Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70058—Mask illumination systems
  • G03F7/70083—Non-homogeneous intensity distribution in the mask plane
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70058—Mask illumination systems
  • G03F7/70075—Homogenization of illumination intensity in the mask plane by using an integrator, e.g. fly's eye lens, facet mirror or glass rod, by using a diffusing optical element or by beam deflection
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
  • G03F7/7055—Exposure light control in all parts of the microlithographic apparatus, e.g. pulse length control or light interruption
  • G03F7/70558—Dose control, i.e. achievement of a desired dose

Definitions

• An embodiment of the invention relates to a lithography apparatus - in particular a lithography apparatus with a faceted field mirror device and/or a faceted pupil mirror device - and to a method of manufacturing devices using such a lithography apparatus.
• Lithography is widely recognized as one of the key steps in the manufacture of integrated circuits (ICs) and other devices and/or structures.
• ICs integrated circuits
• lithography is becoming a more critical factor for enabling miniature IC or other devices and/or structures to be manufactured.
• a lithography apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate.
• a lithography apparatus can be used, for example, in the manufacture of ICs.
• 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.
• a single substrate will contain a network of adjacent target portions that are successively patterned.
• EUV radiation sources are typically configured to output radiation wavelengths of around 5-20 nm, for example, 13.5 nm or about 13 nm or 6.5 - 6.8 nm. Use of EUV radiation may constitute a significant step toward achieving small features printing. Such radiation is termed extreme ultraviolet or soft x-ray, and possible sources include, for example, laser-produced plasma sources, discharge plasma sources, or synchrotron radiation from electron storage rings.
• One design of an illumination system of an EUV optical apparatus employs a field mirror having an array of individually directable reflectors and a faceted pupil mirror.
• the individually directable reflectors are grouped into virtual field facets.
• Each virtual facet directs radiation onto a facet, referred to as a pupil facet, of the faceted pupil mirror.
• Each pupil facet together with any other mirrors in the illumination system, images the virtual field facet onto an illumination field (sometimes referred to as the slit) on the patterning device.
• the images of many virtual field facets overlap in the illumination field to increase uniformity of the illumination.
• a lithography apparatus comprising a field mirror having a plurality of individually directable reflectors and a pupil mirror having a plurality of pupil facets,
• controller configured to control the individually directable reflectors to deliver a desired dose profile to a target portion of a substrate, and a positioner configured to scan the substrate in a scanning direction whilst the substrate is being exposed.
• the lithography apparatus comprising a field mirror having a plurality of individually directable reflectors and a pupil mirror having a plurality of pupil facets, wherein the individually directable reflectors are divided into sets of adjacent individually directable reflectors to form virtual field facets and a pupil facet projects an image of a virtual field facet to fill an illumination field, the method comprising: controlling the individually directable reflectors of one virtual field facet so that a subset of the individually directable reflectors of the one virtual field facet do not direct radiation into the same pupil facet as the other individually directable reflectors of the one virtual field facet;
• the number of individually directable reflectors in the subset varies with time so that a desired dose profile is received by the target portion.
• a lithography apparatus comprising a field mirror having a plurality of individually directable reflectors and a pupil mirror having a plurality of pupil facets, and
• a controller configured to control the individually directable reflectors in a first mode to illuminate the whole of an illumination field with a first radiation intensity and in a second mode to illuminate a region of the illumination field with a second radiation intensity, the region of the illumination field being smaller than the whole illumination field and the second radiation intensity being greater than the first radiation intensity.
• the lithography apparatus comprising a field mirror having a plurality of individually directable reflectors and a pupil mirror having a plurality of pupil facets, wherein the individually directable reflectors are divided into sets of adjacent individually directable reflectors to form virtual field facets and a pupil facet projects an image of a virtual field facet to fill an illumination field, the method comprising: controlling the individually directable reflectors of each virtual field facet so that a subset of the individually directable reflectors of each virtual field facet do not direct radiation into the same pupil facet as the other individually directable reflectors of that virtual field facet;
• the subset of the individually directable reflectors of each virtual field facet are selected to be in at least one end portion of each virtual field facet in the first direction so that an end portion of the illumination field is not illuminated;
• the orientations of the subset of the individually directable reflectors of each virtual field facet are controlled so that they direct radiation into a different one of the pupil facets than the other individually directable reflectors of their virtual field facet.
