Encoder scale for an encoder system, encoder system, manufacturing method for an encoder system, as well as scanning probe microscopy device

Abstract

The invention is directed at an encoder scale for use in an encoder system for providing a position reference in a high precision instrument, such as a scanning probe microscopy device. The encoder scale comprises a carrier substrate, wherein the carrier substrate includes an optical reference pattern for providing said positioning reference. The optical reference pattern comprises a pattern of structures which provide a characteristic local optical reflectivity for enabling said positioning via optical sensing. The encoder scale further comprises a conductive layer of a conductive material for enabling capacitive sensing in addition to said optical sensing. The invention is further directed at an encoder system for use with the above scale, a method of manufacturing an encoder scale, and a scanning probe microscopy device.

Description

[0001]P133176PC00 Title: Encoder scale for an encoder system, encoder system, manufacturing method for an encoder system, as well as scanning probe microscopy device. Field of the invention The present invention is directed at an encoder scale for use in an encoder system for providing a position reference in a high precision instrument, an encoder system, a manufacturing method for an encoder system, as well as scanning probe microscopy device including an encoder scale. Background Encoder systems are typically applied for providing a high precision positioning reference for high precision instruments, such as microscopes. In particular, scanning probe microscopy systems are typically equipped with an encoder system, which includes a highly sensitive and accurate encoder scale that is used for determining the microscope’s exact position on a sample surface to be measured, on a nanometer scale. In view of the level of precision to be achieved with such encoder scales, it is of paramount importance that the scales are well aligned with the preferred direction in the high precision instrument, and that at least their alignment and offset with respect to the coordinates to be measured is well known. Known encoder systems with 2D encoder scale typically allow monitoring of the encoder scale in three degrees of freedom, notably the X and Y direction (in cartesian coordinates) and the Rz orientation (rotation around the z-axis). However, to achieve the highest level of precision, for example required in a scanning probe microscopy system, additional monitoring is desired. For example, a sufficient signal strength of the encoder system signal is important to prevent degrade of the encoder system performance. Summary of the invention It is an object of the present invention to provide an encoder scale that overcomes the disadvantages of existing scales, and that enables a higher level of control of its alignment status. To this end, there is provided herewith an encoder scale for use in an encoder system for providing a position reference in a high precision instrument, wherein the encoder scale comprises a carrier substrate, wherein the carrier substrate includes an optical reference pattern for providing said positioning reference, wherein the optical reference pattern comprises a pattern of structures, the structures providing a characteristic local optical reflectivity for enabling said positioning via optical sensing, wherein the encoder scale further comprises a conductive layer of a conductive material for enabling capacitive sensing in addition to said optical sensing. In the encoder scale of the present invention, the additional conductive layer allows for the use of capacitive sensors by the encoder system, in addition to the optics of the encoder system. These capacitive sensors directly enable the monitoring of the alignment of the encoder scale to preferred directions in additional degrees of freedom. In particular, defining the x- and y-directions in the plane of the encoder scale, this enables the monitoring of alignment in the z-direction and in the Rx and Ry rotation directions. As a result, misalignment of the plane of the encoder system (i.e. in the Rx and / or Ry-direction) becomes measurable via the capacitive sensors and any inaccuracy caused by such misalignment may be resolved (by correcting the alignment in the Rx and Ry rotation directions) and / or accounted for (because the misalignment is known). Also the z-position becomes measurable, i.e. the height of the encoder system above the encoder scale. Therefore, any deviation from an expected height will be known to the system, and may likewise be accounted for during measurement. The carrier substrate may typically be provided by a glass substrate layer, although other suitable materials may of course be applied. For example, the carrier substrate may alternatively be provided by a ceramics layer, or a resin or polymer with suitable properties. Although in many cases, a transparent carrier substrate may provide advantages, this is not a requirement and in some embodiments the carrier substrate may be of an opaque material which may optionally be covered by one or more additional layers. The teachings underlying the present invention may be applied to various kinds of different carrier substrates. In some embodiments, the conductive layer is provided on top of the optical reference pattern including the pattern