NL2015012A

NL2015012A - Lithographic apparatus and device manufacturing method.

Info

Publication number: NL2015012A
Application number: NL2015012A
Authority: NL
Inventors: Huang Yang-Shan; Van Berkel Koos; Johannes Josephus Van Dijsseldonk Antonius; Van Eijk Jan; Bernard Plechelmus Van Schoot Jan; Petrus Martinus Bernardus Vermeulen Johannes
Original assignee: Asml Netherlands Bv
Priority date: 2014-07-24
Filing date: 2015-06-23
Publication date: 2016-06-27
Also published as: WO2016012174A1

Description

LITHOGRAPHIC APPARATUS AND DEVICE MANUFACTURING METHOD

BACKGROUND

Field of the Invention

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

Description of the Related Art 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 such a case, 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. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. In such so-called scanners, both the patterning device and the substrate need to reverse their travelling direction in between the scanning of two target portions. Such a reversal of travelling direction requires that the velocity of the stages supporting the respective patterning device and the substrate is reduced to zero in the scanning direction and subsequently increased to the desired velocity in the opposite direction. In order to decelerate and accelerate the stages, comparatively large forces need to be applied to the stages. Since no exposure is performed during such acceleration and deceleration, it is desirable to keep the time to decelerate and accelerate the stages as short as possible. In order to realize this, conventional lithographic apparatuses are therefore typically equipped with powerful electromagnetic linear motors and actuators to provide the required forces.

The described conventional scanning process has several drawbacks which are in particular caused by the required reversals in between exposures.

During the acceleration and deceleration of the stages, comparatively large Ohmic losses may occur in the motors and actuators that drive the stages. These losses need to be evacuated (e.g. by means of cooling arrangements mounted to the stages), in order to avoid heating (and thus deformation) of the substrate or patterning device that is supported by the stages.

Further, the application of comparatively large forces on the stages, (in order to decelerate and accelerate the stages) may cause deformations, particularly within the stages, and vibrations throughout the lithographic apparatus that may e.g. be transferred to neighbouring machines via the floor. As a result, an alignment of the patterning device and the substrate may adversely be affected.

SUMMARY

It would be desirable to provide in an alternative way of exposing a plurality of target portions on a substrate, whereby at least one of the aforementioned problems is mitigated.

According to a first aspect of the present invention, there is provided a lithographic apparatus comprising: - an illumination system configured to condition a radiation beam; - a rotary drive adapted to move a flexible patterning device along a closed loop trajectory, the closed loop trajectory having a straight portion and a curved portion, a curvature of the flexible patterning device substantially corresponding to a curvature of the closed loop trajectory; - a substrate table constructed to hold a substrate; - wherein the rotary drive comprises a pulley assembly configured to: o engage, during use, the flexible patterning device, and o maintain, during use, a portion of the flexible patterning device that is situated along the straight portion of the trajectory substantially flat, - the substantially flat portion of the patterning device being configured to impart the radiation beam with a pattern in its cross-section to form a patterned radiation beam, and; - a projection system configured to project the patterned radiation beam onto a target portion of the substrate.

According to a second aspect of the present invention, there is provided a lithographic apparatus comprising - an illumination system configured to condition a radiation beam; - a rotary drive comprising a pulley assembly having a substantially cylindrical surface for during use, holding a flexible patterning device, a curvature of the flexible patterning device substantially corresponding to a curvature of the cylindrical surface; - a substrate table constructed to hold a substrate; - wherein the illumination system comprises an optical assembly, the optical assembly being configured to: o condition the radiation beam to have a curved focal plane, a curvature of the curved focal plane substantially matching a curvature of a portion of the flexible patterning device and o project the conditioned radiation beam onto the portion of the flexible patterning device - a projection system configured to project the patterned radiation beam onto a target portion of the substrate.

According to a third aspect of the present invention, there is provided a device manufacturing method comprising projecting a patterned beam of radiation onto a substrate using a lithographic apparatus according to the first or second aspect of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

Figure 1 depicts a lithographic apparatus according to an embodiment of the invention; Figure 2 depicts a typical trajectory to be followed by a substrate during an exposure process performed by a conventional lithographic apparatus.

Figure 3 schematically depicts a front view of a rotary drive as can be applied in a lithographic apparatus according to the present invention;

Figure 4 schematically depicts a flexible patterning device provided with a pattern;

Figure 5 schematically depicts a trajectory as can be followed by a substrate during an exposure process performed by a lithographic apparatus according to the present invention; Figure 6 schematically depicts two rotary drives as can be applied in a lithographic apparatus according to the present invention;

Figure 7 schematically depicts a rotary drive including a single pulley provided with a deformable layer, as can be applied in a lithographic apparatus according to the present invention.

