Lithographic apparatus and method for drift compensation

Abstract

A system, method, lithographic apparatus and software product are described herein configured to determine a drift of a property of illumination and a corresponding drift correction. The system comprises a lithographic apparatus comprising at least two sensors each configured to measure a characteristic related to an illumination area arranged to be used for imaging a substrate. Further, a processor is configured to determine, based on a ratio of the measured characteristics, a drift of the illumination area relative to a reference position, determine, based on the drift of the illumination area, a drift of a property measured by the at least two sensors related to the illumination upstream of the illumination area, and determine, based on the drift of the property, a drift correction to be applied to the property to compensate for the drift of the property.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 960,859, filed January 14, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a photolithography apparatus and an illumination uniformity correction system. The invention generally relates to photolithography, and more specifically to a system and method for compensating for uniformity drift caused by, for example, illumination beam movement, optical column uniformity, uniformity compensator drift, etc. Background Technology

[0004] A photolithography apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Photolithography apparatuses can be used, for example, to manufacture integrated circuits (ICs). In this case, a patterning apparatus (which may alternatively be called a mask or photomask) can be used to generate a circuit pattern corresponding to the various layers of the IC, and this pattern can be imaged onto a target portion (e.g., a portion comprising one or more dies) on a substrate (e.g., a silicon wafer) having a layer of radiation-sensitive material (resist). Generally, a single substrate contains a network of adjacent target portions that are exposed sequentially. Known photolithography apparatuses include so-called steppers, in which each target portion is irradiated by exposing the entire pattern onto the target portion at once; and so-called scanners, in which each target portion is irradiated by scanning the pattern with a beam in a given direction (“scanning” direction) while simultaneously scanning the substrate parallel or antiparallel to that direction.

[0005] Photolithography apparatuses typically include an illumination system arranged to modulate radiation generated by a radiation source before it is incident on the patterning apparatus. The illumination system can, for example, modify one or more characteristics of the radiation, such as polarization and / or illumination mode. The illumination system may include a uniformity correction system arranged to correct or reduce inhomogeneities present in the radiation, such as intensity inhomogeneities. The uniformity correction device may employ actuated fingers inserted into the edge of the radiation beam to correct for intensity variations. However, the width of the spatial time interval of the intensity variation that can be corrected depends on the size of the actuating device used to move the fingers of the uniformity correction system. Furthermore, in some examples, if the size or shape of the fingers used to correct irregularities in the radiation beam is modified, the uniformity correction system may undesirably impair or modify one or more characteristics of the radiation beam, such as the pupil formed by the radiation beam.

[0006] To reduce the manufacturing cost of ICs, multiple substrates are typically exposed for each IC. Similarly, lithography equipment is usually in almost continuous use. That is, to keep the manufacturing cost of all types of ICs as low as possible, the idle time between substrate exposures is also minimized. Therefore, the lithography equipment absorbs heat, which causes the components of the equipment to expand, resulting in drift, migration, and changes in uniformity.

[0007] To ensure good imaging quality on the patterning apparatus and substrate, controlled uniformity of the irradiation beam is maintained. That is, the irradiation beam may have a non-uniform intensity distribution before it is reflected away from or transmitted through the patterning apparatus. It is desirable to control the irradiation beam with at least some uniformity throughout the photolithography process. Uniformity may refer to a constant intensity across the entire irradiation beam, or it may refer to the ability to control the irradiation to the target. Target irradiation uniformity has a flat or non-flat profile. The patterning apparatus imparts a pattern to the irradiation beam and then images the pattern onto the substrate. The image quality of this projected irradiation beam is affected by the uniformity of the irradiation beam.

[0008] The market demands that lithography equipment perform the lithography process as efficiently as possible to maximize manufacturing capabilities while maintaining low cost per device. This means minimizing manufacturing defects, which is why the impact of the uniformity of the irradiation beam can be minimized as much as possible. Summary of the Invention

[0009] In one embodiment, a system is provided, the system comprising: a photolithography apparatus including at least two sensors, each sensor configured to measure characteristics related to an irradiation region configured for imaging a substrate; and a processor configured to determine a drift of the irradiation-related properties. The processor is configured to: determine a drift of the irradiation region relative to a reference position based on a ratio of a measured characteristic measured by one sensor to a measured characteristic measured by the other sensor; determine, based on the drift of the irradiation region, a drift of an irradiation-related property upstream of the irradiation region measured by the at least two sensors; and, based on the drift of the property, determine a drift correction to be applied to the property to compensate for the drift of the property.

[0010] In one embodiment, a method is provided for determining drift correction associated with a photolithography apparatus. The method includes: receiving measurements of characteristics related to an irradiated region configured for imaging a substrate via at least two sensors; determining a drift of the irradiated region relative to a reference position based on a proportion of the measured characteristics; determining a drift of an irradiation-related property upstream of the irradiated region, measured by the at least two sensors, based on the drift of the irradiated region; and determining a drift correction to be applied to the property to compensate for the property drift, based on the property drift.

[0011] Furthermore, in one embodiment, a non-transitory computer-readable medium is provided, including instructions that, when executed by one or more processors, cause the operation of the methods discussed herein.

[0012] Furthermore, in one embodiment, a photolithography apparatus is provided. The apparatus includes: an illumination source and illumination optics configured to image a substrate; at least two sensors configured to measure characteristics related to an illumination region set for imaging the substrate; and a processor configured to determine a drift of an illumination-related attribute. The processor is configured to: determine a drift of the illumination region relative to a reference position based on a proportion of the measured characteristics; determine a drift of an illumination-related attribute upstream of the illumination region, measured by the at least two sensors, based on the drift of the illumination region; and determine a drift correction to be applied to the attribute to compensate for the drift of the attribute, based on the drift of the attribute. A uniformity compensator system is also provided, including one or more uniformity compensators located at one or more locations along the path of the illumination region to intercept one or more corresponding portions of the illumination region at the one or more locations. A uniformity sensitivity model determines an adjustment amount to the one or more uniformity compensators to correct for the drift of the attribute based on the drift of the illumination region or the drift of the attribute. Attached Figure Description

[0013] Now, with reference to the accompanying drawings, embodiments will be described by way of example only, in which:

[0014] Figure 1 This is a diagram of an exemplary photolithography projection apparatus according to an embodiment;

[0015] Figure 2 This is another exemplary photolithography apparatus according to the embodiments;

[0016] Figure 3 An example of a uniformity compensator for the slit of the irradiated beam according to an embodiment is shown;

[0017] Figure 4 The illustration shows a photolithography apparatus according to an embodiment (e.g., Figure 1 and Figure 2 Example positions of two sensors relative to each other and relative to the energy sensor under illumination;

[0018] Figure 5 This is a flowchart of a method for determining drift correction associated with imaging of each wafer within a wafer or batch, according to an embodiment;

[0019] Figure 6 This is a block diagram of an exemplary computer system according to an embodiment;

[0020] Figure 7 This is a diagram of an exemplary extreme ultraviolet (EUV) lithography projection apparatus according to an embodiment;

[0021] Figure 8 According to the embodiments Figure 7 A more detailed view of the exemplary device in the image; and

[0022] Figure 9 According to the embodiments Figure 7 and Figure 8 A more detailed view of the device's source collector module. Detailed Implementation

[0023] Figure 1 An exemplary photolithography projection apparatus according to an embodiment of the present invention can be used in conjunction with the techniques described herein. The apparatus includes:

[0024] - Irradiation system IL, used to adjust the radiation beam B. In this specific case, the irradiation system also includes a radiation source SO;

[0025] - A first object stage (e.g., a pattern forming apparatus stage) MT is provided with a pattern forming apparatus holder to hold a pattern forming apparatus MA (e.g., a mask) and is connected to a first locator to accurately position the pattern forming apparatus relative to an article PS;

[0026] - The second object stage (substrate stage) WT is provided with a substrate holder to hold the substrate W (e.g., a silicon wafer coated with resist) and is connected to the second positioner to accurately position the substrate relative to the article PS.

[0027] - A projection system (“lens”) PS (e.g., a refractive, reflective, or antirefracting optical system) for imaging an illuminated portion of the pattern forming apparatus MA onto a target portion C (e.g., including one or more dies) of the substrate W.

[0028] As described herein, the device is transmissive (i.e., having a transmissive pattern forming apparatus). However, in general, it can also be reflective, for example (having a reflective pattern forming apparatus). The device can employ a pattern forming apparatus of a different type than that of a conventional mask; examples include programmable mirror arrays or LCD matrices.

[0029] A source SO (e.g., a mercury lamp or excimer laser, LPP (laser-generated plasma) EUV source) generates a radiation beam. This beam is either fed directly into an irradiation system (irradiator) IL or fed into the irradiation system (irradiator) IL after passing through a conditioning device (such as, for example, a beam expander Ex). The irradiator IL may include a conditioning device AD ​​for setting the outer radial range and / or inner radial range (typically referred to as σ-outer and σ-inner, respectively) of the intensity distribution in the beam. Additionally, it typically includes various other components, such as an integrator IN and a concentrator CO. Thus, the beam B irradiated onto the patterning apparatus MA has a desired uniformity and intensity distribution across its cross-section.

[0030] about Figure 1 It should be noted that the source SO can be an integral part of the photolithography projection apparatus, for example, inside the housing of the photolithography projection apparatus (e.g., when the source SO is a mercury lamp), but it can also be located away from the photolithography projection apparatus, with the radiation beam generated by the source SO being guided into the apparatus (e.g., by means of a suitable guiding mirror); the latter scenario is typically the case when the source SO is an excimer laser (e.g., based on KrF, ArF, or F2 lasers).

