Methods for temperature control of MEMS micromirrors

Abstract

The invention relates to a method for temperature control of the surfaces of MEMS micromirrors (24) arranged within a micromirror array (10) and exposed to EUV irradiation (12). A surface temperature (20) is detected and a MEMS micromirror (24) is heated by means of a temperature control unit (26) integrated into the MEMS micromirror (24) as a component thereof. A desired temperature T0 (60) on a surface of the MEMS micromirror (24) is determined by an output voltage U. H (58) or based on a current heating current I H (92) set, which is a temperature-dependent resistor R T (42) is abandoned. The temperature at the surface of the MEMS micromirror (24) is essentially maintained at the desired temperature T0 (60) during operation of the micromirror field (10).

Description

Technical area

[0001] The invention relates to a method for controlling the temperature of MEMS micromirrors arranged within a micromirror array and exposed to EUV irradiation. Furthermore, the invention relates to the use of the method for controlling the temperature of MEMS micromirrors in a micromirror array that is operated under vacuum and exposed to EUV irradiation during operation. State of the art

[0002] Devices with, for example, matrix-like, displaceable micromirrors, so-called micromirror arrays or micromirror actuators, are used today in a wide variety of devices, for example in smartphones, projectors, head-up displays, barcode readers, mask exposure units in semiconductor manufacturing, and microscopes. Corresponding micromirror arrays are known, for example, from DE 10 2013 208 446 A1, EP 0 877 272 A1, and WO 2010 / 049076 A1. Disclosures regarding suitable actuator devices for displacing the individual mirrors of a micromirror array of micromirrors can be found, for example, in DE 10 2013 206 529 A1, DE 10 2013 206 531 A1, and DE 10 2015 204 874 A1.

[0003] DE 10 2019 205 251 A1 relates to a projection exposure system, in particular for EUV semiconductor lithography, comprising a heating device for a plurality of individual components, wherein the heating device comprises inductively acting heating elements. The individual components, which may be mirrors, may comprise temperature sensors for monitoring the temperature.

[0004] EP 4 124 910 A1 relates to EUV lithography and discloses a micromirror array comprising a substrate, a plurality of movable micromirrors, an actuator system for controlling the position of the micromirrors with a measuring system for measuring the position of the micromirrors, and further a control unit on a processor, wherein the micromirrors have temperature sensors for measuring the temperatures of the micromirrors. Disclosure of the invention

[0005] According to the invention, a method for temperature control of MEMS micromirrors arranged within a micromirror array is proposed, wherein the individual micromirrors are exposed to EUV irradiation and the following process steps are carried out: a) Detecting a surface temperature and heating a MEMS micromirror by means of a temperature control unit integrated into the MEMS micromirror as a component thereof, wherein b) a desired temperature T0 on a surface of the MEMS micromirror based on an output voltage U H or using a heating current I H which corresponds to a temperature-dependent resistor R T the temperature control unit and c) Maintaining the temperature at the surface of the MEMS micromirror substantially at the desired temperature T0 during operation of the micromirror array.

[0006] The method proposed according to the invention advantageously makes it possible to reduce the installation space and the number of electrical connections between a micromirror and a control ASIC due to the fact that the heating devices and the temperature detection devices act on one and the same electronic components.

[0007] In an advantageous development of the method proposed according to the invention, the temperature control unit integrated into the MEMS micromirror comprises a wire-shaped conductor with a temperature-dependent resistance R T .

[0008] The method proposed according to the invention is characterized in that the output voltage U H by means of a voltage source U S is generated in such a way that in series with the temperature-dependent resistor R T lying resistors R MS , R MHa resulting resistance R M represent, across which a resulting voltage U M falls.

[0009] The method proposed according to the invention is further characterized in that the resulting voltage U M is proportional to the current that passes through the temperature-dependent resistance R T flows through and is fed to a control algorithm as an input variable.

