Euv mask and method of forming the same

Abstract

The present disclosure relates to absorbing materials for extreme ultraviolet masks. An extreme ultraviolet mask includes a substrate, a reflective multilayer stack located over the substrate, a cap layer located over the reflective multilayer stack, a patterned absorbing layer located over a first portion of the cap layer, and a magnetic layer located over a second portion of the cap layer that surrounds the first portion.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to extreme ultraviolet masks and methods of forming the same. BACKGROUND

[0002] The semiconductor industry has experienced exponential growth. Technological advances in materials and design have produced generations of integrated circuits (ICs), with each generation having feature sizes smaller than the last. As the ICs develop, the functionality density, i.e., the number of interconnected devices per chip area, typically increases, while the geometry size, i.e., the smallest component or line that can be created using the manufacturing process, decreases. This shrinking process generally provides benefits through increased production efficiency and reduced associated costs. SUMMARY

[0003] A first aspect of the present disclosure relates to an extreme ultraviolet (EUV) mask comprising a pattern region and a border region, the EUV mask comprising: a substrate; a reflective multilayer stack located over the substrate; a cap layer located over the reflective multilayer stack; a patterned absorber layer located over a first portion of the cap layer; and a magnetic layer located over a second portion of the cap layer surrounding the first portion.

[0004] A second aspect of the present disclosure relates to a method of forming an extreme ultraviolet (EUV) mask, comprising: forming a reflective multilayer stack over a substrate; depositing a cap layer over the reflective multilayer stack; depositing an absorber layer over a first portion of the cap layer; depositing a magnetic layer over a second portion of the cap layer surrounding the first portion; and etching the absorber layer to form a plurality of openings in the absorber layer, the plurality of openings exposing a surface of the cap layer.

[0005] A third aspect of the present disclosure relates to a method of forming an extreme ultraviolet (EUV) mask, comprising: depositing a magnetic layer over a first side of a substrate; forming a reflective multilayer stack over a portion of the magnetic layer, wherein a peripheral portion of the magnetic layer is exposed; depositing a cap layer over the reflective multilayer stack; depositing an absorber layer over the cap layer; and etching the absorber layer to form a patterned absorber layer comprising a plurality of openings in the patterned absorber layer, the plurality of openings exposing a surface of the cap layer. BRIEF DESCRIPTION OF DRAWINGS

[0006] Various aspects of the disclosure can be best understood with reference to the following detailed description when read in conjunction with the accompanying drawings. It is noted that the various features are not drawn to scale. In fact, the dimensions of the various features can be arbitrarily increased or decreased for clarity of discussion.

[0007] Figure 1 is a schematic block diagram of an extreme ultraviolet (EUV) scanner in accordance with some embodiments.

[0008] Figure 2A is a cross-sectional view of a first exemplary EUV mask according to some embodiments.

[0009] Figure 2B is a cross-sectional view of a first exemplary EUV mask according to some alternative embodiments.

[0010] Figure 3 is a flowchart of a method for manufacturing the first exemplary EUV mask according to some embodiments.

[0011] Figures 4A-4M is a cross-sectional view of a first exemplary EUV mask according to some embodiments. Figure 3 various views of the first exemplary EUV mask at various stages of the manufacturing process of

[0012] Figure 5A is a cross-sectional view of a second exemplary EUV mask according to some embodiments.

[0013] Figure 5B is a cross-sectional view of a second exemplary EUV mask according to some alternative embodiments.

[0014] Figure 6 is a flowchart of a method for manufacturing the second exemplary EUV mask according to some embodiments.

[0015] Figures 7A-7M is a cross-sectional view of a second exemplary EUV mask according to some embodiments. Figure 6 various views of the second exemplary EUV mask at various stages of the manufacturing process of DETAILED DESCRIPTION

[0016] The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows can include embodiments in which the first and second features are formed in direct contact, and can also include embodiments in which additional features can be formed between the first and second features, such that the first and second features can not be in direct contact. In addition, the present disclosure can repeat reference numerals and / or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and / or configurations discussed.

[0017] Furthermore, spatially relative terms (for example, "beneath", "below", "lower", "above", "upper", and the like) can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientations depicted in the figures. The devices can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein are to be interpreted accordingly.

[0018] In the manufacture of integrated circuits (ICs), a series of reusable photomasks (also referred to as masks herein) are used to manufacture patterns representing different layers of the IC in order to transfer the design of each layer of the IC onto a semiconductor substrate during a semiconductor device manufacturing process. Thus, any defects in the masks can be transferred to the IC, which can severely impact device performance.

[0019] With the shrinking of IC size, extreme ultraviolet (EUV) light having a wavelength of 13.5 nm is employed in the photolithography process in order to be able to transfer very small patterns (e.g., nanometer-scale patterns) from the mask to the semiconductor wafer. Since most materials have high absorbance at the 13.5 nm wavelength, EUV lithography employs a reflective mask that selectively reflects and absorbs EUV radiation. A pattern formed in an absorption layer of the EUV mask is transferred to the semiconductor wafer by reflecting EUV light from some portions of the reflective surface of the EUV mask.

[0020] EUV lithography is implemented in an EUV scanner 100 as shown in Figure 1 In some embodiments, the EUV scanner 100 includes a light source 102, an illuminator 104, a mask stage 106, a projection optics module 108, and a substrate stage 110.

[0021] The light source 102 is configured to generate EUV light having a wavelength centered at about 13.5 nm.

[0022] The illuminator 104 includes reflective optics, such as a single mirror or a mirror system having multiple mirrors, to direct the light from the light source 102 onto the mask stage 106, specifically, onto an EUV mask 112 fixed on the mask stage 106.

[0023] The mask stage 106 is configured to fix the EUV mask 112. In some embodiments, the mask stage 106 includes an electrostatic chuck (e-chuck) to fix the EUV mask 112. The back surface of the EUV mask 112 is chucked by applying a bias potential of, for example, about 1 kV to the mask stage 106, with the front surface of the EUV mask 112 facing the upper surface of a semiconductor wafer 114 on the substrate stage 110.

[0024] The projection optics module 108 is configured to provide a patterned light beam and project the patterned light beam onto the semiconductor wafer 114 so as to image the pattern of the EUV mask 112 onto the semiconductor wafer 114 fixed on the substrate table 110. Light directed from the EUV mask 112, carrying an image of the pattern defined on the EUV mask 112, is collected by the projection optics module 108. In some embodiments, the illuminator 104 and the projection optics module 108 are collectively referred to as the optical module of the EUV scanner 100.

[0025] The EUV scanner 100 can also include (or be integrated with, or coupled with) other modules. For example, a gas supply module 116 is configured to provide hydrogen gas to the light source 102 to reduce contamination of the light source 12.