Figure 8 schematically depicts a rotary drive including a plurality of actuators for deforming an outer surface of a deformable layer.

Figure 9 schematically depicts a rotary drive and an optical assembly as can be applied in an embodiment of the present invention.

Figure 10 schematically depicts a substrate having target portions consisting of a plurality of sub-portions.

Figure 11 schematically shows the application of two patterns at two sub-portions using a lithographic apparatus according to the present invention.

Figure 12 schematically shows a rotary drive including a plurality of pulley assemblies as can be applied in an embodiment of the present invention.

Figure 13 schematically shows a pair of rotary drives as can be applied in an embodiment of the present invention.

DETAILED DESCRIPTION

Figure 1 schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus includes an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or any other suitable radiation), and a first positioning device PM configured to accurately position a patterning device (e.g. a mask) MA in accordance with certain parameters. In accordance with an embodiment of the present invention, the first positioning device PM is configured to hold and position a flexible patterning device MA. Within the meaning of the present invention, ‘flexible patterning device’ is used to denote a pattering device that is deformable in contrast to known conventional patterning devices which are considered substantially rigid. In particular, a flexible patterning device is considered bendable such that it can be mounted to a cylindrical surface. The flexible patterning devices as may be applied in an apparatus according to the present invention may e.g. be manufactured from a foil or thin film. The apparatus also includes a substrate table (e.g. a wafer table) WT or "substrate support" constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioning device PW configured to accurately position the substrate in accordance with certain parameters. The apparatus further includes a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. including one or more dies) of the substrate W.

The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, actively deformable (e.g. using Piezo-electric actuation), or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.

The first positioning device PM supports, i.e. bears the weight of, the patterning device. It holds the patterning device 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 first positioning device PM may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.”

The term “patterning device” used herein 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 so as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Below, a more detailed description is provided of the patterning devices that can be applied in combination with the present invention. The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic, actively deformable (e.g. using Piezo-electric actuators), optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”.

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

The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques can be used to increase the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that a liquid is located between the projection system and the substrate during exposure.

Referring to figure 1, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD including, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

The illuminator IL may include an adjuster AD configured to adjust 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 include various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section.

The radiation beam B is incident on the patterning device (e.g., mask MA), which is held on the first positioning device PM, and is patterned by the patterning device. Having traversed the 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 positioning device PW and position sensor IF (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 positioning device PM and another position sensor (which is not explicitly depicted in Figure 1) can be used to accurately position the mask MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In accordance with the present invention, movement of the patterning device MA is realized using the first positioning device PM, which includes a rotary drive configured to move a flexible patterning device along a closed loop trajectory. This is explained in more detail below. In general, the movement of the substrate table WT or "substrate support" may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. Mask MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks PI, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks may be located between the dies.

In a conventional lithographic apparatus, the patterning device MA could e.g. be a substantially rigid plate held on a mask table or mask support. Such a support may then be positioned using a positioning device including a long stroke module and a short-stroke module.

Typically, such a conventional apparatus would be operated in a scan mode, whereby the mask table or mask support and the substrate table are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion, e.g. a target portion C as shown in Figure 1. Once such a target portion is scanned (and thus exposed to the patterned radiation beam), a subsequent target portion (e.g. an adjacent target portion) needs to be exposed.

Using the conventional lithographic apparatus, the consecutive scanning of two target portions requires that both the patterning device and the substrate need to reverse their travelling direction in between the scanning of the two target portions.

Such a reversal of travelling direction requires that the velocity of the mask support and the substrate support (supporting the respective patterning device and the substrate) is reduced to zero in the scanning direction and subsequently increased to the desired velocity in the opposite direction. In addition to reversing the direction, the substrate support needs to be displaced in a direction perpendicular to the scanning direction as well, in order to align a next target portion that is to be exposed with the patterned radiation beam.

Figure 2 shows a typical meandering trajectory 200 that is followed by a substrate support (not shown) supporting a substrate 100. The meandering trajectory 200 as shown is an alternating sequence of scanning movements 200.1 and reversal (or meandering) movements 200.2. During the scanning movements, the substrate is moved, at a substantially constant velocity underneath the patterned radiation beam. During the reversal movements, the velocity of the substrate (c.g. the nominal scanning velocity in the Y-direction) is reversed to a nominal velocity in the -Y-direction and, during this reversal, the substrate is displaced, in the X-direction, to align the next target portion that is to be exposed, with the patterned radiation beam.

In order to perform such a meandering trajectory, the supports supporting the patterning device and the substrate need to be appropriately decelerated and accelerated. In order to do so, comparatively large forces need to be applied, i.e. provided by the positioning devices to the supports. Since no exposure is performed during such acceleration and deceleration, it is desirable to keep the time to decelerate and accelerate as short as possible. In order to realize this, conventional lithographic apparatuses are therefore typically equipped with powerful electromagnetic linear motors and actuators to provide the required forces. Despite the use of such powerful motors, typically more than half the operating time of the apparatus is spent on accelerating or decelerating the supports, rather than on exposing the substrate.