[0010] In the method proposed according to the invention, the temperature-dependent resistance R T determined according to RT=UH−UMUM⋅RM with R T : temperature-dependent resistance R T U H : Output voltage U M : resulting voltage

[0011] In this context, the output voltage U H between three voltage values ​​U H1, U H0and 0 volts. U H1 and U H0 either regulated (constant voltage) or measured values. The current switching state and the current voltage value are known to the control algorithm. U H1 is much higher than U H0 . U H1 is used for the heating strategy with a variable heating voltage using a voltage regulator from U S For the pulse width modulation-based heating strategy, U S passed through during heating and appears at the output as U H . U H0 is generated by a small voltage source. This small voltage source can, for example, be a buffered voltage source made up of U S downscaled voltage. Scaling can be achieved using a voltage divider or pulse width modulation. It is also possible that U H0 as a reference voltage from the low voltage domain.

[0012] In an advantageous development of the method proposed according to the invention, a temperature of the surface T M of a micromirror estimated using the following relationship: TM=f(RTCT) with R T : temperature-dependent resistance R T C T : temperature-dependent coefficient of the wire-shaped conductor

[0013] In an advantageous development of the method proposed according to the invention, the control algorithm adjusts its output voltage U H such that errors between the desired temperature T0 and the estimated mirror temperature T M are minimized.

[0014] Advantageously, the control algorithm varies either during a defined heating period t P a first voltage level U H1 the output voltage U H or a constant output voltage U Hover a variable duration of the heating period. To represent the same heating output, the two parameters can therefore be varied differently.

[0015] The method proposed according to the invention is further characterized in that the control algorithm is provided with the desired temperature T0 as input variables, and also the resulting voltage U M and either an output voltage of a voltage source U S or an output current of a current source I S and the control algorithm generates an output voltage U H or a current heating current I H delivers.

[0016] Alternatively, it is possible to design the method proposed according to the invention in such a way that instead of a voltage source U S a current source I Ssupplies an output current to the control algorithm, from which the latter, taking into account the desired temperature T0 and the resulting voltage U M a current heating current I H determined.

[0017] In a further advantageous embodiment of this alternative method, for example, a value for the temperature-dependent resistance R T determined according to the following relationship: RT=UH(RM+RM0)RM0(IH−IM) further IRT=IH−IM and URT=UMRM0(RM+RM0) with U M : resulting voltage R M : resulting series resistance R M0 : resistance in series, either with R MH or R MS

[0018] Furthermore, the invention relates to the use of the method for tempering MEMS micromirrors of a micromirror array which is operated under vacuum and is exposed to EUV irradiation during operation. Advantages of the invention

[0019] The method proposed according to the invention can be used either by using a voltage source U S or a power source I S The heating elements and the temperature-measuring elements use the same electronic components. This drastically reduces the installation space or size of such a temperature control unit, as well as the number of electronic components that need to be installed and interconnected. Finally, the number of electrical connections between each micromirror of the micromirror array and the control ASIC is reduced.

[0020] The solution proposed according to the invention allows temperature monitoring to be carried out at any time, regardless of the operating state, ie whether heating is in progress or not.

[0021] The method proposed by the invention enables heating that enables highly reliable control of the temperature or temperature gradients, thus compensating for mechanical characteristics such as thermal expansion. Furthermore, the method proposed by the invention advantageously allows for final testing of the micromirror array and for compensating for mechanical deformations by controlling individual MEMS micromirrors in the micromirror array.

[0022] Advantageously, the resolution of the determined voltage U M by dynamic adjustment of the series resistance R Moptimized. Thus, the temperature monitoring is very accurate and thus reflects the real-world conditions extremely accurately. Furthermore, the method proposed according to the invention can advantageously be implemented in an electronic component, for example, within an ASIC. Short description of the drawings

[0023] Embodiments of the invention are explained in more detail with reference to the drawings and the following description.

[0024] They show: Fig. 1 an arrangement of a micromirror array with a number of MEMS micromirrors exposed to EUV irradiation, Fig. 2 the structure and integration of a temperature control unit proposed according to the invention including control device, Fig. 2.1 a possible design of the course of a wire-shaped conductor for heating, Fig. 3 a control circuit including control algorithm, fed by a voltage source U S , Fig. 4 the implementation of a possible first heating strategy for the arrangement according to Fig. 3, Fig. 5 an alternative design of the control electronics or the control algorithm, which is fed via a power source and Fig. 6 one for the arrangement according to Fig. 5 implementable heating strategies. Embodiments of the invention

[0025] In the following description of the embodiments of the invention, identical or similar elements are designated by the same reference numerals, whereby a repeated description of these elements is omitted in individual cases. The figures only schematically illustrate the subject matter of the invention.

