Methods for processing analog electrical output signals

Abstract

The invention relates to a method for processing analog electrical signals (48) from a capacitance circuit (50) comprising a first capacitor (14) and at least one further, second capacitor (16). The capacitance circuit (50) is associated with an array of micromirrors for measuring their angles. The following process steps are carried out: a) Within readout periods (58, 60, 62) measured values ​​x1, x2, x3 (64, 66, 68) of the analog electrical output signals (48) are read out and stored, b) at the end of each selection period (58, 60, 62) average values ​​(76) of different combinations of the measured values ​​x1, x2, x3 (64, 66, 68) are calculated. c) Outliers are identified (92) by comparing the average values ​​(78, 80, 82) according to procedure step b) with a threshold value m 1,2,3 (84) and / or an application of logic relations, d) the one of the measured values ​​x1, x2, x3 (64, 66, 68) that differs significantly from the measured values ​​x1, x2, x3 (64, 66, 68) is considered to be an overshooting or undershooting value (88, 90) and e) The average values ​​(78, 80, 82, 84) which contain the excess or insufficient values ​​(88, 90), i.e. the outliers, are deleted and values ​​without outliers are output as valid output values.

Description

Technical area

[0001] The invention relates to a method for processing analog electrical output signals of a capacitive circuit comprising a first capacitor and at least one further, second capacitor, wherein the capacitive circuit is associated with an array of micromirrors for measuring their angles. Furthermore, the invention relates to the use of the method for preventing measurement errors of the angle parameters of a number of micromirrors in a micromirror array caused by EUV-based interference. State of the art

[0002] DE 10 2015 204 874 A1 relates to a device for pivoting a mirror element with two degrees of freedom. For this purpose, a displacement device is provided, which serves to pivot a mirror element with two degrees of freedom. Furthermore, an electrode structure with actuator electrodes is provided, wherein the actuator electrodes are designed as comb electrodes, wherein all actuator electrodes are arranged in a single plane, and wherein the actuator electrodes form a direct drive for pivoting the mirror element.

[0003] DE 10 2013 208 446 A1 relates to an optical assembly. The optical assembly serves to guide a beam of radiation with a plurality of controllably displaceable individual mirrors, for which purpose a control device for the controlled displacement of the individual mirrors is used. The individual mirrors each have a reflective surface with a surface normal, wherein the control device comprises a plurality of application-specific integrated circuits (ASICs), and wherein at least some of the ASICs are arranged offset from one another in the direction of the surface normal.

[0004] For some applications, a number of micromirrors are arranged laterally spaced in a one- or two-dimensional array or field. For example, micromirror arrays are used in modern and future EUV projection exposure systems for microlithography in the semiconductor industry, as described, for instance, in DE 10 2014 203 189 A1 and the aforementioned DE 10 2015 204 874 A1. Adjustable optical paths up to a mask (reticle) can be created in the EUV projection exposure systems using these micromirror arrays, enabling the generation of highly complex exposure conditions on the mask and the writing of structures with extremely small lateral dimensions onto the wafers being exposed.

[0005] For such applications, it is advantageous for the micromirror arrays to have the highest possible fill factor, meaning the largest possible mirror area relative to the total area of ​​the array. In EUV projection exposure systems, this increases the light yield and thus the wafer throughput. For this reason, functional elements such as springs, drive mechanisms, or conductive traces are often positioned below the actual mirror elements in micromirror arrays with a high fill factor. The micromirrors can be coated with a Bragg coating that effectively reflects the central wavelengths. Wavelengths outside the reflection range are absorbed and generate heat in the micromirror, which must be dissipated with the lowest possible thermal resistance.

[0006] Precise positioning of the individual micromirrors in the micromirror array requires a position sensor system controlled by electronic control units. The achievable positioning accuracy of the micromirrors depends on the overall performance of the micromirror position sensor system, including the control electronics, as well as on the temperature distribution and its symmetry or homogeneity within each individual micromirror element.

[0007] Depending on the application, micromirrors can be used in various applications, such as smartphone projectors, head-up displays, barcode readers, and the like.

