Method for detecting positional deviations

Abstract

The invention relates to a method for detecting positional deviations using a laser beam (6), wherein at least two markings (9, 10) are provided on an object (8), each marking having an extent at least in one measurement direction that is less than the wavelength of the laser beam (6), wherein a first marking (9) is provided on the object (8) with spacing in the measurement direction from a second marking (10), wherein the laser light scattered by the markings (9, 10) is detected at at least two spatially separated detection points as a measurement signal while the laser beam (6) carries out relative movement over the at least two markings (9, 10), wherein it is clear from the measurement signal at the detection points at which point in time one of the markings (9, 10) is located in the centre of the laser beam (6), so that the spacing of the markings (9, 10) and thus a positional deviation from target spacing can be determined from the distance between said points in time in the measurement signal.

Description

[0001] Method for detecting position deviations

[0002] The invention relates to a detection method for determining the positioning of markings relative to one another.

[0003] DE102020116790B4 relates to a method for aligning two flat objects to each other. These flat objects are parallel to each other, each object having a marking, and both flat objects are positioned so that both markings are located exactly in the center of a laser beam. A disadvantage is that both flat objects must be positionable, so this method appears difficult to implement in the semiconductor industry.

[0004] In the semiconductor industry, it is extremely important to measure overlay accuracy in multi-stage manufacturing processes during production. Methods such as scanning electron microscopy are complex and can only measure on the surface. Optical measurements are much faster and can be performed on-site, but currently require markers with a large footprint and lack the required accuracy.

[0005] The object underlying the invention is to provide an improved method for detecting position deviations.

[0006] To solve the problem, a method for detecting position deviations using a laser beam is proposed, wherein at least two markings are present on an object, each of which has an extension at least in one measuring direction which is less than the wavelength of the laser beam, wherein a first marking is present on the object at a distance in the measuring direction from a second marking, wherein the measuring signal is the time profile of a reflected or transmitted portion of the laser light scattered by the markings at at least two spatially separated detection points, while a relative movement of the laser beam in the measuring direction takes place successively over the at least two markings, wherein the measuring signal at the detection points indicates at which time of the relative movement one of the markings is in the center of the laser beam,so that from the distance between these points in time in the measurement signal, the distance between the markings and thus a position deviation from a target distance can be determined.

[0007] The arrangement of the laser, two detectors and mirrors can be designed as explained in DE102020116790B4.

[0008] Instead of two detectors, one detector with multiple detection points can also be provided, for example in the form of a line scan camera or an image sensor. The light scattered by the markings is directed onto two different detection points of the one-dimensional or two-dimensional sensor using optics, in particular mirrors. By comparing the intensity of the incident light at the two detection points, it can be determined when a marking is located at the center of the laser beam. Each detection point can comprise one or more pixels.

[0009] The measuring device therefore comprises at least one detector at which scattered light components of the laser beam are detected separately.

[0010] Instead of actively positioning two objects, each having a marking, by superimposing the markings in the center of the laser beam, as in DE102020116790B4, the present invention detects markings that are at a fixed distance from one another, so that the positioning of the markings relative to one another is only controlled.

[0011] The advantage of the present method compared to the prior art is that the markings are present with an extension in the measuring direction which is smaller than the wavelength of the laser beam, so that the space required on the object for the markings and their detection is small. In the present invention, a pattern of small markings with a size below the wavelength of the laser beam is produced on the layers of an object in order to enable balanced homodyne detection (mixture of unscattered and scattered laser light). A laser scans the small markings and by means of balanced homodyne detection the respective positions can be determined with high accuracy.Together with the prior knowledge of the manufactured pattern, a high-resolution measurement signal is obtained that makes the overlay accuracy of the layers detectable with high precision. This leads to high overlay accuracy by intervening in the manufacturing process of subsequent objects or enables the maintenance of high overlay accuracy. The main limitations on measurement accuracy are also related to the manufacturing process of the layers and therefore scale with improvements in the manufacturing process, making the technology future-proof. In other words, as the accuracy of the manufacturing process increases, the accuracy of the method in question also increases.