• a lithography apparatus comprising a field mirror having a plurality of individually directable reflectors and a pupil mirror having a plurality of pupil facets, and
• a controller configured to control a set of adjacent individually directable reflectors so that a first subset of the set of adjacent individually directable reflectors directs radiation to a first pupil facet and a second subset of the set of adjacent individually directable reflectors directs radiation to a second pupil facet, the second subset being selected to provide a desired dose profile in an illumination field.
• the lithography apparatus comprising a field mirror having a plurality of individually directable reflectors and a pupil mirror having a plurality of pupil facets, wherein the individually directable reflectors are divided into sets of adjacent individually directable reflectors to form virtual field facets and a pupil facet projects an image of a virtual field facet to fill an illumination field, the method comprising: controlling the individually directable reflectors of one virtual field facet so that a subset of the individually directable reflectors of the one virtual field facet do not direct radiation into the same pupil facet as the other individually directable reflectors of the one virtual field facet;
• the orientations of the subset of the individually directable reflectors of the one virtual field facet are controlled so that they direct radiation into a different one of the pupil facets than the other individually directable reflectors of the one virtual field facet.
• a lithography apparatus comprising a field mirror having a plurality of individually directable reflectors and a pupil mirror having a plurality of pupil facets, and
• a controller configured to control the individually directable reflectors so that an edge part of a target portion adjacent an edge of a substrate receives a lower dose than a non- edge part of the target-portion.
• the lithography apparatus comprising a field mirror having a plurality of individually directable reflectors and a pupil mirror having a plurality of pupil facets, wherein the individually directable reflectors are divided into sets of adjacent individually directable reflectors to form virtual field facets and a pupil facet projects an image of a virtual field facet to fill an illumination field, the method comprising: controlling the individually directable reflectors of each virtual field facet so that a subset of the individually directable reflectors of each virtual field facet do not direct radiation into the pupil mirror;
• the target portion intersects an edge of the substrate and the subset of the individually directable reflectors is arranged so that an edge part of the target portion, the edge part being adjacent to the edge of the substrate, receives a lower dose than a non-edge part of the target portion, the non-edge part not being adjacent to the edge of the substrate.
• Figure 1 depicts schematically a lithography apparatus having reflective optics according to embodiments of the invention
• Figure 2 is a more detailed view of the apparatus of Figure 1 ;
• Figure 3 depicts a field mirror device having an array of field facets
• Figure 4 depicts a field facet made up of a set of individually directable reflectors
• Figure 5 depicts selective activation of individually directable reflectors to adjust dose
• Figure 6 depicts intensity changing with time
• Figure 7 depicts selective activation of individually directable reflectors to adjust dose across the width of the illumination field
• Figure 8 depicts intensity varying across the width of the slit and with time
• Figures 9, 10 and 11 depict selective activation of individually directable reflectors to control the size of the illumination field
• Figure 12 depicts redirection of radiation from a field mirror device to different facets of a pupil mirror
• Figure 13 depicts virtual field facets arranged to illuminate only a part of the illumination field
• Figure 14 depicts another arrangement of virtual field facets to illuminate only a part of the illumination field
• Figure 15 depicts a virtual field facet arranged to illuminate the whole of the illumination field
• Figure 16 depicts a virtual field facet arranged to illuminate only a part of the illumination field with part of the radiation directed to a beam dump;
• Figure 17 depicts a virtual field facet arranged to illuminate only a part of the illumination field without directing radiation to a beam dump;
• Figure 18 depicts a substrate having target portions overlapping the edge
• Figure 19 depicts an intensity profile varying in the X direction for use with a target portion overlapping the edge of a substrate.
• FIG. 1 schematically depicts a lithography apparatus 4100, including a source collector module SO, according to an embodiment of the invention.
• the apparatus comprises: an illumination system (illuminator) EIL configured to condition a exposure beam EB (e.g. EUV radiation); a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask or a reticle) MA and connected to a first positioner PM configured to accurately position the patterning device; a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate; and a projection system (e.g. a reflective projection system) PS configured to project a pattern imparted to the exposure beam EB by patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.
