TW202414077A - Pellicle, patterning device assembly, and dynamic gas lock assembly for euv lithography - Google Patents

Abstract

A pellicle for EUV lithography comprising: a frame; and a membrane supported by the frame, wherein the membrane comprises: a metallic or semimetallic layer, wherein the membrane comprises pores at a density of at least 5 per µm ². The membrane may have a substrate layer for supporting the metallic or semimetallic layer, the substrate layer comprising for example silicon obtained from silicon on insulator or polysilicon.

Description

Protective film, patterning device assembly and dynamic airlock assembly for EUV lithography

The present invention relates to a pellicle, a diaphragm, a patterning device assembly and a dynamic airlock assembly for extreme ultraviolet (EUV) lithography.

A lithographic apparatus is a machine that applies a desired pattern onto a substrate, typically onto a target portion of the substrate. Lithographic apparatus may be used, for example, in the manufacture of integrated circuits (ICs). In that case, a patterning device (which is alternatively referred to as a mask or reticle) may be used to produce a circuit pattern to be formed on individual layers of the IC. This pattern may be transferred onto a target portion (e.g., a portion comprising a die, a die, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically performed by imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of sequentially patterned adjacent target portions.

Lithography is widely recognized as one of the key steps in the fabrication of ICs and other devices and/or structures. However, as the size of features fabricated using lithography becomes smaller and smaller, lithography is becoming a more decisive factor in enabling the fabrication of small ICs or other devices and/or structures.

The theoretical estimate of the pattern printing limit can be given by the Rayleigh resolution criterion, as shown in equation (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 known as the Rayleigh constant), and CD is the feature size (or critical dimension) of the printed feature. From equation (1), it can be seen that a reduction in the minimum printable size of a feature can be obtained in three ways: by shortening the exposure wavelength λ, by increasing the numerical aperture NA, or by reducing the value of k1.

In order to shorten the exposure wavelength and thus reduce the minimum printable size, it has been proposed to use extreme ultraviolet (EUV) radiation sources. EUV radiation is electromagnetic radiation with a wavelength in the range of 10 to 20 nm, for example in the range of 13 to 14 nm. It has further been proposed to use EUV radiation with a wavelength less than 10 nm, for example in the range of 5 to 10 nm, such as 6.7 nm or 6.8 nm. This radiation is called extreme ultraviolet radiation or soft x-ray radiation. Possible sources include, for example, laser-generated plasma sources, discharge plasma sources, or sources based on synchrotron radiation provided by electron storage rings.

A lithography apparatus includes a patterning device (e.g., a mask or a reticle). Radiation is provided through or reflected from the patterning device to form an image on a substrate. A diaphragm assembly may be provided to protect the patterning device from airborne particles and other forms of contamination. A diaphragm assembly used to protect the patterning device may be referred to as a pellicle. Contamination on the surface of the patterning device may cause manufacturing defects on the substrate. The diaphragm assembly may include a frame and a diaphragm stretched across the frame.

In use, the performance of the diaphragm may degrade over time, especially at higher temperatures. At higher temperatures, the diaphragm may release a gas. It is desirable to keep the temperature of the pellicle relatively low. It is also desirable for the pellicle to transmit a high proportion of EUV radiation and have a low spot on the substrate.

According to one aspect of the present invention, a protective film for EUV lithography is provided, which includes: a frame; and a diaphragm supported by the frame, wherein the diaphragm includes: a metal or semi-metal layer, wherein the diaphragm includes a pore density of at least 5/ ^µm2 .

According to one aspect of the present invention, a diaphragm for a protective film for EUV lithography is provided, which comprises: a non-metallic or semi-metallic layer, wherein the diaphragm comprises pores with a density of at least 5/ ^µm2 .

According to one aspect of the present invention, a method for manufacturing a protective film for EUV lithography is provided, which includes: coating a first material on a second material to form a frame of the protective film; coating a third material to form a metal or semi-metal layer of a diaphragm of the protective film on a substrate layer of the diaphragm; and forming pores in the substrate layer with a density of at least 5/ ^µm2 .

According to one aspect of the present invention, a diaphragm of a protective film for EUV lithography is provided, which includes a grating, which includes a plurality of holes, pores or protrusions. The plurality of holes may, for example, include holes of circular, square, circular blocks or any shape. The diaphragm may, for example, include a main film or main layer. The thickness of the main film or layer in the grating may, for example, be in the range of 20 nm to 100 nm. In one embodiment, the main film or main layer may also be referred to as a core or a diaphragm core. Preferably, the grating spacing is less than 200 nm to ensure good emissivity. The grating spacing can be defined as the distance between the centers of adjacent holes of the grating. In one embodiment, the main grating spacing is preferably less than 100 nm to ensure a low spot at the wafer level. A smaller grating spacing, such as 30 nm or less, can prevent debris particles from falling on the multiplication mask. The diaphragm of a protective film for EUV lithography according to any embodiment may include a metal layer having a thickness between 4 and 15 nm, or a half metal with a thickness in the range of 20 to 80 nm. If the diaphragm is more open, the metal layer is preferably thicker. In one embodiment, the diaphragm grating has substantially square openings (i.e., holes) with a spacing of 30 to 200 nm, such as 100 nm, and a percentage of the open area or an openness defined by the grating opening is 50% to 90%, such as 75% openness or open area. A radiating Ru layer with a thickness of approximately 8 nm has an emissivity of >0.35. The material of the pellicle diaphragm may include, for example, a SOI Si diaphragm core bonded with a metal layer. In another embodiment, the diaphragm grating comprising SOI Si has a substantially circular or square opening covering 50% to 90% of the diaphragm area, a grating pitch less than 100 nm, and a metal layer having a thickness in the range of 5 to 15 nm, the metal layer providing low spot and an emissivity of > 0.2 at the wafer level.

FIG1 schematically depicts a lithography apparatus 100 including a source collector module SO according to one embodiment of the present invention. The apparatus 100 comprises: - an illumination system (or illuminator) IL configured to condition a radiation beam B (e.g., EUV radiation). - a support structure (e.g., a mask stage) MT, which is constructed to support a patterning device (e.g., a mask or a multiplying mask) MA and is connected to a first positioner PM configured to accurately position the patterning device; - a substrate stage (e.g., a wafer stage) WT, which is constructed to hold a substrate (e.g., an anti-etchant coated wafer) W and is connected to a second positioner PW configured to accurately position the substrate; and - a projection system (e.g., a reflective projection system) PS, which is configured to project a pattern imparted to a radiation beam B by the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

The illumination system IL may include various types of optical components for directing, shaping or controlling the radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components or any combination thereof.

The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA, the design of the lithography apparatus, and other conditions, such as whether the patterning device is held in a vacuum environment. The support structure MT may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may be, for example, a frame or a table, which may be fixed or movable as desired. The support structure MT may ensure that the patterning device MA is in a desired position, for example relative 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 pattern to a radiation beam B in its cross-section so as to produce a pattern in a target portion C of a substrate W. The pattern imparted to the radiation beam B may correspond to a specific functional layer in a device (e.g., an integrated circuit) produced in the target portion C.

The patterning device MA may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable liquid-crystal display (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. One example of a programmable mirror array uses a matrix arrangement of mirror facets, each of which can be individually tilted so as to reflect an incident radiation beam in different directions. The tilted mirrors impart a pattern in the radiation beam reflected by the mirror array.

