Method and apparatus for aligning and diagnosing laser beams

Abstract

Methods and apparatus are disclosed for aligning and diagnosing a laser beam passing through an optical train in a highly space-efficient, low-cost, and / or retrofit-friendly manner. The optical components of the optical train are mounted so that one or more of the optical components can direct their outgoing laser beam to sweep partially or fully past one or more downstream sensors. Correlation data between the physical arrangement of the optical components and points of impact data and / or beam quality data is used, among other things, to align and / or diagnose the laser beam, locate fault locations, and / or optimize maintenance schedules.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. non-provisional patent application No. 15 / 655,079, filed on July 20, 2017, the entire contents of which are incorporated herein by reference. Background Art

[0003] Many systems that generate laser beams (such as laser generators) or utilize laser beams (such as photolithography systems) typically include an optical train consisting of one or more optical components (such as mirrors, gratings, prisms, optical switches, filters, etc.). An optical train is a set of optical components through which a laser beam passes. A laser beam enters the optical train and, after passing through it, produces one or more output beams. The optical components of the optical train can fully or partially reflect, process, filter, modify, focus, or expand the laser beam to produce one or more desired laser beam outputs.

[0004] Optimal laser operation typically requires that the laser beam be properly aligned relative to each optical component of the optical train and / or upon exiting the optical train. Alignment refers to the laser beam intersecting or striking one or more desired points (whether real or virtual in space) after traversing one or more optical components (such as after traversing an optical component or traversing part or the entire optical train). Alternatively or additionally, optimal laser operation typically also requires that the beam possess certain desired optical properties, such as footprint, energy, and the like. Laser beam diagnostics is an important task and involves, among other things, characterizing the characteristics of the laser beam so that optimal laser operation can be achieved and / or maintained.

[0005] Improved laser beam alignment and / or laser beam diagnostics apparatus and methods are the subject of embodiments of the present invention. Summary of the Invention

[0006] In one embodiment, the present invention relates to a method for optimizing a laser beam in a lithography system, the laser beam traversing an optical train comprising a plurality of optical components. The method includes performing rastering using a first optical component of the plurality of optical components such that, in response to the rastering using the first optical component, the laser beam exiting the first optical component at least partially sweeps across a first sensor. The method also includes using data acquired from the first sensor during the rastering using the first optical component to form a correlation between a physical configuration of the first optical component and an impact point of the laser beam exiting the first optical component. The method also includes using the data acquired from the correlation to identify a first physical configuration of the first optical component that will cause the impact point of the laser beam exiting the first optical component to impact a desired point on a second optical component. The method also includes aligning the laser beam exiting the first optical component relative to the second optical component by aligning the first optical component according to the first physical configuration determined by the identification.

[0007] In another embodiment, the present invention relates to a lithography system having an optical train including a plurality of optical components configured to at least deliver a laser beam from one location to another. The lithography system includes a first optical component configured to at least rasterize the laser beam exiting the first optical component to cause the laser beam exiting the first optical component to at least partially sweep across a first sensor. The lithography system also includes a second optical component configured to at least receive the laser beam exiting the first optical component and to rasterize the laser beam exiting the second optical component to cause the laser beam exiting the second optical component to at least partially sweep across a second sensor.

[0008] In another embodiment, the present invention relates to a method for diagnosing a laser beam, the laser beam being configured to generate one of deep ultraviolet (DUV) and extreme ultraviolet (EUV) light for use in lithography, the laser beam passing through at least a first optical component and a second optical component of an optical train in a lithography system. The method includes rastering the laser beam using the first optical component such that the laser beam exiting the first optical component at least partially sweeps across a first sensor. The method also includes rastering the laser beam using the second optical component such that the laser beam exiting the second optical component at least partially sweeps across a second sensor. The method also includes determining laser beam characteristics based on data received from the first sensor and the second sensor to facilitate performing laser beam diagnostics.

[0009] In yet another embodiment, the present invention relates to a method for forming a laser beam configured to generate one of deep ultraviolet (DUV) light and extreme ultraviolet (EUV) light for use in lithography, the laser beam passing through at least a first optical component and a second optical component of an optical train in a lithography system. The method includes directing the laser beam to a first subregion of the second optical component using the first optical component during a first operating period of the lithography system. The method also includes thereafter directing the laser beam to a second subregion of the second optical component using the first optical component during a second operating period of the lithography system, whereby one or more components in the optical train are configured to align the laser beam such that an impingement point of the laser beam after exiting the optical train remains constant regardless of whether the lithography system is operating during the first operating period or the second operating period. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements and in which:

[0011] Figure 1 An example simplified optical train is shown with three example optical components (mirrors).

[0012] Figure 2A Shown is a sensor attached to the back side of the mirror.

[0013] Figure 2B is a side view showing the sensor attached to a board with through holes.

[0014] Figure 2C The sensor is shown attached to a fixture that removably extends down in front of the mirror to receive the laser beam as it sweeps across the sensor.

[0015] Figure 2D The sensor is shown positioned outside the periphery of the reflector.

[0016] Figure 3 A method for laser beam alignment according to one or more embodiments of the present invention is shown.

[0017] Figure 4A The laser beam is shown with the laser beam footprint as it passes through the virtual plane.

[0018] Figure 4B shows a laser beam with a rectangular laser beam footprint

[0019] Figure 4C A sensor is shown with a sensor surface area and a perimeter.

[0020] Figure 5AA situation is shown where the laser beam footprint of the laser beam impinges outside the perimeter of the sensor surface.

[0021] Figure 5B A situation is shown where the laser beam footprint of the laser beam overlaps the periphery of the sensor surface.

[0022] Figure 5C A situation is shown in which the laser beam footprint of the laser beam has left the periphery of the sensor surface.

[0023] Figure 6 Three example mirrors and two downstream sensors are shown.

[0024] Figure 7 A method for performing beam diagnostics according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0025] The present invention will now be described in detail with reference to certain embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without some or all of these specific details. In other instances, well-known process steps and / or structures have not been described in detail in order to avoid unnecessarily obscuring the present invention.