[0031] The beam PB then intercepts the pattern forming apparatus MA held on the pattern forming apparatus stage MT. After traversing the pattern forming apparatus MA, the beam B passes through the lens PL, which focuses the beam B onto the target portion C of the substrate W. With the aid of a second positioning device (and an interferometric measuring device IF), the substrate stage WT can be accurately moved, for example, to position the different target portions C within the path of the beam PB. Similarly, the first positioning device can be used to accurately position the pattern forming apparatus MA relative to the path of the beam B, for example, after mechanically retrieving the pattern forming apparatus MA from the pattern forming apparatus library, or during scanning. Generally, this will be achieved by means of a device not in... Figure 1 The long-stroke module (coarse positioning) and short-stroke module (fine positioning) are clearly described in the text to realize the movement of the object stage MT and WT. However, in the case of a stepper (as opposed to a stepping scanning tool), the pattern forming apparatus stage MT can be connected only to the short-stroke actuator, or it can be fixed.

[0032] The irradiation system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for guiding, shaping, or controlling radiation B. The irradiation system IL may also include an energy sensor ES that provides energy (per pulse) measurement, a measurement sensor for measuring beam movement, and a uniformity compensator UC that allows control of the uniformity of the irradiation slit.

[0033] The tools described can be used in two different modes:

[0034] - In step mode, the patterning apparatus stage MT remains essentially stationary, and the entire patterning apparatus image is projected onto the target portion C in a single pass (i.e., a single "flash"). Then, the substrate stage WT is moved along the x and / or y directions, allowing different target portions C to be illuminated by the beam PB;

[0035] In scanning mode, the same scenario is applied, except that the given target portion C is not exposed in a single "flash". Instead, the patterning stage MT can move at a speed v along a given direction (the so-called "scanning direction", e.g., the y-direction) so that the projected beam B scans on the patterning image; simultaneously, the substrate stage WT moves simultaneously in the same or opposite direction at a speed V = Mv, where M is the magnification of the lens PL (typically, M = 1 / 4 or 1 / 5). In this way, a relatively large target portion C can be exposed without compromising resolution.

[0036] - In another mode, the mask stage MT is kept essentially stationary, thus maintaining the programmable patterning apparatus, while the substrate stage WT is moved or scanned, simultaneously projecting the pattern onto the target portion C onto the radiation beam. In this mode, a pulsed radiation source is typically used, and the programmable patterning apparatus is updated as needed after each movement of the substrate stage WT or between consecutive radiation pulses during scanning. This operating mode can be readily applied to maskless lithography utilizing a programmable patterning apparatus, such as programmable mirror arrays of the type described above.

[0037] Alternatively, the above usage patterns or combinations and / or variations of completely different usage patterns can be adopted.

[0038] Figure 2 A photolithography apparatus according to an embodiment of the present invention is depicted. In the example shown, the photolithography apparatus may include a source SO, an illumination system IL, a support structure (not shown) configured to hold a pattern forming apparatus MA, a projection system PL, a substrate stage WT, a calibration module 170, one or more measuring devices 190, and a substrate W located on the substrate stage WT.

[0039] In one example, the illumination system IL may include a collimator 10, a field limiting element 12, a field lens group 14, a uniformity correction system 16, a mask shading plate 18, and a condenser lens 20. The illumination system IL may also include an energy sensor ES that provides energy (per pulse) measurement, a measurement sensor for measuring beam movement, and a uniformity compensator UC that allows control of the uniformity of the illumination slit. In one embodiment, the illumination system IL includes an illumination uniformity correction module (UNICOM). Signals from sensors (e.g., ES at the mask level) are used to control the UNICOM module to correct the illumination slit, thereby compensating for non-uniformities in the illumination.

[0040] In one example, collimator 10 can be used to collimate the radiation beam generated by source SO (the beam is schematically represented by dashed lines). Field limiting element 12 can shape the radiation beam into a field shape that will be projected onto substrate W. The field limiting element can, for example, include two convex lens arrays, with the second array positioned in the focal plane of the first array.

[0041] In one example, the field lens group 14 can focus the radiation beam onto the field plane FP1. In this example, a shielding sheet 18, comprising a pair of sheets movable along the scanning direction of the photolithography apparatus, is located in the field plane FP1.

[0042] In one example, during exposure of a given target area, a masking plate 18 can be used to ensure that radiation does not incident on a target area adjacent to the given target area along the y and / or x directions. The masking plate 18 is located in the field plane FP1 such that the masking provided by the masking plate 18 can be accurately translated (and has sharp edges) onto the pattern forming apparatus MA.

[0043] In one example, the uniformity correction system 16 is located before the mask 18 in the path of the radiation beam, so that the radiation beam can pass through the uniformity correction system before it is incident on the mask 18. Therefore, the uniformity correction system 16 is not located in the field plane FP1, but is displaced from the field plane FP1. The uniformity correction system 16 can spatially control the intensity of the radiation beam; that is, the uniformity correction system 16 can spatially control the intensity of radiation in the field shape to be projected onto the substrate W. In one embodiment, the uniformity correction system 16 includes at least one overlapping array of fingers and / or at least one non-overlapping array of fingers, which can be moved to intersect and not intersect with the radiation beam incident on the fingers in order to selectively correct the intensity of portions of the radiation beam. It should be understood that although seven fingers are shown in each group, any number of fingers can be used. The terms “group of fingers,” “set of fingers,” or “group” are used interchangeably in this application.

[0044] In one example, after passing through the shielding plate 18, the radiation beam is incident on the condenser lens 20. The condenser lens 20 can focus the radiation onto another field plane FP2. The pattern forming device MA located in the field plane FP2 can apply a pattern to the radiation beam.

[0045] In one example, a patterned radiation beam passes through a projection system PL and reaches a substrate W. The substrate W is located in another field plane FP3. The projected patterned beam transfers the pattern onto the substrate.

[0046] In one example, the correction module 170 can determine adjustments to the variables of the correction system 16 to meet desired uniformity specifications. The correction module 170 can determine one or more correction parameters 175 based on the determined adjustments and transmit these parameters to the correction system 16. The correction parameters control adjustable variables within the correction system 16. The correction module 170 can also receive irradiation field data 185 collected from one or more uniformity measuring devices 190 located at field plane FP3 or field plane FP2 of the patterning apparatus MA.

[0047] By manipulating the adjustable variables of the correction system 16 according to the correction parameters, the characteristics of the irradiated beam can be altered. More specifically, the correction parameters can provide details on how to adjust the variables of the correction system 16 to achieve a desired uniformity distribution (e.g., the flattest uniformity or shape most favorable to the photolithography process). For example, the correction parameters can describe one or more groups of fingers (e.g., Figure 3 Which fingers of the multiple uniformity compensators 1120 need to be moved, and which need to be moved to a distance that intersects or does not intersect with the incident radiation beam, in order to selectively correct the intensity of a portion of the radiation beam incident on the uniformity correction system 16.

[0048] In one example, the correction module 170 may include one or more processors 172 and memory 174. The one or more processors 172 may execute software that causes the uniformity correction system 16 to adjust variables to achieve a desired uniformity criterion for the radiated beam. Memory 174 may include main memory (e.g., random access memory (RAM)). In one embodiment, memory 174 may also include secondary memory. Secondary memory may include, for example, a hard disk drive and / or a removable storage drive. A computer program may be stored in memory 174. Such a computer program, when executed, may allow the processors 172 in the correction module 170 to perform features of embodiments of the invention as discussed herein. In embodiments using software to implement a method for adjusting elements of the uniformity correction system 16, the software may be stored in a computer program product and loaded into the correction module 170 using a removable storage device, hard disk drive, or communication interface. Alternatively, the computer program product may be downloaded to the correction module 170 via a communication path. Additionally, in one embodiment, the correction module 170 is coupled to one or more remote processors. The correction module 170 may then remotely receive instructions and / or operating parameters.

[0049] Figure 3 The illustration shows the mechanical components of a uniformity refresh (UR) correction system 1100 according to an embodiment of the present invention. Figure 3 In this invention, the uniformity refresh (UR) correction system 1100 includes an energy sensor (ES) 1110 and a plurality of uniformity compensators 1120. The UR correction system 1100 can modify the illumination beam during a photolithography operation. In at least one embodiment of the invention, the illumination beam is shaped into an arc and is referred to as an illumination slit 1130. The uniformity of the illumination slit 1130 can be controlled by controlling the movement of the respective uniformity compensators 1120 in and out of the illumination slit 1130. The uniformity compensators 1120 may also be referred to as fingers. Example operation of the uniformity compensators can be found in commonly owned, pending U.S. Patent No. 8,629,973, the entire contents of which are incorporated herein by reference.

[0050] In one example Figure 3 The fingers shown can be individually controlled to modify the intensity of the irradiation slit in order to achieve target uniformity.

