Lithographic apparatus and device manufacturing method

A lithographic apparatus includes an illumination system that supplies a beam of radiation, an array of individually controllable elements that pattern the beam, a substrate table for supporting a substrate, and a projection system that projects the patterned beam onto a target portion of the substrate. The projection system comprises an array of lenses arranged to receive the patterned beam, divide the patterned beam into a plurality of substantially polygonal portions, and focus each substantially polygonal portion to form a respective radiation spot on the target portion of the substrate. In one example, the illumination system comprises an illuminator arranged to receive a beam of radiation from a radiation source, the illuminator comprising an array of lenses arranged to divide the beam of radiation from the source into a plurality of substantially polygonal portions and to focus each substantially polygonal portion onto a respective one of the array of individually controllable elements.

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, print heads, micro or nano-fluidic devices, 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, may 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 may comprise an array of individually controllable elements that generate the circuit pattern.

In general, a single substrate will contain a collection 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 antiparallel to this direction.

In maskless lithography it is known to project the patterned beam onto a target portion of the substrate using a projection system that comprises an array of lenses arranged such that each lens receives and focuses a respective portion of the patterned beam. Each lens of the array of lenses thus projects a respective spot of radiation onto the substrate, and the array of lenses collectively projects a radiation pattern on the substrate. Such systems are generally referred to as microlens array or MLA systems. In these systems, the patterned beam is typically projected onto array of lenses through a beam expander that comprises a series of optical components and is arranged to provide a substantially parallel radiation beam.

It will be appreciated that an inherent disadvantage of using a MLA of the is that a portion of the patterned beam incident on the MLA is lost, i.e., a portion does not reach the target surface of the substrate. This lost portion is the part of the beam which falls between the lenses of the MLA (i.e. the part that falls on a masking structure of the MLA). To reduce the amount of the beam cross section that is blocked (i.e., to maximize the proportion reaching the target substrate) openings or windows in the masking structure of the MLA may be made as large as possible. However, even with the MLA having larger windows, the proportion of the patterned beam cross section being lost (i.e., not reaching the substrate) can still be about 21.5%. With this result, a maximum fill ratio for a rectangular array of circular lenses is 78.5%. In practice, the maximum achievable fill ratio maybe lower than 70%.

Therefore, what is needed is a more efficient MLA.

SUMMARY OF THE INVENTION

According to one embodiment, there is provided a lithographic apparatus comprising an illumination system for supplying a beam of radiation, an array of individually controllable elements serving to impart the beam with a pattern in its cross-section, a substrate table for supporting a substrate, and a projection system for projecting the patterned beam onto a target portion of the substrate. The projection system comprises an array of lenses arranged to receive the patterned beam, divide the patterned beam cross-section into a plurality of substantially polygonal portions, and focus each substantially polygonal portion to form a respective radiation spot on the target portion of the substrate.

In this embodiment, the array of lenses in is arranged to focus polygonal portions of the beam cross section. In one example, a maximum fill ratio of 78.5% inherent when using rectangular arrays of circular lenses is avoided. A greater portion of the patterned beam may be directed onto the target substrate, and this portion may be as high as 100%.

In one example, each substantially polygonal portion is substantially rectangular. In another example, each substantially polygonal portion is substantially square. Dividing the patterned beam cross section into squares is particularly desired when the beam patterning means is in the form of a square grid of controllable elements, as each projected radiation spot may thus correspond to a respective one of the elements.

In one example, the array of lenses comprises a first array of cylindrical lenses, each cylindrical lens being arranged to receive a respective rectangular portion of the patterned beam cross section and to focus that respective portion towards a respective focal line. The focal lines of the cylindrical lenses are substantially parallel to each other and to a first axis. The first axis is transverse to the beam direction. In one example, the focal lines of the cylindrical lenses of the first array are coplanar, and the array itself may be a generally planar structure, with the lenses being provided by parallel portions of a common transparent substrate for example.

In one example, the array of lenses further comprises a second array of cylindrical lenses arranged to receive the focused, patterned beam from the first array, (i.e., the first and second arrays may be arranged in series along the beam). In this example, each cylindrical lens of the second array is arranged to receive a respective rectangular portion of the focused patterned beam cross section and to further focus that respective portion towards a respective focal line. The focal lines of the cylindrical lenses of the second array are substantially parallel to each other and to a second axis. The second axis is transverse to the beam direction and substantially perpendicular to the first axis. Again, the focal lines of the cylindrical lenses of the second array are coplanar, and the second array itself may be a generally planar structure, with the lenses being provided by parallel portions of a common transparent substrate.

