Membrane assembly and particle trap

Particle trap assemblies configured to reduce the possibility of contaminant particles with a large range of sizes, materials, travel speeds and angles of incidence reaching a particle-sensitive environment. The particle trap may be a gap geometric particle trap located between a stationary part and a movable part of the lithography apparatus. The particle trap may also be a surface geometric particle trap located on a surface of a particle sensitive environment in lithography or metrology apparatus.

FIELD

The present disclosure relates to a membrane assembly and a particle trap design for EUV lithography.

BACKGROUND

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

A theoretical estimate of the limits of pattern printing can be given by the Rayleigh criterion for resolution as shown in equation (1):

CD=k1*λNA(1)
where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection system used to print the pattern, k1 is a process-dependent adjustment factor, also called the Rayleigh constant, and CD is the feature size (or critical dimension) of the printed feature. It follows from equation (1) that reduction of the minimum printable size of features can be obtained in three ways: by shortening the exposure wavelength λ, by increasing the numerical aperture NA or by decreasing the value of k1.

In order to shorten the exposure wavelength and, thus, reduce the minimum printable size, it has been proposed to use an extreme ultraviolet (EUV) radiation source. EUV radiation is electromagnetic radiation having a wavelength within the range of 10-20 nm, for example within the range of 13-14 nm. It has further been proposed that EUV radiation with a wavelength of less than 10 nm could be used, for example within the range of 5-10 nm such as 6.7 nm or 6.8 nm. Such radiation is termed extreme ultraviolet radiation or soft x-ray radiation. Possible sources include, for example, laser-produced plasma sources, discharge plasma sources, or sources based on synchrotron radiation provided by an electron storage ring.

A lithographic apparatus includes a patterning device (e.g., a mask or a reticle). Radiation is provided through or reflected off the patterning device to form an image on a substrate. A membrane assembly may be provided to protect the patterning device from airborne particles and other forms of contamination. The membrane assembly for protecting the patterning device may be called a pellicle. Contamination on the surface of the patterning device can cause manufacturing defects on the substrate. The membrane assembly may comprise a border and a membrane stretched across the border.

In use the membrane is required to be fixed relative to the patterning device by mounting features, for example. It is desirable to reduce the amount of space taken up by the mounting features. It is also desirable for the membrane assembly to take up less space while it is being transported into position for mounting to the patterning device. It is also desirable to reduce the possibility of contaminant particles reaching a region between the membrane and the patterning device.

SUMMARY OF THE DISCLOSURE

According to an aspect of the disclosure, there is provided a membrane assembly for EUV lithography, the membrane assembly comprising: a planar membrane; a border configured to hold the membrane; and a frame assembly connected to the border and configured to releasably attach to a patterning device for EUV lithography, wherein the frame assembly comprises a resilient member; wherein the frame assembly is connected to the border in a direction perpendicular to the plane of the membrane such that in use the frame assembly is between the border and the patterning device.

According to an aspect of the disclosure, there is provided a patterning device assembly for EUV lithography, the patterning device assembly comprising: a planar patterning device; at least one protrusion protruding from the patterning device; and the membrane assembly of any preceding claim, the frame assembly being connected to the patterning device via the at least one protrusion; wherein the at least one protrusion is between the border and the patterning device.

According to an aspect of the disclosure, there is provided a membrane assembly for EUV lithography, the membrane assembly comprising: a planar membrane; and a frame assembly configured to hold the membrane and to attach to a patterning device for EUV lithography; wherein the frame assembly has a locked state in which the frame assembly is locked to the patterning device such that the membrane is held a predetermined distance from the patterning device, and an unlocked state in which the membrane is less than the predetermined distance from the patterning device.

According to an aspect of the disclosure, there is provided a patterning device assembly for EUV lithography, the patterning device assembly comprising: a planar patterning device for EUV lithography; a membrane assembly comprising: a planar membrane; and a frame assembly configured to hold the membrane and to attach to the patterning device, wherein a gap is formed between opposing surfaces of the frame assembly and the patterning device; wherein the frame assembly comprises an elongate baffle configured to restrain contaminant particles from entering the gap, wherein the elongate baffle extends beyond the opposing surface of the patterning device at a location beyond the planar extent of the patterning device.

According to an aspect of the disclosure, there is provided a patterning device assembly for EUV lithography, the patterning device assembly comprising: a planar patterning device; a membrane assembly comprising a planar membrane and a border configured to hold the membrane; at least one protrusion protruding from one of the patterning device and the border, wherein the at least one protrusion is between the border and the patterning device; and a frame assembly connected to the other of the patterning device and the border, wherein the frame assembly is configured to attach to the at least one protrusion between the border and the patterning device.

According to an aspect of the disclosure, there is provided a loading apparatus for temporarily housing a membrane assembly that is mounted onto a patterning device for EUV lithography, the loading apparatus comprising protrusions at an inner surface of the loading apparatus, wherein the protrusions are configured to press a membrane holder of the membrane assembly towards the patterning device when the loading apparatus houses the membrane assembly.

According to an aspect of the disclosure, there is provided a patterning device comprising a first structure of the patterning device having a first surface, a second structure of the patterning device having a second surface, wherein the first and second surfaces oppose each other, and a trap formed on the first surface and opposing the second surface, the trap comprising a plurality of baffles. A gap is formed between the opposing first and second surfaces.

According to an aspect of the disclosure, there is provided an apparatus comprising a first structure of a patterning device having a first surface, a second structure of the patterning device having a second surface, and a gap is formed between the first and second surfaces. The apparatus further comprising a first trap attached to the first surface, with the first trap comprising a plurality of baffles protruding from the first surface.

According to an aspect of the disclosure, there is provided an apparatus comprising a trap configured to restrain contaminant particles. The trap is formed on a surface of the apparatus and comprises a plurality of baffles protruding from the surface.

DETAILED DESCRIPTION

FIG. 1schematically depicts a lithographic apparatus100including a source collector module SO according to one embodiment of the disclosure. The apparatus100comprises:an illumination system (or illuminator) IL configured to condition a radiation beam B (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; anda projection system (e.g., a reflective projection system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

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

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

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

As here depicted, the lithographic apparatus100is of a reflective type (e.g., employing a reflective mask).

The lithographic apparatus100may be of a type having two (dual stage) or more substrate tables WT (and/or two or more support structures MT). In such a “multiple stage” lithographic apparatus the additional substrate tables WT (and/or the additional support structures MT) may be used in parallel, or preparatory steps may be carried out on one or more substrate tables WT (and/or one or more support structures MT) while one or more other substrate tables WT (and/or one or more other support structures MT) are being used for exposure.

In such cases, the laser is not considered to form part of the lithographic apparatus100and the radiation beam B is passed from the laser to the source collector module SO with the aid of a beam delivery system comprising, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the source collector module SO, for example when the source is a discharge produced plasma EUV generator, often termed as a DPP source.

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

A controller500controls the overall operations of the lithographic apparatus and in particular performs an operation process described further below. Controller500can be embodied as a suitably-programmed general purpose computer comprising a central processing unit, volatile and non-volatile storage means, one or more input and output devices such as a keyboard and screen, one or more network connections and one or more interfaces to the various parts of the lithographic apparatus100. It will be appreciated that a one-to-one relationship between controlling computer and lithographic apparatus100is not necessary. In an embodiment of the disclosure one computer can control multiple lithographic apparatuses100. In an embodiment of the disclosure, multiple networked computers can be used to control one lithographic apparatus100. The controller500may also be configured to control one or more associated process devices and substrate handling devices in a lithocell or cluster of which the lithographic apparatus100forms a part. The controller500can also be configured to be subordinate to a supervisory control system of a lithocell or cluster and/or an overall control system of a fab.

