the beam strikes each spot in the target area at a different elevation angle and applying lateral correction results in lateral correction so that the overlap between each spot is maximized. Including selecting. In the disclosed embodiment, the spot has a dimension of 50 μm or less in the direction across the beam axis.

  Typically, applying lateral correction includes shifting at least one of the beam and the sample in a direction parallel to the surface of the sample.

  According to an embodiment of the present invention, an apparatus for analyzing a sample, comprising: a radiation source configured to direct a radiation beam over a range of elevation angles toward a target area on the surface of the sample; A detector assembly configured to sense radiation scattered from the sample and control the beam so that the radiation is within a range and at a plurality of consecutive different elevation angles on a target area along the beam axis A beam limiter configured to impinge, a movable assembly configured to displace at least one of the beam and the sample in a direction across the beam axis, and a beam in a direction across the beam axis at each of the different elevation angles. Record each offset and compensate for each offset while the movable assembly illuminates the target area at each of the different elevation angles of the beam. Therefore, the apparatus comprising a processor coupled to control to apply lateral correction to at least one beam and the sample are also provided.

  According to an embodiment of the invention, a method for analyzing a sample, wherein a radiation beam is directed to strike a target area on the surface of the sample at each of a plurality of different elevation angles along the beam axis. Determining a respective offset of the beam in a direction transverse to the beam axis for each different angle, sensing radiation scattered from the sample at each successive different elevation angle; A method additionally comprising applying a lateral correction to at least one of the beam and the sample to compensate for a respective offset at each of the different elevation angles while sensing radiation at each of the different elevation angles. Provided.

  The invention will be more fully understood from the following detailed description of the embodiments, taken together with the drawings.

  FIG. 1 is a schematic diagram of a system 20 for X-ray reflectometry (XRR) of a sample, such as a semiconductor wafer 22, according to an embodiment of the present invention. The system 20 can be used, for example, in semiconductor manufacturing facilities to identify process defects and estimate process parameters at different stages of the wafer manufacturing process. The sample 22 is mounted on a mounting assembly, such as a movable stage 24, allowing precise adjustment of the sample position and orientation. The X-ray source 26 irradiates a target region 28 on the sample 22 with an X-ray focused beam 27. X-rays in the diverging beam 29 scattered from the sample are typically collected by a detector assembly 30 comprising a detector array. Details of the X-ray source and detector assembly that can be used in this configuration are described in the references cited in the "Background of the Invention".

For XRR measurements, the focused beam 27 can be a wider or narrower range, but typically the region 28 at a grazing angle over a range of incident angles from about 0 ° to 4.5 °. It hits. In this configuration, the detector assembly 30 has a diverging beam 29 over a range of angles in the vertical direction as a function of elevation angle (φ) between about 0 ° and at least 2 °, typically up to 3 °. Condensing. This range includes angles below and above the critical angle Φ _{c of the} sample for total external reflection. (For clarity of illustration, the angular range shown in the figure is exaggerated, such as the elevation of the x-ray source 26 and detector assembly 30 from the surface of the sample 22. Convenience and clarity. Thus, in this figure and in the following description, the sample surface is an arbitrary XY plane, where the Y axis is parallel to the projection of the axis of the X-ray beam on the sample surface. Vertical direction and perpendicular to the sample surface).

  A dynamic beam control assembly 36 and a shutter assembly 38 are used to limit the angular spread of the incident beam 27 of x-rays in the vertical (Z) and horizontal (X) directions. The beam control assembly comprises a knife edge unit 39 which will be described in detail with reference to the subsequent figures. The height of the knife edge unit and shutter relative to the sample surface can be adjusted according to the type of measurement being performed and the range of measurement angles of interest.

  The signal processor 40 receives and analyzes the output of the detector assembly 30 to determine the distribution 42 of x-ray photon flux scattered from the sample 22 as a function of angle at a given energy or over a range of energy. To do. Typically, the sample 22 has one or more thin surface layers, such as thin films, in the region 28, and the distribution 42 as a function of angle is determined by the boundary between the outer layers and the layers. A characteristic structure for the interference effect by the surface is presented. The processor 40 analyzes the characteristics of the angular distribution to determine the characteristics of one or more surface layers of the sample and also functions as a system controller to set the position and configuration of other system components. , And adjust.

