Optical position assessment apparatus and method

A lithographic apparatus comprises a substrate table that supports a substrate having alignment marks on a surface thereof. The apparatus further comprises a frame moveable relative to the substrate to provide for a scanning or stepping mode of operation. An array of projection systems is disposed across the frame for projecting respective patterned beams onto a target portion of the substrate. A plurality of alignment mark detectors are attached to the frame and are moveable with respect to the frame using respective linear drive mechanisms. A position sensor is associated with each alignment mark detector for determining the position of the detector relative to the frame. A control system is responsible for both initial positioning of the detectors above alignment mark patterns on the substrate, and for dynamic alignment of the frame and substrate during a lithographic process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lithographic apparatus and a device manufacturing method.

2. Related Art

A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. The lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs), flat panel displays, and other devices involving fine structures. In a conventional lithographic apparatus, a patterning means, which is alternatively referred to as a mask or a reticle, can be used to generate a circuit pattern corresponding to an individual layer of the IC (or other device), and this pattern can be imaged onto a target portion (e.g., comprising part of one or several dies) on a substrate (e.g., a silicon wafer or glass plate) that has a layer of radiation-sensitive material (e.g., resist). Instead of a mask, the patterning means can comprise an array of individually controllable elements that generate the circuit pattern.

In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and scanners, in which each target portion is irradiated by scanning the pattern through the beam in a given direction (the “scanning” direction), while synchronously scanning the substrate parallel or anti-parallel to this direction.

It will be appreciated that, whether or not a lithographic apparatus operates in stepping or scanning mode, it is desired that the patterned beam or beams is/are directed onto the appropriate target portion of the substrate surface. In many circumstances, multi-layer structures are built up on the surface of the substrate as a result of a sequence of lithographic processing steps. It is of course desired that the successive layers formed in the substrate are correctly in register with each other. Thus, great care is taken to ensure that the position of the substrate relative to the beam projection system is accurately known.

Various techniques are used to determine the position of a substrate relative to the beam projection system. These generally rely upon the substrate having formed upon it alignment marks that are arranged around the periphery of areas of the substrate onto which active circuit components or the like are to be formed. These marks are located to provide reference points relative to which the position of target portions on the substrate are determined. The alignment marks can be detected optically using the beam projection system, which is also used to project patterns onto the substrate. Such a “through the lens” or TTL approach to the problem of locating alignment marks allows for the position measurement location to be the same as the image formation location. Thus, “Abbe” errors are minimized. In other systems, the alignment mark detectors and the main beam projection system have different optical axes, in which case some means can be provided for compensating for relative movement of these axes.

In an example of a scanning-based system, as the frame supporting the beam projection system and the alignment mark detectors is scanned across the surface of a substrate by moving the substrate, the position of the substrate in the direction perpendicular to the scan direction and the scan speed is adjusted in dependence upon the measured positions of the alignment marks. Alternatively, or additionally, the digital image to be projected can be adjusted. In the case where the patterning means comprises an array of individually controllable elements, this can involve translating or otherwise adjusting the digital pattern applied to the array. The height of the substrate can also be controlled using some type of level sensor arrangement.

Typically, a lithographic apparatus of a given production facility is designed (or configured in a relatively inflexible way) for use with substrates of a fixed size. In the case of flat panel displays or color filter plates, the substrate dimensions can be of the order of several meters, with multiple panels being formed on each substrate. The alignment marks are provided around the periphery of the substrate, as well as between panels. However, there is a desire to introduce flexibility in the layout of panels on the substrates, such that a given production facility can be used to produce panels with different dimensions. This has meant that, for non-standard panel layouts, either only alignment marks around the periphery of the substrate can be used (as the periphery is the only “blank” region common to all substrate layouts), or some manual realignment of the detectors must be carried out While a continuous array of alignment mark detectors positioned across the substrate to detect alignment marks in various intermediate positions can be desirable, this is not practical due to the very high resolution required and the number of detectors that that would necessitate.

