Patent Application
20150362340
The invention relates to a position sensor for detecting a relative position of a measurement object, in particular of an optical element of a lithography apparatus, and to a sensor arrangement and to a lithography apparatus comprising such a position sensor.
Lithography apparatuses are used, for example, during the production of integrated circuits or ICs in order to image a mask pattern in a mask onto a substrate, such as e.g. a silicon wafer. In this case, a light beam is generated by a light source. In the case of EUV (with wavelengths in the range of 5 nm-30 nm), this can be a plasma source, a synchrotron source or else a free electron laser. In the case of VUV or DUV, the light source can be an excimer laser, and an arc lamp in the case of I-line. The light generated by the light source is transformed by an illumination system such that both field and pupil on the mask to be imaged are filled, wherein the pupil forms chosen can be different in accordance with the structures to be imaged. The light reflected by the mask bears the information about the structures to be imaged, which are imaged onto the silicon substrate (wafer) via a projection lens. In the case of EUV, the short wavelengths mentioned make it possible to image tiny structures on the wafer. Since light in this wavelength range is absorbed by atmospheric gases, the beam path of such EUV lithography apparatuses is situated in a high vacuum. Furthermore, there is no material which is sufficiently transparent in the wavelength range mentioned, for which reason mirrors are used as optical elements for shaping and guiding the EUV radiation.
The individual mirrors and other optical elements should be positioned as exactly as possible with regard to their orientation, since even small deviations of the position of the mirrors can lead to the imaged structures being impaired, which can lead to defects in the integrated circuits produced. In order to monitor and, if appropriate, readjust the position of the individual mirrors, the lithography apparatus is provided with position sensors that detect the position and orientation of the mirrors, that is to say the position of the mirrors with respect to the six degrees of freedom (three translational and three rotational). Depending on the design of the lithography apparatus, it is also possible for fewer than six degrees of freedom to be actuated and, consequently, for correspondingly fewer sensor axes to be required.
The requirements made of the position sensors are very high. Firstly, their resolution and drift stability must be high enough to make possible, via a closed control loop, a sufficient positional stability in the controlled degrees of freedom of the optical element. Furthermore, they should be compact, since the space in the mirror optical unit of the lithography apparatus is very limited. Particularly in the case of adaptive optical elements that usually consist of a multiplicity of actuated elements closely strung together, sensors are required which can be close packed on a regular grid. Furthermore, the sensors should be suitable for vacuum, in order to be able to be accommodated in the vacuum region of the lithography apparatus. Finally, they should be robust toward high temperatures such as can occur near the radiation path of the lithography apparatus.
It is possible to use capacitive displacement sensors for detecting the position or the displacement of optical elements in a lithography apparatus. The basic principle of such capacitive displacement sensors consists in providing one or a plurality of metal strips provided opposite a metal strip on a measurement object. The capacitance formed by the metal strips lying opposite one another changes in the event of a displacement of the measurement object in the plane of the metal strips. By measuring the capacitance, it is thus possible to deduce the position of the measurement object.
However, the power of the measurement signal of such a capacitive displacement sensor is generally very small and therefore has a comparatively small signal-to-noise ratio. In some types of capacitive sensors, the capacitance is greatly dependent on the distance between the metal strips lying opposite one another, that is to say on the position of the measurement object perpendicular to the plane of the metal strips. Finally, it is difficult to use a displacement sensor to detect the position of the measurement object with regard to more than one degree of freedom, since this requires a complex and voluminous arrangement of the metal strips.
U.S. Pat. No. 6,483,295B2 describes an inductive position sensor comprising an oscillator circuit, which generates a periodic AC voltage signal and couples it into an excitation coil, comprising a plurality of reception coils, wherein the excitation coil and the reception coils are embodied as conductor tracks on a carrier board, and comprising an evaluation circuit for evaluating the signals induced in the reception coils, and a movable inductive coupling element, which influences the strength of the inductive coupling between the excitation coil and the reception coils. In this case, the evaluation circuit is arranged within the geometry of the transmission and/or reception coils and the effective areas of the reception coils in the beginning and/or end region of the sensor are embodied in such a way that when the movable element is not present, the summation voltage of zero arises at the taps of the reception coils. The arrangement in the document does not take into account, however, the fact that the reception voltage induced in the reception coil is not only dependent on the position of the measurement object in the measurement direction (that is to say in a shear direction), but also greatly dependent on the distance between the measurement object and the position sensor, that is to say on the distance of the measurement object in the direction with respect to the coil axis. Consequently, the arrangement disclosed in the document is suitable only for cases in which the distance between the measurement object and the position sensor is fixedly defined, e.g. via a corresponding mounting. By contrast, the arrangement is unsuitable for cases in which the distance between the measurement object and the position sensor is unknown or variable.
Document DE 697 17 188 T2 describes a varying magnetic field position and movement detector. The detector determines the position and movement of a part that contains at least a metallic section. The device comprises a primary coil which induces a magnetic field and two secondary coils to detect the magnetic field. The two secondary coils are contained within the plane so that they are parallel to the plane of the part and have a differential structure with respect to the primary coil. The part has zones of weak and strong magnetic permeability, so that the fields induced at the secondary coils are modified by the presence of zones of weak and strong permeability so that the speed or position of the part may be determined.