[0008] The micromirrors can be coated with a Bragg coating that effectively reflects the central wavelengths. Wavelengths outside the reflection range are absorbed and generate heat in the micromirror, which must be dissipated with the lowest possible thermal resistance.

[0009] The positional accuracy of the micromirror depends on the performance of the micromirror position sensor system. This system is dependent on manufacturing tolerances, temperature stability in conjunction with temperature variance, and long-term stability in conjunction with the product's lifespan and the intervals at which the device requires recalibration.

[0010] Capacitance-to-voltage converters are used to convert capacitance values ​​into electrical signals. These converters comprise at least two capacitors that are subjected to a voltage. The capacitance values ​​measured by the capacitors change with the change in the reflection angle. The resulting difference in capacitance values ​​is determined. According to this approach, the capacitors are charged and discharged by an excitation voltage applied via an electrode. The magnitude of the electrical charge through the capacitors indicates the capacitance of the first and second capacitors, respectively. The charges are transferred to an operational amplifier, and the charge difference is converted into a voltage signal. This voltage signal is then processed in a further data processing chain. This capacitance measurement concept allows for high resolution with relatively small signals. The excitation voltage V excitationThe signal is essentially periodic and rectangular. The voltage fluctuates between a high and a low level. The high level allows for capacitance measurement and thus represents the active measurement step. The lower voltage level corresponds to the passive measurement step and is typically set to 0 volts.

[0011] Capacitance voltage conversion normally occurs in two steps. In the first step, the excitation voltage V drops. excitation At their low value, a first and a second switch are closed to discharge capacitors CS1 and CS2. In a second step, the excitation voltage V increases. excita-tionto their high value. At the same time, the two switches are opened. Two integrating capacitors integrate the charges, and the operational amplifier converts these different charge values ​​into voltage values. This conversion is one way to determine capacitance-dependent angular positions.

[0012] Irradiation can occur, inducing photoelectric and charge carrier effects and creating electric currents that flow along the mirror surface and throughout the entire mirror structure. Such currents can be modeled by pulsed current sources. These sources generally comprise an initial set of several pulses with a repetition rate f. rep The individual pulses have a waveform that follows a Gaussian distribution with a pulse width of T. p similar. The repetition rate f rep and the pulse duration T pThese pulses are not necessarily constant and can vary within a certain range. If the MMU (micro mirror unit) is not irradiated, the pulses disappear. Otherwise, the resulting electrical current is a parasitic current that reduces the accuracy of the capacitance measurements and therefore significantly impairs the angular position measurements. Disclosure of the invention

[0013] According to the invention, a method for processing analog electrical output signals of a capacitance circuit is proposed, wherein the capacitance circuit is provided with a first capacitor and at least one further, second capacitor and is assigned to an array of micromirrors for measuring their angle, and wherein the following process steps are carried out: a) Within readout periods, measured values ​​x1, x2, x3 of the analog electrical output signals are read out and stored, b) at the end of each selection period, average values ​​are calculated from different combinations of the measured values ​​x1, x2, x3, c) Outliers are identified by comparing the average values ​​according to procedure step b) with a threshold value m 123 and / or an application of logic relationships, d) The one of the measured values ​​x1, x2, x3 that differs significantly from the measured values ​​x1, x2, x3 is considered to be an overshooting or undershooting value and e) The average values, which contain the excess or insufficient values, i.e. the outliers, are deleted and values ​​without outliers are output as valid output values.

[0014] The method proposed according to the invention advantageously eliminates errors caused by EUV-based interference or superposition. Advantageously, in the method proposed according to the invention, the analog electrical signal at the end of a sensing circuit, here a capacitive circuit, outliers (both high and low) are identified, and interference-free average values ​​are output. The threshold value m is used for an interference-free readout period. 123 issued if m 23 , m 13 and m 12 should be identical; otherwise, one of three valid average values ​​will be output according to the outlier detection principle.

[0015] In an advantageous further development of the method proposed according to the invention, each of the selection periods according to method step a) comprises three measurement events for the measurements of the values ​​x1, x2, x3.

[0016] The method proposed according to the invention is further characterized in that each measurement event comprises two time periods and the measurement is carried out in the first time period, with the capacitance circuit returning to its standby mode during a second time period. The method proposed according to the invention further provides that the two time periods are either of equal length or can have different durations.