[0012] Particularly preferably, at least three markings are present on the object, with the relative movement of the laser beam occurring across the at least three markings. Preferably, the relative position of one of these markings with respect to the other two markings is determined. This can be achieved, in particular, by ensuring that the target position of one of the markings is exactly midway between the other two markings.

[0013] The method can be useful in manufacturing processes for an object in which structures or layers of the object are produced in a chronological sequence and / or using multiple devices. At least two markings are applied at different stages of the process and / or using different application devices, so that the positioning accuracy between the process stages and / or the different application devices can be controlled.

[0014] The purpose of this control may in particular be to correct a detected positional deviation during the production of a subsequent object.

[0015] The markings are preferably applied using devices that also produce structures or layers on the object.

[0016] The method is particularly preferably used to detect markings on semiconductor elements, wherein the markings are formed during the application or structuring of at least one layer on a wafer. Preferably, the markings are produced in different process steps and therefore in different layers of the semiconductor element in order to be able to determine the positions of the different layers relative to one another.

[0017] In the version with three markings, two markings are produced in a first layer and the third marking in a second layer. The third marking can be located between the first two markings in the measuring direction.

[0018] The wafer can be a silicon wafer, with silicon being transparent to light in a wavelength range of 1.1–7 pm. In one embodiment, the laser beam has a wavelength in this range, particularly in the range of 1.1–2 pm, for example, 1550 nm.

[0019] However, the laser beam can also have a shorter wavelength, in which case the reflected scattered light must be measured.

[0020] The material of the marking can be identical to the material of the object, i.e. identical to the substrate of the object or identical to at least one material of the object applied to the substrate.

[0021] The material of the markings can be different from the material of the object, in particular the wafer, for example the latter can have different optical properties than the wafer at the wavelength of the laser used.

[0022] However, the markings can also be made of the same material as the wafer and differ from the regions of the wafer surrounding the markings by at least one feature. In particular, the material at the marking can be thinner or thicker than the material of the surrounding region. The markings can be produced, for example, by etching the wafer or a layer applied to the wafer.

[0023] More generally, the markings present on the object and the areas of the object surrounding the marking have at least one different feature which leads to a distinguishable scattering of the laser beam.

[0024] By arranging and moving the laser beam over at least two markings, the positioning accuracy in a first direction of the object can be determined.

[0025] In order to control the positioning accuracy in a second direction of the object, at least two markings can be present on the object in this second direction, which are then traversed by the laser beam in this second direction.

[0026] This is sufficient to measure the positioning accuracy of structures or components in a two-dimensional configuration.

[0027] The markings are preferably point-shaped. A marking is considered point-shaped if its extent is smaller than the wavelength of the laser beam. Along each measuring line of the laser beam, there are at least two, preferably at least three, point-shaped markings.

[0028] The markings in the first and second directions can, less preferably, be formed by common marking objects, for example by concentric circles in the desired position which are traversed in two different spatial directions. Another option is marking objects in the form of lines which are parallel in the desired position and which are traversed by the laser beam transversely to the longitudinal direction of the lines. The parallelism of the lines can be checked by traversing the lines at two points along their longitudinal course which are spaced apart from one another. A marking is therefore also to be understood as an area of ​​a marking object which is present in the measuring direction and which has an extension in the measuring direction which is less than the wavelength of the laser beam.

[0029] Preferably, however, the markings are point-shaped, so that in every possible measuring direction they have an extension that is less than the wavelength of the laser beam.

[0030] The distance between two marks is greater than the wavelength of the laser beam.

[0031] The minimum distance between the markings and the maximum extent of the markings therefore depend on the wavelength of the laser used.

[0032] The distance between two markers can be, for example, approximately 3pm.

[0033] The invention is illustrated by drawings:

[0034] Fig. 1: shows schematically a first variant of a measuring setup which is suitable for carrying out the method in question.

[0035] Fig. 2: shows schematically a second variant of a measuring setup which is suitable for carrying out the method in question.