Document US 2009/0309578 A1 shows sensor inductors, sensors for monitoring movements and positioning, apparatus, systems and methods therefore. The planar shaped inductor is particularly adaptable for use in motion or position sensors. One inductor can function as a signal input unit and another as a pick up unit in an arrangement wherein both inductors are placed in a generally parallel juxtaposition for flux flow there between. A movable armature is located between the inductors to control the amount of flux transmission between inductors. The position of the armature relative to the inductors controls the output signal generated by the pickup inductor that are adapted to be converted into indications of displacements.
Document US 2007/0001666 A1 describes a linear and rotational inductive position sensor. The position sensor is configured to provide a signal related to a position of a part including an exciter coil, and a receiver coil disposed proximate to the exciter coil. The exciter coil generates magnetic flux when the exciter coil is energized by a source of electrical energy, such as an alternating current source. The receiver coil generates a receiver signal when the exciter coil is energized, due to an inductive coupling between the receiver coil and the exciter coil. The receiver coil has a plurality of sections, the inductive coupling tending to induce opposed voltages in at least two of the sections.
Consequently, one object of the present invention is to provide a compact and precise position sensor which meets the requirements mentioned above. In particular, one object is to provide a position sensor with which a displacement of a measurement object in a shear direction can be detected precisely even if the distance between the measurement object and the position sensor is unknown or variable. A further object is to provide a position sensor with which the position of a measurement object, such as e.g. an optical element of a lithography apparatus, can be detected with respect to more than one degree of freedom in a simple manner.
At least one of the objects is achieved—via a position sensor for detecting a position of a measurement object, in particular of an optical element of a lithography apparatus, comprising a transmission coil and a reception coil, which are arranged on different parallel planes of a printed circuit board, wherein the transmission coil and the reception coil are arranged in such a way that when a temporally variable transmission signal is applied to the transmission coil, a temporally variable reception signal is generated at the reception coil, wherein the ratio of reception signal to transmission signal contains information about the relative position of the measurement object with respect to the reception coil.
Providing the transmission coil and a reception coil on a printed circuit board makes it possible to produce a precise and compact position sensor cost-effectively. Furthermore, there is a high degree of freedom for the layout of the transmission coil and of the reception coil. The “different parallel planes of a printed circuit board” can be the front and rear sides of the printed circuit board, or else planes arranged there between parallel thereto within the printed circuit board. The transmission signal can be a transmission voltage or a transmission current. The reception signal is typically a reception voltage.
In this case, the reception coil has a first reception coil section and a second reception coil section, wherein the first reception coil section and the second reception coil section are connected to one another in such a way that when the transmission signal is applied to the transmission coil, a reception voltage is generated at the reception coil,—the reception voltage corresponding to a difference between the voltage at the first reception coil section and the voltage at the second reception coil section. In other words, the first and the second reception sections can therefore be connected in antiseries with one another, as a result of which it is possible to realize a differential sensor arrangement which responds very sensitively to changes in the position of the measurement object.
The first reception coil section and the second reception coil section are arranged on different parallel planes of the printed circuit board and are connected to one another in such a way that the transfer response of transmission coil and reception coil contains information about the position of the measurement object in a distance direction relative to the reception coil. A compact distance sensor can be realized in this way. In this case, the first reception coil section and the second reception coil section can be arranged on different sides of the transmission coil. In other words, the transmission coil and the first and second reception coil sections can be arranged, for example, on three substantially parallel planes, wherein the transmission coil is arranged between the first and second reception coil sections. Consequently, the distance sensor is more sensitive than when both reception coil sections are arranged on the same side of the transmission coil. The transfer response of transmission coil and reception coil may include or may be the transfer function.
The first reception coil section and the second reception coil section can be arranged in such a way that when a transmission voltage is applied to the transmission coil in the absence of the measurement object, substantially no voltage is present at the reception coil.
Particularly if the position sensor is designed as a distance sensor, the first reception coil section and the second reception coil section can be substantially congruent with the transmission coil. In this case, “congruent” can mean that the reception coil section have substantially (that is to say with deviations of not greater than 20%, preferably not greater than 10%) the same dimensions as the transmission coil. Particularly if the position sensor is designed as a shear sensor, the first reception coil section and the second reception coil section can each have substantially half of the area extent of the transmission coil. It is thus possible to achieve a high degree of coupling between transmission and reception coils in conjunction with a compact arrangement.
In one possible embodiment, a first and a second reception coil are provided, which each have a first and a second reception coil section, wherein the first and the second reception coil sections are in each case connected to one another in such a way that when the transmission signal is applied to the transmission coil, a reception signal is in each case generated at the first and second reception coils, wherein the ratio of reception signal to transmission signal contains information about the position of the measurement object in a shear direction relative to the reception coil. Consequently, two shear sensor signals are thus generated, such that a particularly precise measurement is made possible for example by averaging these sensor signals.