[0051] An example method for controlling the profile of an illumination slit is discussed in U.S. Patent No. 8,629,973, the entire contents of which are incorporated herein by reference. In one embodiment, uniformity correction is based on a first set of inputs, which may be related to a curve representing a target flat profile of the finger at its center location and a uniformity measurement of the finger at its center location. A second set of inputs may be related to a curve representing the attenuation at each insertion point of the finger into the illumination beam, a value for the current finger position, and a corresponding attenuation value. In one example, the uniformity refresh correction system method begins at the start of each batch of substrates. In one step, the uniformity of the illumination slit is measured (e.g., by integrating the intensity through the slit, or by averaging the slit scan using discrete intensity samples along the slit). The uniformity refresh (UR) correction system calculates the uniformity compensator (e.g., the finger) position based on a flat intensity distribution across the slit. Alternatively, the uniformity refresh (UR) correction system is based on non-flatness (aka... Or the DoMa intensity distribution is used to calculate the location of the uniformity compensator (e.g., a finger). Regarding Examples of embodiments can be found in U.S. Patent No. 7,532,308, issued May 12, 2009, the entire contents of which are incorporated herein by reference.

[0052] Another example of an apparatus and method for dynamically adjusting an illumination field to provide desired exposure and control and reduce linewidth variations is discussed in U.S. Patent No. 6,097,474, the entire contents of which are incorporated herein by reference. That patent describes an exposure calculator coupled to the actuator control, which provides a drive signal to the actuator control that controls the movement of each of a plurality of adjustable fingers (or links) into and out of the illumination area to provide a predetermined adjusted exposure dose. For example, when imaging of a variety of different linewidths is desired, the exposure dose varies according to the linewidth. A preferred exposure dose can be calculated based on existing techniques and can take into account variables such as the type of resist, substrate material, illumination energy, illumination wavelength, scan speed, etc.

[0053] The thermal load of the batch irradiation system causes dose drift. In the prior art, the magnitude of dose drift and the resulting imaging yield are acceptable. For future higher power, for example, lithography devices with greater than or equal to 400W and even greater than or equal to 1kW, the thermal load may increase by approximately two times or more. This higher power leads to greater dose drift, which reduces imaging yield.

[0054] Prior art includes a single diode energy sensor for shutting off the energy loop of an irradiation source by measuring the intensity on both sides of an irradiation slit. This single energy sensor measures the intensity of the entire slit (per pulse). In this invention, additional sensors (e.g., Figure 4 Sensors 401 and 402 in the sensor are used to measure, for example, the Y position of the irradiation slit for each wafer. Measurements from the additional sensor provide input to adjust the corresponding dose drift correction for each wafer's UNICOM finger during chuck exchange.

[0055] The present invention proposes the use of multifaceted energy sensors (e.g., 401 and 402) to measure slit position drift during a batch, thereby enabling dose drift correction within a batch via UNICOM without limiting the throughput of UR per wafer.

[0056] This invention offers several advantages, including improved dose drift during batches. For example, in the prior art, for power greater than (or equal to) 500 W, dose drift within a batch due to thermal effects within the irradiator can significantly exceed specifications (~2x), resulting in imaging loss during batches. Therefore, reducing dose drift during imaging, for example, of one or more (or each) wafers within a batch, can improve imaging performance.

[0057] In one embodiment, starting from the moment of batch start (and thus during uniformity refresh or slit integral energy (SLIE) measurement), dose drift during the batch (or even more frequently if needed) can be corrected using UNICOM calibration for each wafer by continuously measuring the irradiation slit position using a multifaceted energy sensor. A new UR is completed when the next batch starts by default, and the calibration cycle within the batch using the multifaceted ES can begin again.

[0058] In embodiments of the invention, the lithography apparatus includes an energy sensor consisting of two facets, for example, configured to measure the Y-position of a slit in each wafer. For example, an initial ratio of the two facets can be measured or determined during a UNICOM refresh or batch start-up. Further, any changes in the initial ratio can be tracked during the batch (e.g., within 15-minute intervals) to measure slit position drift. Based on the slit drift and existing UNICOM sensitivity, the corresponding dose drift can be corrected by applying UNICOM correction to each wafer. A key advantage is that this can be done without actually performing an additional uniformity refresh on each wafer. In one embodiment, such a sensor can also use a ratio of ES / (measurement of 401 + measurement of 402) to determine the slit position drift in x. This can be used for uniformity correction if desired.

[0059] Figure 4 The illustration shows example positions of two sensors relative to each other and relative to the energy sensor in the illumination of the photolithography apparatus (e.g., Figure 1 and Figure 2 These two sensors are examples of multifaceted energy sensors configured to determine slit drift in a lithography apparatus (e.g., DUV, EUV, etc.). According to an embodiment, sensors 401 and 402 can be configured to measure characteristics of an irradiated region (e.g., an irradiated slit) (denoted as a dashed ellipse), and the proportion of these characteristics can be used to determine the drift of the irradiated region. For example, as shown, the irradiated slit can drift between positions P1, P2, and RP within a batch of wafers due to dose drift during the patterning process. In one embodiment, the measured characteristic can be the intensity of a portion of the irradiated region. The proportion of the measured characteristic is tracked to determine, for example, the drift of the irradiated slit's position relative to a reference position RP.

[0060] like Figure 4 As shown, at position RP of the irradiated area (e.g., the irradiated slit), sensor 401 detects the intensity of a portion of the irradiated slit, while sensor 402 detects the intensity of another portion of the same irradiated slit. The ratio of the detected intensities can be, for example, 100. As the patterning process proceeds, the slit may drift to position P1. At position P1, the ratio of the intensities measured by sensors 401 and 402 will change. For example, this ratio can be 900. The ratios at positions P1 and RP can then be compared to determine the drift of the irradiated slit (e.g., y1). For example, a change in ratio of 100 (i.e., 1000 - 900) can indicate a drift of y1 nm (e.g., 2 nm) in the irradiated slit. In another example, the slit may drift to position P2. At position P2, the ratio of the intensities measured by sensors 401 and 402 will change. For example, this ratio can be 1100. The ratios at positions P2 and RP can then be compared to determine the drift of the irradiated slit (e.g., y2). For example, a change in the scale of -100 (i.e., 1000-1100) can indicate a drift of y2 nm (e.g., -2 nm) in the irradiated slit.

[0061] In one embodiment, a relationship can be established experimentally or by testing a wafer between the drift of the illumination slit and the ratio of characteristics measured by two sensors. This relationship can then be used during the patterning process to determine the drift of the illumination slit based on the characteristic ratio. Furthermore, based on the drift of the illumination slit, an existing relationship between the drift of the illumination slit and dose drift can be used to determine dose drift. Similarly, the drift of the illumination slit can be used to determine the drift of other properties related to the source or pupil.

[0062] It should be understood that this system or method is not limited to two sensors (e.g., 401 and 402). Those skilled in the art can modify the system to include three, four, or more sensors placed adjacent to each other and around the illumination slit. This sensor positioning generates a multifaceted sensor, where each sensor can detect a portion of the illumination and can acquire and track the ratio between different measurements to determine the drift of the illumination slit, such as the drift of the slit position relative to an initial or reference position. The drift of the illumination slit may be caused by dose drift or pupil drift (e.g., a change in pupil shape). Therefore, appropriate corrections can be applied to the source or pupil to reduce dose drift or pupil drift, which in turn will reduce the drift of the illumination slit. These dose or pupil corrections can improve the imaging performance of the lithography apparatus without affecting the yield of the patterning process.

[0063] When describing sensors 401 and 402 as "at the mask level" or "near the patterning apparatus," it is undesirable to approach the fixed threshold of the patterning apparatus. However, the purpose of the sensors is to detect offsets in the uncorrected illumination slits within the illumination adjustment optics of the illumination module IL. The sensors may be located between the UNICOM and the patterning apparatus. In one embodiment, the sensors may be arranged to detect radiation reflected from the peripheral portion of the patterning apparatus.

[0064] In one embodiment, the present invention describes a system including a photolithography apparatus and a processor configured to determine drift corrections associated with the photolithography apparatus. The system includes a photolithography apparatus (e.g., Figure 2 The photolithography apparatus has at least two sensors (e.g., Figure 4 401 and 402 in the above are configured to measure characteristics related to an illumination slit set for imaging a wafer; and a processor (e.g., Figure 1 The processor 104 (or a processor as part of sensors 401 and 402) is configured to determine the drift of the irradiation slit, the drift of the attribute (e.g., dose drift), and corrections related to the drift of the attribute. In one embodiment, the measured characteristic is an irradiation intensity value measured by a first sensor (e.g., 401) and a second sensor (e.g., 402), respectively.

[0065] In one embodiment, at least two sensors include a first sensor 401 located at a first position of the illumination slit (e.g., at 1110 on the upper left side), and a second sensor 402 located at a second position of the illumination slit (e.g., at 1110 on the upper left side). In one embodiment, the properties to be corrected are the dose and / or pupil of the photolithography apparatus (e.g., Figure 1 , Figure 2 and Figure 7Therefore, attribute drift can be dose drift relative to the nominal dose, and / or pupil drift relative to the reference pupil. Thus, drift correction can be dose drift correction or pupil drift correction.

[0066] Those skilled in the art will understand that the system (e.g., Figure 2 This is not limited to the location of the processor or sensors 401 and 402. For example, the sensors can be located at different locations along the illumination slit. In one embodiment, the sensor can be located in front of the mask stage. In another example, an additional sensor can be placed after the mask stage.

