Multi head scanning lithographic laser writer

Abstract

A scanning lithography laser writer (1) includes a substrate holder (60), an illumination configuration (2), and a control unit (40). The illumination configuration has a laser source (10), a multi-head modulator configuration (4), and at least two write head configurations (50). The illumination configuration is configured to provide laser light to the write head configurations via the multi-head modulator configuration to illuminate a substrate plane. The control unit is configured to control a relative mechanical displacement between the substrate holder (60) and the write head configurations, and to control a sweep of the laser light emitted from the write head configurations. The multi-head modulator configuration is configured to split an input beam using an acoustic crystal and modulate it into at least one modulated beam for each of the write head configurations. The write head configurations are positioned such that the laser light emitted from the write head configurations is displaced relative to each other.

Description

[Technical Field]

[0001] This technology generally relates to photolithography writers, and more particularly to scanning photolithography writers and methods for operating scanning photolithography writers. [Previous Technology]

[0002] All currently commercially available laser mask writers are equipped with a single final lens. In this single-head design, light is delivered to the magnifying mask through an optical-mechanical assembly called a printhead. The printhead is thus configured to influence one or more modulated laser beams with a common single final lens. These laser beams are focused by this lens onto their respective small spots. The position of these spots typically changes rapidly and periodically, causing the beam trajectory to form a line (or multiple parallel lines) of laser light under the final lens. This is generally referred to as a sweep, and the direction of the sweep is generally indicated by the Y-direction. In some devices, the printhead assembly moves relative to the magnifying mask in a direction transverse to the sweep direction. This direction of movement is generally indicated by the X-direction. In other devices, the magnifying mask moves instead relative to the printhead assembly. The edge-to-edge travel is called the X-stroke, and the length of the aforementioned line under the single final lens is generally referred to as the sweep. Both of these design solutions result in the magnifying glass being sequentially, stroke-by-stroke, exposed to light of a modulated intensity produced in the patterned mask. If multiple beams are used together with a common single final lens, their parallel lines are offset in the X direction.

[0003] This writing concept imposes limitations on the printing speed of the writer. Given a specific speed of the X-stage or alternatively the print head during the X-stroke, the length of the X-stroke, and the number of beams in a common single final lens, the magnified mask area covered per unit time is defined solely by the length of the sweep. Therefore, an increased printing speed can be achieved by increasing the sweep length or increasing the number of parallel beams in the common single final lens. Currently, up to 15 parallel beams are used in a common single final lens, and this number can be further increased. However, even adding 15 additional parallel beams (which is not entirely easy to achieve technically) will only double the total printing speed. Further increases in printing speed are required.

[0004] Several years ago, attempts were made to improve printing speed by increasing the sweep speed. A new tellurium oxide deflector was developed to provide one of two sweep lengths. New optics for the write head that could support the new sweep length were designed and procured. Unfortunately, masks printed with the full sweep length provided by this deflector exhibited a visible defect called moiré. This moiré is attributed to the overlap of the sweep length intervals. If this separation is too large, small defects in the overlap area appear to be detectable by the human eye. In terms of printing speed, simply increasing the sweep length does not seem to be a viable path forward.

[0005] Furthermore, in other writers that do not require moiré patterns, any increase in printing speed is desirable, as this only increases the writer's profitability.

[0006] International Patent Application WO 2020 / 120725 A1 discloses a method for reducing the effects of crosstalk between transducers in driving an acousto-optic modulator in a single-head multi-beam writer. The method includes operating transducers mechanically coupled to an acousto-optic modulator medium (where different frequencies are applied to adjacent transducers) and generating a time-varying phase relationship between carriers on spatially adjacent modulation channels emanating from adjacent transducers (where a frequency interval between carriers on adjacent channels is from 400 kHz to 20 MHz).

[0007] U.S. Patent Application US 2020 / 0166852 A1 discloses a lithography apparatus for writing to a substrate wafer. The apparatus includes a light generating device comprising a plurality of light sources for generating light, a writing device, and a light transmitting device comprising a plurality of optical waveguides for transmitting light from the light generating device to the writing device. The writing device includes a plurality of individually controllable writing heads for projecting light from one or more light sources onto different regions of a substrate wafer. The apparatus also includes a transport device for moving the substrate wafer relative to the writing device in a predefined transport direction, and a control device for controlling the writing process on the substrate wafer. Modulation is performed by an electro-optic modulator, and the light comes from a plurality of light sources that eliminate the need for a beam splitter.

[0008] U.S. Patent Application US 2009 / 0273793 A1 discloses a drawing position measurement method and apparatus, and a drawing method and apparatus. At least three slits are provided in a plane identical to the drawing plane. Light modulated by a drawing point forming member and transmitted through the at least three slits is detected. Two position information items regarding the drawing point are obtained based on relative movement position information items of the drawing plane corresponding to the time point at which the light transmitted through the at least three slits is detected. The position of the drawing point is measured based on the at least two position information items. [Summary of the Invention]

[0009] Therefore, the general objective of this technology is to find a way to increase printing speed without causing moiré effects.

[0010] The above-mentioned objective is achieved by a method and apparatus according to an independent technical solution. Preferred embodiments are defined in the accompanying technical solutions.

[0011] Generally, in a first embodiment, a scanning lithography laser writer includes a substrate holder, an illumination configuration, and a control unit. The substrate holder has an attachment member for holding a substrate having a laser photosensitive surface in a substrate plane. The illumination configuration includes a laser source, a multi-head modulator configuration, and m write heads, where m ≥ 2. The illumination configuration is configured to provide laser light from the laser source to the m write heads via the multi-head modulator configuration to illuminate the substrate plane. The control unit is configured to control a relative mechanical displacement between the substrate holder and the m write heads in at least one scanning direction parallel to the substrate plane. The control unit is configured to control the laser light emitted from the m write heads to sweep in a sweeping direction parallel to the substrate plane and transverse to the scanning direction. The multi-head modulator configuration is configured to split an input beam originating from one of the laser sources using an acoustic crystal and modulate it into n modulated beams for each of the m write head configurations, where n ≥ 1. The m heads are positioned such that the laser light emitted from each of the m write head configurations is shifted relative to each other by a predetermined non-zero distance in the sweep direction.