A number of factors, for example thermal effects, can cause local variations in the shape of a substrate. It is therefore desirable to provide alignment marks at relatively small intervals across the surface of the substrate. However, the approach described in the previous paragraph mitigates against this as the entire central area of the substrate is effectively unusable for the placement of alignment marks.

Therefore, what is needed is a lithographic apparatus and method that allow for the flexible positioning of alignment marks within the central area of a substrate to be patterned.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a lithographic apparatus comprising a substrate table, a frame, one or more projection systems, one or more alignment mark detectors, and a position sensor. The substrate table supports a substrate having alignment marks provided on a surface thereof. The frame is moveable relative to the substrate. The one or more projection systems projecting a patterned beam onto a target portion of the substrate. Each projection system is attached to the frame. The one or more alignment mark detectors are attached to the frame and moveable with respect to the frame. The position sensor is associated with each alignment mark detector, and determine the position of the detector relative to the frame or projection system(s).

In this embodiment, the invention makes it possible to use a single lithographic apparatus, in a stable operating configuration, for the production of panels or other devices having variable dimensions. Alignment mark detectors can be moved relative to the frame supporting the detectors and the projection system(s) in order to accommodate substrates having alignment marks placed at differing locations within their central areas. It is no longer necessary to rely upon only peripheral alignment marks to align the projection system(s) to the substrate. Improved production accuracy and flexibility can therefore be achieved.

It will be appreciated that the frame can be moveable relative to the substrate by moving the frame, the substrate, or both.

In one example, the frame can be moveable relative to the substrate along a first linear movement axis, the “scan direction,” parallel to the plane of the substrate. Each alignment mark detector is then movable relative to the frame along a second linear axis, substantially perpendicular to the first axis, again in a plane parallel to the plane of the substrate.

In one example, each alignment mark detector can have a range of movement sufficient to provide coverage of substantially the whole dimension of the substrate in the direction of the second axis. In the case of multiple detectors, the movement of the detectors is non-overlapping. Each detector is arranged to provide an output signal indicative of the positions of detected alignment marks.

In one example, each alignment mark detector can comprise an illumination system for supplying an alignment beam of radiation, a projection system for projecting the alignment beam onto a target portion of the substrate, and a sensor for detecting radiation reflected from the substrate.

In one example, each position sensor can comprise a laser interferometer. In one example, the laser interferometer comprises a reflector or mirror surface fixed relative to the associated alignment mark detector, and a laser and a radiation detector fixed relative to the frame. Alternatively, a linear grating system can be used.

In one example, the lithographic apparatus can comprise a linear motor associated with each alignment mark detector, which provides linear movement of the detector relative to the frame, and control means coupled to each linear motor for controlling the position of the motor(s) in dependence upon operator inputs.

In one example, the lithographic apparatus can comprise an alignment controller for receiving an output of the or each position sensor and of the or each alignment mark detector. In dependence upon the received signals, the controller is arranged to adjust the position of the substrate relative to the frame and/or the scanning speed of the substrate and/or the patterned beam generated by the or each projection system.

According to a further aspect of the invention there is provided a method of aligning a substrate with one or more projection systems of a lithographic apparatus. Each projection systems being fixed to a frame that is moveable relative to the substrate. The method comprises the following steps. Determining the approximate positions of alignment marks provided on a surface of the substrate. Moving one or more alignment mark detectors, relative to the frame or to the projection system(s), to positions at which the alignment marks can be detected.

In one example, the step of moving the one or more alignment mark detectors comprises monitoring the output of one or more detector position sensors to provide detector position feedback, the position sensor(s) being fixed to the frame and/or the alignment mark detector(s).

In one example, the step of moving one or more alignment mark detectors comprises applying drive signals to a linear drive mechanism associated with each alignment mark detector. Each linear drive mechanism can comprise a linear motor.

In various examples, the present invention is applicable to lithographic apparatus relying upon either a mask or arrays of individually controllable elements to impart a pattern to the projected beam.