In a further possible embodiment, the position sensor comprises a plurality of reception coil sections, and a switch element having a first and a second switch position, wherein the reception coil sections are interconnected to form a first reception coil in the first switch position in such a way that when a transmission signal is applied to the transmission coil, a first reception signal is generated at the first reception coil, wherein the ratio of the first reception signal to the transmission signal contains information about the position of the measurement object in a shear direction relative to the first reception coil, and wherein the reception coil sections are interconnected to form a second reception coil in the second switch position in such a way that when a transmission signal is applied to the transmission coil, a second reception voltage is generated at the second reception coil, wherein the ratio of the second reception signal to the transmission signal contains information about the position of the measurement object in a distance direction relative to the second reception coil. In accordance with this embodiment, the position sensor can optionally be operated as a shear sensor or as a distance sensor. Depending on the switching state, the reception signal in this case correlates more strongly with displacements of the measurement object in a distance direction or with displacements of the measurement object in a shear direction.
In a further possible embodiment, the position sensor comprises a first and a second reception coil, which are designed in such a way that when a transmission signal is applied to the transmission coil, a first reception signal is generated at the first reception coil, wherein the ratio of the first reception signal to the transmission signal contains information about the position of the measurement object in a shear direction relative to the first reception coil, and when a transmission signal is applied to the transmission coil, a second reception voltage is generated at the second reception coil, wherein the ratio of the second reception signal to the transmission signal contains information about the position of the measurement object in a distance direction relative to the second reception coil. Consequently, it is possible to provide a position sensor which, with a compact arrangement, can detect the position of a measurement object with respect to a plurality of degrees of freedom. In the embodiments described above, the first reception coil and the second reception coil can be arranged on different sides of the transmission coil.
The position sensor can furthermore comprise a drive device, which applies an alternating transmission signal to the transmission coil, and an evaluation device, which evaluates the reception signal at the reception coil. The drive device and the evaluation device can be arranged on the same printed circuit board as the transmission coil and the reception coil, or on different printed circuit boards. If the drive device and the evaluation device are arranged on a different printed circuit board from the transmission coil and the reception coil, then a particularly compact arrangement can be obtained if the printed circuit boards are connected to one another in a planar manner, wherein a metal film is provided between the printed circuit boards. In this case, the metal film constitutes a barrier for parasitic inductive and capacitive coupling between the transmission and reception coils of the printed circuit board, on the one hand, and the drive and evaluation devices, on the other hand. Providing the metal film therefore ensures that the position measurement is not influenced and thus corrupted by parasitic coupling between coils and drive and evaluation devices.
In accordance with a further aspect of the invention, a position sensor for detecting a position of a measurement object, in particular of an optical element of a lithography apparatus, comprises a transmission coil, a reception coil, which is arranged in such a way that when a transmission signal is applied to the transmission coil, a reception voltage is generated at the reception coil, and an evaluation device, which links a transmission voltage signal generated in a manner dependent on the transmission signal with a reception voltage signal generated in a manner dependent on the reception voltage and generates a sensor output signal containing information about the relative position of the measurement object with respect to the coils of the position sensor. In this case, the transmission voltage signal is dependent on the distance between the position sensor and the measurement object. Consequently, it is possible to provide a position sensor with which a displacement of a measurement object in a shear direction can be detected precisely even if the distance between the measurement object and the position sensor is unknown or variable.
In one possible configuration, the evaluation device comprises a first analog-to-digital converter, which converts the voltage generated by the reception coil or an analog signal derived therefrom into a digital signal, and a second analog-to-digital converter, which converts the voltage present at the transmission coil or an analog signal derived therefrom into a digital signal.
The evaluation device can form, for example, a cross-correlation of the transmission signal with the reception signal. As an alternative thereto, the evaluation device can have a memory in which a look-up table is stored, which assigns the values of the transmission signal and of the reception signal to an output value representing the position of the measurement object relative to the position sensor. Consequently, it is possible to correct the shear sensor signal with regard to displacements of the measurement object in the distance direction.
The transfer function H(ω) of a transformer describes the ratio of the output voltage amplitude to the transmission voltage amplitude as a function of the excitation frequency ω:
For non-periodic temporally variable input signals such as white noise, for example, it is possible to determine the transfer function in a generalized form via the autocorrelation and the cross-correlation functions or from the corresponding auto and cross power densities of the input and output voltages:
The position sensor can furthermore comprise a drive device, which applies an alternating transmission signal to the transmission coil. In one possible configuration, in this case, the drive device can vary the transmission signal in a manner dependent on a sensor output signal. Consequently, the transmission signal can be adapted to the distance of the measurement object, and the influence of the distance of the measurement object on the sensor signal can be suppressed.
Furthermore, the drive device can have an impedance matching network. The reactive power that is output can thus be reduced. In one possible configuration, the impedance matching network can have an adjustable capacitor which is adjustable in a manner dependent on the sensor output signal. Consequently, the transmission signal can be adapted to the distance of the measurement object.
Furthermore, it is possible, in a sensor arrangement, to arrange a plurality of the above-described position sensors alongside one another. In this case, the position sensors can be arranged into a series alongside one another or else in a two-dimensional array. In this case, it can be provided that transmission signals having different frequencies can be applied to adjacent position sensors. Crosstalk between adjacent position sensors can thus be suppressed.
Further exemplary embodiments will be explained with reference to the accompanying drawings.