Thus, the division of the beam cross section into rectangular portions, and focusing of those portions down to an array of rectangular spots on the target substrate may conveniently be achieved by a series combination of crossed cylindrical lens arrays.

In one example, the cylindrical lenses of the first array have a first common focal length and the cylindrical lenses of the second array have a second common focal length. The first common focal length is longer than the second common focal length. In another example, these first and second arrays with different focal lengths are arranged, such that the focal lines of the lenses of the first array and the focal lines of the lenses of the second array fall on the same common plane. Thus, although the first and second cylindrical lens arrays are different distances from the target plane (e.g., they may be at different heights above the target substrate) because they are arranged in series along the beam direction, they may each focus onto the target plane. In other words, the two lens arrays may have a common focal plane. It will thus be appreciated that the lenses of the first cylindrical lens array may have a different curvature to those of the second.

The first and second arrays of cylindrical lenses may be provided by physically separate structures, but in alternative embodiments they may be provided by respective portions of a common substrate.

In one example, the first array of cylindrical lenses comprises a first transparent substrate. Each cylindrical lens of the first array is provided by a respective portion of the first substrate. The second array of cylindrical lenses comprises a second transparent substrate. Each cylindrical lens of the second array being provided by a respective portion of the second substrate. The second substrate is attached to the first substrate. This attachment may be by means of bonding, for example with a suitable adhesive, or with other bonding techniques, such as eutectic bonding or direct bonding using van der Waals forces.

It will thus be appreciated that one form of lens array suitable for use in embodiments and examples of the invention described above comprises a first parallel array of cylindrical lenses, to extend across the patterned beam in a first direction, arranged in series with a second parallel array of cylindrical lenses, to extend across the patterned beam in a second direction, perpendicular to the first. However, in alternative embodiments the first and second arrays of cylindrical lenses may not be perpendicular to one another.

In one example, array of lenses may comprise no masking structure, and the proportion of the patterned beam reaching the target substrate may be as high as 100%. Alternatively, a masking structure may be employed to block a portion of the patterned beam, for example to reduce “crosstalk” between adjacent projected radiation spots (which may also be referred to as pixels). The masking structure may, for example, take the form of blocking material arranged on a surface of a lens substrate (e.g., a line of material separating adjacent cylindrical lenses on a common substrate), or may be located elsewhere in the projection system. For example, in embodiments in which array of lenses comprises a series arrangement of crossed cylindrical lens arrays, a mask may be arranged between the two arrays.

In one example, the array of lenses is arranged to focus at least 90% of the patterned beam cross section onto the target portion of the substrate, so providing a significant improvement over the conventional MLAs which could deliver a theoretical maximum of only 78.5%.

In one example, the array of individually controllable elements may be a rectangular array. The array of lenses is arranged, such that the projected spots form a rectangular array, each spot corresponding to a respective one of the controllable elements.

Another embodiment provides a lithographic apparatus comprising an illumination system for supplying a beam of radiation, an array of individually controllable elements serving to impart the beam with a pattern in its cross section, a substrate table for supporting a substrate, and a projection system for projecting the patterned beam onto a target portion of the substrate. The illumination system comprises an illuminator arranged to receive a beam of radiation from a radiation source. The illuminator comprising an array of lenses arranged to divide the cross section of the beam of radiation from the source into a plurality of substantially polygonal portions and to focus each substantially polygonal portion onto a respective one of the array of individually controllable elements.

In one example, the proportion of the beam “lost” or wasted in the patterning process is reduced. The array of lenses is able to focus portions of the supplied beam that would otherwise have fallen between the patterning elements, onto the elements.

It will be appreciated that lens arrays as described above in relation to the projection system of the first embodiment of the invention, may be used with corresponding illuminator of this second embodiment.

In this embodiment, a pair of cylindrical lens arrays may be used in the illumination system, close to the contrast device, to generate spot illumination of the elements (which may also be referred to as pixels) of the contrast device.

According to a further embodiment, there is provided a device manufacturing method comprising the steps of providing a substrate, providing a beam of radiation using an illumination system, using an array of individually controllable elements to impart the beam with a pattern in its cross section, and projecting the patterned beam of radiation onto a target portion of the substrate. The step of projecting comprises the steps of dividing the patterned beam cross section into a plurality of substantially polygonal portions and focusing each substantially polygonal portion to form a respective radiation spot on the target portion of the substrate.