The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers can indicate identical or functionally similar elements.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Overview and Terminology

Although specific reference can be made in this text to the use of lithographic apparatus in the manufacture of integrated circuits (ICs), it should be understood that the lithographic apparatus described herein can have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, 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 can be considered as synonymous with the more general terms “substrate” or “target portion,” respectively. The substrate referred to herein can be processed, before or after exposure, in for example a track (e.g., a tool that typically applies a layer of resist to a substrate and develops the exposed resist) or a metrology or inspection tool. Where applicable, the disclosure herein can be applied to such and other substrate processing tools. Further, the substrate can be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein can also refer to a substrate that already contains multiple processed layers.

The term “array of individually controllable elements” as here employed should be broadly interpreted as referring to any device that can be used to endow an incoming radiation beam with a patterned cross-section, so that a desired pattern can be created in a target portion of the substrate. The terms “light valve” and “Spatial Light Modulator” (SLM) can also be used in this context. Examples of such patterning devices are discussed below.

A programmable mirror array can comprise a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such an apparatus is that, for example, addressed areas of the reflective surface reflect incident light as diffracted light, whereas unaddressed areas reflect incident light as undiffracted light. Using an appropriate spatial filter, the undiffracted light can be filtered out of the reflected beam, leaving only the diffracted light to reach the substrate. In this manner, the beam becomes patterned according to the addressing pattern of the matrix-addressable surface.

It will be appreciated that, as an alternative, the filter can filter out the diffracted light, leaving the undiffracted light to reach the substrate. An array of diffractive optical micro electrical mechanical system (MEMS) devices can also be used in a corresponding manner. Each diffractive optical MEMS device can include a plurality of reflective ribbons that can be deformed relative to one another to form a grating that reflects incident light as diffracted light.

A further alternative embodiment can include a programmable mirror array employing a matrix arrangement of tiny mirrors, each of which can be individually tilted about an axis by applying a suitable localized electric field, or by employing piezoelectric actuation means. Once again, the mirrors are matrix-addressable, such that addressed mirrors will reflect an incoming radiation beam in a different direction to unaddressed mirrors; in this manner, the reflected beam is patterned according to the addressing pattern of the matrix-addressable mirrors. The required matrix addressing can be performed using suitable electronic means.

In both of the situations described here above, the array of individually controllable elements can comprise one or more programmable mirror arrays. More information on mirror arrays as here referred to can be gleaned, for example, from U.S. Pat. Nos. 5,296,891 and 5,523,193, and PCT patent applications WO 98/38597 and WO 98/33096, which are incorporated herein by reference in their entireties.

A programmable LCD array can also be used. An example of such a construction is given in U.S. Pat. No. 5,229,872, which is incorporated herein by reference in its entirety.

It should be appreciated that where pre-biasing of features, optical proximity correction features, phase variation techniques and multiple exposure techniques are used, for example, the pattern “displayed” on the array of individually controllable elements can differ substantially from the pattern eventually transferred to a layer of or on the substrate. Similarly, the pattern eventually generated on the substrate can not correspond to the pattern formed at any one instant on the array of individually controllable elements. This can be the case in an arrangement in which the eventual pattern formed on each part of the substrate is built up over a given period of time or a given number of exposures during which the pattern on the array of individually controllable elements and/or the relative position of the substrate changes.

Although specific reference can 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 can have other applications, such as, for example, the manufacture of DNA chips, MEMS, MOEMS, integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, 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 can be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein can 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) or a metrology or inspection tool. Where applicable, the disclosure herein can be applied to such and other substrate processing tools. Further, the substrate can be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein can also refer to a substrate that already contains multiple processed layers.

The illumination system can also encompass various types of optical components, including refractive, reflective, and catadioptric optical components for directing, shaping, or controlling the beam of radiation, and such components can also be referred to below, collectively or singularly, as a “lens.”

Further, the apparatus can be provided with a fluid processing cell to allow interactions between a fluid and irradiated parts of the substrate (e.g., to selectively attach chemicals to the substrate or to selectively modify the surface structure of the substrate).

Lithographic Projection Apparatus

FIG. 1schematically depicts a lithographic projection apparatus100according to an embodiment of the invention. Apparatus 100 includes at least a radiation system102, an array of individually controllable elements104, an object table106(e.g., a substrate table), and a projection system (“lens”)108.