[0067] In one embodiment, the processor is configured to: determine the drift of the illumination slit relative to a reference position of the illumination slit based on the proportion of the measured characteristics; and determine the drift of attributes related to illumination upstream of the illumination region, measured by at least two sensors, based on the drift of the illumination slit. For example, these attributes are related to the illumination source and / or pupil used for photolithography to image the wafer. For example, in Figure 1 , Figure 2 , Figure 7 and Figure 8 In this configuration, the energy sensor ES and the uniformity compensator UC can be considered upstream, and these properties are related to, for example, an illumination source and / or a pupil upstream of ES. Further, the processor determines a drift correction based on the drift of the properties, which is to be applied to the illumination source or pupil to compensate for the drift. In one embodiment, the drift of the properties is caused by one or both of contamination of the illumination optics collector and the power level of the illumination source.

[0068] In one embodiment, the reference location is the slit position measured at the start of imaging of the wafer in the batch. In another embodiment, the reference location is at the center of the slit.

[0069] In one embodiment, a uniformity compensator system (e.g., Figure 3 (as shown in the diagram) to determine drift correction. In one embodiment, a first sensor is located at a first end of the uniformity compensator system, while a second sensor is located at a second end of the uniformity compensator system. In one embodiment, the uniformity compensator system includes one or more uniformity compensators at one or more locations in the path of the irradiation slit to intercept one or more corresponding portions of the irradiation slit at one or more locations. In one embodiment, the one or more uniformity compensators include one or more opaque finger members.

[0070] Furthermore, the uniformity sensitivity model determines the adjustment amount to one or more uniformity compensators to correct for attribute drift based on the drift of the irradiation slit or attribute drift. In one embodiment, attribute drift is caused by one or both of contamination of the irradiation optics collector and the power of the irradiation source. In one embodiment, attribute drift is determined by converting the irradiation slit drift into attribute drift based on the correlation between the irradiation slit drift and attribute drift.

[0071] In one embodiment, a drift correction is determined for each wafer within a batch. Thus, each wafer within a batch can be corrected for dose drift, such as that which might cause slit drift. This correction results in improved imaging performance for the batch. This differs from a typical uniform refresh process, in which drift correction is performed at the beginning of each batch.

[0072] Figure 5 This is a flowchart of a method 500 for determining drift correction associated with a photolithography apparatus used for imaging a batch of wafers. Method 500 includes: at process P501, receiving measurements of characteristics related to setting an illumination slit for imaging wafers within a batch via at least two sensors 401 and 402. In one embodiment, the at least two sensors include a first sensor located at a first position of the illumination slit and a second sensor located at a second position of the illumination slit. Reference Figure 4 Example locations for sensors 401 and 402 are discussed. In one embodiment, the measured characteristic is the irradiation intensity value measured by the first and second sensors, respectively, of at least two sensors.

[0073] At process P503, the method includes: determining a reference position of the illumination slit relative to the illumination slit based on a proportion 501 of the measured characteristics (e.g., Figure 4 The drift 503 of the RP in the irradiation slit (also known as the drift 503 of the irradiation slit). In one embodiment, the reference position (e.g., Figure 4 The reference position (RP) is the slit location measured at the start of imaging of the first wafer in the batch. In one example, the reference position is at the center of the slit. Figure 4 An example of determining the drift of the illumination slit is discussed. For instance, the drift of the illumination slit 503 can be determined by tracking the change in the ratio 501 relative to a reference ratio determined at the first wafer in the batch.

[0074] At process P505, the method includes: determining a drift 505 of an attribute related to an illumination source or a pupil used for imaging a wafer, based on a drift of the illumination slit 503. In one embodiment, the drift of the illumination slit 503 is converted into a drift of the attribute 505 based on a correlation between the drift of the illumination slit 503 and the drift of the attribute 505, thereby determining the drift of the attribute 505. In one embodiment, the correlation may be established based on a test wafer, or an existing correlation, such as between the drift of the illumination slit and the dose drift, may be employed. For example, the drift of the illumination slit 503 may be used to determine the dose drift 505 based on an existing relationship between the drift of the illumination slit and the dose drift.

[0075] At process P507, the method includes determining a drift correction 507 based on attribute drift 505, which is to be applied to the illumination source or pupil to compensate for attribute drift 505. In one embodiment, the drift correction 507 is determined for each wafer within a batch. Thus, each wafer within a batch can be corrected for dose drift, for example, that may cause slit drift. This correction results in improved imaging performance for the batch. This differs from a typical uniform refresh process, in which drift correction is performed at the beginning of each batch.

[0076] In one embodiment, the attribute may be the dose and / or the pupil of a photolithography apparatus used to image a wafer. Therefore, the attribute drift 505 may be a dose drift relative to a nominal dose, and / or a pupil drift relative to a reference pupil. Drift correction 507 may be dose drift correction or pupil drift correction.

[0077] In one embodiment, determining the correction 507 to be applied to the illumination source or illumination pupil includes: performing a uniformity sensitivity model using a property drift 505 (e.g., in...). Figure 2 The uniformity correction system is implemented in the UNICOM module to determine the adjustment of one or more uniformity compensators. The uniformity sensitivity model determines the adjustment amount of one or more uniformity compensators (e.g., 1120) to correct for attribute drift based on the drift of the irradiation slit 503 or attribute drift 505. In one embodiment, drift correction for attribute drift includes positioning one or more uniformity compensators at one or more locations in the path of the irradiation slit to intercept one or more corresponding portions of the irradiation slit at one or more locations. As previously mentioned, the one or more uniformity compensators include one or more opaque finger-like members. Furthermore, as previously discussed, a first sensor may be located at a first end of the uniformity compensator, and a second sensor may be located at a second end of the uniformity compensator.

[0078] In one embodiment, a photolithography apparatus (e.g., as shown in the image) is provided. Figure 1 , Figure 2 and Figure 7 As shown). According to the present invention, the photolithography apparatus (e.g., Figure 1 , Figure 2 and Figure 7 The image (shown) includes an illumination source and illumination optics configured to image a wafer; at least two sensors configured to measure characteristics related to an illumination slit configured for imaging the wafer; and a processor configured to determine drift of the illumination slit and drift of properties of the lithography apparatus (e.g., dose or pupil). For example, the processor is configured to: determine, based on a proportion of the measured characteristics, the drift of the illumination slit relative to a reference position of the illumination slit; determine, based on the drift of the illumination slit, the drift of properties related to the illumination source or the illumination pupil used for imaging the wafer; and determine, based on the drift of the properties, a drift correction to be applied to the illumination source or the illumination pupil to compensate for the drift of the properties.

[0079] Furthermore, the photolithography apparatus includes a uniformity compensator system (e.g., Figure 3 (As shown). The uniformity compensator system includes one or more uniformity compensators at one or more locations along the path of the irradiation slit to intercept one or more corresponding portions of the irradiation slit at one or more locations. The uniformity sensitivity model determines the adjustment amount of the one or more uniformity compensators based on the drift or property drift of the irradiation slit to correct for the property drift.

[0080] In one embodiment, for each wafer within a batch processed in the photolithography apparatus, a drift correction is determined and the offset correction is applied. In one embodiment, at least two sensors include a first sensor located at a first location of the illumination slit and a second sensor located at a second location of the illumination slit. In one embodiment, the first sensor is located at a first end of the uniformity compensator system, while the second sensor is located at a second end of the uniformity compensator system. In one embodiment, at least two sensors are located near an energy sensor that measures the intensity of the illumination slit.

[0081] In one embodiment, the attribute may be the dose and / or the pupil of the lithography apparatus. Therefore, the drift of the attribute may be a dose drift relative to the nominal dose, and / or a pupil drift relative to the reference pupil, and the drift correction may be a dose drift correction or a pupil drift correction.

[0082] In one embodiment, the method discussed herein may be provided as a computer program product or a non-transitory computer-readable medium having instructions recorded thereon, which, when executed by a computer, implement the operation of the method 500 discussed above.

[0083] For example, Figure 6 The example computer system 100 includes a non-transitory computer-readable medium (e.g., memory) comprising instructions that, when executed by one or more processors (e.g., 104), cause the computer to: receive measurements of characteristics relating to an illumination slit configured for imaging a wafer via at least two sensors; determine a drift of the illumination slit relative to a reference position of the illumination slit based on the scale of the measured characteristics; and determine a drift of attributes relating to illumination upstream of an illumination region measured by the at least two sensors based on the drift of the illumination slit. For example, these attributes relate to an illumination source or pupil used for imaging the wafer. Further, the processor determines a drift correction to be applied to the illumination source or pupil to compensate for the drift of the attributes based on the drift of the attributes. In one embodiment, the at least two sensors include a first sensor located at a first position of the illumination slit and a second sensor located at a second position of the illumination slit.

[0084] In one embodiment, the measured characteristic is the irradiation intensity value measured by a first sensor and a second sensor, respectively, of at least two sensors.

[0085] In one embodiment, the reference position is the slit position measured at the start of imaging of the wafer in the batch. In another embodiment, the reference position is at the center of the irradiated slit.

[0086] In this embodiment, the attribute is dose and / or pupil. Therefore, attribute drift is dose drift relative to the nominal dose and / or pupil drift relative to the reference pupil, and drift correction is dose drift correction or pupil drift correction.

[0087] In one embodiment, a non-transitory computer-readable medium determines the drift correction for each wafer within a batch.

[0088] In one embodiment, a non-transient computer-readable medium determines the drift of an attribute by converting the drift of an irradiated slit into the drift of an attribute based on the correlation between the drift of the irradiated slit and the drift of an attribute.