Unless indicated otherwise, identical reference signs in the figures designate identical or functionally identical elements. Furthermore, it should be noted that the illustrations in the figures are not necessarily true to scale.
The principle of a differential inductive position sensor 100 in accordance with a first exemplary embodiment is explained below with reference to
The transmission coil 104 and the reception coil 106 are arranged on different planes of a printed circuit board. By way of example, the transmission coil 104 can be arranged on one side (first plane) and the reception coil 106 can be arranged on the other side (second plane) of a printed circuit board, wherein the transmission coil 104 and the reception coil 106 be electrically isolated by an insulating layer 110 of the printed circuit board, as is indicated in
In the example illustrated in
It should be noted that in this case “coil” can be understood to mean a conductor arrangement which is substantially looped, that is to say for example a conductor arrangement running in sections in the +y-direction, +z-direction, −y-direction, and −z-direction. These conductor sections can be arranged in one plane, namely the coil plane, on or in the printed circuit board to which the coil axis is perpendicular.
The drive device 102 applies a temporally variable transmission voltage Vt (transmission signal) to the transmission coil 104. The temporally variable transmission voltage Vt can be, for example, an AC voltage of 1V and having a frequency of 1 MHz. There is no particular restriction with regard to the waveform of the AC voltage Vt, and the latter can be, for example, sinusoidal, pulsed or the like. A sinusoidal AC voltage is advantageous, however, with regard to the suppression of high-frequency components. On account of this AC voltage, an AC current It (transmission current) flows through the transmission coil 104, which current has the effect that the transmission coil 104 generates a magnetic field that is strongest in the direction of the coil axis (that is to say in the x-direction in the figures). In the coil plane, the magnetic field is oriented perpendicularly to the plane. The magnetic field is an alternating magnetic field whose frequency corresponds to the frequency of the AC voltage Vt. On account of this alternating magnetic field, a voltage Vza and Vzb is respectively induced in the reception coil sections 106a and 106b. On account of the antiseries connection of the reception coil sections 106a and 106b, the voltages Vza and Vzb mutually cancel one another out, such that overall the difference voltage Vz=Vza−Vzb is present at the reception coil 106. If the arrangement comprising transmission coil 104 and reception coil 106 is substantially symmetrical and no further metallic articles are situated in the vicinity, then the difference voltage is substantially Vz=0.
The arrangement described here makes it possible to detect the position of an electrically conductive measurement object 150. The measurement object 150 can be a metal strip, for example, which is arranged substantially parallel to the coils 104, 106. It is also possible for the measurement object 150 to consist of a doped semiconductor or the like. In a basic position, the measurement object 150 is arranged symmetrically with respect to the two reception coil sections 106a and 106b and in this case covers, as viewed from above (that is to say in the x-direction), an identical area proportion of the reception coil sections 106a and 106b. In the conductive measurement object 150, the magnetic field generated by the transmission coil 104 induces an eddy current that in turn generates an opposite magnetic field. The measurement object 150 therefore to an extent reflects the magnetic field generated by the transmission coil 104. The resulting total magnetic field passing through the reception coil sections 106a and 106b is therefore correspondingly smaller, with the result that the voltages Vza and Vzb induced in the reception coil sections 106a and 106b are also reduced. This reduction of the voltages Vza and Vzb corresponds to the extent to which the reception coil sections 106a and 106b are covered by the measurement object 150. As already indicated above, the measurement object 150 in its basic position substantially covers the same area proportion of the reception coil sections 106a and 106b, with the result that the reception voltage Vz is substantially zero. However, if the measurement object 150 is displaced parallel to the reception coils 106a and 106b (to put it more precisely in the z-direction), then it covers different area proportions of the reception coil sections 106a and 106b, with the result that the reception voltages Vza and Vzb differ. A reception voltage Vz different from zero thus results,—the reception voltage being present at the reception coil 106, wherein the amplitude of—the reception voltage Vz corresponds to the displacement of the measurement object 150 in the z-direction relative to the reception coil sections 106a and 106b. Furthermore, from the phase of the reception voltage Vz it is possible to derive whether the measurement object 150 was displaced in the z-direction or −z-direction. Furthermore, the ratio of reception signal (reception voltage Vz) to transmission signal (transmission voltage Vt) contains information about the relative position of the measurement object 150 with respect to the reception coil 106.
This position sensor 100 therefore functions as a shear sensor, wherein at the reception coil 106 a reception voltage Vz is generated which is lower than the voltages Vza and Vzb respectively generated at the reception coil sections 106a and 106b and which contains information about the relative position of the measurement object 150 in a shear direction (z-direction), with respect to the reception coil 106. Furthermore, the position sensor 100 is designed as a differential sensor, which therefore enables a more precise measurement result than a position sensor having only one reception coil.
The evaluation device 108 evaluates the reception voltage Vz and can demodulate and digitize the reception voltage Vz, for example, as will also be described in detail further below. The evaluation device 108 can output a digital signal Sz, for example, which represents the displacement of the measurement object 150 in a shear direction (z-direction) relative to the reception coil 106.