of structures. Although this may be counter- intuitive in view of the optical properties, the conductive layer becomes well measurable if located above the optical reference pattern. Furthermore, in this orientation the conductive layer may even contribute to the optical signal e.g. by operating as an anti-reflection layer or otherwise improving the optical signal strength or the contrast between regions of different optical properties within the optical reference pattern. For example, in some embodiments the encoder scale is configured for enabling said positioning via optical sensing using optical radiation of a first wavelength, wherein the conductive layer has a thickness dependent on the first wavelength. It has been found that a proper matching of the thickness of the conductive layer to the (first) wavelength of the optical radiation causes the conductive layer to decrease optical losses and thereby to improve the signal strength of the optical signal. Without being bound by theory, this is believed to be connected to the conductive layer to be operating as an anti-reflection layer, i.e. a quarter wave layer that reduces the directly reflected optical signal. Any part of the optical signal that is reflected from the surface of the scale, prior to reaching the structures that form the optical reference pattern, reduces the signal-to-noise ratio (SNR) of the optical output signal. This part of the radiation namely is of exact same wavelength, but does not convey any information because it has not been reflected from the optical reference pattern. Reducing this fraction of radiation thus yields a better SNR. In some of these embodiments, the thickness of the conductive layer is smaller than 2 micrometer; preferably smaller than 1 micrometer. Yet in some further or other embodiments, the thickness of the conductive layer is a fraction of the first wavelength, wherein said fraction is between 0.2 and 0.3, preferably approximately 0.25 times the first wavelength. In this case, the functioning of the layer as quarter wave layer will improve. In some embodiments, the first wavelength is between 850 and 900 nanometer and the thickness is between 170 nanometer and 250 nanometer, or a multiple thereof. It has been found that this combination of radiation with the proposed thickness of the conductive layer provides a strong optical signal, whilst at the same time achieving the advantages described above – i.e. enabling the use of capacitive sensors for monitoring z-position and alignment to Rx and Ry rotation axes. In some embodiments, the pattern of structures is obtained by surface modification of the carrier substrate, and wherein the conductive material is a metal. Here, the structure underneath the metal layer provides for the local optical differences that are desired for obtaining an optical reference pattern, whereas the metal layer itself functions as the conductive layer that enables the use of capacitive sensors described above. Without being bound by theory, the structure underneath the metal layer is believed to modify the roughness of the surface, as a result of earlier surface modification that have been performed in order to pattern the optical reference pattern. Due to the changed roughness (typically higher roughness) light will be scattered differently. For example, an increased roughness will lead to more scattering rather than single direction (specular) reflection. In yet further embodiments, the conductive material is an optically transparent conductive material, such as a semiconducting oxide of at least one of tin, indium, zinc, cadmium, and metals such as silver, gold, and titanium nitride; for example indium tin oxide (ITO). For example, indium-tin-oxide is a highly suitable material. The use of an optically transparent conductive layer is preferred over an opaque layer from an optical perspective, and achieves each of the above advantages of enabling capacitive sensing while also allowing the conductive layer to provide preferred optical properties as described above. For example, the thickness of the transparent conductive layer may likewise be matched to the wavelength of the optical radiation in order to improve the optical signal strength while further providing the conductive properties to the encoder scale of the present class of embodiments of the invention. In some embodiments, the carrier substrate may be covered by a metal layer, wherein the pattern of structures is obtained by surface modification of said metal layer, and wherein the conductive layer is on top of the metal layer. For example, the metal layer may be covered by an ITO layer of proper thickness, the thickness being matched to the wavelength of optical radiation that is used to perform optical sensing. In accordance with a second aspect, there is provided an encoder system for use with an encoder scale according to the first aspect, wherein the encoder system comprises one or more capacitive sensors in addition to an optical sensor, for enabling a measuring of a proximity of the encoder scale to the one or more capacitive sensors. Yet in accordance with a third aspect, there is provided a method of manufacturing an encoder scale for use in an encoder system for providing a position reference in a high precision instrument, wherein the method comprises the steps of: providing a carrier substrate; modifying a surface of the carrier substrate such as to obtain an