In addition to the large amount of idle time during which there is no exposure performed, the above described conventional way of scanning a substrate has the following additional drawbacks: During the acceleration and deceleration of the supports, comparatively large Ohmic losses may occur in the positioning devices that position the supports. These losses need to be evacuated (e.g. by means of cooling arrangements mounted to the stages), in order to avoid heating (and thus deformation) of the substrate or patterning device that is supported by the supports.

Further, the application of comparatively large forces on the supports, (in order to decelerate and accelerate the supports) may cause deformations, particularly within the stages, and vibrations throughout the lithographic apparatus that may be transferred to neighbouring machines via the floor. As a result, an alignment of the patterning device and the substrate may be adversely affected.

In order to at least partly overcome or mitigate these adverse effects, the present invention proposes an alternative way of scanning a substrate.

In accordance with the present invention, a rotary drive is used to position a patterning device, in particular a flexible patterning device.

In accordance with the present invention, the conventional positioning device as applied to position a mask support or mask table (to which a substantially rigid, plate shaped, patterning device or mask is mounted) is replaced by a rotary drive configured to move a flexible patterning device along a closed loop trajectory.

By doing so, the scanning of a row or column of adjacent target portions on a substrate can be performed without requiring reversal movements as described above. Rather, by moving the patterning device along a closed loop trajectory, the patterning device can keep moving in the same direction in between the scanning of two adjacent target portions of the same row or column. In accordance with the first aspect of the invention, the closed loop trajectory followed by the flexible pattering device has a straight portion and a curved portion, a curvature of the flexible patterning device substantially corresponding to a curvature of the closed loop trajectory.

Figure 3 schematically shows a first embodiment of a rotary drive as can be applied in the present invention.

Figure 3 schematically shows a rotary drive 300 including a pulley assembly, the pulley assembly comprising a pair of pulleys 310.1 and 310.2 and a belt 320 that is looped over the pulleys 310.1, 310.2. The rotary drive further includes a rotary motor 330 for driving the pulley assembly as indicated by the arrow 340, thereby driving the belt 320 as indicated by the arrows 350.

In the embodiment as shown, an outer surface 322 of the belt 320 forms a closed loop surface to which a flexible patterning device can be mounted or connected.

Within the meaning of the present invention, a flexible patterning device is a patterning device that can undergo substantial deformations such as bending. As a result, a curvature of the flexible patterning device can adjust to a curvature of a closed loop trajectory imposed by a rotary drive to which it is mounted. In accordance with the first aspect of the present invention, the pulley assembly is configured to engage, during use, with a flexible pattering device 360. When the belt 320 is driven by the rotary motor 330, the flexible patterning device 360 thus travels along the closed loop trajectory defined by the outer surface 322 of the belt 320.

In accordance with the first aspect of the present invention, the closed loop trajectory followed by the flexible patterning device has a straight portion 372 and a curved portion 374 . Further, the pulley assembly of the rotary drive 300 is configured to maintain, during use, a portion of the flexible patterning device that is situated along the straight portion of the trajectory substantially flat. This can e.g. be achieved, as shown in Figure 3, by providing two or more pulleys over which a belt is looped. As a consequence, parts of the belt that are not contacting the outer surface of any of the pulleys will remain substantially straight or flat and, as a result, portions of the flexible patterning device that are situated along those parts are maintained substantially flat as well. As shown in more detail below, the pulley assembly may comprise further measures to maintain or control the flatness of a portion of the flexible patterning device.

In the embodiment as shown, the flexible patterning device 360 is a reflective patterning device. During use, a radiation beam 380 (e.g. provided by an illumination system IL as shown in Figure 1) is provided (i.e. projected) onto a substantially flat portion of the flexible patterning device, e.g. the portion of the flexible patterning device that is located on the straight portion of the closed loop trajectory . The reflected radiation beam 382 is a patterned radiation beam which can be provided to a conventional projection system PL as e.g. shown in Figure 1.

Because the radiation beam 380 is provided to a substantially flat portion of the flexible patterning device, no particular measures need to be taken with respect to the illumination system or the projection system to obtain the patterned radiation beam and provide the patterned radiation beam to a substrate.

In order to appropriately pattern the radiation beam with the pattern of the patterning device, the pattern needs to be provided in a focal plane of the illumination system. Typically, such a focal plane is substantially flat. Therefore, by ensuring that the radiation beam is imparted by a substantially flat portion of the patterning device, the focal plane as provided by the illumination system need not be modified, to obtain a patterned radiation beam.