FIG. 2shows the lithographic apparatus100in more detail, including the source collector module SO, the illumination system IL, and the projection system PS. An EUV radiation emitting plasma210may be formed by a plasma source. EUV radiation may be produced by a gas or vapor, for example Xe gas, Li vapor or Sn vapor in which the radiation emitting plasma210is created to emit radiation in the EUV range of the electromagnetic spectrum. In an embodiment, a plasma of excited tin (Sn) is provided to produce EUV radiation.

The radiation emitted by the radiation emitting plasma210is passed from a source chamber211into a collector chamber212. The collector chamber212may include a radiation collector CO. Radiation that traverses the radiation collector CO can 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 SO is arranged such that the virtual source point IF is located at or near an opening221in the enclosing structure220. The virtual source point IF is an image of the radiation emitting plasma210. Subsequently the radiation traverses the illumination system IL, which may include a facetted field mirror device22and a facetted pupil mirror device24arranged to provide a desired angular distribution of the unpatterned beam21, at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA. Upon reflection of the unpatterned beam21at the patterning device MA, held by the support structure MT, a patterned beam26is formed and the patterned beam26is imaged by the projection system PS via reflective elements28,30onto a substrate W held by the substrate table WT.

More elements than shown may generally be present in the illumination system IL and the projection system PS. 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 inFIG. 2.

Alternatively, the source collector module SO may be part of an LPP radiation system.

As depicted inFIG. 1, in an embodiment the lithographic apparatus100comprises an illumination system IL and a projection system PS. The illumination system IL is configured to emit a radiation beam B. The projection system PS is separated from the substrate table WT by an intervening space. The projection system PS is configured to project a pattern imparted to the radiation beam B onto the substrate W. The pattern is for EUV radiation of the radiation beam B.

The space intervening between the projection system PS and the substrate table WT can be at least partially evacuated. The intervening space may be delimited at the location of the projection system PS by a solid surface from which the employed radiation is directed toward the substrate table WT.

In an embodiment the lithographic apparatus100comprises a dynamic gas lock. The dynamic gas lock comprises a membrane assembly80. In an embodiment the dynamic gas lock comprises a hollow part covered by a membrane assembly80located in the intervening space. The hollow part is situated around the path of the radiation. In an embodiment the lithographic apparatus100comprises a gas blower configured to flush the inside of the hollow part with a flow of gas. The radiation travels through the membrane assembly before impinging on the substrate W.

In an embodiment the lithographic apparatus100comprises a membrane assembly80. As explained above, in an embodiment the membrane assembly80is for a dynamic gas lock. In this case the membrane assembly80functions as a filter for filtering DUV radiation. Additionally or alternatively, in an embodiment the membrane assembly80is pellicle for the patterning device MA for EUV lithography. The membrane assembly80of the present disclosure can be used for a dynamic gas lock or for a pellicle or for another purpose such as a spectral purity filter. In an embodiment the membrane assembly80comprises a membrane40, which may also be called a membrane stack. In an embodiment the membrane is configured to transmit at least 80% of incident EUV radiation.

In an embodiment the membrane assembly80is configured to seal off the patterning device MA to protect the patterning device MA from airborne particles and other forms of contamination. Contamination on the surface of the patterning device MA can cause manufacturing defects on the substrate W. For example, in an embodiment the pellicle is configured to reduce the likelihood that particles might migrate into a stepping field of the patterning device MA in the lithographic apparatus100.

If the patterning device MA is left unprotected, the contamination can require the patterning device MA to be cleaned or discarded. Cleaning the patterning device MA interrupts valuable manufacturing time and discarding the patterning device MA is costly. Replacing the patterning device MA also interrupts valuable manufacturing time.

FIG. 3schematically depicts, in cross-section, part of a membrane assembly80according to an embodiment of the disclosure. The membrane assembly80is for EUV lithography. The membrane assembly80comprises a membrane40. The membrane40is emissive for EUV radiation. Of course the membrane40may not have 100% emissivity for EUV radiation. However, the membrane may have, for example, at least 50% emissivity. As shown inFIG. 3, in an embodiment the membrane40is substantially planar. In an embodiment the plane of the membrane40is substantially parallel to the plane of the patterning device MA.

The membrane assembly80has a shape such as a square, a circle or a rectangle, for example. The shape of the membrane assembly80is not particularly limited. The size of the membrane assembly80is not particularly limited. For example, in an embodiment the membrane assembly80has a diameter in the range of from about 100 mm to about 500 mm, for example about 200 mm.

As depicted inFIG. 3, in an embodiment the membrane assembly80comprises a border81. The border81is configured to hold the membrane40. The border81provides mechanical stability to the membrane40. The border81is configured to reduce the possibility of the membrane40being deformed away from its planar shape. In an embodiment, a pre-tension is applied to the membrane40during its manufacture. The border81is configured to maintain the tension in the membrane40so that the membrane40does not have an undulating shape during use of the lithographic apparatus100. In an embodiment the border81extends along the perimeter of the membrane40. The outer periphery of the membrane40is positioned on top of the border81(according to the view ofFIG. 3). The border81may be at least partly formed by part of the membrane40which is left over from the process of manufacturing the membrane assembly80. Hence the border81may not be a separate component from the membrane40.

The thickness of the border81is not particularly limited. For example, in an embodiment the border81has a thickness of at least 300 μm, optionally at least 400 μm. In an embodiment the border81has a thickness of at most 1,000 μm, optionally at most 800 μm. In an embodiment the border81has a width of at least 1 mm, optionally at least 2 mm, optionally at least 4 mm. In an embodiment the border81has a width of at most 10 mm, optionally at most 5 mm, optionally at most 4 mm.

As depicted inFIG. 3, in an embodiment the membrane assembly80comprises a frame assembly50. The frame assembly50is connected to the border81. In an embodiment the frame assembly50comprises a frame surface in contact with the border81. In an embodiment the frame assembly50is initially manufactured as a separate component from the border81and subsequently connected to the border81. For example, the combination of the membrane40with the border81may be manufactured together, while the frame assembly50may be manufactured separately. In a subsequent manufacturing step, the frame assembly50may be attached or fixed to the border81.

In an embodiment the frame assembly50has a width of at least 2 mm, optionally at least 5 mm, optionally at least 8 mm. In an embodiment the frame assembly50has a width of at most 20 mm, optionally at most 10 mm, optionally at most 8 mm.

In an embodiment the frame assembly50comprises a frame51. The frame51is the part of the frame assembly50that is connected to the border81. In an embodiment the frame51is made of the same material as the border81. For example, in an embodiment both the border81and the frame51are made of a material comprising silicon. In an embodiment the border81is made of silicon. In an embodiment the frame51is made of silicon. In an embodiment the thermal expansion of the border81substantially matches the thermal expansion of the frame51. In an embodiment the frame51is attached to the border81by an adhesive. In an embodiment the thermal expansion of the adhesive substantially matches the thermal expansion of the frame51and/or the border81.

As depicted inFIG. 3, the frame assembly50is configured to attach to the patterning device MA. In an embodiment the frame assembly50comprises a frame surface configured to contact the patterning device MA. The frame assembly50is for holding the position of the membrane40relative to the patterning device MA. Although the embodiment is described with reference to a patterning device MA, the disclosure is equally applicable to a membrane assembly80that connects to a different component other than the patterning device MA.

In an embodiment the frame assembly50is connected to the border81in a direction perpendicular to the plane of the membrane40. This is shown inFIG. 3. InFIG. 3, the plane of the membrane40extends left to right and into and out of the paper. The direction perpendicular to the plane of the membrane40corresponds to the vertical (i.e. up and down) direction inFIG. 3. The frame assembly50is connected directly below the border81. The border81and the frame assembly50are aligned in the vertical direction inFIG. 3. In an embodiment the interface between the border81and the frame assembly50is in a plane that is substantially parallel to the plane of the membrane40.