• an illumination system illumination system
• EIL configured to
• the support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device, the design of the lithography apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment.
• the support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device.
• the support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system.
• patterning device should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate.
• the pattern imparted to the radiation beam may correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.
• the patterning device may be transmissive or reflective.
• Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels.
• Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types.
• An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix.
• the projection system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of a vacuum. It may be desirable to use a vacuum for EUV radiation since gases may absorb too much radiation. A vacuum environment may therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.
• the apparatus is of a reflective type (e.g. employing a reflective mask).
• the lithography apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables). In such "multiple stage” machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure.
• the illuminator EIL receives an extreme ultra violet radiation beam from the source collector module SO.
• Methods to produce EUV radiation include, but are not necessarily limited to, converting a material into a plasma state that has at least one element, e.g., xenon, lithium or tin, with one or more emission lines in the EUV range.
• LPP laser produced plasma
• the desired plasma can be produced by irradiating a fuel, such as a droplet, stream or cluster of material having the required line-emitting element, with a laser beam.
• the source collector module SO may be part of an EUV radiation system including a laser, not shown in Figure 1 , for providing the laser beam exciting the fuel.
• the resulting plasma emits output radiation, e.g. EUV radiation, which is collected using a radiation collector, disposed in the source collector module.
• output radiation e.g. EUV radiation
• the laser and the source collector module may be separate entities, for example when a C0 2 laser is used to provide the laser beam for fuel excitation.
• the laser is not considered to form part of the lithography apparatus and the radiation beam is passed from the laser to the source collector module with the aid of a beam delivery system comprising, for example, suitable directing mirrors and/or a beam expander.
• the source may be an integral part of the source collector module, for example when the source is a discharge produced plasma EUV generator, often termed as a DPP source.
• the illuminator EIL may comprise an adjuster for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as ⁇ -outer and ⁇ -inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted.
• the illuminator EIL may comprise various other components, such as faceted field and pupil mirror devices. The illuminator EIL may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section.
• the exposure beam EB is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device MA. After being reflected from the patterning device (e.g. mask) MA, the exposure beam EB passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor PS2 (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the exposure beam EB.
• the second positioner PW and position sensor PS2 e.g. an interferometric device, linear encoder or capacitive sensor
• the first positioner PM and another position sensor PS1 can be used to accurately position the patterning device (e.g. mask) MA with respect to the path of the exposure beam EB.
• Patterning device (e.g. mask) MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks PI, P2.
• the lithography apparatus can operate in a scan mode in which the support structure (e.g. mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the exposure beam EB is projected onto a target portion C (i.e. a single dynamic exposure).
• the velocity and direction of the substrate table WT relative to the support structure (e.g. mask table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.
• FIG. 2 shows the lithography apparatus 4100 in more detail, including the source collector module SO, the illuminator EIL, and the projection system PS.
• the source collector module SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 4220 of the source collector module SO.
• a plasma 4210 which emits EUV radiation may be formed by a laser produced plasma source. EUV radiation may be produced by a gas or vapor, for example Xe gas, Li vapor or Sn vapor in which the plasma 4210 is created to emit radiation in the EUV range of the electromagnetic spectrum.
• the plasma 4210 is created by, for example, a pulsed laser beam.
• Partial pressures of, for example, 10 Pa of Xe, Li, Sn vapor or any other suitable gas or vapor may be needed for efficient generation of the radiation.
• a plasma of excited tin (Sn) is provided to produce EUV radiation.
• the radiation emitted by the plasma 4210 is passed from a source chamber 4211 into a collector chamber 4212 via an optional gas barrier or contaminant trap 4230 (in some cases also referred to as contaminant barrier or foil trap), which is positioned in or behind an opening in source chamber 4211.
• the contaminant trap 4230 may include a channel structure.
• Contamination trap 4230 may also include a gas barrier or a combination of a gas barrier and a channel structure.
• the collector chamber 4212 may include a radiation collector CO which may be a so-called grazing incidence collector. Radiation that traverses collector CO can be reflected off a grating spectral purity filter 4240 to be focused in a virtual source point IF.