[0026] Due to the extremely short exposure wavelength of 13.5 nm, small perturbations in the surface of the EUV mask 112 can cause phase defects in the reflection, which can blur the pattern transferred onto the semiconductor wafer 114. Some phase defects are caused by magnetic particles such as iron (Fe) or nickel (Ni) from components of the EUV scanner 100 or the semiconductor wafer 114. During EUV lithography, these contaminant particles can adhere to the pattern area of the EUV mask 112, causing critical dimension errors during wafer exposure.

[0027] In embodiments of the present disclosure, a binary absorption material is used to prevent magnetic particles from landing on the pattern area of the EUV mask. In embodiments of the present disclosure, a patterned absorption layer composed of a non-magnetic material is provided in the pattern area of the EUV mask, and a magnetic layer composed of a magnetic material is used in the border area of the EUV mask. During the EUV lithography process, a bias potential used to electrically clamp the EUV mask to the mask table of the EUV scanner can generate a magnetic field. Under this magnetic field, the magnetic layer in the border area of the EUV mask attracts magnetic particles, thereby helping to deflect magnetic particles that would otherwise adhere to the pattern area of the EUV mask. By preventing magnetic particles from adhering to the pattern area of the EUV mask, patterned errors caused by contaminant particles on the pattern area of the EUV mask during EUV lithography can be avoided. Depending on the magnetic strength and etching characteristics of the magnetic material, the magnetic layer can be formed adjacent to the patterned absorption layer or directly on top of the substrate of the EUV mask.

[0028] Figure 2A is a cross-sectional view of a first exemplary EUV mask 200 according to some embodiments of the present disclosure. Figure 2B is a cross-sectional view of a first exemplary EUV mask 200 according to some alternative embodiments of the present disclosure. Reference is made to Figure 2A and Figure 2BEUV mask 200 includes a substrate 202, a reflective multilayer stack 210 located over a front surface of substrate 202, a cap layer 220 located over reflective multilayer stack 210, a patterned absorber layer 230P located over a portion of cap layer 220, and a magnetic layer 240 located over a peripheral portion of cap layer 220 and surrounding patterned absorber layer 230P. EUV mask 200 also includes a conductive layer 204 located over a back surface of substrate 202 opposite the front surface.

[0029] Patterned absorber layer 230P includes a pattern of openings 252 corresponding to a circuit pattern to be formed on a semiconductor wafer. The pattern of openings 252 is located in a pattern region 200A of EUV mask 200, exposing a surface of cap layer 220. Pattern region 200A is surrounded by a border region 200B of EUV mask 200. Border region 200B corresponds to a non-patterned region of EUV mask 200 that is not used during exposure during IC fabrication. In some embodiments, pattern region 200A of EUV mask 200 is located in a central region of substrate 202, and border region 200B is located in a peripheral portion of substrate 202. Pattern region 200A is separated from border region 200B by a trench 254. Trench 254 extends through patterned absorber layer 230P, cap layer 220, and reflective multilayer stack 210, exposing the front surface of substrate 202. In some embodiments, and as shown, a first portion of patterned absorber layer 230P is located in pattern region 200A of EUV mask 200, while a second portion of patterned absorber layer 230P and magnetic layer 240 are located in border region 200B of EUV mask 200. In some other embodiments, and as shown, the entire patterned absorber layer 230P is located in pattern region 200A of EUV mask 200, while magnetic layer 240 is located in border region 200B of EUV mask 200. Figure 2A Figure 2B

[0030] During EUV lithography, magnetic layer 240 in border region 200B of EUV mask 200 attracts and holds magnetic particles thereon. Thus, contaminant particles that can otherwise attach to pattern region 200A of EUV mask 200 in EUV scanner 100 Figure 1 are deflected away by magnetic layer 240. The introduction of magnetic layer 240 around patterned absorber layer 230P helps prevent contaminant particles from attaching to pattern region 200A of EUV mask 200 during EUV lithography, which in turn helps improve fidelity of lithographic transfer patterns and reduce patterning errors.

[0031] Figure 3 ​​is a flowchart of a method 300 for fabricating an EUV mask (e.g., EUV mask 200) according to some embodiments. Figures 4A to 4M are various views of the EUV mask 200 at various stages of the fabrication process according to some embodiments. The method 300 is discussed in detail below with reference to the EUV mask 200. In some embodiments, additional operations are performed before, during, and / or after the method 300, or some of the operations described are replaced and / or eliminated. In some embodiments, some of the features described below are replaced or eliminated. Those of ordinary skill in the art will appreciate that although some embodiments discuss operations being performed in a particular order, the operations can be performed in another logical order.

[0032] Referring to Figure 3 , the method 300 includes, according to some embodiments, an operation 302 in which a reflective multilayer stack 210 is formed over a substrate 202. Figure 4A is a top view of an initial structure of the EUV mask 200 after the reflective multilayer stack 210 is formed over the substrate 202 according to some embodiments. Figure 4A is a cross-sectional view of the initial structure of the EUV mask 200 along line B-B’. Figure 4A

[0033] Referring to Figure 4A and Figure 4A , the initial structure of the EUV mask 200 includes a substrate 202 made of glass, silicon, or other low thermal expansion material. The low thermal expansion material helps to minimize image distortion due to mask heating during use of the EUV mask 200. In some embodiments, the substrate 202 includes fused silica, fused quartz, calcium fluoride, silicon carbide, black diamond, or titanium oxide-doped silicon oxide (SiO2 / TiO2). In some embodiments, the substrate 202 has a thickness in a range of about 1 mm to about 7 mm. If the thickness of the substrate 202 is too small, the risk of the EUV mask 200 breaking or warping is increased in some instances. On the other hand, if the thickness of the substrate is too large, the weight of the EUV mask 200 is unnecessarily increased in some instances.

[0034] ​In some embodiments, the conductive layer 204 is disposed on a back surface of the substrate 202. In some embodiments, the conductive layer 204 is in direct contact with the back surface of the substrate 202. The conductive layer 204 provides a conductive plane to allow electrostatic clamping of the EUV mask 200 to a mask table during fabrication and use of the EUV mask 200. In some embodiments, the conductive layer 204 includes chromium nitride (CrN) or tantalum boride (TaB). In some embodiments, the conductive layer 204 is formed by a deposition process, such as chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), or physical vapor deposition (PVD). The thickness of the conductive layer 204 is controlled such that the conductive layer 204 is optically transparent.

[0035] The reflective multilayer stack 210 is disposed on a front surface of the substrate 202 opposite the back surface. In some embodiments, the reflective multilayer stack 210 is in direct contact with the front surface of the substrate 202. The reflective multilayer stack 210 provides high reflectivity for EUV light. In some embodiments, the reflective multilayer stack 210 is configured to achieve a reflectivity of about 60% to about 75% at a peak EUV illumination wavelength (e.g., EUV illumination at 13.5 nm).