In an embodiment the membrane assembly80is configured to be removable from the patterning device MA. This allows intermediate inspections of the patterning device MA to take place. In an embodiment the frame assembly50is configured to be repeatedly attached to and detached from the patterning device MA.

In use, the frame assembly50is between the border81and the patterning device MA. This arrangement is different from arrangements in which the frame assembly is positioned radially outwards from the border. An embodiment of the disclosure is expected to achieve a reduction in space around the membrane40required to hold the membrane40in position relative to the patterning device MA.

According to a comparative example, a membrane assembly has a frame assembly radially outwards from the border. The frame assembly is required to be accessed in the radial direction so as to attach/detach the frame assembly to/from the patterning device. A space of about 16 mm may be required to accommodate the border, the frame assembly and space for accessing the frame assembly.

In contrast in an embodiment the frame assembly50is positioned below the border81, thereby reducing radial space required to accommodate the border81and the frame assembly50. For example, in an embodiment the radial space required to accommodate the border81, the frame assembly50and space for accessing the frame assembly50is about 12 mm.

An embodiment of the disclosure is expected to achieve a reduction in the required space in the region of the patterning device MA for mounting features. Mounting features are features that are used to mount the membrane assembly80onto the patterning device MA. In an embodiment a mounting feature is provided between the border81and the patterning device MA. This is shown inFIG. 3and will be explained in further detail below.

In an embodiment the frame assembly50comprises at least one hole52. In an embodiment the hole52is a cavity or chamber or an opening within the frame51of the frame assembly50. The hole52is configured to receive a protrusion (e.g. a stud60). The stud60protrudes from the patterning device MA. In an alternative embodiment the frame assembly50is permanently attached to the patterning device MA and the stud60protrudes from the border81of the membrane assembly80.

FIG. 3shows the stud60fixed to the patterning device MA. In an embodiment the stud60is glued onto the patterning device MA using an adhesive. Alternatively, the stud60may be formed integrally with the patterning device MA. As a further alternative, the stud60may be initially manufactured as a separate component from the patterning device MA and subsequently fixed to the patterning device MA using means other than an adhesive, for example a screw.

The stud60and the hole52are mounting features. In an embodiment the stud60and the hole52are provided between the border81and the patterning device MA. This is different from previously known arrangements in which the mounting features are positioned radially outwards from the border81.

As depicted inFIG. 3, in an embodiment the hole52at least partially overlaps the border81when viewed in the direction perpendicular to the plane of the membrane40. This is shown inFIG. 3, where the hole52partially overlaps the border81when viewed in the vertical direction. Looking atFIG. 3, a vertical line can be drawn that extends through both the border81and the hole52.

In an embodiment the frame assembly50comprises a locking mechanism55. The locking mechanism55is configured to lock the frame assembly50to the stud60. In an embodiment the locking mechanism55comprises a resilient member53. In an embodiment the locking mechanism55comprises a resilient member53for each hole52. In an embodiment the frame assembly50comprises a plurality of holes52, for example two, three, four or more holes52. A resilient member53is provided corresponding to each hole52.

As depicted inFIG. 3, in an embodiment the resilient member53comprises a spring. For example, the spring may be a coil spring or a leaf spring. In an alternative embodiment the resilient member53comprises a resilient material such as rubber. In an alternative embodiment the resilient member53comprises a flexure. The flexure may be machined using an electrical discharge machining process, for example.

FIGS. 4 to 6schematically depict stages of use of the locking mechanism55.FIGS. 4 to 6are shown in plan view.FIG. 4depicts an initial state in which the frame assembly50is positioned over the stud60so that the stud60is received into the hole52. The resilient member53is not compressed. As depicted inFIG. 4, the resilient member53extends into the hole52. Accordingly, the stud60can come into contact with the resilient member53when the stud60is received into the hole52. The resilient member53is configured to be deformable (e.g. compressible) when the stud60received in the hole52presses against the resilient member53in a direction within the plane of the membrane40. For example, inFIG. 4the stud60can press against the resilient member53in the direction to the right in the Figure.

As depicted inFIGS. 3 to 6, in an embodiment the locking mechanism55comprises a locking member54for each hole52. The locking member54is configured to be movable to a locking position where the locking member54extends into the hole52. In the locking position the compressed resilient member53exerts a force on the stud60received in the hole52towards the locking member54. This is shown in the sequence fromFIG. 4toFIG. 6.

As shown in the transition fromFIG. 4toFIG. 5, the stud60and the frame assembly50are moved relative to each other so that the stud60presses against the resilient member53. The stud60compresses the resilient member53, as shown inFIG. 5.

As shown in the transition fromFIG. 5toFIG. 6, the locking member54is moved to the locking position where the locking member54extends into the hole52. For example, as shown inFIGS. 4 to 6, in an embodiment the frame assembly50comprises at least one locking aperture56. The locking member54passes through the locking apertures56.

FIG. 6shows the locking member54in the locking position. The resilient member53exerts a force on the stud60in the direction of the locking member54. In the situation shown inFIG. 5, an external force is required to be exerted on the frame assembly50and/or on the stud60so that the stud60compresses the resilient member53. Once the locking member54is in the locking position (e.g. as shown inFIG. 6), it is no longer necessary for the external force to be applied. This is because the locking member54holds the stud60and the frame assembly50in position relative to each other. As explained above, the stud60is positioned under the border81, instead of radially outward of the border81. This may require an increase in the distance (also known as standoff) between the patterning device MA and the membrane40. The distance between the surface of the patterning device MA and the membrane40substantially corresponds to the combined height of the frame assembly50and the border81. In an embodiment the30combined height of the frame assembly50and the border81is at least 1 mm, at least 2 mm, and optionally at least 5 mm. In an embodiment the combined height of the frame assembly50with the border81is at most 20 mm, optionally at most 10 mm, and optionally at most 5 mm.

In an embodiment the resilient member53comprises a spring made of a material such as stainless steel. In an embodiment the resilient member53is connected to a contact pad57made of a different material from the resilient member53. For example, the contact pad57may be made of the same material as the stud60and/or the locking member54. In an embodiment the contact pad57comprises titanium. In an embodiment the locking member54comprises titanium. In an embodiment the stud60comprises titanium. Titanium is known to provide a ductile contact. However, in an alternative embodiment, other materials can be used for the contact pad57, the stud60and the locking member54.

As shown inFIGS. 4 to 6, in an embodiment the cross-sectional area of the hole52is greater than the cross-sectional area of the stud60in plan view. The hole52is oversized relative to the stud60. In an embodiment the resilient member53is provided against an end stop (not shown in the Figures). The resilient member53protrudes into the hole52when viewed in plan view (as shown inFIG. 4). Accordingly, the resilient member53effectively reduces the cross-sectional area of the hole52in plan view. The remaining cross-sectional dimensions of the hole52are larger than the dimensions of the stud60. Accordingly, the stud60can be received into the hole52when the frame assembly50is moved vertically over the stud60. The frame assembly50is pushed sideways against the resilient member53so that the resilient member53is deflected inwards. The locking member54is placed preventing the frame assembly50from bending back. In an embodiment the locking member54is a pin. The locking member54can be inserted from the side or from the top. After the locking member54has been inserted, the frame assembly50is locked to the patterning device MA.

In an embodiment the frame assembly50comprises four holes52evenly distributed around the frame assembly50. In an embodiment the frame assembly50has a similar shape to the border81, following the perimeter of the membrane40.FIG. 3depicts the resilient member53radially inward of the hole52. However, this is not necessarily the case. The resilient member53may be radially outward of the hole52or neither radially inward nor outward relative to the hole52. The hole52is positioned between the resilient member53and the locking member54.