[0026] In one or more embodiments of the present invention, improved apparatus and methods for laser beam alignment and laser beam diagnostics are disclosed. In one or more embodiments, the physical setup of an upstream optical component is changed over time (preferably over a short period of time) such that the laser beam rasterizes (or sweeps) across a portion or the entire downstream sensor in accordance with the changed physical setup of the upstream optical component. During the sweep of the laser beam, the physical setup of the upstream optical component is recorded and correlated with the laser beam impact location on the downstream sensor, thereby establishing correlation data between the physical setup of the upstream optical component and the laser beam impact point on the downstream sensor. Note that according to one or more embodiments of the present invention, the alignment method relies on collecting data related to multiple laser impact points on the sensor in response to the changing physical setup of the upstream optical component to establish the correlation. This allows the use of a sensor that is much smaller than the laser beam footprint to establish the correlation, as will be discussed later in this document.

[0027] The physical setup of an optical component may refer to an X / Y / Z translation of the position of the optical component relative to some reference position. Alternatively or additionally, the physical setup of an optical component may refer to how the optical component is "pointed". That is, the physical setup of an optical component may refer to the pitch, yaw and / or tilt pointing of the optical component relative to some pitch / yaw / tilt reference. Further, the physical setup of an optical component may refer to any behavior of the optical component that causes a laser beam exiting the optical component to change the subsequent impact point of the laser beam after exiting the optical component. For example, changing the curvature of a mirror or using an optical component to electronically and / or optically manipulate the beam can change the next downstream impact point of the laser beam after exiting the optical component, and are also examples of changing the physical setup of an optical component that performs rasterization. In the examples herein, translation and pointing changes are used as examples to simplify the discussion, but it should be understood that this does not limit the definition of changing the physical setup of an optical component for the purpose of rasterizing a laser beam exiting the optical component. The physical setup can be performed manually (i.e., by hand) on an optical assembly mounted on a fixture that allows adjustment of the physical setup, or more preferably, by an electromechanical actuator that adjusts the physical setup in response to a control signal, and more preferably, under the control of a digital computer in response to a control signal.

[0028] To further discuss this point using a specific example, for example, if the optical component is a mirror, the physical setup of the mirror may include how to translate the mirror in the X / Y / Z directions and / or the pitch / yaw / tilt pointing of the mirror. As an example, and not intended to be limiting, when a given mirror is translated (i.e., moved in the X, Y, or Z directions) and / or when its pointing is changed (i.e., its pitch, yaw, and / or tilt) to change the impingement point of a laser beam exiting the given mirror on a downstream component (such as a downstream sensor and / or a downstream optical component), such movement or motion (involving translation and / or pointing changes) is referred to herein as "rastering" the given optical component.

[0029] In one or more embodiments (but not a requirement or limitation of the embodiments of the invention herein), the downstream sensor is physically and / or logically associated with a downstream optical component downstream of the upstream optical component. For example, there may be an upstream optical component A and a downstream sensor B, where downstream sensor B is associated with downstream optical component C. Downstream sensor B may be attached directly or indirectly via some mounting device (e.g., an arm or plate) in front of, beside, or behind downstream optical component C. When upstream optical component A changes its physical configuration, the laser beam sweeps across part or all of downstream sensor B, thereby generating the aforementioned correlation data.

[0030] Once the correlation data is generated, the relationship between the physical setup of the upstream optical component and the laser beam impact point on the downstream element is known. It is now also known how changing the physical setup of the upstream optical component will change the downstream impact point. The physical setup of the upstream optical component can then be adjusted to obtain the desired impact point, thereby achieving alignment. In other words, the laser beam can be aligned by performing appropriate translations on the position of the optical component and / or changing the orientation of the optical component to cause the impact point of the laser beam leaving the optical component to impact the desired spatial location, a desired location on the downstream optical component, or a desired location on the downstream sensor. The same technique can be applied continuously (and iteratively, if necessary) to other optical component / sensor pairs downstream of the original upstream optical component to achieve alignment of the entire optical system.

[0031] The correlation data may also be stored in a computer system and / or computer-readable media, and / or made available via a computer network for use by other devices and / or for future use. Such uses may include alignment, beam diagnostics, fault location, maintenance optimization, and the like. The term "computer" or "computer system" as used herein refers to any device having one or more logic units and one or more storage units capable of performing calculations, storing results, and the like, regardless of form factor. For example, a computer may comprise a standalone device and / or a network device and / or a virtual computing device (such as cloud computing).

[0032] In the examples herein, a mirror is used as the optical component to simplify the discussion, although it should be understood that a variety of different types of optical components may be involved in a real-world optical system. Furthermore, for example, changes in pitch angle (up or down) and / or yaw angle (left or right) are used to represent changes in the physical setup of the optical component's mirror. However, it should also be understood that any type of physical setup change (e.g., X / Y / Z translation and / or tilt / pitch / yaw pointing changes) may be involved according to one or more embodiments of the present invention.

[0033] In order to achieve the aforementioned physical setting changes, such an optical assembly can be mounted on an appropriate mount for the appropriate physical setting changes. For example, such an optical assembly can be mounted on a spring-biased frame to press against an adjustment screw, mounted to be moved via an adjustment mechanism such as a manual adjustment, a voice coil, a linear or nonlinear electromechanical actuator, or a motor. A stepper motor is an example of an electromechanical actuator that can directly or indirectly (e.g., via screws, gears, chains, belts, etc.) perform physical setting changes on a suitably mounted optical assembly. Even manually adjustable mounts can be provided to allow manual alignment by, for example, rotating a screw with a hand tool, or manually adjusting the mounting angle / translation distance via appropriate manual operation on the manually adjustable mount. These are merely examples and are not intended to limit the various embodiments of the present invention.

[0034] Figure 1 An example simplified optical train 100 is shown having three mirrors 102, 104, and 106. Mirror 106 is downstream relative to mirror 104, which is downstream relative to mirror 102. A laser beam 108 enters optical train 100 in the direction of arrow 110A and exits optical train 100 in the direction of arrow 110B.

[0035] Also shown are two sensors 114 and 116. Sensor 114 is downstream of reflector 102, while sensor 116 is downstream of reflector 104. In one embodiment, sensor 114 is attached to the back of reflector 104. In one embodiment, sensor 114 and / or sensor 116 are configured to detect a laser wavelength of approximately 193 nm. In another embodiment, sensor 114 and / or sensor 116 are configured to detect a laser wavelength of approximately 248 nm. The term "approximately 193 nm" refers to a wavelength of 193 nm + / - 10%, more preferably 193 nm + / - 5%, and even more preferably 193 nm + / - 2% or less. The term "approximately 248 nm" refers to a wavelength of 248 nm + / - 10%, more preferably 248 nm + / - 5%, and even more preferably 248 nm + / - 2% or less. However, it should be understood that embodiments of the present invention are not limited to any particular laser wavelength, even though they may be very useful for laser wavelengths employed to generate deep ultraviolet (DUV) or extreme ultraviolet (EUV) light for photolithography of semiconductor wafers.

