Masking device and control method thereof

Abstract

Disclosed is a method for controlling an exposure dose at a substrate using a masking device including a first blade and a second blade. The method includes providing a radiation pulse at the masking device to expose the substrate, exposing an exposure area at the substrate by moving the first blade in a first direction relative to a slit center and moving the second blade in a second direction opposite the first direction, and maintaining a constant amount of radiation received at the exposure area. The moving of the first and second blades is defined by a velocity profile of a substrate support supporting the substrate.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS)

[0001] This application claims priority to European Patent Application No. 22217160.5, filed December 29, 2022, which is incorporated herein by reference in its entirety.

[0002] The present invention relates to an apparatus and a method for controlling an exposure dose, in particular to a masking device that can be arranged in an illumination system and a method for controlling the same, and an illumination system including the masking device that forms part of a lithographic apparatus to control the exposure dose on a substrate that is exposed at a non-constant scan speed. [Background technology]

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern (often referred to as a "design layout" or "design") on a patterning device (e.g., a mask or reticle), supported by a mask support, onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., a wafer). A substrate support (e.g., a wafer table or wafer holder) constructed to hold the substrate (e.g., a resist-coated wafer) may be moved precisely to position various target portions at focused and aligned positions in the path of the radiation beam, for example, so as to project the pattern onto the substrate.

[0004]

[0004] As semiconductor manufacturing processes continue to advance, the dimensions of circuit elements are constantly shrinking while substrate throughput is increasing. This places ever-tighter constraints on lithography systems. With increasing substrate throughput, the exposure time per target area decreases. Since the total dose at the target area needs to be kept constant (for proper exposure of the resist), the radiation flux needs to be adapted. Dose control is typically set in the radiation system (e.g., a laser system) by directly controlling the number of radiation pulses, the pulse repetition rate, and / or the radiation pulse intensity.

[0005] Typically, exposure radiation is provided through a slit that scans across the substrate surface. The dose at the substrate is governed by the actual velocity of the substrate support supporting the substrate and the exposure area of ​​the substrate, the so-called slit. The slit is defined by the shape of an opening formed by a shielding means. The shielding means is, for example, a masking device including a masking blade positioned near a reticle (see U.S. Patent Application Publication No. 2005012913). In particular, the position of the masking blade in the scan direction controls the illuminated area during an exposure cycle or exposure period. Before exposure of the target area, the masking blade can be set to not form an opening (i.e., close the slit) to avoid unintentional exposure of the substrate. To allow exposure of the target area, a first masking blade moves linearly away from a second masking blade (opposite the fixed-position first masking blade) and opens the shielding means until the maximum slit area is reached. The system is then ready to expose the target area. Exposure of the target area is typically performed by a support stage with a constant velocity. For example, as disclosed in U.S. Patent Application Publication No. 2005157285A1, the first and second masking blades are configured to move synchronously with the patterning device, such that the distance between the two blades remains constant during exposure. Thus, the shape of the aperture in the shielding means remains constant (i.e., the relative positions of the masking blades remain constant) for a certain period of time. After exposure of the target area is complete, the second masking blade begins to move linearly toward the first masking blade, closing the aperture at the edge of the target area.

[0006] To achieve increased substrate throughput in a lithography system without requiring excessively high accelerations and velocities of the mask support and substrate support, substrate exposure is performed at a non-constant velocity, as disclosed, for example, in U.S. Pat. No. 678,839 B2. This means that the target area is not only exposed when the substrate support moves at a constant velocity, but also during acceleration and deceleration of the substrate support (before and after the exposure period when the substrate support reaches a constant velocity). To provide a sufficient dose to the target area, the time interval between successive light pulses (e.g., from an excimer laser) is inversely proportional to the velocity of the substrate support. This means that the laser pulse rate is adapted to the substrate support velocity during acceleration and deceleration of the substrate support. Controlling the exposure dose by varying the laser power (or the output of the radiation system) according to the velocity of the substrate support can result in instability or undesired fluctuations of the laser (or the radiation system). As a result, the exposure dose at the substrate is not at the required level in at least a portion of the target area, which can result in low die yields. Summary of the Invention

[0007] According to a first aspect of the present disclosure, there is provided a method for controlling an exposure dose at a substrate using a masking device including a first blade and a second blade, the method comprising: providing a radiation pulse at the masking device to expose the substrate; exposing an exposure area at the substrate by moving the first blade in a first direction relative to a slit center and moving the second blade in a second direction opposite the first direction; and keeping an amount of radiation received at the exposure area constant, wherein the moving of the first and second blades is defined by a velocity profile of a substrate support supporting the substrate.

[0008]

[0008] Controlling the movement of the blade in response to the velocity profile of the substrate support and / or mask support provides a means for controlling the radiation dose at the substrate without disturbing the radiation system, so that the radiation system remains stable even during substrate exposure with variable speed supports.

[0009]

[0009] During exposure of a substrate, the velocity profile may include a non-constant velocity of the substrate support and / or the mask support. Exposing the substrate by scanning exposure while the substrate support is moving at a non-constant velocity, i.e. while the support is accelerating or decelerating, may be beneficial in terms of substrate throughput. Furthermore, during scanning exposure, lower acceleration and deceleration may be used.