optical reference pattern for providing a positioning reference, wherein said the optical reference pattern is provided by a pattern of structures, the structures providing a characteristic local optical reflectivity for enabling said positioning via optical sensing; covering the optical reference pattern by a conductive layer of a conductive material for enabling capacitive sensing in addition to said optical sensing. In some embodiments, said conductive layer is provided having a predetermined thickness, such as to match the thickness of the conductive layer to a wavelength of optical radiation used for performing said optical sensing. For example, the thickness may be smaller than 2 micrometers or smaller than 1 micrometers. In other embodiments, the matching may be such that the thickness of the conductive layer is a fraction of the wavelength of the optical radiation used in the encoder system for optical sensing of the position. In some embodiments, prior to said step of modifying, the carrier substrate is covered with a metal layer, and wherein during the step of modifying, a step of patterning is performed on the metal layer for providing the pattern of structures; wherein the step of covering the optical reference pattern by the conductive layer is performed by covering the optical reference pattern by a transparent conductive layer. For example, in some embodiments, the transparent conductive material comprises indium tin oxide (ITO) or a further semiconducting oxide of at least one of tin, indium, zinc, cadmium, and metals such as silver, gold, and titanium nitride. In other or further embodiments, the carrier substrate, during the step of modifying, is subjected to a step of patterning for providing the pattern of structures, wherein the step of covering the optical reference pattern by the conductive layer is performed by covering the patterned carrier substrate by a metal layer. In yet à fourth aspect of the invention, there is provided scanning probe microscopy device comprising an encoder system for providing a high precision position reference, wherein at least one of: the encoder system is an encoder system in accordance with the second aspect; the encoder system comprises an encoder scale according to the first aspect; or the encoder system comprises an encoder scale manufactured using a method according to the third aspect. Brief description of the drawings The invention will further be elucidated by description of some specific embodiments thereof, making reference to the attached drawings. The detailed description provides examples of possible implementations of the invention, but is not to be regarded as describing the only embodiments falling under the scope. The scope of the invention is defined in the claims, and the description is to be regarded as illustrative without being restrictive on the invention. In the drawings: Figures 1A to 1G schematically illustrate an encoder system, encoder scale and encoder system in accordance with various embodiments of the present invention, including various exemplaric optical reference patterns; Figures 2A to 2D schematically illustrate a method of manufacturing an encoder scale in accordance with an embodiment of the invention; Figures 3A to 3C schematically illustrate a method of manufacturing an encoder scale in accordance with a further embodiment of the invention; Figure 4 schematically illustrates a cross section of an encoder scale in accordance with yet another embodiment of the present invention; Figure 5 is a graph of the reflectivity of an encoder scale in accordance with an embodiment, dependent on a thickness of a conductive layer and for a particular wavelength of sensing radiation; Figure 6 schematically illustrates a scanning probe microscopy system in accordance with an embodiment of the invention; and Figure 7 schematically illustrates a method of manufacturing an encoder scale in accordance with an embodiment of the invention. Detailed description Figure 1A schematically illustrates an encoder system 2 in accordance with an embodiment of the present invention. The encoder system 2 comprises an encoder scale 6 cooperating with an encoder system 15, each of which is separately illustrated in figures 1B and 1C respectively in more detail. In figure 1A, the encoder scale 6 includes an optical reference pattern 7 schematically illustrated as a checkered surface of the scale 6. The skilled person will appreciate that the checkered pattern 7 is merely illustrative, and by no means limiting on the invention. In reality, the optical reference pattern 7 may be provided in many different variants and designs, each suitable for a particular use or provide its own advantages. For example, although a checkered pattern such as the illustrated optical reference pattern 7 may be useable for indicating cartesian coordinates, a completely different type of pattern may be applied as well for cartesian coordinates, or may be suitable for a different type of coordinate system. For example in the cylindrical coordinate system, the use of a checkered pattern may not be very useful, and alternatively the pattern may for example be comprised of a plurality of concentric circles and radially outgoing angle indicator lines. Furthermore, Figure 1D schematically illustrates an alternative encoding in optical reference pattern 7’, which is more commonly applied in atomic force microscopes. The pattern 7’ is again