[0012] In a second embodiment, a method for operating a scanning lithography laser writer includes providing a laser input beam. The laser input beam is split and modulated by acousto-optic modulation into n modulated beams for each of m write head configurations, where m ≥ 2, and n ≥ 1. The n modulated beams for the m write head configurations are optically connected to the respective write head configurations. A substrate plane of the scanning lithography laser writer is illuminated by the n modulated beams for the m write head configurations. The substrate plane and the m write head configurations are displaced relative to each other in at least one scanning direction parallel to the substrate plane. The n modulated beams emitted from the m write head configurations are swept in a sweeping direction parallel to the substrate plane and transverse to the scanning direction. In all embodiments, the n modulated beams emitted from each of the m write head configurations are displaced relative to each other by a predetermined non-zero distance in the sweeping direction.

[0013] One advantage of the proposed technology is that the printing speed increases proportionally to the number of printheads, while most parts of existing equipment can be used without extensive modifications. Other advantages will be apparent when reading the detailed description.

Implementation Method

[0015] Throughout the diagram, the same element symbols are used for similar or corresponding elements.

[0016] To better understand the proposed technology, it may be helpful to begin with a brief overview of a segmented multichannel acousto-optic modulator. In Figure 1, a single-head modulation configuration 3 with one of four write beams is schematically illustrated. An input laser beam 5 is split into (in this example) four split input beams 6A to 6D in a beam splitter 22. Each split input beam 6A to 6D is connected to a respective modulator segment 25A to 25D of an acousto-optic modulator 20. An electrical connection 26 is provided to enable radio frequency signals to be provided to transducers 24A to 24D, each modulator segment 25A to 25D. Each modulator segment 25A to 25D of the acousto-optic modulator 20 individually modulates the split input beams 6A to 6D into modulated beams 7A to 7D. The modulated beams 7A to 7D are then provided to a single write head, allowing the modulated beams 7A to 7D to reach the surface to be unfolded in the X direction for writing. Each modulated beam 7A to 7D also sweeps synchronously and parallel to each other in the Y direction.

[0017] Depending on the actual design, the number of split input beams can be varied. However, there is usually a maximum limitation set by different design features. This means that the "X" direction of the acousto-optic modulator 20 cannot be further utilized.

[0018] Figure 2 schematically illustrates the conditions during writing. A write head 50 is scanned in a scanning direction 90, also indicated as the X direction. Several beams (four beams in this particular embodiment) are separated by a distance m in the X direction and swept in a sweeping direction 91, also indicated as the Y direction. This sweep illuminates four stripes 92 of a laser photosensitive surface 64 in a substrate plane supported by a substrate holder 60. The write head 50 is scanned a distance d in the X direction relative to the substrate holder 60, and a new exposure is made to the laser photosensitive surface 64. When the entire write head 50 has passed a portion of the laser photosensitive surface 64, the stripes 93 cover that entire portion.

[0019] In an alternative method, the relative scan of the first 50 can be a continuous program, whereby the sweep direction of stripes 92 and 93 is not completely perpendicular to the scan direction, but still transverse to the scan direction. However, the basic function is similar to the method proposed above.

[0020] According to this technology, the cross-sectional dimensions of the acousto-optic modulator 20 can be alternatively used to achieve an additional modulated beam that can be used.

[0021] Figure 3 is a schematic diagram of one embodiment of a multi-head modulation configuration 4. Most parts are similar to those shown in Figure 1; however, in most cases, the component symbols are simplified and the distinguishing letters A to D are omitted. In this particular embodiment, the acousto-optic modulator 20 is operated to output three different modulated beams 7 from each modulator segment 25. As will be further discussed below, this can be achieved by supplying multi-frequency signals to the transducer 24 or, as indicated by the dashed lines, by supplying different single-frequency signals to multiple transducers in each modulator segment 25. Also, as indicated by the dashed lines, an additional beam splitter configuration 21 can be provided in front of the acousto-optic modulator 20.

[0022] Depending on the output angle, the output modulated beam 7 is divided into groups 51A, 51B, and 51C. Each group 51A, 51B, and 51C is provided to its respective write head, wherein the beam within each group is spread in the X direction, similar to the example in Figure 1, but the different groups also have a spacing in the Y direction. This will be discussed further below. All modulated beams are individually modulated, contributing to the overall write speed. The Y direction of the acousto-optic modulator 20 is thus used to provide the modulated beam to multiple write heads.

[0023] In the above figure, four modulator segments are shown. However, anyone skilled in this art will understand that any number of modulator segments from 1 to more can be used, provided that the remaining equipment can handle that number of parallel beams for each write head.

[0024] Figure 4 schematically illustrates one embodiment of a scanning lithography laser writer 1. The scanning lithography laser writer 1 includes a substrate holder 60 having an attachment member for holding a substrate 62 having a laser photosensitive surface 64 in a substrate plane. The scanning lithography laser writer 1 further includes an illumination configuration 2. The illumination configuration 2 has a laser source 10, a multi-head modulator configuration 4, and at least two write head configurations 50. The illumination configuration 2 is configured to provide laser light from the laser source 10 to the write head configurations via the multi-head modulator configuration 4 to illuminate the substrate plane. The scanning lithography laser writer 1 also includes a control unit 40. The control unit 40 is configured to control a relative mechanical displacement between the substrate holder 60 and the write head configurations 50 in at least one scanning direction X parallel to the substrate plane. Typically, the control unit 40 is configured to control a relative mechanical displacement between the substrate holder 60 and the write head configurations 50 also in a direction perpendicular to the scanning direction to allow for multiple scans. Control unit 40 is also configured to control the laser light emitted from the write head configuration to sweep in a sweep direction Y parallel to the substrate plane and transverse to the scanning direction X. Multi-head modulator configuration 4 is configured to split an input beam originating from laser source 10 using an acoustic crystal and modulate it into at least one, and preferably multiple, modulated beams for each of the write head configurations. This will be described further below. Control unit 40 is also typically responsible for other requested tasks, such as active focus control, for example, control of the lens-to-mask distance. Therefore, this control is well known to anyone skilled in the art and will not be described further. The plurality of write head configurations are positioned such that the laser light emitted from each write head configuration is shifted relative to each other in the sweep direction Y by a predetermined non-zero distance.