[0036] In some embodiments, the reflective multilayer stack 210 includes an alternating stack of high and low refractive index materials. Materials with a high refractive index have a tendency to scatter EUV light, while on the other hand, materials with a low refractive index have a tendency to transmit EUV light. Pairing these two types of materials together provides a resonant reflectivity. In some embodiments, the reflective multilayer stack 210 includes an alternating stack of molybdenum (Mo) and silicon (Si). In some embodiments, the reflective multilayer stack 210 includes an alternating stack of Mo and Si, where Si is at the topmost layer. In some embodiments, the Mo layers are in direct contact with the front surface of the substrate 202. In other embodiments, the Si layers are in direct contact with the front surface of the substrate 202. Alternatively, the reflective multilayer stack 210 includes an alternating stack of Mo and beryllium (Be).

[0037] The thickness of each layer in the reflective multilayer stack 210 depends on the EUV wavelength and the angle of incidence of the EUV light. The thickness of the alternating layers in the reflective multilayer stack 210 is tuned to maximize constructive interference of the reflected EUV light at each interface and to minimize total absorption of the EUV light. In some embodiments, the reflective multilayer stack 210 includes 30 to 60 pairs of alternating Mo and Si layers. Each Mo / Si pair has a thickness ranging from about 2 nm to about 7 nm, with a total thickness ranging from about 100 nm to about 300 nm.

[0038] In some embodiments, each layer of the reflective multilayer stack 210 is deposited on the substrate 202 and the underlying layer using ion beam deposition or DC magnetron sputtering. The deposition method used helps ensure that the thickness uniformity of the reflective multilayer stack 210 is better than approximately 0.85 on the substrate 202. For example, to form the Mo / Si reflective multilayer stack 210, a Mo target is used as the sputtering target and argon (Ar) gas (at a pressure of 1.3 × 10⁻⁶) is used. -2 Pa up to 2.7 × 10 -2 Mo layers were deposited at a deposition rate of 0.03 to 0.30 nm / sec using a sputtering gas of 1.3 × 10⁻⁶ Pa as the sputtering gas (with an ion acceleration voltage of 300 V to 1500 V). Then, a Si target was used as the sputtering target and Ar gas (at a pressure of 1.3 × 10⁻⁶ Pa) was used. -2 Pa up to 2.7 × 10 -2 Si layers are deposited at a deposition rate of 0.03 to 0.30 nm / sec using Pa as the sputtering gas (where the ion acceleration voltage is 300 V to 1500 V). Mo / Si reflective multilayer stacks are deposited by stacking Si and Mo layers in 40 to 50 cycles (each cycle including the steps described above).

[0039] In operation 304 of method 300, according to some embodiments, a capping layer 220 is deposited on the reflective multilayer stack 210. Figure 4B This is according to some embodiments after the cap layer 220 is deposited on the reflective multilayer stack 210. Figure 4A and Figure 4A A top view of the structure. Figure 4B 'yes Figure 4B The cross-sectional view of the structure along line B-B'.

[0040] refer to Figure 4B and 4B A cap layer 220 is disposed on the uppermost surface of the reflective multilayer stack 210. The cap layer 220 helps protect the reflective multilayer stack 210 from oxidation and any chemical etchants that may be exposed to during subsequent mask manufacturing processes.

[0041] In some embodiments, the capping layer 220 comprises a material resistant to oxidation and corrosion and has low chemical reactivity with common atmospheric gas species such as oxygen, nitrogen, and water vapor. In some embodiments, the capping layer 220 comprises: a transition metal, such as zirconium (Zr) or ruthenium (Ru); a ruthenium compound, such as RuB or RuO; a ruthenium alloy, such as RuNb; or a ruthenium alloy compound, such as RuNbO.

[0042] In some embodiments, the cap layer 220 is formed using a deposition process (e.g., ion beam deposition, chemical vapor deposition (CVD), physical vapor deposition (PVD) (e.g., DC magnetron sputtering), or atomic layer deposition (ALD)). In an example where a Ru layer is formed as the cap layer 220 using ion beam deposition, the deposition can be performed by using a Ru target as a sputtering target in an Ar atmosphere.

[0043] At operation 306 of the method 300, according to some embodiments, a deposition of an absorption layer 230 is performed over a portion of the cap layer 220. Figure 4C is a cross-sectional view of a structure according to some embodiments after the deposition of the absorption layer 230 over the portion of the cap layer 220. Figure 4B and Figure 4B is a cross-sectional view of a structure according to some embodiments after the deposition of the absorption layer 230 over the portion of the cap layer 220. Figure 4C is a cross-sectional view of a structure according to some embodiments after the deposition of the absorption layer 230 over the portion of the cap layer 220. Figure 4C is a cross-sectional view of a structure according to some embodiments after the deposition of the absorption layer 230 over the portion of the cap layer 220.

[0044] Reference is made to Figure 4C and 4CThe absorption layer 230 is disposed on a central portion of the cap layer 220. The absorption layer 230 can be used to absorb radiation of EUV wavelengths that is projected onto the EUV mask 200. The absorption layer 230 includes a material that has a high absorption coefficient in EUV wavelengths. In some embodiments, the absorption layer 230 includes a material that has a high absorption coefficient at 13.5 nm wavelengths. In some embodiments, the absorption layer 230 includes chromium (Cr), chromium oxide (CrO), titanium nitride (TiN), tantalum nitride (TaN), tantalum (Ta), titanium (Ti), Mo, aluminum copper (AlCu), palladium (Pd), tantalum boron nitride (TaBN), tantalum boron oxide (TaBO), aluminum oxide (AI2O3), silver oxide (Ag2O), or a combination thereof. In some embodiments, the absorption layer 230 has a single layer structure. In some other embodiments, the absorption layer 230 has a multi-layer structure. In some embodiments, the absorption layer 230 is formed by a deposition process, e.g., CVD, PECVD, PVD, e.g., DC magnetron sputtering, ion beam deposition, or ALD. In some embodiments, the absorption layer 230 is deposited by sputtering an absorption material target in an argon atmosphere. During the deposition process, a shield plate is placed between the substrate 202 and the target to control the location and size of the absorption layer 230. In some embodiments, the shield plate is positioned to shadow the peripheral portion of the cap layer 220 so that sputtered atoms are only received by the unshadowed central portion of the cap layer 220. As a result, the absorption layer 230 is only formed on the central portion of the cap layer 220 but not on the peripheral portion of the cap layer 220. In some embodiments, the absorption layer 230 is formed to have a first strip extending in a first direction and a second strip extending in a second direction that crosses the first direction. In some embodiments, each of the first strip and the second strip has a length of 132 cm and a width of 104 cm or a length of 134 cm and a width of 106 cm, but other lengths and widths are also possible.