illustrated in perspective, and in top view (not shown) typically comprises straight lines and straight angles. Although again this is not to be considered limiting on the invention. The pattern could likewise comprise oblique lines and faces, and / or sharp or wide angles. In particular, it is also possible to apply a position encoder grid, wherein the actual location may be deduced from the local line pattern and / or the thickness ratio’s of lines or dimensions of the faces. Various alternative patterns 7’’, 7’’’ and 7’’’’ are illustrated in figures 1E, 1F and 1G. The pattern in 1E includes position encoding. The patterns 7’’’ and 7’’’’ in figures 1F and 1G are different from the patterns 7 and 7’ in figures 1A and 1D, but are well useable in a scanning probe microscopy (SPM) system as well. Many different types of optical patterns are available to the skilled person that may be suitably used with a variety of different coordinate systems, and which may be used in combination with the present invention. In general, it is observed that the invention as described herein should not be interpreted as being limited to the explicitly described embodiments thereof. Many of the features described are not essential to the inventive concept, and are mainly described here in order to be illustrative, such as to increase intelligibility of the invention. The various grid patterns are a good example thereof; the skilled person will appreciate that the invention may be applied in combination with other patterns than the ones described here. To this end, the extent of protection should be understood to cover the general concept of the invention. Considering the example illustrated in figures 1A through 1C, the encoder system 15 may typically comprise optical sensors 11, 12-1 and 12-2 in order to respectively determine the particular x-coordinate as well as the y-coordinate relative to a reference point. For example, the sensors 11 and 12-1, 12-2 respectively enable the determination of the present x-coordinate and two measurements of a y-coordinate of a specific point that is fixed in relation to the locations of the sensors 11, 12-1 and 12-2. In addition thereto, by performing two measurements of a y-coordinate, the sensors 12-1 and 12-2 also enable to determine a deviation in the alignment along the x- and y- directions. By determining an alignment error in the y-direction, because the x- direction is perpendicular to the y-direction, the alignment error in the x-direction will also be known. This alignment error is typically caused by a dis-alignment or rotation around the z-axis, and in terms of degrees of freedom may be referred to as the Rz orientation. The coordinate system cross 20 shows the respective perpendicular axes in the x-, y- and z-direction, as well as the rotation of degrees of freedom Rx, Ry and Rz (the rotational arrows around each of the axes). The encoder scale 6 without the encoder system 15 is schematically illustrated in figure 1B for clarity. In figure 1C, an enlargement of the encoder system 15 in accordance with an embodiment of the present invention is illustrated. The encoder system 15 comprises the optical sensors 11 for the x-direction as well as the optical sensors 12-1 and 12-2 for the y-direction and for the Rz direction. In addition thereto, the encoder system 15 comprises three capacitive sensors 14-1, 14-2 and 14-3. The capacitive sensors 14-1 through 14-3 cooperate with a conductive layer 25 that covers the encoder scale 6. Each of the capacitive sensors 14-1 through 14-3 enables to measure the local height above the surface of encoder scale 6 (i.e. transverse to the surface thereof). By measuring this height at three location, as illustrated in figure 1C, it is possible to derive therefrom the z-position, as well as the dis-alignment in the Rx and Ry rotation directions. As a result, together with the optical sensors 11, 12-1 and 12-2, the capacitive sensors 14-1, 14-2 and 14-3 enable to determine the exact position in three dimensions x, y and z, as well as the rotational dis-alignment in each of the rotation directions Rz, Rx and Ry. This is in particular useful in a high precision measurement instrument such as a microscope, in particular a scanning probe microscopy system for example. However, the encoder scale of the present invention may also be applied in many other high precision instruments, which for determining a current position relies on the use of an encoder scale 6. Figures 2A through 2D schematically illustrate a method of manufacturing an encoder scale 6 in accordance with an embodiment of the present invention. In such a method, in a first step illustrated in figure 2A, a carrier substrate 21 is provided. For example the carrier substrate may be a glass plate or may be a different kind of substrate, such as a ceramic material, a resin, a polymer surface or the like, which can be used in order to create a highly accurate optical structure thereon, which is suitable for optical sensing. Starting with the glass carrier substrate 21, a contrast layer 22 may be applied to a top surface of the carrier substrate 21. The contrast layer may for example comprise a metal or a different material that is suitable for providing sufficient contrast to the encoder scale 6 in order to create the optical reference pattern 7 thereon. For example in the embodiment illustrated in figures 2A through 2D, a metal layer 22 may have been