[0036] exist Figure 1 In the example shown, although the reflector 104 is primarily designed to reflect light, a small amount of light can pass through its reflective layer and be sensed by the sensor 114. In one example, it has been observed that the sensor is generally able to detect light even when the reflective layer of the reflector in front of the reflector reflects more than 99% of the light striking the reflective layer. According to one or more embodiments of the present invention, this method of attaching a sensor to the back of an optical assembly (such as the reflector 104) is a highly space-efficient method for achieving laser beam alignment. Additionally, the space efficiency and simplicity of this method make it simple to retrofit an existing optical train design with a sensor to achieve laser beam alignment.

[0037] This is Figure 2A, where the sensor 114A is shown as being attached to the back side of the reflector 104A. For example, the attachment may be performed using an appropriate bonding method, or may be performed using a mechanical clamp. The sensor 114A may be attached directly to the back side of the reflector 104A, with the sensor surface pointing to receive light entering the reflective layer from upstream. Alternatively, a physical component having a plate-like or any other physical shape may have one or more small holes drilled therein, and the sensor surface may face the physical component so that only a small portion of the sensor is available for receiving light. The component comprising the sensor and the physical component may then be positioned so that the mirror 104A is disposed between the upstream optical component that performs rasterization on the light beam and the component comprising the sensor and the physical component. This allows a relatively large sensor (which may be cheaper or easier to produce) to be presented as a smaller sensor because it only receives a portion of the laser beam footprint, thereby increasing the detection granularity and / or accuracy, thereby improving the correlation data.

[0038] Figure 2B 2 is a side view showing sensor 222 attached to plate 224 (a plate is used as an example here and is not intended to limit the shape of the physical component, which limits the size of the laser beam that strikes the sensor), which is in turn attached to the back of mirror 226. A hole 228 in plate 224 allows only a portion of sensor 222 to receive light via hole 228, with other portions of the sensor surface of sensor 222 being blocked by plate 224, thereby allowing sensor 222 to act as a much smaller sensor than the physical size of the sensor surface of sensor 222 would indicate.

[0039] The downstream sensor can also be mounted on a fixture to removably extend into the laser path in front of the downstream reflector to receive light from the upstream reflector. Figure 2C 246 so as to receive the laser beam 248 as it sweeps past the sensor 242. In this position, the sensor 242 and the fixture 244 are positioned so that the components including the sensor 242 and the fixture 244 are disposed between the downstream mirror and the upstream mirror that performs the rasterization of the raster beam. After alignment is complete, the fixture 244 and the sensor 242 can be withdrawn or moved upwardly so as not to interfere with laser operation.

[0040] The downstream sensor can also be removably or permanently mounted beside (i.e., outside of the periphery of) a downstream optical component (such as a mirror) to receive light from an upstream optical component that performs rasterization on the beam. Side mounting is beneficial in situations where the normal beam path needs to be changed to obtain correlation data (such as in an optical resonator), or when it is desirable to minimize the exposure of the sensor to laser light during the production process (e.g., after alignment is performed and the optical train is used for lithography production purposes, minimizing the exposure of the sensor to laser light during the production process can extend the useful life of the sensor). This is particularly useful in situations where the normal beam path needs to be changed to obtain correlation data (such as in an optical resonator), or when it is desirable to minimize the exposure of the sensor to laser light during the production process (e.g., after alignment is performed and the optical train is used for lithography production purposes, minimizing the exposure of the sensor to laser light during the production process can extend the useful life of the sensor). Figure 2D , where the sensor 252 is removably or permanently disposed on the side of (ie, outside of the periphery of) the reflector 254 on the fixture 256.

[0041] In one or more embodiments, the downstream sensor does not need to be logically or physically associated with the downstream optical component in order to receive light from the upstream optical component and achieve alignment. What is important is that the downstream sensor and the upstream optical component are paired so that the downstream sensor can receive light and establish data correlation when the physical arrangement of the upstream optical component changes; how the sensor is mounted and whether it is logically or physically associated with any other component is specific to the embodiment and not central to the present invention.

[0042] Figure 3 A method for laser beam alignment according to one or more embodiments of the present invention is shown. In step 302, a laser beam is provided and caused to strike an upstream optical component (such as Figure 1 In step 306, the physical configuration of the upstream optical assembly is changed over time to allow the laser beam exiting the upstream optical assembly to sweep across a portion or the entire downstream sensor. For example, the physical configuration of the upstream optical assembly may be changed via X / Y / Z translation and / or pitch / yaw / tilt pointing changes.

[0043] As the laser beam sweeps across the downstream sensor, data regarding the impact of the laser beam on the sensor surface is collected from the downstream sensor (step 308). Data regarding the physical setup of the upstream optical assembly is also collected from hardware associated with the upstream optical assembly. For example, the yaw, pitch, and / or tilt pointing angles of the mirror can be obtained from the mirror's electromechanical actuator or from other mounting hardware (if no electromechanical actuator is employed) and correlated with the laser beam impact data on the sensor.

[0044] In step 310, a table or database of correlation data is then generated to indicate the laser beam impingement point as a function of the physical setup of the upstream optical component and / or to tell how the laser beam impingement point changes over time as the physical setup of the upstream optical component changes.

[0045] In step 312, the correlation data is used to determine a physical setup (e.g., X / Y / Z translation and / or yaw / pitch / tilt pointing) of the upstream optical assembly suitable for achieving a desired laser beam impingement point on the downstream optical assembly and / or downstream sensor.

[0046] In step 314, the upstream optical component physical setup is changed to achieve a desired laser beam impingement point on the downstream optical component and / or the downstream sensor using the correlation data calculated in step 310 and / or the desired physical setup data determined in step 312. At this point, the laser beam exiting the upstream component is aligned relative to the downstream optical component (e.g., the downstream optical component and / or the downstream sensor).