In an embodiment a resilient member53is radially inward of a hole52at one side of the membrane assembly80, whereas another resilient member53is radially outward of another hole52at the opposite side of the membrane assembly80. This allows the studs60at opposite sides of the patterning device MA to compress both resilient members52with one movement of the membrane assembly80relative to the patterning device MA. In an embodiment the membrane assembly80is configured such that all of the studs60received in corresponding holes52compress corresponding resilient members52with one movement of the membrane assembly80relative to the patterning device MA.

As shown inFIGS. 4 to 6, in an embodiment the locking member54is provided as a loose part. In an alternative embodiment the locking member may be formed to be integral with the rest of the frame assembly50, provided that the locking member54can be slid into the locking position.

In an embodiment the stud60has a diameter (in plan view) of at least 1 mm, optionally at least 2 mm, and optionally at least 3 mm. In an embodiment the stud60has a diameter of at most 10 mm, optionally at most 5 mm, and optionally at most 3 mm.

As explained above, in an embodiment the resilient member53extends into the hole52when it is not compressed. In an embodiment the resilient member53extends into the hole52by a distance of at least 0.1 mm, optionally at least 0.2 mm, and optionally at least 0.5 mm. In an embodiment the resilient member53extends into the hole52by a distance of at most 2 mm, optionally at most 1 mm, and optionally at most 0.5 mm.

As mentioned above, the hole52has a diameter that is larger than the diameter of the stud60. In an embodiment the diameter of the hole is greater than the diameter of the stud60by at least 0.2 mm, optionally at least 0.5 mm, and optionally at least 1 mm. In an embodiment the diameter of the hole52is greater than the diameter of the stud60by at most 5 mm, optionally at most 2 mm, and optionally at most 1 mm. In an embodiment the locking member54has a length of at least 1 mm, optionally at least 2 mm, and optionally at least 4 mm.

In an embodiment the locking member54has a length of at most 10 mm, optionally at most 5 mm, and optionally at most 4 mm. In an embodiment the locking member54has a width of at least 0.2 mm, optionally at least 0.5 mm, and optionally at least 1 mm. In an embodiment the locking member54has a width of at most 5 mm, optionally at most 2 mm, and optionally at most 1 mm.

An embodiment of the disclosure is expected to achieve a reduction in tooling steps required for attaching/detaching the member assembly80to/from the patterning device MA.

FIG. 7schematically depicts, in cross-section, a membrane40according to an embodiment of the disclosure. As shown inFIG. 7, the membrane40comprises a stack. The stack comprises a plurality of layers.

In an embodiment the stack comprises at least on silicon layer41. The silicon layer41comprises a form of silicon. In an embodiment the stack comprises at least one silicon compound layer43. The silicon compound layer43is made of a compound of silicon and another element selected from the group consisting of boron, phosphorus, bromine and sulphur. However, other elements may also be used. In particular, in an embodiment the element that combines with the silicon to form the silicon compound layer43is any element that can be used as a dopant material for doping the silicon layer41. The embodiment will be described with boron as the element that combines with the silicon, merely for convenience. The embodiment is not limited to the element being boron.

In an embodiment the silicon compound layer43comprises a silicon boride. Silicon boride has the chemical formula SiBx, where x can be 3, 4, 6, 14, 15, 40 etc. Silicon boride has metallic properties. In particular, the silicon compound layer43has the property of metal that it increases the emissivity for EUV radiation of the membrane40. A membrane made of only the silicon layer41would have a low emissivity, perhaps of the order of 3%. The emissivity dramatically increases if a metal or a compound that has metallic properties is added to the membrane40.

Metals are known to limit the practical thickness of the membrane due to EUV absorption. By providing the silicon membrane layer43, an embodiment of the disclosure is expected to achieve an increase in possible thickness of a membrane40that has sufficient emissivity for use in the lithographic apparatus100.

As depicted inFIG. 7, in an embodiment the silicon compound layer43is formed as an interlayer between the silicon layer41and a non-metallic layer42comprising the element that combines with silicon to form the silicon compound layer43. For example, in an embodiment the non-metallic layer42comprises boron. In an embodiment the boron is provided in the form of boron carbide. However alternative forms of boron can be used.

In an embodiment the silicon layer41is initially provided adjacent to the non-metallic layer42. The boron in the non-metallic layer42locally dopes the silicon in the silicon layer41. The boron dopes the silicon to the extent that silicon boride is produced to form the silicon compound layer43. The boron dopes the silicon such that there are more boron atoms than silicon atoms in the doped silicon, i.e. forming silicon boride.

In an embodiment, silicon layers41and non-metallic layers42are provided as multilayers. Locally, boron silicide can strengthen the membrane40(by a laminate effect and by radiation hardening of boron in silicon) so that the membrane40can withstand higher temperatures.

As depicted inFIG. 7, in an embodiment the stack comprises a plurality of silicon layers41, a plurality of non-metallic layers42and a silicon compound layer43between each pair of silicon layers41and a non-metallic layer42.

As depicted inFIG. 7, in an embodiment the stack comprises layers in the following order: a non-metallic layer42, a silicon compound layer43, a silicon layer41, a silicon compound layer43, a non-metallic layer42, a silicon compound layer43, a silicon layer41, a silicon compound layer43, a non-metallic layer42, a silicon compound layer43, a silicon layer41, a silicon compound layer43and a non-metallic layer42. This is a multilayer stack. In an embodiment the stack may comprise a non-metallic layer42and then repeated cycles of a set of four layers comprising a silicon compound layer43, a silicon layer41, a silicon compound layer43and a non-metallic layer42.

In an embodiment each non-metallic layer42has a thickness of at least 0.5 nm, optionally at least 1 nm and optionally at least 2 nm. In an embodiment each non-metallic layer42has a thickness of at most 10 nm, optionally at most 5 nm, and optionally at most 2 nm.

In an embodiment each silicon compound layer43has a thickness of at least 0.5 nm, optionally at least 1 nm, and optionally at least 2 nm. In an embodiment each silicon compound layer43has a thickness at most 10 nm, optionally at most 5 nm, and optionally at most 2 nm.

In an embodiment each silicon layer41has a thickness of at least 2 nm, optionally at least 5 nm, and optionally at least 8 nm. In an embodiment each silicon layer41has a thickness of at most 20 nm, optionally at most 10 nm, optionally at most 8 nm.

The embodiment depicted inFIG. 7with silicon layers41of 8 nm thickness, non-metallic layers42of 2 nm thickness and silicon compound layers43of 2 nm thickness is expected to be achieve an emissivity for EUV radiation of about 90%.

FIG. 8depicts an alternative embodiment in which the stack comprises layers in the following order: a non-metallic layer42, a silicon compound layer43, a silicon layer41, a silicon compound layer43and a non-metallic layer42.

As depicted inFIG. 8in an embodiment the membrane40comprises only one silicon layer41. In such an embodiment the silicon layer41can have a thickness of at least 10 nm, optionally at least 20 nm, and optionally at least 38 nm. In an embodiment the single silicon layer41has a thickness of at most 100 nm, optionally at most 50 nm, and

optionally at most 38 nm. The embodiment shown inFIG. 8and having a silicon layer41of 38 nm thickness, non-metallic layer42of 4 nm thickness and silicon compound layer43of 2 nm thickness is expected to achieve an emissivity for EUV radiation of about 90%.

In an embodiment a total combined thickness of silicon compound layers43in the stack is at most about 20 nm. Metal and compounds having metallic properties improve the emissivity of the membrane40provided that the combined thickness is not too thick. For layers of metal or compounds having metallic properties that are too thick, the emissivity can be reduced.