[0089] In one embodiment, a non-transient computer-readable medium determines the correction to be applied to the illumination source or illumination pupil by performing a uniformity sensitivity model using attribute drift to determine adjustments to the uniformity compensators. The uniformity sensitivity model determines the amount of adjustment to one or more uniformity compensators to correct for attribute drift based on the drift of the illumination slit or attribute drift.

[0090] In one embodiment, a non-transitory computer-readable medium determines to position one or more uniformity compensators at one or more locations in the path of the illumination slit to intercept one or more corresponding portions of the illumination slit at one or more locations. In one embodiment, the one or more uniformity compensators include one or more opaque finger-like members.

[0091] In one embodiment, the first sensor is located at the first end of the uniformity compensator, while the second sensor is located at the second end of the uniformity compensator.

[0092] Figure 6 This is a block diagram illustrating an exemplary computer system 100 configured to assist in implementing the methods and processes disclosed herein according to embodiments of the present invention. Computer system 100 includes a bus 102 or other communication mechanism for conveying information, and a processor 104 (or a plurality of processors 104 and 105) coupled to the bus 102 for processing information. Computer system 100 also includes main memory 106, such as random access memory (RAM) or other dynamic storage device, coupled to the bus 102 for storing information and instructions to be executed by processor 104. Main memory 106 may also be used to store temporary variables or other intermediate information during execution of instructions to be executed by processor 104. Computer system 100 also includes read-only memory (ROM) 108 or other static storage device coupled to the bus 102 for storing static information and instructions of processor 104. Storage device 110, such as a disk or optical disk, is provided and coupled to the bus 102 for storing information and instructions.

[0093] Computer system 100 can be coupled to display 112, such as a cathode ray tube (CRT) or flat panel or touch panel display, via bus 102 for displaying information to the computer user. Input device 114, including alphanumeric keys and other keys, is coupled to bus 102 for conveying information and command selections to processor 104. Another type of user input device is cursor controller 116, such as a mouse, trackball, or cursor arrow keys, for conveying directional information and command selections to processor 104 and for controlling cursor movement on display 112. This input device typically has two degrees of freedom on two axes (a first axis (e.g., x) and a second axis (e.g., y)), which allows the device to specify a position in a plane. Touch panel (screen) displays can also be used as input devices.

[0094] According to one embodiment, in response to processor 104 executing one or more sequences of one or more instructions contained in main memory 106, computer system 100 may execute portions of a process. Such instructions may be read into main memory 106 from another computer-readable medium, such as storage device 110. Execution of the sequence of instructions contained in main memory 106 causes processor 104 to perform the processing steps described herein. One or more processors in a multiprocessor arrangement may also be used to execute the sequence of instructions contained in main memory 106. In an alternative embodiment, hardwired circuitry may be used in place of or in combination with software instructions. Therefore, the description herein is not limited to any particular combination of hardware circuitry and software.

[0095] As used herein, the term "computer-readable medium" refers to any medium that participates in providing instructions to processor 104 for execution. Such media can take many forms, including but not limited to non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical discs or magnetic disks, such as storage device 110. Volatile media include dynamic memory, such as main memory 106. Transmission media include coaxial cables, copper wires, and optical fibers, including conductors forming bus 102. Transmission media can also take the form of sound waves or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example, floppy disks, flexible disks, hard disks, magnetic tapes, any other magnetic media, CD-ROMs, DVDs, any other optical media, punched cards, paper tape, any other physical media with a perforated pattern, RAM, PROMs and EPROMs, FLASH-EPROMs, any other memory chips or cartridges, carrier waves as described below, or any other medium from which a computer can read.

[0096] Various forms of computer-readable media may involve carrying one or more sequences of one or more instructions to processor 104 for execution. For example, the instructions may initially be carried on a disk of a remote computer. The remote computer may load the instructions into its dynamic memory and transmit the instructions over a telephone line using a modem. A modem local to computer system 100 may receive data over the telephone line and convert the data into an infrared signal using an infrared transmitter. An infrared detector coupled to bus 102 may receive the data carried in the infrared signal and place the data on bus 102. Bus 102 transfers the data to main memory 106, from which processor 104 retrieves and executes the instructions. The instructions received by main memory 106 may optionally be stored on storage device 110 before or after execution by processor 104.

[0097] Computer system 100 also expects to include a communication interface 118 coupled to bus 102. Communication interface 118 provides bidirectional data communication coupled to network link 120 connected to local network 122. For example, communication interface 118 may be an Integrated Services Digital Network (ISDN) card or modem to provide data communication connectivity with a corresponding type of telephone line. As another example, communication interface 118 may be a Local Area Network (LAN) card to provide data communication connectivity with a compatible LAN. Wireless links may also be implemented. In any such implementation, communication interface 118 transmits and receives electrical, electromagnetic, or optical signals carrying digital data streams representing various types of information.

[0098] Network link 120 typically provides data communication to other data devices via one or more networks. For example, network link 120 may provide a connection to host computer 124 or data devices operated by Internet service provider (ISP) 126 via local network 122. ISP 126, in turn, provides data communication services via a global packet data communication network now commonly referred to as the “Internet” 128. Both local network 122 and Internet 128 use electrical, electromagnetic, or optical signals that carry digital data streams. Signals through various networks and on network link 120, as well as signals through communication interface 118 (which carries digital data to and from computer system 100), are example forms of carrier waves for transmitting information.

[0099] Computer system 100 can send messages and receive data, including program code, via one or more networks, network links 120, and communication interfaces 118. In an Internet example, server 130 can transmit application request code via the Internet 128, ISP 126, local network 122, and communication interface 118. For example, an application downloaded in this way can provide illumination optimizations for an embodiment. The received code can be executed by processor 104 and / or stored in storage device 110 or other non-volatile memory for later execution when it is received. In this way, computer system 100 can obtain application code in carrier form.

[0100] Figure 7 Another exemplary photolithography projection apparatus 1000 according to an embodiment of the present invention is depicted. Apparatus 1000 includes:

[0101] - The source collector module SO is used to provide radiation.

[0102] - Irradiation system (irradiator) IL is configured to modulate the radiation beam B (e.g., UV radiation) from source collector module SO;

[0103] - A support structure (e.g., a mask stage) MT is configured to support a pattern forming apparatus (e.g., a mask or a mask plate) MA and is connected to a first locator PM, which is configured to precisely position the pattern forming apparatus.

[0104] - A substrate stage (e.g., a wafer stage) WT is configured to hold a substrate (e.g., a wafer coated with resist) W and is connected to a second positioner PW configured to precisely position the substrate; and

[0105] - A projection system (e.g., a refractive projection lens system) PS is configured to project a pattern, which is imparted to a radiation beam B by a pattern forming apparatus MA, onto a target portion C (e.g., including one or more dies) of a substrate W.

[0106] As described herein, apparatus 1000 is reflective (e.g., employing a reflective mask). It should be noted that because most materials are absorptive in the EUV wavelength range, the patterning apparatus can have multilayer reflectors comprising, for example, stacks of molybdenum and silicon. In one example, the multilayer reflector has 40 layers of molybdenum and silicon pairs, with each layer having a thickness of a quarter wavelength. Even smaller wavelengths can be produced using X-ray lithography. Since most materials are absorptive at both EUV and X-ray wavelengths, the patterned sheets of absorbing material on the morphology of the patterning apparatus (e.g., a TaN absorber on top of a multilayer reflector) define the locations where features may be printed (positive resist) or not printed (negative resist).

[0107] refer to Figure 7 The irradiator IL receives an extreme ultraviolet (EUV) radiation beam from the source collector module S. Methods for generating EUV radiation include, but are not limited to, converting a material into a plasma state having at least one element (e.g., xenon, lithium, or tin) using one or more emission lines in the EUV range. In one such method, a plasma, commonly referred to as laser-generated plasma (“LPP”), can be generated by irradiating a fuel, such as a droplet, stream, or cluster of material having a line-emitting element, using a laser beam. The source collector module S may include a laser ( Figure 7 As part of an EUV radiation system (not shown), the laser is used to provide a laser beam for exciting the fuel. The resulting plasma emits output radiation, such as EUV radiation, which is collected using a radiation collector disposed in a source collector module. The laser and the source collector module can be separate entities, for example, when a CO2 laser is used to provide a laser beam for fuel excitation.

[0108] In this case, the laser is not considered part of the lithography apparatus, and the radiation beam is delivered from the laser to the source collector module by means of a beam delivery system including, for example, suitable directional mirrors and / or beam expanders. In other cases, the radiation source may be an integral part of the source collector module, for example, when the radiation source is a plasma EUV generator produced by a discharge, commonly referred to as a DPP radiation source.

[0109] An irradiator IL may include an adjuster configured to adjust the angular intensity distribution of the radiated beam. Typically, at least the outer radial extent and / or inner radial extent (often referred to as σ-outer and σ-inner, respectively) of the intensity distribution in the pupil plane of the irradiator can be adjusted. Additionally, the irradiator IL may include various other components, such as faceted field mirror devices and faceted pupil mirror devices. The irradiator can be used to adjust the radiated beam to have a desired uniformity and intensity distribution in its cross-section.