[0010]

[0010] The velocity profile may comprise a sinusoidal velocity profile, which may reduce mechanical disturbances in the lithography system.

[0011]

[0011] Furthermore, the radiation dose can be controlled by an exposure control metric, which is the number of pulses (N) within a slit or radiation dose. slit )

[0012]

[0012] The method according to the first aspect is particularly advantageous for use in a control unit, which may include means for setting the position of a masking blade arranged in the masking device, such that the control unit is operable to perform the method for controlling the exposure dose at the substrate.

[0013] According to a second aspect of the present disclosure, there is provided a masking device for selectively shielding portions of a patterning device from a radiation beam, the masking device including a plurality of masking blades mechanically separated from one another, a control unit configured to control a position of each of the plurality of masking blades, and a position of at least two of the plurality of masking blades defined by a velocity profile of a substrate support supporting a substrate.

[0014] During exposure of the substrate, the velocity profile may comprise a non-constant velocity of the substrate support and / or the mask support. The velocity profile may comprise a sinusoidal velocity profile.

[0015]

[0015] The masking device according to the second aspect is particularly useful for use in an illumination system, which may be part of a lithographic apparatus.

[0016] According to a third aspect of the present disclosure, there is provided a method for controlling a masking blade position of a masking device, the method comprising receiving at a control unit a first input comprising information of a velocity profile of a mask support and / or a substrate support used during exposure, receiving at the control unit a second input being an exposure control metric, determining a position setpoint for the masking blade during exposure, and moving the masking blade to the determined position setpoint.

[0017]

[0017] As an exposure control metric, the number of pulses within a slit or radiation dose (N slit ) can be used. A method for controlling masking blade position can receive a signal at a masking control unit corresponding to the blade position, the signal being used as a feedforward signal or a feedback signal. [Brief explanation of the drawings]

[0018]

[0018] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which: [Figure 1] 1 depicts a schematic diagram of a lithographic apparatus; [Figure 2] 2 shows a schematic diagram of a part of the lithographic apparatus shown in FIG. 1 showing a masking blade; [Figure 3A] 2 shows an exploded view of a masking device according to an embodiment of the present disclosure, which may form part of the lithographic apparatus shown in FIG. 1; [Figure 3B] 2 shows a three-dimensional schematic view of a masking device according to an embodiment of the present disclosure that may form part of the lithographic apparatus shown in FIG. 1, illustrating the openings between the blades; [Figure 4] 1 shows the masking blade position as a function of time during a conventional exposure of a target area. [Figure 5] 1 shows a schematic front view of a masking device. [Figure 6A] The velocity profiles of the mask support and the substrate support are shown as a function of time. [Figure 6B] 6B illustrates masking blade positions at various times during exposure of a target area using the velocity profile of FIG. 6A, in accordance with one embodiment of the present invention. [Figure 7] 2 shows a schematic diagram of a method for controlling a masking device according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0019]

[0019] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g., having a wavelength of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and EUV (extreme ultraviolet radiation, e.g., having a wavelength in the range of about 5 to 100 nm).

[0020] The terms "reticle," "mask," or "patterning device," as used herein, may be broadly interpreted as referring to a general-purpose patterning device that can be used to impart a patterned cross-section to an incoming radiation beam, corresponding to the pattern to be created in a target portion of a substrate. The term "light valve" can also be used in this context. Besides the classic mask (transmissive or reflective mask, binary mask, phase-shifting mask, hybrid mask, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

[0021]

[0021] For clarity of the present invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes: x-axis, y-axis, and z-axis. Each of the three axes is orthogonal to the other two axes. Rotation about the x-axis is referred to as Rx rotation. Rotation about the y-axis is referred to as Ry rotation. Rotation about the z-axis is referred to as Rz rotation. The Cartesian coordinate system does not limit the present invention and is used for clarity only.

[0022] 1 schematically illustrates a lithographic apparatus LA. The lithographic apparatus LA includes an illumination system (also referred to as an illuminator) IL configured to condition a radiation or light beam LB (e.g. UV radiation, DUV radiation, or EUV radiation), a mask support (e.g. a mask table) MT configured to support a patterning device (e.g. a mask) MA and connected to a first positioner configured to accurately position the patterning device MA according to certain parameters, and a substrate support (e.g. a wafer table) WT configured to hold a substrate (e.g. a resist-coated wafer) W. A second positioner may be provided, configured to accurately position the substrate according to certain parameters. A projection lens system (e.g. a refractive projection lens system) PL is configured to project a pattern imparted to the radiation beam LB by the patterning device MA (a patterned projection beam) onto a target portion of the substrate W (e.g. comprising one or more dies).

[0023]

[0023] In operation, the illumination system IL receives a radiation beam from the radiation source SR, for example via a beam delivery system. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof, for directing, shaping and / or controlling the radiation. The illumination system IL can be used to condition the radiation beam LB so that it has a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0024]

[0024] The term "projection system" PL as used herein should be interpreted broadly and may encompass various types of projection systems, including refractive optical systems, reflective optical systems, catadioptric optical systems, anamorphic optical systems, magnetic optical systems, electromagnetic optical systems, and / or electrostatic optical systems, or any combination thereof, as appropriate to the exposure radiation used and / or other factors such as the use of an immersion liquid or a vacuum. Where the term "projection lens" is used herein, it may be considered as synonymous with the more general term "projection system" PL.