FIG. 9schematically depicts an alternative embodiment of a membrane40. As depicted inFIG. 9, in an embodiment the stack comprises at least one silicon layer41, at least one capping layer46and at least one anti-migration layer47. In an embodiment the capping layer46comprises ruthenium. The capping layer46is provided at an external surface of the membrane40. The anti-migration layer47comprises at least one of molybdenum and titanium. The anti-migration layer47is adjacent to each capping layer46.

The capping layer46comprising ruthenium improves the emissivity of the membrane40. The capping layer46reduces the possibility of the membrane40oxidizing. The capping layer46is configured to protect the membrane40from hydrogen gas.

During use of the lithographic apparatus100, the membrane40can heat up due to absorbing radiation. When the capping layer46heats up, the material (e.g. ruthenium) of the capping layer46can migrate. The migration is the transport of the material caused by the gradual movement of the ions in the capping layer46. When the material starts to migrate, the material can form islands in the capping layer46. When the material starts to migrate, the effectiveness of the capping layer46in reducing oxidation, protecting from hydrogen gas and improving emissivity is reduced. Hence, during use of the lithographic apparatus100, the membrane40can start to oxidize and the emissivity can decrease.

By providing the anti-migration layer47, migration of the capping layer46is reduced. Molybdenum and titanium are metals that have relatively high melting temperatures and good emissivity for UV radiation. Titanium and molybdenum do not migrate as much has ruthenium when they are heated. Titanium and molybdenum have good metal to metal contact with ruthenium. By providing the anti-migration layer47adjacent to the capping layer46, migration of the capping layer46is reduced. As a result, even when the capping layer46is heated during use of the lithographic apparatus100, the good properties of the capping layer46are retained at higher temperatures.

As depicted inFIG. 9, in an embodiment the stack comprises layers in the following order: a capping layer46comprising ruthenium at an external surface of the membrane40, an anti-migration layer47comprising at least one of molybdenum and titanium, a silicon layer41, an anti-migration layer47comprising at least one of molybdenum and titanium, and a capping layer46comprising ruthenium at the other external surface of the membrane40. In an embodiment a capping layer46comprising ruthenium is provided at both external surfaces of the membrane40.

FIG. 10depicts an alternative embodiment of a membrane in which the use of the anti-migration layer47is combined with the idea of using the silicon compound layer43.

As depicted inFIG. 10in an embodiment the stack comprises layers in the following order: a capping layer46comprising ruthenium at an external surface of the membrane40, an anti-migration layer47comprising at least one of molybdenum and titanium, a silicon layer41, a silicon compound layer43and a non-metallic layer42.

During manufacture of the membrane assembly80, the boron carbide layer can protect the silicon layer41chemically from etching processes. In an embodiment the membrane40comprises a periodic structure. In an embodiment the period is not set to be equal to 6.6 nm or 6.7 nm. If the period is at or close to 6.7 nm the membrane may act as a mirror for the EUV radiation.

Silicon can crystallize in a diamond cubic crystal structure. In an embodiment the border81comprises a cubic crystal of silicon. In an embodiment the border81has a <100> crystallographic direction.

In an embodiment the silicon layer41is formed from polycrystalline or nanocrystalline silicon. Polycrystalline or nanocrystalline silicon has a brittle nature. Hence, a membrane40that comprises a silicon layer41formed from polycrystalline or nanocrystalline silicon can shatter into many particles when the membrane assembly80breaks. An embodiment of the disclosure is expected to achieve an improvement in the mechanical properties of the membrane assembly80.

Polycrystalline silicon and nanocrystalline silicon each have high transmission for EUV radiation. Polycrystalline silicon and nanocrystalline silicon each have good mechanical strength. However, it is not essential for the membrane of the silicon layer41to be formed from polycrystalline or nanocrystalline silicon. For example, in an alternative embodiment the silicon layer41is formed from a multi-lattice membrane or a silicon nitride.

In a further alternative embodiment the silicon layer41is formed from monocrystalline silicon. In such an embodiment the monocrystalline silicon membrane can be formed by a silicon on insulator (SOI) technique. The starting material for this product is a so-called SOI substrate. An SOI substrate is a substrate comprising a silicon carrier substrate with a thin, monocrystalline silicon layer on top of a buried isolating SiO2 layer. In an embodiment the thickness of the monocrystalline silicon layer can range between about 5 nm to about 5 μm. In an embodiment the silicon layer41is present on the SOI substrate before the SOI substrate is used in the method of manufacture.

In an embodiment the silicon layer41comprises silicon in one of its allotrope forms such as amorphous, monocrystalline, polycrystalline or nanocrystalline silicon. A nanocrystalline silicon means a polycrystalline silicon matrix containing a certain amorphous silicon content. In an embodiment polycrystalline or nanocrystalline silicon is formed by crystallising amorphous silicon in the silicon layer41. For example, in an embodiment a silicon layer41is added to the stack as an amorphous silicon layer. The amorphous silicon layer crystallises into a polycrystalline or nanocrystalline silicon layer when a certain temperature is exceeded. For example, the silicon layer41as an amorphous silicon layer transforms into the silicon layer41as a polycrystalline or nanocrystalline silicon layer.

In an embodiment the amorphous silicon layer is in-situ doped during its growth. In an embodiment the amorphous silicon layer is doped after its growth. By adding a p- or n-type dopant the silicon conductivity increases, which has a positive effect on the thermomechanical behavior due to the power of the EUV source.

In an embodiment the membrane40is thin enough that its transmission for EUV radiation is sufficiently high, for example greater than 50%. In an embodiment the thickness of the membrane40is at most about 200 nm, and optionally at most about 150 nm. A 150 nm Si membrane would transmit about 77% of incident EUV radiation. In an embodiment the thickness of the membrane40is at most about 100 nm. A 100 nm Si membrane would transmit about 84% of incident EUV radiation. A 60 nm Si membrane would transmit about 90% of incident EUV radiation.

In an embodiment the membrane40is thick enough that it is mechanically stable when the membrane assembly80is fixed to the patterning device MA of the lithographic apparatus100and during use of the lithographic apparatus100. In an embodiment the thickness of the membrane40is at least about 10 nm, optionally at least about 20 nm, and optionally at least about 35 nm. In an embodiment the thickness of the membrane40is about 55 nm.

In an embodiment the membrane assembly80is applied as a pellicle or as part of a dynamic gas lock. Alternatively, the membrane assembly80can be applied in other filtration areas such as identification, or for beam splitters.

FIG. 11schematically depicts, in cross-section, a membrane assembly80according to an alternative embodiment of the disclosure. The membrane assembly80is for EUV lithography.

The membrane assembly80comprises a planar membrane40. Only part of the membrane40is shown inFIG. 11. The membrane assembly80comprises a frame assembly50.FIG. 11shows a cross-sectional view of the frame assembly50on one side of the membrane40. The frame assembly50is configured to hold the membrane40. The frame assembly50is configured to attach to a patterning device MA for EUV lithography. As depicted inFIG. 11, in an embodiment the frame assembly50is configured to hold the membrane40via a border81. The construction of the membrane40and the border81can be the same as in any of the other embodiments described in this document.

FIGS. 11 to 14schematically depict various stages of a process of attaching the frame assembly50to the patterning device MA.FIG. 13schematically depicts the frame assembly50attached to the patterning device MA. As depicted inFIG. 13, in an embodiment the frame assembly50has a locked state. In the locked state, the frame assembly50is locked to the patterning device MA such that the membrane40is held a predetermined distance D1from the patterning device MA. The predetermined distance is shown inFIG. 13. The predetermined distance D1is measured in the direction perpendicular to the plane of the membrane40and the plane of the patterning device MA. The frame assembly50is biased into the locked state by the resilient member53.