A flexible patterning device as can be applied in the embodiment shown in Figure 3 can e.g. be a flexible rectangular shaped foil- or film-like structure as e.g. shown in Figure 4.

The structure has a width W and a length L and is provided with a pattern P, having a width w and a length 1.

In an embodiment, the pulley assembly is configured such that the length of the closed loop trajectory substantially corresponds to the length L of the patterning device.

In a preferred embodiment, the length L of the patterning device is selected such that the length L corresponds to (D+d)*M, wherein: D equals the length of a target portion on the substrate, d equals the length of a gap between adjacent target portions in the scanning direction and M equals the magnification of the projection system PL, typically 1/4 or 1/5. By doing so, both the rotary drive as applied in the first aspect of the present invention, and the positioning device used to position the substrate table holding the substrate can operate at a substantially constant speed during the scanning of an entire column of target portions. Figure 5 schematically shows the scanning of an entire column of target portions 500 on a substrate 510, as can be realised using the apparatus according to the present invention. Compared to the meandering process as e.g. shown in Figure 2, the apparatus according to the present invention enables a scanning of an entire column along a substantially straight line 500, during which scanning all target portions along the line can be provided with a pattern A of a patterning device. Distances D and d as described above are also indicated in Figure 5.

As mentioned, in order to realise such substantially continuous scanning of an entire column, the length of the patterning device as applied to the rotary drive should preferably correspond to the length of the closed loop trajectory defined by the pulley assembly.

The pulley assembly as schematically shown in Figure 3 comprises two pulleys. Alternative embodiments may include more than two pulleys as e.g. illustrated in Figure 6.

Figure 6 schematically shows two alternative embodiments whereby the pulley assembly includes 3 respectively 4 pulleys 610 about which a belt 620 is provided. In the embodiments as shown, a rotary motor 630 is schematically shown for driving one of the pulleys 610 and the belt 610.

It may be advantageous to limit the number of pulleys to two, as shown in Figure 3. During the scanning operating, the flexible patterning device is deformed as it complies to the curvature of the closed loop trajectory. As such, each portion of the flexible patterning device is altematingly flattened and bend, whereby the bending radius of the flexible patterning device is determined by the outer radius of the pulley increased with the thickness of the belt. It may be advantageous to have this bending radius as large as possible, in order to avoid or mitigate effects of fatigue in the patterning device or the belt. For a given length of the flexible patterning device, the bending radius when using only two pulleys may be selected larger compared to when more than two pulleys are used.

Note that, in an embodiment, more than one rotary motor may be provided to drive the various pulleys of the pulley assembly.

As mentioned, it may be advantageous to ensure that the pulley assembly is configured such that the length of the closed loop trajectory substantially corresponds to the length L of the patterning device applied. In order to accommodate for flexible patterning devices having a different length, various options exist.

In an embodiment, the rotary drive comprises a plurality of pulley assemblies (which may be driven by the same rotary motor or by separate motors) having belts of a different length, so as to provide in closed loop trajectories of a different length.

As an alternative, or in addition, a distance between the pulleys of the pulley assembly can be made adjustable thereby adjusting the length of the belt defining the closed loop trajectory.

In an alternative embodiment, the pulley assembly does not comprise a belt. Rather, the flexible patterning device is directly looped around the pulleys of the pulley assembly.

In such arrangement, it may be advantageous to drive each of the pulleys so as to reduce the tensile stress in the patterning device.

Such an arrangement can be made easily adjustable to accommodate flexible patterning devices of different lengths by making the distance between the pulleys adjustable.

In an embodiment, the pulley assembly of the rotary drive comprises a single pulley. In such embodiment, an outer surface of the pulley may be provided with a deformable layer to which the flexible patterning device can be mounted.

In an embodiment, the deformable layer comprises a plurality of actuators, configured to control a thickness of the deformable layer.

Figure 7 schematically shows such an embodiment of a rotary drive as can be applied in an apparatus according to the first aspect of the invention.

Figure 7 schematically shows a rotary drive 700 comprising a pulley assembly that comprises a pulley 710 and a deformable layer 720 looped around the pulley 710. A flexible patterning device 760 (e.g. a foil or film-like stmeture provided with a pattern) is mounted to the outer circumference of the deformable layer 720. The rotary drive further comprises a rotary motor 730 for driving the pulley assembly, as indicated by the arrow 740. As can be seen in Figure 7, the deformable layer 720 is deformed in such manner that a part 750 of the outer circumference of the deformable layer 720 is substantially flat. The outer circumference of the deformable layer 720 thus defines, in a similar manner as the outer surface of the belt 320 of Figure 3, a closed loop trajectory having a curved portion and a straight portion. In this embodiment, in a similar manner as described in Figure 3, a radiation beam 380 (e.g. provided by an illumination system TL as shown in Figure 1) can be projected onto the substantially flat portion 750 of the flexible patterning device. The reflected radiation beam 382 is a patterned radiation beam which can be provided to a conventional projection system PL as e.g. shown in Figure 1.