[0017] In an advantageous further development of the method proposed according to the invention, the readout frequency is selected such that it is higher than a bandwidth of the angular signals to be measured from the micromirrors.

[0018] In the method proposed according to the invention, the pulse width of the interference signals is shorter than either of the first or second time intervals of the measurement events. The pulse width remains relatively constant and is much narrower than the period of the pulse sequence. The repetition rate of the pulse sequence is within a known range. The first and second time intervals are design parameters chosen such that they are both longer than the pulse width. Therefore, this assumption can be made.

[0019] In the method proposed according to the invention, the duration of the readout periods according to process step a) is chosen such that the readout periods always include more interference-free measurement events than interference-prone measurement events.

[0020] In the method proposed according to the invention, if each of the readout periods includes a faulty measurement event, the number of measurement events per readout period is set to 3.

[0021] Advantageously, in the method proposed according to the invention, a variable f can be used. 12 , f 13 , f 23 as a result of comparing average values ​​m 12 , m 13 , m 23 with the threshold value m 123 won according to f12:m12>m123,f12=1 if m12>m123,otherwise f12=0 f13:m13>m123,f13=1 if m13>m123,otherwise f13=0 f23:m23>m123,f23=1 if m23>m123,otherwise f23=0

[0022] The invention further relates to the use of the method for avoiding incorrect measurements of angular parameters of a number of micromirrors of a micromirror field, which are due to EUV-based disturbances. Advantages of the invention

[0023] The method proposed according to the invention, particularly the fact that the analog electrical output signals are tapped and processed at the end of a sensing circuit, such as a capacitor circuit, requires no modifications to the sensing circuit, for example, the capacitor circuit. The method proposed according to the invention can be adapted to a variety of sensing principles. In particular, when applying the method proposed according to the invention, there is no need to incorporate additional sensing analog circuits to detect interference pulses. Furthermore, the algorithm includes simple and fast-processing averaging operations and logic applications that can be handled with low complexity and, in particular, low power consumption.In the method proposed according to the invention, measured angles are always calculated as average values ​​and therefore have a lower lower noise level and higher accuracy than the direct output values ​​of the sensing circuit, in this case the capacitance circuit.

[0024] Furthermore, it should be emphasized that the method proposed according to the invention can be implemented using the same hardware, for example, ASICs, as the circuit sensing. Moreover, it is entirely possible to implement the essential parts or process steps, such as the averaging and the decision logic, in digital hardware, such as microcontrollers, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), or digital ASICs. Brief description of the drawings

[0025] Embodiments of the invention are explained in more detail with reference to the drawings and the following description.

[0026] They show: Fig. 1 a circuit with an operational amplifier and integrating capacitors connected in parallel to it, as well as first and second switches, Fig. 2 a representation of the method proposed according to the invention with tapping of the analog electrical signals to be processed behind a sensing circuit, in the present case a capacitive circuit, Fig. 3 the representation of the signal processing proposed according to the invention and Fig. 4.1 and 4.2 different procedures for identifying outliers to determine a final valid output result.

[0027] Fig. 1 shows that an excitation voltage of 10 (V) is used here. excitation) as a periodic square wave signal 12, here applied via a feed electrode 18 to two capacitors, namely a first capacitor 14 and a second capacitor 16. An operational amplifier 20, which has an input side 22, is connected to the outputs of the two capacitors 14 and 16. On the input side 22 are a negative input 24 and a positive input 26, and on its output side 28 are, in reverse order, a positive output 30 and a negative output 32. In parallel to the operational amplifier 20 are the first switch 34 and the second switch 36, as well as a first integrating capacitor 38 and a second integrating capacitor 40. On the output side of the operational amplifier 20, further signal processing 42 is connected. Fig. 1. A capacitor is used for voltage conversion in two steps. In the first step, the excitation voltage 10 drops to its low value, thus constituting a passive measurement step. The first and second switches 34, 36 are closed, so that the capacitors 14, 16 are discharged. In the second step, the excitation voltage 10 (V) rises. excitation ) to their high value, thus initiating the active measurement step. At the same time, the first switch 34 and the second switch 36 are opened, and the integrating capacitors 38, 40 integrate the charges, while the operational amplifier 20 converts the various charges into voltage values. The capacitance / voltage conversion is merely one way to perform capacitance-relevant angle measurements. Embodiments of the invention

[0028] In the following description of embodiments of the invention, identical or similar elements are designated by the same reference numerals, and repeated descriptions of these elements are omitted in individual cases. The figures represent the subject matter of the invention only schematically.