Radiation system102can be used for supplying a beam110of radiation (e.g., UV radiation), which in this particular case also comprises a radiation source112.

An array of individually controllable elements104(e.g., a programmable mirror array) can be used for applying a pattern to beam110. In general, the position of the array of individually controllable elements104can be fixed relative to projection system108. However, in an alternative arrangement, an array of individually controllable elements104can be connected to a positioning device (not shown) for accurately positioning it with respect to projection system108. As here depicted, individually controllable elements104are of a reflective type (e.g., have a reflective array of individually controllable elements).

Object table106can be provided with a substrate holder (not specifically shown) for holding a substrate114(e.g., a resist coated silicon wafer or glass substrate) and object table106can be connected to a positioning device116for accurately positioning substrate114with respect to projection system108.

Projection system108(e.g., a quartz and/or CaF2lens system or a catadioptric system comprising lens elements made from such materials, or a mirror system) can be used for projecting the patterned beam received from a beam splitter118onto a target portion120(e.g., one or more dies) of substrate114. Projection system108can project an image of the array of individually controllable elements104onto substrate114. Alternatively, projection system108can project images of secondary sources for which the elements of the array of individually controllable elements104act as shutters. Projection system108can also comprise a micro lens array (MLA) to form the secondary sources and to project microspots onto substrate114.

Source112(e.g., an excimer laser) can produce a beam of radiation122. Beam122is fed into an illumination system (illuminator)124, either directly or after having traversed conditioning device126, such as a beam expander, for example. Illuminator124can comprise an adjusting device128for setting the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in beam122. In addition, illuminator124will generally include various other components, such as an integrator130and a condenser132. In this way, beam110impinging on the array of individually controllable elements104has a desired uniformity and intensity distribution in its cross section.

It should be noted, with regard toFIG. 1, that source112can be within the housing of lithographic projection apparatus100(as is often the case when source112is a mercury lamp, for example). In alternative embodiments, source112can also be remote from lithographic projection apparatus100. In this case, radiation beam122would be directed into apparatus100(e.g., with the aid of suitable directing mirrors). This latter scenario is often the case when source112is an excimer laser. It is to be appreciated that both of these scenarios are contemplated within the scope of the present invention.

Beam110subsequently intercepts the array of individually controllable elements104after being directed using beam splitter118. Having been reflected by the array of individually controllable elements104, beam110passes through projection system108, which focuses beam110onto a target portion120of the substrate114.

With the aid of positioning device116(and optionally interferometric measuring device134on a base plate136that receives interferometric beams138via beam splitter140), substrate table6can be moved accurately, so as to position different target portions120in the path of beam110. Where used, the positioning device for the array of individually controllable elements104can be used to accurately correct the position of the array of individually controllable elements104with respect to the path of beam110, e.g., during a scan. In general, movement of object table106is realized with the aid of a long-stroke module (course positioning) and a short-stroke module (fine positioning), which are not explicitly depicted inFIG. 1. A similar system can also be used to position the array of individually controllable elements104. It will be appreciated that beam110can alternatively/additionally be moveable, while object table106and/or the array of individually controllable elements104can have a fixed position to provide the required relative movement.

In an alternative configuration of the embodiment, substrate table106can be fixed, with substrate114being moveable over substrate table106. Where this is done, substrate table106is provided with a multitude of openings on a flat uppermost surface, gas being fed through the openings to provide a gas cushion which is capable of supporting substrate114. This is conventionally referred to as an air bearing arrangement. Substrate114is moved over substrate table106using one or more actuators (not shown), which are capable of accurately positioning substrate114with respect to the path of beam110. Alternatively, substrate114can be moved over substrate table106by selectively starting and stopping the passage of gas through the openings.

Although lithography apparatus100according to the invention is herein described as being for exposing a resist on a substrate, it will be appreciated that the invention is not limited to this use and apparatus100can be used to project a patterned beam110for use in resistless lithography.

The depicted apparatus100can be used in four preferred modes:

1. Step mode: the entire pattern on the array of individually controllable elements104is projected in one go (i.e., a single “flash”) onto a target portion120. Substrate table106is then moved in the x and/or y directions to a different position for a different target portion120to be irradiated by patterned beam110.