[0026] Fig. 1 shows an exemplary arrangement of a micromirror array 10. This is exposed to EUV irradiation 12 and operates under the influence of a vacuum 14. In the Fig. The individual mirrors 16 indicated in Figure 1, which can have an individual inclination 18, are MEMS micromirrors 24. These are microelectromechanical mirrors that can be tilted independently of one another via actuators not shown in detail. The individual surfaces of the MEMS micromirrors 24 have surface temperatures 20, which can each be individual. They are in Fig. 1 through T1 to T N according to the number of MEMS micromirrors 24 shown.

[0027] Fig. 2 shows the structure and integration of a temperature control unit proposed according to the invention including a control device,

[0028] According to the invention, it is proposed that each of the MEMS micromirrors 24 be provided with a temperature control unit 26 formed as a component thereof. For example, the plate-shaped temperature control unit 26 can be arranged between a carrier plate 28 below the MEMS mirror 24. Electrical connections 34 can run through a spring structure 30, which connects the carrier plate 28 to the base plate 32. The Fig. 1, the individual inclinations 18 of individual MEMS micromirrors 24 can be realized. The electrical connections 34 extend from the temperature control unit 26, which is a component of the MEMS micromirror 24, to a control unit 36.

[0029] The temperature control unit 26 can be arranged as shown in Fig. 2.1 as a wire-shaped conductor 38. The wire-shaped conductor 38 can, for example, be Fig. 2.1 shown meander shape 40. The wire-shaped conductor 38 represents a temperature-dependent resistance R T 42. Instead of the meander shape 40, as in Fig. 2.1, other conductor geometries or conductor paths are also possible for generating a heating surface, for example circular, rectangular, elliptical, polygonal, square or any other geometries that have a planar character.

[0030] According to the illustration Fig. 3 shows a first embodiment of the control unit 36, which comprises a control algorithm 68. The control unit 36 ​​in its embodiment according to Fig. 3 is supplied via a voltage source U S 44. Via the voltage source U S 44 an output voltage is fed into the control algorithm 68 as described in Fig. 3 is indicated schematically. Furthermore, the control algorithm 68 is given a desired temperature T0 60 as an input variable and a resulting voltage U M 52. The voltage source U S 44 provides a constant supply voltage for the heating process. Two resistors, a first resistor R MS 46 and a second resistor R MH 48 are provided and are connected in series to the temperature-dependent resistor R T 42. While the first resistor R MS 46 in a comparable size to the resistance range of the temperature-dependent resistor R T 42, the temperature-dependent resistance R T 42 is several orders of magnitude larger than the second resistor R MH 48. The corresponding values ​​are determined in such a way that the resulting voltage U M52 is of a comparable order of magnitude and can be assigned to the control algorithm 68.

[0031] A resulting series resistance R M 54 is either through the first resistor R MS 46 or the second resistor R MH 48. The resulting voltage U M 52, which via the resulting series resistance R M 54 is measured. The resulting voltage U M 52 is proportional to the current flowing through the temperature-dependent resistor R T 42 and is applied as an input to the control algorithm 68. Since the voltage across the temperature-dependent resistor R T 42 is known, a value for the temperature-dependent resistance R T 42 according to the following relationship: RT=UH−UMUM⋅RM

[0032] The output voltage U H 58 is switched between three voltage values ​​U H , 64, UH0 66 and 0 volts switched. U H1 64 and U H0 66 are either controlled (i.e., constant) or measured values. The current switching state and the current voltage value are known to the control algorithm 68. U H1 64 is much higher than U H0 66. U H1 64 is used for the heating strategy with a variable heating voltage using a voltage regulator from U S 44 is generated. For a pulse width modulation-based heating strategy, U S 44 during heating and appears at the output as U H 58. U H0 66 is generated by a small voltage source. This small voltage source can, for example, be a buffered voltage source made up of U S 44 scaled-down voltage. Scaling can be achieved using a voltage divider or pulse width modulation. Furthermore, it is possible that U H066 can also be a reference voltage from the low voltage domain.