As depicted inFIG. 14, in an embodiment the frame assembly50has an unlocked state. In the unlocked state the membrane assembly50is not locked to the patterning device MA. In the unlocked state, the membrane40is less than the predetermined distance D1from the patterning device MA. For example, as shown inFIG. 14, in the unlocked state the membrane40is an unlocked state distance D2from the patterning device MA. The unlocked state distance D2is less than the predetermined distance D1. As shown from a comparison betweenFIG. 13andFIG. 14, in the unlocked state the resilient member53is compressed, with a membrane holder58of the frame assembly50forced closer to the patterning device MA.

The membrane40is used for mitigating any defect in the front side of the patterning device MA. The membrane40reduces the possibility of contaminant particles reaching the patterning device MA. In an embodiment the membrane assembly80is loaded into the lithographic apparatus100in a loading apparatus70(shown inFIGS. 15 to 17). As shown inFIGS. 15 to 17, in an embodiment the loading apparatus70comprises a cut-out portion for accommodating the membrane40. It is desirable for the loading apparatus70to be as thin as possible. The thickness of the loading apparatus70is shown in the up and down directions inFIGS. 15 to 17.

In practice, the membrane40can sag under its own weight. It is desirable for the membrane40to avoid touching the inside of the loading apparatus70, so as to avoid any damage to the membrane40. It is desirable for the membrane40to be thin so as to be able to transmit a higher proportion of EUV radiation. However, thinner membranes40tend to sag more. Hence, there is a trade-off between the thinness of the membrane40and the thinness of the loading apparatus70.

It is desirable for there to be a large standoff between the membrane40and the patterning device MA in use of the lithographic apparatus100. The standoff is the distance between the patterning device MA and the membrane40when the lithographic apparatus100is in use. Accordingly, it is not desirable to increase the space for the membrane40to sag simply by reducing the standoff between the membrane40and the patterning device MA.

Instead, the embodiment shown inFIGS. 11 to 14allows the membrane40to be temporarily pressed towards the patterning the device MA while the membrane40is being transported in the loading apparatus70. For example,FIGS. 15 and 16show the membrane40in the temporary state of being pressed upwards towards the patterning device MA. This allows the membrane40to sag more without touching the inside of the loading apparatus70. Meanwhile,FIG. 17shows the membrane assembly80out of the loading apparatus70. The membrane40is no longer pressed upwards towards the patterning device MA such that the membrane40has the predetermined distance D1from the patterning device MA.

Accordingly, an embodiment of the disclosure is expected to allow the membrane40to be made according to a greater level of design freedom (because a greater level of sagging is allowed), without increasing the thickness of the loading apparatus70.

As depicted inFIG. 11, in an embodiment the frame assembly50comprises a resilient member53. In an embodiment the resilient member53comprises a preload spring. The resilient member53may be a torsion spring or a leaf spring, for example. As depicted inFIG. 11, in an embodiment the frame assembly50comprises a membrane holder58. The membrane holder58is configured to hold the membrane40. The membrane holder58makes up most of the frame assembly50. The membrane holder58has a fixed position relative to the membrane40. When the membrane holder58moves, the membrane40also moves together with the membrane holder58.

As depicted inFIG. 11, in an embodiment the membrane holder58comprises an end stop surface33. The end stop surface33is configured to contact a locking surface34of the stud52protruding from the patterning device MA. When the frame assembly50is in the locked state, the end stop surface33of the membrane holder58abuts the locking surface34of the stud52. In an embodiment the end stop surface33is on top of the locking surface34of the stud52. This is different from previously known mechanisms in which a fixed end stop is positioned below the stud. According to the present disclosure, the membrane holder58can be pressed upward, against the resilient member53.

As depicted inFIG. 11, in an embodiment the frame assembly50comprises a clamping member59. The clamping member59is movable relative to the membrane holder58. In an embodiment the frame assembly50comprises a resilient member53. The resilient member53connects the membrane holder58to the clamping member59. The membrane holder58can move relative to the clamping member59by compression of the resilient member53. The membrane holder58is movable relative to the clamping member59in a direction perpendicular to the plane of the membrane40.

FIG. 11depicts a point in time in which the frame assembly50is in an initial state. In the initial state, the resilient member53is in a substantially uncompressed state. The frame assembly50cannot fit over the stud52because there is insufficient space between the end stop surface33of the membrane holder58and the abutment surface31of the clamping member59. The abutment surface31is configured to contact an engagement surface32of the stud52. The engagement surface32of the stud52faces away from the patterning device MA.

FIG. 12schematically depicts the frame assembly50in a preparatory state. In the preparatory state, the resilient member53is compressed such that the distance between the end stop surface33of the membrane holder58and the abutment surface31of the clamping member59is increased. A special tool may be used to perform this operation. In particular, the tool may be used to hold the clamping member59. With the clamping member59held in position, the tool is used to apply a force pressing the membrane holder58in the direction of the patterning device MA. Accordingly, the resilient member53is compressed and the membrane holder58is forced towards the patterning device MA. The frame assembly50and the patterning device MA are then maneuvered with respect to each other such that the stud52(or part of the stud52) enters between the end stop surface33of the membrane holder58and the abutment surface31of the clamping member59.

FIG. 13depicts the frame assembly50in the locked state. In the transition from the preparatory state shown inFIG. 12to the locked state shown inFIG. 13, the force on the membrane holder58is released. As a result, the resilient member53expands. The abutment surface31of the clamping member59comes into contact with the engagement surface32of the stud52. The end stop surface33of the membrane holder58comes into contact with the locking surface34of the stud52. The locking surface34of the stud52faces towards the patterning device MA.

FIG. 14schematically depicts the frame assembly50in the unlocked state. In the unlocked state, the abutment surface31of the clamping member59remains in contact with the engagement surface32of the stud52. The membrane holder58is forced towards the patterning device MA such that the end stop surface33of the membrane holder58moves away from the locking surface34of the stud52. Accordingly, the frame assembly52is no longer locked to the patterning device MA. The membrane40is closer to the patterning device MA compared to in the locked state shown inFIG. 13. When the resilient member53is compressed, the membrane holder58moves towards the patterning device MA.

FIG. 15schematically depicts the membrane assembly80attached to the patterning device MA and stored in the loading apparatus70. The loading apparatus70may alternatively be called a load lock or an inner pod. As shown inFIG. 15, in an embodiment the loading apparatus70comprises at least one protrusion71. The protrusions71are for pressing up the membrane holder58of the frame assembly50. The protrusions71protrude from the inside surface (or the base plate) of the loading apparatus70. As can be seen fromFIG. 15, by pressing the resilient members53by the protrusions71, the membrane holder58can be pressed towards the patterning device MA. This adds clearance for the membrane40towards the inner surface of the loading apparatus70.

In an embodiment the distance between the membrane40and the inner surface of the loading apparatus70is increased from about 0.5 mm to about 1.5 mm by compressing the resilient members53by the protrusions71. In an embodiment the clearance of the membrane40towards the patterning device MA is temporarily reduced from about 2.5 mm to about 1.5 mm. The clearance of the membrane40towards the patterning device MA is subsequently increased back up to about 2.5 mm when the membrane assembly80is released from the loading apparatus70.

An embodiment of the disclosure is expected to reduce the risk of electrostatic discharge between the loading apparatus70and the membrane40. This is because of the increased clearance between the membrane40and the inner surface of the loading apparatus70.

As depicted inFIG. 16, in an embodiment the membrane assembly80comprises a sealing frame72. The sealing frame72is provided to control the opening of the volume between the membrane40and the patterning device MA. In an embodiment the sealing frame72is positioned around the membrane40. In an embodiment the sealing frame72comprises a plurality of seal openings73. When the membrane holder58is pressed upwards towards the patterning device MA, frame openings74in the frame assembly50will line up with the seal openings73to allow high speed pressure equalization, as shown inFIG. 16. The frame openings74line up with the seal openings73so that gas (e.g. air) can pass through.