[0025] In the embodiment illustrated above, the multi-head modulator configuration 4 is shown to move together with the write head configuration 50. However, in an alternative embodiment, the multi-head modulator configuration 4 may be positioned between the laser source 10 and the write head configuration 50, but configured not to move during the X-stroke.

[0026] Figure 5 schematically illustrates the situation at the substrate plane according to one embodiment. Three write head configurations 50A, 50B, and 50C are shifted relative to each other in the Y direction. Each write head configuration 50A to 50C results in an illumination scan that increases the available write speed. In this embodiment, the scans of the different write head configurations 50A to 50C do not overlap in the Y direction. However, as will be discussed further below, in other embodiments, the scans of the different write head configurations 50A to 50C may overlap and / or undergo multiple exposures in the Y direction.

[0027] Figure 6 schematically illustrates one embodiment of an illumination configuration 2. An input laser beam 5 is provided from a laser source 10 to a multi-head modulation configuration 4 including an acoustic-optical modulator 20. The multi-head modulation configuration 4 splits the light and modulates it into modulated beams 7 provided to a plurality of write head configurations 50. Each write head configuration 50 can be configured to handle one or more modulated beams 7, as indicated by the dashed lines.

[0028] Figure 7 illustrates one embodiment of an acoustic-optical modulator 20. For simplicity, only one modulator segment is shown; however, those skilled in the art will recognize that parallel modulator segments may exist. Therefore, the function of an acoustic-optical modulator (AOM) is known in the prior art and will not be described in detail further. Generally, a transducer 24 is induced to vibrate at a radio frequency, thereby generating acoustic waves in a crystal 27. A commonly used crystal material is, for example, quartz. The acoustic waves are ultimately absorbed by a sound absorber 23 to avoid any resonant behavior. When incoming light encounters the acoustic waves, the interaction between the phonons of the acoustic waves and the photons of the light causes scattering and interference, thereby causing a deflected beam.

[0029] When light is incident on the direction perpendicular to the propagation of the sound wave at a Bragg angle as defined below, the highest efficiency of the deflected beam is typically achieved under the Bragg condition: where is the wavelength of light in vacuum, is the refractive index, and is the wavelength of the sound. The highest diffraction intensity then occurs at an exit angle corresponding to the Bragg angle.

[0030] In Figure 7, this is illustrated by a (split) input beam 6 incident on the AOM crystal 27, where sound wave 29 is generated by exciting transducer 24. A transmitted beam 8 is illustrated together with a modulated beam 7. The modulated beam 7 exits the AOM crystal 27 at a Bragg angle. The amount of light diffracted by the sound wave depends on the intensity of the sound. Therefore, by changing the excitation of the transducer's vibration, the intensity of the emitted light can be modulated, thus providing a modulated beam 7.

[0031] Even if the most effective diffraction occurs at an incident angle equal to one of the Bragg angles, diffraction also occurs at other incident angles. This can be used to obtain multiple diffracted beams.

[0032] Figure 8 illustrates one embodiment of an acoustic-optical modulator 20. An input beam 6 illuminates the light source at an angle of entry. A transducer 24 is supplied as a signal consisting of the sum of two single radio frequency signals F1 and F2. These radio frequency signals induce acoustic waves 29 with corresponding frequencies in a crystal 27. An undiffracted beam 8 exits the crystal 27 at an exit angle equal to the angle of entry. The acoustic wave 29 of frequency F1 induces a first diffracted modulated beam 7' at a first diffraction angle. Similarly, the acoustic wave 29 of frequency F2 induces a second diffracted modulated beam 7' at a second diffraction angle. Depending on the bandwidth properties of the crystal, the first and second diffraction angles can have sufficient intensity while still being separated by a non-negligible angle. Therefore, the modulated beams can be separated and used in different write heads. Preferably, the Bragg angle is located between or equal to one of the first and second diffraction angles.

[0033] This embodiment will require the RF bandwidth of the acousto-optic modulator 20 to be large enough to support the above-mentioned beam separation requirements. For the quartz acousto-optic modulator 20 and the 405 nm wavelength, a bandwidth of approximately 60 MHz will be required.

[0034] Figure 9A illustrates another embodiment of the acousto-optic modulator 20. Here, the acousto-optic modulator 20 is equipped with two transducers 24A and 24B, which are physically separated in the direction of irradiating the input light 6. A single radio frequency signal of frequency F1 is provided to the first transducer 24A and a single radio frequency signal of frequency F2 is provided to the first transducer 24B. The transducers 24A and 24B thereby induce two acoustic waves 29 having frequencies F1 and F2 in the crystal 27. Thereby, the input light beam 6 first interacts with the acoustic wave 29 of frequency F2 and achieves a second diffracted modulated beam 7' of a second diffraction angle. Subsequently, the input light beam 6 interacts with the acoustic wave 29 of frequency F1 and achieves a first diffracted modulated beam 7' of a first diffraction angle.