[0029] Fig. Figure 2 shows a circuit arrangement in which an excitation voltage of 10 (V) excitation) is also applied as a periodic square wave signal 12 via the feed electrode 18, the first capacitor 14, and the second capacitor 16. The output signals from the positive output 30 and negative output 32 of the two capacitors 14 and 16 are present as analog electrical signals at the inputs 24 and 26 of a capacitor circuit 50. These signals are processed within the capacitor circuit 50, and analog electrical output signals 48 are therefore present at a signal tap 49. These are further processed in a result determination circuit 52, which is analogous to the representation shown. Fig. 1 a further signal processing unit 54 (reference 42 there) may be connected downstream, as well as an ADC 56 shown here only schematically.

[0030] In the method proposed according to the invention, a number of superimposed process steps are schematically represented over the time axis. From the representation according to Fig. Figure 3 shows that in the method proposed according to the invention, different readout periods 58 (N-1), 60 (N), and 62 (N+1) are traversed. The readout periods 58, 60, and 62 are traversed parallel to the time axis. During each of the readout periods 58, 60, and 62, three measurement events occur. Three measured values ​​are recorded for each of the three measurement events: a first measured value x1 64, a second measured value x2 66, and a third measured value x3 68. These measured values ​​64, 66, and 68 are stored and retained in a first sample and hold stage 70, a second sample and hold stage 72, and a third sample and hold stage 74, respectively. Fig. Figure 3 shows that the first sample & hold level 70 is assigned to the first measured value x1 64, while the second sample & hold level 72 stores and retains the second measured value x2 66. The same applies to the third sample & hold level 74, which is assigned to the third measured value x3 68.

[0031] Furthermore, the presentation according to Fig. 3 schematically indicated that the formation of 76 average values ​​78 m 12 , 80 m 13 82 m 23 and a threshold of 84 m 123 an outlier analysis (92) follows, which leads to a decision 94 on the valid results to be evaluated.

[0032] Based on the Fig. Sections 4.1 and 4.2 demonstrate how to identify excessive or insufficient values ​​(88, 90) and how to make a decision. The following descriptive section focuses on the Fig. Referring to 4.1 and 4.2, it is assumed that the third measured value x3 68 in the case of the representation according to Fig. 4.1 represents an excessive value of 88 and in the case of Fig. 4.2 a different value of 90.

[0033] As in Fig. As shown in 4.1, for example, the first average value m 12 78, the second average value m 13 80 and the third average value m 23 82 with the threshold value m 123 84 compared. The undisturbed first average value m 12 78 is less than the threshold value m 123 84 and the two other average values, i.e., the second average value m 13 80 and the third average value m 23 82 are above the threshold value m 123 84 in Fig. 4.1 case considered.

[0034] From the representation according to Fig. 4.2 shows that the first threshold is m 1278 is greater than the threshold value m 123 84, while the other two average values ​​m 13 80 and m 23 82 both are smaller and below the threshold m 123 84 are located.

[0035] In both cases, which are in the Fig. As shown in 4.1 and 4.2, the undisturbed average value always represents the minority.