FIG. 17schematically depicts the membrane assembly80outside of the loading apparatus70. The seal openings73do not line up with the frame openings74such that the path for gas and particles is blocked. Accordingly, the sealing frame72seals the space between the membrane40and the patterning device MA.

FIG. 18schematically depicts a gap G between the membrane assembly80and the patterning device MA. In positions where the studs52are not provided, contaminant particles can potentially pass through the gap G and enter into the space or region between the patterning device MA and the membrane40. The gap G may have a thickness of about 300 μm, for example.

The membrane assembly80is vulnerable to allowing particles that are smaller than the size of the gap G to reach the space between the membrane40and the patterning device MA. For example, contaminant particles that originate from outside of the space and have a size of less than about 200 μm can pass through the gap G either in a straight line or with some bouncing between the patterning device MA and the frame assembly50.

FIG. 19schematically depicts, in cross-section, a variation of a membrane assembly80. This variation shown inFIG. 19can be applied to any of the embodiments of the membrane assembly80described in this document.

The variation of the membrane assembly80shown inFIG. 19is for reducing the possibility of particles entering the region between the membrane40and the patterning device MA from outside that region. Additionally, variation of the membrane assembly80shown inFIG. 19is for reducing the possibility of particles that originate in the gap G exiting the region between the membrane40and the patterning device MA. As depicted inFIG. 19, in an embodiment the membrane assembly80comprises a frame assembly50configured to hold the membrane40and to attach to the patterning device MA. A gap G is formed between opposing surfaces of the frame assembly50and the patterning device MA.

In an embodiment the frame assembly50comprises an elongate baffle75. The elongate baffle75is configured to restrain contaminant particles from entering the gap G. As shown inFIG. 19, the elongate baffle75extends beyond the opposing surface of the patterning device MA. In an embodiment the elongate baffle75extends beyond the opposing surface of the patterning device MA at a location beyond the planar extent of the patterning device MA.

The membrane assembly80reduces the possibility of particles reaching the space between the patterning device MA and the membrane40. As depicted inFIG. 19, in an embodiment the frame assembly50comprises at least one further baffle76. Each further baffle76is configured to restrain contaminant particles from entering the gap G. Each further baffle76extends towards the patterning device MA.

In an embodiment the frame assembly50comprises three or four grooves (i.e. spaces between the elongate baffle75and each of the further baffles76). In an embodiment the grooves do not have equal widths. In other words the elongate baffle75and the further baffles76may not be equally spaced. Particles that are released within the region between the membrane40and the patterning device MA (e.g. particles released from the side of the membrane40facing the patterning device MA) and travel towards the frame assembly50are less likely to be reflected back to the patterning device MA. The particles can become trapped within the grooves.

In an embodiment the elongate baffle75has a height of greater than or equal to about 1 mm. In an embodiment the distance between the elongate baffle75(and further baffles76) and the patterning device MA is selected so as to encourage pressure equalization during operation of the lithographic apparatus100. In an embodiment the distance between the elongate baffle75and the nearest further baffle76is about 300 μm. In an embodiment the distance between the further baffle76closest to the elongate baffle75and the next further baffle76is about 1.2 to 1.5 times greater than the distance between the elongate baffle75and the nearest further baffle76. In an embodiment the distance between the further baffle76in the middle of the three shown inFIG. 19and the further baffle76that is furthest from the elongate baffle75is about 1.2 to 1.5 times the distance between the two further baffles76in the center and to the right of the three further baffles76shown inFIG. 19. In an embodiment each further baffle76has a height of about 600 μm. In an embodiment the width of the grooves between baffles increases by about 20% to 50% in the direction from the elongate baffle75.

In an embodiment the elongate baffle75and the further baffles76are positioned between the center of the patterning device MA and the studs52. Accordingly, the baffle structures can constrain particles of, for example, titanium alloy, released by the studs52. Hence, in an embodiment the elongate baffle75extends beyond the opposing surface of the patterning device MA at a location that is not beyond the planar extent of the patterning device MA.

In an embodiment the elongate baffle75and/or the further baffles76are made of a material that has a high Hamaker constant. In an embodiment the frame assembly50is made of a material that has a high Hamaker constant. An embodiment of the disclosure is expected to reduce the possibility of particles with a large range of sizes, materials, travel speeds and angles of incidence from reaching the patterning device MA.

FIGS. 20A-20Cschematically depict, in cross-section, various embodiments of gap particle traps90located in a reticle stage region of a patterning device. Gap particle trap90shown inFIGS. 20A-20Ccan be applied to any of the embodiments of membrane assembly80and other suitable components of lithography apparatus100as described in this disclosure, or other particle sensitive apparatus such as metrology systems, tubes, gas flow ducts, or boxes of gas ducts/pipes. In general, gap particle trap90may be located in any particle sensitive apparatus to reduce the number of undesired contaminant particles.

In one example, gap particle traps90shown inFIGS. 20A-20Care used for reducing the possibilities of particles entering a reticle stage region RS where a patterning device MA is mounted. As depicted inFIGS. 20A-20C, the reticle stage region RS comprises a stationary part, for example, a support structure MT, and a movable part MRS. Note that the terms stationary and movable are interchangeable and only used to describe the relative movements between different parts of reticle stage region RS. It is possible that support structure MT is movable and movable part MRS is stationary, or both are movable or stationary as needed. Patterning device MA is mounted on movable part MRS. Movable part MRS may be a frame or a table, for example, which may be fixed or movable as required. Movable part MRS may also comprise devices for changing or blocking patterning device MA. An exemplary device for moving and changing patterning device MA is a rotational exchange device (RED), and an exemplary device for blocking patterning device MA is a movable reticle-masking (REMA) blade. Both exemplary devices are manufactured by ASML, Veldhoven, The Netherlands, and are respectively described in U.S. Pat. Nos. 9,268,241 and 7,359,037 and incorporated by reference herein in their entirety.

In embodiments where a physical barrier is not allowed between the stationary and movable parts of reticle stage region RS, a gap G is formed between opposing surfaces of support structure MT and movable part MRS. The environment between support structure MT and movable part MRS contains parts that may be contaminant particle sources, for example, cables or cable slab boxes (not shown inFIGS. 20A-20C). Various designs or devices may be implemented in particle sensitive apparatus to reduce particle contamination, such as gas flow manipulation. However, these methods may not be sufficient to prevent all contaminant particles, therefore a gap particle trap is located in gap G to further reduce the amount of particles that could potentially pass through gap G and eventually come in contact with patterning device MA. Specifically, gap particle trap may block more particles from passing through gap G than just parallel surfaces alone. It should be noted that suitable surfaces of lithographic apparatus may be used to form gap particle traps90, in accordance with various embodiments. For example, during the manufacturing of reticle stage RS, surfaces of various parts of the reticle stage RS may form the mechanical structure of gap particle traps90, thus gap particle traps90may be integrated parts of reticle stage RS. Gap particle traps90may also be attachable parts that can be mounted on support structure MT or movable part MRS as needed, in accordance with other embodiments.

As shown inFIG. 20A, gap particle trap90is placed in gap G and formed on the surface of movable part MRS, in accordance with an embodiment. To capture contaminant particle with various speeds, incident angles, or other particle properties, gap particle trap90may also be formed on the surfaces of support structure MT, or on both surfaces of support structure MT and movable part MRS, in accordance with various embodiments, and shown inFIGS. 20B and 20Crespectively. For simplicity, structure details of gap particle trap90are not shown inFIGS. 20A-20C, but shown inFIGS. 21A-21D.

