NL2010629A - Linear imager for wide pellicle detection. - Google Patents

Description

LINEAR IMAGER FOR WIDE PELLICLE DETECTION

Field

[0001] Embodiments of the present invention relates to a system and method to detect the size of reticles and/or films using pellicle dimensions, such that pellicles attached to reticles with a size greater than a threshold are not moved to high speed reticle stage. The invention also relates to reticles and lithographic apparatus that use pellicles. Background

[0002] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., including part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned.

[0003] Lithography is widely recognized as one of the key steps in the manufacture of ICs and other devices and/or stmctures. However, as the dimensions of features made using lithography become smaller, lithography is becoming a more critical factor for enabling miniature IC or other devices and/or stmctures to be manufactured.

[0004] A lithographic apparatus typically includes an illumination system configured to condition a radiation beam, a support structure constructed to hold a patterning device, such as a reticle or mask, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam, a substrate table constructed to hold a substrate, and a projection system configured to project the patterned radiation beam onto a target portion of the substrate.

[0005] Current lithography systems project mask pattern features that are extremely small. Dust or extraneous particulate matter appearing on the surface of the reticle can adversely affect the resulting product. Any particulate matter that deposits on the reticle before or during a lithographic process is likely to distort features in the pattern being projected onto a substrate. Therefore, the smaller the feature size, the smaller the size of particles that it is critical to eliminate from the reticle.

[0006] A pellicle is often used with a reticle. A pellicle is a thin transparent layer that may be stretched over a frame above the surface of a reticle. Pellicles are used to block particles from reaching the patterned side of a reticle surface. Any particles on the pellicle surface are out of the focal plane and should not form an image on the wafer being exposed. However, it is still preferable to keep the pellicle surfaces as particle-free as possible.

SUMMARY

[0007] Therefore, apparatuses and method are needed to efficiently and more precisely measure dimensions of reticles and/or pellicles. To meet this need, embodiments of the present invention are directed to dimension measurements using imaging, and applications thereof.

[0008] According to a first embodiment, an apparatus is provided that includes an illumination source, a sensor, and a processor. The illumination source provides an illumination beam to illuminate a surface of a pellicle. The sensor receives light from the illuminated surface of the pellicle. The processor determines dimensions of the pellicle and determines whether the pellicle be moved for further processing.

[0009] According to another embodiment, there is provided a method for illuminating a surface of a pellicle with an illumination beam. The method further includes receiving light from the illuminated surface of the pellicle and processing the received light for determining dimensions of the pellicle and for determining whether the pellicle be moved for further processing.

[0010] Another embodiment includes a lithography system, which includes a measurement system, a second illumination source, and a projection system. The measurement system includes an illumination source for providing an illumination beam to illuminate a surface of a pellicle, a sensor for receiving light from the illuminated surface of the pellicle, and a processor for determining dimensions of the pellicle and for determining whether the pellicle be moved for further processing. The second illumination source provides a light beam and the projection system projects patterned light beam from a reticle onto a substrate.

[0011] According to a further embodiment, there is provided a method for device manufacturing including assessing dimensions of a pellicle. Assessing dimensions of the pellicle includes illuminating a surface of the pellicle with an illumination beam, receiving light from the illuminated surface of the pellicle, and processing the received light for determining dimensions of the pellicle and for determining whether the pellicle be moved for further processing. The method further includes producing a second illumination beam and illuminating a reticle with the second illumination beam. The method also includes generating a pattern of the second illumination beam from the reticle and projecting the patterned second illumination beam onto a target portion of a substrate.

[0012] Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art(s) to make and use the invention.

[0014] Figure 1 schematically depicts a lithographic apparatus according to an embodiment of the invention.

[0015] Figure 2 is a more detailed schematic view of the lithographic apparatus.

[0016] Figure 3 illustrates a bottom view of an implementation of a pellicle frame width measurement device.

[0017] Figures 4A and 4B illustrate a side view and a bottom view, respectively, of a dimension measurement system using imaging, according to an embodiment.

[0018] Figure 5 illustrates a flow diagram illustrating an example method for dimension measurement using imaging, according to another embodiment.

[0019] Figure 6 illustrates an example computer system that can be used to implement features and embodiments of the present invention.