[0025]

[0025] The lithographic apparatus LA may be of a type in which at least a portion of the substrate W is covered by a liquid having a relatively high refractive index, such as water, so as to fill a space between the projection system PL and the substrate W. This is also known as immersion lithography. Further information about immersion techniques is given in US Patent No. 6,952,253, which is incorporated herein by reference.

[0026] Lithographic apparatus LA may also be of a type having two (also called "dual stage") or more substrate supports WT. In such a "multi-stage" machine, the substrate supports WT can be used in parallel and / or a substrate W placed on one substrate support WT can be used to expose a pattern thereon while a substrate W placed on another substrate support WT is undergoing preparation steps for a subsequent exposure.

[0027] In addition to the substrate table WT, the lithographic apparatus LA may include a measurement stage. The measurement stage is arranged to hold a sensor and / or a cleaning device. The sensor can be arranged to measure a property of the projection system PL or a property of the radiation beam LB. The measurement stage can hold multiple sensors. The cleaning device can be arranged to clean part of the lithographic apparatus, for example part of the projection system PL or part of the system for providing immersion liquid. When the substrate support WT is remote from the projection system PL, the measurement stage can be moved below the projection system PL.

[0028]

[0028] In operation, the radiation beam LB is incident on the patterning device (or mask) MA, which is held on the mask support MT, and is patterned according to a pattern (design layout) present on the patterning device MA. After traversing the mask MA, the radiation beam LB passes through the projection system PL, which focuses the beam onto a target portion of the substrate W. With the aid of a second positioner and position measurement system, the substrate support WT can be precisely moved, for example, to position various target portions at focused and aligned positions in the path of the radiation beam LB. Similarly, the first positioner and possibly further position sensors (not explicitly shown in Figure 1) can be used to precisely position the patterning device MA with respect to the path of the radiation beam LB. The patterning device MA and substrate W can be aligned using mask alignment marks and substrate alignment marks. Substrate alignment marks may occupy dedicated target portions, but may also be located in spaces between target portions. When the substrate alignment marks are located between the target portions, they are known as scribe-line alignment marks.

[0029] A masking device MD is provided for selectively blocking parts of the patterning device MA from the radiation beam LB. In other embodiments not shown in Figure 1, a masking device MD may be provided for selectively blocking parts of the patterned projection beam. As shown in Figure 1, relay optics (or relay lens) RL is provided for projecting the radiation that passes through the masking device onto the patterning device MA.

[0030] FIG. 2 shows a cross-section in the yz plane of a portion of the lithographic apparatus LA shown in FIG. 1. A masking device MD according to an embodiment of the present invention is illustrated schematically. The masking device MD includes a first masking structure and a second masking structure. These masking structures may be plates or blades or other structures suitable for selectively obscuring (at least partially) a location where a patterning device is located in use. That is, the masking structures are capable of blocking a provided radiation beam. The masking device MD preferably includes masking blades 10, 11, 20, 21, which are arranged to form two sets of blades: X-blades 20, 21 and Y-blades 10, 11. The two sets of blades are mechanically isolated from each other. That is, the blades are mounted such that vibrations generated by either the X-blades or the Y-blades are not transmitted to the Y-blades or the X-blades, and vice versa.

[0031]

[0031] The masking blades 10, 11, 20, and 21 can also be considered as plates or other structures suitable for obscuring. According to one embodiment of the present invention, the Y-blades 10 and 11 are driven (i.e., operated to move) in the y-direction during substrate exposure, while the X-blades 20 and 21 are stationary during exposure. However, the present invention is not limited in this respect, and the Y-blades may be stationary. That is, the Y-blades 10 and 11 may be stationary while the X-blades 20 and 21 are movable. The blades that move during scanning, hereinafter referred to as Y-blades for convenience, are controlled by software and electronics, and their positions can be adjusted by actuators. It should be noted that the X-blades are similarly controlled by software and electronics (and actuators). It is common for both Y-blades to move a specified distance apart in the y-direction. The y-direction corresponds to the scan direction, i.e., the direction in which the mask table / holder MT and the substrate table / holder WT move during scanning exposure. The moving blades are controlled to move according to a desired scan profile or trajectory.

[0032]

[0032] The blades can be set so that there is a predetermined distance between the X-blades 20, 21 and between the Y-blades 10, 11. Conventionally, the Y-blades 10, 11 are arranged to be movable during scanning, and the X-blades 20, 21, although movable, are generally arranged to be stationary during scanning. If the X-blades 20, 21 are moved, this is typically done between two scans (exposure periods). In a static exposure, the X-blades can be moved between exposures. In a scanning exposure, the Y-blades 10, 11 are particularly arranged to perform an additional movement that allows the patterning device MA to be scanned by the radiation beam LB.

[0033]

[0033] Referring to Figure 2, the features of the masking device MD, in particular the masking blades 10, 11, 20, and their arrangement relative to each other and other components of the lithographic apparatus are described in further detail in U.S. Patent Application Publication No. 2005157285A1, which is incorporated herein by reference.