Yet another embodiment provides a device manufacturing method comprising the steps of providing a substrate, providing a beam of radiation using an illumination system, using an array of individually controllable elements to impart the beam with a pattern in its cross section, and projecting the patterned beam of radiation onto a target portion of the substrate. The step of providing a beam comprises the steps of providing a beam of radiation from a source, dividing the cross section of the beam of radiation from the source into a plurality of substantially polygonal portions, and focusing each substantially polygonal portion onto a respective one of the array of individually controllable elements.

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

DETAILED DESCRIPTION OF THE EMBODIMENTS

Overview and Terminology

It will be appreciated that the term “focus” is to be interpreted in a broad sense, meaning that an array of lenses is arranged to concentrate each polygonal portion to a certain degree, to form the respective radiation spots. In other words, the array of lenses causes rays of each polygonal portion to converge to form the radiation spot. However, each radiation spot is not necessarily a sharp image, although in certain embodiments it may be.

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 may 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 may 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 prebiasing 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 may differ substantially from the pattern eventually transferred to a layer of or on the substrate. Similarly, the pattern eventually generated on the substrate may not correspond to the pattern formed at any one instant on the array of individually controllable elements. This may 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.

Further, the apparatus may 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).

FIRST EXEMPLARY LITHOGRAPHIC APPARATUS

FIG. 2depicts part of a lithographic apparatus. A beam PB from a collimated source, such as a mercury lamp or a laser, is directed onto an array of controllable elements PPM. The patterned beam reflected from the array PPM is projected onto a MLA by a beam expander BE. The MLA projects an array of radiation spots onto a target surface of a substrate W.

FIG. 3is a simplified plan view of a micro lens array (MLA) andFIG. 4is a cross section, along line AA, of the MLA ofFIG. 3. The MLA comprises a body of transparent material having a flat upper surface and a lower surface shaped to define a plurality of spherical lenses SL. The MLA also comprises a mask structure, in the form of a layer LM of opaque material attached to first, flat surface of the transparent body. An array of circular windows CW is formed in the opaque layer LM, each window CW being centered on a respective one of the lens portions SL. AlthoughFIG. 3shows an array of just nine windows, it will be appreciated that, in practice, the MLA may comprise as many as one million microlenses, or more.

FIG. 5is a schematic representation of a MLA used in a lithographic apparatus, also showing the corresponding pattern of projected radiation spots. To reduce the amount of the beam cross section that is blocked (i.e., to maximize the proportion reaching the target substrate) the windows may be made as large as possible. The projected image spots I on the underlying substrate also being shown. These image spots are circular (aerial).

SECOND EXEMPLARY LITHOGRAPHIC APPARATUS

FIG. 1schematically depicts a lithographic projection apparatus100according to an embodiment of the invention. Apparatus100includes 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 elements104may 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 CaF2 lens 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 system108may project an image of the array of individually controllable elements104onto substrate114. Alternatively, projection system108may project images of secondary sources for which the elements of the array of individually controllable elements104act as shutters. Projection system108may 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 expander126, for example. Illuminator124may comprise an adjusting device128for setting the outer and/or inner radial extent (commonly referred to as σ outer and a 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 source112may be within the housing of lithographic projection apparatus100(as is often the case when source112is a mercury lamp, for example). In alternative embodiments, source112may 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 directing 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 table106can 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 may also be used to position the array of individually controllable elements104. It will be appreciated that beam110may alternatively/additionally be moveable, while object table106and/or the array of individually controllable elements104may have a fixed position to provide the required relative movement.

In an alternative configuration of the embodiment, substrate table106may 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, substrate114may 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 apparatus100maybe 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.

THIRD EXEMPLARY LITHOGRAPHIC APPARATUS

FIG. 6depicts part of a lithographic apparatus, according to one embodiment of the invention.FIG. 6comprises an illumination system arranged to supply a beam1of radiation. Beam1is directed by a beam splitter4onto an array2of controllable elements21. Control means (not shown) controls states of elements21, so that a desired pattern can be imparted to beam1. The patterned beam10, reflected from array of elements21, then passes through beam splitter4and is projected by a projection system5onto a target surface31of a substrate3.