  In certain XRR applications, such as testing a thin film layer on a patterned semiconductor wafer, the spot size of the X-ray beam in the target region 28 is on the order of about 1 to 10 μm, at least in the lateral (X) dimension. It is desirable to make it very small. With a focal spot of this size, along with proper positioning of the movable stage 24, the target area of the incident X-ray beam is made into a uniform area of the wafer, such as a scribe line between dies aligned along the Y axis. Can be stacked. “Uniform” in this case means that the surface layer of the wafer and the underlying thin film are each uniform over the entire area of the focal spot. Under this condition, the blur effect due to non-uniformity is reduced, so the resolution with respect to the angle of the distribution 42 is improved. Of course, the spatial resolution at the sample surface also increases. These improvements are achieved by a new design of the beam control assembly 36 described below.

  2A and 2B show details of the knife edge unit 39 according to an embodiment of the present invention. 2A is a bottom view (viewed from the surface of the wafer 22), and FIG. 2B is a side view. The unit 39 includes a beam blocker 52 having a longitudinal slit 53 in which a beam limiter 54 is accommodated. In this way, the beam limiter is simply referred to as the slit 53, but is divided into a front slit 53a and a rear slit 53b. Both the beam blocker and the beam limiter are made of metal or other X-ray absorbing material. For example, the beam blocker and beam limiter can be composed of tungsten-carbon with nickel attached.

  Typically, the position (and especially the height) of the beam limiter is adjustable with respect to the beam blocker. Alternatively, although the beam blocker and beam limiter are shown and described as separate units for clarity, they can also be fabricated integrally from a single material. Further alternatively or additionally, the beam blocker 52 is shown in the figure as a solid single block material, but is described herein and achieves the structural and functional features recited in the claims. Other configuration modes can be used for this purpose. An exemplary alternative embodiment is described below with reference to FIGS. 3A-3C and FIGS. 4A-4B.

  The beam blocker 52 has a lower side 50 that defines a surface, and is located close to the surface of the wafer 22 and a small distance above the surface. The lower side is shown in the figure as being flat and single, with a surface parallel to the wafer surface, but may alternatively have a recess or other surface deformation. In some embodiments, the underside of the beam blocker can define a surface in a “virtual surface”, ie, a space defined by the function of the beam blocker proximate to the wafer surface. The alternative embodiments of FIGS. 3A-3C, FIGS. 4A and 4B have a lower side of this type.

  In FIG. 2B, the distance between the lower side 50 and the wafer surface 22, indicated by h, may be at a level of about 10 μm, although longer or shorter distances are used depending on application conditions. You can also. The width of the beam blocker 52 in the axis (Y) direction, labeled W in FIG. 2B, is typically much larger than h. The slit 53 defines a beam plane that is aligned with the incident X-ray beam in the YZ plane and thus passes through the target region 28. The slit is typically about 50 μm wide, but can be narrowed to the desired width in the transverse (X) direction to limit the beam spread (this is technically possible). ). For example, the lateral dimension of the slit may be 10 μm or less to thereby limit the lateral dimension of the X-ray spot on the sample 22. The beam blocker 52 is positioned such that the front slit 53 a is located between the radiation source 26 and the target area 28, while the rear slit 53 b is located between the target area and the detector array 32. In this way, X-rays in the YZ plane in the slit, such as the light ray 56, pass through the slit 53a over the entire range of elevation angles, and are reflected by the surface of the wafer 22 below the beam limiter 54, and the slit. It exits from 53b and strikes the detector array 32.

X-rays outside the slit 53 are blocked by the front of the beam blocker 52 or pass through a gap between the lower side of the beam blocker and the wafer surface. The latter ray, such as ray 58, that strikes the wafer surface at an elevation angle greater than some minimum angle α _min is reflected off the wafer and strikes the lower side of the beam blocker 52 and is absorbed there. It can be seen that for a given W and h, α _min ≈2 h / W. Light rays that are incident at an angle less than α _min are blocked by proper setting of the shutter 38. In a typical XRR configuration, α _min can be set to an angle slightly smaller than the critical angle Φ _c of the wafer 22, ie α _min = 0.2 °. Under these conditions, at h = 10 μm, a beam blocker with a width W ≧ 5.73 mm will block substantially all rays that exceed α _min .

Alternatively, α _min may be changed according to application conditions. For example, the blocker 52 may be installed above the wafer 22 and at a higher position that does not affect the measurement at a small angle. Since the XRR signal from the surface layer tends to increase in intensity at such a small angle, the region outside the desired measurement region (from the scribe line when measured along the scribe line) The influence of background noise mixed in the signal from a remote area is negligible. The slit 53 still restricts the beam at larger angles where the effects of background noise are more problematic.