[0047] The sensor downstream of the optical assembly can be used to align the subsequent optical assembly downstream of the downstream optical assembly in optional step 316. Alignment can be performed continuously (and iteratively if necessary) until the entire optical train is aligned with the laser beam.

[0048] As discussed, as the physical setup of the upstream optical components changes, the laser beam sweeps across part or all of the downstream sensor. When using sensor data to determine the laser beam impingement point, there are a few considerations that may be helpful. For the purposes of this discussion, the concept of a laser beam footprint is used. Figure 4A A laser beam is shown having a laser beam footprint 404 as it passes through a virtual plane 406. The footprint can have any shape, including a circle (in Figure 4A 404 in the case of rectangle ( Figure 4B 408) or any arbitrary shape. Figure 4C A sensor 420 is shown having a sensor surface area 422 and a perimeter 424. Figure 4A and 4B Coverage area and Figure 4C The example of a sensor is used to discuss some considerations that may be useful in creating the above correlation data.

[0049] In one or more embodiments, the sensor employed may have a sensor surface area that is smaller than the footprint of the laser beam. In some cases, sensors large enough to sense the entire laser beam footprint may be prohibitively expensive or unavailable, particularly in the high-frequency range of lasers, and smaller versions of such sensors may be available at a more affordable price.

[0050] When the laser beam's footprint begins its scan in response to a change in the physical setup of the upstream optical components, there may initially be no overlap between the laser beam's footprint and the sensor surface. Figure 5A5 (Case 1), where the laser beam footprint 502 of the laser beam impinges outside of the perimeter 506 of the sensor surface 508. At this point, the sensor registers that no laser light is impinging upon it.

[0051] At some point, the laser beam footprint 502 begins to intersect the perimeter 506 of the sensor surface 508. Figure 5B As shown in Figure 2 (case 2), as the laser beam begins to intersect the sensor surface during scanning, the sensor will sense some laser light impinging on its sensor surface, and the data output by the sensor will change. This information is recorded along with the corresponding physical setup data of the upstream optical components at the time the intersection begins.

[0052] The laser beam footprint 502 continues to sweep across the sensor surface 508 and at some point leaves the sensor surface 508. As the laser beam footprint 502 leaves and no longer overlaps the perimeter 506 of the sensor surface 508 ( Figure 5C In case 3) shown, the sensor transitions from detecting some laser light to detecting no laser light, and its sensor output changes accordingly. Note this, along with the corresponding physical setup data for the upstream optical components at the end of the intersection.

[0053] The physical setup data collected in Case 2 (overlap start) and Case 3 (overlap end) provide information about the impact point of the laser beam relative to the physical setup data of the upstream optical component (e.g., obtained from the electromechanical actuator of the optical component).

[0054] In some cases, multiple passes across part or all of the sensor's surface in one or more directions (such as horizontal, vertical, or horizontal+vertical) or on overlapping or non-overlapping paths (may be in response to Figure 5B In other cases, data collection continues up to the overlap start point (case 2) when the data sensed in case 2 ( Figure 5B ) and case 3 at the end of overlap ( Figure 5C ) to facilitate extrapolation to alternatively or additionally improve the correlation data regarding the position of the laser beam footprint relative to the position of the sensor surface. This allows for more precise determination of the laser beam impact point, thereby improving the accuracy of the correlation data. This is true even if the size of the sensor surface is equal to or larger than the laser beam footprint, as this embodiment relies at least in part on when the overlap begins and / or ends, rather than solely on whether the sensor surface can capture the entire footprint of the laser beam.

[0055] As mentioned, the sensor can be mounted to a physical component (such as, but not limited to, a plate) that has a hole drilled in it, and the sensor receives laser light through the hole in the physical component so that the active sensor area appears smaller relative to the received laser light. This has the advantage of improving the data resolution and granularity, thereby also improving the accuracy of the correlation data.

[0056] Regarding laser beam diagnostics, the laser light received by the sensor can also be used to characterize or diagnose the laser beam. This can be accomplished by the sensor receiving laser light from its upstream optical component and comparing the laser light characteristics to a reference. As another example, existing laser beam diagnostic software and / or techniques can be used to analyze the relevant characteristics of the laser beam. The laser light characteristics can be, for example, one or more of its brightness, frequency, phase, energy, etc. The sensor can also maintain a history of the laser light characteristics received over time. This has the advantage of enabling engineers to perform data analysis to identify which optical components tend to fail earlier and more quickly and address weak links in the optical train (because the failure of any one poorly designed optical component can cause damage to the entire optical train, even if other optical components may have a long service life). This also has the advantage of enabling engineers to detect degradation in optical characteristic patterns and predict when maintenance is needed to optimize maintenance plans and / or schedules.

[0057] In one or more embodiments, monitoring multiple sensors in an optical train generates a coarse determination of the location of a fault in the optical train. For example, if sensor A deems the laser beam characteristics satisfactory, but sensor B, located immediately downstream, detects an anomaly, this evidence may indicate that the fault is somewhere between sensor A and sensor B in the optical train, allowing engineers to more quickly locate the fault and repair it. In an optical train that can have 20 to 40 optical components, the ability to quickly locate the fault can save valuable time.

[0058] Because the downstream sensor is placed at or near the back of the downstream optical assembly in a space-saving manner (as previously described), embodiments of the present invention allow for quick and cost-effective retrofitting of existing optical trains to provide the capability to perform laser beam diagnostics.

[0059] When performing laser beam diagnostics, smaller sensors allow for greater granularity relative to damage inspection of upstream optical components. This is contrary to the current school of thought, which focuses on making sensors large enough to cover the laser footprint. As discussed, physical components with holes can be used to provide small holes for sensing by the sensor, thereby improving diagnostic accuracy. However, even larger sensors can be used for diagnostic purposes (for example, by considering energy levels or some composite information) to localize problems between two sensors in the optical train and to establish a history of laser beam characteristics over time for improving optical component design and optimizing maintenance.