Similar to the illumination system IL, the projection system PS may include various types of optical components appropriate to the exposure radiation used or to other factors such as the use of a vacuum, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components or any combination thereof. A vacuum may be required for EUV radiation since other gases may absorb too much radiation. Therefore, a vacuum environment may be provided to the entire beam path by means of vacuum walls and a vacuum pump.

As depicted herein, lithography apparatus 100 is of the reflective type (eg, using a reflective reticle).

The lithography apparatus 100 may be of a type having two (dual-stage) or more substrate tables WT (and/or two or more supporting structures MT). In such a "multi-stage" lithography apparatus, additional substrate tables WT (and/or additional supporting structures MT) may be used in parallel, or preparatory steps may be performed on one or more substrate tables WT (and/or one or more supporting structures MT) while one or more other substrate tables WT (and/or one or more other supporting structures MT) are being used for exposure.

Referring to FIG. 1 , an illumination system IL receives an extreme ultraviolet radiation beam from a source collector module SO. Methods for generating EUV light include, but are not necessarily limited to, converting a material into a plasma state having at least one element (e.g., xenon, lithium, or tin) using one or more emission lines in the EUV range. In one such method, often referred to as laser produced plasma "LPP," the desired plasma may be generated by irradiating a fuel (e.g., a droplet, stream, or cluster of material having the desired 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 FIG. 1 ) for providing a laser beam that excites the fuel. The resulting plasma emits output radiation (e.g., EUV radiation) which is collected using a radiation collector disposed in a source collector module. For example, when a _CO2 laser is used to provide the laser beam for fuel excitation, the laser and source collector module SO may be separate entities.

In such cases, the laser is not considered to form part of the lithography apparatus 100, and the radiation beam B is delivered from the laser to the source collector module SO by means of a beam delivery system comprising, for example, suitable steering mirrors and/or a beam expander. In other cases, for example when the source is a discharge produced plasma EUV generator (often referred to as a DPP source), the source may be an integral part of the source collector module SO.

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

A radiation beam B is incident on a patterning device (e.g., a mask) MA held on a support structure (e.g., a mask table) MT and is patterned by the patterning device MA. After reflection from the patterning device (e.g., a mask) MA, the radiation beam B passes through a projection system PS which focuses the radiation beam B onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor PS2 (e.g., an interferometric measurement device, a linear encoder or a capacitive sensor), the substrate table WT can be accurately moved, for example, so that different target portions C are positioned in the path of the radiation beam B. Similarly, a first positioner PM and a further position sensor PS1 can be used to accurately position the patterning device (e.g., a mask) MA relative to the path of the radiation beam B. The patterning device (eg, mask) MA and the substrate W may be aligned using the mask alignment marks M1, M2 and the substrate alignment marks P1, P2.

The controller 500 controls the overall operation of the lithography apparatus 100, and in particular executes the operating procedures further described below. The controller 500 can be embodied as a suitably programmed general-purpose computer, which includes a central processing unit, volatile and non-volatile storage components, one or more input and output devices (such as a keyboard and screen), one or more network connections to various parts of the lithography apparatus 100, and one or more interfaces. It should be understood that a one-to-one relationship between the control computer and the lithography apparatus 100 is not necessary. In one embodiment of the present invention, one computer can control multiple lithography apparatuses 100. In one embodiment of the present invention, multiple networked computers can be used to control one lithography apparatus 100. The controller 500 may also be configured to control one or more associated process devices and substrate handling devices in a lithography unit or cluster of which the lithography apparatus 100 forms a part. The controller 500 may also be configured to be subordinate to a supervisory control system of the lithography unit or cluster and/or a master control system of a fab.

FIG2 shows the lithography apparatus 100 in more detail, including a source collector module SO, an illumination system IL, and a projection system PS. An EUV radiation emitting plasma 210 may be formed by a plasma source. EUV radiation may be generated by a gas or vapor (e.g., Xe gas, Li vapor, or Sn vapor), wherein the radiation emitting plasma 210 is generated to emit radiation in the EUV range of the electromagnetic spectrum. In one embodiment, an excited tin (Sn) plasma is provided to generate EUV radiation.

Radiation emitted by radiation emitting plasma 210 is transmitted from source chamber 211 to collector chamber 212.

The collector chamber 212 may include a radiation collector CO. Radiation traversing the radiation collector CO may be focused into a virtual source point IF. The virtual source point IF is often referred to as an intermediate focus, and the source collector module SO is configured such that the virtual source point IF is located at or near an opening 221 in the enclosure 220. The virtual source point IF is an image of the radiation emitting plasma 210.

The radiation then traverses the illumination system IL which may include a faceted field mirror device 22 and a faceted pupil mirror device 24 which are configured to provide a desired angular distribution of the unpatterned light beam 21 at the patterning device MA, and a desired uniformity of the radiation intensity at the patterning device MA. After reflection of the unpatterned light beam 21 at the patterning device MA held by the support structure MT, a patterned light beam 26 is formed and is imaged by the projection system PS via reflective elements 28, 30 onto a substrate W held by a substrate table WT.

More elements than shown may typically be present in the illumination system IL and the projection system PS. Furthermore, there may be more mirrors than shown in the figures, for example, there may be 1 to 6 additional reflective elements in the projection system PS than shown in FIG. 2 .

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

As depicted in FIG1 , in one embodiment, a lithography apparatus 100 includes 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 a 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 may be at least partially evacuated. The intervening space may be bounded at the location of the projection system PS by a solid surface from which the employed radiation is directed towards the substrate table WT.

In one embodiment, the lithography apparatus 100 includes a dynamic airlock. The dynamic airlock includes a diaphragm assembly 80. In one embodiment, the dynamic airlock includes a hollow portion covered by the diaphragm assembly 80 located in the intervening space. The hollow portion is located around the path of radiation. In one embodiment, the lithography apparatus 100 includes a blower configured to use an airflow to flush the interior of the hollow portion. The radiation travels through the diaphragm assembly and then irradiates the substrate W.

In one embodiment, the lithography apparatus 100 includes a diaphragm assembly 80. As explained above, in one embodiment, the diaphragm assembly 80 is used for a dynamic airlock. In this case, the diaphragm assembly 80 acts as a filter for filtering DUV radiation. Additionally or alternatively, in one embodiment, the diaphragm assembly 80 is a protective film for a patterning device MA for EUV lithography. The diaphragm assembly 80 of the present invention can be used for a dynamic airlock or for a protective film or for another purpose, such as a spectral purity filter. In one embodiment, the diaphragm assembly 80 includes a diaphragm 40, which may also be referred to as a diaphragm stack. In one embodiment, the diaphragm is configured to transmit at least 80% of the incident EUV radiation.

In one embodiment, the diaphragm assembly 80 is configured to seal 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 one embodiment, the pellicle is configured to reduce the possibility that particles may migrate into the step-in field of the patterning device MA in the lithography apparatus 100.

If the patterning device MA is not protected, contamination will require the patterning device MA to be cleaned or discarded. Cleaning the patterning device MA will interrupt valuable manufacturing time, and discarding the patterning device MA is costly. Replacing the patterning device MA will also interrupt valuable manufacturing time.