[0036] Fig . 3 : Shows schematically the use of a one- or two-dimensional detector .

[0037] Fig. 4: shows schematically the resulting signal of the measuring setup when a laser beam is passed over the marking arrangement with a symmetrical arrangement of the markings.

[0038] Fig . 5 : shows schematically the resulting signal of the measuring setup when passing over the marking arrangement with a laser beam with an asymmetric arrangement of the markings .

[0039] Fig. 6-14: illustrate possible design variants of markings on the object.

[0040] The arrangement of the laser 1, the evaluation electronics 2, the at least two detectors 3, 4 and the mirror arrangement 5 shown in Figs. 1 and 2 is known from DE102020116790B4.

[0041] The detectors 3, 4 form spatially separated detection points of the device.

[0042] Fig. 3 illustrates that instead of two detectors 3, 4, a single one- or two-dimensional detector 12 can also be present, which comprises at least two spatially separated detection points.

[0043] Object 8, which is present in the measuring range of the measurement setup, differs from the two objects in DE102020116790B4.

[0044] The physical measuring principle is that a marking 9, 10 scattering the laser light 6, the extent of which is normal to the direction of the laser beam 6 is smaller than the wavelength of the laser light, causes a symmetrical scattering of the laser beam 6 when it is located in the center of the laser beam 6. The scattered light can be detected either by means of the transmitted scattered laser light 7 (Fig. 1) or by means of the reflected scattered laser light 7 (Fig. 2) by providing at least two detection points (as detectors 3, 4 or at a detector 12) at which spatially different scattered light components of the scattered laser light 7 impinge by means of a beam splitter 15. For example, this can be a left scattered light component at the first detection point (detector 3 in Fig. 1 and 2) and a right scattered light component at the second detection point (detector 4 in Fig. 1 and 2). When constructing Fig.2, in addition to the reflected laser light 7, a portion of the laser beam 6 is also guided as a reference beam by means of the four left-hand mirrors directly to the detectors 3, 4. If the measured intensities of the two detectors 3, 4 are subtracted, a zero crossing results in the case of symmetry, i.e. when a marking 9, 10 is located in the center of the laser beam 6. In the case of a one- or two-dimensional detector 12, the intensity of the light incident at the spatially separated detection points is compared. Here, too, the intensity measured at the first detection point can be subtracted from the intensity measured at the second detection point.

[0045] If the marking 9, 10 is moved from the center of the laser beam 6, one of the two detectors 3, 4 (or one of the two detection points of the detector 12) receives a stronger signal than the other. This applies to movement in both directions, so that the zero crossing when the laser beam 6 passes over the marking 9, 10 lies between a positive maximum and a negative maximum of the measurement signal, as illustrated in Figs. 4 and 5.

[0046] Since only the position of a marking 9, 10 in relation to the laser beam 6 can be determined from this information, the method according to the invention provides for at least one first marking 9 to be present, the extent of which is normal to the direction of the laser beam and is smaller than the wavelength of the laser light, which first marking 9 is present at a distance from a second marking 10 on a common object 8.

[0047] By passing over both markings 9, 10 with the laser beam 6, the distance between the two markings 9, 10 can be measured, whereby the accuracy is limited by the optical, electronic and mechanical components of the measuring arrangement.

[0048] In order to largely rule out sources of error, a preferred variant provides for the position of a second marking 10 to be determined relative to two first markings 9. It is advantageous if the second marking 10, in its desired position, lies exactly in the middle between the two first markings 9, since in this case, any influence of the measuring signal by the markings 9, 10 themselves has no effect on the measuring signal (for example, an adjacent first marking 9 could reflect stray light components when the laser beam 6 is located at the second marking 10).

[0049] In Fig. 4 and 5 the measurement signal is shown as the difference between the signal of the first detector 3 or detection point (left) and the second detector 4 or detection point (right), which results when the laser beam 6 passes over the three markings 9, 10. Whenever the laser beam 6 is located centrally above a marking 9, 10, the measurement signal passes through zero. If the zero crossings occur regularly, i.e. at the same distance from one another, this means that the second marking 10 is exactly in the middle between the first two markings 9, as illustrated in Fig. 4.