[0020] The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.

DETAILED DESCRIPTION

[0021] This specification discloses embodiments that incorporate the features of this invention. The disclosed embodiments merely exemplify the invention. The scope of the invention is not limited to the disclosed embodiments. The invention is defined by the clauses appended hereto.

[0022] The embodiments described, and references in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiments described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, stmcture, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, stmcture, or characteristic in connection with other embodiments whether or not explicitly described.

[0023] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion,” respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

[0024] In some embodiments, a lithographic apparatus can include an extreme ultraviolet (EUV) source, which is configured to generate a beam of EUV radiation for EUV lithography. In general, the EUV source is configured in a radiation system (see below), and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

[0025] In the embodiments described herein, the terms “lens” and “lens element,” where the context allows, may refer to any one or combination of various types of optical components, comprising refractive, reflective, magnetic, electromagnetic and electrostatic optical components.

[0026] Further, the terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, comprising ultraviolet (UV) radiation (for example, having a wavelength λ of 365, 248, 193, 157 or 126 nm), extreme ultra-violet (EUV or soft X-ray) radiation (for example, having a wavelength in the range of 5-20 nm, for example, 13.5 nm), or hard X-ray working at less than 5nm, as well as particle beams, such as ion beams or electron beams. Generally, radiation having wavelengths between about 780-3000 nm (or larger) is considered IR radiation. UV refers to radiation with wavelengths of approximately 100-400 nm. Within lithography, it is usually also applied to the wavelengths, which can be produced by a mercury discharge lamp: G-line 436 nm; H-line 405 nm; and/or 1-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by air), refers to radiation having a wavelength of approximately 100-200 nm. Deep UV (DUV) generally refers to radiation having wavelengths ranging from 126 nm to 428 nm, and in an embodiment, an excimer laser can generate DUV radiation used within the lithographic apparatus. It should be appreciated that radiation having a wavelength in the range of, for example, 5-20 nm relates to radiation with a certain wavelength band, of which at least part is in the range of 5-20 nm.

[0027] In the prior known art, devices with proximity sensors (e.g., pellicle frame width measurement devices) are used to make certain that reticles with pellicles wider than a threshold (e.g., 117 mm) are not moved to a high speed reticle stage as this can damage the reticle and/or the stage. The implementation of pellicle frame width measurement devices used four single point sensors that are mounted on a frame such that only two of the sensors should “see” a reticle and/or its corresponding pellicle of an acceptable width. Detecting the pellicles surface is a demanding process due to the fact that pellicles are designed to have very low reflectivity, and their reflectivity is decreasing with advances in reticle designs. In addition, the strong reflection from the pellicle frame can cause crosstalk between the sensors producing ambiguous signals.

[0028] The four single point sensors use software to evaluate the possible combinations of sensor detections and whether the reticle should be passed. This leaves some ambiguity for reticles near the pass criteria. The ambiguity can happen because a sensor may go from 0 -> 1, i.e., indicate a detection falsely for some reason. For example, the sensors detect reflectivity from the pellicle surface it can falsely receive reflectivity from the chrome layer of the reticle as these sensors are made more and more sensitive due to decrease in reflectivity of pellicle. The other reason could be that there may be some play between the reticle vs. robot causing the reticle to shift side-to-side and leading to a sensor falsely tripping from 0 -> 1.

[0029] FIG. 3 illustrates a bottom-view of an implementation of a pellicle frame width measurement device 305, which includes four proximity sensors 307a - 307d. The pellicle frame width measurement device 305 can be used to determine whether a reticle 301 with pellicle 303 is wider than a threshold. Proximity sensors 307a - 307d output a 0 or 1 if something is detected in their reflective beam. They do not measure the width of reticle 301 and/or pellicle 305 and are very sensitive to how they are calibrated and in particular the sensitivity of the surface they are sensing.