FIG. 21Aschematically depicts, in cross-section, gap particle trap90according to an embodiment of the disclosure. Gap particle trap90comprises baffles92. Baffles92are configured to restrain contaminant particles that entered gap G from reaching patterning device MA. As shown inFIG. 21A, baffles92may have rectangular cross-sections, with each baffle92having height H and width W. Baffles92may also have any appropriate cross-section shape, for example, near rectangular, triangular, near triangular, rhomboid, or near rhomboid. Further examples of these configurations are shown inFIGS. 21B-21D. The width W of baffle92may be equal to or different from height H. In an embodiment, gap particle trap90comprises a plurality of grooves (i.e., spaces between each baffle92). In an embodiment the grooves do not have equal widths, in other words the baffles92may not be equally spaced. In another embodiment, baffles92are equally spaced. For example, the distance between opposing sidewalls of adjacent baffles92is about 500 μm. In other embodiments, there may be no grooves between baffles. The height H, width W, and spacing of baffles92may be configured based on the properties of targeted contaminant particles. For example, the configuration of baffles92may be different at least based on the velocity, angle of incidence, dimension, material, or weight of the contaminant particles. An embodiment of the disclosure is expected to reduce the possibility of particles with a large range of sizes, materials, travel speeds and angles of incidence from reaching the patterning device MA.

An exemplary operation of gap particle trap90is explained below, with reference toFIG. 20A. Contaminant particles may enter gap G from the contaminant sources between support structure MT and movable part MRS, and eventually travel toward patterning device MA. These contaminant particles will collide with the surfaces of support structure MT and gap particle trap90. The contaminant particles are likely to collide a number of times with the sidewall and/or groove surfaces of gap particle trap90. With each collision, the particle loses kinetic energy, and with low enough velocity or kinetic energy, the particle will stick to the gap particle trap's surface due to van der Waals interaction. In an embodiment, baffles92are made of materials with a high Hamaker constant to increase the van der Waals force between contaminant particles and surfaces of gap particle trap90, giving the contaminant particles a higher probability of sticking to the trap surfaces. The collisions of particles with the gap particle trap significantly reduces the contaminant particle's kinetic energy such that the particles become trapped in the grooves or on the surfaces of gap particle trap90. Even if a particle has remaining energy sufficient to exit the groove and projects back into the gap, its speed will be reduced and therefore the particle is more controllable by the purge gas flow. The particle's velocity may also be reversed or partially reversed due to collisions with the gap particle trap and as a result the particle may travel away from gap G and toward a preferred direction.

In embodiments where contaminant particles traveled through the gap particle trap and entered into the environment where patterning device MA is located, a surface particle trap may be formed on appropriate surfaces of support structure MT or movable part MRS to reduce the amount of particles that could contact patterning device MA. Similar to gap particle trap90disclosed above, it should be noted that suitable surfaces of lithographic apparatus may be used to form surface particle traps, in accordance with various embodiments. For example, during the manufacturing stages of reticle stage RS, surfaces of various parts of the reticle stage RS may form the mechanical structure of surface particle trap. Surface particle traps may also be attachable parts that can be mounted on support structure MT or movable part MRS as needed, in accordance with other embodiments.

As shown inFIG. 22A, surface particle trap94is located on the surfaces of support structure MT, in accordance with some embodiments. To capture contaminant particle with various speeds, incident angles, or other particle properties, surface particle traps94may also be formed on other surfaces of support structure MT, or on both surfaces of support structure MT and movable part MRS, in accordance with various embodiments, and shown inFIG. 22B. For simplicity, structure details of surface particle trap94are not shown inFIGS. 22A and 22B, but shown inFIGS. 23A-23F. As mentioned above, although surface particle traps94shown inFIGS. 22A and 22Bare attachable parts, surface particle traps94may also be integrated parts of reticle stage RS and formed using the surfaces of various components of reticle stage RS.

FIGS. 23A-23Eschematically depict, in cross-section, various embodiments of surface particle traps94. Surface particle trap94comprises baffles96that are configured to trap contaminant particles and preventing them from reaching patterning device MA. As shown inFIG. 23A, baffles96may have a triangular cross-section area, with each baffle96having height H and width W, in accordance with an embodiment. For illustration purposes, each baffle96has peak P and trough T which are the highest and lowest point of the triangular cross-section area, respectively. Baffles96may also have a near-triangular cross-section area as shown inFIG. 23Bwhich may be preferred for giving reflected particles a desired travel direction. It should be noted that baffles96may have a variety of cross-section shapes, for example, a trapezoid shaped cross-section. In an embodiment, no spacing exists between each baffle (i.e., the baffles form a zig-zag pattern). For illustration purposes, angles θ1and θ2are angles measured between the surface (or imaginary surface formed by adjacent troughs) of structure support MT and each side of baffle96, respectively, as seen from the cross-section view of surface particle trap94inFIG. 23A.

In an embodiment, angles θ1and θ2can be configured such that a contaminant particle may not be able to exit the surface particle trap based on its angle of incidence. For example,FIG. 23Ashows that angles θ1and θ2are equal. In another example, shown inFIG. 23C, the upper surface of baffle96is perpendicular or nearly perpendicular to the surface of support structure MT on which the surface particle trap is formed. Therefore angle θ1would be equal or close to 90°. InFIG. 23D, the lower surface of baffle96is perpendicular or nearly perpendicular to the surface of support structure MT on which the surface particle trap is formed. Therefore angle θ2would be equal or close to 90°.FIGS. 23E and 23Fshow further examples of surface particle trap96. InFIG. 23E, angles θ1and θ2are separately configured for each baffle96, such that angles θ1or θ2for a first baffle may be different than the corresponding angles θ1′ or θ2′ for an adjacent second baffle. InFIG. 23F, angles θ1and θ2are different angles but each of the baffles96are identical.

FIGS. 24A and 24Bschematically depict, in plan view, various embodiments of surface particle traps94.FIG. 24Amay be a plan view of surface particle trap94described inFIG. 23A. As shown inFIG. 24A, rows of baffles96are parallel with each other, with equal spacing between adjacent peaks or troughs. Alternatively, each row of baffles96may also be arranged to form specific shapes. As shown inFIG. 24B, each row is formed into a V shape and the rows of baffles96are in parallel with each other, while spacing between adjacent peaks or troughs may be different.

An embodiment of the disclosure is expected to reduce the possibility of particles with a large range of sizes, materials, travel speeds and angles of incidence from reaching the patterning device MA. Surface particle trap94may be installed or formed in other particle-sensitive environments of lithography apparatus100as described in this document, or other particle sensitive apparatus such as metrology systems, tubes, gas flow ducts, or boxes of gas ducts/pipes. In general, surface particle trap94may be located in any particle sensitive apparatus to reduce the number of contaminant particles.

An exemplary operation of surface particle trap94is explained below, with reference toFIG. 22A. Contaminant particles that are generated between support structure MT and movable part MRS may exit gap G and eventually travel toward patterning device MA. These contaminant particles are likely to collide with surface particle trap94and collide a number of times with baffles96. With each collision, the particle loses kinetic energy, and with low enough velocity or kinetic energy the particle will stick to the surface particle trap due to van der Waals interaction. In an embodiment, baffles96are made of materials with a high Hamaker constant to increase the van der Waals force between contaminant particles and surfaces of surface particle trap94, giving the contaminant particles a higher probability of sticking to the trap surfaces. The collisions in the surface particle trap significantly reduces the contaminant particle's kinetic energy and the particles become trapped between the baffles.

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, LCDs, thin-film magnetic heads, etc. 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.

While specific embodiments of the disclosure have been described above, it will be appreciated that the disclosure may be practiced otherwise than as described. For example, the various photo resist layers may be replaced by non-photo resist layers that perform the same function.

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 disclosure as described without departing from the scope of the claims set out below.