Because the radiation beam 380 is provided to a substantially flat portion 750 of the flexible patterning device, no particular measures need to be taken with respect to the illumination system or the projection system to obtain the patterned radiation beam and provide the patterned radiation beam to a substrate.

In order to deform the deformable layer 720 to which the flexible patterning device 760 is mounted, several options exist.

In a first example, external forces can be exerted on the deformable layer in order to provide the desired local deformation of the layer, so as to arrive at the substantially flat portion 750. A gas flow may e.g. be directed to the outer surface of the deformable layer 720, thereby compressing the layer.

In a second example, a plurality of actuators is provided to deform the deformable layer. Such actuators may e.g. be provided along the circumference of the deformable layer, e.g. incorporated in the deformable layer or as an interface layer between the pulley and the deformable layer.

An example of the latter arrangement is schematically shown in Figure 8.

Figure 8 schematically shows a detail of a rotary drive as can be applied in a lithographic apparatus according to the present invention.

The rotary drive as shown in Figure 8 comprises a pulley 810 and a rotary motor 830 for driving the pulley. Mounted to the pulley 810 is a deformable layer 820. The deformable layer 820 is mounted to the pulley 810 via a plurality of actuators 850. These actuators 850 can e.g. be piezo-electrical actuators, configured to deform when a voltage is applied to them. In particular, the actuators can be configured to shorten (in the direction indicated by the arrows 840) when a voltage, an electric charge or a current is supplied. By doing so, the deformable layer 820 that is connected to the actuators 850 is pulled inward. By appropriate control of the voltages applied to the plurality of actuators, the deformable layer 820 can be deformed such that a portion 840 of the outer circumference of the deformable layer 820 is substantially flat. When a flexible patterning device is mounted to the outer circumference of the deformable layer, a portion of the flexible patterning device will thus be substantially flat and may be used to impart a radiation beam, as e.g. shown in Figure 3.

Other types of actuators such as magneto-strictive, electromagnetic or micro-electromechanical systems (MEMS)-based actuators may be applied as well to deform the deformable layer. Although the embodiments shown in Figures 3 and 6 are configured such that a part of the flexible patterning device is substantially flat, additional measures as described in relation to Figures 7 and 8 could be applied as well in these embodiments, in order to control the position and flatness of the relevant part of the flexible patterning device, i.c. the part that is subjected to the radiation beam. In particular, the flatness of the flexible patterning device can e.g. be controlled by: exerting electromagnetic forces onto the belt and / or the flexible patterning device, exerting air-pressure forces onto the belt and/or flexible patterning device.

- MEMS-type actuators incorporated in the belt and/or the flexible patterning device.

As such, embodiments may be devices whereby the actuators are either moving along with the flexible patterning device (included in the belt or the patterning device itself) or are substantially stationary relative to the flexible patterning device (e.g. using external forces such as air-pressure forces).

In an embodiment, the flexible patterning device may e.g. be manufactured based on Al, Ag or Au. The embodiments as describes above make use of a flexible patterning device which can be deformed such that, while the flexible patterning device is moved along a closed loop trajectory, part of the flexible patterning device can be maintained substantially flat. As a result, the radiation beam as provided by an illumination system IL (which typically has a flat focal plane) can be readily projected onto the substantially flat portion of the flexible patterning device, in order to form the patterned radiation beam.

In accordance with the second aspect of the present invention, an alternative to the above embodiments is presented. In the alternative arrangement, it is not required to provide in a substantially flat portion to impart the radiation beam. Rather, in accordance with the second aspect of the present invention, the illumination system of the lithographic apparatus comprises an optical assembly, that is configured to: - condition the radiation beam to have a curved focal plane, a curvature of the curved focal plane substantially matching a curvature of a portion of a flexible patterning device (which can e.g. be mounted to a cylindrical surface of a pulley driven by a rotary motor) and - project the conditioned radiation beam onto the portion of the flexible patterning device, to obtain a patterned radiation beam.

Figure 9 schematically shows a rotary drive and an optical assembly of the illumination as can be applied in a lithographic apparatus according to the second aspect of the present invention. Figure 9 schematically shows a rotary drive comprising a pulley 910 and a rotary motor 930 for driving the pulley. A flexible patterning device 960 is mounted to an outer, substantially cylindrical surface of the pulley 910. This substantially cylindrical surface may be considered to form a closed loop trajectory in a similar manner as described above.