• the virtual source point IF is commonly referred to as the intermediate focus, and the source collector module is arranged such that the intermediate focus IF is located at or near an opening 4221 in the enclosing structure 4220.
• the virtual source point IF is an image of the radiation emitting plasma 4210.
• the radiation traverses the illuminator EIL, which may include a faceted field mirror device 422 and a faceted pupil mirror device 424 arranged to provide a desired angular distribution of the exposure beam EB, at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA.
• the faceted field mirror device 422 has a plurality of field facets.
• the faceted pupil mirror device has a plurality of pupil facets.
• the illuminator EIL also includes illuminator mirrors 423, 425 which cooperate with faceted pupil mirror device 424 to project an image of each facet of faceted field mirror device 422 onto an illumination field (also referred to as the slit) IS.
• the illuminator EIL is arranged to provide Kohler illumination of the illumination slit IS.
• a patterned beam 426 is formed and the patterned beam 426 is imaged by the projection system PS via reflective elements 428, 430 onto a substrate W held by the wafer stage or substrate table WT.
• illuminator EIL and projection system PS More elements than shown may generally be present in illuminator EIL and projection system PS.
• the grating spectral purity filter 4240 may optionally be present, depending upon the type of lithography apparatus. Further, there may be more mirrors present than those shown in the Figures, for example there may be 1- 6 additional reflective elements present in the projection system PS than shown in Figure 2.
• Collector CO is depicted as a nested collector with grazing incidence reflectors, just as an example of a collector (or collector mirror).
• a collector CO of this type is desirably used in combination with a discharge produced plasma source, often called a DPP source.
• the source collector module SO may be part of an LPP radiation system.
• a laser arranged to deposit laser energy into a fuel, such as xenon (Xe), tin (Sn) or lithium (Li), creating the highly ionized plasma 4210 with electron temperatures of several 10's of eV.
• Xe xenon
• Sn tin
• Li lithium
• the energetic radiation generated during de-excitation and recombination of these ions is emitted from the plasma, collected by a near normal incidence collector CO and focused onto the opening 4221 in the enclosing structure 4220.
• the illumination of the patterning device is very important.
• the illuminator EIL is desirably arranged to provide Kohler illumination and has a field mirror which is imaged onto the illumination field by a pupil mirror and any other optical components of the illuminator.
• Kohler illumination the angular distribution of the radiation at the illumination system is conveniently described in terms of the spatial distribution of the radiation in a pupil plane, e.g. the plane of the pupil mirror.
• so-called conventional illumination mode the radiation uniformly fills a circular region of the pupil plane centered on the optical axis.
• the radiation fills two regions of the pupil plane that are spaced apart from the optical axis.
• Many other illumination modes are known. In principle, an optimum illumination mode can be defined to image a given pattern under given conditions. Therefore, it is desirable to provide flexibility in the illumination mode.
• the uniformity of the illumination is also very important.
• the uniformity of illumination affects the uniformity of dose to which the target portion of the substrate exposed, which affects CD-uniformity, an important measure of the uniformity of the dimension of features formed on the substrate.
• a faceted field mirror device can be used as the field mirror and a faceted pupil mirror device as the pupil mirror.
• the illuminator is arranged so that each field facet is imaged on the illumination field IS in an overlapping manner. Desirably, each image of a field facet fills the illumination slit IS. The overlap of the images of the field facets evens out any irregularities in the exposure beam EB provided by the source collector module SO.
• a faceted field mirror device having a large number of individually directable reflectors is described in US 2011/0001947 Al and WO 2014/019675.
• Such individually directable reflector may be for example a multilayer mirror.
• Each individually directable reflector can have its orientation controlled about one or two axes so that the position on the pupil plane to which radiation is directed can be controlled.
• the individually directable reflectors are divided into groups, each group being regarded as a virtual field facet.
• Pupil facets image the virtual field facets into the illumination field.
• the individually directable reflectors of each virtual field facet are controlled to direct radiation to a selected one of the pupil facets.
• Some pupil facets may receive radiation from more than one virtual field facet; other pupil facets may receive no radiation. This arrangement can be used to effect a large number of different illumination modes.