applied which is thereafter modified in order to create the optical reference pattern 7. In figure 2C, the surface of the encoder scale 6 has been modified in order to create thereon a plurality of optical structures 23 which together form the optical reference pattern 7. For example, the layer 22 may have been modified by patterning therein the channels 24 in multiple directions in order to create the structures 23, e.g. as individual isles on the surface of a glass substrate 21. The patterning may be performed by any suitable method, such as laser patterning, etching, etcetera. This creates the optical reference pattern 7 that may be sensed using optical sensing by the optical sensors 11 and 12-1, 12-2. In figure 2C, layer 22 has been interrupted by channels 24. The channels may alternatively be deeper than drawn in figure 2C and at least partly extend in layer 21. Next, in step 2D, in accordance with the present invention, a conductive layer 25 is applied on top of the optical reference pattern 7 to the encoder scale 6. As may be appreciated, although the metal forming the metal layer 22 of figure 2B may be electrically conductive, after patterning in figure 2C, the layer 22 may no longer conductive because of the channels 24 formed therein that interrupt the conductivity. The conductive layer 25 in figure 2D adds conductivity again to the surface of the encoder scale 6. As a result, the capacitive sensors 14-1 through 14-3 of figure 1C may be used in order to locally determine the height of the encoder system 15 above the surface of encoder scale 6. The layer 25 may for example be created by an optically transparent conductive layer. For example a layer of indium tin oxide (ITO) provides excellent results in preserving the optical characteristics of the optical pattern 7, while adding conductivity to the surface of the encoder scale 6 usable for the capacitive sensors 14. As will be explained further below in relation to figure 5, further advantages may be obtained by tuning the thickness of the layer 25 to the preferred wavelength of optical radiation used for optical sensing by the sensors 11 and 12-1, 12- 2. This will be further explained below. An alternative method of manufacturing an encoder scale 6 is illustrated in figures 3A through 3C. In figure 3A, a suitable carrier substrate 21 is provided, which for example may be again a glass plate. The surface of the carrier substrate 21 is modified in figure 3B for providing the optical reference pattern 7. A plurality of channels 26 in two perpendicular directions (or a different pattern) may be formed by patterning (e.g. by laser patterning, or etching, or a different suitable patterning method). This provides the optical structures 23 on the surface that together form the optical reference pattern 7. Next, in step 3C, the surface of the carrier substrate 21 will be covered with a metal layer 27 which is electrically conductive. This will enable the capacitive sensors 14 to obtain information on the z-position and the rotation alignment in the Rx and Ry rotation directions. As may be appreciated, by requiring less steps to manufacture the encoder scale 6, the method illustrated in figures 3A through 3C provides a convenient alternative to the more complex method of figures 2A through 2D. In the latter however, i.e. the method of figures 2A through 2D, typically a better measurability of each of the degrees of freedom is obtained, because the encoder scale 6 created using the method of figures 2A through 2D provides good optical characteristics of the optical reference pattern 7 as well as optimal electrical properties of the surface of the encoder scale 6. In the embodiment created using the method figures 3A through 3C, the optical characteristics of the encoder scale 6 obtained in figure 3C are somewhat diminished by the optical properties of the metal layer 27, although they are still good enough to obtain acceptable results with an encoder system 15 in various applications. A further alternative embodiment is illustrated, in cross section, in figure 4. Here, the class carrier substrate 21 has been patterned using laser patterning for providing the optical reference pattern 7. This optical reference pattern is immediately covered by the transparent conductive layer 27’, which may be formed of ITO. Optionally, the surfaces of either the isles 23 or the channels 28 may have been modified in order to further improve a contrast of the optical reference pattern 7. Of the described alternative, the alternative obtained using the manufacturing method of figures 2A through 2D obviously provide the most optimal electrical and optical properties. Figure 5 illustrates the effect of matching the thickness of the ITO layer 25 to the wavelength used for optical sensing. The graph in figure 5 illustrates the reflectivity of the encoder scale 6 for two angles of incidence (AoI): perpendicular on the surface (0 degrees) in graph 51, and under an angles of 45 degrees with the surface in graph 52. The wavelength of optical radiation applied is indicated to be 900 nanometers. For this wavelength, an optimum appears to be obtained at approximately 230 nanometers, which is more or less a quarter wave. As may be appreciated, with this thickness, the ITO layer may act as a quarter wave layer which counteracts surface reflections from the surface of the encoder scale 6. Therefore, the usable part of the output signal, being