[0110] A radiation beam B is incident on a patterning apparatus (e.g., a mask) MA, which is held on a support structure (e.g., a mask stage) MT, and patterned by the patterning apparatus. After reflection from the patterning apparatus (e.g., the mask) MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. The substrate stage WT can be accurately moved, for example, to position different target portions C within the path of the radiation beam B, by means of a second locator PW and a position sensor PS2 (e.g., an interferometer device, a linear encoder, or a capacitive sensor). Similarly, a first locator PM and another position sensor PS1 can be used to accurately position the patterning apparatus MA relative to the path of the radiation beam B. The patterning apparatus (e.g., the mask) MA and the substrate W can be aligned using patterning apparatus alignment marks M1, M2 and substrate alignment marks P1, P2.

[0111] The depicted device 1000 can be used in at least one of the following modes:

[0112] 1. In step mode, the support structure (e.g., mask stage) MT and substrate stage WT remain substantially stationary, while the entire pattern imparted to the radiation beam is projected onto the target portion C in a single exposure (i.e., single static exposure). The substrate stage WT is then offset along the X and / or Y directions to allow different target portions C to be exposed.

[0113] 2. In scanning mode, the support structure (e.g., mask stage) MT and the substrate stage WT are scanned simultaneously, while the pattern imparted to the radiation beam is projected onto the target portion C (i.e., single dynamic exposure). The velocity and direction of the substrate stage WT relative to the support structure (e.g., mask stage) MT can be determined by the magnification (reduction ratio) and image inversion characteristics of the projection system PS.

[0114] 3. In another mode, the support structure (e.g., mask stage) MT remains substantially stationary, thereby holding the programmable patterning apparatus in place, while the substrate stage WT moves or scans, simultaneously projecting the pattern onto the target portion C onto the radiation beam. In this mode, a pulsed radiation source is used to update the programmable patterning apparatus as needed, either after each movement of the substrate stage WT or between consecutive radiation pulses during scanning. This mode of operation can be readily applied to maskless lithography utilizing a programmable patterning apparatus, such as programmable mirror arrays of the type described above.

[0115] Figure 8 The apparatus 1000 is shown in more detail, comprising a source collector module SO, an irradiation system IL, and a projection system PS. The source collector module SO is constructed and arranged such that a vacuum environment can be maintained within an enclosure structure 220 of the source collector module SO. EUV radiation-emitting plasma 210 can be formed by a plasma radiation source generated by a discharge. EUV radiation can be generated by a gas or vapor, such as Xe gas, Li vapor, or Sn vapor, wherein a very hot plasma 210 is generated to emit radiation in the EUV range of the electromagnetic spectrum. For example, the very hot plasma 210 is generated by a discharge that causes at least partial ionization of the plasma. For example, a partial pressure of 10 Pa of Xe, Li, Sn vapor, or any other suitable gas or vapor may be required to effectively generate radiation. In one embodiment, a plasma that excites tin (Sn) is provided to generate EUV radiation.

[0116] Radiation emitted by thermal plasma 210 enters collector chamber 212 from source chamber 211 via an optional gas barrier or contaminant trap 230 (also referred to in some cases as a contaminant barrier or foil trap), which is located in or behind an opening in source chamber 211. Contaminant trap 230 may include a channel structure. Contaminant trap 230 may also include a gas barrier or a combination of a gas barrier and a channel structure. Contaminant traps or contaminant barriers 230 further indicated herein include at least channel structures known in the art.

[0117] Collector chamber 212 may include a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation traversing the collector CO may be reflected from a grating spectral filter 240 to be focused along the optical axis indicated by the dashed line 'O' into a virtual source point IF. The virtual source point IF is often referred to as the intermediate focus, and the source collector module is arranged such that the intermediate focus IF is located at or near the opening 221 in the enclosure structure 220. The virtual source point IF is an image of the radiative emission plasma 210.

[0118] Subsequently, radiation traverses an illumination system IL, which may include a faceted field mirror assembly 22 and a faceted pupil mirror assembly 24. These two assemblies are arranged to provide a desired angular distribution of the radiation beam 21 at the patterning apparatus MA and a desired uniformity of radiation intensity at the patterning apparatus MA. When the radiation beam 21 is reflected at the patterning apparatus MA, held by the support structure MT, a patterned beam 26 is formed, and this patterned beam 26 is imaged by the projection system PS via reflective elements 28 and 30 onto the substrate W, held by the substrate stage WT.

[0119] The illumination optics unit IL and projection system PS can typically contain more components than shown. Depending on the type of lithography apparatus, a grating spectral filter 240 may optionally be present. Furthermore, more mirrors than are shown in the figure may be present; for example, the projection system PS may contain more than [number missing in original text]. Figure 8 The reflective elements shown have 1 to 6 additional reflective elements.

[0120] like Figure 8 As shown, the collector optics CO is depicted as a nested collector with grazing incidence reflectors 253, 254, and 255, merely as an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254, and 255 are arranged symmetrically about the optical axis O, and this type of collector optics CO is ideally used in combination with a plasma radiation source generated by a discharge.

[0121] Alternatively, the source collector module SO can be as follows: Figure 9 This is part of the LPP radiation system shown. A laser (LAS) is arranged to deposit laser energy onto a fuel such as xenon (Xe), tin (Sn), or lithium (Li), thereby generating a highly ionized plasma 210 with electron temperatures of tens of eV. Energy radiation generated during the deexcitation and recombination of these ions is emitted from the plasma, collected by a collector optics (CO) with approximately perpendicular incidence, and focused onto an opening 221 in the enclosure structure 220.

[0122] The concepts revealed in this paper can be used to simulate or mathematically model any general imaging system for imaging sub-wavelength features, and are particularly applicable to emerging imaging techniques capable of producing wavelengths of increasingly smaller sizes. Emerging techniques already in use include EUV (Extreme Ultraviolet) lithography, which can produce wavelengths of 193 nm using ArF lasers and even 157 nm using fluorine lasers. Furthermore, EUV lithography can generate wavelengths in the 20 nm to 5 nm range by using synchrotrons or by bombarding materials (solid-state or plasma) with high-energy electrons, thereby generating photons within this range.

[0123] While the concepts disclosed herein can be used for imaging on substrates such as silicon wafers, it should be understood that the disclosed concepts can be used in any type of lithography imaging system, for example, for imaging on substrates other than silicon wafers.

[0124] While specific examples of use in IC manufacturing may be mentioned herein, it should be understood that the embodiments described herein can have many other possible applications. For example, these embodiments are used for manufacturing integrated optical systems, guiding and detection patterns for magnetic domain memories, liquid crystal displays (LCDs), thin-film magnetic heads, micromechanical systems (MEMS), etc. Those skilled in the art will appreciate that, in the context of such alternative applications, any use of the terms “mask,” “wafer,” or “die” herein can be considered synonymous or interchangeable with the more general terms “patterning apparatus,” “substrate,” or “target portion,” respectively. The substrate referred to herein may be processed, for example, in a track (a tool typically applied to the substrate and developed by the exposed resist) or a measurement or inspection tool before or after exposure. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Furthermore, the substrate may be processed, for example, more than once, to produce, for example, a multilayer IC; therefore, the term “substrate” as used herein may also refer to a substrate that already contains multiple processed layers.

[0125] In this document, the terms “radiation” and “beam” as used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having wavelengths of 365 nm, 355 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having wavelengths in the range between 5 nm and 20 nm) as well as particle beams (such as ion beams or electron beams).

[0126] These embodiments may be further described using the following terms:

[0127] 1. A system comprising:

[0128] A photolithography apparatus, comprising at least two sensors, each configured to measure characteristics relating to an irradiated area set for imaging a substrate; and

[0129] The processor is configured as follows:

[0130] The drift of the irradiated area relative to a reference position is determined based on the ratio of the measured characteristic measured by one sensor to the measured characteristic measured by the other sensor.

[0131] Based on the drift of the irradiated area, the drift of irradiation-related properties upstream of the irradiated area, measured by at least two sensors, is determined, and

[0132] Based on attribute drift, determine the drift correction to be applied to the attribute to compensate for the drift.

[0133] 2. The system according to Clause 1, wherein drift correction is determined using a uniformity compensator system.

[0134] The uniformity compensator system includes one or more uniformity compensators at one or more locations along the path of the irradiation area to intercept one or more corresponding portions of the irradiation area at one or more locations, and

[0135] The uniformity sensitivity model determines the adjustment amount of one or more uniformity compensators based on the drift of the irradiated area or the drift of the attribute, in order to correct the drift of the attribute.

[0136] 3. The system according to Clause 2, wherein one or more uniformity compensators include one or more opaque finger members.

[0137] 4. The system according to any one of Clauses 1 to 3, wherein the drift of the properties is caused by one or both of contamination of the irradiation optical collector and the power of the irradiation source.

[0138] 5. The system according to any one of Clauses 1 to 4, wherein drift correction is determined for each substrate within a batch.

[0139] 6. The system according to any one of Clauses 1 to 4, wherein the drift of the irradiation area is converted into the drift of the attribute based on the correlation between the drift of the irradiation area and the drift of the attribute, thereby determining the drift of the attribute.

[0140] 7. The system according to any one of Clauses 1 to 6, wherein at least two sensors comprise: a first sensor located at a first position in the irradiation area, and a second sensor located at a second position in the irradiation area.

[0141] 8. The system according to any one of Clauses 7, wherein the first sensor is located at a first end of the uniformity compensator system and the second sensor is located at a second end of the uniformity compensator system.

[0142] 9. The system according to any one of Clauses 1 to 8, wherein the properties are dose and / or pupil.

[0143] The attribute drift is a dose drift relative to the nominal dose and / or a pupil drift relative to the reference pupil, and

[0144] Drift correction includes dose drift correction or pupil drift correction.