[0035] In other words, Figure 9A illustrates an embodiment of a phase array transducer. For quartz, commercially available phase arrays support a bandwidth of 250 MHz. However, there are no commercially available multi-frequency and multi-channel acousto-optic modulator devices equipped with a phase array. This embodiment provides an alternative implementation in which separate transducers are driven by different frequencies. This simplifies the requirements for RF delivery electronics because the RF wave is a pure sine wave rather than the sum of those sine waves, but limits the amount of diffracted beam depending on the size of the phase array.

[0036] Figure 9B illustrates another embodiment of the acousto-optic modulator 20. Here, the acousto-optic modulator 20 is also equipped with two transducers 24A and 24B that are physically separated in the direction of the input light 6. Transducers 24A and 24B are supplied as a signal that is the sum of two single radio frequency signals F1 and F2. However, compared to the signal supplied to transducer 24B, the signal supplied to transducer 24A has a different phase relationship between the two single radio frequency signals F1 and F2. These radio frequency signals induce two sound waves 29 with corresponding frequencies in the crystal 27.

[0037] Due to the phase difference, the directions of the respective sound waves are different. Therefore, the input beam 6 has a first angle of entry relative to the first sound wave and a second angle of entry relative to the second sound wave. The input beam 6 interacts with the sound wave 29 of frequency F1 and achieves a first diffracted modulated beam 7' with a first diffraction angle. The input beam 6 also interacts with the sound wave 29 of frequency F2 and achieves a second diffracted modulated beam 7'' with a second diffraction angle.

[0038] In the embodiment illustrated above, two diffracted modulated beams are generated by using two different transducer frequencies. However, this principle can be generalized to using more than two different radio frequencies, thereby providing more than two diffracted modulated beams. The maximum number of diffracted modulated beams is determined by the bandwidth properties and geometric considerations of the crystal.

[0039] In other words, in a particular embodiment, the input beams for each modulator segment of the acousto-optic modulator are provided to the acousto-optic crystal as a single incident beam. One radio frequency bandwidth of the acousto-optic crystal realizes a diffracted beam associated with a plurality of head-assigned frequencies. Preferably, the single incident beam is provided to the acousto-optic crystal at an angle of incidence within an interval between a Bragg angle associated with the highest of the head-assigned frequencies and a Bragg angle associated with the lowest of the head-assigned frequencies.

[0040] If sound waves with different directions are provided, a single incident beam can be provided with a Bragg angle relative to one of the two sound waves by adjusting the phase difference between frequencies F1 and F2.

[0041] Another problem with this design is that the diffraction efficiency of both the first diffracted modulated beam 7' and the second diffracted modulated beam 7" depends at least in part on the power of the two radio frequency signals. This means that a change in the power of one frequency will affect not only the diffraction efficiency of the diffracted modulated beam associated with that frequency, but also the diffraction efficiency of the other diffracted modulated beam. Therefore, there is crosstalk between the modulation of the two modulated beams. To achieve a high-accuracy modulation, this crosstalk must be pre-compensated, which is usually a very difficult task. Given a current data timing speed of 50 MHz to 65 MHz, it may require a synchronization and rise time of one nanosecond or several nanoseconds for the electrical RF signals.

[0042] Another alternative is to use dominant diffraction under the Bragg condition. If a diffraction with an associated Bragg angle or very close to that associated Bragg angle is used for a frequency, then another frequency associated with another Bragg angle will result in a very small diffraction. This will eliminate or at least significantly reduce any crosstalk. However, instead, control over the input angle must be provided.

[0043] Figure 10A illustrates another embodiment of the acousto-optic modulator 20. Here, the acousto-optic modulator 20 is provided with two input beams 6', 6" having a respective entry angle. These entry angles are preferably Bragg angles associated with the frequencies F1 and F2 supplied to the transducer 24. Each input beam 6', 6" results in a respective diffracted beam 7', 7" If the entry angle of one of the beams is close to the associated Bragg angle, then the diffraction of the other input beam becomes substantially negligible, and vice versa. In this way, any modulation of the diffracted beam 7' does not significantly affect the modulation of the diffracted beam 7" and any modulation of the diffracted beam 7" does not significantly affect the modulation of the diffracted beam 7'. Therefore, virtually any crosstalk is removed.

[0044] FIG11A schematically illustrates another embodiment of an acousto-optic modulator 20 having more than one input beam but having separate transducers 24A, 24B for different frequencies F1 and F2.

[0045] Figure 11B schematically illustrates another embodiment of an acousto-optic modulator 20 having more than one input beam and having one of separate transducers 24A and 24B. As shown in Figure 9B, transducers 24A and 24B are supplied as a signal being the sum of two single radio frequency signals F1 and F2. Compared to the signal supplied to transducer 24B, the signal supplied to transducer 24A has a different phase relationship between the two single radio frequency signals F1 and F2, thereby causing a directional difference between the supplied sound waves 29.

[0046] If sound waves with different directions are provided, a single incident beam can be provided with a Bragg angle relative to one of the two sound waves by adjusting the phase difference between frequencies F1 and F2.

[0047] The embodiments of Figures 10 and 11A to 11B require multiple incident beams. Each of the incident beams will be diffracted by a different RF frequency provided by a transducer or a transducer phase array. Crosstalk is avoided because the Bragg condition for a given incident beam will be satisfied by only a single RF frequency. Unless phase matching occurs, the RF frequency will not affect the beam intensity.

[0048] The principle of performing two modulations simultaneously in a single acousto-optic modulator as shown in Figures 8 to 11B can of course be applied to achieve more than two simultaneous modulations by using more than two excitation frequencies.

[0049] In other words, in one embodiment, the multi-head modulator configuration includes an acousto-optic modulator having at least one modulator segment. The segment or segments are configured to split an input beam originating from a laser source and modulate it into one of the modulated beams for use in a plurality of writehead configurations.

[0050] If each of the write head configurations operates with a plurality of parallel beams, this division is performed before the acousto-optic modulator, as can be seen (for example) in Figure 3. Thereby, the acousto-optic modulator includes a plurality of modulator segments, each modulator segment being configured to split an input beam originating from a laser source and modulate it into one of the modulated beams for each of the plurality of write head configurations.