It should be noted that the measurement object 150 need not necessarily be strip-shaped. Rather, it suffices if, on account of the magnetic field generated by the transmission coil 104, an eddy current that generates a magnetic field in the opposite direction can be induced in the measurement object 150. The measurement object 150 can therefore also be embodied in a ring-shaped fashion, for example. However, a strip-shaped measurement object 150 enables a precise sensor arrangement.
The transmission coil 104 and the reception coil 106 are arranged on or in a first printed circuit board 120, whereas the drive device 102 and the evaluation device 108 are arranged on a second printed circuit board 122. The first printed circuit board 120 and the second printed circuit board 122 are separated from one another by a thin metal film 124 (e.g. composed of aluminum). This ensures that leakage fields emerging from the drive device 102 and the evaluation device 108 do not influence the reception voltage Vz and thus the measurement result. Furthermore, a very compact and flat arrangement is thus achieved.
The drive device 102 and the evaluation device 108 are connected to the transmission coil 104 and the reception coil 106 for example via flexible lines led outside the printed circuit boards or via (correspondingly insulated) through-holes in the printed circuit boards 120, 122 and the metal film 124. Furthermore, the drive device 102 and the evaluation device 108 are connected to an external control device or the like via lines (not illustrated in more specific detail) through holes in the housing 112. In this case, the housing 112 can be closed in an air-tight fashion, such that the position sensor 100 is suitable in particular for use in high-vacuum environments (e.g. in EUV lithography apparatuses or the like).
As is illustrated in
The position sensor 100 can be designed to be very compact and flat. Since the transmission coil 104 and the reception coil 106 are arranged in different planes of the printed circuit board 120, there is a high degree of freedom with regard to the layout of the transmission coil 104 and the reception coil 106. In particular, the transmission coil 104 and the reception coil 106 can be designed in such a way that they have substantially the same area extent and are provided near one another in a manner overlapping one another. Consequently, a high degree of coupling between the transmission coil 104 and the reception coil 106 can be achieved even in the case of a compact layout. Since the transmission coil 104 and the reception coil 106 are provided on or in a printed circuit board 120, they can be produced cost-effectively and with extremely high precision.
A position sensor 200 in accordance with a second embodiment is explained below with reference to
In the embodiment illustrated in
One end in each case of the first and the second reception coil sections 206a, 206b is connected to the evaluation device 208. A reception voltage Vxa and Vxb is respectively present at the ends of the reception coil sections 206a and 206b. In this arrangement, too, on account of the antiseries connection of the reception coil sections 206a and 206b, at the reception coil 206 overall a difference voltage Vx=Vxa−Vxb is present which is lower than the reception voltage Vxa and Vxb at the individual reception coil sections 206a and 206b, respectively. If the arrangement comprising transmission coil 204 and reception coil 206 is substantially symmetrical and there are no further metallic articles or the measurement object in the vicinity, then the difference voltage is substantially Vx=0.
If the measurement object 150 is then brought near to the position sensor 200 from the side of the reception coil section 206b, the self-inductances of the reception coil sections 206a and 206b are then altered. In this case, the self-inductance of the reception coil section 206b changes more than the self-inductance of the reception coil section 206a on account of the smaller distance to the measurement object 150. Consequently, Vxb<Vxa arises, with the result that Vx=Vxa−Vxb≠0. In this case, the amplitude of this reception voltage Vx corresponds to the distance or the displacement of the measurement object 150 in the x-direction relative to the reception coil 206.
This position sensor 200 therefore functions as a distance sensor, wherein at the reception coil 206 a reception voltage Vx is generated which is lower than the voltages Vxa and Vxb respectively generated at the reception coil sections 206a and 206b and which contains information about the relative position of the measurement object 150 in a distance direction (x-direction) with respect to the reception coil 206. In this case, too, it holds true that the ratio of reception signal (reception voltage Vx) to transmission signal (transmission voltage Vt) contains information about the relative position of the measurement object 150 with respect to the reception coil 206.
The arrangement of the position sensor 200 in a housing can be implemented similarly to the arrangement of the position sensor 100 in accordance with the first embodiment as shown in
The concept underlying the third embodiment is to combine features of the coil arrangements of the first and second embodiments with one another.
In the embodiment illustrated in
In this case, the reception coil sections 306a and 306c can have approximately the same extent as viewed from above, that is to say are illustrated in a manner nested one in the other only for illustrative reasons in
With this arrangement of transmission coil 304 and reception coil sections 306a-306d, position sensors 300 which function as a shear sensor or as a distance sensor can be realized in a simple manner. The fact of whether a position sensor 300 functions as a shear sensor or as a distance sensor depends in this case on the connection of the ends of the reception coil sections 306a-306d. This is explained with reference to
In a further development of the position sensor 300 in
The first reception coil section 306a and the second reception coil section 306b are arranged in the same plane, spatially parallel to the transmission coil 304, and together form a reception coil section which corresponds topologically to the reception coil section 206a in
As is evident from
A position sensor 400 in accordance with a fourth embodiment is explained below with reference to
In the embodiment illustrated in
The reception coil sections 406a to 406h are interconnected to form two reception coils. Specifically, the reception coils 406a, 406b, 406g and 406h are interconnected to form a first reception coil in such a way that a voltage Vz is generated at the reception coil during operation, the voltage containing information about a displacement of the measurement object 150 in a shear direction (z-direction) and being fed to the evaluation device 408. In this case, the reception coil sections 406a and 406g are interconnected in series with one another in a manner overlapping one another with the same winding direction in different planes of the printed circuit board, that is to say can also be regarded as individual coil windings of this first reception coil. The same applies to the reception coil sections 406b and 406h. In this case, the reception coil sections 406b and 406h are connected in antiseries with the reception coil sections 406a and 406g, that is to say with the opposite winding direction, thus resulting in the functionality explained for the first embodiment.