In this embodiment, projection system5includes a beam expander, which comprises a first lens61arranged to receive the patterned beam10and focus it through an aperture in an aperture stop62. A further lens63is located in the aperture. Beam10then diverges and is focused by a third lens64(e.g., a field lens) to form a substantially parallel, expanded, and patterned beam11. Projection system5further comprises an array of lenses7arranged to receive expanded and patterned beam11. Array of lenses7divides expanded and patterned beam11cross section into a plurality of substantially polygonal portions, and focuses each substantially polygonal portion to form a respective radiation spot12on target surface31of substrate3. Array of lenses7divides beam11in the sense that each radiation spot12on target surface31is derived from a respective polygonal portion of beam11. In one example, array of lenses7is arranged to focus square portions of the beam cross section to form corresponding square radiation spots12on target surface31.

Array of lenses7comprises a first parallel array of cylindrical lenses71in series with a second parallel array of cylindrical lenses72. An arbitrary set of axes, X, Y & Z, is shown inFIG. 6, and in this example the Z direction is parallel to the beam projection direction.

First array71of cylindrical lenses is arranged such that each of its cylindrical lenses focuses a portion of beam11towards a focal line, which is parallel to the X axis. The cylindrical lenses of first array71can be regarded as extending across the beam direction in a first direction.

Second array72of cylindrical lenses comprises lenses of the same size and pitch as those of first array71, but each cylindrical lens of second array72extends in a second direction across the beam, so that it focuses incident radiation towards a focal line that is parallel to the Y axis. First and second arrays71and72can be regarded as being arranged such that they are generally parallel to target surface31of substrate3, but second array72has been rotated 90° about the X axis with respect to first array71, so that the cylindrical lenses of the two arrays are crossed. It is to be appreciated, the size and pitch of the lenses of the two arrays may not be the same.

The series combination of crossed cylindrical lens arrays has the effect of focusing beam11into an array of radiation spots12. In this example, each radiation spot12corresponds to a respective one of controllable elements21.

In one example, a number N of cylindrical lenses in first array71is equal to that in second array72, and a number of projected radiation spots12is equal to N×N. In this example, first array71has a longer focal length than does the second array72, and the focal planes of both arrays71,72are arranged to be coplanar, falling on target surface31.

The distance between first lens array71and target substrate31is generally referred to as a free working distance, and this should be as large as possible. It will be appreciated that the free working distance is determined by the focal length of second lens array72.

In one example, first lens array71may have a focal length of approximately 1 mm, and second lens array72may have a thickness of approximately 200 microns, giving a maximum free working distance of 800 microns if second lens array72is as close as possible to first array71.

In one example, a combined lens array formed from first and second arrays71,72may, have a numerical aperture of about 0.15.

It will be appreciated that although the lenses of first and second lens arrays71,72are being described as cylindrical, this does not necessarily mean that their curved surfaces exactly follow circular paths; they may have different curvature. In its broadest sense, a cylindrical lens should be interpreted as any lens which focuses incident parallel light to a focal line.

FIG. 7is a schematic representation of a lens array and illustrates the focusing action of array of lenses on an incident patterned beam, according to one embodiment of the invention. This Figure shows a focusing action of a lens array suitable for use in embodiments of the invention, such as that illustrated inFIG. 6. Again, array of lenses comprises a first array71of cylindrical lenses A, B, C in series with a second array72of parallel, cylindrical lenses A, B, C. First array71receives beam11, which may or may not have been previously expanded. Second array72then receives the resultant focused patterned beam from first array71.

It will be appreciated that each of the arrays71and72is shown to have three cylindrical lenses only for simplicity. There may be in excess of 1,000 microcylindrical lenses in each array.

In one example, first array71comprises a substrate (or body)73of transparent material and cylindrical lenses A, B, and C are provided by respective portions of substrate73. A lower surface75of substrate73is substantially flat and is arranged so as to be parallel with the X Y plane. An upper surface of substrate73is shaped to form three cylindrical lenses A, B, and C. Each cylindrical lens comprises a cylindrical surface74.

In this example, the boundaries between adjacent cylindrical lenses A, B, and/or C run parallel to the X direction and each cylindrical lens portion focuses incident radiation to a focal line, which is also parallel to the X axis. The focal lines of all three lenses of first array71are coplanar.