[0034]

[0034] Figures 3A and 3B show an exploded view and a three-dimensional schematic diagram of the masking device MD of the lithographic apparatus LA shown in Figure 1. These figures give an example of the arrangement of the blades 10, 11, 20, 21 relative to each other. The double-headed arrows indicate the direction of movement of each blade.

[0035] As shown in Figure 3B, the blades 10, 11, 20, 21 can be set so that an aperture 30 is formed between them. The aperture 30 allows a portion of the radiation beam LB provided via the illuminator IL to pass through the masking device MD towards the relay lens RL. The size of the radiation passage area 30 defined by the apertures between the blades determines what is called the scan slit shape. By controlling the position of the blades, the size of the aperture 30 (or passage area) can be controlled. This makes it possible to control and define the amount of radiation that passes through the masking device MD and interacts with the patterning device MA. Furthermore, the position of the aperture 30 is defined by the position of each blade. The blade positions can be set using a controller.

[0036] 4 shows the blade positions relative to the center of the slit (aperture) 30 during a conventional exposure cycle of a target area on a substrate. The solid lines, designated by reference numerals 50 and 51, show the position of the first blade (first Y-blade) 11 as a function of time. The dotted lines, designated by reference numerals 52 and 53, show the position of the second blade (second Y-blade) 10 as a function of time. At the start of the exposure cycle, both blades are at the same y-position, as indicated by the intersection of the solid and dotted lines (bottom left of the graph). This means that before the start of the exposure cycle, these blades are positioned so that no radiation is incident on the patterning device MA. When the exposure cycle starts, the first blade 11 moves a defined distance, indicated by the first part of the solid line 50, from the second blade 10 to create the aperture 30. Once the aperture 30 is formed (at the start of the solid line designated by reference numeral 51), the actual exposure is carried out. When the exposure is finished (end of dotted line 52), the second blade (second Y-blade) 10 is specifically moved (towards the first blade 11) to a position where it does not allow radiation to be incident on the patterning device MA, as shown by dotted line 53. Thus, at the end of the exposure cycle, the aperture 30 is closed and no radiation is allowed to be incident on the patterning device MA.

[0037] During conventional exposure, the Y-blades 10, 11 remain at a constant distance from each other (i.e. a constant slit width), as shown by the solid and dotted lines 51 and 52 in Figure 4. This keeps the size of the area where radiation is incident on the patterning device constant. Note that the patterning device MA moves at a predetermined constant scan speed while being exposed by the radiation beam LB passing through the opening between the blades 10, 11, 20, 21.

[0038] To achieve increased throughput, the velocity (or scan velocity) of the mask support MT and the substrate support WT during exposure must be increased. Therefore, the acceleration and the power required to achieve this acceleration must be significantly increased to achieve a constant high velocity during exposure. A secondary effect is that the wafer stage trajectory can excite undesirable vibrations in the system. To minimize these vibrations, sudden changes in acceleration and deceleration must be avoided. This can be achieved by making the velocity profiles of the stages MT and WT continuous or smooth (e.g., curved) profiles. Such velocity profiles can also be non-constant velocities. For example, as disclosed in U.S. Patent Application Publication No. 5,995,203 A, substrate exposure can be performed during stage acceleration and deceleration. The velocity of the mask support MT and the substrate support WT can be described as a sinusoid with no constant velocity zones. It should be noted that similar velocity profiles including constant velocity zones can also be used. In these exposure settings, the blade acceleration and velocity are increased to open and close the blades 10 and 11 (as described above), which can introduce additional vibrations or disturbances.

[0039]

[0039] Radiation dose control is typically performed by multiple (in-line) radiation detectors, uniformity correction using gray filters, or attenuation fingers, etc. The objective of dose control is to provide a consistent amount of energy uniformly on the substrate W. In radiation dose control, varying scan speeds (or speeds of the mask support MT and substrate support WT) at constant radiation power and attenuation will result in radiation dose variations within the field and / or across the dies of the substrate W, which is undesirable.

[0040] When exposure is performed with a non-constant stage velocity, the radiation dose received by the exposure area varies within the area. That is, the radiation dose received by the exposure area depends on the actual stage velocity. This means that for a constant radiation dose provided by the radiation source SR, a first area exposed with a relatively low stage velocity will receive a higher dose than a second area exposed with a relatively high stage velocity. Therefore, the introduction of a non-uniform velocity profile without any countermeasures will result in a radiation dose variation at substrate level that is inversely proportional to the stage velocity.

[0041]

[0041] Variations in the radiation dose in the exposure area can be prevented or minimized by adapting the amount of radiation provided by the radiation source SR to the velocity of the stages MT, WT. The adaptation of the radiation dose can be performed by controlling the radiation source output. For example, the amount of radiation can be adjusted by modulating the radiation power, by modulating the interval between radiation pulses (e.g. laser pulses), or a combination thereof. This is disclosed in US Patent Application Publication No. 5,995,203 A. This control can be provided by a feedback control loop or a feedforward control loop. Typically, the radiation output of the radiation source SR is synchronized to the velocity of the stages MT, WT.

[0042] The inventors have recognized that modulating the radiation source SR in response to the stage velocity may require a relatively large dynamic range of the radiation source SR in terms of output power and pulse adjustment, which may lead to instability of the radiation source SR. Instability may cause uncontrolled fluctuations in the energy, wavelength, and / or bandwidth of the radiation beam. For some types of radiation sources, such as excimer lasers, performance is specified only for radiation pulses of a certain repetition rate. To ensure the performance of the radiation source SR, it is desirable to minimize modulation of the radiation source.