the part that is reflected at the optical reference pattern 7 below the conductive layer 25, becomes more prominent in the output signal in absence of glare from the surface of the encoder scale 6. Thus, adding the transparent conductive ITO layer 25 with a carefully selected thickness, which is matched with respect to the desired wavelength, allows to reduce the optical noise signals caused by e.g. glare from the surface of the encoder system, and therefore improves the signal-to-noise ratio (SNR) of decoder signal. As a result, the conductive layer 25 not only allows to determine the exact position and alignment status in 6 degrees of freedom, but it also enhances the optical output signal the encoder system which thereby increases the accuracy of the positioning obtained. As follows further from figure 5, the effect on reflectivity also occurs at multiples of the above thickness of 230 nanometers. Thus, selecting a different thickness, e.g. around 470 nanometers (or maybe around 700 nanometers), may likewise improve the SNR of the output signal while further enhancing the conductivity. As may be appreciated, thicker layers may however at the same time diminish the optical properties by reducing the intensity of the reflected radiation (which has to be conveyed through a thicker layer). Hence, an optimum can be found between the optical properties and electrical properties by carefully selecting the thickness while taking the above into account. In figure 6, a scanning probe microscopy system 1 in accordance with an aspect of the invention is schematically illustrated. The system 1 comprises an encoder system 15 in accordance with an aspect of the invention, wherein the encoder system 15 cooperates with an encoder scale 6 in accordance with the present invention. In figure 6, the scanning probe microscopy system 1 comprises a base 5 and a substrate carrier 3. The figure shows only part of a substrate carrier 3 and base 5 of the SPM system 1, the dotted line indicating where the figure is truncated for illustrative purposes only. The base 5 comprises an encoder scale 6 providing a coordinate reference grid plate. The encoder scale 6 is part of a grid encoder system, which consists of the scale 6 and at least one encoder system 15. Although the application of a single encoder system 15 may in many embodiments be sufficient in order to provide accurate positioning information for a scan head 30, alternatively in a system such as the system 1 in accordance with some embodiments of the present invention, a plurality of encoder systems 15 may cooperate with the encoder scale 6. For example, each element that is moving within the working space 2 between the sample carrier 3 and the encoder scale 6 may comprise an encoder system 15 that cooperates with the encoder scale 6 in order to determine its position based on the coordinate reference grid plate of the scale 6. Such an element may for example be provided by scan head 30 illustrated in figure 6. The encoder system 15, and each further encoder system cooperating with the scale 6 (if any), cooperates with the reference grid in order to obtain the coordinate data of its current location on the scale 6. A scan head 30 may comprise a variety of different elements, but at least includes the encoder system 31 and the miniature atomic force microscope unit 32. The miniature AFM unit 32 includes a probe 35 including a cantilever 36 and a probe tip 37. The probe tip 37 is used to scan across the surface of e.g. a substrate, in order to determine the geometry of the surface topography of the substrate or the exact locations of embedded structures underneath the surface of the substrate using e.g. an acoustic signal applied to the substrate or the probe 35 or both. In the example illustrated in figure 1C a regular topography measurement is illustrated schematically. The miniature AFM 32 thus comprises a probe 35, a laser 41 (e.g. a semiconductor laser) and an optical sensor 38. The laser 41 and the optical sensor 38 together form an optical beam deflection unit (OBD unit) which enables to exactly determine the deflection of the probe tip 37 due to surface structures sensed with the AFM. The laser 41 and the optical sensor 38 are controlled by controller 40 which also obtains the sensor signal from optical sensor 38 and e.g. location data from the encoder system 31. This is transmitted to the system electronics 1. In the embodiment illustrated in figure 1C, the scan head 30 comprises an onboard processor 40 that is used as a controller of a scan head. The skilled person may appreciate that a decentral controller may be located somewhere in the SPM system to perform the same and / or additional tasks as described herein. In figure 6, the encoder system 15 is mounted on the scan head 30, which in turn is mounted to an arm 10 of a positioning unit. Electrical connections 19-1 and 19- 2 for data transfer from the scan head 30 and encoder system 15 to a central controller (not illustrated) of the system 1 are provided via the electrical connection interface 18 at the end of arm 10 where the scan head 30 is connected. Figure 6 illustrates a separate connection 19-2 from the encoder system 15 to the central controller, but the skilled person may appreciate that data transfer may alternatively be consolidated via controller 40 and conveyed via a single connection 19. The encoder system 15 in the system 1 of figure 6 is similar to the