2. Scan mode: essentially the same as step mode, except that a given target portion120is not exposed in a single “flash.” Instead, the array of individually controllable elements104is movable in a given direction (the so-called “scan direction”, e.g., the y direction) with a speed v, so that patterned beam110is caused to scan over the array of individually controllable elements104. Concurrently, substrate table106is simultaneously moved in the same or opposite direction at a speed V=Mv, in which M is the magnification of projection system108. In this manner, a relatively large target portion120can be exposed, without having to compromise on resolution.

3. Pulse mode: the array of individually controllable elements104is kept essentially stationary and the entire pattern is projected onto a target portion120of substrate114using pulsed radiation system102. Substrate table106is moved with an essentially constant speed such that patterned beam110is caused to scan a line across substrate106. The pattern on the array of individually controllable elements104is updated as required between pulses of radiation system102and the pulses are timed such that successive target portions120are exposed at the required locations on substrate114. Consequently, patterned beam110can scan across substrate114to expose the complete pattern for a strip of substrate114. The process is repeated until complete substrate114has been exposed line by line.

4. Continuous scan mode: essentially the same as pulse mode except that a substantially constant radiation system102is used and the pattern on the array of individually controllable elements104is updated as patterned beam110scans across substrate114and exposes it.

Combinations and/or variations on the above described modes of use or entirely different modes of use can also be employed.

Exemplar Scanning and Detection Systems

FIG. 2illustrates in plan view a scanning lithographic apparatus, according to one embodiment of the present invention.FIG. 3illustrates in side elevation view the apparatus ofFIG. 2viewed in the direction of Arrow A. These are directed to a scanning-based mode of operation.

InFIG. 2, the lithographic apparatus is arranged to scan a two-dimensional pattern in one direction, the “x” direction, across the surface of a substrate2. The apparatus comprises a substrate table1on which is mounted substrate2. Substrate table1is moveable in the scanning direction, i.e., the x direction, as well as in the y (and z) directions, by a drive device (not shown inFIG. 2), which operates under the control of a control system3.

Mounted above substrate2and substrate table1is a trolley frame4that is fixed relative to substrate table1. As illustrated inFIG. 3, frame4includes support legs5a,5band a gantry6. Gantry6is supported on support legs5a,5band crosses the space over substrate table1. Gantry6supports a set of projection systems7(eleven such systems are illustrated inFIG. 2), each as described above with reference toFIG. 1. As frame4is scanned over substrate2, projection systems7are positioned towards the trailing edge of gantry6and are arranged so that the generated patterned beams combined to provide complete coverage of substrate2in the y direction.

In one example, each projection system7can be individually controlled to alter the position at which patterned light impinges on substrate2, as well as to alter the shape of the beam. As mentioned above, this is generally achieved by shifting the digital pattern applied to array of individually controllable elements forming patterning means104. The digital signals applied to the projection systems7are generated by control system3.

A set of alignment mark detectors9are located towards the leading edge of gantry6. It is to be appreciated that, althoughFIGS. 2 and 3illustrate five such detectors, this number can vary. Each detector9is arranged to detect the position of alignments marks10on the surface of substrate2. Also, each detected9detects which alignment marks10pass through the field-of-view of detectors9, relative to the position of trolley frame4, allowing for the determination of the position of projection systems7.

FIG. 4illustrates schematically an alignment mark detector409, according to one embodiment of the present invention. Detector409is one example arrangement for detector9. Each alignment mark detector409comprises a radiation source11that operates at a wavelength that will not cause exposure of a photoresist on a surface of substrate2. For example, source11can produce red light that is shifted with respect to the light that provides the exposing beams (e.g., 350 to 450 nm) used by projection systems7. The radiation is projected onto the surface of substrate2, via a beam splitter12, using projecting optics13. A radiation sensor14is provided to detect light reflected from the surface of substrate2. Typically, alignment marks10(not shown inFIG. 4) are provided by exposed and developed regions of the photoresist on the substrate2, and will cause a high level of reflection to occur. Sensor14detects the alignment mark10by looking for a change from a low level of reflection to a high level of reflection, and back to a low level. Sensor14provides an output signal to control system3(i.e., the control system being arranged to determine the position of the detected alignment mark10with respect to trolley frame4) and any deviation of that position from the expected position.