FIG3 schematically depicts in cross section a portion of a diaphragm assembly 80 according to one embodiment of the present invention. The diaphragm assembly 80 is for EUV lithography. The diaphragm assembly 80 includes a diaphragm 40. The diaphragm 40 is emissive to EUV radiation. Of course, the diaphragm 40 may not have an emissivity of 100% to EUV radiation. However, the diaphragm may have an emissivity of, for example, at least 20%. As shown in FIG3 , in one embodiment, the diaphragm 40 is substantially planar. In one embodiment, the plane of the diaphragm 40 is substantially parallel to the plane of the patterning device MA.

For example, the diaphragm assembly 80 has a shape such as a square, a circle, or a rectangle. The shape of the diaphragm assembly 80 is not particularly limited. The size of the diaphragm assembly 80 is not particularly limited. For example, in one embodiment, the diameter of the diaphragm assembly 80 is in the range of about 100 mm to about 500 mm, such as about 200 mm.

As depicted in FIG3 , in one embodiment, the diaphragm assembly 80 includes a frame 81. The frame 81 is configured to hold the diaphragm 40. The frame 81 provides mechanical stability to the diaphragm 40. The frame 81 is configured to reduce the likelihood that the diaphragm 40 will deform away from its planar shape. In one embodiment, a pre-tension is applied to the diaphragm 40 during manufacture of the diaphragm 40. The frame 81 is configured to maintain tension in the diaphragm 40 so that the diaphragm 40 does not have an undulating shape during use of the lithography apparatus 100. In one embodiment, the frame 81 extends along the periphery of the diaphragm 40. The outer periphery of the diaphragm 40 is positioned on top of the frame 81 (from the view of FIG3 ).

As depicted in FIG3 , in one embodiment, the frame 81 includes a border portion directly connected to the diaphragm 40. The border portion of the frame 81 is formed of a second material 74 described later in the present invention. As shown in FIG3 , in one embodiment, the frame 81 further includes an extension portion that makes it easier for the diaphragm assembly 80 to be fixed relative to the patterning device MA. The border portion and the extension portion of the frame 81 can be adhered to each other.

As depicted in Figure 3, in one embodiment, the diaphragm assembly 80 includes a clip 50. The clip 50 is configured to be removably coupled to a stud 60 fixed relative to the pattern device MA. Additional details of the assembly are described in WO 2016079051 A2, particularly in Figures 11 and 28 to 31 and the associated description.

The performance of the diaphragm 40 may degrade over time. Degradation of the diaphragm 40 may result in undesirable reticulated reticle imprinting of the pellicle. The degradation problem of the diaphragm 40 may be more severe when relatively high power EUV radiation is incident on the diaphragm 40. At high temperatures, the diaphragm 40 may undesirably release gases (i.e., outgas). For example, the diaphragm 40 may release gases that include oxides. Outgassing of oxides may be accelerated by light induced etching. It is desirable to keep the temperature of the pellicle low to reduce the possibility of outgassing.

As explained above, in one embodiment, the protective film includes a frame 81 and a diaphragm 40. The diaphragm 40 is supported by the frame 81. The diaphragm 40 includes a metal or semi-metal layer 72.

FIG. 7 shows a cross-section of a diaphragm 40 according to one embodiment of the present invention. As shown in FIG. 7 , in one embodiment, the diaphragm 40 includes a substrate layer 71. The substrate layer 71 is used to support a metal or semi-metal layer 72. As shown in FIG. 7 , in one embodiment, the substrate layer 71 is thicker than the metal or semi-metal layer 72. The substrate layer 71 is configured to provide structural stability to the diaphragm 40.

In one embodiment, the diaphragm 40 includes an interlayer between the substrate layer 71 and the metal or semi-metal layer 72. The interlayer is configured to reduce the possibility of cracking of the metal or semi-metal layer 72. At higher temperatures, the possibility of such cracking is greater. In one embodiment, the interlayer includes Mo. In one embodiment, the interlayer has a thickness in the range of about 1 nm to about 2 nm. In one embodiment, the interlayer is formed of a material different from the metal or semi-metal layer 72. In one embodiment, the interlayer is thinner than the metal or semi-metal layer 72.

In one embodiment, the substrate layer 71 comprises single crystal Si released from a silicon on insulator (SOI) wafer. In an alternative embodiment, the substrate layer 71 comprises polysilicon (polycrystalline silicon).

However, the diaphragm 40 does not necessarily include such a substrate layer 71. For example, in an alternative embodiment, a metal or semi-metal layer 72 provides its own structural stability. For example, in one embodiment, the same metal layer 72 forms at least 90% of the total thickness of the diaphragm 40.

FIG8 shows a plan view of a membrane 40 according to one embodiment of the present invention. As shown in FIG8, in one embodiment, the membrane 40 includes pores 73. The pores 73 extend through the thickness of the membrane 40. The membrane 40 is not continuous. By providing the membrane 40 includes pores 73, the membrane 40 can transmit a higher proportion of EUV radiation incident thereon. This reduces the amount of EUV radiation that can unnecessarily heat the membrane 40.

Although FIG8 shows the regular distribution of the pores 73 on the diaphragm 40, the arrangement of the pores 73 is not particularly limited. The pores 73 may be regularly, semi-regularly or randomly distributed on the diaphragm 40.

It is desirable that the pores 73 be positioned relatively closely together. In one embodiment, the density of the pores is at least 5/µm ² . The distance between the centers of adjacent pores 73 is referred to as the pitch p. The pitch p is shown in FIG8 . In general, a greater density of pores 73 corresponds to a smaller pitch p. For irregularly distributed pores 73, different pitches may actually exist at different locations of the diaphragm 40. However, the main pitch may be determined by considering the average distance between pores 73 over an area of the diaphragm 40 having a size of at least 1 μm ^2. A density of 5 pores 73/μm ² corresponds to a pitch p of approximately 450 nm.

By providing a density of pores 73 of at least 5/ ^μm2 , the primary spacing p of pores 73 is less than 1 μm. The spacing p is less than the wavelength of the radiation (ie, infrared radiation) emitted by membrane 40. The inventors have found that this helps to increase the emissivity E of membrane 40.

By providing a density of pores 73 of at least 5/μm ² , the emissivity E of the membrane 40 can be kept relatively high. In general, the pores 73 cause the emissivity E of the membrane 40 to be reduced relative to a continuous membrane 40 (i.e., a membrane without pores). A higher density of pores 73 (corresponding to a smaller pitch p) is preferred for a higher emissivity E.

FIG5 is a graph showing the relationship between the incident radiation and the angle θ of the emissivity E of the membrane 40. Angle θ is the angle of the EUV radiation relative to the plane normal of the membrane 40. Line 91 is for a membrane 40 having a lateral spacing of 200 nm (corresponding to a density of 25 pores/μm ² ). Line 92 is for a membrane 40 having the same characteristics, except having a lateral spacing p of 2000 nm (corresponding to a density of about 0.25 pores/μm ² ). Line 93 is for a membrane 40 having similar characteristics, except having a lateral spacing p of 20000 nm (corresponding to a pore density of about 0.0025 pores/μm ² ). Other key characteristics of the membrane 40 are that 75% of its area is formed by pores 73 and that the metal layer 72 is formed of Ru with a thickness of 4 nm.

As shown in Figure 5, the emissivity E of the diaphragm 40 increases for decreasing the lateral spacing p. A higher emissivity E is desirable so that the diaphragm 40 radiates more of the energy it absorbs, thereby keeping the temperature of the diaphragm 40 reduced. One embodiment of the present invention contemplates achieving a reduced temperature of the diaphragm 40 during use.