[0060] In one or more embodiments, an upstream optical component can be "inspected" a small area at a time. For example, a mirror can be inspected a small area of its surface at a time using the techniques disclosed herein. Figure 6 Three example mirrors 602, 604, and 606 are shown, with mirror 606 downstream of mirror 604. Mirror 604, in turn, is downstream of mirror 602. Sensor 614 is downstream of mirror 602, while sensor 616 is downstream of mirror 604. By changing the physical setup of mirror 602 (e.g., X / Y / Z translation and / or yaw / pitch / tilt orientation), the laser beam reflected from mirror 602 can strike a different area of mirror 604 (such as 630 or 632). Each time a new area of mirror 604 is illuminated, that area of mirror 604 can be inspected by a sensor downstream of the mirror. Inspection can be performed by changing the physical setup of mirror 604 (e.g., by changing its pitch / yaw / tilt orientation) so that the beam exiting mirror 604 sweeps across downstream sensor 616. Sensor 616 can then record the characteristics of the beam to confirm the health of that area (such as 630 or 632) on its upstream reflector 604. In this way, each area of the reflector 604 can be sequentially inspected for problems such as localized reflective surface degradation. In an example embodiment, multiple areas of the reflector 604 can be sequentially inspected using this technique.

[0061] Figure 7 A method for performing beam diagnostics according to an embodiment of the present invention is shown. In step 702, a laser beam is provided and incident upon an upstream optical component such as Figure 1 The optical train 100 is configured to be aligned with the optical system 102. In step 706, the physical configuration of the upstream optical assembly is changed to allow the laser beam to sweep across part or all of the downstream sensor. For example, the physical configuration of the upstream optical assembly can be changed via X / Y / Z translation and / or pitch / yaw / tilt pointing changes.

[0062] As the laser beam sweeps past the downstream sensor, data regarding the characteristics of the laser beam to be monitored is collected by the downstream sensor (step 708). Figure 3 step), correlation data has already been acquired earlier to facilitate accurate laser beam pointing, and physical setup data can be provided to enable the upstream optical assembly to point the laser beam, for example, directly at the downstream sensor to save time.

[0063] In step 710, the laser beam characteristics are analyzed to detect problems with the laser beam characteristics (which may indicate a problem with one or more upstream optical components). For example, the laser beam characteristics received by the one or more sensors may be compared with reference laser beam characteristics to detect whether one or more relevant characteristics (e.g., power, coherence, divergence, etc.) have fallen below an acceptable performance threshold. Diagnosis may also include comparing the laser beam characteristics received by the one or more sensors with historical laser beam characteristic data acquired in the past for the same one or more sensors to detect possible changes or degradation trends in beam quality. In one embodiment, the laser beam characteristic data received by the one or more sensors over time can help engineers confirm maintenance predictions regarding when optical components upstream of the sensors need to be maintained / replaced.

[0064] If multiple sensors are monitored in the optical train, any issues can be localized to the components (optical or non-optical) between the two sensors, as previously described. For example, if the laser beam characteristics at sensors 1, 2, and 3 are confirmed to be acceptable, but sensor 4 in the optical train reports that the laser beam quality has been compromised, engineers can reasonably conclude that the problem is likely localized to the components between sensors 3 and 4 (in this example, the laser beam traverses a path detectable by sensors 1, 2, 3, and 4, in sequence).

[0065] In optional step 712, laser beam characteristics may be recorded over time to create a database of time-stamped laser beam characteristic data. This database enables engineers to optimize maintenance and / or predict failures and / or perform failure analysis.

[0066] In one or more embodiments, the desired alignment of each optical component may include consideration of directing the laser beam to strike different sub-regions of the downstream optical component to avoid overstressing any particular sub-region of the downstream optical component. For example, during a first period of photolithographic production of several weeks or months or multiple laser pulses (e.g., for production processing of semiconductor wafers), the upstream optical component X may direct the outgoing laser beam to strike a sub-region of the downstream optical component Y. At the expiration of the first operating period, the upstream optical component X may change its physical setup to direct the outgoing laser beam to strike a different sub-region B of the downstream optical component Y. This approach is similar to combining Figure 3The alignment steps discussed above now include the desired alignment step, which now includes consideration for switching between different sub-regions of the downstream optical assembly to avoid over-stressing any one sub-region over time. Alignment of the laser beam can be performed by the downstream optical assembly Y or by a component downstream thereof to ensure that the laser beam exiting the optical train strikes the desired location / target, regardless of which sub-region / operating period is involved. This alignment aspect has already been discussed herein.

[0067] A schedule can be pre-established to expose different sub-regions of the downstream optical assembly to the laser beam over time to avoid overstressing any sub-region. Switching between sub-regions of the downstream optical assembly can also be performed in response to diagnostic data from a sensor that informs of laser beam quality degradation issues at the upstream optical assembly(ies) (e.g., using the positioning concepts discussed previously). Furthermore, since the entire optical train or a portion thereof can be aligned as previously discussed, modeling can be employed to calculate various alternative laser beam paths in response to different physical setup settings of the individual optical components to ensure that no sub-region on any optical assembly is overstressed and that the laser beam is properly aligned for use upon exiting the optical train, as previously described. This approach can advantageously allow the optical train to operate for a longer period of time before maintenance may be required due to laser beam quality issues caused by degradation of optical components (such as mirrors).

[0068] From the foregoing it can be appreciated that embodiments of the present invention allow for alignment and / or diagnosis of laser beams in a highly space efficient, low cost and / or retrofit friendly manner when involving a single optical component or when involving multiple optical components in an optical train.

[0069] The following examples are various example implementations of devices and processes illustrating some implementations contemplated in this disclosure.

[0070] Example 1. A method for optimizing a laser beam in a lithography system, the laser beam passing through an optical train including a plurality of optical components, the method comprising:

[0071] performing rastering using a first optical component of the plurality of optical components such that the laser beam exiting the first optical component at least partially sweeps across a first sensor in response to the rastering using the first optical component;

[0072] forming a correlation between a physical setup of the first optical assembly and an impingement point of the laser beam using data acquired from the first sensor during the rasterization using the first optical assembly;

[0073] using data obtained from the correlation to confirm a first physical configuration of the first optical component that causes the impingement point of the laser beam exiting the first optical component to impinge on a desired point on a second optical component; and

[0074] The laser beam exiting the first optical assembly is aligned relative to the second optical assembly by aligning the first optical assembly according to the first physical arrangement.

[0075] Example 2. The method of example 1, wherein the first sensor has a footprint smaller than a footprint of the laser beam.

[0076] Example 3. The method of example 1, wherein rastering the laser beam exiting the first optical component comprises changing a pointing direction of the first optical component.

[0077] Example 4. The method of example 1, wherein rastering the laser beam exiting the first optical component comprises translating a position of the first optical component.