Furthermore, the reception coil sections 406c, 406d, 406e and 406f are interconnected to form a second reception coil in such a way that a voltage Vx is generated at the reception coil during operation, the voltage containing information about a displacement of the measurement object 150 in a distance direction (x-direction) and being fed to the evaluation device 408. In this case, the reception coil sections 406a and 406g are interconnected in series with one another in a manner overlapping one another in different planes of the printed circuit board. The same applies to the reception coil sections 406b and 406h. Furthermore, the reception coil sections 406c and 406e (and 406d and 406f) arranged in different planes have different winding directions and the reception coil sections 406c and 406d (and 406e and 406f) arranged in the same plane have the same winding direction in each case. This results in an arrangement which corresponds to the position sensor in accordance with the second embodiment, with corresponding functionality. This second reception coil therefore likewise comprises reception coil sections which are arranged on different planes of the printed circuit board, on different sides of the transmission coil 404.
The voltages Vx and Vz present at the first and the second reception coils consisting of the reception coil sections 406a to 406h are fed to the evaluation device 408 and processed further by the latter. Consequently, the position sensor 404 can detect displacements of the measurement object with respect to two degrees of freedom, namely in the x-direction and z-direction. Furthermore, this position sensor 400 is also compact and flat and suitable in particular for use in high vacuum, e.g. in EUV lithography apparatuses.
In this case, the transmission coil 404 of the position sensor 400 has two coil windings, and the two reception coils of the reception coil arrangement 406 also have double coil windings in each case. Consequently, the inductance of the transmission coil 404 and of the reception coil arrangement 406 is greater than in the case of single windings. To put it another way, it is thus possible to create coils having the same inductance with a smaller area requirement, such that an even more compact position sensor is made possible with this embodiment.
It should be clear that the arrangements described above are merely by way of example. In particular, the transmission coil and the reception coils can be provided with further winding planes in order to increase their inductance further.
In the case of the above-described position sensor 100 in accordance with the first embodiment, the amplitude of the reception voltage Vz or the output signal of the evaluation device 108 is dependent on the distance between the reception coil 106 and the measurement object 150. To put it more precisely, the amplitude of the reception voltage Vz decreases with increasing distance of the measurement object 150 in the x-direction. The position sensor 100 is therefore sensitive not only in the z-direction, but also in the x-direction. This is unimportant if the distance of the measurement object 150 in the x-direction is known and in particular invariable (e.g. by virtue of a corresponding mounting), such that a corresponding calibration is possible. However, if the position of the measurement object 150 with respect to the z-direction and the x-direction is unknown or variable, then measures are required in order to compensate for or correct the dependence of the output signal on the distance of the measurement object 150 in the x-direction. Such measures are discussed below.
In the embodiments explained above, the focus was on the arrangement of the coils, whereas in this fifth embodiment, and the following embodiments, the focus is on the drive and evaluation electronics. The coil arrangement of the sensor is illustrated as a transformer in
The alternating transmission current generated by the drive device 502 generates a voltage Vt at the transmission coil 504, which voltage, in the case of a predetermined amplitude of the transmission current, correlates with the distance of the measurement object 150 in the x-direction, that is to say in other words represents a measure of the distance of the measurement object 150. By contrast, the ratio Vz/Vt between the output voltage Vz present at the reception coil and the voltage Vt at the transmission coil 504 is a measure of the displacement of the measurement object 150 in the z-direction. Although this output voltage Vz also depends on the distance of the measurement object 150 in the x-direction, this dependence can be compensated for by adding the voltage Vt, as will also be explained further below.
The transmission coil 504 can be designed like each of the transmission coils from the embodiments described above. In principle, the reception coil 506 can be designed like each of the reception coils from the embodiments described above, and can be designed in particular as a reception coil which responds to a displacement of the measurement object (not illustrated in
The evaluation device 508 comprises a first analog-to-digital converter 510, a second analog-to-digital converter 512 and a digital signal processing device 514. The first analog-to-digital converter 510 receives the analog reception voltage (e.g. Vz) present at the reception coil 506 and converts it into a digital signal S1, which is fed to the signal processing device 514. The second analog-to-digital converter 512 receives the analog transmission voltage Vt present at the transmission coil 504 on the input side and converts it into a digital signal S2, which is fed to the signal processing device 514. The analog-to-digital converters 510, 512 can be operated for example with a sampling rate that corresponds to the frequency of the transmission voltage Vt, as a result of which a demodulation of the alternating reception voltage is simultaneously achieved.