• Substantially all individually directable reflectors of the field mirror may be grouped into virtual field facets. By grouping substantially all individually directable reflectors of the field mirror into virtual field facets the radiation intensity is optimized.
• a faceted field mirror device 422 shown in Figure 3, comprises a plurality of field facets 50-1 to 50-n (n being an integer).
• Each of the field facets, as shown in Figure 4, is made up of a plurality of individually directable reflectors 4221.
• the allocation of individually directable reflectors to field facets is not fixed but can be changed whilst the lithography apparatus is in use.
• the field facets can be referred to as virtual field facets.
• Each of the individually directable reflectors 4221 has one or more actuators by which the individually directable reflector 4221 can be rotated about an axis or two orthogonal axes. Thereby, each individually directable reflector 4221 can be controlled to direct radiation in a specific direction.
• the individually directable reflectors 4221 can be micro-electromechanical systems (MEMS). There can be greater than 100,000 individually directable reflectors 4221 in the faceted field mirror device 442.
• a set of individually directable reflectors 4221 making up one of the field facets 50- 1 to 50-n comprises a plurality of adjacent individually directable reflectors 4221 in a shape corresponding to the shape of the illumination field IS.
• the set of individually directable reflectors 4221 is imaged by one or more pupil facets, in combination with illuminator mirrors 423, 425, to fill the illumination slit IS. Note that the shape and size of each field facet may not be exactly the same as the illumination field IS but depends on the
• the illumination field IS may be curved or straight.
• the field facets are elongate and are projected onto the illumination field IS so that the longitudinal direction of the image of the field facet is perpendicular to the scanning direction, e.g. the Y direction, and the transverse direction of the image of the field facet is parallel to the scanning direction.
• Each field facet can comprise a few hundred or more individually directable reflectors 4221.
• each set has 1000 mirrors arranged in 10 rows of 100 individually directable reflectors 4221 each. The rows can be aligned so that there are 100 columns of 10 individually directable reflectors 4221. Some of the columns can be offset from adjacent columns to form an approximately curved shape.
• the individually directable reflectors of a set are adjacent so that the virtual field facet occupies a single contiguous area. In an embodiment, some or all of the individually directable reflectors of a set are not adjacent each other.
• Each individually directable reflector 4221 can be set to at least two states: an inactive state in which it directs radiation received from the intermediate focus IF in a direction such that the radiation does not reach the illumination field IS; and an active state in which it directs radiation received from the intermediate focus IF in a direction such that the radiation does reach the illumination field IS.
• an inactive state in which it directs radiation received from the intermediate focus IF in a direction such that the radiation does not reach the illumination field IS
• an active state in which it directs radiation received from the intermediate focus IF in a direction such that the radiation does reach the illumination field IS.
• each individually directable reflector 4221 directs radiation to a pupil facet.
• An individually directable reflector 4221 can have multiple active states; in each active state radiation is directed to a different one of the pupil facets and therefore arrives at the illumination field IS from a different angle. Different illumination modes can therefore be effected by controlling the individually directable reflectors 4221 to be in appropriate states.
• a beam dump can be provided to receive the radiation
• selected ones of the individually directable reflectors 4221 of each set are set to their inactive states to control the dose delivered to the target portion of the substrate.
• the ones of the individually directable reflectors 4221 that are set to their inactive states are referred to below as inactive reflectors.
• the inactive reflectors 4223 (indicated by shading in the figure) are distributed across the field facet 50 and form a subset of the individually directable reflectors 4221.
• the field facet 50 is shown as straight for convenience of illustration but may be curved as described above.
• the number and/or distribution of the inactive reflectors 4223 is changed with time so that the dose I received by the substrate W varies with time T as indicated in Figure 6.
• an inter-exposure dose control mode the distribution of inactive reflectors is substantially uniform across the longitudinal direction of the field facet 50 and is constant during the time taken for exposure of one target portion. However, the number of inactive reflectors varies from one exposure of one target portion to another exposure of another target portion.
• the dose used to expose a target portion in a given position on one substrate of a batch can be the same as or different to the dose used to expose a target portion in a corresponding position on another substrate of the batch.
• different target portions can be exposed with different doses to correct for variations of imaging parameters, such as CD or CD-uniformity, between target portions on a substrate.