  The beam limiter 54 is held by the unit 39 in a plane crossing the slit 53 and blocks at least the lower side of the slit. The beam limiter has a knife edge 60 that generally projects from below the lower side of the beam blocker 52. Alternatively, in some applications, the beam limiter may be retracted so that the knife edge is above the lower side of the beam blocker. In order to minimize the horizontal (Y) dimension of the X-ray spot on the wafer 22 surface, a knife edge 60 may be placed close to the wafer surface, for example in the range of 1 to 3 μm from the surface. it can. In order to reduce the possibility of damage to the wafer and to maintain an effective height of the knife edge on the wafer that is uniform throughout the angular range of interest, the above-mentioned US Patent Application Publication No. 2006/0062351 described above. The edge 60 can also be rounded as described in. For example, the edge 60 may comprise a tantalum wire of an appropriate diameter. Alternatively, edge 60 may be fabricated by any other suitable process, may comprise any other material (such as the tungsten / carbon / nickel material described above), and is known in the prior art. May have any other suitable shape.

  3A-3C, a beam control assembly 70 is schematically shown according to another embodiment of the present invention. The assembly 70 can be used in place of the beam control assembly 39 in the system of FIG. 3A is a bottom view of the assembly 70 (when viewed from the wafer 22 along the Z-axis), and FIGS. 3B and 3C are cross-sectional views taken along lines IIIB-IIIB and IIIC-IIIC, respectively, of FIG. 3A. is there.

  The operating principle of assembly 70 is similar to assembly 39, and in the various figures, similar elements are numbered the same. However, in the assembly 70, the front and rear blocker units 72 and 74 are replaced with the beam blocker 52. The blocker unit has front and rear slits 76 and 78 that serve as slits 53a and 53b, respectively. Typically, blocker units 72 and 74 are aligned and held together on a mount, which moves the unit up and down with respect to wafer 22. In this case, the lower edges of the two blocker units constitute the lower part of the beam blocker and define a surface that is positioned at a height h above the wafer. Alternatively, the two blocker units may be individually adjustable.

  Beam limiter 80 is positioned between blocker units 72 and 74 across the plane of slits 76 and 78 and blocks at least a portion of the radiation on this plane. Typically, the beam limiter edge 60 is positioned very close to the surface of the wafer 22 below the lower surface defined by the lower edge of the blocker unit. Alternatively, the beam limiter 80 may be raised to a higher position.

  As shown in FIG. 3C, the beam limiter 80 may be significantly wider than the slits 76 and 78. This type of wide beam limiter is effective in reducing the amount of stray radiation that scatters below the beam blocker unit and strikes the detector array 32. On the other hand, wide beam limiters present difficulties when positioning the edge 60 in parallel and very close to the wafer surface, especially because the wafer surface is not perfectly flat. In order to improve such difficulty, as shown in the figure, the edge 60 may be formed only in the central portion of the beam limiter 80, and the outer edge 82 may be inclined slightly upward. For visual clarity, the outer edge 82 is inclined acutely with respect to the edge 60 in FIG. 3C, but in practice the outer edge is on the order of 0.1 ° to 1 °, and more Inclined upward at a small angle.

  4A and 4B schematically illustrate a beam control assembly 90 according to yet another embodiment of the present invention. The assembly 90 can be used in place of the assembly 39 in the system of FIG. 1, and similar features are again numbered the same. 4A is a bottom view of assembly 90 and FIG. 4B is a side view.

  The assembly 90 includes a beam blocker 92 having a slit 94 extending therethrough. Similar to the beam blocker 39, the slit 94 is divided by the beam limiter 54 into front and rear slits 94a and 94b. The slits 94a and 94b have an outer shape with a non-uniform width in the X direction as shown in FIG. 4A, and have relatively wide outer ends on the front and rear surfaces of the beam blocker, Has a narrow waist. In this example, the outline of the slit is triangular, but other non-uniform outlines can be used as well. Since the convergent beam 27 converges in the X direction (with the convergence in the Z direction in FIG. 1), the triangular slit increases the power of the beam incident on the target region 28 and reflected on the detector array 32. Is effective.