[0078] Example 5. The method of Example 1, wherein the first sensor is disposed outside of a periphery of the second optical assembly.

[0079] Example 6. The method of example 1, wherein the first sensor is positioned such that the second optical component is disposed between the first sensor and the first optical component.

[0080] Example 7. The method of Example 6, wherein the first sensor is attached to the second optical component using an adhesive, wherein the second optical component is a mirror.

[0081] Example 8. The method of Example 6, wherein the first sensor is attached to the second optical component using a mechanical clamp, wherein the second optical component is a mirror.

[0082] Example 9. The method of Example 6, further comprising a physical component having a hole configured to allow only a portion of the laser beam exiting the first optical component to enter the first sensor through the hole, the physical component being positioned between the first optical component and the first sensor, the hole having a footprint that is smaller than a footprint of the laser beam exiting the first optical component, wherein the first sensor and the physical component are positioned such that the second optical component is disposed between the first optical component and a component including the first sensor and the physical component.

[0083] Example 10. The method of Example 6, further comprising a physical component having a hole configured to allow only a portion of the laser beam exiting the first optical component to enter the first sensor through the hole, the physical component being positioned between the first optical component and the first sensor, the hole having a footprint that is smaller than a footprint of the laser beam exiting the first optical component, wherein the first sensor and the physical component are positioned such that a component including the first sensor and the physical component is disposed between the second optical component and the first optical component.

[0084] Example 11. The method of Example 1, wherein the first sensor is disposed between the second optical component and the first optical component.

[0085] Example 12. A method according to Example 1, wherein the first sensor is set on a movable fixture so that the first sensor can be moved away from a first sensor position during lithography production, wherein when the first sensor is positioned at the first sensor position during the rasterization performed using the first optical component, the first sensor is set between the first optical component and the second optical component.

[0086] Example 13. The method of Example 1, wherein the first sensor is configured to detect a laser wavelength of approximately 193 nm.

[0087] Example 14. The method of Example 1, wherein the first sensor is configured to detect a laser wavelength of approximately 248 nm.

[0088] Example 15. The method of Example 1, further comprising:

[0089] performing rastering using the second optical component of the plurality of optical components such that the laser beam exiting the second optical component at least partially sweeps across a second sensor in response to the rastering using the second optical component;

[0090] using data acquired from the second sensor during the rasterization using the second optical assembly, forming a correlation between a physical setup of the second optical assembly and an impingement point of the laser beam exiting the second optical assembly;

[0091] using data obtained from the correlation between the physical setting of the second optical component and the impingement point of the laser beam exiting the second optical component, identifying a second physical setting of the second optical component that will cause the impingement point of the laser beam exiting the second optical component to impinge on a desired point on a third optical component; and

[0092] The laser beam exiting the second optical assembly is aligned relative to the third optical assembly by aligning the second optical assembly according to the second physical setting determined by confirming the second physical setting.

[0093] Example 16. A lithography system having an optical train including a plurality of optical components configured to deliver at least a laser beam from one location to another, the lithography system comprising:

[0094] a first optical assembly configured to perform at least rasterization on the laser beam exiting the first optical assembly to cause the laser beam exiting the first optical assembly to at least partially sweep across a first sensor; and

[0095] A second optical assembly is configured to at least receive the laser beam exiting the first optical assembly and perform rasterization on the laser beam exiting the second optical assembly to cause the laser beam exiting the second optical assembly to at least partially sweep across a second sensor.

[0096] Example 17. The lithography system of Example 16, wherein a footprint of the first sensor is smaller than a footprint of the laser beam exiting the first optical assembly.

[0097] Example 18. The lithography system of Example 16, wherein performing the rasterization using the first optical component comprises changing an orientation of the first optical component.

[0098] Example 19. The lithography system of Example 16, wherein performing the rasterization using the first optical component comprises translating a position of the first optical component.

[0099] Example 20. The lithography system of Example 16, wherein the first sensor is positioned such that the second optical component is disposed between the first sensor and the first optical component.

[0100] Example 21. The lithography system of Example 20, wherein the first sensor is attached to the second optical component using an adhesive, wherein the second optical component is a mirror.

[0101] Example 22. A lithography system according to Example 20, wherein the first sensor is coupled to a physical component having a hole, the hole being configured to allow only a portion of the laser beam exiting the first optical component to enter the first sensor through the hole, the footprint of the hole being smaller than the footprint of the laser beam exiting the first optical component, wherein the first sensor and the physical component are positioned such that the second optical component is disposed between the first optical component and a component including the first sensor and the physical component.

[0102] Example 23. The lithography system of Example 16, wherein the first sensor is configured to detect a laser wavelength of approximately 193 nm.

[0103] Example 24. The lithography system of Example 16, wherein the first sensor is configured to detect a laser wavelength of approximately 248 nm.

[0104] Example 25. A method for diagnosing a laser beam configured to generate one of deep ultraviolet (DUV) light and extreme ultraviolet (EUV) light for use in lithography, the laser beam passing through at least a first optical component and a second optical component of an optical train in a lithography system, the method comprising:

[0105] rastering using the first optical assembly so that the laser beam exiting the first optical assembly at least partially sweeps across a first sensor;

[0106] rastering using a second optical assembly so that the laser beam exiting the second optical assembly at least partially sweeps across a second sensor; and

[0107] Laser beam characteristics are identified based on data received from the first sensor and the second sensor to facilitate performing the diagnostics of the laser beam.

[0108] Example 26. The method of Example 25, wherein the diagnosing comprises localizing a laser beam quality problem to a component in a segment of the optical train between the first sensor and the second sensor.

[0109] Example 27. The method of Example 25, wherein the diagnosing comprises comparing laser beam characteristics from data acquired by at least one of the first sensor and the second sensor with reference laser beam characteristics.

[0110] Example 28. The method of Example 25, wherein the diagnosing comprises comparing laser beam characteristics from data acquired by the first sensor with historical laser beam characteristic data acquired from the first sensor in the past.

[0111] Example 29. The method of Example 25, further comprising confirming a maintenance prediction for the first optical assembly from a laser beam quality degradation trend derived from data received by the first sensor over time.