• the distribution of inactive reflectors is made nonuniform according to a desired arrangement across the length X of the field facet 50 as shown in Figure 7, and therefore across the length of the illumination field IS.
• the arrangement of inactive reflectors is chosen to effect a desired variation in dose across the X direction of the target portion C and is changed with time in synchronism with the scanning of the patterning device MA and substrate W to effect a desired variation in dose across the Y direction of the target portion C, as shown in Figure 8.
• the intensity variations in Figure 8 are exaggerated for the purposes of illustration; in a practical embodiment the dose variations are likely to be less than 5% of the maximum dose.
• the intra-exposure mode can be used to effect the same dose profile on each target portion of a substrate.
• the intra-exposure mode can be combined with the inter-exposure mode so that the dose profile differs between target portions on a substrate or in a batch.
• an embodiment of the invention is used to reduce the intensity of the radiation in the projection beam by an amount in the range of from about 10% to about 30% of the maximum power that can be delivered.
• Such coarse control is effected by setting from about 10% to about 30% of the individually directable reflectors to an inactive state.
• the individually directable reflectors that are set to the inactive state are distributed evenly across the field facet.
• the distribution of individually directable reflectors that are set to the inactive state can be pseudo random.
• the distribution of individually directable reflectors set to the inactive state can be constant during the course of an exposure or can vary whilst maintaining the total number of individually directable reflectors in the inactive state constant and ensuring that a uniform dose is received across the exposed target region.
• the coarse dose control can be useful when using a radiation-sensitive layer (e.g. resist) with a high sensitivity, i.e. requiring a low dose to expose.
• the EUV source is optimized to emit radiation at a particular power level and it may not be possible to turn it down. It is possible to reduce the dose at substrate level whilst keeping the EUV source power constant by increasing the speed of movement of the patterning device and substrate during the exposure scan. However, counter-intuitively, increasing the scan speed can lead to a reduction in throughput due to the additional time required to accelerate and decelerate the patterning device and substrate table between exposure scans. Therefore, coarse dose control can be used to increase throughput when using a radiation- sensitive layer (e.g. resist) with a high sensitivity.
• the patterning device When target portions are exposed in a scan mode, the patterning device needs to be brought up to the scan speed before the exposure begins.
• the patterning device e.g. a mask
• the border may be absorbing.
• a leading edge of the pattern area MF moves into the illumination field IS and then across the illumination field. Before the leading edge reaches the illumination field, the exposure radiation would impinge upon the border which may cause undesirable heating thereof.
• the length of the illumination field in the X direction corresponds to the maximum width of a target portion C that can be exposed.
• the pattern that is to be imparted to the substrate is smaller in the X direction than the length of the illumination field in the X direction.
• the illumination field may have a different dimension in the X direction (i.e. perpendicular to the scanning direction) than the maximum dimension that can be exposed. Parts of the border that extend in the Y direction may therefore come within the illumination field during the exposure and so receive radiation during the exposure.
• the illumination field may have a different dimension in the Y direction (i.e. parallel to the scanning direction) than the maximum dimension that can be exposed.
• So-called Y-masking blades extend parallel to the X direction and are movable in the Y direction. They are used to define the exposure in the Y direction.
• So-called X-masking blades extend parallel to the Y direction and are movable in the X direction. They are used to define the exposure in the Y direction.
• the Y-masking blades are closed before an exposure and open in synchronism with the movement of the leading edge of the pattern area into the illumination field. At the end of an exposure they are closed in synchronism with a trailing edge of the pattern area moving out of the illumination field.
• the X-masking blades are set to match the width of the pattern area in the X direction and are static during an exposure.
• WO 2014/019675 discloses setting some individually directable reflectors to an position where they don't reflect radiation to the mask in order to effect functionality similar to the movable masking blades.
• FIGS. 9, 10 and 11 illustrate the switching of individually directable reflectors in one field facet in a masking mode.
• the individually directable reflectors of all sets, corresponding to all field facets are controlled in the same way during the exposure. Initially, all individually directable reflectors are set to an inactive state, which state is indicated in the Figures 9 to 11 by diagonal hatching, so no radiation reaches the illumination field. As the pattern area MF moves into the illumination field, rows of individually directable reflectors corresponding to parts of the illumination field which the leading edge of the pattern area MF has reached are switched to the active state.