[0030] According to the implementations of pellicle frame width measurement devices, as illustrated in FIG. 3, the inner sensors 307a and 307b and the outer sensors 307c and 307d are located such that a reticle and/or a pellicle with a width of less than a first threshold (e.g., 115 mm) can pass the detection device for further processing. However, a reticle and/or a pellicle with a width of more than a second threshold (e.g., 117 mm) cannot pass the detection device for further processing. Detecting the pellicles surface is a demanding process due to the fact that pellicles are designed to have very low reflectivity and their reflectivity is decreasing with advances in reticle designs. In addition, the strong reflection from the pellicle frame can cause crosstalk between the sensors producing ambiguous signals. Since only four sensors are used a truth table can be implemented in software to evaluate the possible combinations of sensor detections and whether the reticle should be passed. However, this leaves some ambiguity for reticles near the pass criteria.

[0031] Before describing such embodiments in more detail, however, it is instructive to present an example environment in which embodiments of the present invention may be implemented.

[0032] Figure 1 schematically depicts a lithographic apparatus 100 including a source collector apparatus SO according to one embodiment of the invention. The apparatus comprises: an illumination system (illuminator) IL configured to condition a radiation beamB (e.g., EUV radiation); a support structure (e.g., a mask table) MT constructed to support a patterning device (e.g., a mask or a reticle) MA and connected to a first positioner PM configured to accurately position the patterning device; a substrate table (e.g., a wafer table) WT constructed to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate; and a projection system (e.g., a reflective projection system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0033] The illumination system 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 directing, shaping, or controlling radiation.

[0034] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system.

[0035] The term “patterning device” should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. The pattern imparted to the radiation beam may correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.

[0036] The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam, which is reflected by the mirror matrix.

[0037] The projection system, like the illumination system, may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of a vacuum. It may be desired to use a vacuum for EUV radiation since other gases may absorb too much radiation. A vacuum environment may therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.

[0038] As here depicted, the apparatus is of a reflective type (e.g., employing a reflective mask).

[0039] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables). Tn such “multiple stage” machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure.

[0040] Referring to Figure 1, the illuminator IL receives an extreme ultra violet radiation beam from the source collector apparatus SO. Methods to produce EUV radiation include, but are not necessarily limited to, converting a material into a plasma state that has at least one element, e.g., xenon, lithium or tin, with one or more emission lines in the EUV range. In one such method, often termed laser produced plasma (“LPP”) the required plasma can be produced by irradiating a fuel, such as a droplet, stream or cluster of material having the required line-emitting element, with a laser beam. The source collector apparatus SO may be part of an EUV radiation system including a laser, not shown in Figure 1, for providing the laser beam exciting the fuel. The resulting plasma emits output radiation, e.g., EUV radiation, which is collected using a radiation collector, disposed in the source collector apparatus. The laser and the source collector apparatus may be separate entities, for example when a CO2 laser is used to provide the laser beam for fuel excitation.

[0041] In such cases, the laser is not considered to form part of the lithographic apparatus and the laser beam is passed from the laser to the source collector apparatus with the aid of a beam delivery system comprising, for example, suitable directing mirrors and/or a beam expander.

[0042] The illuminator IL may comprise an adjuster for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may comprise various other components, such as facetted field and pupil mirror devices. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section.

[0043] The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. After being reflected from the patterning device (e.g., mask) MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor PS2 (e.g., an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor PS 1 can be used to accurately position the patterning device (e.g., mask) MA with respect to the path of the radiation beam B. Patterning device (e.g., mask) MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks PI, P2.

[0044] The depicted apparatus could be used in at least one of the following modes:

[0045] 1. In step mode, the support structure (e.g., mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e., a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed.

[0046] 2. In scan mode, the support structure (e.g., mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (e.g., mask table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0047] 3. In another mode, the support structure (e.g., mask table) MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above.

[0048] Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.

[0049] Figure 2 shows the apparatus 100 in more detail, including the source collector module SO, the illumination system IL, and the projection system PS. The source collector module SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 220 of the source collector module SO. An EUV radiation emitting plasma 210 may be formed by a laser produced plasma (LPP) source. EUV radiation may be produced by a gas or vapor, for example Xe gas, Li vapor or Sn vapor in which the very hot plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. As will be discussed in more detail below in the case of a laser produced plasma (LPP) source the very hot plasma 210 is created by configuring laser LA to emit a beam of laser radiation 205 that is focused on target area 211 to which is supplied a first fuel, e.g., a droplet of tin (Sn), from a first fuel supply. The laser generates a plasma of Sn vapour, which emits EUV radiation as is known in the art.