[0043] According to one embodiment of the present invention, the amount of radiation incident on the patterning device MA, and thereby used to expose the substrate W, is controlled by controlling the amount of radiation passing through the masking device MD. More specifically, the control of the radiation dose is performed by the first and second Y-blades 10, 11 in response to the velocity of the mask support MT and / or the substrate support WT during scanning exposure of the substrate W.

[0044] The amount of radiation reaching the exposure area of ​​the substrate is obviously limited, as mentioned above, by the blades 10, 11, 20, 21. By varying the insertion of the Y-blades 10, 11 according to the field position during the scanning exposure (e.g. the field position of the exposure area on the substrate W and / or patterning device MA) or according to the point in time during the exposure cycle, the aperture 30 can be manipulated so that the radiation dose is controlled. The Y-blades therefore move as a function of the velocity profile of the mask support MT and / or the substrate support WT.

[0045] According to one embodiment of the present invention, there is provided a method for controlling a masking device, which aims to determine and set the position of the Y-blades 10, 11 as a function of time (within an exposure cycle) and thereby keep the number of radiation pulses in the slit constant. The number of pulses in the slit is N slit This metric indicates the number of radiation pulses received by each "pixel" on the substrate. N slit The higher the value, the more pulse averaging occurs during the scanning exposure, resulting in better dose performance in the exposure area on the substrate W.

[0046]

[0046] According to another embodiment of the present invention, a method is provided for controlling a masking device that determines and sets the position of the Y-blades 10, 11 as a function of time (within an exposure cycle), thereby setting the radiation dose in the slit to be constant.

[0047] As mentioned above, N is used as the exposure control metric. slit Both control methods, using either the Y-blades 10, 11 of the masking device MD, result in the opening 30 having a non-constant shape or size during an exposure cycle, and in particular during exposure of the substrate W, as will now be explained in more detail.

[0048] 7 shows a schematic diagram of a method 100 for controlling a masking device according to an embodiment of the present invention. A controller (or control unit) 103 is configured to receive a first input 101 comprising information of a velocity profile of the mask support MT and / or the substrate support WT used during an exposure (exposure cycle). Based on the first input 101, set points for the blades 10, 11, 20, 21 are defined. As mentioned above, N slit The exposure control metric may be the dose or the Y-blade velocity. This exposure control metric is received or provided by a second input 102. Based on the received first input 101 and second input 102, the control unit 103 calculates / determines the set points of the blades during exposure. The set points may be stored in a memory (e.g., in the form of a look-up table). The control unit 103 provides signals (voltage or current signals) to one or more actuators 104 to set or move the blades 105 (10, 11) of the masking device MD to the desired (calculated / determined) positions. Because the mask support MT and the substrate support WT (also referred to as the stage) are constantly moving during scanning exposure, especially during scanning exposure using a non-velocity profile, the controller 103 continuously commands the actuators 104 to synchronize the movement of the Y-blades 10, 11 with the movement of the stage and their velocity profile (first input 101).

[0049]

[0049] Each blade can be connected to at least one actuator.

[0050] According to another embodiment of the method 100 for controlling a masking device, the control unit 103 may further receive a blade position signal 106. The blade position signal 106 contains information of the actual position of the blade 105, which may be used to calculate / determine a set point for the blade during exposure. The blade position signal 106 may be used as a feedforward signal or a feedback signal. The blade position information may be provided by one or more position sensors provided on the blade 105. These sensors may be electromechanical, magnetic, inductive, capacitive, photoelectric, and / or ultrasonic sensors.

[0051]

[0051] Note that the first signal 101 may include position information of the stage (mask support MT, substrate support WT) to ensure that the position of the Y-blades 10, 11 is synchronized with the stage position. The controller can use the stage position information received by the first input and the blade position information received by the blade position signal 106 to set and control the blade 105 by commands sent to the actuator 104.

[0052] The method for controlling the masking device may use or include a controller (or control unit) to define and control the positioning and movement of the masking blades 10, 11, 20, 21. The controller may receive one or more signals corresponding to the velocity of the mask support MT and / or the substrate stage. The one or more signals may be provided by one or more stage controllers.

[0053] Furthermore, a radiation detector may be provided downstream of the masking device MD to measure and monitor the radiation dose and radiation pulse rate passing through the masking device MD. The radiation detector may be arranged to provide a detector signal to the controller. The detector signal includes information regarding the measured radiation dose and / or radiation pulse rate.

[0054] One or more radiation detectors may be provided. The one or more radiation detectors may be arranged in the relay optics RL, the mask support MT, the projection system PL, and / or the substrate support WT. Each radiation detector may provide a signal to the controller. A signal corresponding to the radiation dose measured by the one or more radiation detectors may be provided as a third input to the control unit 103 (not shown in Figure 7).

[0055] In one embodiment, the method includes adjusting radiation characteristics of the radiation source, which may include pulse length, pulse energy, and pulse repetition rate.