[0033] The temperature of the surface of the MEMS micromirror 24 is estimated according to the following relationship: TM=f(RT,CT) with C T : known temperature coefficient of conductor material of the temperature-dependent resistance.

[0034] Thus, f (R T , C T ) a known function of the values ​​of the temperature-dependent resistance R T 42 and the temperature coefficient C T of the wire-shaped conductor 38.

[0035] The control algorithm 68, as described in Fig. 3, now adjusts the output voltage U H 58 so that an error between the desired temperature T0 60 and the estimated mirror temperature T M 20 are minimized.

[0036] According to the illustration Fig. 4 shows a possible first heating strategy 70, with which a temperature control or heating of individual MEMS micromirrors 24 of the micromirror field 10 can be achieved according to the schematic representation in Fig. 1 can be done.

[0037] In the representation according to Fig. 4 are the output voltage U H 58 and the resulting series resistance R M 54 plotted over time.

[0038] The output voltage U H 58 is switched between three different levels, namely a first level U H1 64, a second level U H0 66 and 0 volts. The first level U H1 64 is higher than the second level U H0 66 > 0 volts. The first level U H1 64 is used to heat the MEMS micromirror 24 and at the same time to apply an electrical voltage to measure the temperature-dependent resistance R T42 of the wire-shaped conductor 38 of the temperature control unit 26. The second level U H0 66 is used to determine the temperature-dependent resistance R T 42 when the temperature control unit 26 is switched off. The second level U H0 66 is dimensioned such that its contribution to heating or its influence on the heating accuracy is negligible. The second level U H0 66 can be set to 0 volts in case the temperature dependent resistance R T 42 only during a heating period t P 72 is measured.

[0039] The control algorithm 68, as described in Fig. 3, determines the energy required for heating either by influencing a heating time at a voltage level, namely the first level U H1 64 or by adjusting the first level U H1 64 over a certain period of time. The Fig. The first heating strategy 70 shown in Figure 4 is operated similarly to pulse width modulation. The control algorithm 68 initiates heating for each heating period t P 72. A heating period t H 74 denotes the heating time. Now the resulting series resistance R M 54 through the second resistor R MH 48 formed. In a first phase t S 76 of the heating period t P 72 the value of the temperature-dependent resistance R T 42. The error between the real and reference temperatures is calculated as soon as the temperature-dependent resistance R T 42 and a surface temperature T M 56 of the MEMS micromirror 24.

[0040] The control algorithm 68 determines a remaining heating time t H 74-t S 76. After the heating phase, the output voltage U H 58 to the second level U H066, which during the interval t P 72 - t H 74. Within this interval 80, the resulting series resistance R M 54 to the first resistor R MS 46 and the temperature-dependent resistance R T 42 is measured by applying the lower second voltage level U H0 66.

[0041] The combination of the second level U H0 66 with the relatively high first resistance R MS 46 is required to ensure a low influence of the second level U H0 66 on the heating accuracy and a sufficiently large resolution for the resulting voltage U M 52. The first phase t S 76 can be set to zero in case the temperature is only to be measured when the temperature control unit 26 is switched off.

[0042] Fig. 5 shows an alternative embodiment of the control unit 36, in which instead of the voltage source U S 44 a current source I S 90 is used.

[0043] In the representation according to Fig. 5 is the current source I S designated 90. A current heating current I H 92 represents the actual current provided by the control algorithm 68 for heating. A current supplied via the temperature-dependent resistor R T 42 falling voltage is called voltage U RT 94, which is determined by the temperature-dependent resistance R T 42 flowing current with I RT 96. These values ​​are used to estimate the respective value of the temperature-dependent resistance R T 42 measured. A resistance R M0 98 is either in series with the first resistor R MS 46 or the second resistor R MH 48 and is used to determine the voltage U RT94 and stream I RT 96 is required. It should be noted that the value of the second resistor R MH 48 is several orders of magnitude larger than the temperature-dependent resistance R T 42 and the value of the second resistor R MH 48 comparable to the resistance value of the resistor R M0 98. In this context, it is assumed that the sum of the resistances, ie the first resistance R MS 46 and the resistance R M0 98 of a comparable order of magnitude to the temperature-dependent resistance R T 42 lie.