encoder system 15 illustrated in figure 1C. As can be seen, the encoder system 15 comprises the optical sensors 11, 12-1 and 12-2, and further includes the capacitive sensors 14-1 through 14-3. Figure 7 further schematically illustrates a method of manufacturing an encoder scale 6 in accordance with an embodiment of the present invention. The method 60 starts by providing a carrier substrate in step 62. On the carrier substrate, a contrast layer may be applied in step 64. For example, this may be the contrast layer 22 illustrated in figure 2D as well. This contrast layer may be patterned by performing step 66, for example using laser patterning or different suitable technique. The patterning creates a pattern of structures (e.g. 23) with trenches or openings (e.g. 26) that works as an optical reference pattern 7 e.g. when illuminated with optical sensing radiation. Thereafter, in step 68, a conductive layer may be applied to the surface of the encoder scale 6. As may be appreciated, step 64 may be omitted, as is illustrated in figures 3A through 3C, in certain embodiments of the present invention. Terminology used for describing particular embodiments is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term "and / or" includes any and all combinations of one or more of the associated listed items. It will be understood that the terms "comprises" and / or "comprising" specify the presence of stated features but do not preclude the presence or addition of one or more other features. It will be further understood that when a particular step of a method is referred to as subsequent to another step, it can directly follow said other step or one or more intermediate steps may be carried out before carrying out the particular step, unless specified otherwise. Likewise it will be understood that when a connection between structures or components is described, this connection may be established directly or through intermediate structures or components unless specified otherwise. The invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. In the drawings, the absolute and relative sizes of systems, components, layers, and regions may be exaggerated for clarity. Embodiments may be described with reference to schematic and / or cross-section illustrations of possibly idealized embodiments and intermediate structures of the invention. In the description and drawings, like numbers refer to like elements throughout. Relative terms as well as derivatives thereof should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the system be constructed or operated in a particular orientation unless stated otherwise. The present invention has been described in terms of some specific embodiments thereof. It will be appreciated that the embodiments shown in the drawings and described herein are intended for illustrated purposes only and are not by any manner or means intended to be restrictive on the invention. It is believed that the operation and construction of the present invention will be apparent from the foregoing description and drawings appended thereto. It will be clear to the skilled person that the invention is not limited to any embodiment herein described and that modifications are possible which should be considered within the scope of the appended claims. Also kinematic inversions are considered inherently disclosed and to be within the scope of the invention. Moreover, any of the components and elements of the various embodiments disclosed may be combined or may be incorporated in other embodiments where considered necessary, desired or preferred, without departing from the scope of the invention as defined in the claims. In the claims, any reference signs shall not be construed as limiting the claim. The term 'comprising' and ‘including’ when used in this description or the appended claims should not be construed in an exclusive or exhaustive sense but rather in an inclusive sense. Thus the expression ‘comprising’ as used herein does not exclude the presence of other elements or steps in addition to those listed in any claim. Expressions such as "consisting of", when used in this description or the appended claims, should be construed not as an exhaustive enumeration but rather in an inclusive sense of "at least consisting of". Furthermore, the words ‘a’ and ‘an’ shall not be construed as limited to ‘only one’, but instead are used to mean ‘at least one’, and do not exclude a plurality. Features that are not specifically or explicitly described or claimed may be additionally included in the structure of the invention within its scope. Any of the claimed or disclosed devices or portions thereof may be combined together or separated into further portions unless specifically stated otherwise, without departing from the claimed invention. Expressions such as: "means for ...” should be read as: "component configured for ..." or "member constructed to ..." and should be construed to include equivalents for the structures disclosed. The use of expressions like: "critical", "preferred", "especially preferred" etc. is not intended to limit the invention. Additions, deletions, and modifications within the purview of the skilled person may generally be made without departing from the spirit and scope of the invention, as is determined by the claims. The invention may be practiced otherwise then as specifically described herein, and is only limited by the appended claims.