[0145] 10. The system according to any one of clauses 1 to 9, wherein the measured characteristic is an irradiation intensity value measured by a first sensor and a second sensor of at least two sensors, respectively.

[0146] 11. The system according to any one of clauses 1 to 10, wherein the irradiation area is an irradiation slit.

[0147] 12. The system according to any one of clauses 1 to 10, wherein the reference position is the position of the illumination slit measured at the start of imaging of the substrate in the batch.

[0148] 13. The system according to any one of clauses 1 to 11, wherein the reference position is at the center of the slit.

[0149] 14. A method for determining drift correction associated with a photolithography apparatus, the method comprising:

[0150] Measurements of characteristics related to the irradiated area used for imaging the substrate are received via at least two sensors;

[0151] Based on the proportion of the measured characteristics, the drift of the irradiated area relative to the reference position is determined;

[0152] Based on the drift of the irradiated area, the drift of irradiation-related properties upstream of the irradiated area, measured by at least two sensors, is determined, and

[0153] Based on attribute drift, determine the drift correction to be applied to the attribute to compensate for the drift.

[0154] 15. The method according to Clause 14, wherein drift correction is determined for each substrate within the batch.

[0155] 16. The method according to any one of Clauses 14 to 15, wherein determining the drift of the attribute comprises:

[0156] The drift of the irradiated area is converted into the drift of the attribute based on the correlation between the drift of the irradiated area and the drift of the attribute.

[0157] 17. The method according to any one of clauses 14 to 16, wherein at least two sensors comprise: a first sensor at a first location in the irradiation area and a second sensor at a second location in the irradiation area.

[0158] 18. The method according to any one of Clauses 14 to 17, wherein the properties are dose and / or pupil.

[0159] The attribute drift is a dose drift relative to the nominal dose and / or a pupil drift relative to the reference pupil, and

[0160] Drift correction includes dose drift correction or pupil drift correction.

[0161] 19. The method according to any one of clauses 14 to 18, wherein the measured characteristic is an irradiation intensity value measured by a first sensor and a second sensor of at least two sensors, respectively.

[0162] 20. The method according to any one of clauses 14 to 19, wherein the irradiation area is an irradiation slit.

[0163] 21. The method according to any one of clauses 14 to 20, wherein the reference position is the position of the illumination slit measured at the start of imaging of the substrate in the batch.

[0164] 22. The method according to any one of clauses 14 to 21, wherein the reference position is at the center of the irradiation slit.

[0165] 23. The method according to any one of clauses 14 to 22, wherein determining the correction to be applied to the attribute comprises:

[0166] The uniformity sensitivity model is performed using attribute drift to determine the adjustment for one or more uniformity compensators.

[0167] The uniformity sensitivity model determines the adjustment amount of one or more uniformity compensators based on the drift of the irradiated area or the drift of the attribute, in order to correct the drift of the attribute.

[0168] 24. The method according to Clause 23, wherein drift correction for attribute drift includes:

[0169] Position one or more uniformity compensators at one or more locations along the path of the irradiated area to intercept one or more corresponding portions of the irradiated area at one or more locations.

[0170] 25. The method according to any one of Clauses 23 to 24, wherein one or more uniformity compensators comprise one or more opaque finger members.

[0171] 26. The method according to any one of clauses 23 to 25, wherein the first sensor is located at a first end of the uniformity compensator and the second sensor is located at a second end of the uniformity compensator.

[0172] 27. The method according to any one of Clauses 14 to 26, wherein the properties are dose and / or pupil.

[0173] The attribute drift is a dose drift relative to the nominal dose and / or a pupil drift relative to the reference pupil, and

[0174] Drift correction includes dose drift correction or pupil drift correction.

[0175] 28. A non-transitory computer-readable medium having instructions thereon, which, when executed by a computer, cause the computer to:

[0176] Measurements of characteristics related to the irradiated area used for imaging the substrate are received via at least two sensors;

[0177] Based on the proportion of the measured characteristics, the drift of the irradiated area relative to the reference position is determined;

[0178] Based on the drift of the irradiated area, the drift of irradiation-related properties upstream of the irradiated area, measured by at least two sensors, is determined, and

[0179] Based on attribute drift, determine the drift correction to be applied to the attribute to compensate for the drift.

[0180] 29. The non-transitory computer-readable medium as described in Clause 28, wherein drift correction is determined for each substrate within a batch.

[0181] 30. A non-transitory computer-readable medium according to any one of clauses 28 to 29, wherein drift in determining attributes comprises:

[0182] The drift of the irradiated area is converted into the drift of the attribute based on the correlation between the drift of the irradiated area and the drift of the attribute.

[0183] 31. A non-transitory computer-readable medium according to any one of clauses 28 to 30, wherein at least two sensors comprise: a first sensor located at a first position in the irradiated area, and a second sensor located at a second position in the irradiated area.

[0184] 32. A non-transitory computer-readable medium pursuant to any of Clauses 28 to 31, wherein the attributes are dose and / or pupil.

[0185] The attribute drift is a dose drift relative to the nominal dose and / or a pupil drift relative to the reference pupil, and

[0186] Drift correction includes dose drift correction or pupil drift correction.

[0187] 33. A non-transitory computer-readable medium according to any one of clauses 28 to 32, wherein the measured characteristic is an irradiation intensity value measured by a first sensor and a second sensor of at least two sensors, respectively.

[0188] 34. The non-transitory computer-readable medium according to any one of clauses 28 to 33, wherein the irradiation area is an irradiation slit.

[0189] 35. A non-transitory computer-readable medium according to any one of clauses 28 to 34, wherein the reference position is the position of the illumination slit measured at the start of imaging of the substrate in a batch.

[0190] 36. The non-transitory computer-readable medium according to any one of Clauses 28 to 35, wherein the reference location is at the center of the irradiated area.

[0191] 37. A non-transitory computer-readable medium according to any one of clauses 28 to 36, wherein determining the correction to be applied to the attribute includes:

[0192] Use attribute drift to perform a uniformity sensitivity model to determine the adjustment of one or more uniformity compensators.

[0193] The uniformity sensitivity model determines the adjustment amount of one or more uniformity compensators based on the drift of the irradiated area or the drift of the attribute, in order to correct the drift of the attribute.

[0194] 38. The non-transitory computer-readable medium as described in Clause 37, wherein drift correction for drift of an attribute includes:

[0195] Position one or more uniformity compensators at one or more locations along the path of the irradiated area to intercept one or more corresponding portions of the irradiated area at one or more locations.

[0196] 39. The non-transitory computer-readable medium according to any one of Clauses 37 to 38, wherein one or more uniformity compensators include one or more opaque finger members.

[0197] 40. A non-transitory computer-readable medium according to any one of clauses 37 to 39, wherein a first sensor is located at a first end of a uniformity compensator, and a second sensor is located at a second end of a uniformity compensator.

[0198] 41. A photolithography apparatus, the apparatus comprising:

[0199] An illumination source and illumination optics configured to image a substrate; and

[0200] At least two sensors are configured to measure characteristics related to an irradiated area set up for imaging a substrate;

[0201] The processor is configured as follows:

[0202] Based on the proportion of the measured characteristics, the drift of the irradiated area relative to the reference position is determined;

[0203] Based on the drift of the irradiated area, the drift of irradiation-related properties upstream of the irradiated area, measured by at least two sensors, is determined, and

[0204] Based on attribute drift, determine the drift correction to be applied to the attribute to compensate for the attribute drift.

[0205] A uniformity compensator system includes one or more uniformity compensators at one or more locations along the path of the irradiated area to intercept one or more corresponding portions of the irradiated area at one or more locations, and

[0206] The uniformity sensitivity model determines the adjustment amount of one or more uniformity compensators based on the drift of the irradiated area or the drift of the attribute, in order to correct the drift of the attribute.

[0207] 42. The lithography apparatus according to Clause 41, wherein drift correction is determined and applied to each substrate within a batch.

[0208] 43. The lithography apparatus according to any one of clauses 41 to 42, wherein at least two sensors comprise: a first sensor located at a first position in the irradiation area and a second sensor located at a second position in the irradiation area.

[0209] 44. The lithography apparatus according to any one of clauses 41 to 43, wherein the first sensor is located at a first end of the uniformity compensator system and the second sensor is located at a second end of the uniformity compensator system.

[0210] 45. The photolithography apparatus according to any one of clauses 41 to 44, wherein the properties are dose and / or pupil.

[0211] The attribute drift is a dose drift relative to the nominal dose and / or a pupil drift relative to the reference pupil, and

[0212] Drift correction includes dose drift correction or pupil drift correction.

[0213] 46. ​​The lithography apparatus according to any one of clauses 41 to 45, wherein at least two sensors are located near an energy sensor that measures the intensity of the irradiated area.

[0214] As used herein, the terms "optimizing" and "optimization" refer to or imply adjusting patterning apparatus (e.g., photolithography apparatus), patterning processes, etc., to give the results and / or processes more desirable characteristics, such as higher projection accuracy of the design layout on the substrate, a larger process window, etc. Therefore, as used herein, the term "optimization" refers to or implyes the process of identifying one or more values ​​of one or more parameters that, when compared to an initial set of one or more values ​​of the one or more parameters, provide an improvement in at least one relevant metric, such as a local optimum. "Optimum" and other related terms should be interpreted accordingly. In one embodiment, optimization steps may be applied iteratively to provide further improvements in one or more metrics.