[0050] The source module SO further includes a radiation collector CO that collects the generated EUV radiation and focuses the EUV radiation at a virtual source point IE. The virtual source point IF is commonly referred to as the intermediate focus, and the source collector module is arranged such that the intermediate focus IF is located at or near an opening 221 in the enclosing structure 220. The virtual source point IF is an image of the radiation emitting plasma 210.

[0051] Subsequently the radiation traverses the illumination system IL, which may include a facetted field mirror device 22 and a facetted pupil mirror device 24 arranged to provide a desired angular distribution of the radiation beam 21, at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA. Upon reflection of the beam of radiation 21 at the patterning device MA, held by the support structure MT, a patterned beam 26 is formed and the patterned beam 26 is imaged by the projection system PS via reflective elements 28, 30 onto a substrate W held by the wafer stage or substrate table WT.

[0052] Combinations and/or variations on the described modes of use or entirely different modes of use may also be employed.

[0053] FIG. 4A illustrates a system for dimension measurements of a pellicle attached to a reticle using imaging, according to an embodiment. Specifically, FIG. 4A depicts a system 400 for measuring and/or detecting dimensions of a pellicle 405 attached to a reticle 401.

[0054] FIG. 4A schematically illustrates a cross-sectional view through an embodiment of a reticle assembly according to some embodiments, the reticle assembly being suitable for use in the lithographic apparatus as set out in FIG. 1 and/or FIG 2. The pellicle 405_comprises a frame 403. The pellicle 405 is attached to the reticle 402. The frame 403 having edges and a width such that a sensor of the system for dimension measurements detects the edges of the frame 403 to determine the width of the pellicle 405. Reticle 401 is shown with patterned surface having the frame 403 mounted on the patterned surface of reticle 401. Pellicle 405, according to an embodiment, is mounted tensioned on frame 403 over reticle 401.

[0055] In one example, when the reticle assembly is used in the lithographic apparatus as set out in FIG. 1 and/or FIG. 2, an DUV/EUV radiation beam passes through pellicle 405 to impinge upon a patterned surface of reticle 401, acquiring a pattern therefrom, and reflecting from reticle 401 as a patterned DUV/EUV beam, which passes back through the pellicle 405.

[0056] FIG. 4A also illustrates a side view of a sensor 407. According to one example, sensor 407 can be part of a measurement system, which can include sensor 407, one or more illumination sources (such as illumination sources 413 and 415 of FIG. 4B), and an optical system (not shown). According to one example, the optical system (not shown) can include an optic or optics such as one or more lenses, for example, located between reticle 401 and sensor 407. The purpose of the optical system can be to intercept scattered light from the illuminated reticle 401 and/or pellicle 405, to project a real image onto sensor 407, and to magnify or demagnify as necessary.

[0057] According to some embodiments, sensor 407 can be a linear or large area sensor, and can include, but is not to be limited to, a CMOS sensor array or a charge-coupled device (CCD). For example, sensor 307 can include a linear CCD or a large area CCD. There are a variety of linear and large area CCDs currently on the market that can be used in system 400, including CCDs from companies such as Fairchild Imaging of Milpitas, California, Atmel Corporation of San Jose, California, and DALSA Corporation of Waterloo, Ontario, Canada.

[0058] In one example, sensor 407 covers the entire width of reticle 401 and can detect and/or measure the pellicle frame size, making the system independent of pellicle reflectivity. According to one example, linear single-row and multi-row (e.g., up to 256) CCDs can be used as part of sensor 407 containing many thousands of pixels. Accordingly, CCDs mounted on a bracket as sensor 407, instead of proximity sensors as currently used in pellicle frame width measurement devices, can easily image the area where pellicle 405 is attached to reticle 401 and can accommodate all possible pellicle widths. Tn one embodiment, the sensor 407 is configured to image an underside of the reticle 301 to determine a size of the frame 403 of the pellicle 405.

[0059] Further, with calibration of the pixel locations the exact actual dimensions of reticle 401 and/or pellicle 405 can be measured to within the pixel size or better (depending on how much processing will be performed) yielding high measurement accuracy. For example, most CCDs can be equipped with microlens arrays which may be adequate given the small distance between reticle 401 and sensor 407. According to one embodiment, a small lens array or cylindrical lens can also be used as sensor 407.