[0112] Example 30. A method for forming a laser beam configured to generate one of deep ultraviolet (DUV) light and extreme ultraviolet (EUV) light for use in lithography, the laser beam passing through at least a first optical component and a second optical component of an optical train in a lithography system, the method comprising:

[0113] During a first operating period of the lithography system, directing the laser beam to a first sub-region of the second optical assembly using the first optical assembly; and

[0114] Thereafter, during a second operating period of the lithography system, the laser beam is directed to a second sub-region of the second optical assembly using the first optical assembly, whereby one or more components of the optical train are configured to align the laser beam such that an impingement point of the laser beam after exiting the optical train does not change regardless of whether the lithography system is operating during the first operating period or the second operating period.

[0115] Example 31. The method of Example 30, wherein the switching from the first sub-area to the second sub-area is performed in response to a predetermined schedule.

[0116] Example 32. The method of Example 30, wherein switching from the first sub-region to the second sub-region is performed in response to an analysis of laser beam characteristics of the laser beam exiting the second optical component.

[0117] Although the present invention has been described in terms of several preferred embodiments, there are variations, permutations, and equivalents that fall within the scope of the present invention. It should be understood that the present invention also includes these variations, permutations, and equivalents. It should also be noted that there are many alternative ways to implement the method and apparatus of the present invention. Although various examples are provided herein, it is intended that these examples are illustrative and not limiting of the present invention.

[0118] The embodiments may be further described using the following terms:

[0119] 1. A method for optimizing a laser beam in a lithography system, wherein the laser beam passes through an optical train comprising a plurality of optical components, the method comprising:

[0120] performing rastering using a first optical component of the plurality of optical components such that the laser beam exiting the first optical component at least partially sweeps across a first sensor in response to the rastering using the first optical component;

[0121] using data acquired from the first sensor during the rasterization using the first optical assembly to form a correlation between a physical setup of the first optical assembly and an impingement point of the laser beam;

[0122] using data obtained from the correlation to confirm a first physical configuration of the first optical component that causes the impingement point of the laser beam exiting the first optical component to impinge on a desired point on a second optical component; and

[0123] The laser beam exiting the first optical assembly is aligned relative to the second optical assembly by aligning the first optical assembly according to the first physical arrangement.

[0124] 2. The method of clause 1, wherein the first sensor has a footprint smaller than the laser beam's footprint.

[0125] 3. The method of clause 1, wherein rastering the laser beam exiting the first optical component comprises changing the pointing direction of the first optical component.

[0126] 4. The method of clause 1, wherein rastering the laser beam exiting the first optical component comprises translating a position of the first optical component.

[0127] 5. The method of clause 1, wherein the first sensor is disposed outside of a periphery of the second optical assembly.

[0128] 6. The method of clause 1, wherein the first sensor is positioned such that the second optical assembly is disposed between the first sensor and the first optical assembly.

[0129] 7. The method of clause 6, wherein the first sensor is attached to the second optical component using an adhesive, wherein the second optical component is a mirror.

[0130] 8. The method of clause 6, wherein the first sensor is attached to the second optical component using a mechanical clamp, wherein the second optical component is a mirror.

[0131] 9. The method according to clause 6 further includes a physical component having a hole, wherein the hole is configured to allow only a portion of the laser beam leaving the first optical component to enter the first sensor through the hole, the physical component is positioned between the first optical component and the first sensor, and the coverage area of the hole is smaller than the coverage area of the laser beam leaving the first optical component, wherein the first sensor and the physical component are positioned so that the second optical component is disposed between the first optical component and a component including the first sensor and the physical component.

[0132] 10. The method according to clause 6 further includes a physical component having a hole, wherein the hole is configured to allow only a portion of the laser beam leaving the first optical component to enter the first sensor through the hole, the physical component is positioned between the first optical component and the first sensor, and the coverage area of the hole is smaller than the coverage area of the laser beam leaving the first optical component, wherein the first sensor and the physical component are positioned so that the components including the first sensor and the physical component are disposed between the second optical component and the first optical component.

[0133] 11. The method of clause 1, wherein the first sensor is disposed between the second optical component and the first optical component.

[0134] 12. A method according to claim 1, wherein the first sensor is disposed on a movable fixture so that the first sensor can be moved away from a first sensor position during lithography production, wherein when the first sensor is positioned at the first sensor position during the rastering performed using the first optical component, the first sensor is disposed between the first optical component and the second optical component.

[0135] 13. The method of clause 1, wherein the first sensor is configured to detect a laser wavelength of approximately 193 nm.

[0136] 14. The method of clause 1, wherein the first sensor is configured to detect a laser wavelength of approximately 248 nm.

[0137] 15. The method of clause 1, further comprising:

[0138] performing rastering using the second optical component of the plurality of optical components such that the laser beam exiting the second optical component at least partially sweeps across a second sensor in response to the rastering using the second optical component;

[0139] using data acquired from the second sensor during the rasterization using the second optical assembly, forming a correlation between a physical setup of the second optical assembly and an impingement point of the laser beam exiting the second optical assembly;

[0140] using data obtained from the correlation between the physical setting of the second optical component and the impingement point of the laser beam exiting the second optical component, identifying a second physical setting of the second optical component that causes the impingement point of the laser beam exiting the second optical component to impinge on a desired point on a third optical component; and

[0141] The laser beam exiting the second optical assembly is aligned relative to the third optical assembly by aligning the second optical assembly according to the second physical setting determined by confirming the second physical setting.

[0142] 16. A lithography system having an optical train comprising a plurality of optical components configured to deliver at least a laser beam from one location to another, the lithography system comprising:

[0143] a first optical assembly configured to perform at least rasterization on the laser beam exiting the first optical assembly to cause the laser beam exiting the first optical assembly to at least partially sweep across a first sensor; and

[0144] A second optical assembly is configured to at least receive the laser beam exiting the first optical assembly and perform rasterization on the laser beam exiting the second optical assembly to cause the laser beam exiting the second optical assembly to at least partially sweep across a second sensor.

[0145] 17. The lithographic system of clause 16, wherein a footprint of the first sensor is smaller than a footprint of the laser beam exiting the first optical assembly.

[0146] 18. The lithography system of clause 16, wherein performing the rasterizing using the first optical component comprises changing an orientation of the first optical component.

[0147] 19. The lithography system of clause 16, wherein performing the rasterizing using the first optical component comprises translating a position of the first optical component.

[0148] 20. The lithographic system of clause 16, wherein the first sensor is positioned such that the second optical assembly is disposed between the first sensor and the first optical assembly.