[0215] Various aspects of the present invention can be implemented in any convenient form. For example, embodiments can be implemented by one or more suitable computer programs that can be carried on a suitable carrier medium, which can be a tangible carrier medium (e.g., a disk) or an intangible carrier medium (e.g., a communication signal). Embodiments of the present invention can be implemented using suitable means, which can specifically take the form of a programmable computer running a computer program arranged to implement the methods described herein. Thus, embodiments of the present invention can be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention can also be implemented as instructions stored on a machine-readable medium that can be read and executed by one or more processors. A machine-readable medium can include any mechanism for storing or transmitting information in a machine-readable (e.g., computing device) form. For example, a machine-readable medium can include read-only memory (ROM), random access memory (RAM), disk storage media, optical storage media, flash memory devices, electrical, optical, acoustic, or other forms of propagation signals (e.g., carrier waves, infrared signals, digital signals, etc.). Further, firmware, software, routines, and instructions can be described herein as performing certain actions. However, it should be understood that such descriptions are for convenience only, and such actions are actually produced by computing devices, processors, controllers, or other devices that execute firmware, software, routines, instructions, etc.

[0216] In the block diagrams, the illustrated components are depicted as discrete functional blocks; however, the embodiments are not limited to systems in which the functions described herein are organized as illustrated. The functionality provided by each component may be provided by software or hardware modules organized differently from the currently depicted modules. For example, such software or hardware may be hybrid, federated, replicated, decomposed, distributed (e.g., within a data center or geographically), or organized differently. The functions described herein may be provided by one or more processors of one or more computers executing code stored on a tangible, non-transitory, machine-readable medium. In some cases, a third-party content delivery network may host some or all of the information transmitted over the network, in which case, with regard to the information (e.g., content) being said to be supplied or otherwise provided, the information may be provided by sending an instruction to retrieve the information from the content delivery network.

[0217] Unless otherwise expressly stated, it is evident from the discussion that throughout the specification, discussions using terms such as “processing,” “computing,” “calculating,” and “determining” refer to the actions or processes of a particular device (such as a dedicated computer or similar dedicated electronic processing / computing equipment).

[0218] Readers should understand that this application describes several inventions. Instead of dividing these inventions into multiple separate patent applications, the applicant has grouped them into a single document because their related subject matter makes the application process more economical. However, the unique advantages and aspects of these inventions should not be confused. In some cases, embodiments resolve all the deficiencies pointed out herein; however, it should be understood that the invention is independently useful, and some embodiments solve only a subset of these problems or provide other unmentioned benefits that will be apparent to those skilled in the art upon review of this disclosure. Due to cost limitations, some inventions disclosed herein may not currently be claimed and may be claimed in a later application (such as a continuation application or by amending the claims). Similarly, due to space limitations, the abstract or summary of the invention in this document should not be construed as a comprehensive enumeration of all such inventions or all aspects of such inventions.

[0219] It should be understood that the specification and drawings are not intended to limit the invention to the specific forms disclosed, but rather are intended to cover all modifications, equivalents and alternatives that fall within the spirit and scope of the invention as defined by the appended claims.

[0220] Given this description, modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art. Therefore, this description and drawings should be interpreted as illustrative only, intended to teach those skilled in the art the general manner of carrying out the invention. It should be understood that the forms of the invention shown and described herein will be considered as examples of embodiments. It will be apparent to those skilled in the art who have benefited from the description of the invention that elements and materials may be substituted for those illustrated and described herein, portions and materials may be reversed or omitted, certain features may be utilized independently, and features of embodiments or embodiments may be combined. Changes may be made to the elements described herein without departing from the spirit and scope of the invention as set forth in the appended claims. The headings used herein are for organizational purposes only and are not intended to limit the scope of this specification.

[0221] As used throughout the application, the word “may” is used in a broad sense (i.e., meaning potential) rather than a mandatory sense (i.e., meaning must). Words such as “include,” “including,” and “includes” mean, but are not limited to, other than. As used throughout the application, the singular forms “a,” “an,” and “the” include plural indicators unless explicitly stated otherwise. Thus, for example, a reference to an element “a” or “one” includes a combination of two or more elements, although other terms and phrases such as “one or more” are used for one or more elements. Unless otherwise stated, “or” is non-exclusive, i.e., encompasses both “and” and “or.” Terms describing conditional relationships (e.g., "in response to X, Y", "at X, Y", "if X, Y", "when X, Y") encompass causal relationships, where the antecedent is a necessary causal condition, a sufficient causal condition, or a contributing causal condition to the consequent. For example, "state X occurs when condition Y is obtained" is interchangeable with "X occurs only when Y" and "X occurs at Y and Z". Such conditional relationships are not limited to consequences immediately following the antecedent, as some consequences may be delayed, and in conditional statements, the antecedent is associated with its consequence; for example, the antecedent relates to the likelihood of subsequent occurrence. Unless otherwise stated, statements in which multiple attributes or functions are mapped to multiple objects (e.g., one or more processors performing steps A, B, C, and D) encompass situations where all these attributes or functions are mapped to all these objects and subsets of attributes or functions are mapped to subsets of attributes or functions (e.g., all processors each perform steps A through D, and processor 1 performs step A, processor 2 performs a portion of steps B and C, and processor 3 performs a portion of steps C and D). Furthermore, unless otherwise stated, a statement that a value or action is “based on” another condition or value encompasses both examples where the condition or value is the only factor and examples where the condition or value is one of multiple factors. Unless otherwise stated, a statement that “each” example of a set has some property should not be interpreted as excluding the possibility that some other identical or similar members in a large set do not have that property; that is, each does not necessarily mean every single one. References selected from a range include the endpoints of the range.

[0222] In the above description, any process, description, or block in the flowchart should be understood as representing a module, segment, or portion of code including one or more executable instructions for implementing a specific logical function or step in the process, and alternative implementations are included within the scope of the exemplary embodiments of this improvement, wherein, depending on the function involved, the function may be performed in a different order than the order shown or discussed, including substantially simultaneous or in reverse order, as understood by those skilled in the art.

[0223] To the extent that certain U.S. patents, U.S. patent applications, or other materials (e.g., articles) are incorporated by reference, the text of such U.S. patents, U.S. patent applications, and other materials is incorporated by reference only to the extent that there is no conflict between such materials and the statements and figures set forth herein. In the event of such conflict, any such conflicting text of the U.S. patents, U.S. patent applications, and other materials incorporated by reference is not explicitly incorporated herein by reference.

[0224] While certain embodiments have been described, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. In fact, the novel methods, apparatuses, and systems described herein can be embodied in various other forms; furthermore, various omissions, substitutions, and changes can be made to the forms of the methods, apparatuses, and systems described herein without departing from the spirit of the invention. The appended claims and their equivalents are intended to cover these forms or modifications that fall within the scope and spirit of the invention.

Claims

1. An optical system, comprising: A photolithography apparatus includes at least two sensors, each configured to measure characteristics related to an irradiated area set up for imaging a substrate; as well as The processor is configured as follows: The drift of the central portion of the irradiated area relative to a reference position is determined based on the ratio of the measured characteristic measured by one of the sensors to the measured characteristic measured by the other sensor. Based on the drift of the irradiated area, the drift of the attribute related to irradiation upstream of the irradiated area, measured by the at least two sensors, is determined, and Based on the drift of the attribute, determine a drift correction to be applied to the attribute to compensate for the drift of the attribute. The irradiation area is the irradiation slit, and The reference position is the position of the illumination slit measured at the start of imaging of the substrate in the batch.

2. The optical system of claim 1, wherein the drift correction is determined using a uniformity compensator system. The uniformity compensator system includes one or more uniformity compensators at one or more locations along the path of the irradiation area to intercept one or more corresponding portions of the irradiation area at said one or more locations, and The uniformity sensitivity model determines the adjustment amount of the one or more uniformity compensators to correct the drift of the attribute based on the drift of the irradiated area or the drift of the attribute.

3. The optical system of claim 2, wherein the one or more uniformity compensators comprise one or more opaque finger-like components.

4. The optical system according to any one of claims 1 to 3, wherein the drift of said property is caused by one or both of contamination of the irradiation optical device collector and the power of the irradiation source.

5. The optical system according to any one of claims 1 to 4, wherein the drift correction is determined for each substrate within a batch.

6. The optical system according to any one of claims 1 to 4, wherein the drift of the attribute is determined by converting the drift of the irradiation area into the drift of the attribute based on the correlation between the drift of the irradiation area and the drift of the attribute.

7. The optical system according to any one of claims 1 to 6, wherein the at least two sensors comprise: A first sensor located at a first position in the irradiation area, and a second sensor located at a second position in the irradiation area.

8. The optical system according to any one of claims 2 to 3, wherein the first sensor is located at a first end of the uniformity compensator system, and the second sensor is located at a second end of the uniformity compensator system.

9. The optical system according to any one of claims 1 to 8, wherein said property is dose and / or pupil. The drift of the aforementioned attribute is a dose drift relative to the nominal dose and / or a pupil drift relative to the reference pupil, and The drift correction mentioned above is either dose drift correction or pupil drift correction.

10. The optical system according to any one of claims 1 to 9, wherein the measured characteristic is an illumination intensity value measured by a first sensor and a second sensor of the at least two sensors, respectively.

11. The optical system according to any one of claims 1 to 10, wherein the reference position is at the center of the slit.

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