[0051] In other words, in one embodiment, when the acousto-optic modulator includes a plurality of modulator segments, the multi-head modulator configuration includes a first beam splitter configuration that splits a beam from a laser source into one of a plurality of input beams, wherein each of the plurality of input beams is provided to a respective modulator segment of the modulator segments.

[0052] In Figures 9A and 11A, the acousto-optic modulator includes two transducers associated with each of the write heads of the write head, each excited by a single-frequency signal. This concept can, of course, also be used with more than two transducers. In other words, in one embodiment, each modulator segment of the acousto-optic modulator includes a plurality of transducers. Each of these plurality of transducers is driven by a respective head assignment frequency, which is different from the head assignment frequency of the other transducers.

[0053] In Figures 9B and 11B, each of the transducers 24A and 24B is driven by a radio frequency signal F1+F2, which is a sum of radio frequency signals F1 and F2, each having a different frequency F1 and F2, wherein the frequency offset is different from the head assignment frequencies F1 and F2 of the other transducer 24A and 24B. This can of course be generalized to more than two frequencies and more than two transducers.

[0054] In Figures 8 and 10, the acousto-optic modulator includes a single transducer excited by a radio frequency signal that is the sum of two single-frequency signals. These single-frequency signals are associated with respective write heads of a write head. This concept can, of course, also be used for more than two transducers. In other words, in one embodiment, each modulator segment of the acousto-optic modulator includes a common transducer. This transducer is driven by a radio frequency signal that is the sum of a plurality of radio frequency signals, each having a different head assignment frequency.

[0055] In embodiments based on a plurality of incident beams of an acousto-optic modulator, the incident beams must be provided at different incident angles. Preferably, the different incident angles correspond to their respective Bragg angles associated with the head assignment frequency.

[0056] A configuration for achieving this is schematically illustrated in FIG12. An input beam 6 is guided to two consecutive beam splitter devices 70 and a final mirror 72, thereby dividing the input beam 6 into three parallel split input beams 6A to 6C. A lens configuration 74 is used to focus the different split input beams 6A to 6C to one common focal point in an acousto-optic modulator 20. The acousto-optic modulator 20 is driven by three different radio frequency drives, preferably adapted to provide a Bragg angle equal to the angle at which the split input beams 6A to 6C arrive at the acousto-optic modulator 20. Thereby, the diffracted modulated beams 7A to 7C are provided at three different exit angles, and a second lens configuration 76 causes these diverging beams to form parallel modulated beams. In this particular embodiment, three modulated beams 7A to 7C are provided, but any number of modulated beams 7A to 7C can be achieved in this way.

[0057] The above principle of providing separate beams incident on the acousto-optic modulator 20 at different angles is only one illustrative example. Anyone skilled in the art will recognize that many other optical configurations resulting in the same beam geometry are available in the prior art.

[0058] In other words, in one embodiment, the multi-head modulator configuration includes a plurality of second beam splitter configurations, each modulator segment of the acousto-optic modulator having one second beam splitter configuration, the plurality of second beam splitter configurations being configured to split the input beam into a plurality of incident beams provided to the acousto-optic crystal at different incident angles.

[0059] The above presents four specific embodiments. All of them utilize a novel multi-channel, multi-frequency acousto-optic modulator. The main difference from currently used acousto-optic modulators is that, in each individual segment of the acousto-optic modulator, there are multiple beams emitted in the Y direction of the writer. In current designs, a single beam is diffracted only by a single acousto-optic modulator channel. These multiple beams are both intensity-modulated and angled at a sufficiently large angle, allowing each individual acousto-optic modulator channel to support pattern printing through different optical heads.

[0060] As mentioned above, the modulation of the acousto-optic modulator is controlled by the intensity of different frequency components provided to one or more transducers of the acousto-optic modulator. Referring to FIG4, in a preferred embodiment, the control unit 40 is used to provide appropriate signals to the transducers of the acousto-optic modulator in the multi-head modulation configuration 4. The intensity of the individual modulated beams emitted from the acousto-optic modulator can thereby be adapted to a predetermined printed pattern. This adaptation must also be synchronized with the scanning of the laser light performed by the write head and with the relative movement between the substrate and the write head.

[0061] In other words, in one embodiment, the control unit is configured to modify the head assignment frequency of each modulator segment of the acousto-optic modulator according to a predetermined printed pattern, depending on the sweeping of laser light emitted from the plurality of write head configurations and the relative mechanical displacement between the substrate holder and the plurality of write head configurations, in order to adjust the intensity of one of the beams emitted from the acousto-optic crystal.

[0062] Figure 13 is a flowchart of the steps of one embodiment of a method for operating a scanning lithography laser writer. In step S10, a laser input beam is provided. In step S20, the laser input beam is split and modulated into n modulated beams by acousto-optic modulation, where n≥1. This is performed for each of m write head configurations, where m≥2. Preferably, the steps of splitting and modulating the laser input beam are performed in n segmented steps, where each segmented step modulates one beam for each of the m write head configurations.

[0063] In one embodiment, when n > 1, the steps of splitting and modulating the laser input beam include step S22 of splitting the laser input beam into n input beams. In step S24, each of the n input beams is split in one of the segmentation steps and modulated by acousto-optic modulation.

[0064] In step S30, n modulated beams for the m write head configurations are optically connected to their respective write head configurations. In all examples, the n modulated beams emitted from each of the m write head configurations are shifted relative to each other by a predetermined non-zero distance in the sweep direction. In step S40, a substrate plane of the scanning lithography laser writer is illuminated by the n modulated beams for the m write head configurations. In step S50, the substrate plane and the m write head configurations are shifted relative to each other in at least one scan direction parallel to the substrate plane. In step S60, the n modulated beams emitted from the m write head configurations are swept in a sweep direction parallel to the substrate plane and transverse to the scan direction.