The reception coil 506 can be designed to respond to a displacement of the measurement object in a shear direction (that is to say in the z-direction), such that the output voltage Vz at the reception coil arrangement, and thus also the output signal S1 of the first analog-to-digital converter 510, is dependent on the position of the measurement object in a shear direction (z-direction) relative to the reception coil 506. Furthermore, the analog transmission voltage Vt at the reception coil 504 depends on the position of the measurement object in a distance direction (x-direction) relative to the reception coil 506. To put it more precisely, the self-inductance of the transmission coil 504 varies in a manner dependent on the distance between the measurement object and the transmission coil 504. This principle is used in eddy current sensors, for example: in this case, the transmission coil is part of a resonant circuit, for example, and the change in the resonant frequency or the damping of the resonant circuit can serve as a measure of position or the distance of the measurement object.
On the input side, a resonant circuit (not illustrated in more specific detail in
If the drive device 502 feeds a predetermined current to the transmission coil 504, then the digital signal S2 generated by the second analog-to-digital converter 512 is dependent on the distance of the measurement object (in the x-direction). The signal processing device 514 processes further the signals fed to it and outputs a sensor signal Sz, for example, which represents the displacement of the measurement object in a shear direction (z-direction). It is furthermore possible for the signal processing device 514 additionally also to output a sensor signal Sx representing the displacement of the measurement object in a distance direction (x-direction). The digital signal processing device 514 can be designed as a microprocessor or the like, for example, and can be program-controlled, in particular.
As already explained above, the reception voltage Vz at the reception coil arrangement 506 depends not only on the displacement of the measurement object in a shear direction (z-direction) but also on the displacement of the measurement object in a distance direction (x-direction). In accordance with the present fifth embodiment, the signal processing device 514 utilizes the signal S2 containing information about the displacement of the measurement object 150 in a distance direction (x-direction) in order to correct the sensor signal Sz or to compensate for the influence of the distance of the measurement object 150 on the z-position measurement.
In a first variant, the signal processing device 514 calculates the sensor signal Sz as a cross-correlation of the signals S1 and S2 divided by the autocorrelation of the signal S2. A corrected signal Sz that is normalized to the input variable, that is to say the voltage at the transmission coil 104, is thus generated.
In a second variant, the signal processing device 514 comprises a look-up table, to which the values of the digital signals S1 and S2 are fed as input variables. The two signals S1 and S2 are actually dependent in each case on the position of the measurement object with respect to the position sensor 500. However, a unique assignment between the values of the signals S1 and S2 and the actual positions of the measurement object with respect to the position sensor 500 prevails at least in regions. The look-up table thus assigns to the values of the signals S1 and S2 output values which represent the z- and x-positions of the measurement object, and the signal processing device 514 outputs corresponding sensor signals Sz and Sx. It goes without saying that it is also possible that, with the aid of the look-up table, the z-value is corrected and the signal processing device 514 only outputs a corresponding sensor signal Sz corrected with respect to the x-displacement.
With the position sensor 500 in accordance with the fifth embodiment as described here, the sensor signal Sz representing a displacement of the measurement object in a shear direction (z-direction) can be corrected in a simple manner with regard to changes in distance with respect to the measurement object. In this case, it is possible to detect displacements of the measurement object with respect to two spatial directions with a compact sensor arrangement. Furthermore, the position sensor 500 in accordance with the fifth embodiment has an excellent temperature stability since the latter depends principally on the DAC and the ADCs. Furthermore, the advantages explained in connection with the first four embodiments can also be achieved. In particular, it is possible to accommodate the drive device 502, the coils 504 and 506 and the evaluation device 508 on a single printed circuit board or in a compact printed circuit board assemblage (cf.
It should be noted that, in the embodiment described above, the drive device 502 is embodied with a DAC as current source. Consequently, a predetermined current as transmission signal is fed to the transmission coil 504 and the voltage Vt present at the transmission coil 504 depends on the distance of the measurement object in the x-direction. As an alternative thereto, however, it is also possible to embody the drive device 502 as a voltage source, such that a predetermined voltage as transmission signal is fed to the transmission coil 504. In this case, the current flowing through the transmission coil 504 is dependent on the distance of the measurement object in the x-direction, and can thus be used as a measure of the distance and for the compensation of the sensor signal for the shear direction. It holds true in both cases, however, that the ratio of reception signal to transmission signal contains information about the relative position of the measurement object with respect to the reception coil.
In a third variant of the fifth embodiment, which is illustrated in
A precise position sensor 500 can be realized with the fifth embodiment described above. However, operation at high frequencies and with high resolution requires DACs, ADCs and differential amplifiers which are operated at high speed and thus have a comparatively high power consumption.
The evaluation device 608 comprises two differential amplifiers 610, 612, two mixers 614, 616, two filters 618, 620, two analog-to-digital converters 622 and 624, and a digital signal processing device 626. The differential amplifier 610 amplifies the reception voltage present at the reception coil 606. The signal amplified by the differential amplifier 610 is demodulated with the aid of the mixer 614 by being multiplied by a signal proportional to cos 2πfct. This demodulated signal is filtered with the aid of the filter 618, which is embodied as a low-pass filter or as a bandpass filter, and the signal obtained is converted into a digital signal S1 with the aid of the analog-to-digital converter 622 and fed to the signal processing device 626. As described for the fifth embodiment, this output signal S1 of the first analog-to-digital converter 622 is dependent on the position of the measurement object in a shear direction (z-direction) relative to the reception coil 606.