It is to be appreciated that other detector arrangements can be used, including those which share components, e.g., the radiation source, between detectors9.

With reference again toFIG. 3, in this example each alignment mark detector9is mounted on a linear drive mechanism15, which comprises a linear motor. Drive mechanism15is able to drive detector9across gantry6in the y direction, across some range of movement. Typically, this allows each detector9to move half way across the space between each of the detectors9, such that in combination detectors9give full coverage across substrate2in the y direction.

Each drive mechanism15is coupled to control system3that controls the position of detector9. In this example, control system3receives detector position information from a set of laser interferometry systems16. Interferometry systems16comprises, for each alignment mark detector9, a mirror fixed to detector9, and a laser and sensor arrangement fixed to frame4. Control system3monitors the outputs of the respective sensors as detectors9are moved in order to count interference fringes and determine the positions of detectors9. In the interests of clarity, only a single interferometry system16is illustrated inFIGS. 2 and 3, although it will be appreciated that one such system can be provided for each detector9.

In another example, control system3receives position information from operator inputs.

Exemplary Substrates

FIGS. 5 and 6illustrate in plan view substrates17and18, respectively, with various panel layouts, according to various embodiments of the present invention. Substrates17,18have the same overall dimensions, but are designed to accommodate different flat panel display sizes. Substrate17ofFIG. 5is designed to accommodate four panels19of equal size, while substrate18ofFIG. 6is designed to accommodate nine panels20of equal size. Alignment marks10on each panel are arranged to suit the panel layouts and to maximize the accuracy with which substrates17,18can be aligned during exposure.

FIG. 8illustrates in plan view a substrate21′ with panels having various sizes A, B and C, which in the example shown are not equal to each other.

Exemplary Operation

With reference toFIGS. 2,3, and5, in preparation for exposure substrate17is loaded onto substrate table1. This process can usually be done with an accuracy of a few millimeters. In one example, an operator programs into control system3characteristics of substrate17, e.g., a number of rows of alignment marks10and the positions of the rows (in the y direction). In another example, the operator enters a substrate type code, where the alignment mark data for each substrate type having been pre-programmed into control system3. In either example, this operation causes an appropriate number of alignment mark detectors9to be activated, in this case three, and moved by means of the respective linear drive mechanisms15to appropriate positions above the rows of alignment marks10. In one example, fields-of-view of detectors9are sufficient to accommodate positioning errors of substrate17on substrate table1to within a few millimeters or so. Alternatively, some scanning procedure could be carried out to center each detector9above the corresponding alignment mark row.

In this example, during positioning of detectors9, their positions can be accurately recorded using laser interferometry system16. Final position information is fed to control system3. Typically, control system3uses this information prior to scanning to shift substrate table1in the y direction to correctly align the projection systems with the substrate. The fields-of-view of detectors9are sufficient to accommodate this slight shift of substrate17. Exposure then commences, with substrate17being scanned under trolley frame4in the x-direction. As each detector9detects the passage of an alignment mark10, position information is fed to control system3. As already described, control system3acts on the received alignment mark position data to correctly align projection systems7and substrate17by adjusting the projection systems' optics, adjusting the digital pattern applied to the array of individually controllable elements, adjusting the substrate table position, or any combination of these adjustments.

With reference again toFIGS. 2,3, and6, the data input by the operator causes four of detectors9on gantry6to be activated and moved into position. The use of four rows of alignment marks10on substrate18is facilitated by the arrangement and number of panels20, and generally increases the alignment accuracy during the exposure procedure.

FIG. 7is a flow diagram illustrating a method700of operation, according to one embodiment of the present invention. In step702, a substrate is positioned on a substrate table. In step704, an appropriate number of align mark detectors are selected and moved to in-use positions. In step706, scanning exposure is performed.

Conclusion