[0056]

[0056] Figure 5 shows schematically the masking blades 10, 11, 20, 21 of the masking device MD from different perspectives, for example the path of the radiation beam LB in the illuminator IL (as shown for example in Figure 3B).

[0057] FIG. 6A shows the mask support (mask support velocity V MT ) and the substrate support (substrate support speed V WT 1 shows velocity profiles of the mask support MT and the substrate support WT that allow a high substrate (wafer) throughput of the lithography system without requiring excessively high accelerations and velocities of the mask support MT and the substrate support WT. During the exposure period indicated by the grey filled area in the graph, substrate exposure is performed with a non-constant (or non-uniform) velocity of both stages (mask support MT and substrate support WT). Although a sinusoidal velocity profile is proposed in this example, other velocity profiles that deviate from sinusoidal can also be used for the same purpose. The present invention provides a method for controlling the mask support velocity V MT and substrate velocity V WT It will be appreciated by those skilled in the art that the present invention is not limited to a sinusoidal velocity profile of 1:1, where in a 1:4 magnification exposure system the velocity of the mask support MT is four times faster than the velocity of the substrate support WT.

[0058]

[0058] Figure 6B shows the masking blade positions at various times during exposure of a target area when both the mask support MT and the substrate support WT follow sinusoidal velocity profiles (Figure 6A) according to one embodiment of the present invention. The positions of the first blade 11 and the second blade 10 as a function of time are shown by the dotted trajectory 11a and the solid trajectory 10a, respectively, during the exposure period (e.g., the grey-filled area in the middle of Figure 6A). The inset shows the positions of both blades during the exposure period using a similar perspective as shown in Figure 5.

[0059] 6A and 6B, the trajectories of both blades relative to the slit center are plotted as a function of time. The inset adjacent to the graph in Fig. 6B provides a more detailed understanding of the blade position and movement during exposure using the non-constant velocity profile shown in Fig. 6A.

[0060] At the beginning of an exposure period (or exposure cycle), both Y-blades 10, 11 are positioned so that there is no aperture between them. The location of the slit area 30 is indicated by the dashed rectangle 31 (maximum slit area), and the slit area center 32 is indicated by a dotted line. The aperture 30 is obtained by moving the first blade 11 upward, as indicated by the upward arrow, and moving the second blade 10 downward, as indicated by the downward arrow. In this way, the Y-blades 10, 11 move away from each other.

[0061] II The mask support and substrate support continue to increase in speed. The opening 30 becomes larger as the first blade 11 continues to move upwards, further away from the slit center 32 (albeit more slowly), and the second blade 10 continues to move downwards (also further away from the slit center).

[0062] III and IV: Midway through the exposure period, the stage approaches maximum velocity. Before the stage reaches maximum velocity (decrease in acceleration), the second blade 10 reaches an extreme position relative to the slit center, as shown in III. After the stage reaches maximum velocity, it begins to decelerate and its velocity decreases. The first blade 11 reaches an extreme position relative to the slit center, as shown in IV in FIG. 6B. During this time frame, the aperture 30 (slit area) is at its maximum width.

[0063] At a later point during the V exposure period, the stage continues to accelerate (slow stage velocity) and the first and second blades move towards the slit centre 32 and move closer to each other.

[0064] VI. At the end of the exposure period, both the first blade 11 and the second blade 10 are positioned so that there is no opening between them. No radiation passes through the masking device MD.

[0065] The trajectories of the Y-blades, shown by the solid line 10a and the dotted line 11a, are governed by the velocity profile and control metrics of the stage (mask support MT and substrate support WT). Both trajectories demonstrate that the shape of the aperture 30 (i.e., the slit shape) is not constant during exposure when the stage follows a non-constant velocity profile, such as a sinusoidal velocity profile, as highlighted in the inset of FIG. 6B. Furthermore, although the first blade 11 and the second blade 10 are designed to symmetrically remove (or block) energy from both sides of the slit based on field position, the slit becomes asymmetric due to the non-linear movement of the mask support MT and the substrate support WT.

[0066] As mentioned above, according to one embodiment of the present invention, the position or trajectory of each Y-blade 10, 11 depends on the velocity profile of the stage (mask support MT and substrate support WT), as shown in Figure 6B. According to the conventional approach, the position or trajectory of each blade is independent of the stage velocity, as shown in Figure 4. By comparing both figures, a clear difference in the blade trajectories between the conventional approach (Figure 4) and the present invention (Figure 6B) can be observed.

[0067] According to one embodiment of the present invention, there is provided a method for controlling an exposure dose at a substrate W using a masking device MD including a first blade 11 and a second blade 10. The method comprises providing radiation pulses at the masking device MD to expose the substrate W through a scanning slit, exposing an exposure area on the substrate W by moving the first blade 11 and the second blade 10 independently of each other, and keeping the amount of radiation received at the exposure area constant. The first and second blades move according to a velocity profile of a substrate support WT supporting the substrate W.

[0068]

[0063] Keeping the amount of radiation received at the exposure area constant is achieved by adjusting the number of pulses in the slit (N slit ) can be controlled and achieved by keeping N slit , mask support speed V MT , and / or the substrate support velocity V WT In this configuration, the blade position can be controlled as a function of N slit is set as the control metric.

[0069]

[0064] The dose accuracy is 1 / sqrt(N slit ) and scale it by N slit It is desirable to keep it constant.