[0065] The different steps are depicted as consecutive steps in the diagram. However, anyone familiar with this technique will recognize that most steps are actually performed simultaneously and repeatedly in combination with each other, as indicated by the dashed arrows.

[0066] In one embodiment, step S20 of splitting and modulating the laser input beam includes driving an acousto-optic modulator by means of m transducers. Each of the m transducers is driven by a head assignment frequency that is different from the head assignment frequencies of the other transducers.

[0067] In another embodiment, step S20 of splitting and modulating the laser input beam includes driving an acousto-optic modulator by means of a common transducer. The transducer is driven by a radio frequency signal that is the sum of m radio frequency signals, each having a different head assignment frequency.

[0068] In a further embodiment, driving the acousto-optic modulator includes a step of depending on the laser light emitted from the m write head configuration and a step of shifting the substrate holder and the m write head configuration relative to each other. In each segmented step, a signal that modifies the head assignment frequency of the acousto-optic modulator according to a predetermined printing pattern is used to adjust the intensity of one of the beams emitted from the acousto-optic crystal.

[0069] In one embodiment, the input laser beam for each segmented step is provided to the acousto-optic crystal as a single incident beam. One radio frequency bandwidth of the acousto-optic crystal enables a diffracted beam associated with m head assignment frequencies. Preferably, this step includes providing the single incident beam to the acousto-optic crystal at an incident angle within an interval between a Bragg angle associated with the highest of the head assignment frequencies and a Bragg angle associated with the lowest of the head assignment frequencies.

[0070] In one embodiment, the input laser beam is split into m incident beams and the m incident beams are provided to the acousto-optic crystal at different incident angles. Preferably, the different incident angles correspond to respective Bragg angles associated with the head assignment frequency.

[0071] In all the above embodiments, at least two modulated beams are provided in the diffraction direction of the acousto-optic crystal. A plurality of modulated beams may also be simultaneously separated in a direction perpendicular to the diffraction direction, with each modulator segment having one modulated beam. Therefore, in the overview, an array of n x m modulated beams is simultaneously output from the acousto-optic crystal, where n ≥ 1 and m ≥ 2. The m output modulated beams exiting the acousto-optic crystal at the same angle are intended for use in the same writer head configuration.

[0072] In a preferred embodiment, the step of optically connecting the n modulated beams for each of the m write head configurations to their respective write head configurations includes splitting a beam of parallel modulated beams from an acousto-optic modulator into m separate groups of n modulated beams, with each write head configuration having one group.

[0073] Furthermore, in a preferred embodiment, the sweeping steps described above provide synchronous sweeping for one of all write head configurations.

[0074] Figure 14 schematically illustrates a portion of configuration 2 used to provide one of two modulated laser beams 7 to each of two different write head configurations 50. Laser source 10 provides input beam 5 to multi-head modulator configuration 4. Four modulated beams 7 exit multi-head modulator configuration 4, with two modulated beams 7 intended for each write head configuration 50. The modulated beams 7 are guided to their respective write head configurations 50 via a set of mirrors 82. In this particular embodiment, a beam splitter 80, shaped like a pickup mirror, is configured to reflect only one pair of modulated beams into separate beams or groups. Other optical components of different types (not shown) may also be present to control the properties of the modulated beams. These components are well known to anyone skilled in the art and therefore will not be described further.

[0075] Therefore, in a preferred embodiment, the illumination configuration 2 further includes a beam splitter configured to separate a beam of parallel modulated light from an acousto-optic modulator into m separate groups of n modulated light beams, each write head configured with one group.

[0076] Separate beams or groups are configured to have the same travel distance to their respective write head configurations so as not to introduce any optical path differences between beams. At the exit of the multi-head modulator configuration 4, a lens or lens system is typically provided for focusing the beam onto a specific plane in the write head (which is conjugate to one of the pupil planes of a final lens). Since the same lens configuration acts on the beams of all write heads, the optical path must be identical to maintain the focusing properties. This is typically achieved by providing an appropriate delay line 84. Alternatively, after the separation of the different write heads, a separate focusing lens configuration is provided to each beam.

[0077] Each modulated beam 7 is provided to a write head configuration 50 such that each modulated beam 7 is separated by a distance in the scanning direction X at the laser photosensitive surface 64. The write head configuration 50 is shifted by a non-zero distance in the scanning direction Y and possibly also in the X direction.

[0078] The above diagram illustrates a two-write-head configuration with two modulated beams per write head. However, the number of frequencies and therefore the number of diffracted beams can be significantly larger. A design using five to ten write-head configurations is believed to be technically possible. Furthermore, the number of modulated beams per write head configuration can also vary, and it is technically entirely possible to configure up to at least 15 modulated beams per write head.

[0079] Figure 15 schematically illustrates three write head configurations 50. Each write head configuration controls the sweeping of five modulated beams (indicated by horizontal lines) separated in the scan direction X. The write head configuration 50 is offset by an amount ΔY in the scan direction Y. Typically, there is also an offset in the scan direction X between the write head configurations 50.

[0080] In a preferred embodiment, when m is greater than 1, the control unit is configured to synchronize the sweep control of the laser light emitted from the m write head configurations. This facilitates the control logic because the dependency of the scan movement then becomes the same for all different write head configurations.

[0081] Since all write heads are preferably configured to move at the same speed relative to the laser photosensitive surface, the sweep time must be the same for all heads. One way to achieve this is to use the same pixel clock value for all write head configurations. This, in turn, requires that the intensity of the cylindrical lens used to compensate for astigmatism caused by the linear frequency chirp of the deflector RF frequency must be tuned to the pixel clock value. This problem can be solved by using a focal length adjustable cylindrical lens.