[0060] In some embodiments, the measurement system, which includes sensor 407, can also include a computer system 409 coupled to sensor 407. Computer system 409 can be programmed to analyze images obtained from sensor 407 to measure and/or detect dimensions of reticle 401 and/or pellicle 405. Computer system 409 can also be used to compare the detected measurements to predetermined thresholds (or other predetermined limits) in order to determine whether pellicle 405 attached to reticle 401 has dimensions greater than the predetermined thresholds, and therefore stop further processes. Therefore, according to one exemplary embodiment, the width of reticle 40lor the frame 403 can be measured and/or detected by imaging and detecting the edges of, for example, frame 403 of pellicle 405. It is noted that although a separate computer system 409 is shown, all or part of the processes performed by computer system 409 can be performed by sensor 407.

[0061] FIG. 4B depicts a bottom view of sensor 407 and a top view of reticle 401. Sensor 407 can include linear CCD 411 and one or more illumination sources 413 and 415. According to one example, illumination sources 413 and 415 can include compact linear illuminators mounted to either side (or both sides) of linear CCD 411. This illuminator can consist of an array of light emitting diodes (LEDs), which are inexpensive with low power consumption and long life. It is noted that only one illumination source or more illumination sources can be implemented in system 400. Also, although the illumination sources 413 and 415 are depicted as being arranged on sensor 407, it is noted that any number, any shape, and/or any other arrangements of illumination sources are possible. The illumination sources 413 and 415 can be, for example, standard LEDs, flash light emitting diodes (flash LEDs), or laser diodes, but are not to be limited to these as other types of illumination sources can also be used.

[0062] By viewing a large area using sensor 407, the exact edges of pellicle frame will be detected. The pellicle frame 403 has higher reflectivity than the pellicle 405 itself. Since pellicle 405 and its frame 403 is imaged, rather than just looking at a threshold of reflected light, common image processing techniques can be used to improve contrast and edge detection to make it robust in even very demanding situations. Employing an optical system (not shown), can facilitate imaging.

[0063] According to some embodiments, the illumination sources (such as sources 413 and 415) can be arranged to illuminate reticle 401 at an oblique angle. Alternatively, sensor 407 can be arranged to “look” at reticle 401 at an oblique angle with illumination sources (such as sources 413 and 415) providing normal light.

[0064] Also, other operations useful to the reticle handler can be performed using system 400. For example, reticle 401 can include a 1 -dimensional (ID), 2-dimensional (2D), or any type of encoding barcode 417. In current implementations, the barcode of any reticle moved to a turret is checked with barcode readers installed at, for example, load-ports. This adds reticle handling time to any moves. However, by using sensor 407 over reticle 401, barcode 417 can also be read while a robot moves reticle 401 into the turret area. In one example, barcode 417 can always be presented to the same set of pixels of CCD 411.

[0065] According to another example, the images sensed by sensor 407 can be saved in a memory (not shown - e.g., in accordance with computer system 409) for further processing. An exemplary process that can be performed on the saved images can include analysis of state of the clamping area or squareness on the turret.

[0066] According to another example, reticle 401 can include one or more alignment marks 419 and 421. Alignment marks 419 and 421, in accordance with sensor 407 can provide higher accuracy for pre-alignment.

[0067] In one example, sensor 407 and illumination sources 413 and 415 can be used for evaluation of particulate contamination on reticle 401 and/or pellicle 405.

[0068] According to another example, a patterned area of reticle 401 can be imaged using sensor 407 as reticle 401 passes sensor 407, enabling determination of pattern density for reticle 401 heating compensation and control.

[0069] FIG. 5 is a flowchart depicting a method 500, according to an embodiment. For example, method 500 can efficiently and more precisely measure and/or detect reticle and/or pellicle dimensions. In one example, method 500 is performed by system 400. It is to be appreciated not all steps may be needed or performed in the order shown in FIG. 5. Reference is made to system 400 in FIG. 4 merely for convenience of discussion. Other system may be used to perform the method.