[0045] At operation 308 of the method 300, according to some embodiments, a magnetic layer 240 is deposited on portions of the cap layer 220 that are not occupied by the absorption layer 230. Figure 4D is a structure of the EUV mask 200 after the magnetic layer 240 is deposited on the portions of the cap layer 220 that are not occupied by the absorption layer 230, according to some embodiments. Figure 4C and Figure 4C is a top view of a structure of the EUV mask 200. Figure 4D is a top view of a structure of the EUV mask 200. Figure 4D is a cross-sectional view of a structure of the EUV mask 200 along line B-B’.

[0046] Reference is made to Figure 4D and Figure 4DThe magnetic layer 240 is disposed on the peripheral portion of the cap layer 220, laterally abutting the absorber layer 230. In some embodiments, the magnetic layer 240 includes a magnetic material having a sufficient magnetic strength to attract magnetic particles during EUV lithography. In some embodiments, the magnetic layer 240 includes iron (Fe), nickel (Ni), cobalt (Co), an alloy thereof, or a combination thereof, such as CoFe, FeNi, or CoFeNi. In some embodiments, the magnetic layer 240 is formed by a deposition process, such as CVD, PECVD, PVD, such as DC magnetron sputtering, ion beam deposition, or ALD. In some embodiments, the magnetic layer 240 is deposited by sputtering a target of the magnetic material in an argon atmosphere. A shadow mask is placed between the substrate 202 and the target during the deposition process to control the location and size of the magnetic layer 240. In some embodiments, the shadow mask is positioned to shield the central portion of the cap layer 220 (where the absorber layer 230 is located) so that sputtered atoms are only received by the unshielded peripheral portion of the cap layer 220. As a result, the magnetic layer 240 is only formed on the peripheral portion of the cap layer 220, but not on the central portion of the cap layer 220.

[0047] At operation 310 of the method 300, a hard mask layer 250 is deposited over the absorber layer 230 and the magnetic layer 240, according to some embodiments. Figure 4E is a structure after the hard mask layer 250 is deposited over the absorber layer 230 and the magnetic layer 240, according to some embodiments. Figure 4D and 4D is a top view of the structure of Figure 4E is a structure after the hard mask layer 250 is deposited over the absorber layer 230 and the magnetic layer 240, according to some embodiments. Figure 4E is a cross-sectional view of the structure of

[0048] Referring to Figure 4E and 4E The hard mask layer 250 is disposed directly over the absorber layer 230 and the magnetic layer 240, according to some embodiments. In some embodiments, the hard mask layer 160 includes a dielectric oxide (such as silicon dioxide) or a dielectric nitride (such as silicon nitride). In some embodiments, the hard mask layer 250 is formed using a deposition process (such as CVD, PECVD, or PVD).

[0049] At operation 312 of the method 300, a first photoresist layer 260 is applied over the hard mask layer 250, according to some embodiments. Figure 4F is a structure after the first photoresist layer 260 is applied over the hard mask layer 250, according to some embodiments. Figure 4E and Figure 4E is a cross-sectional view of the structure of

[0050] Referring to Figure 4FA first photoresist layer 260 is disposed directly on top of the hard mask layer 250. The first photoresist layer 260 includes a photosensitive material that can be patterned by radiation. In some embodiments, the first photoresist layer 260 includes a positive photoresist material, a negative photoresist material, or a hybrid photoresist material. In some embodiments, the first photoresist layer 260 is applied to the surface of the hard mask layer 250, for example, by spin coating.

[0051] At operation 314 of the method 300, the first photoresist layer 260 is lithographically patterned to form a patterned first photoresist layer 260P, according to some embodiments. Figure 4G is a cross-sectional view of the structure after the first photoresist layer 260 is lithographically patterned to form a patterned first photoresist layer 260P, according to some embodiments. Figure 4F is a cross-sectional view of the structure after the first photoresist layer 260 is lithographically patterned to form a patterned first photoresist layer 260P, according to some embodiments.

[0052] Referring to Figure 4G The first photoresist layer 260 is patterned by subjecting the first photoresist layer 260 to a pattern of radiation. Next, depending on whether a positive resist or a negative resist is used in the first photoresist layer 260 with the resist developer, the exposed or unexposed portions of the first photoresist layer 260 are removed, thereby forming the patterned first photoresist layer 260P (with a pattern of openings 262 formed therein). The openings 262 expose some portions of the hard mask layer 250. The openings 262 are located in the pattern region 200A and correspond to locations in the EUV mask 200 where the openings 252 are present Figure 2A and 2B ).

[0053] At operation 316 of the method 300, the hard mask layer 250 is etched using the patterned first photoresist layer 260P as an etch mask to form a patterned hard mask layer 250P, according to some embodiments. Figure 4H is a cross-sectional view of the structure after the hard mask layer 250 is etched to form a patterned hard mask layer 250P, according to some embodiments. Figure 4G is a cross-sectional view of the structure after the hard mask layer 250 is etched to form a patterned hard mask layer 250P, according to some embodiments.

[0054] Referring to Figure 4HSome portions of the hardmask layer 250 exposed by the openings 262 in the patterned first photoresist layer 260P are etched to form openings 264. The openings 264 extend through the hardmask layer 250, exposing some portions of the underlying absorber layer 230. In some embodiments, the hardmask layer 250 is etched using an anisotropic etch. In some embodiments, the anisotropic etch is a dry etch (e.g., reactive ion etching (RIE)), a wet etch, or a combination thereof. The etch is selective to the material providing the absorber layer 230 and removes the material providing the hardmask layer 250. The remaining portions of the hardmask layer 250 constitute a patterned hardmask layer 250P. If the patterned first photoresist layer 260P is not completely consumed during etching of the hardmask layer 250, the patterned first photoresist layer 260P is removed from the surface of the patterned hardmask layer 250P after etching of the hardmask layer 250, e.g., using a wet strip or plasma ashing.

[0055] At operation 318 of the method 300, the patterned hardmask layer 250P is used as an etch mask to etch the absorber layer 230 to form a patterned absorber layer 230P, according to some embodiments. Figure 4I is a cross-sectional view of a structure after etching the absorber layer 230 to form a patterned absorber layer 230P, according to some embodiments. Figure 4G is a cross-sectional view of a structure after etching the absorber layer 230 to form a patterned absorber layer 230P, according to some embodiments.

[0056] Reference is made to Figure 4I Some portions of the absorber layer 230 exposed by the openings 264 in the patterned hardmask layer 250P are etched to form openings 252. The openings 252 extend through the absorber layer 230, exposing some portions of the underlying cap layer 220. In some embodiments, the absorber layer 230 is etched using an anisotropic etch process. In some embodiments, the anisotropic etch is a dry etch (e.g., RIE), a wet etch, or a combination thereof, which is selective to the material providing the cap layer 220 and removes the material providing the absorber layer 230. For example, in some embodiments, the absorber layer 230 is dry etched with a chlorine-containing gas (e.g., Cl2or BCl3) or a fluorine-containing gas (e.g., NF3). Ar can be used as a carrier gas. In some embodiments, oxygen (O2) can also be included as a carrier gas. The etch rate and etch selectivity depend on the etchant gas, etchant flow rate, power, pressure, and substrate temperature. After etching, the patterned hardmask layer 250P is removed, e.g., by an oxygen plasma. The remaining portions of the absorber layer 230 constitute a patterned absorber layer 230P.