[0082] The increase in write speed that can be achieved by increasing the number of write head configurations can be utilized in different ways. The selected method is related to a predetermined non-zero distance between each write head configuration and each other. The simplest and most understandable utilization of the increased write speed is to position the write head configurations shifted by an effective sweep length. The sweeps of different scans may overlap or not. An overlap between consecutive scans can be used, for example, to reduce any edge effects. Depending on the sensitivity of the pattern to edge effects, the overlap (if any) may also have different values. Herein, the effective sweep length is defined as the sweep length of one write head configuration minus a sweep overlap distance. This sweep overlap distance is equal to or greater than zero.

[0083] This method using a two-write-head configuration is illustrated in FIG16A. Exposures 90A, 90B from the two write-head configurations for a full sweep length S are shifted relative to each other by a predetermined non-zero distance ΔY. When the next scan is to be performed, the write-head configuration moves a scan width distance W in the Y direction. The result after a complete set of scans is illustrated in FIG16B, where regions 91, 92 exposed by only one of the write-head configurations intersect with an overlapping region 93 having a sweep overlap distance O, wherein the two write-head configurations facilitate the exposure. In this embodiment, it can be seen that the predetermined non-zero distance ΔY is equal to the sweep length S minus the sweep overlap distance O.

[0084] In an alternative configuration, the increased write speed can be used to improve exposure uniformity. Lasers always exhibit some variation in the intensity of the laser beam provided. Laser manufacturers certainly attempt to minimize any such variation, but minor fluctuations may still exist. Similarly, non-repetitive variations in the optical system can also cause the laser intensity reaching the laser photosensitive surface to differ slightly from the expected intensity. Some of these fluctuations are temporal. If the same area at the laser photosensitive surface is exposed in more than one time slot, such that the total exposure equals the requested exposure, the actual exposure will be the sum of the exposures in different portions. Any temporal fluctuations in laser intensity will thus be averaged over all exposure times, and this averaging will thereby reduce the impact of any temporal fluctuations in laser intensity.

[0085] Figure 17A illustrates one embodiment with two write head configurations, wherein a predetermined non-zero distance ΔY between the write head configurations is equal to the effective sweep length divided by 2. When the next scan is to be performed, the write head configuration moves a scan width distance W in the Y direction. Here it can be seen that each region at the laser photosensitive surface will be exposed at least once by each write head configuration. Alternatively, the scan width distance W becomes smaller, which increases the total write time compared to the configuration in Figure 16A.

[0086] The result after a complete scan is illustrated in Figure 17B, where region 94, exposed once by each write head configuration, intersects with overlapping regions 95 and 96, where one write head configuration has been exposed twice and the other write head configuration has been exposed once. Therefore, an averaging of intensity is achieved during these different exposure periods. The shortened distance between overlapping regions also reduces the risk of moiré patterns.

[0087] These principles can be generalized to more than two write head configurations. Different write head configurations can then be used to increase actual write speed or improve strength averaging, as described above.

[0088] In other words, in one embodiment, the predetermined non-zero distance between each write head configuration and one or both of the other write head configurations is equal to an effective sweep length divided by an integer k, where k ≤ m.

[0089] In summary, this technology has many advantages. One important advantage is that the printing speed of the writer will increase proportionally to the number of write heads configured. In addition, the quasi-multiple pass strategy improves many critical lithography parameters (such as placement, critical size uniformity (CDU), and moiré).

[0090] The embodiments described above should be understood as several illustrative examples of the present invention. Those skilled in the art will understand that various modifications, combinations, and changes can be made to the embodiments without departing from the scope of the present invention. Specifically, where technically possible, different partial solutions in different embodiments can be combined in other configurations. However, the scope of the present invention is defined by the claims of the appended invention applications. [Simplified Explanation of the Diagram]

[0014] The invention, together with its further objects and advantages, will be better understood by referring to the following description taken in conjunction with the accompanying drawings, in which: Figure 1 is a schematic illustration of one single-head modulation configuration; Figure 2 schematically illustrates the conditions during writing in a single-head modulation, multi-beam configuration; Figure 3 is a schematic illustration of one multi-head modulation configuration; Figure 4 schematically illustrates one embodiment of a scanning lithography laser writer; Figure 5 schematically illustrates the conditions during writing in a multi-head modulation, multi-beam configuration; Figure 6 schematically illustrates one embodiment of an illumination configuration; Figure 7 illustrates one embodiment of an acousto-optic modulator; Figure 8 illustrates one embodiment of an acousto-optic modulator operating with more than one frequency and a common transducer; Figure 9A illustrates one embodiment of an acousto-optic modulator operating with more than one frequency and separate transducers; Figure 9B illustrates another embodiment of an acousto-optic modulator operating with more than one frequency and separate transducers; Figure 10 illustrates one embodiment of an acousto-optic modulator operating with more than one incident beam, more than one frequency, and a common transducer; Figure 11A illustrates one embodiment of an acousto-optic modulator operating with more than one incident beam, more than one frequency, and separate transducers; Figure 11B illustrates another embodiment of an acousto-optic modulator operating with more than one incident beam, more than one frequency, and separate transducers; Figure 12 schematically illustrates one embodiment of a beam configuration providing beams with different incident angles; Figure 13 is a flowchart of the steps of one embodiment of a method for operating a scanning lithography laser writer; Figure 14 schematically illustrates a portion of one embodiment of an illumination configuration; Figure 15 illustrates the geometric relationship of one embodiment of a plurality of write head configurations; Figure 16A schematically illustrates the exposure result of a sweep for one embodiment of a write head configuration; Figure 16B illustrates the final exposure of the embodiment of Figure 16A; Figure 17A schematically illustrates the exposure result of a sweep for another embodiment of the write head configuration; and Figure 17B illustrates the final exposure of the embodiment of Figure 17A.