[0070] In step 501, a surface of an item, such as reticle 401, pellicle 405, and/or frame 403 of FIG. 4 is illuminated with an illumination beam. In one example, illumination sources 413 and 415 are used to illuminate the surface of the object.

[0071] In step 503, the light scattered from the object is received by, for example, sensor 407. Although not shown, an optical system can be used between the object and sensor 407, to intercept the scattered light and project an image of a desired area of the object onto sensor 407.

[0072] In step 505, the received scattered light from the object can be processed. In one example, sensor 407 alone or in combination with computer system 409 can process the received light and/or the received image to determine and/or detect the dimensions of the object.

[0073] In step 507, the determined dimensions can be compared with predetermined thresholds to determine, in step 509, whether the object can be passed for further processing. According to this example, if the dimensions of the object are less than a first threshold, the object can move for further processing. However, if the dimensions of the object are greater than a second threshold, system 400 can generate a notice indicating that the object is larger/wider than the predetermined threshold. The first and second threshold can have same or different values.

[0074] Embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (for example, a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices, or the like. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the finnware, software, routines, instructions, etc.

[0075] An example of a computer system 600 is shown in Figure 6. Computer system 600 can also be used as computer system 409, as described above.

[0076] The computer system 600 includes one or more processors, such as processor 604. Processor 604 may be a general purpose processor (such as, a CPU) or a special purpose processor (such as, a GPU). Processor 604 is connected to a communication infrastructure 606 (e.g., a communications bus, cross-over bar, or network). Various software embodiments can be described in terms of this exemplary computer system. After reading this description, it will become apparent to a person skilled in the relevant art(s) how to implement the invention using other computer systems and/or architectures.

[0077] Computer system 600 (optionally) includes a display interface 602 that forwards graphics, text, and other data from communication infrastructure 606 (or from a frame buffer not shown) for display on display unit 630.

[0078] Computer system 600 also includes a main memory 608, preferably random access memory (RAM), and may also include a secondary memory 610. The secondary memory 610 may include, for example, a hard disk drive 612 and/or a removable storage drive 614, representing a floppy disk drive, a magnetic tape drive, an optical disk drive, etc. The removable storage drive 614 reads from and/or writes to a removable storage unit 618 in a well-known manner. Removable storage unit 618 represents a floppy disk, magnetic tape, optical disk, etc. which is read by and written to by removable storage drive 614. As will be appreciated, the removable storage unit 618 includes a computer-readable storage medium having stored therein computer software and/or data.

[0079] In alternative embodiments, secondary memory 610 may include other similar devices for allowing computer programs or other instructions to be loaded into computer system 600. Such devices may include, for example, a removable storage unit 622 and an interface 620. Examples of such may include a program cartridge and cartridge interface, a removable memory chip (such as an erasable programmable read only memory (EPROM), or programmable read only memory (PROM)) and associated socket, and other removable storage units 622 and interfaces 620, which allow software and data to be transferred from the removable storage unit 622 to computer system 600.

[0080] Computer system 600 may also include a communications interface 624. Communications interface 624 allows software and data to be transferred between computer system 600 and external devices. Examples of communications interface 624 may include a modem, a network interface (such as an Ethernet card), a communications port, a Personal Computer Memory Card International Association (PCMCIA) slot and card, etc. Software and data transferred via communications interface 624 are in the form of signals 628 which may be electronic, electromagnetic, optical or other signals capable of being received by communications interface 624. These signals 628 are provided to communications interface 624 via a communications path (e.g., channel) 626. This channel 626 carries signals 628 and may be implemented using wire or cable, fiber optics, a telephone line, a cellular link, an radio frequency (RF) link and other communications channels.

[0081] In this document, the terms “computer program medium” and “computer-readable storage medium” are used to generally refer to media such as removable storage drive 614 and a hard disk installed in hard disk drive 612. These computer program products provide software to computer system 600.

[0082] Computer programs (also referred to as computer control logic) are stored in main memory 608 and/or secondary memory 610. Computer programs may also be received via communications interface 624. Such computer programs, when executed, enable the computer system 600 to perform features of the present invention, such as analyzing a surface of an object as discussed herein. In particular, the computer programs, when executed, can enable the processor 604 to perform the features of the present invention, including the implementation of the methods illustrated in FIG. 5 discussed herein. Accordingly, such computer programs represent controllers of the computer system 600.