[0070] According to another configuration, a constant amount of radiation received at the exposure area can be controlled and achieved by keeping the radiation dose constant. The controller 103 controls the radiation dose, the mask support velocity V MT , and / or the substrate support velocity V WT In this configuration, the radiation dose is set as the control metric.

[0071] According to one embodiment of the present invention, the velocity profile of the substrate support WT comprises (at least) a non-constant velocity during exposure of the substrate, The velocity profile comprises (at least partly) a sinusoidal velocity profile.

[0072]

[0067] According to yet another embodiment of the present invention, the first blade 10 moves in a first direction relative to the center of the scan slit, and the second blade 11 moves in a second direction opposite to the first direction.

[0073]

[0068] N slit While the velocity and dose can be used as control metrics, it may be advantageous to control the exposure dose at the exposure area by modulating the radiation source SR in response to the stage velocity as an additional control parameter. In this way, the exposure dose is not only controlled by the Y-blade position, but also by controlling the output of the radiation source SR. The output of the radiation source SR can therefore vary in pulse repetition rate, number of pulses, and / or intensity. This additional control parameter allows for a more flexible control method as well as optimized control to be achieved.

[0074] According to one embodiment of the present invention, there is provided a controller (or control unit) 103 operable to perform the method for controlling the exposure dose at the substrate W, as disclosed above. The controller may receive one or more signals (or information) during an exposure cycle, which may include a mask support velocity V MT , substrate support speed V WT, radiation dose, radiation pulse characteristics (e.g., pulse length, pulse energy, pulse repetition rate), position of the masking blades, position of the mask support MT, and position of the substrate support WT. The one or more signals may be provided by a sensor or detector.

[0075]

[0070] The controller may comprise means for setting and adjusting the position of the masking blades in response to one or more signals (information) received. The adjustment of the blades may be performed by actuators controlled by the controller 103. The controller 103 may be part of or located in the masking device MD.

[0076]

[0071] It will be appreciated by those skilled in the art that the positions of the X-blades 20, 21 may be controlled in response to input signals by a control unit (controller) 103. However, the positions of the X-blades 20, 21 may remain unchanged during exposure of the substrate W.

[0077] The controller may include means for setting and adjusting the radiation pulse characteristics of the radiation source SR (eg pulse length, pulse energy, pulse repetition rate).

[0078] According to an embodiment of the present invention, there is provided a lithographic apparatus LA configured to expose a semiconductor substrate with radiation. The lithographic apparatus comprises an illuminator IL, a masking device MD, a mask support, a projection system PL, and a substrate support WT. Further, the lithographic apparatus LA may include a controller configured to control an exposure dose at the substrate W.

[0079]

[0074] One or more detectors and / or sensors may be arranged in the lithographic apparatus LA to provide one or more signals to the controller. The one or more signals that may be provided by the one or more detectors and / or sensors may include the mask support velocity V MT , substrate support speed V WT, radiation dose, radiation pulse characteristics (e.g. pulse length, pulse energy, pulse repetition rate), position of the masking blades, position of the mask support MT, and position of the substrate support WT. One or more detectors and / or sensors may be disposed on the masking device MD, for example to measure the position of the blades and their velocity.

[0080]

[0075] It will be appreciated by those skilled in the art that features of the various aspects of the invention as described above may be combined.

[0081]

[0076] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be appreciated that the lithographic apparatus described herein have other applications. Other possible applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0082] Although particular reference is made herein to embodiments of the invention in the context of lithography apparatus, embodiments of the invention may also be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatus may be generally referred to as lithography tools. Such lithography tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0083] Where the context permits, embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Also, embodiments of the present invention may be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and / or instructions may be described herein as performing certain actions. However, it will be recognized that such descriptions are merely for convenience and that such actions actually result from a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, etc., which, when executed, cause actuators or other devices to interact with the physical world.

[0084]