Figure 9 further shows an optical assembly 980 which is part of the illumination system of the lithographic apparatus according to the second aspect of the invention, the optical assembly 980 being configured to convert a substantially parallel radiation beam 985 to a converging radiation beam 986 having a curved focal plane 988, the curved focal plane substantially coinciding with a portion of the flexible patterning device 960 that is mounted to the pulley 910.

In order to realise such a conversion from a substantially parallel radiation beam 985 to a converging radiation beam 986 having a curved focal plane 988, the optical assembly 980 can e.g. comprise MEMS based deformable optics, e.g. a deformable two-dimensional mirror array. As an alternative, or in addition, the optical assembly 980 may comprise one or more deformable lenses. In an embodiment, the optical assembly 980 is configured such that the angle of convergence of the converging radiation beam 986 can be adjusted. By doing so, the curvature of the curved focal plane 988 can be adjusted, enabling the use of pulleys having different diameters, e.g. to accommodate flexible patterning devices of different lengths.

When the embodiment as shown is implemented, the reflected patterned radiation beam (assuming a reflective patterning device is used) will be a diverging patterned radiation beam. In an embodiment of the lithographic apparatus according to the second aspect of the present invention, the projection system comprising an optical assembly for converting the diverging patterned radiation beam to a parallel patterned radiation beam that is projected, by the projection system onto the target portion of the substrate. Such an optical assembly thus performs the inverse conversion of the conversion provided by the optical assembly 980. The same optical components (e.g. MEMS based deformable optics, deformable lenses) may be applied in such optical assembly.

Compared to the embodiments of the lithographic apparatus according to the first aspect of the present invention, the patterning device as applied in the lithographic apparatus according to the second aspect of the present invention is not deformed during the scanning process. The patterning device as e.g. mounted to the cylindrical outer surface of the pulley 910 maintains it cylindrical shape. As such, the patterning device is not subjected to any fatigue stress.

As an example of a patterning device which can be applied in the lithographic apparatus according to the second aspect of the present invention, a cylindrical patterning device can be mentioned. In such arrangement, the patterning device may thus be a solid cylindrical or tubular device whereby the pattern to be projected is provided on an outer surface of the cylinder or tube.

In such arrangement, care should be taken to ensure that the surface to which the pattern is provided (e.g. by etching) is sufficiently smooth i.e. corresponds to the required cylindrical shape. In case the shape of the surface locally deviates from the desired cylindrical shape, this may be compensated by the optical assembly. In order to provide such compensation, the optical assembly may comprise one or more deformable components such as deformable mirrors or lenses.

In order to appropriately position the patterning device, the rotary drive may e.g. include a 6 DOF controllable magnetic bearing. The use of such a magnetic bearing is also effective in controlling unwanted vibrations of the patterning device.

The lithographic apparatuses according to both the first and second aspect of the present invention provide substantial advantages over the conventional way of scanning (and thus exposing) a substrate.

In a conventional lithographic apparatus, a mask table or "mask support" (to which a substantially rigid, plate shaped patterning device is mounted) and a substrate table or "substrate support" are scanned synchronously while a pattern of the patterning device imparted to the radiation beam is projected onto a target portion (i.e. a single dynamic exposure). The velocity and direction of the substrate table or "substrate support" relative to the mask table or "mask support" may be determined by the (de-)magnification and image reversal characteristics of the projection system. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. When a target portion has been scanned, both the mask table and substrate table need to reverse their direction of movement, e.g. illustrated by the meandering pattern shown in Figure 2.

Such reversals take up a considerable part of the time available for processing the substrate.

When using a lithographic apparatus according to the present invention, the throughput of the apparatus (i.e. the number of substrates processed per unit of time) can be increased by a factor of ~2 or more.

Additional advantages are: - a reduced power requirement for the positioning devices used, i.e. the positioning device used to position the substrate and the rotary drive for driving the flexible patterning device.

- less force- and thermo-dynamical induced deformations and vibrations may result in an improved accuracy with respect to overlay and CD (critical dimension).

Due to the reduced power requirements, power sources and positioning devices can be reduced in size, thus reducing the operational cost of the lithographic tool for the customer.

As discussed above, it may be advantageous to ensure that the length of the patterning device substantially corresponds to the length of the closed loop trajectory (as shown in Figures 3 or 6-8) or the circumference of the pulley as shown in Figure 9. In such configuration, both the rotary drive and the substrate table can move at a substantially constant speed while scanning an entire column of target portions (as e.g. shown in Figure 5). In case the flexible patterning device does not cover the entire circumference or closed loop trajectory, it may be beneficial to altematingly scan a target portion and skip a target portion while traversing a column of the substrate.

In an embodiment, multiple flexible patterning devices or flexible patterning devices having multiple patterns may be applied to the pulley assemblies as described.