[0050] If the second marking 10 is not in its target position 11 , the corresponding zero crossing is shifted towards the zero crossing of one of the two outer first markings 9 .

[0051] The deviation ( of fset dx ) between the actual position of the marking 10 and its target position 11 can be determined therefrom.

[0052] In Figs. 6-14, possible non-limiting arrangements of markings 9 and 10 are illustrated, with the aid of which a deviation of the position of the second marking 10 relative to at least one first marking 9 can be detected.

[0053] As shown in Figs. 6-11, the first markings 9 and second markings 10 can be in the form of points which, perpendicular to the laser beam 6, have an extension in all directions which is less than the wavelength of the laser beam 6. As illustrated in Fig. 6, there can be only a single first marking 9 and a single second marking 10, which are traversed by the laser beam 6 along a single first measuring line 13.

[0054] As illustrated in Fig. 7, there may be two outer first markings 9 and a single central second marking 10, which are traversed by the laser beam 6 along a single first measuring line 13.

[0055] As illustrated in Fig. 8, in a first direction there may be only a single first marking 9 and a single second marking 10, and in a second direction there may be only a single first marking 9 and a single second marking 10, which are traversed by the laser beam 6 along a single first measuring line 13 and a single second measuring line 14, which measuring lines 13, 14 run along the first and second directions.

[0056] As illustrated in Fig. 9, in a first direction there may be two outer first markings 9 and a single central second marking 10, and in a second direction there may be two outer first markings 9 and a single second marking 10, which are traversed by the laser beam 6 along a single first measuring line 13 and a single second measuring line 14, which measuring lines 13, 14 run along the first and second directions.

[0057] As illustrated in Figs. 8 and 9, one of the markings 9, 10 can be used for both measuring lines 13, 14. However, the two measuring lines 13, 14 can also be independent of each other, so that each marking 9, 10 belongs to only one measuring line 13, 14.

[0058] As illustrated in Fig. 10, two parallel measuring lines 13 may be present in a first direction, each having only a single first marking 9 and a single second marking 10. As illustrated in Fig. 11, two parallel measuring lines 13 may be present in a first direction, each having two outer first markings 9 and a single central second marking 10.

[0059] As shown in Fig. 12, first markings 9 and second markings 10 can less preferably be present in the form of at least two marking objects, the lines and / or points of which perpendicular to the laser beam 6 when traversed in at least two directions have an extension which is less than the wavelength of the laser beam 6, so that when traversing the marking objects along the at least two directions at least two point-shaped scatterers are produced in each case in order to obtain a measurement signal in each of the directions, as shown in Figs. 4 and 5. The markings 9 and 10 can, for example, be circles which are concentric in the desired position, or as shown a point as a marking 10 within a circle which forms two markings 9 around the marking 10 in each of the directions perpendicular to the laser beam.

[0060] As shown in Fig. 13, associated markings 9 and 10 can be formed by lines that are parallel in the desired position. At another location on the object 8, additional lines can be present that run in a different direction, in particular perpendicular to the first lines.

[0061] Fig. 14 shows that position deviations can be detected by passing the laser beam 6 or two laser beams 6 over lines forming the markings 9, 10 at at least two points along their longitudinal extent, transverse to the longitudinal extent. This makes it possible to determine a parallel displacement and an angular deviation between a first structure or layer, to which at least one marking 9 is assigned, and a second structure or layer, to which at least one marking 10 is assigned. The same can also be achieved with the arrangements in Figs. 10 and 11.

[0062] To illustrate the advantages of the present method, a minimum detectable position difference of 0.2 angstroms was calculated for silicon structures as an example, using a laser with a wavelength of X = 1550 nm and a laser power of 100nW, which is focused with a numerical aperture of 0.5 and an integration time of 1 ms.