[0079] Aspects of the present invention are described in the following clauses. 1. A method for controlling an exposure dose in a substrate using a masking device including a first blade and a second blade, comprising: providing a radiation pulse in the masking device to expose the substrate; exposing an exposure area on the substrate by moving the first blade in a first direction relative to a slit center and moving the second blade in a second direction opposite the first direction; and keeping the amount of radiation received in the exposure area constant, wherein the moving of the first and second blades is determined by a velocity profile of a substrate support that supports the substrate. 2. The method of clause 1, wherein the velocity profile includes a non-constant velocity of the substrate support. 3. The method of clause 1 or 2, wherein the velocity profile comprises a sinusoidal velocity profile. 4. The method of any of clauses 1 to 3, wherein the amount of radiation is controlled by an exposure control metric. 5. The method of clause 4, wherein the exposure control metric is Nslit or dose. 6. A control unit comprising means for setting the position of a masking blade arranged in a masking device, the control unit being operable to perform a method for controlling exposure dose according to any of clauses 1 to 5. 7. A control unit according to clause 6, further comprising means for setting and adjusting the radiation (pulse) characteristics of the radiation source used during exposure of the substrate. 8. A masking device for selectively shielding portions of a patterning device from a radiation beam, comprising: a plurality of masking blades, each masking blade being mechanically separated from one another; and a control unit configured to control the position of each of the plurality of masking blades, wherein the positions of at least two of the plurality of masking blades are defined by a velocity profile of a substrate support that supports the substrate. 9. A masking device as described in clause 8, wherein the speed profile includes a non-constant speed. 10. A masking device according to clause 8 or 9, wherein the velocity profile comprises a sinusoidal velocity profile. 11. A lighting system comprising a masking device according to any of clauses 8 to 10. 12. An exposure apparatus (or lithographic apparatus) comprising an illumination system according to clause 11. 13. A method for controlling a masking blade position of a masking device, the method comprising: receiving at a control unit a first input comprising information of a velocity profile of a mask support and / or a substrate support used during exposure; receiving at the control unit a second input being an exposure control metric; determining a position setpoint for the masking blade during exposure; and moving the masking blade to the determined position setpoint. 14. The method of clause 13, wherein the exposure control metric is Nslit or dose. 15. The method of clause 13 or 14, further comprising receiving at the control unit a masking blade position signal for use as a feedforward or feedback signal. 16. The method of any of clauses 13 to 15, wherein moving the masking blade is performed by commanding one or more actuators connected to the masking blade. 17.N slit and a controller configured to control the position of the masking blade as a function of the mask support speed and / or the substrate support speed, slit is the control metric,controller. 18. A controller configured to control a position of a masking blade as a function of a radiation dose and a mask support velocity and / or a substrate support velocity, wherein the radiation dose is a control metric. 19. A controller according to clause 17 or 18, wherein the velocity profile of the substrate support includes a non-constant velocity during at least exposure of the substrate. 20. The controller of clause 19, wherein the velocity profile comprises an at least partially sinusoidal velocity profile. 21. An exposure apparatus according to clause 12 that is a lithographic apparatus, further comprising a mask support, a projection system, and a substrate support. 22. An exposure apparatus according to clause 12 or 21, comprising one or more detectors for providing one or more signals to the control unit. 23. An exposure apparatus according to clause 22, wherein the one or more signals provided by the one or more detectors comprise information of a mask support velocity, a substrate support velocity, a radiation dose, a radiation pulse characteristic, a masking blade position, a mask support position, or a substrate support position. 24. A controller according to any of clauses 17 to 20, further comprising means for setting and adjusting the radiation characteristics of the radiation source. 25. The method of any of clauses 1 to 5, further comprising controlling the output of a radiation source that provides the radiation pulses. 26. The method of any of clauses 1 to 5 and 25, further comprising adjusting the radiation characteristics of the radiation source. 27. A masking device according to any of clauses 8 to 12, 21 and 22, further comprising an actuator for moving the plurality of blades. 28. A masking device according to any of clauses 8 to 12, 21, 22 and 27, further comprising one or more detectors for measuring the position and / or speed of the masking blades.

[0085]

[0080] While specific embodiments of the present invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The foregoing description is illustrative and not limiting. Accordingly, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set forth below.

Claims

1. 1. A method for controlling an exposure dose at a substrate utilizing a masking device including a first blade and a second blade, comprising: providing a pulse of radiation at the masking device to expose the substrate; exposing an exposure area on the substrate, moving the first blade in a first direction relative to a slit center; exposing an exposure area on the substrate by moving the second blade in a second direction opposite to the first direction; maintaining a constant amount of radiation received at the exposure area; wherein moving the first and second blades is defined by a velocity profile of a substrate support supporting the substrate.

2. The method of claim 1 , wherein the velocity profile comprises a non-constant velocity of the substrate support.

3. The method of claim 1 or 2, wherein the velocity profile comprises a sinusoidal velocity profile.

4. The method of claim 1 , wherein the amount of radiation is controlled by an exposure control metric.

5. The exposure control metric is N ｓｌｉｔ or the radiation dose.

6. A control unit comprising means for setting the position of masking blades arranged in a masking device, the control unit being operable to carry out a method for controlling an exposure dose according to any one of claims 1 to 5.

7. 7. A control unit according to claim 6, further comprising means for setting and adjusting radiation characteristics of a radiation source used during said exposure of said substrate.

8. a masking device for selectively shielding parts of a patterning device from a radiation beam, comprising: a plurality of masking blades, each of which is mechanically isolated from the others; a control unit configured to control a position of each of the plurality of masking blades, wherein the positions of at least two of the plurality of masking blades are defined by a velocity profile of a substrate support, the velocity profile being provided to the control unit.

9. The masking device of claim 8 , wherein the velocity profile includes a non-constant velocity.

10. 10. A masking device according to claim 8 or 9, wherein the velocity profile comprises a sinusoidal velocity profile.

11. An illumination system comprising a masking device according to any one of claims 8 to 10.

12. An exposure apparatus comprising the illumination system according to claim 11.

13. 1. A method for controlling a masking blade position of a masking device, comprising: receiving a first input at a control unit comprising information of a velocity profile of a mask support and / or a substrate support used during exposure of a substrate; receiving a second input at the control unit, the second input being an exposure control metric; determining a masking blade position set point during said exposure; moving the masking blade to the determined position set point; A method comprising:

14. The exposure control metric is N ｓｌｉｔ or the radiation dose.

15. 15. The method of claim 13 or 14, further comprising receiving a masking blade position signal at the control unit for use as a feedforward or feedback signal.

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