In this example, second array72of cylindrical lenses has the same structure as first array71, but the cylindrical lenses A, B, and C are orientated such that their focal lines are parallel to the Y axis (i.e., perpendicular to the X axis). A patterned beam11, incident on the series combination of crossed cylindrical lens arrays, is shown. Patterned beam cross section is denoted by reference numerical13. The combined effect of the two cylindrical arrays on beam11is, effectively, to divide its cross section13into a plurality (e.g., 9) rectangular portions14. Each rectangular portion14is focused (i.e., concentrated) to form a respective radiation spot12on a target plane (not shown), which, can correspond to a position of a target surface of a substrate.

In this example, the array of lenses projects a radiation pattern, which is a rectangular array of circular radiation spots12. Each radiation spot12is the result of the combined focusing action of a respective cylindrical lens in first array71and a respective cylindrical lens in second array72. A rectangular portion14aof beam cross section13is focused by lens A of first array71and then by lens A of second array72to form radiation spot12a. Similarly, a rectangular portion14bis focused by lens B of first array and lens C of second array to form spot12b.

In one example, the two cylindrical lens arrays71,72can be regarded as being assembled to form a 2D lens array. The image of this 2D lens array is projected onto the target substrate.

In one example, the two cylindrical lens arrays71and72have a same pitch. For example, the pitch between the cylindrical lenses may be between approximately 0.05 and approximately 1.5 mm. The numerical aperture (NA) of the 2D lens array may, for example, be between approximately 0.05 and approximately 0.3 depending on the imagining resolution requirements.

In this embodiment, lens arrays71and72comprise no masking structure, and an aperture opening of each cylindrical lens array71and72is as large as the pitch. Theoretically, therefore, 100% of the beam cross section13is focused onto the target substrate.

In this embodiment, lens arrays71,72are formed from separate respective substrates73. They may be rigidly attached together, for example by bonding first surface of second array72to second surface of first array71at contact points (or lines) using suitable adhesive. Alternatively, first and second arrays71and72may be rigidly attached together, to support the lenses in the appropriate series configuration. Thus, the lenses may be manufactured, then glued together.

InFIG. 7, the curved lens surfaces are shown formed on first surfaces of substrates73. It will be appreciated that in alternative embodiments the curved lens surfaces may be formed on second surface, for one or both arrays71and/or72. Also, although the lenses inFIG. 7have the same pitch, in alternative embodiments the pitches may differ.

It will be appreciated that array of lenses shown inFIG. 7is particularly suited for projecting a beam patterned by a rectangular array of controllable elements, such that each projected radiation spot12corresponds to a respective one of the controllable elements. It will also be appreciated that a lens array of the type shown inFIG. 7may also be used in an illuminator of apparatus, such as that shown inFIG. 1, to divide the radiation beam provided from the source into a plurality of rectangular portions, and focus each rectangular portion onto a respective one of the controllable elements in the rectangular patterning array, such as is shown inFIGS. 10 and 11.

FIG. 8is a schematic representation of a lens array and also depicts the corresponding array of projected radiation spots, according to one embodiment of the invention. This shows a plan view of a simplified lens array7. Lens array7represents a 2D lens array formed by two crossed cylindrical lens arrays. Array of lenses7comprises a plurality of lenses, each of which is arranged to receive and focus an incident rectangular portion of a patterned beam. Each lens76of lens array7has a square aperture. Each lens76may be provided by a single lens component or a series of lens components along a beam direction. Lenses76are arranged to provide a high fill ratio, which may be 98% or more. This figure corresponds to the proportion of the incident beam cross section that is focused onto the target substrate.

FIG. 9is a schematic representation of a lens array, according to one embodiment of the invention. A cylindrical lens array71comprises a transparent substrate73having a substantially flat upper surface75and a lower surface that comprises cylindrical portions74arranged to define an array of three parallel cylindrical lenses. In this embodiment, a masking structure in the form of lines77of radiation blocking material is formed on first surface75. In certain applications this provision of a masking structure may be desirable to prevent cross talk. Even with the masking structure, however, array of lenses71is arranged to focus 95% of an incident beam11. Each cylindrical lens focuses a respective rectangular portion14of a patterned beam cross section13. For example, cylindrical lens A receives and focuses portion14a, and can thus deliver a focused rectangle of radiation15ato some other component (e.g., a “crossed” second array of cylindrical lenses) or to a target surface. The masking structure77of the array71blocks a portion17of incident beam11.

CONCLUSION