Claims

Claims 1. Encoder scale for use in an encoder system for providing a position reference in a high precision instrument, wherein the encoder scale comprises a carrier substrate, wherein the carrier substrate includes an optical reference pattern for providing said positioning reference, wherein the optical reference pattern comprises a pattern of structures, the structures providing a characteristic local optical reflectivity for enabling said positioning via optical sensing, wherein the encoder scale further comprises a conductive layer of a conductive material for enabling capacitive sensing in addition to said optical sensing.

2. Encoder scale according to claim 1, wherein the conductive layer is provided on top of the optical reference pattern including the pattern of structures.

3. Encoder scale according to claim 2, wherein the encoder scale is configured for enabling said positioning via optical sensing using optical radiation of a first wavelength, wherein the conductive layer has a thickness dependent on the first wavelength.

4. Encoder scale according to claim 3, wherein at least one of: the thickness of the conductive layer is smaller than 2 micrometer; preferably smaller than 1 micrometer; or the thickness of the conductive layer is a fraction of the first wavelength, wherein said fraction is between 0.2 and 0.3, preferably approximately 0.25 times the first wavelength; or wherein the first wavelength is between 850 and 900 nanometer and the thickness is between 170 nanometer and 250 nanometer or a multiple thereof.

5. Encoder scale according to any one or more of the preceding claims, wherein the pattern of structures is obtained by surface modification of the carrier substrate, and wherein the conductive material is a metal.

6. Encoder scale according to any one or more of the claims 1-4, wherein the conductive material is an optically transparent conductive material, such as asemiconducting oxide of at least one of tin, indium, zinc, cadmium, and metals such as silver, gold, and titanium nitride; for example indium tin oxide (ITO).

7. Encoder scale according to claim 6, wherein the carrier substrate is covered by a metal layer, wherein the pattern of structures is obtained by surface modification of said metal layer, and wherein the conductive layer is on top of the metal layer.

8. Encoder scale according to any one or more of the preceding claims, wherein the carrier substrate is a glass plate.

9. Encoder system for use with an encoder scale according to any one or more of the preceding claims, wherein the encoder system comprises one or more capacitive sensors in addition to an optical sensor, for enabling a measuring of a proximity of the encoder scale to the one or more capacitive sensors.

10. Method of manufacturing an encoder scale for use in an encoder system for providing a position reference in a high precision instrument, wherein the method comprises the steps of: providing a carrier substrate; modifying a surface of the carrier substrate such as to obtain an optical reference pattern for providing a positioning reference, wherein said the optical reference pattern is provided by a pattern of structures, the structures providing a characteristic local optical reflectivity for enabling said positioning via optical sensing; covering the optical reference pattern by a conductive layer of a conductive material for enabling capacitive sensing in addition to said optical sensing.

11. Method according to claim 10, wherein said conductive layer is provided having a predetermined thickness, such as to match the thickness of the conductive layer to a wavelength of optical radiation used for performing said optical sensing.

12. Method according to any one or more of claims 10 or 11, wherein prior to said step of modifying, the carrier substrate is covered with a metal layer, and wherein during the step of modifying, a step of patterning is performed on the metal layer for providing the pattern of structures; wherein the step of covering the optical referencepattern by the conductive layer is performed by covering the optical reference pattern by a transparent conductive layer.

13. Method according to claim 12, wherein the transparent conductive material comprises indium tin oxide (ITO) or a further semiconducting oxide of at least one of tin, indium, zinc, cadmium, and metals such as silver, gold, and titanium nitride.

14. Method according to any one or more of claims 10 or 11, wherein the carrier substrate, during the step of modifying, is subjected to a step of patterning for providing the pattern of structures, wherein the step of covering the optical reference pattern by the conductive layer is performed by covering the patterned carrier substrate by a metal layer.

15. Scanning probe microscopy device comprising an encoder system for providing a high precision position reference, wherein at least one of: the encoder system is an encoder system according to claim 9; the encoder system comprises an encoder scale according to any one or more of claims 1-8; or the encoder system comprises an encoder scale manufactured using a method according to any one or more of claims 10-13.

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