[0063] 0.2 angstroms is about three orders of magnitude smaller than the current feature size in the semiconductor industry.

Claims

Patent claims 1. Method for detecting position deviations using a laser beam (6), characterized in that at least two markings (9, 10) are present on an object (8), each of which has an extension at least in one measuring direction which is smaller than the wavelength of the laser beam (6), wherein a first marking (9) with a distance in the measuring direction to a second mark (10) is present on the object (8), wherein the time profile of a reflected or transmitted portion of the laser light scattered by the markings is detected at at least two spatially separated detection points as the measurement signal, while a relative movement of the laser beam (6) takes place in the measurement direction successively over the at least two markings (9, 10), wherein the measurement signal at the two detection points indicates at which time of the relative movement one of the markings (9, 10) is located in the center of the laser beam (6), so that the distance between the markings (9, 10) and thus a position deviation from a target distance can be determined from the distance between these times in the measurement signal.

2. Method according to claim 1, characterized in that at least three markings (9, 10) are present on the object, wherein the relative movement of the laser beam in the measuring direction takes place via the at least three markings (9, 10), wherein the relative position of a second marking (10) with respect to two first markings (9) is determined.

3. Method according to claim 2, characterized in that the target position (11) of the second marking (10) lies exactly in the middle between the two first markings (9).

4. Method according to one of claims 1 to 3, characterized in that the object (8) has structures or layers, wherein the structures or layers of the object (8) are formed in temporally successive process steps and / or be produced by a plurality of devices, wherein the application of at least one first marking (9) and at least one second marking (10) takes place at different temporal process stages and / or with different devices, so that the positional accuracy between the temporally successive process stages and / or the different devices with which the object (8) was produced can be controlled via the distance between the markings (9, 10) from one another.

5. Method according to claim 4, characterized in that in the event of a position deviation, the manufacturing process for subsequent objects (8) is adapted.

6. Method according to claim 4 or 5, characterized in that the production of the markings (9, 10) is carried out with devices which also form the structures or layers on the object (8).

7. Method according to one of claims 4 to 6, characterized in that it is carried out for detecting markings (9, 10) on an object (8) in the form of a semiconductor element, wherein the at least one first marking (9) and the at least one second marking (10) are produced in different method steps and therefore in different layers of the semiconductor element in order to be able to control the positioning of the different layers relative to one another.

8. Method according to one of claims 1 to 7, characterized in that at least two measuring lines (13, 14) are present on the object, each of which has at least one first marking (9) and at least one second marking (10).

9. Method according to claim 8, characterized in that the at least two measuring lines (13, 14) each have two outer first markings (9) and a middle second marking (10).

10. Method according to one of claims 1 to 9, characterized in that the object (8) has at least one first marking (9) and one second marking (10) perpendicular to the direction of the laser beam, which are spaced apart from one another in a first measuring direction, wherein at least one first marking (9) and at least one second marking (10) are also present in a second measuring direction, wherein in order to determine the position deviation in two dimensions, at least two markings (9, 10) are passed over by one or more laser beams (6) along each of the two measuring directions.

11. Method according to one of claims 1 to 10, characterized in that at least one measuring pattern is present on the object (8), which enables at least two markings (9, 10) to be passed over in different measuring directions, the markings (9, 10) having an extension in the respective measuring direction which is smaller than the wavelength of the laser beam (6).

12. Method according to one of claims 1 to 11, characterized in that the object (8) is moved relative to a stationary laser beam (6), or the laser beam (6) is moved relative to a stationary object (8).

13. Method according to one of claims 1 to 12, characterized in that the at least two spatially separated detection points are present as separate detectors (3, 4).

14. Method according to one of claims 1 to 13, characterized in that the at least two spatially separated detection points are present as separate areas of a one- or two-dimensional detector (12).

15. Method according to one of claims 1 to 14, characterized in that the markings (9, 10) are in the form of dots.

16. Method according to one of claims 1 to 15, characterized in that the distance between the markings (9, 10) is greater than the wavelength of the laser beam (6).

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