In one embodiment, the density of pores 73 is at least 20/ ^μm2 . This corresponds to a lateral spacing of approximately 220 nm. As shown in Figure 5, this increases the emissivity E of the membrane 40. This in turn helps keep the membrane 40 cooler during use.

In one embodiment, the density of the pores is at least 100/μm ² . This corresponds to a lateral spacing p of about 100 nm. By providing a density of pores of at least 100/μm ² (i.e., a lateral spacing p of at most 100 nm), the spot from the membrane 40 to the substrate W can be reduced. The spot is related to the proportion of the energy of the EUV incident on the membrane 40 that is scattered on the substrate W. In one embodiment, the membrane 40 is configured so that the spot on the substrate W is at most 0.25%. This helps to provide good quality imaging. If the spot is too high, this may undesirably affect the imaging on the level of the substrate W.

The inventors have found that the membrane 40 with the apertures 73 acts as a diffraction grating. When the lateral spacing p is at most 150 nm, the spot of the normal incident illumination is substantially zero. The inventors have found that, in practice, a lower maximum lateral spacing p of about 100 nm provides a substantially zero spot for the substrate W in any illumination mode.

The following table shows examples of spot values for diaphragms 40 with different lateral spacings p and different metal and semi-metal layers 72. The material and thickness of the metal or semi-metal layer 72 are shown at the top of each row of the table. The values in the table are percentages of the spot toward the substrate W.

Pitch/nm 8nm Ru 4nm Ru 4nm Zr 8nm Zr 8nm Zr and 8nm ^SiO2 100 0 0 0 0 0 150 0 0 0 0 0 160 00.53 0.15 0.032 0.09 0.23 180 1.1 0.31 0.063 0.18 0.47 300       0.065 0.19    400       0.12 0.35    600       0.16 0.46   

As shown in the table, the spot of the Ru metal layer tends to be higher than that of the Zr metal layer. This is because Ru is optically stronger than Zr. Other characteristics of the diaphragm 40 on which the calculations in the table are based are: it has a substrate layer 71 of 50 nm thick silicon and 75% of the open area (i.e., 75% of the area of the diaphragm 40 is formed by pores 73).

In one embodiment, the metal layer 72 has a thickness of at least 4 nm. This helps to increase the emissivity E of the diaphragm 40. Figure 6 is a graph showing the relationship between the incident radiation of the diaphragm 40 and the angle θ of the emissivity E. There are three lines corresponding to different types of diaphragms 40. For all diaphragms 40, the pores 73 have a lateral spacing p of approximately 200 nm. The pores 73 form approximately 75% of the area of the diaphragm 40. Line 61 is for a diaphragm 40 having a metal layer 72 formed of Ru with a thickness of 8 nm. Line 62 is for a diaphragm 40 having a metal layer 72 formed of Ru with a thickness of 4 nm. Line 63 is for a diaphragm 40 having a metal layer 72 formed of Zr with a thickness of 8 nm.

6, in general, a thicker metal or semi-metal layer 72 increases the emissivity E of the diaphragm 40. By providing the metal layer 72 with a thickness of at least 4 nm, the emissivity E can be kept relatively high even when the pores 73 form a relatively high percentage of the total area of the diaphragm 40.

In one embodiment, metal layer 72 has a thickness of at least 8 nm. As shown in FIG6 , this further increases the emissivity E of diaphragm 40 . Of course, there is a tradeoff in that a thicker metal layer 72 may result in greater absorption of incident radiation. It is desirable to provide a good balance between the proportion of EUV radiation transmitted by diaphragm 40 and the emissivity of diaphragm 40 .

For example, in one embodiment, the protective film satisfies , where E is the emissivity for incident EUV radiation and T is the proportion of incident EUV radiation that is transmitted through membrane 40. For example, in one embodiment, the emissivity E may be about 0.2 and the EUV transmittance T may be about 95%. This would provide a ratio of E:(1-T) of 4. In one embodiment, this ratio is at least 5, at least 6, at least 7, at least 8, at least 9, or at least 10.

As described above, instead of the metal layer, there may be a semi-metal layer 72. When the semi-metal layer is provided instead of the metal layer, it is desirable that the thickness of the semi-metal layer 72 is greater. For example, in one embodiment, the semi-metal layer has a thickness of at least 10 nm.

As further explained above, when providing the semi-metal layer 72, it may not be necessary to provide a separate substrate layer 71. However, when no additional substrate layer 71 is provided, it is desirable that the semi-metal layer 72 is thicker. For example, in one embodiment, the semi-metal layer 72 has a thickness of at least 20 nm.

In one embodiment, the pores 73 form at least 50% of the total area of the membrane 40. FIG. 4 is a graph showing the relationship between the angle θ of the incident radiation and the emissivity E of the membrane 40. Different lines 41 to 45 are used for different membranes 40 that are similar except for having different degrees of openness. Line 41 is used for a continuous membrane with no pores. Line 42 is used for a porous membrane 42 that is 9% open (i.e., the pores 73 form 9% of the total area of the membrane 40). Line 43 is used for a membrane 40 that is 36% open. Line 44 is used for a membrane 40 that is 64% open. Line 45 is used for a membrane 40 that is 81% open.

4 , increasing the openness of membrane 40 decreases the emissivity E. However, increasing the openness increases the EUV transmittance T of membrane 40 . One embodiment of the present invention contemplates increasing the proportion of EUV radiation transmitted by membrane 40 .

In one embodiment, the pores form at least 75% of the total area of the membrane 40. This can reduce the proportion of EUV radiation not transmitted by the membrane 40 by a factor of about 5. Thus, although the emissivity E is reduced by a factor of about 2, there is still a significant overall benefit. The amount of energy required to heat the membrane 40 is generally reduced.

As shown in FIG8 , in one embodiment, the pores 73 are circular. The diameter of the pores 73 is d. The diameter d can be selected to provide a desired fill factor for the diaphragm 40.

However, the pores 73 need not be circular. FIG. 9 shows an alternative embodiment in which the pores 73 are square. The pores 73 have a dimension d. The dimension d may be selected to provide a desired fill factor for the diaphragm 40.

The shape of the pore 73 is not particularly limited. In one embodiment, the pore 73 does not have any regular shape.

One embodiment of the present invention is expected to reduce the amount of EUV radiation absorbed in the diaphragm 40. A greater proportion of the incident EUV radiation is transmitted by the diaphragm 40. However, not all of the additional transmitted EUV radiation is transmitted to the substrate W. In particular, the apertures 73 divert the radiation so that the transmitted EUV radiation reaches other areas outside of the substrate W. This means that the imaging at the level of the substrate W can remain high quality.

In one embodiment, the membrane 40 is configured to have a specular EUV transmission of at least 80%. In one embodiment, the membrane 40 is configured to have a non-specular EUV transmission to the substrate W of at most 0.25% (e.g., having an angle of less than 4.7 degrees relative to the normal to the plane of the membrane 40). In one embodiment, the membrane 40 is configured to have a EUV absorptivity of at most 10% in the membrane 40. In one embodiment, the membrane 40 is configured to have a non-specular EUV transmission of at most 10%, which does not enter the projection optics or the substrate W. The specular EUV transmission, non-specular EUV transmission, and absorptivity total 100%.

The metal of the metal layer 72 is not particularly limited. Some metals may oxidize during use. In one embodiment, an oxidation protection layer is provided. For example, an oxidation protection layer formed of boron may be provided. The oxidation protection layer is used to reduce oxidation of the metal layer 72. The oxidation protection layer may be coated on the metal layer 72.