  As shown in FIG. 4B, the lower side of the beam blocker 92 is not flat and is recessed for convenient alignment with the surface of the wafer 22. The lower surface at height h on the wafer surface is in this case defined by front and rear lower edges 96 and 98. The shape of the beam blocker 92 (similar to the shape of the other beam blockers and beam limiters shown above) is shown only as an example, and other shapes that can be used to achieve a similar effect are It will be apparent to those skilled in the art and are intended to be within the scope of the present invention.

  FIG. 5 is a plot of beam offset as a function of elevation angle according to an embodiment of the present invention. To draw this plot, the beam from the radiation source 26 (FIG. 1) was irradiated onto the test surface, and the detector assembly 30 measured the intensity of the reflected beam as a function of elevation. The intensity of the signal output from each element of detector assembly 32 was monitored as a vertical knife edge (not shown) moved slowly in the X direction across the incident beam. The X coordinate of the knife edge where the signal from one detector element falls to half its original intensity was taken as the center of the incident beam for the corresponding elevation angle. In this way, the processor 40 can determine the lateral (X direction) offset of the center of the spot formed in the target region 28 by the beam 27 for different elevation angles.

  If the x-ray source 26 is optically perfect, the center of the beam will have the same x coordinate regardless of elevation angle. However, it can be seen from FIG. 5 that the center of the beam is shifted approximately 25 μm in total when the elevation angle is increased from 0 ° to 4 °. Obviously, this shift is due to aberrations in the x-ray equipment used to focus the beam 27 onto the target area 28. (However, the shift correction method described below can be used regardless of the cause of the shift). If this shift cannot be controlled, the spot on the target area 28 is effectively widened by the total shift. That is, when the lateral size of the focal spot at a single elevation angle is 40 to 50 μm, the actual spot size over an angular range between 0 ° and 4 ° is about 65 to 75 μm. This reduces the detection resolution of the system 20.

  6A-6C are schematic side views of the elements of the beam limiter and movable control assembly according to an embodiment of the present invention that can be used to solve this problem. The beam limiter in this embodiment includes a shutter 100 and a beam clipper 102, which may be similar in configuration and operation to the shutter described above. Alternatively, other types of beam limiting devices can be used to achieve the purpose of this beam limiter, which will be apparent to those skilled in the art.

  In each of FIGS. 6A-6C, the shutter 100 and clipper 102 are tuned to accept radiation over a different range of elevation angles within the beam 27 while blocking radiation at angles outside the range. Thus, for example, FIG. 6A shows an adjustment configuration that allows radiation in the range of 0 ° to 1 ° to strike the target region 28, while the adjustment configurations of FIGS. 6B and 6C are respectively Allows radiation in the range of 1 ° to 2 ° and 2 ° to 3 °. (The angles are exaggerated in these figures for visual clarity.) Alternatively, the beam limiter can be tuned to accept radiation over a different range that is greater than or less than the above range, less or more.

  The processor 40 (FIG. 1) advances the beam limiter at successive, different elevation angles. For each range, the processor determines a lateral beam offset value associated with the elevation angle of the corresponding beam axis. These offset values are typically tabulated in advance using a calibration procedure as described above with reference to FIG. The processor can use, for example, the offset value measured at the center of each range, or it can use the average of the offset values over each range. A movable assembly, such as a translation stage, is then driven to perform lateral correction on the position of the wafer 22 so that the offset is accurately compensated. That is, for example, referring to the calibration data shown in FIG. 5, for the XRR measurement in the range of 0 to 1 ° in FIG. 6A, the processor drives the stage 24 to Shift by -5 μm. Then, for the measurement in the range of 1 to 2 ° in FIG. 6B, the stage is driven +3 μm with respect to the zero reference position, and this is continued thereafter. Alternatively, the movable assembly may shift the x-ray source to compensate for the offset instead of or in addition to shifting the wafer 22.

  As a result of this calibration and correction procedure, the mutual overlap of the spots of the target area 28 formed by the beam 27 is maximized at different elevation angles. Therefore, the practical lateral spot size is limited to a value close to the focusing limit of the X-ray instrument without aberrations that depend on the elevation angle.

  Alternatively, other means can be used to limit the range of elevation angles over which the reflected radiation is perceived. For example, in one embodiment (not shown), the beam limiter is positioned to limit the beam 29, rather than the beam 27, to the desired range of angles, as shown. As yet another example, the range of elevation angles can be limited by successively selecting different elements, or groups of elements, of the detector array 22 while appropriately adjusting the lateral correction.