[0036] A truth table is used to represent the disturbance-free average values, which ultimately constitute the final output of the system. Three input variables f 12 , f 13 and f 23 are formed as results of three comparisons with the threshold value m 123 , the aforementioned further average value of 84. A logical value "1" and a logical value "0" in the truth table represent values ​​that are greater or less than the respective threshold value of 84: f12:m12>m123,f12=1 if m12>m123, otherwise f12=0 f13:m13>m123,f13=1 if m13>m123, otherwise f13=0 f23:m23>m123,f23=1 if m23>m123, otherwise f23=0 Input Output f 12 f 13 f 23 m 12 m 13 m 23 m 123 0 0 0 0 0 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 0 1 1 1 0 0 0 1 0 0 1 0 0 0 1 0 1 0 1 0 0 1 1 0 0 0 1 0 1 1 1 X X X X

[0037] The final result is that the decision-making process 94 is determined via, for example, the following logical relationships: Output m123:f12¯∩f13¯∩ Output m12:(f12¯∩f13∩f23)∪(f12∩f13¯∩ Output m13:(f12¯∩f13∩f23¯)∪(f12∩f13¯∩ Output m23:(f12¯∩f13¯∩f23)∪(f12∩f13∩

[0038] These logical relationships can be easily determined using specific digital logic blocks.

[0039] Furthermore, the invention relates to the use of the method for avoiding incorrect measurements of angular positions of individual micromirrors of a micromirror field or array, which are due to EUV-based disturbances.

[0040] The invention is not limited to the embodiments described here and the aspects highlighted therein. Rather, numerous modifications are possible within the scope of the claims, which are within the scope of one skilled in the art. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2015 204 874 A1 [0002, 0004] DE 10 2013 208 446 A1

[0003] DE 10 2014 203 189 A1

[0004]

Claims

[1] Method for processing analogue electrical output signals (48) of a capacitance circuit (50) with a first capacitor (14) and at least one further, second capacitor (16), wherein the capacitance circuit (50) is assigned to an array of micromirrors for their angle measurement, with the following method steps: a) Within readout periods (58, 60, 62), measured values ​​x1, x2, x3 (64, 66, 68) of the analogue electrical output signals (48) are read out and stored, b) At the end of each reading period (58, 60, 62) a formation (76) of average values ​​(78, 80, 82, 84) of different combinations of the measured values ​​x1, x2, x3 (64, 66, 68) takes place, c) An outlier determination (92) is carried out by comparing the average values ​​(78, 80, 82) according to method step b) with a threshold value m 123 (84) and / or an application of logical relationships, d) the one of the measured values ​​x1, x2, x3 (64, 66, 68) which has a value significantly different from the measured values ​​x1, x2, x3 (64, 66, 68) is considered as an overshooting or undershooting value (88, 90) and e) The average values ​​(78, 80, 82) which contain the overshooting or undershooting values ​​(88, 90), ie the outliers, are deleted and outlier-free values ​​are given as valid output values. [2] Method according to claim 1, characterized by that each of the readout periods (58, 60, 62) according to method step a) comprises three measurement events for the measurements of the values ​​x1, x2, x3 (64, 66, 68). [3] Method according to claims 1 and 2, characterized by that each measurement event comprises two time periods and the measurement is carried out in the first time period and the capacitance circuit (50) returns to its standby mode during a second time period. [4] Method according to claims 1 to 3, characterized by that the two time periods are of equal length or have different durations. [5] Method according to claims 1 to 4, characterized by that the readout frequency is higher than a bandwidth of the angle signals of the micromirrors to be recorded. [6] Method according to claims 1 to 5, characterized by that a pulse width of interference signals is shorter than each of the first and second time periods [7] Method according to claims 1 to 6, characterized by that a duration of the readout periods (58, 60, 62) according to method step a) is selected such that the readout periods (58, 60, 62) always include more interference-free measurement events than interference-affected measurement events. [8] Method according to claims 1 to 7, characterized bythat in the event that each of the readout periods (58, 60, 62) includes a faulty measurement event, the number of measurement events per readout period (58, 60, 62) is set to 3. [9] Method according to claims 1 to 8, characterized by that variable f 12 , f 13 , f 23 as a result of comparing the average values ​​m 12 , m 13 , m 12 (78, 80, 82) with the threshold value m 123 (84) according to f12:m12>m123,f12=1, if m12>m123, otherwise f12=0 f13:m13>m123,f13=1, if m13>m123, otherwise f13=0 f23:m23>m123,f23=1, if m23>m123, otherwise f23=0 be formed. [10] Use of the method according to one of claims 1 to 9 for avoiding incorrect measurements of angle parameters of a number of micromirrors of a micromirror array which are due to EUV-based disturbances.

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