Furthermore, the differential amplifier 612 amplifies the reception voltage present at the transmission coil 604. The signal amplified by the differential amplifier 612 is demodulated with the aid of the mixer 616 by being multiplied by a signal proportional to cos 2πfct. This demodulated signal is filtered with the aid of the filter 620, which is embodied as a low-pass filter or as a bandpass filter, and the signal obtained is converted with the aid of the analog-to-digital converter 624 into a digital signal S2 and fed to the signal processing device 626. As described for the fifth embodiment, this output signal S2 of the second analog-to-digital converter 624 is dependent on the position of the measurement object in a distance direction (x-direction) relative to the reception coil 606.
The signal processing device 626 processes the signals S1 and S2 fed to it, e.g. in the manner described for the fifth embodiment, and outputs sensor signals Sz and/or Sx representing the position of the measurement object relative to the position sensor 600.
The position sensor 600 in accordance with the sixth embodiment thus differs from the position sensor 500 in accordance with the fifth embodiment in that firstly a demodulation of the reception voltage and of the transmission voltage takes place in each case before the demodulated signals are digitized. A so-called “down-conversion system” is therefore involved here. Consequently, the evaluation device 608 can be realized with components of lower power. Furthermore, the position sensor 600 in accordance with the sixth embodiment is more robust in relation to noise, in particular low-frequency noise. Furthermore, the position sensor 600 likewise has an excellent temperature stability.
If the sensor coils behave purely inductively, then a direct conversion system requires that fc=fm, where fm is the frequency of the transmission current and fc is the frequency of the demodulation signal. In order thus to achieve a precise detection of the x-position of the measurement object, the amplitude of the transmission current has to be known, which can require a known AC source. Otherwise, it is not possible to distinguish fluctuations in the AC source from fluctuations in the position of the measurement object. If the AC source is not known sufficiently, a further ADC channel can be established in order to detect the transmission current. This is explained on the basis of the further development of the position sensor 600 in accordance with the sixth embodiment as illustrated in
The position sensor 600 in accordance with this further development differs from the position sensor 600 shown in
Furthermore, fc≠fm can hold true in this further development. Consequently, a displacement of the measurement object in a distance direction (x-direction) is detected with the aid of a quadrature detection, wherein transmission voltage and current and reception voltage are firstly down-modulated to an intermediate frequency. This intermediate frequency should be at least double the bandwidth of the position sensor 600, that is to say e.g. fm−fc≧20 [kHz] for fc<fm and fc−fm≦20 [kHz] for fc>fm.
With this further development of the sixth embodiment, the advantages of a quadrature detection, that is to say e.g. greater robustness relative to interference, can be achieved in addition to the advantages mentioned above.
The digital signal source 642 outputs a pulsed signal. Since the coils and 646 and capacitors 648 form a low-pass filter, this pulsed signal is converted into a sinusoidal transmission signal. Furthermore, the coils and 646 and capacitors 648 together with the transmission coil 604 form a resonant circuit having a predetermined resonant frequency. If the signal source 642 is operated close to this resonant frequency, the reactive power that is output can then be reduced.
In a modification of this variant, it is also possible for the input-side impedance matching network comprising the resistor 644, the coils 646 and the capacitors 648 to be matched in a manner dependent on an output signal of the evaluation device 608. By way of example, one of the capacitors 648 can be designed as a variable capacitor that can be adjusted in a manner dependent on an output signal. If the evaluation device 608 then provides an output signal whose level depends on the distance of the measurement object 150 in the z-direction, a correction of the level of the transmission current It can thus be achieved, and the influence of the distance of the measurement object 150 in the z-direction on the measurement of the position of the measurement object 150 in the shear direction can be suppressed.
It should be noted that the embodiments described above are merely by way of example and can be varied diversely in the context of the scope of protection of the patent claims. In particular, the features of the embodiments described above can also be combined with one another.
In this regard, by way of example, in the embodiments described above, the conductor tracks which connect the transmission coils and the reception coil arrangements to the drive and evaluation orientation proceed from the longitudinal sides thereof. However, it is also possible for these connecting conductor tracks to proceed from the shorter sides of the coils. This has the advantage that a more symmetrical arrangement can be achieved in the region situated opposite the measurement object.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102013204494.1 | Mar 2013 | DE | national |
The present application is a continuation of, and claims benefit under 35 USC 120 to, international application PCT/EP2014/055138, filed Mar. 14, 2014, which claims benefit under 35 USC 119 of German Application No. 10 2013 204 494.1, filed Mar. 14, 2013. International application PCT/EP2014/055138 also claims priority under 35 USC 119(e) to U.S. Provisional Application No. 61/782,101, filed Mar. 14, 2013. The entire disclosure of each of International application PCT/EP2014/055138 and German Application No. 10 2013 204 494.1 is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61782101 | Mar 2013 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2014/055138 | Mar 2014 | US |
| Child | 14834561 | US |