In such arrangement, the patterns as provided can either be the same or they may be different.

The latter case may advantageously be applied in case a target portion consists of multiple sub-portions that need to be exposed to different patterns.

Figure 10 schematically shows a substrate 1000 having a number of target portions 1010, each having 4 sub-portions that need to be exposed to a different pattern, whereby the target portion 1010 cannot be exposed by a single patterning device. Such a situation may occur under the following conditions:

In order to increase the Numerical Aperture of the projection system, the demagnification between the patterning device and the substrate may be increased, e.g. by a factor of two. When the width of patterned radiation beam as provided to the projection system is unaltered, the width of the exposed area is reduced by the same factor. In order to arrive at the size of a nominal target portion such as target portion 1010, several sub-portions need to be exposed and combined, such process being known as stitching. As shown, target portion 1010 needs to be exposed to 4 patterns, indicated as A, B, C and D.

When using an apparatus according to the present invention, patterns A and B may e.g. provided on a pulley assembly as described, whereupon a scanning as shown in Figure 5 can be performed. As a result of such scanning an exposed substrate as shown in Figure 11 is obtained.

In a similar manner, patterns C and D can be exposed to arrived at the desired pattern as shown in Figure 10.

As an alternative, the patterns A, B, C, and D can be exposed in one scanning movement, when the 4 patterns are provided one behind the other on a single patterning device. In such arrangement, an exchange of the patterning device need not be made. When such patterning device is used, the combined patterns (i.e. the assembly of patterns A, B, C and D provided on a target portion) are however no longer in line but are altematingly shifted by one sub-portion.

In an embodiment, the lithographic apparatus according to the present invention may comprise a plurality of rotary drives (each including a pulley assembly) as described or a rotary drive comprising a plurality of pulley assemblies.

Figure 12 schematically shows an embodiment of the latter, i.e. a rotary drive comprising a plurality of pulley assemblies.

The upper part of Figure 12 shows a rotary drive including a rotary motor 1200 configured to drive three pulley assemblies 1210.1, 1210.2 and 1210.3 via a shaft 1220, each of the pulley assemblies having a different diameter and configured to hold a flexible patterning device on an outer surface of the pulley assemblies.

Figure 12 further shows a radiation beam 1240 which can be projected onto one of the pulley assemblies in order to generate a patterned radiation beam. By displacing the rotary drive along the direction indicated by the arrow 1250, a different pulley assembly can be brought in front of the radiation beam 1240, in order to apply a different pattern. Clearly, pulley assemblies having the same diameter may be combined as well. In a similar manner, pulley assemblies as e.g. shown in Figures 3 or 6 may be combined in order to accommodate multiple patterning devices, thereby enabling a fast switching between different patterns to be exposed.

When a scanning process as e.g. shown in Figure 5 or Figure 11 is performed using a lithographic apparatus according to the present invention, both the substrate table and the rotary drive need to reverse their velocity.

As an alternative to reversing the velocity of the rotary drive, a pair of rotary drives may be applied, each driving a pulley assembly provided with a flexible patterning device, the drives rotating in opposite direction.

Figure 13 schematically shows such an arrangement including a pair of rotary motors 1300.1, 1300.2 driving a respective pulley assembly 1310.1, 1310.2 via shafts 1320.1 and 1320.2, whereby the drives are configured to drive the pulley assemblies in opposite direction, as indicated by the arrows 1330.

In such arrangement, when a column has been scanned, e.g. by projecting the radiation beam 1240 onto the pulley assembly 1310.2, the drives may be moved to the left in order to bring the pulley assembly 1310.1 in front of the radiation beam.

In such arrangement, the rotary drives need not reverse their velocity.

In order to drive the pulley assemblies as described in accordance with the present invention, electromagnetic motors are generally preferred. In a preferred embodiment, magnetic bearings are applied in order for the drives to operate substantially frictionless. In such arrangement, maintaining the pulley assemblies at a constant speed can be realized with a comparatively low power requirement.

Preferably, a thermal conditioning system is provided to control the temperature of the flexible patterning device. The illumination of the patterning device causes a thermal load on the patterning device. In order to be able to control the thermally induced deformation of the patterning device, the heat put into the patterning device need to be extracted.

Various options are available for implementing the thermal conditioning system.

As a first option, one could thermally condition the patterning device via the pulley assembly such as via pulleys 310.1 and 310.2 in the embodiment of Fig.3 or via pulley 710 in the embodiment of Fig.7. That is, the surface of the pulleys that is in contact with the flexible patterning device could be made of a thermally highly conductive material and cooled in order to create a temperature gradient pointing from the flexible patterning device to the pulley. As a result heat will be transferred from the flexible patterning device to the pulley. The heat received by the pulley could then be extracted elsewhere in the system, e.g., by a fluid flow interacting with the pulley.