[0044] The following relationships arise: IM=UMRM0 URT=UMRM0(RM+RM0) IRT=IH−IM RT=UM(RM+RMO)RM0(IH−IM)

[0045] In this context, the resulting series resistance R M 54, depending on the circuit according to Fig. 5 either the first resistor R MS46 or the second resistor R MH 48.

[0046] The control algorithm 68 according to Fig. 5 is comparable to that in Fig. 3 shown.

[0047] Fig. 6 shows a heating strategy 70, which is configured with the control unit 36 ​​according to Fig. 5 using a current source I S 90 can be implemented. The current heating current I H 92 is switched between three levels, namely a first level I H1 102, a second Level I H0 104 and 0 amps. The first Level I H1 102 is above the second level I H0 104. Furthermore, the second level I H0 104 over 0 amperes. The current heating current I H 92 is used to heat the respective MEMS micromirror 24 and at the same time to provide an electric current to adjust the temperature-dependent resistance R T42 during heating. The second level I H0 104 is used to measure the temperature-dependent resistance R T 42 while the temperature control unit 26 is switched off. The second level I H0 104 is so small that its contribution to heating or its influence on accuracy is negligible. The second Level I H0 104 can be set to 0 amperes in case the temperature dependent resistance R T 42 is only measured during the heating phase.

[0048] The Fig. 5 schematically illustrated control algorithm 68 determines the heating energy either by influencing the heating time with a constant first level I H1 102 or by variation of the first level I H1 102 over a certain period of time.

[0049] The control algorithm 68 starts heating all heating periods t P 72, as in Fig.6. Heating takes place during a heating period t H 74. The resulting series resistance R M 54 is connected to the second resistor R MH 48. Within the first phase t S 76 of the heating period t P 72 the value of the temperature-dependent resistance R T 42. The error between the real temperature value and the reference temperature is calculated as soon as the temperature-dependent resistance R T 42 and thus the surface temperature of the MEMS micromirror 24 T M 56. Based on a temperature error, the control algorithm 68 determines a remaining heating time T H 74-T S 76. After the heating phase T H 74 the current heating current I H 92 to the second level I H0 104, which for the interval 80 t P 72 - t H74. Within this interval 80, the resulting series resistance R M 54 to the first resistor R MS 46 (low resistance), so that it is ensured that only a slight influence on the heating accuracy by the second level I H0 104 is given and a sufficient resolution for the resulting voltage U M 52 is present. The first phase t S 76 can be set to zero in case the temperature is to be measured when the temperature control unit 26 as part of the MEMS micromirror 24 is switched off.

[0050] The proposed method can be used for tempering, in particular for heating, individual micromirrors within a sub-vacuum operated micromirror array 10, wherein the micromirror array 10 is under EUV irradiation 12.

[0051] The solution proposed according to the invention further comprises a device for temperature control of MEMS micromirrors 24, which are arranged within a micromirror field 10 and are exposed to EUV irradiation 12. Individual mirrors 16 of the micromirror field 10 each have a temperature control unit 26 integrated into the individual mirrors 16, which detects their surface temperature 20 and heats the individual mirror 16, and a desired temperature T0 60 on a surface of the individual mirror 16 is controlled by means of a control algorithm 68. The temperature control unit 26 is designed as at least one wire-shaped conductor 38 with a temperature-dependent resistance R T 42. In the device proposed according to the invention, the control algorithm 68 is integrated into the control unit 36 ​​in such a way that the control algorithm 68 is supplied with either an output voltage of a voltage source U S 44 or an output current of a current source I S90. Furthermore, the control unit 36 ​​is constructed in such a way that it has a first resistance R MS 46 and a second resistor R MH 48. Via a switch 62, with which either the first resistor R MS 46 or the second resistor R MH 48 is switched, the resulting voltage U M 52 can be set.