[0057] At operation 320 of the method 300, a patterned second photoresist layer 270P is formed over the patterned absorber layer 230P, the magnetic layer 240, and the cap layer 220, including a pattern of openings 272, according to some embodiments. Figure 4J andFigure 4K is a structure according to some embodiments Figure 4I is a cross-sectional view of a structure after a patterned second photoresist layer 270P (including openings 272) is formed over the patterned absorber layer 230P, the magnetic layer 240, and the cap layer 220.

[0058] Referring to Figure 4J and Figure 4K , the openings 272 in the patterned second photoresist layer 270P expose portions of the patterned absorber layer 230P at which the trenches 254 in the EUV mask 200 will be formed. In some embodiments, and as shown in Figure 4J , the opening locations are selected so that the openings 272 expose portions of the patterned absorber layer 230P at the periphery of the patterned absorber layer 230P. In some other embodiments, and as shown in Figure 4K , the opening locations are selected so that the openings 272 expose portions of both the patterned absorber layer 230P and the magnetic layer 240.

[0059] To form the patterned second photoresist layer 270P, a second photoresist layer (not shown) is applied over the exposed surfaces of the patterned absorber layer 230P, the magnetic layer 240, and the cap layer 220. The second photoresist layer fills the openings 252 in the patterned absorber layer 230P. In some embodiments, the second photoresist layer comprises a positive photoresist material, a negative photoresist material, or a hybrid photoresist material. In some embodiments, the second photoresist layer comprises the same material as the first photoresist layer 260 described above in Figure 4F . In some embodiments, the second photoresist layer comprises a different material than the first photoresist layer 260. In some embodiments, the second photoresist layer is formed, for example, by spin coating. Subsequently, the second photoresist layer is patterned by exposing the second photoresist layer to a pattern of radiation, and using a resist developer to remove either the exposed portions or the unexposed portions of the second photoresist layer depending on whether a positive resist or a negative resist is used. The remaining portions of the photoresist layer constitute the patterned second photoresist layer 270P.

[0060] At operation 322 of the method 300, the patterned second photoresist layer 270P is used as an etch mask to etch the patterned absorber layer 230P, the cap layer 220, and the reflective multilayer stack 210 to form the trenches 254, according to some embodiments. Figure 4L is a structure according to some embodiments Figure 4J is a cross-sectional view of a structure after the patterned absorber layer 230P, the cap layer 220, and the reflective multilayer stack 210 are etched to form the trenches 254. Figure 4M is a structure according to some embodiments Figure 4Kthe structure in cross-section after etching the patterned absorber layer 230P, the cap layer 220, and the reflective multilayer stack 210 to form the trench 254.

[0061] Referring Figure 4L and Figure 4M The trench 254 extends through the patterned absorber layer 230P, the cap layer 220, and the reflective multilayer stack 210 to expose the surface of the substrate 202. The trench 254 surrounds the pattern area 200A of the EUV mask 200, separating the pattern area 200A from the border area 200B.

[0062] In some embodiments, the patterned absorber layer 230P, the cap layer 220, and the reflective multilayer stack 210 are etched using a single anisotropic etching process. The anisotropic etching can be a dry etching (e.g., RIE), a wet etching, or a combination thereof, which is selective to the material providing the substrate 202 and removes the material of the respective patterned absorber layer 230P, cap layer 220, and reflective multilayer stack 210. In some embodiments, multiple different anisotropic etching processes are used to etch the patterned absorber layer 230P, the cap layer 220, and the reflective multilayer stack 210. Each anisotropic etching can be a dry etching (e.g., RIE), a wet etching, or a combination thereof. In some embodiments, the etching also removes portions of the magnetic layer 240 exposed by the openings 272, such that the trench 254 also extends through the magnetic layer 240.

[0063] If not completely consumed during etching the patterned absorber layer 230P, the cap layer 220, and the reflective multilayer stack 210, the patterned second photoresist layer 270P is removed from the surface of the magnetic layer 240, the patterned absorber layer 230P, and the cap layer 220 after etching, e.g., using a wet strip or plasma ashing, thereby providing the EUV mask 200 Figure 2A and Figure 2B ).

[0064] After removing the patterned second photoresist layer 270P, the EUV mask 200 is cleaned to remove any contaminants therein. In some embodiments, the EUV mask 200 is cleaned by immersing the EUV mask 200 in an ammonium hydroxide (NH4OH) solution. In some embodiments, the EUV mask 200 is cleaned by immersing the EUV mask 200 in a dilute hydrofluoric acid (HF) solution.

[0065] The EUV mask 200 is subsequently irradiated with, e.g., ultraviolet light having a wavelength of 193 nm, for inspection of any defects in the pattern area 200A. Foreign matter can be detected by diffuse reflection of the light. If contaminants are detected, the EUV mask 200 is further cleaned using an appropriate cleaning process.

[0066] Figure 5Ais a cross-sectional view of a second exemplary EUV mask 500 according to some embodiments of the present disclosure. Figure 5B is a cross-sectional view of a second exemplary EUV mask 500 according to some alternative embodiments of the present disclosure.

[0067] Referring to Figure 5A and Figure 5B , the EUV mask 500 includes a substrate 502, a magnetic layer 506 over a front surface of the substrate 502, and a mask material stack over a portion of the magnetic layer 506. The mask material stack includes, from bottom to top, a reflective multilayer stack 510, a cap layer 520, and a patterned absorber layer 530P. The EUV mask 500 also includes a conductive layer 504 over a back surface of the substrate 502 opposite the front surface.