[0149] 21. The lithographic system of clause 20, wherein the first sensor is attached to the second optical component using an adhesive, wherein the second optical component is a mirror.

[0150] 22. A lithography system according to claim 20, wherein the first sensor is coupled to a physical component having a hole, the hole being configured to allow only a portion of the laser beam exiting the first optical component to enter the first sensor through the hole, the footprint of the hole being smaller than the footprint of the laser beam exiting the first optical component, wherein the first sensor and the physical component are positioned such that the second optical component is disposed between the first optical component and a component including the first sensor and the physical component.

[0151] 23. The lithographic system of clause 16, wherein the first sensor is configured to detect a laser wavelength of approximately 193 nm.

[0152] 24. The lithographic system of clause 16, wherein the first sensor is configured to detect a laser wavelength of approximately 248 nm.

Claims

1. A method for optimizing a laser beam in a lithography system, wherein the laser beam passes through an optical train comprising a plurality of optical components, the method comprising: performing rastering using a first optical component of the plurality of optical components such that the laser beam exiting the first optical component at least partially sweeps across a first sensor in response to the rastering using the first optical component; forming a correlation between a physical setup of the first optical assembly and an impingement point of the laser beam using data acquired from the first sensor during the rasterization using the first optical assembly; using data obtained from the correlation to identify a first physical configuration of the first optical component that will cause the impingement point of the laser beam exiting the first optical component to impinge on a desired point on a second optical component; as well as By aligning the first optical assembly according to the first physical setup, the laser beam exiting the first optical assembly is aligned relative to the second optical assembly. 2 . The method of claim 1 , wherein the first sensor has a footprint smaller than the laser beam's footprint.

3. The method of claim 1 , wherein rastering the laser beam exiting the first optical assembly comprises: The orientation of the first optical component is changed.

4. The method of claim 1 , wherein rastering the laser beam exiting the first optical assembly comprises: The position of the first optical component is translated. The method of claim 1 , wherein the first sensor is disposed outside a periphery of the second optical assembly. 6 . The method of claim 1 , wherein the first sensor is positioned such that the second optical assembly is disposed between the first sensor and the first optical assembly. 7 . The method of claim 6 , wherein the first sensor is attached to the second optical component using an adhesive, wherein the second optical component is a mirror.

8. The method of claim 6, wherein the first sensor is attached to the second optical component using a mechanical fixture, wherein the second optical component is a mirror.

9. The method of claim 6 , further comprising a physical assembly having an aperture configured to allow only a portion of the laser beam exiting the first optical assembly to pass through the aperture to the first sensor, the physical assembly being positioned between the first optical assembly and the first sensor, the aperture having a footprint that is smaller than a footprint of the laser beam exiting the first optical assembly, wherein the first sensor and the physical assembly are positioned such that the second optical assembly is disposed between the first optical assembly and a component comprising the first sensor and the physical assembly.

10. The method of claim 6, further comprising a physical assembly having an aperture configured to allow only a portion of the laser beam exiting the first optical assembly to enter the first sensor through the aperture, the physical assembly being positioned between the first optical assembly and the first sensor, the aperture having a footprint that is smaller than a footprint of the laser beam exiting the first optical assembly, wherein the first sensor and the physical assembly are positioned such that components including the first sensor and the physical assembly are disposed between the second optical assembly and the first optical assembly.

11. The method of claim 1, wherein the first sensor is disposed between the second optical assembly and the first optical assembly.

12. The method of claim 1 , wherein the first sensor is disposed on a movable fixture such that the first sensor can be moved away from a first sensor position during lithography production, wherein when the first sensor is positioned at the first sensor position during the rastering performed using the first optical component, the first sensor is disposed between the first optical component and the second optical component.

13. The method of claim 1, wherein the first sensor is configured to detect a laser wavelength of approximately 193 nm or approximately 248 nm.

14. The method of claim 1, wherein the first sensor is configured to detect a laser wavelength of approximately 248 nm.

15. The method according to claim 1, further comprising: performing rastering using the second optical component of the plurality of optical components such that the laser beam exiting the second optical component at least partially sweeps across a second sensor in response to the rastering using the second optical component; using data acquired from the second sensor during the rasterization using the second optical assembly, forming a correlation between a physical setup of the second optical assembly and an impingement point of the laser beam exiting the second optical assembly; using data obtained from the correlation between the physical setting of the second optical component and the impingement point of the laser beam exiting the second optical component, identifying a second physical setting of the second optical component that will cause the impingement point of the laser beam exiting the second optical component to impinge on a desired point on a third optical component; as well as The laser beam exiting the second optical assembly is aligned relative to the third optical assembly by aligning the second optical assembly according to the second physical setting determined by confirming the second physical setting.

16. A lithography system having an optical train comprising a plurality of optical components configured to deliver at least a laser beam from one location to another, the lithography system comprising: a first optical assembly configured to perform at least rastering on the laser beam exiting the first optical assembly to cause the laser beam exiting the first optical assembly to at least partially sweep across a first sensor; as well as a second optical assembly configured to at least receive the laser beam exiting the first optical assembly and perform rasterization on the laser beam exiting the second optical assembly to cause the laser beam exiting the second optical assembly to at least partially sweep across a second sensor; wherein the first sensor is coupled to a physical assembly having an aperture configured to allow only a portion of the laser beam exiting the first optical assembly to enter the first sensor through the aperture, the aperture having a footprint that is smaller than a footprint of the laser beam exiting the first optical assembly, wherein the first sensor and the physical assembly are positioned such that the second optical assembly is disposed between the first optical assembly and a component including the first sensor and the physical assembly.

17. The lithographic system of claim 16, wherein a footprint of the first sensor is smaller than a footprint of the laser beam exiting the first optical assembly.

18. The lithography system of claim 16, wherein performing the rasterization using the first optical assembly comprises: The orientation of the first optical component is changed.

19. The lithography system of claim 16, wherein performing the rasterization using the first optical assembly comprises: The position of the first optical component is translated.

20. The lithographic system of claim 16, wherein the first sensor is attached to the second optical component using an adhesive, wherein the second optical component is a mirror.

21. The lithographic system of claim 16, wherein the first sensor is configured to detect a laser wavelength of approximately 193 nm.

22. The lithographic system of claim 16, wherein the first sensor is configured to detect a laser wavelength of approximately 248 nm.

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