In one embodiment, the metal of the metal layer 72 is not gold. In one embodiment, the metal is a transition metal. In one embodiment, the metal is a transition metal from Group 3 to Group 10. In one embodiment, the metal is a transition metal from Period 4 to Period 5.

In one embodiment, the metal is a transition metal. The specific transition metal is not particularly limited, but can be, for example, Zr, Y, Mo, Cr, Hf, Ir, Mn, Nb, Os, Pd, Pt, Re, Rh, Ru, Ta, Ti, V or W.

In one embodiment, the diaphragm assembly 80 is applied as a protective film or as part of a dynamic air lock. Alternatively, the diaphragm assembly 80 can be applied in other filtering areas such as identification, or in a beam splitter. In one embodiment, the dynamic air lock is configured to block debris within the lithography apparatus 100. In one embodiment, the dynamic air lock is positioned between the projection system PS and the substrate W. The dynamic air lock reduces the possibility of particles from the substrate W or from near the substrate W reaching the optical components in or around the projection system PS. Similarly, the dynamic air lock can protect the illumination system IL. In an alternative embodiment, the dynamic air lock is positioned at the virtual source point IF. For example, the dynamic air lock can be positioned between the source collector module SO and the illumination system IL.

According to one embodiment, a method for manufacturing a pellicle for EUV lithography is provided. Figures 10 to 13 schematically illustrate different stages of a method for manufacturing a pellicle according to one embodiment of the present invention.

As shown in FIG. 10 , in one embodiment, a method includes coating a first material on a second material 74. The second material 74 is used to form a portion of a frame 81 of a diaphragm assembly 80. The present invention will be described with respect to an embodiment in which the first material is used to form a substrate layer 71. However, as will be described in more detail subsequently, the first material may alternatively form a sacrificial layer on which the substrate layer 71 is formed.

10, in one embodiment, the first material forming the substrate layer 71 is coated onto all sides (in cross section) of the second material 74. The method of depositing the first material on the second material 74 is not particularly limited.

11, in one embodiment, the method includes patterning the first material at the back side of the second material 74. The back side is the side opposite to the side of the diaphragm 40 that forms the diaphragm assembly 80. The first material is patterned to form a mask for subsequently etching the second material 74.

As shown in FIG. 11 , in one embodiment, the method includes coating a third material to form a metal or semi-metal layer 72 of the diaphragm 40 on the substrate layer 71. The third material is a metal or semi-metal such as Ru or Zr as described above. The method of coating the third material on the substrate layer 71 is not particularly limited. In one embodiment, the third material is deposited by physical vapor deposition.

As shown in FIG. 12 , in one embodiment, the method includes forming pores 73 in a substrate layer 71. The pores 73 may be formed at a density of at least 5 μm ^2. As shown in FIG. 12 , in one embodiment, the pores 73 are opened on a combined stack of a metal or semi-metal layer 72 and a substrate layer 71. As shown in the process of FIG. 11 to FIG. 12 , in one embodiment, a third material (which forms the metal or semi-metal layer 72) is coated on the substrate layer 71 before forming the pores 73. This allows the pores 73 to be formed in both the metal or semi-metal layer 72 and the substrate layer 71 in substantially the same process steps. This helps to provide good uniformity of the shape of the pores 73 in the metal or semi-metal layer 72 and the substrate layer 71. There are various methods for forming the apertures 73 in the substrate layer 71, as will be described in more detail below.

In one embodiment, the method includes coating a sacrificial layer 75 on the stack of the metal or semi-metal layer 72 and the substrate layer 71. In one embodiment, the method includes coating a mechanical support layer 76 on the sacrificial layer 75 and the side of the diaphragm assembly 80. In a subsequent step, the method includes etching the second material 74 to expose the back side of the diaphragm 40 (the diaphragm 40 is formed by the metal or semi-metal layer 72 on the substrate layer 71).

The method of etching the second material 74 to expose the diaphragm 40 is not particularly limited. In one embodiment, the second material 74 is etched by performing a wet anisotropic etch. The mechanical support layer 76 is used to provide mechanical support to the diaphragm assembly 80 during the step of etching the second material 74. This reduces the possibility of damage (e.g., cracking) to the diaphragm 40 during the etching step. The mechanical support layer 76 is configured to protect the top side of the stack from the etchant that removes the second material 74.

In one embodiment, the second material includes silicon. As described above, in one embodiment, the second material can be etched by performing a wet etch. Alternatively, a dry etch process can be used to etch the second material.

As shown in FIG. 13 , in one embodiment, the method includes removing the mechanical support layer 76. The method of removing the mechanical support layer 76 is not particularly limited. As shown in FIG. 13 , in one embodiment, the method includes removing the sacrificial layer 75. The sacrificial layer 75 is used to protect the top side of the diaphragm 40 when the mechanical support layer 76 is removed. For example, the sacrificial layer 75 can protect the top side of the diaphragm 40 from any reagents used to remove the mechanical support layer 76. The method of removing the sacrificial layer 75 is not particularly limited.

The sacrificial layer 75 acts as a protective layer to prevent oxidation of the substrate layer 71 and/or the metal or semi-metal layer 72. The process of removing the sacrificial layer 75 can be performed without damaging or oxidizing the substrate layer 71 or the metal or semi-metal layer 72.

13, by removing the mechanical support layer 76 and the sacrificial layer 75, a diaphragm 40 formed of a metal or semi-metal layer 72 is formed on a substrate layer 71. The diaphragm 40 extends through a boundary portion of a frame 81 formed of a second material.

A modification of the process described above with reference to Figures 10 to 13 will now be described.

In one embodiment, the first material forming the substrate layer 71 is a low stress nitride such as polysilicon nitride. Low stress nitrides are resistant to wet etching. This means that during the wet etching step (i.e., when etching away a large portion of the second material 74), the substrate layer 71 does not require an additional sacrificial layer to protect it. Low stress nitrides are also suitable for forming a hard etch mask on the back side of the assembly, as shown in FIG. 11 .

However, in one embodiment, the substrate layer 71 comprises polysilicon. When the substrate layer 71 is formed of polysilicon, then the first material does not form a substrate layer. Instead, when the second material 74 is etched, the first material acts as a sacrificial layer to protect the polysilicon substrate layer. Therefore, the method may include a step of coating the first material with polysilicon (or other material that will form the substrate layer of the diaphragm 40) before the step of etching the second material 74. When the first material acts as a sacrificial layer to protect the substrate layer, the first material may include _SiO2 .

In the process described above, the third material is coated on the substrate layer 71 before the pores 73 are formed. However, this is not necessarily the case. Figures 14 to 16 show different stages of an alternative method in which the third material is coated on the substrate layer 71 after the pores 73 are formed.

In this alternative embodiment, the first material is coated on the second material 74, as shown in Figure 10. However, as shown in Figure 14, the back side of the first material is patterned to form a hard mask without depositing a metal or semi-metal layer 72 on the top side.

As shown in FIG15 , pores 73 are formed in substrate layer 71. This step is performed before providing metal or semi-metal layer 72. Therefore, pores 73 are not formed in metal or semi-metal layer 72 at the same time.

Then, a sacrificial layer 75 and a mechanical support layer 76 are coated around the substrate layer 71. This allows the second material to be etched away.