[0068] The patterned absorber layer 530P includes a pattern of openings 552 corresponding to a circuit pattern to be formed on a semiconductor wafer. The pattern of openings 552 is located in a pattern region 500A of the EUV mask 500 that exposes a surface of the cap layer 520. The pattern region 500A is surrounded by a border region 500B of the EUV mask 500. The border region 500B corresponds to a non-patterned region of the EUV mask 500 that is not used in an exposure process during IC fabrication. In some embodiments, the pattern region 500A of the EUV mask 500 is located in a central region of the substrate 502, and the border region 500B is located in a peripheral portion of the substrate 502. The pattern region 500A is separated from the border region 500B by a trench 554. The trench 554 extends through the patterned absorber layer 530P, the cap layer 520, the reflective multilayer stack 510, and the magnetic layer 506, exposing the front surface of the substrate 202. In some embodiments, and as shown in FIG. 5A, the trench 554 divides the mask material stack (510, 520, 530P) into two portions. Thus, a first portion of the mask material stack (510, 520, 530P) is located in the pattern region 500A of the EUV mask 500, while a second portion of the mask material stack (510, 520, 530P) and a peripheral portion of the magnetic layer 506 not covered by the mask material stack (510, 520, 530P) are located in the border region 500B of the EUV mask 500. In some other embodiments, and as shown in FIG. 5B, the entire mask material stack (510, 520, 530P) is located in the pattern region 500A of the EUV mask 500, while a peripheral portion of the magnetic layer 506 not covered by the mask material stack (510, 520, 530P) is located in the border region 500B of the EUV mask 500. Figure 5A Figure 5B

[0069] ​​During EUV lithography, the exposed portions of the magnetic layer 506 in the border region 500B of the EUV mask 500 attract and hold contamination particles thereon. Thus, contamination particles that can otherwise attach to the pattern region 500A of the EUV mask 500 in the EUV scanner 100 Figure 1 ) can be deflected away by the exposed portions of the magnetic layer 506 that are not covered by the mask material stack (510, 520, 530P). The introduction of the magnetic layer 506 thus helps to prevent contamination particles from attaching to the pattern region 500A of the EUV mask 500, which in turn helps to improve the fidelity of the lithographically transferred pattern and reduce pattern errors.

[0070] Figure 6 is a flowchart of a method 600 for fabricating an EUV mask (e.g., the EUV mask 500) according to some embodiments. Figures 7A to 7M are various views of the EUV mask 500 at various stages of the fabrication process according to some embodiments. The method 600 is discussed in detail below with reference to the EUV mask 500. In some embodiments, additional operations are performed before, during, and / or after the method 600, or some of the described operations are replaced and / or eliminated. In some embodiments, some of the features described below are replaced or eliminated. Persons of ordinary skill in the art will understand that although some embodiments discuss operations being performed in a particular order, the operations can be performed in another logical order.

[0071] Referring to Figure 6 , the method 600 includes, according to some embodiments, an operation 602 in which a magnetic layer 506 is deposited over a substrate 502. Figure 7A is a top view of an initial structure of the EUV mask 500 after the magnetic layer 506 is deposited over the substrate 502 according to some embodiments. Figure 7A is a cross-sectional view of the structure of Figure 7A along the line B-B’.

[0072] Referring to Figure 7A and Figure 7A , the initial structure of the EUV mask 500 includes a substrate 502 made of a low thermal expansion material as described above with respect to the substrate 502 in Figure 4A and 4A , In some embodiments, the substrate 502 includes fused silica, fused quartz, calcium fluoride, silicon carbide, black diamond, or titanium oxide-doped silicon oxide (Si02 / Ti02).

[0073] In some embodiments, a conductive layer 504 is disposed on a back surface of the substrate 502. In some embodiments, the conductive layer 504 is in direct contact with the back surface of the substrate 502. The conductive layer 504 provides a conductive plane to allow the EUV mask 500 to be electrically grounded, for example.Figure 5A and Figure 5B ) is electrostatically clamped to the mask table during manufacturing and use of the EUV mask 500. In some embodiments, the conductive layer 504 comprises CrN or TaB. In some embodiments, the conductive layer 504 is formed by a deposition process, such as CVD, PECVD, or PVD. The thickness of the conductive layer 504 is controlled such that the conductive layer 504 is optically transparent.

[0074] The magnetic layer 506 is disposed in direct contact with a front surface of the substrate 502 opposite the back surface. In some embodiments, the magnetic layer 506 comprises a magnetic material having sufficient magnetic strength to attract magnetic particles during EUV lithography. In some embodiments, the magnetic layer 506 comprises Fe, Ni, Co, or alloys thereof, such as CoFe, FeNi, or CoFeNi. In some embodiments, the magnetic layer 506 is formed by a deposition process, such as CVD, PECVD, PVD, such as DC magnetron sputtering, ion beam deposition, or ALD.

[0075] At operation 604 of the method 600, a reflective multilayer stack 510 is formed over a portion of the magnetic layer 506, according to some embodiments. Figure 7B is a top view of a structure according to some embodiments Figure 7A and Figure 7A ’ is a top view of a structure after the reflective multilayer stack 510 is formed over the portion of the magnetic layer 506. Figure 7B ’ is Figure 7B is a cross-sectional view of the structure of

[0076] Referring to Figure 7B and Figure 7B ’ the reflective multilayer stack 510 is disposed over a central portion of the magnetic layer 506. The reflective multilayer stack 510 provides high reflectivity to EUV light. In some embodiments, the reflective multilayer stack 510 is configured to achieve a reflectivity of about 60% to about 75% at a peak EUV illumination wavelength (e.g., EUV illumination at 13.5 nm).

[0077] In some embodiments, the reflective multilayer stack 510 includes an alternating stack of high and low refractive index materials. Materials with a high refractive index have a tendency to scatter EUV light, while on the other hand, materials with a low refractive index have a tendency to transmit EUV light. Pairing these two types of materials together provides a resonant reflectivity. In some embodiments, the reflective multilayer stack 510 includes an alternating stack of Mo and Si. In some embodiments, the reflective multilayer stack 510 includes an alternating stack of Mo and Si, where Si is at the topmost layer. In some embodiments, the Mo layers are in direct contact with the magnetic layer 506. In other embodiments, the Si layers are in direct contact with the magnetic layer 506. Alternatively, the reflective multilayer stack 210 includes an alternating stack of Mo and Be.

[0078] The thickness of each layer in the reflective multilayer stack 510 depends on the EUV wavelength and the angle of incidence of the EUV light. The thickness of the alternating layers in the reflective multilayer stack 510 is tuned to maximize constructive interference of the reflected EUV light at each interface and to minimize total absorption of the EUV light. In some embodiments, the reflective multilayer stack 510 includes 30 to 60 pairs of alternating Mo and Si layers. Each Mo / Si pair has a thickness ranging from about 2 nm to about 7 nm, with a total thickness ranging from about 100 nm to about 300 nm.

[0079] In some embodiments, each layer in the reflective multilayer stack 510 is deposited on the magnetic layer 506 and the underlying layers using ion beam deposition or DC magnetron sputter deposition. The deposition method used helps ensure that the thickness uniformity of the reflective multilayer stack 510 is better than about 0.85 on the substrate 202. For example, to form a Mo / Si reflective multilayer stack 510, Mo layers are deposited using a Mo target, followed by Si layers deposited using a Si target. The Mo / Si reflective multilayer stack is deposited by stacking Si layers and Mo layers in 40 to 50 cycles, each cycle including the above steps.