As a second option, one could cool the flexible reticle by exposing the flexible patterning device to a fluid flow, e.g., an air flow. Preferably, the fluid flow interacts at any moment with that part of the flexible patterning device that is remote from the other part that is illuminated at the moment. For example, in the embodiment of Fig.3, the part that is being illuminated by the radiation beam 380 lies on the straight part 372 at the bottom of the Fig.3. The fluid flow then interacts with the opposite straight part at the top of Fig.3. This way, any vibrations that might be introduced through the interaction of the rotating patterning device and the fluid flow have time to die out or to get absorbed or damped by the pulley 310.2 so as to avoid any undesirable vibrations at the part being illuminated.

As a third option, the flexible patterning device is cooled by a fluid flow, e.g., air flow, at that part of the patterning device that is lying against one of the pulleys, or at those respective parts of the patterning device that are lying against a respective one of the pulleys.

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.

Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.

The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of or about 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.

The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.

The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the clauses set out below. Other aspects of the invention are set out as in the following numbered clauses: 1. A lithographic apparatus comprising: - an illumination system configured to condition a radiation beam; - a rotary drive adapted to move a flexible patterning device along a closed loop trajectory, the closed loop trajectory having a straight portion and a curved portion, a curvature of the flexible patterning device substantially corresponding to a curvature of the closed loop trajectory; - a substrate table constructed to hold a substrate; - wherein the rotary drive comprises a pulley assembly configured to: o engage, during use, the flexible patterning device, and o maintain, during use, a portion of the flexible patterning device that is situated along the straight portion of the trajectory substantially flat, - the substantially flat portion of the patterning device being configured to impart the radiation beam with a pattern in its cross-section to form a patterned radiation beam, and; - a projection system configured to project the patterned radiation beam onto a target portion of the substrate.

2. The lithographic apparatus according to clause 1, wherein the pulley assembly comprises a pair of pulleys and a belt that is looped around the pulleys, the belt having an outer surface for holding the flexible patterning device.

3. The lithographic apparatus according to clause 3, wherein a length of the belt substantially corresponds to a length of the flexible patterning device.

4. The lithographic apparatus according to clause 1, wherein the pulley assembly comprises two or more pulleys, the flexible patterning device during use being looped around the two or more pulleys.

5. The lithographic apparatus according to clause 1, wherein the pulley assembly comprises a pulley and a deformable layer looped around the pulley, an outer surface of the deformable layer being configured to hold the flexible patterning device.

6. The lithographic apparatus according to clause 4, further comprising a plurality of actuators configured to control a thickness of the deformable layer, so as to maintain a portion of the outer surface of the deformable layer substantially flat.

7. The lithographic apparatus according to clause 6, wherein the plurality of actuators includes piezo-electric actuators or MEMS-type actuators.

8. The lithographic apparatus according to any preceding clause, wherein the rotary drive comprises a rotary motor for driving the pulley assembly.

9. A lithographic apparatus comprising - an illumination system configured to condition a radiation beam; - a rotary drive comprising a pulley assembly having a substantially cylindrical surface for during use, holding a flexible patterning device, a curvature of the flexible patterning device substantially corresponding to a curvature of the cylindrical surface; - a substrate table constructed to hold a substrate; - wherein the illumination system comprises an optical assembly, the optical assembly being configured to: o condition the radiation beam to have a curved focal plane, a curvature of the curved focal plane substantially matching a curvature of a portion of the flexible patterning device and o project the conditioned radiation beam onto the portion of the flexible patterning device - a projection system configured to project the patterned radiation beam onto a target portion of the substrate.

10. The lithographic apparatus according to clause 9, wherein the flexible patterning device is a reflective patterning device and wherein the conditioned radiation beam is a converging radiation beam that is projected onto the reflective flexible patterning device, thereby forming a diverging patterned radiation beam, the projection system comprising an optical assembly for converting the diverging patterned radiation beam to a parallel patterned radiation beam that is projected, by the projection system onto the target portion of the substrate.

11. The lithographic apparatus according to clause 9 or 10, wherein the optical assembly of the illumination system and/or the optical assembly of the projection system comprises a deformable optical assembly.

12. The lithographic apparatus according to clause 11, wherein the deformable optical assembly comprises a two-dimensional micro-mirror array or a deformable lens.

13. A device manufacturing method comprising projecting a patterned beam of radiation onto a substrate using a lithographic apparatus according to any of the preceding clauses.

Claims

A lithography device comprising: an exposure device adapted to provide a radiation beam; a carrier constructed to support a patterning device, the patterning device being capable of applying a pattern in a section of the radiation beam to form a patterned radiation beam; 5 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.