[0083] It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the clauses. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, are not intended to limit the present invention and the appended clauses in any way.

[0084] The present invention has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.

[0085] The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.

The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following clauses and their equivalents. Other aspects of the invention are set out as in the following numbered clauses: WHAT IS CLAIMED IS: 1. A system, comprising: an illumination source configured to provide an illumination beam to illuminate a surface of a pellicle; a sensor configured to receive light from the illuminated surface of the pellicle; and a processor configured to determine dimensions of the pellicle and to determine whether the pellicle be moved for further processing.

2. The system of clause 1, wherein the pellicle is attached to a reticle.

3. The system of clause 2, wherein the pellicle comprises a frame having edges and a width such that the sensor detects the edges of the frame to determine the width of the pellicle.

4. The system of clause 3, wherein the sensor is configured to image an underside of the reticle to determine a size of the frame of the pellicle.

5. The system of clause 1, wherein the processor compares the determined dimensions of the pellicle with a threshold, generates a notice if the determined dimensions of the pellicle are greater than the threshold, and allows for the further processing if the determined dimensions of the pellicle are less that the threshold.

6. The system of clause 1, further comprising: an optic configured to intercept the light from the illuminated surface of the pellicle and projecting a real image of the surface of the pellicle to the sensor.

7. The system of clause 1, wherein the illumination source and the sensor are integrated into a lithography system for enabling the system to perform detection of pellicles.

8. The system of clause 1, wherein the sensor further comprises a linear charge-coupled device (CCD).

9. A method, comprising: illuminating a surface of a pellicle with an illumination beam; receiving light from the illuminated surface of the pellicle; and processing the received light for determining dimensions of the pellicle and for determining whether the pellicle be moved for further processing.

10. The method of clause 9, wherein the pellicle is attached to the reticle.

11. The method of clause 10, wherein the pellicle comprises a frame having edges and a width such that determining dimensions of the pellicle includes detecting the edges of the frame to determine the width of the pellicle.

12. The method of clause 9, further comprising: comparing the determined dimensions of the pellicle with a threshold; generating a notice if the determined dimensions of the pellicle are greater than the threshold; and allowing for the further processing if the determined dimensions of the pellicle are less that the threshold.

13. The method of clause 9, further comprising: intercepting the light from the illuminated surface of the pellicle; and projecting a real image of the surface of the pellicle to the sensor.

14. The method of clause 9, wherein the receiving light from the illuminated surface of the pellicle is performed by a linear charge-coupled device (CCD).

15. A lithography system, comprising: a measurement system including an illumination source configured to provide an illumination beam to illuminate a surface of a pellicle, a sensor configured to receive light from the illuminated surface of the pellicle, and a processor configured to determine dimensions of the pellicle and for determining whether the pellicle be moved for further processing, a second illumination source configured to provide a light beam; and a projection system configured to project patterned light beam from a reticle onto a substrate.

16. The lithography system of clause 15, wherein the processor compares the determined dimensions of the pellicle with a threshold, generates a notice if the determined dimensions of the pellicle are greater than the threshold, and allows for the further processing if the determined dimensions of the pellicle are less that the threshold.

17. The lithography system of clause 15, further comprising: an optic configured to intercept the light from the illuminated surface of the pellicle and projecting a real image of the surface of the pellicle to the sensor.

18. The lithography system of clause 15, wherein the sensor further comprises a linear charge-coupled device (CCD).

19. The lithography system of clause 15, wherein the pellicle is attached to a reticle.

20. The lithography system of clause 19, wherein the pellicle comprises a frame having edges and a width such that the sensor detects the edges of the frame to determine the width of the pellicle.

Claims (1)

A lithography device comprising: an exposure device adapted to provide a radiation beam; a carrier configured to support a patterning device, which patterning device is capable of applying a pattern in a section of the radiation beam to form a patterned radiation beam; a substrate table constructed to support a substrate; and a projection device adapted to project the patterned radiation beam onto a target area of the substrate, characterized in that the substrate table is adapted to position the target area of the substrate in a focal plane of the projection device.