  While the features of the system 20 have been described with specific reference to XRR, the principles of the present invention, particularly the beam control assembly shown above, are not limited to X-ray analysis, such as SAXS and XRD. The same can be applied to these areas. Furthermore, these principles are not restricted to the X-ray field and can be applied to analyzes using electromagnetic radiation in other wavelength ranges such as gamma radiation as well as particle beam irradiation that strikes the sample at an angle. . Therefore, it will be understood that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Further, the scope of the present invention can be conceived by those skilled in the art by reading the above description, and various features described above as well as variations and modifications not disclosed in the prior art. And partial combinations are also included.

FIG. 1 is a schematic side view of an XRR system according to an embodiment of the present invention. FIG. 2A is a schematic bottom view and a side view, respectively, of a beam control assembly according to an embodiment of the present invention. FIG. 2B is a schematic bottom view and a side view, respectively, of a beam control assembly according to an embodiment of the present invention. FIG. 3A is a schematic bottom view of a beam control assembly according to another embodiment of the present invention. 3B is a schematic cross-sectional view of the beam control assembly of FIG. 3A taken along lines IIIB-IIIB and IIIC-IIIC, respectively, in FIG. 3A. 3C is a schematic cross-sectional view of the beam control assembly of FIG. 3A taken along lines IIIB-IIIB and IIIC-IIIC, respectively, in FIG. 3A. FIG. 4A is a schematic bottom view and a side view, respectively, of a beam control assembly according to yet another embodiment of the present invention. FIG. 4B is a schematic bottom view and a side view, respectively, of a beam control assembly according to yet another embodiment of the present invention. FIG. 5 is a schematic plot of the lateral beam offset as a function of elevation angle. FIG. 6A is a schematic side view of a beam limiter at three different angle settings according to an embodiment of the present invention. FIG. 6B is a schematic side view of a beam limiter at three different angle settings according to an embodiment of the present invention. FIG. 6C is a schematic side view of a beam limiter at three different angle settings according to an embodiment of the present invention.

Claims (26)