[0080] During the deposition process, a shadow mask is positioned to shield the peripheral portions of the magnetic layer 506 so that sputtered atoms are received only by the unshielded central portion of the magnetic layer 506. As a result, the reflective multilayer stack 510 is formed only on the central portion of the magnetic layer 506, but not on the peripheral portions of the magnetic layer 506. In some embodiments, the magnetic layer 506 can have a square cross-sectional shape; each side has a length of about 148 cm or 152 cm. In some embodiments, the reflective multilayer stack 510 can also have a square cross-sectional shape; each side has a length of about 138 cm.

[0081] At operation 606 of the method 600, a cap layer 520 is deposited on the reflective multilayer stack 510, according to some embodiments. Figure 7C is a method of fabricating a reflective multilayer stack 510 according to some embodiments Figure 7B and 7BFIG. 6B is a top view of the structure of FIG. 6A after deposition of a cap layer 520 over the reflective multilayer stack 510. Figure 7C FIG. 6C is a cross-sectional view of the structure of FIG. 6A along line B-B’. Figure 7C FIG. 6D is a top view of the structure of FIG. 6C after deposition of a cap layer 520 over the reflective multilayer stack 510.

[0082] Referring to FIG. 6A, a cap layer 520 is disposed over the uppermost surface of the reflective multilayer stack 510. The cap layer 520 helps protect the reflective multilayer stack 510 from oxidation and any chemical etchants to which the reflective multilayer stack 510 can be exposed in subsequent mask fabrication processes. Figure 7C 7C In some embodiments, the cap layer 520 includes a material that is resistant to oxidation and corrosion, and has low chemical reactivity with common atmospheric gas species such as oxygen, nitrogen, and water vapor. In some embodiments, the cap layer 520 includes Zr, Ru, RuB, RuO, RuNb, or RuNbO.

[0083] In some embodiments, the cap layer 520 is formed using a deposition process (e.g., ion beam deposition, CVD, PVD, or ALD). In an example where a Ru layer is formed as the cap layer 520 using ion beam deposition, the deposition can be performed by using a Ru target as a sputtering target in an Ar atmosphere. In the deposition process, a shadow mask is positioned to shadow the peripheral portions of the magnetic layer 506, such that sputtered atoms are received only by the unshadowed portions of the reflective multilayer stack 510. As a result, the cap layer 520 is formed only on the reflective multilayer stack 510, but not on the peripheral portions of the magnetic layer 506.

[0084] At operation 608 of the method 600, an absorbing layer 530 is deposited over the cap layer 520, according to some embodiments. FIG. 7B is a top view of the structure of FIG. 7A after deposition of an absorbing layer 530 over the cap layer 520.

[0085] FIG. 7C is a cross-sectional view of the structure of FIG. 7A along line B-B’. Figure 7D FIG. 7D is a top view of the structure of FIG. 7C after deposition of an absorbing layer 530 over the cap layer 520. Figure 7C FIG. 7E is a cross-sectional view of the structure of FIG. 7C along line B-B’. 7C FIG. 7F is a top view of the structure of FIG. 7E after deposition of an absorbing layer 530 over the cap layer 520. Figure 7D FIG. 7G is a cross-sectional view of the structure of FIG. 7E along line B-B’. Figure 7D FIG. 7H is a top view of the structure of FIG. 7G after deposition of an absorbing layer 530 over the cap layer 520.

[0086] Referring to FIG. 7A, an absorbing layer 530 is disposed over the cap layer 520. The absorbing layer 530 can be formed using a deposition process (e.g., ion beam deposition, CVD, PVD, or ALD). In an example where the absorbing layer 530 is formed using ion beam deposition, the deposition can be performed by using a target of the absorbing material as a sputtering target in an Ar atmosphere. In the deposition process, a shadow mask is positioned to shadow the peripheral portions of the cap layer 520, such that sputtered atoms are received only by the unshadowed portions of the cap layer 520. As a result, the absorbing layer 530 is formed only on the cap layer 520, but not on the peripheral portions of the cap layer 520. Figure 7D 7D ​The absorption layer 530 can be used to absorb radiation of EUV wavelengths projected onto the EUV mask 500. The absorption layer 530 comprises a material having a high absorption coefficient in EUV wavelengths. In some embodiments, the absorption layer 530 comprises a material having a high absorption coefficient at 13.5 nm wavelengths. In some embodiments, the absorption layer 530 comprises Cr, CrO, TiN, TaN, Ta, Ti, Mo, Pd, TaBN, TaBO, AI2O3, Ag2O, or an alloy such as AlCu or TaPd. In some embodiments, the absorption layer 530 has a single layer structure. In some other embodiments, the absorption layer 530 has a multi-layer structure. In some embodiments, the absorption layer 530 is formed by a deposition process, e.g., CVD, PECVD, PVD, e.g., DC magnetron sputtering, ion beam deposition, or ALD. In some embodiments, the absorption layer 530 is deposited by sputtering an absorption material target in an argon atmosphere. During the deposition process, a shield plate is placed between the substrate 502 and the target to shield the peripheral portion of the magnetic layer 506 so that sputtered atoms are only received by the unshielded portion of the cap layer 520. Thus, the absorption layer 530 is only formed on the cap layer 520, but not on the peripheral portion of the magnetic layer 506.

[0087] At operation 610 of the method 600, a hard mask layer 540 is deposited over the absorption layer 530, according to some embodiments. Figure 7E is a structure of Figure 7D and 7D is a top view of a structure after the hard mask layer 540 is deposited over the absorption layer 530, according to some embodiments. Figure 7E is a cross-sectional view of a structure of Figure 7E along line B-B’.

[0088] Referring to Figure 7E and 7E , the hard mask layer 540 is disposed directly over the absorption layer 530. In some embodiments, the hard mask layer 540 comprises a dielectric oxide (e.g., silicon dioxide) or a dielectric nitride (e.g., silicon nitride). In some embodiments, the hard mask layer 540 is formed using a deposition process, e.g., CVD, PECVD, PVD, e.g., DC magnetron sputtering, ion beam deposition, or ALD. In some embodiments, the hard mask layer 540 is deposited by sputtering a hard mask dielectric material target in an argon atmosphere. During the deposition process, a shield plate is placed between the substrate 502 and the target to shield the peripheral portion of the magnetic layer 506 so that sputtered atoms are only received by the unshielded portion of the absorption layer 530. Thus, the hard mask layer 540 is only formed on the absorption layer 530, but not on the peripheral portion of the magnetic layer 506.

[0089] At operation 612 of the method 600, a first photoresist layer 550 is applied over the hard mask layer 540 and the magnetic layer 506, according to some embodiments.Figure 7F is a cross-sectional view of the structure of 7E and 7E’ after a first photoresist layer 550 is applied over the hardmask layer 540, according to some embodiments.