[0052] 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 expert practice. 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 2013 208 446 A1

[0002] EP 0 877 272 A1

[0002] WO 2010 / 049076 A1

[0002] DE 10 2013 206 529 A1

[0002] DE 10 2013 206 531 A1

[0002] DE 10 2015 204 874 A1

[0002] DE 10 2019 205 251 A1

[0003] EP 4 124 910 A1

[0004]

Claims

[1] Method for tempering MEMS micromirrors (24) arranged within a micromirror array (10) and exposed to EUV irradiation (12), comprising the following method steps: a) detecting a surface temperature (20) and heating a MEMS micromirror (24) by means of a temperature control unit (26) integrated into the MEMS micromirror (24) as a component thereof, wherein b) a desired temperature T0 (60) on a surface of the MEMS micromirror (24) based on an output voltage U H (58) or by means of a heating current I H (92) is set, which corresponds to a temperature-dependent resistor R T (42) of the tempering unit (26) and c) maintaining the temperature at the surface of the MEMS micromirror (24) substantially at the desired temperature T0 (60) during operation of the micromirror array (10). [2] Tempering method according to claim 1,characterized by that the temperature control unit (26) integrated into the MEMS micromirror (24) comprises a wire-shaped conductor (38) with temperature-dependent resistance R T (42). [3] Method according to claims 1 and 2, characterized by that to generate the output voltage U H (58) a voltage source U S (44) is used in such a way that in series connection (50) to the temperature-dependent resistor R T (42) lying resistances R MS , R MH (46, 48) a resulting resistance R M (54), across which a resulting voltage U M (52) falls. [4] Method according to claims 1 to 3, characterized by that the resulting voltage U M (52) proportional to the current and the temperature-dependent resistance R T (42) and is given as input to a control algorithm (68). [5] Method according to claims 1 to 4, characterized bythat the temperature-dependent resistance R T (42) results in RT=UH−UMUM⋅RM [6] Method according to claims 1 to 5, characterized by that a surface temperature T M (56) is estimated according to TM=f(RT,CT) with R T : temperature-dependent resistance R T (42) C T : temperature-dependent coefficient of the wire-shaped conductor (38) [7] Method according to claims 1 to 6, characterized by that the control algorithm (68) adjusts its output voltage U H (58) such that errors between the desired temperature T0 (60) and the estimated temperature of the surface of the micromirror (24) T M (20) are minimized. [8] Method according to claims 1 to 7, characterized by that the control algorithm (68) either during a defined heating period (72) t P a first voltage level U H1(64) the output voltage U H (58) varies, or a constant output voltage U H (58) over a variable duration of the heating period (72) t P delivers. [9] Method according to claims 1 to 8, characterized by that the control algorithm (68) is given as input the desired temperature T0 (60), the resulting voltage U M (52) and either an output voltage of a voltage source U S (44) or an output current of a current source I S (90), and the control algorithm (68) generates an output voltage U H (58) or a current heating current I H (92) presents. [10] Method according to claim 1, characterized by that a current source I S (90) supplies an output current to the control algorithm (68), from which the latter, taking into account the desired temperature T0 (60) and the resulting voltage U M (52) a current heating current I H(92) determined. [11] Method according to claim 10, characterized by that a value for the temperature-dependent resistance R T (42) is determined according to RT=UM(RM+RM0)RM0(IH−IM) IRT=IH−IM URT=UMRM0(RM+RM0) with U M : resulting voltage (52) R M : resulting series resistance (54) R MO : resistance in series, either with R MH (48) or R MS (46) [12] Device for temperature control of MEMS micromirrors (24) arranged within a micromirror field (10) and exposed to EUV irradiation (12), characterized bythat individual mirrors (16) of the micromirror field (10) each have a temperature control unit (26) integrated into the individual mirrors (16), which detects its surface temperature (20) and heats the individual mirror (16), wherein a desired temperature T0 (60) on a surface of the individual mirror (16) is controlled by means of a control algorithm (68). [13] Device according to claim 12, characterized by that the temperature control unit (26) has at least one wire-shaped conductor (38) with a temperature-dependent resistance R T (42). [14] Device according to claims 12 and 13, characterized by that the control algorithm (68) is integrated into a control device (36) which is suitable for supplying the control algorithm (68) with either an output voltage source U S (44) or an output current of a current source I S (90) to give up. [15] Use of the method according to claims 1 to 11 for tempering MEMS micromirrors (24) of a micromirror array (10) which is operated under vacuum (14) and is exposed to EUV irradiation (12) during operation.

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