• the pattern area has moved a distance equivalent to two rows Rl, R2 of individually directable reflectors into the illumination field and so the individually directable reflectors in the first two rows that are within the width of the pattern area MF are switched to the active state, which state is indicated in Figures 9 to 11 by no hatching.
• the pattern area has moved another row R3 into the illumination field and the individually directable reflectors of another row are switched to the active state.
• the pattern area has moved another row R4 into the illumination field and again the individually directable reflectors of another row are switched to the active state. At this stage only the individually directable reflectors of the final row R5 are in the inactive state but these will be switched to the active state when the pattern area advances further.
• the pattern area MF is smaller than the illumination field in the X direction.
• Columns CI to C3 and Cn-2 to Cn of the individually directable reflectors are imaged in the illumination field outside the pattern area. It is undesirable for these mirrors to be switched to the active state along with the rest of the individually directable reflectors as the pattern area advances because the radiation they direct would cause an unnecessary heat load on the patterning device.
• the individually directable reflectors of columns CI to C3 and Cn-2 to Cn could be switched to the inactive state throughout the exposure.
• edge reflectors columns of individually directable reflectors C 1 to C3 and Cn-2 to Cn, which are imaged in the illumination field outside the pattern area, referred to as edge reflectors, are not switched to the inactive state.
• the edge reflectors switched to their normal active state. Rather, the edge reflectors are switched to a second active state in which they direct radiation to a different pupil facet than the individually directable reflectors that are imaged in the illumination field inside the pattern area MF, referred to as medial reflectors.
• the second active state is indicated in Figures 9 to 11 by horizontal hatching.
• the medial reflectors are set to direct radiation to a first pupil facet and the edge reflectors are set to direct radiation to a second pupil facet, different from the first pupil facet.
• FIG. 12 shows how the redirection of radiation is achieved.
• Pupil mirror device 424 comprises a plurality of pupil facets 4241-1 to 4241-M.
• the number of pupil facets is greater than the number of field facets, e.g. 3 to 5 times greater.
• Each field facet is associated with a number, e.g. 3 to 5, of the pupil facets.
• Each of the individually directable reflectors of a field facet can be set to direct radiation into any one of the pupil facets associated with that field facet.
• the edge reflectors of a first virtual field facet can direct radiation to the same pupil facet as the medial reflectors of a second virtual field facet.
• Figures 13 to 17 illustrate a method according to an embodiment of the invention which redirects radiation from individually directable reflectors that are located at the edges of virtual field facets when exposing a device pattern that is smaller than the largest device pattern that can be imaged in the lithography apparatus.
• Figure 13 shows a row of virtual field facets 50-1 to 50-5 each of which has a length LI that can be imaged onto the illumination field IS, which also has a length LI, as shown in Figure 15.
• Virtual field facets 50-1 to 50 -5 are depicted as straight, but may instead be curved. For ease of explanation it is assumed that the optical system between field facet 50 and patterning device MA has a magnification of 1 , if the magnification is not 1 , then the field facets are scaled accordingly.
• Each field facet 50 has a medial portion 51 of length L2 in which the individually directable reflectors are set to a first active state.
• the medial portion 51 is imaged onto the illumination slit IS so that only a length L2, which is less than LI, of the illumination slit IS is illuminated.
• Length L2 corresponds to the width of a device pattern to be imaged, where the device pattern is smaller than the largest device pattern imagable by the lithography apparatus.
• Each field facet 50 also has two edge portions 52 which would be imaged in the illumination slit IS outside the region corresponding to the device pattern to be imaged.
• the individually directable reflectors in the edge portions 52 can be set to an inactive state in which they direct radiation to a beam dump 60, as shown in Figure 16. However, directing the radiation to beam dump 60 is wasteful in the sense that the radiation directed to the beam dump serves no purpose.
• the allocation of the individually directable reflectors is changed when exposing a device pattern that is smaller than the largest device pattern that can be imaged in the lithography apparatus.
• Figure 14 shows a row of second virtual field facets 55-1 to 55-6 which occupy the same length of the field mirror device as virtual field facets 50-1 to 50-5.