Claims

1. A scanning photolithography laser writer (1), comprising: A substrate holder (60) having an attachment member for holding a substrate (62) having a laser photosensitive surface (64) in a substrate plane; an irradiation configuration (2); the irradiation configuration (2) having a laser source (10); wherein the irradiation configuration (2) is configured to provide laser light from the laser source (10) to irradiate the substrate plane; and a control unit (40), characterized in that the irradiation configuration (2) further has a multi-head modulator configuration (4) and m write head configurations (50), wherein m≥2; the irradiation configuration (2) is configured to provide the laser light from the laser source (10) to the m write head configurations (50) via the multi-head modulator configuration (4) to irradiate the substrate plane; the control unit (40) is configured to control a relative mechanical displacement between the substrate holder (60) and the m write head configurations (50) in at least one scanning direction (X) parallel to the substrate plane; The control unit (40) is configured to control the laser light emitted from the m write head configuration (50) to sweep in a sweep direction (Y) parallel to the substrate plane and transverse to the scanning direction (X); wherein the multi-head modulator configuration (4) is configured to split an input beam (5) from the laser source (10) into n beams (7) by using an acoustic crystal (27), wherein n≥1, for each of the m write head configurations (50), and wherein the m write head configurations (50) are further configured to simultaneously modulate the n beams (7) into n modulated beams; wherein the m write head configurations (50) are positioned such that the laser light emitted from each of the m write head configurations (50) is shifted relative to each other in the sweep direction (Y) by a predetermined non-zero distance (ΔY).

2. As in request item 1, the scanning lithography laser writer, wherein, The multi-head modulator configuration (4) includes an acousto-optic modulator (20) having one of n modulator segments (25), wherein each segment (25) is configured to split an input beam (6) originating from the laser source (10) and modulate it into a modulated beam (7) for one of the m write head configurations (50).

3. The scanning lithography laser writer as requested in item 2, wherein each modulator segment (25) of the acousto-optic modulator (20) includes m transducers (24A, 24B).

4. The scanning laser writer as described in claim 3, wherein each of the m transducers (24A, 24B) is driven by a separate head assignment frequency (F1, F2) that is different from the head assignment frequencies (F1, F2) of the other transducers (24A, 24B).

5. The scanning laser writer as claimed in claim 3, wherein each of the m transducers (24A, 24B) is driven by an RF signal that is a sum (F1+F2) of m RF signals each having a different frequency (F1, F2), wherein the frequency offset is different from the head assignment frequencies (F1, F2) of the other transducers (24A, 24B).

6. The scanning lithography laser writer as claimed in claim 2, wherein each modulator segment (25) of the acousto-optic modulator (20) includes a common transducer (24), wherein the transducer (24) is driven by an RF signal as a sum (F1+F2) of m RF signals each having a different head assignment frequency.

7. A scanning lithography laser writer as claimed in any of items 3 to 6, wherein the multi-head modulator configuration (4) includes m beam splitter configurations (70), each modulator segment (25) of the acousto-optic modulator having one beam splitter configuration (70), the m beam splitter configurations (70) being configured to split the input beam (6) into m incident beams (6A to 6C), the m incident beams (6A to 6C) being provided to the acousto-optic crystal (27) at different incident angles (,) relative to the acousto-optic modulator.

8. A scanning lithography laser writer as requested in any of items 1 to 6, wherein the predetermined non-zero distance (ΔY) of each of the write head configurations (50) relative to one or both of the other write head configurations (50) is equal to an effective sweep length divided by an integer k, where k ≤ m, and wherein the effective sweep length is the sweep length (S) of one of the write head configurations (50) minus a sweep overlap distance (O), the sweep overlap distance (O) being equal to or greater than zero.

9. A scanning lithography laser writer as claimed in any of claims 1 to 6, further comprising a beam splitter (80) configured to split a parallel modulated beam from the acousto-optic modulator (20) into m separate groups of n modulated beams, each write head configured (50) of one group.

10. A method for operating a scanning photolithography laser writer (1), comprising the following steps: Provide (S10) a laser input beam (5); split the laser input beam into n beams, and simultaneously modulate (S20) the n beams into n modulated beams (7) by acousto-optic modulation, where n≥1, for each of the m write head configurations (50), where m≥2; optically connect (S30) the n modulated beams (7) for the m write head configurations (50) to the respective write head configurations (50); illuminate (S40) one of the substrate planes of the scanning lithography laser writer (1) by the n modulated beams (7) for the m write head configurations (50); shift the substrate plane and the m write head configurations (50) relative to each other in at least one scanning direction (X) parallel to the substrate plane (S50). The n modulated beams (7) emitted from the m write head configuration (50) are swept (S60) in a sweep direction (Y) parallel to the substrate plane and transverse to the scan direction (X); thereby, in all cases, the n modulated beams (7) emitted from each of the m write head configurations (50) are shifted relative to each other in the sweep direction (Y) by a predetermined non-zero distance (ΔY).

11. As in request item 10, wherein, The splitting and modulation (S20) are performed in n segmentation steps, wherein each segmentation step modulates one beam of each of the m write head configurations (50).

12. The method of claim 11, wherein the step of splitting and modulating (S20) the laser input beam includes driving an acoustic-optical modulator (20) by means of m transducers (24A, 24B).

13. The method of claim 12, wherein each of the m transducers (24A, 24B) is driven by a respective head assignment frequency (F1, F2) which is different from the head assignment frequencies (F1, F2) of the other transducers (24A, 24B).

14. The method of claim 12, wherein each of the m transducers (24A, 24B) is driven by a radio frequency signal as a sum (F1+F2) of m radio frequency signals each having a different frequency (F1, F2), wherein the frequency offset is different from the head assignment frequencies (F1, F2) of the other transducers (24A, 24B).

15. The method of claim 11, wherein the splitting and the modulation (S20) includes driving an acoustic-optical modulator (20) by a transducer (24), wherein the transducer (24) is driven by a radio frequency signal, the radio frequency signal being the sum of one of m radio frequency signals (F1+F2), each of the m radio frequency signals having a different head assignment frequency.

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