An apparatus for analyzing a sample,
A radiation source configured to direct a radiation beam along a beam axis and impinge on a target area on the surface of the sample;
A detector assembly configured to sense the radiation scattered from the sample;
A beam blocker having a lower portion adjacent to the surface of the sample, orthogonal to the lower portion, including the beam axis, and including a front and a rear slit defining a beam surface passing through the target region. A beam control assembly comprising: the front slit is located between the radiation source and the target area; and the rear slit is located between the target area and the detector assembly ;
The beam blocker has a width between the front and rear slits, and is positioned so that the lower side is separated from the surface of the sample by a gap having a predetermined height. Is selected to prevent the radiation emitted from the radiation source at an elevation angle greater than a predetermined angle relative to the surface of the sample from passing through the gap and impinging on the detector assembly. ,
The width and height are selected so as to satisfy the relation α _min ≈2h / W, where α _min is the predetermined angle, h is the height, and W is the width. apparatus.   The radiation source is configured to generate the beam to converge the radiation to the target region over a range of elevations with respect to the surface of the sample, and the detector assembly includes the scattering assembly The apparatus of claim 1, wherein the apparatus is configured to resolve the emitted radiation as a function of elevation angle.   3. The radiation according to claim 2, wherein the radiation includes x-rays and the detector assembly is configured to detect a reflection spectrum of the x-ray that is characteristic of a thin film on the surface of the sample in the target region. The device described. The apparatus of claim 1 , comprising a shutter positioned between the radiation source and the sample and positioned to block the radiation emitted from the radiation source less than the predetermined angle.   The beam control assembly includes a beam limiter positioned between the front and rear slits across the beam surface, the beam limiter between the lower side of the beam blocker and the sample. A knife edge adjacent to and parallel to the surface of the sample in a region, the knife edge defining a gap between the surface of the sample and the knife edge and not passing through the gap The apparatus of claim 1, wherein the apparatus blocks a portion of the beam. The apparatus of claim 5 , wherein a lower side of the knife edge adjacent to the target area is rounded. The apparatus according to claim 5 , wherein the gap is 3 μm or less. The beam limiter includes a central portion, the central portion delimits the beam surface, includes the knife edge, is adjacent to the surface of the sample outside the central portion, and is inclined upwardly away from the knife edge. 6. The apparatus of claim 5 , comprising an outer edge that is connected.   The beam blocker comprises a single block of material, the single block having a longitudinal slit formed therethrough, the longitudinal slit comprising the front and rear slits. The apparatus according to 1.   The apparatus of claim 1, wherein the beam blocker comprises separate front and rear blocker units, each including the front and rear slits.   The apparatus of claim 1, wherein at least one of the front and rear slits has a non-uniform width profile in a direction across the beam surface.   The apparatus of claim 1, wherein the front and rear slits have dimensions in a direction transverse to the beam axis that is 50 μm or less. The apparatus according to claim 8 , wherein a dimension of the slit is 10 μm or less. A method for analyzing a sample comprising:
Directing a radiation beam along the beam axis and hitting a target area on the surface of the sample;
A beam blocker is interposed in the beam, the beam blocker including the beam axis, including a front slit and a rear slit defining a beam surface passing through the target region, and the beam blocker is interposed by the beam blocker interposed. The lower side of the sample is adjacent to the surface of the sample, the radiation beam passes through the front slit before hitting the target region, and the radiation scattered from the sample in the beam plane is Passing through the rear slit,
Sensing the radiation scattered from the sample after the radiation has passed through the rear slit , and
The beam blocker has a width between the front and rear slits, and the interposition of the beam blocker positions the beam blocker so that the lower portion has a predetermined height gap. The radiation is separated from the surface of the sample and the width and height are selected so that the radiation is at an elevation angle greater than a predetermined angle with respect to the surface of the sample. Preventing passage through the gap, and
The width and height are the relational expression α _min ≈2h / W, where α _min is selected to satisfy the relational expression where the predetermined angle, h is the height, and W is the width. A method characterized by being made . The beam is directed so that the radiation converges on the target area over a range of elevation angles with respect to the surface of the sample, and sensing the radiation causes the scattered radiation as a function of elevation angle. The method of claim 14 , comprising decomposing. 16. The radiation of claim 15 , wherein the radiation includes x-rays, and decomposing the scattered radiation comprises detecting a reflection spectrum of the x-ray that is indicative of a thin film characteristic on the surface of the sample in the target region. The method described. 15. The method of claim 14 , wherein directing the beam comprises positioning a shutter between a radiation source and the sample, thereby blocking the radiation below the predetermined angle. A beam limiter comprising a knife edge is positioned between the front and rear slits across the beam surface so that the knife edge is between the lower side of the beam blocker and the sample. Projecting adjacent and parallel to the surface of the sample within, defining a gap between the surface of the sample and the knife edge, and blocking a portion of the beam that does not pass through the gap. Item 15. The method according to Item 14 . The method of claim 18 , wherein a lower side of the knife edge adjacent to the target area is rounded. The method according to claim 18 , wherein the gap is 3 μm or less. The method of claim 14 , wherein the front and rear slits have a dimension across the beam axis that is 50 μm or less. The method of claim 21 , wherein the dimension of the slit is 10 μm or less. An apparatus for analyzing a sample,
A radiation source configured to direct a radiation beam along a beam axis and impinge on a target area on the surface of the sample;
A detector assembly configured to sense the radiation scattered from the sample;
A lower side interposed between the radiation source and the sample, thereby limiting the size of the beam impinging on the sample to 50 μm or less in a direction transverse to the beam axis and adjacent to the surface of the sample A beam control assembly having a portion ,
The beam control assembly is positioned such that the lower side is separated from the surface of the sample by a gap of a predetermined height, and the dimensions and height are from the radiation source and the surface of the sample. Is selected to prevent the radiation emitted at an elevation angle greater than a predetermined angle from passing through the gap and striking the detector assembly;
The dimension and height are selected so as to satisfy the relation α _min ≈ 2 h / W, where α _min is the predetermined angle, h is the height, and W is the dimension. apparatus. 24. The apparatus of claim 23 , wherein the dimension is 10 [mu] m or less. A method for analyzing a sample comprising:
Directing a radiation beam along the beam axis and hitting a target area on the surface of the sample;
Applying a beam control assembly to limit the size of the beam impinging on the sample to 50 μm or less in a direction across the beam axis;
Sensing the radiation scattered from the sample , and
The beam control assembly has a lower side adjacent to the surface of the sample, and the beam control assembly is applied to the surface of the sample by a gap of a predetermined height. And selecting the dimensions and height to prevent the radiation from passing through the gap at an elevation angle greater than a predetermined angle with respect to the surface of the sample. To be able to
The dimensions and height are related to α _min ≈ 2h / W, where α _min is the predetermined angle, h is the height, and W is the size. A method characterized by being made . 26. The method of claim 25 , wherein the dimension is 10 [mu] m or less.

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