As shown in Figure 16, the mechanical support layer 76 and the sacrificial layer 75 can then be removed in the same manner as described above. As shown in Figure 16, this allows the substrate layer 71 to extend through the border portion of the frame 81 formed by the second material 74.

A third material may then be applied to form the metal or semi-metal layer 72 of the diaphragm 40 on the substrate layer 71. This produces the assembly shown in FIG.

Various methods of forming the pores 73 are described below.

Figures 17 to 20 schematically depict different stages of a process for forming the pores 73. Specifically, Figures 17 to 20 depict stages of a process of nanoimprint lithography.

As shown in FIG. 17 , in one embodiment, the process of forming the aperture 73 includes pressing a mold 77 onto a mask material 79 covering the substrate layer 71. The mold 77 is a substantially flat plate including indentations 78. The indentations 78 are arranged in a pattern corresponding to the desired aperture locations (i.e., the locations where the apertures 73 are intended to be located in the diaphragm 40). In one embodiment, the mold 77 is flexible. In one embodiment, the mold 77 is made of a material that is substantially transparent to UV radiation. This allows the mask material 79 to be irradiated by UV radiation when the mold 77 is applied to the mask material 79.

The type of the photomask material is not particularly limited. In one embodiment, the photomask material is a photoresist. Alternatively, the photomask material may be a sol-gel.

As shown in FIG. 18 , by pressing a mold 77 onto a mask material 79, an embossed pattern is formed in the mask material 79 corresponding to the locations of the apertures. The application of the mold 77 results in the mask material 79 having a contrasting thickness. Specifically, the mask material 79 has pillars 82 and recesses 83. The mold 77 is pressed into the mask material 79 and then cured by UV radiation to harden/cure the mask material 79. The mold 77 is then removed to expose the now cured (solid) and patterned layer.

As shown in FIG. 19 , in one embodiment, the process of forming the aperture 73 includes etching a mask material 79 to form a void corresponding to the aperture location. In one embodiment, reactive ion etching is used to etch the mask material 79. The reactive ion etching process is substantially homogenous. The etching process causes the recess 83 to be etched away, thereby exposing the underlying substrate layer 71 at the void corresponding to the aperture location. The pillar 82 is also etched away, but continues to cover the substrate layer 71, thereby acting as a mask.

As shown in FIG. 20 , in one embodiment, the process of forming the pores 73 includes etching the substrate layer 71 through the voids to form the pores 73. Pillars 82 of the mask material 79 protect some areas of the substrate layer 71 from being etched. Where the substrate layer 71 is exposed, it is etched away to form the pores 73. The pores 73 are formed at locations corresponding to the indentations 78 of the mold 77. The mold 77 can be designed to provide the desired pattern of pores 73 in the substrate layer 71 of the diaphragm 40.

The process of nanoimprint lithography makes it possible to finely adjust the periodicity of the pores 73 and the filling factor of the protective film. This can be achieved by properly designing the mold 77. The mold 77 can be reused. This helps to reduce manufacturing costs.

Figures 21 to 24 schematically depict different stages of an alternative process for forming pores 73. As shown in Figure 21, in one embodiment, the process for forming pores 73 includes depositing spheres 84 on substrate layer 71. Spheres 84 are deposited in a pattern corresponding to the desired pore locations. Specifically, the center of each sphere 84 is positioned at a location corresponding to the center of pore 73. The process shown in Figures 21 to 24 can be referred to as nanosphere lithography. Nanosphere lithography is an alternative to nanoimprint lithography. The nanosphere lithography shown in Figures 21 to 24 can replace the steps shown in Figures 12 and 15 above.

The material of the spheres 84 is not particularly limited. In one embodiment, the spheres are made of polystyrene. In one embodiment, the spheres 84 are arranged in a hexagonal tight packing layer. In one embodiment, the layer of spheres 84 is a single layer.

As shown in the transition from FIG. 21 to FIG. 22, in one embodiment, the process includes reducing the size of the sphere 84. For example, the size of the sphere 84 can be reduced by etching the sphere 84. For example, plasma etching can be used. The step of reducing the size of the sphere is optional. For example, if the sphere 84 coated on the substrate layer 71 already has a suitable size, it may not be necessary to reduce its size.

As shown in FIG. 22 , in one embodiment, the process of forming the pores 73 includes coating a third material on the spheres 84 and the substrate layer 71. The third material is used to form the metal or semi-metal layer 72 of the diaphragm 40. As shown in FIG. 22 , the third material covers the top of the spheres 84 and covers the portion of the substrate layer 71 between the spheres 84. The pattern of the pores 73 formed in the diaphragm 40 can be controlled by controlling the size and arrangement of the spheres 84 on the substrate layer 71.

As shown in FIG. 23 , in one embodiment, the process of forming the aperture 73 includes removing the sphere 84. This forms an exposed portion of the substrate layer 71 corresponding to the location of the aperture. This causes the third material to form a mask that protects the appropriate portion of the substrate layer 71. In addition to forming the metal or semi-metal layer 72, the third material acts as a mask.

24, in one embodiment, the process of forming the pore 73 includes etching the exposed portion of the substrate layer 71 to form the pore 73. As just one example, a plasma etching process may be used to etch the appropriate portion of the substrate layer 71.

The size of the spheres 84 can be selected so as to provide appropriately sized and configured pores 73. Generally, the size of the spheres 84 corresponds to the size of the pores 73. In one embodiment, the size of the spheres 84 is at least 100 nm and at most 10 μm.

FIG. 25 is an image of a metal layer in an alternative process for forming aperture 73. In an alternative process for forming aperture 73, metal is applied to substrate layer 71. For example, the metal may be silver or gold. Other metals suitable for metal assisted chemical etching processes may be used. In one embodiment, the metal is initially applied as a substantially uniform layer (i.e., having a uniform thickness) over the entire substrate layer 71.

In one embodiment, the process of forming the pores 73 includes annealing the metal to form metal islands 85 on the substrate layer 71. The metal islands 85 are visible in FIG. 25. The metal islands 85 are separated from each other. The annealing process causes the metal to be completely dehumidified. Specifically, the annealing process causes fractures in the metal layer. As the annealing process continues, the fractures connect together to form a network, as seen in FIG. 25, leaving individual metal islands 85. When the metal is annealed to a sufficiently high temperature, the metal particles move to a more energetically favorable configuration. This results in the formation of metal islands 85.

In one embodiment, the process of forming the pores 73 includes performing metal assisted chemical etching to etch a portion of the substrate layer 71 below the metal islands 85, thereby forming the pores 73. The metal islands 85 act as a catalyst to etch the substrate layer 71 below each metal island 85 (i.e., metal droplet).

FIG. 26 is an image of a metal or semi-metal layer 72 used in an alternative process for forming pores 73. In one embodiment, a third material forming the metal or semi-metal layer 72 is coated on a substrate layer 71. In one embodiment, the process for forming pores 73 includes annealing the third material to form voids in the metal or semi-metal layer 72. These voids are visible in the image of FIG. 26. The conditions (e.g., temperature, time) of the annealing process can be selected so that voids are formed as shown in FIG. 26, but the voids are not connected together to form a network of isolated metal islands as shown in FIG. 25. FIG. 26 shows the result of partial dewetting of the third material (rather than complete dewetting as shown in FIG. 25).

The resulting metal or semi-metal lattice shown in FIG26 can be used as an etching mask for etching the substrate layer 71. In one embodiment, the process of forming the pores 73 includes etching the substrate layer 71 through the voids to form the pores 73. The metal or semi-metal lattice can then remain as the metal or semi-metal layer 72, thereby increasing the emissivity of the diaphragm 40.