• six second virtual field facets are made up from the individually directable reflectors that were used to make five virtual field facets.
• Each of the second virtual field facets 55-1 to 55-6 is imaged on to the illumination field IS and forms an illuminated region with a length L2, where L2 ⁇ LI as shown in Figure 17. In this way a smaller device pattern can be illuminated with no waste of radiation.
• the intensity of the radiation at the illumination field is higher than when the full length of the illumination field is illuminated, therefore the scanning speed can be increased. Therefore throughput can be increased.
• Substantially all individually directable reflectors of the field mirror may be grouped into virtual field facets. By grouping substantially all individually directable reflectors of the field mirror into virtual field facets the radiation intensity is maximized. With certain dimensions of an illumination field, it may not be possible to distribute all individually directable reflectors equally over virtual field facets. In this situation, not all individually directable reflectors may be set to active. In the described example, the number of virtual field facets in a row is enlarged from five to six. The invention is not limited to this embodiment. Other number of virtual field facets within one row is possible.
• FIG. 18 depicts a rectangular grid of target portions C imposed on a circular substrate W. As can be seen, certain cells E in the grid extend over the edge of the substrate. Such cells, referred to as edge-dies, cannot be used to manufacture useful devices.
• the arrangement of the useable target portions C on the substrate may be varied from the simple grid illustrated in order to maximize the number of usable target portions C per substrate and/or to maximize throughput. Nevertheless, there will be some edge dies E in any arrangement.
• edge dies cannot be used to manufacture useful devices, it is customary to expose and process the edge dies in the same way as the useful target portions C. This is because, if the edge dies are not exposed and processed, as layers are built up on the usable target portions during the manufacture of devices, a difference in height between the edge dies and the usable target portions can arise. Differences in internal stress in the substrate can also arise. These differences can lead to deformation of the substrate. Also, during a process step, the environment experienced by a target portion C that is adjacent to an edge die that had not been exposed and processed would be different than the environment experienced by a target portion in the centre of the substrate.
• the present inventors have determined that debris can be caused if edge dies are exposed.
• an edge die is exposed so that thin structures, e.g. isolated lines, are formed close to the edge of the substrate there is a significant possibility that parts of the structure will break off, creating debris.
• Various problems might be caused by debris.
• the debris might contaminate or damage other target portions of the substrate.
• the debris might contaminate a part of the lithography apparatus.
• the debris might fall on a target portion that has not yet been exposed and cause an imaging fault.
• an edge die mode in which the dose by which at least a part of an edge die is exposed is reduced compared to the dose used to expose a usable target portion.
• the part of the edge die receiving the reduced dose is adjacent the edge of the substrate and is referred to as an edge part.
• the dose is reduced in cases where the resist type, pattern and recipe are such that reducing the dose will result in features being formed that are larger and/or more robust.
• the dose used to expose the edge part is not uniform, but rather is reduced towards the edge of the substrate.
• Figure 19 depicts, by way of an example, a dose profile useful for exposure of an edge die on the +X side of the substrate.
• a left hand side (-X side) of the edge die receives a standard dose, substantially equal to the dose used to expose usable target portions.
• the dose tapers off toward the right hand side (+X side) in an edge part of the edge die so that feature sizes adjacent the edge of the substrate increase. As depicted, the dose taper is linear but it need not be so.
• the dose is reduced to zero. By reducing the dose to zero at the very edge of the substrate, there is no overspill of radiation onto the substrate holder or substrate table which prevents a heat load thereon and avoids degradation of coatings thereon.
• the edge of the substrate is not straight and not aligned with the Y direction (scanning direction). Therefore, the tapered dose profile may not be constant during an exposure of an edge die but is adjusted dynamically according to the momentary position of the projection beam relative to the edge of the substrate.
• a constant profile can however be used for edge dies where the edge of the substrate is nearly parallel to the Y direction.
• a different dose profile is determined for edge dies in different positions relative to the edge.
• the dose profile may be constant in X but vary with time in synchronism with movement of the substrate.
• lithography apparatus in the manufacture of ICs
• the lithography 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.
• LCDs liquid-crystal displays
• 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.

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