In one embodiment, annealing and etching steps may be performed instead of the steps shown in FIG. 12 . Alternatively, annealing and etching steps may be performed at the end of the method of making the pellicle. For example, the pellicle may be formed from a membrane having a continuous surface (i.e., without pores 73). Annealing and etching steps may then be performed to create pores 73. Thus, annealing and etching steps may be performed after the continuous membrane diaphragm is released.

27 is an image of a honeycomb structure 86 in an alternative process for forming the aperture 73. In one embodiment, the process for forming the aperture 73 includes providing the honeycomb structure 86 as an etching mask. For example, the honeycomb structure 86 can be positioned above the substrate layer 71.

In one embodiment, the honeycomb structure 86 comprises highly ordered and homogeneous nanopores. For example, in one embodiment, the honeycomb structure comprises porous anodic alumina.

In one embodiment, the process for forming the pores 73 includes etching the substrate layer 71 through the honeycomb structure 86 to form the pores 73. The honeycomb structure 86 is then removed.

For example, the process of providing the honeycomb structure and etching may be performed instead of the steps shown in FIGS. 12 and 15 .

In one embodiment, the honeycomb structure 86 is applied to the stack via an adhesive layer. Alternatively, the honeycomb structure 86 can be created during the manufacturing process.

According to one aspect of the present invention, a diaphragm for a protective film for EUV lithography is provided, which includes a grating, which includes a plurality of holes, pores or protrusions. The plurality of holes may, for example, include circular, square, circular blocks or holes of any shape. The diaphragm may, for example, include a main film or a main layer. The thickness of the main film or layer in the grating may, for example, be in the range of 20 nm to 100 nm. In one embodiment, the main film or main layer may also be referred to as a core or a diaphragm core. Preferably, the grating spacing is less than 200 nm to ensure good emissivity. The grating spacing can be defined as the distance between the centers of adjacent holes of the grating. In one embodiment, the main grating spacing is preferably less than 100 nm to ensure low spot at the wafer level. Smaller grating spacings, such as 30 nm or less, can prevent debris particles from falling on the multiplication mask. The diaphragm of the protective film for EUV lithography according to any embodiment may include a metal layer having a thickness between 4 and 15 nm, or a semi-metal with a thickness in the range of 20 to 80 nm. If the diaphragm is more open, the metal layer is preferably thicker. In one embodiment, the diaphragm grating has substantially square openings (i.e., holes) with a spacing of 30 to 200 nm, such as 100 nm, and the percentage of open area or the openness defined by the grating opening is 50% to 90%, such as 75% openness or open area. A radiative Ru layer with a thickness of approximately 8 nm has an emissivity of >0.35. The material of the overcoat diaphragm may include, for example, a SOI Si diaphragm core bonded with a metal layer. In another embodiment, a diaphragm grating comprising SOI Si has a substantially circular or square opening covering 50% to 90% of the diaphragm area, a grating pitch less than 100 nm, and a metal layer having a thickness in the range of 5 to 15 nm, which provides low spot and an emissivity of > 0.2 at the wafer level.

Although specific reference may be made herein to the use of lithography equipment in IC manufacturing, it should be understood that the lithography equipment described herein may have other applications, such as manufacturing integrated optical systems, guide and detection patterns for magnetic resonance memory, flat panel displays, LCDs, thin film heads, etc. The substrates mentioned herein may be processed before or after exposure in, for example, a coating and development system (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 disclosures herein may be applied to these and other substrate processing tools. In addition, a substrate may be processed more than once, for example, to produce a multi-layer IC, so that the term "substrate" used herein may also refer to a substrate that already contains multiple processed layers.

Although specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced in other ways than those described. For example, various photoresist layers may be replaced by non-photoresist layers that perform the same function. The above description is intended to be illustrative and not restrictive. Therefore, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims and clauses set forth below. 1. A pellicle for EUV lithography comprising: a frame; and a diaphragm supported by the frame, wherein the diaphragm comprises: a metal or semi-metal layer, wherein the diaphragm comprises pores having a density of at least 5/µm ^2. 2. A pellicle as in clause 1, wherein the density of the pores is at least 20/µm ² . 3. A protective film as in item 1, wherein the density of pores is at least 100/ ^µm2 . 4. A protective film as in any of the preceding items, wherein the diaphragm comprises: a substrate layer for supporting a metal or semi-metal layer. 5. A protective film as in any of item 4, wherein the substrate layer comprises silicon obtained from silicon or polycrystalline silicon on an insulator. 6. A protective film as in any of the preceding items, wherein the metal layer has a thickness of at least 4 nm. 7. A protective film as in any of the preceding items, wherein the metal layer has a thickness of at least 8 nm. 8. A protective film as in any of the preceding items, wherein the semi-metal layer has a thickness of at least 10 nm. 9. A protective film as in any of the preceding items, wherein the semi-metal layer forms at least 90% of the total thickness of the diaphragm. 10. A protective film as in any of the preceding clauses, wherein the semi-metal layer has a thickness of at least 20 nm. 11. A protective film as in any of the preceding clauses, wherein the pores form at least 50% of the total area of the membrane. 12. A protective film as in any of the preceding clauses, wherein the pores form at least 75% of the total area of the membrane. 13. A protective film as in any of the preceding clauses, wherein the metal is a transition metal from Group 3 to Group 10. 14. A protective film as in any of the preceding clauses, wherein the metal is a transition metal from Period 4 to Period 5. 15. A protective film as in any of the preceding clauses, wherein the metal is selected from the group consisting of: Zr, Y, Mo, Cr, Hf, Ir, Mn, Nb, Os, Pd, Pt, Re, Rh, Ru, Ta, Ti, V and W. 16. A protective film as in any of the preceding clauses, wherein the pores are circular or square. 17. A protective film as in any of the preceding clauses, satisfying , where E is the emissivity of incident EUV radiation and T is the proportion of incident EUV radiation transmitted through the diaphragm. 18. A pellicle as in any of the preceding clauses, having an emissivity of at least 0.2 for incident EUV radiation. 19. A pellicle as in any of the preceding clauses, configured to transmit at least 95% of incident EUV radiation. 20. A pellicle for EUV lithography comprising: a non-metal or semi-metal layer, wherein the diaphragm comprises pores at a density of at least 5/ ^µm2 . 21. A pellicle for EUV lithography comprising: a frame; and a diaphragm as in clause 20, supported by the frame. 22. A patterning device assembly for EUV lithography comprising a pellicle as in any of clauses 1 to 19 or 21. 23. A dynamic airlock assembly for EUV lithography, comprising a pellicle as claimed in any one of claims 1 to 19 or 21. 24. A method of manufacturing a pellicle for EUV lithography, comprising: coating a first material on a second material to form a frame of the pellicle; coating a third material to form a metal or semi-metal layer of a diaphragm of the pellicle on a substrate layer of the diaphragm; and forming pores in the substrate layer at a density of at least 5/ ^µm2 . 25. The method of clause 24, wherein the first material forms the substrate layer. 26. The method of clause 24 or 25, wherein the third material is coated on the substrate layer before the pores are formed. 27. The method of clause 24 or 25, wherein the third material is coated on the substrate layer after the pores are formed. 28. The method of any one of clauses 24 to 27, wherein forming the pores comprises: pressing a mold onto a mask material overlying the substrate layer to form an embossed pattern in the mask material corresponding to the location of the pores; etching the mask material to form voids corresponding to the location of the pores; and etching the substrate layer through the voids to form the pores. 29. The method of any one of clauses 24 to 27, wherein forming the pores comprises: depositing spheres on the substrate layer in a pattern corresponding to the location of the pores; coating a third material over the spheres and the substrate layer; removing the spheres to form exposed portions of the substrate layer corresponding to the location of the pores; and etching the exposed portions of the substrate layer to form the pores. 30. The method of any one of clauses 24 to 27, wherein forming the pores comprises: coating a metal on a substrate layer; annealing the metal to form metal islands on the substrate layer; and performing metal assisted chemical etching to etch a portion of the substrate layer below the metal islands to form the pores. 31. The method of any one of clauses 24 to 27, wherein forming the pores comprises: annealing a third material to form voids in the metal or semi-metal layer; and etching the substrate layer through the voids to form the pores. 32. The method of any one of clauses 24 to 27, wherein forming the pores comprises: providing a honeycomb structure as an etching mask; etching the substrate layer to form the pores; and removing the honeycomb structure. 33. The method of clause 32, wherein the honeycomb structure comprises porous anodic alumina. 34. A diaphragm for a pellicle for EUV lithography, the diaphragm comprising a grating comprising a plurality of holes. 35. The diaphragm of clause 34, wherein the grating has a grating pitch of <200 nm, preferably <100 nm, more preferably <30 nm. 36. The diaphragm of clause 34 or 35, wherein the grating comprises a core having a thickness between 20 nm and 100 nm. 37. The diaphragm of any of clauses 34 to 36, wherein the grating comprises a metal or a semi-metal. 38. The diaphragm of any of clauses 34 to 37, wherein the grating comprises a SOI Si diaphragm core. 39. The diaphragm of clause 38, wherein the grating further comprises one or more metal layers. 40. A diaphragm as claimed in clause 38 or 39, wherein the grating comprises substantially circular or square openings and an open area between 50% and 90%, preferably between 70% and 80%.

21: unpatterned beam 22: faceted field mirror device 24: faceted pupil mirror device 26: patterned beam 28: reflective element 30: reflective element 40: diaphragm 41: wire 42: wire 43: wire 44: wire 45: wire 50: fixture 60: stud 61: wire 62: wire 63: wire 71: substrate layer 72: metal or semi-metal layer 73: aperture 74: second material 75: sacrificial layer 76: mechanical support layer 77: mold 78: indentation 79: mask material 80: diaphragm assembly 81: frame 82: post 83: depression 84: sphere 85: metal island 86: honeycomb structure 91: line 92: line 93: line 100: lithography equipment 210: radiation emitting plasma 211: source chamber 212: collector chamber 220: enclosure structure 221: opening 500: controller B: radiation beam C: target part CO: radiation collector d: diameter E: emissivity IF: virtual source point IL: illumination system M1: mask alignment mark M2: mask alignment mark MA: patterning device MT: support structure p: spacing P1: substrate alignment mark P2: substrate alignment mark PM: first positioner PS: projection system PS1: position sensor PS2: Position sensor PW: Second positioner SO: Source collector module W: Substrate WT: Substrate stage

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

FIG. 1 depicts a lithography apparatus according to an embodiment of the present invention;

FIG2 is a more detailed view of the lithography equipment;

FIG3 schematically depicts a portion of a diaphragm assembly according to an embodiment of the present invention in cross section;

FIG. 4 is a graph showing the relationship between the angle of incident radiation and the emissivity for diaphragms having different fill factors;

FIG5 is a graph showing the relationship between the angle of incident radiation and the emissivity for membranes having different distances between pores;

FIG6 is a graph showing the relationship between the angle of incident radiation and the emissivity for diaphragms having different metal layers;

FIG. 7 is a cross-sectional view of a diaphragm of a protective film according to an embodiment of the present invention;

FIG8 is a plan view of a diaphragm having a protective film with circular pores according to an embodiment of the present invention;

FIG. 9 is a plan view of a diaphragm having a protective film with square pores according to an embodiment of the present invention;

10 to 13 schematically illustrate the stages of a method for manufacturing a protective membrane diaphragm according to an embodiment of the present invention;

14 to 16 schematically illustrate different stages of an alternative method for manufacturing a protective membrane diaphragm according to an embodiment of the present invention;

17 to 20 schematically illustrate different stages of forming pores in the diaphragm of the protective film according to an embodiment of the present invention;

21 to 24 schematically illustrate different stages of an alternative method for forming pores in a membrane of a protective film according to an embodiment of the present invention;

FIG. 25 is an image of metal islands used to form pores in a membrane of a protective film according to an embodiment of the present invention;

FIG. 26 is an image of a metal layer of a diaphragm of a protective film according to an embodiment of the present invention; and

FIG. 27 is an image of a honeycomb structure for forming pores in a membrane of a protective film according to an embodiment of the present invention.

40: Diaphragm

73: Porosity

d: Diameter

p: Spacing

Claims (17)

A membrane of a pellicle for EUV lithography includes a grating having a plurality of holes. A membrane as claimed in claim 1, wherein the grating has a grating pitch, the grating pitch is less than 200 nm, preferably less than 100 nm, and more preferably less than 30 nm. A membrane as claimed in claim 1 or 2, wherein the grating comprises a core having a thickness between 20 nm and 100 nm. A diaphragm as claimed in claim 1 or 2, wherein the grating comprises a metal or a semi-metal. A diaphragm as claimed in claim 1 or 2, wherein the grating comprises a SOI Si diaphragm core. A diaphragm as in claim 5, wherein the grating further comprises one or more metal layers. A diaphragm as claimed in claim 5, wherein the grating comprises a substantially circular or square opening and an opening area between 50% and 90%, preferably between 70% and 80%. A membrane as claimed in claim 1 or 2, wherein the pores form at least 75% of a total area of the membrane. A diaphragm as claimed in claim 1 or 2, having an emissivity of at least 0.2 for incident EUV radiation. The diaphragm of claim 1 or 2, configured to transmit at least 95% of incident EUV radiation. A patterning device assembly or a dynamic airlock assembly for EUV lithography, comprising a diaphragm as claimed in any one of claims 1 to 10. A method for manufacturing a pellicle for EUV lithography comprises: coating a first material on a second material to form a frame of the pellicle; coating a third material to form a metal or semi-metal layer of a diaphragm of the pellicle on a substrate layer of the diaphragm; and forming pores in the substrate layer at a density of at least 5/ ^µm2 . The method of claim 12, wherein the first material forms the substrate layer. A method as claimed in claim 12 or 13, wherein the third material is coated on the substrate layer before forming the pores. A method as claimed in claim 12 or 13, wherein the third material is coated on the substrate layer after forming the pores. A method as claimed in claim 12 or 13, wherein forming the pores comprises: Pressing a mold onto a mask material covering the substrate layer to form a pattern of imprints in the mask material corresponding to the pore locations; Etching the mask material to form gaps corresponding to the pore locations; and Etching the substrate layer through the gaps to form the pores. The method of claim 12 or 13, wherein forming the pores comprises: depositing spheres on the substrate layer in a pattern corresponding to the pore locations; coating the third material on the spheres and the substrate layer; removing the spheres to form exposed portions of the substrate layer corresponding to the pore locations; and etching the exposed portions of the substrate layer to form the pores.