[0090] Referring to Figure 7F , the first photoresist layer 550 is disposed to the peripheral portion of the magnetic layer 506, the reflective multilayer stack 510, the cap layer 520, the absorber layer 530, and the exposed surface of the hardmask layer 540. The first photoresist layer 550 includes a photosensitive material that is patternable by radiation. In some embodiments, the first photoresist layer 550 includes a positive photoresist material, a negative photoresist material, or a hybrid photoresist material. In some embodiments, the first photoresist layer 550 is applied, for example, by spin coating.

[0091] At operation 614 of the method 600, the first photoresist layer 550 is lithographically patterned to form a patterned first photoresist layer 550P, according to some embodiments. Figure 7G is a cross-sectional view of the structure of 7E and 7E’ after the first photoresist layer 550 is lithographically patterned to form the patterned first photoresist layer 550P, according to some embodiments. Figure 7F

[0092] Referring to Figure 7G , the first photoresist layer 550 is patterned by subjecting the first photoresist layer 550 to a pattern of radiation. Next, depending on whether a positive resist or a negative resist is used in the first photoresist layer 550 with the resist developer, either the exposed portions or the unexposed portions of the first photoresist layer 550 are removed, thereby forming the patterned first photoresist layer 550P (with a pattern of openings 562 formed therein). The openings 562 expose some portions of the hardmask layer 540. The openings 562 are located in the pattern region 200A and correspond to locations where the openings 552 are present in the EUV mask 500 (and the hardmask layer 540). Figure 5A and 5B ).

[0093] At operation 616 of the method 600, the hardmask layer 540 is etched using the patterned first photoresist layer 550P as an etch mask to form a patterned hardmask layer 540P, according to some embodiments. Figure 7H is a cross-sectional view of the structure of 7E and 7E’ after the hardmask layer 540 is etched to form the patterned hardmask layer 540P, according to some embodiments. Figure 7G

[0094] Referring to Figure 7H ​​The portions of the hardmask layer 540 exposed by the openings 562 in the patterned first photoresist layer 550P are etched to form openings 564. The openings 564 extend through the hardmask layer 540, exposing some portions of the underlying absorber layer 530. In some embodiments, an anisotropic etch is used to etch the hardmask layer. In some embodiments, the anisotropic etch is a dry etch (e.g., RIE), a wet etch, or a combination thereof. It is selective to the material providing the absorber layer 530, and etches away the material providing the hardmask layer 540. The remaining portions of the hardmask layer 540 constitute a patterned hardmask layer 540P. If the etch of the hardmask layer 540 does not completely consume, after etching the hardmask layer 540, the patterned first photoresist layer 550P is removed from the structure, e.g., using a wet strip or plasma ashing.

[0095] At operation 618 of the method 600, according to some embodiments, the absorber layer 530 is etched using the patterned hardmask layer 540P as an etch mask to form a patterned absorber layer 530P. Figure 7I is a cross-sectional view of a structure according to some embodiments Figure 7H is a cross-sectional view of a structure after etching the absorber layer 530 to form the patterned absorber layer 530P.

[0096] Referring to Figure 7I The portions of the absorber layer 530 exposed by the openings 564 in the patterned hardmask layer 540P are etched to form openings 552. The openings 552 extend through the absorber layer 530, exposing some portions of the underlying cap layer 520. In some embodiments, an anisotropic etch process is used to etch the absorber layer 530. In some embodiments, the anisotropic etch is a dry etch (e.g., RIE), a wet etch, or a combination thereof, which is selective to the material providing the cap layer 520, and etches away the material providing the absorber layer 530. For example, in some embodiments, the absorber layer 530 is dry etched with a chlorine-containing gas (e.g., Cl2or BCl3) or a fluorine-containing gas (e.g., NF3). Ar can be used as a carrier gas. In some embodiments, oxygen can also be included as a carrier gas. The etch rate and etch selectivity depend on the etchant gas, etchant flow rate, power, pressure, and substrate temperature. After etching, the patterned hardmask layer 540P is removed, e.g., by an oxygen plasma. The remaining portions of the absorber layer 530 constitute a patterned absorber layer 530P.

[0097] At operation 620 of the method 600, according to some embodiments, a patterned second photoresist layer 570P is formed over the peripheral portions of the magnetic layer 506, the reflective multilayer stack 510, the cap layer 520, and the exposed surfaces of the patterned absorber layer 530P (including the pattern of openings 572). Figure 7J and Figure 7K is a cross-sectional view of a structure according to some embodiments Figure 7Ithe structure of FIG. 5B after forming a patterned second photoresist layer 570P (including openings 572) over the peripheral portions of the magnetic layer 506, the reflective multilayer stack 510, the cap layer 520, and the exposed surface of the patterned absorber layer 530P.

[0098] Referring to Figure 7J and Figure 7K , the openings 572 in the patterned second photoresist layer 570P expose portions of the patterned absorber layer 530P at which the trenches 554 in the EUV mask 500 will be formed. Figure 5A and Figure 5B In some embodiments, and as shown in Figure 7J , the opening locations are selected so that the openings 572 expose portions of the patterned absorber layer 530P at the periphery of the patterned absorber layer 530P. In some other embodiments, and as shown in Figure 7K , the opening locations are selected so that the openings 572 expose portions of both the patterned absorber layer 530P and the peripheral portions of the magnetic layer 506.

[0099] To form the patterned second photoresist layer 570P, a second photoresist layer (not shown) is applied over the patterned absorber layer 530P, the cap layer 520, and the peripheral portions of the magnetic layer 506. The second photoresist layer fills the openings 552 in the patterned absorber layer 530P. In some embodiments, the second photoresist layer comprises a positive photoresist material, a negative photoresist material, or a hybrid photoresist material. In some embodiments, the second photoresist layer comprises the same material as the first photoresist layer 550 described above in Figure 7F . In some embodiments, the second photoresist layer comprises a different material than the first photoresist layer 550. In some embodiments, the second photoresist layer is formed, for example, by spin coating. Subsequently, the second photoresist layer is patterned by exposing the second photoresist layer to a pattern of radiation, and using a resist developer to remove either the exposed portions or the unexposed portions of the second photoresist layer depending on whether a positive resist or a negative resist is used. The remaining portions of the photoresist layer constitute the patterned second photoresist layer 570P.

[0100] At operation 622 of the method 600, the patterned second photoresist layer 570P is used as an etch mask to etch the patterned absorber layer 530P, the cap layer 520, the reflective multilayer stack 510, and the magnetic layer 506 to form the trenches 554, according to some embodiments. Figure 7L is a cross-sectional view of the structure of FIG. 5B after etching the patterned absorber layer 530P, the cap layer 520, the reflective multilayer stack 510, and the magnetic layer 506 to form the trenches 254. Figure 7J is a cross-sectional view of the structure of FIG. 5B after forming a patterned second photoresist layer 570P (including openings 572) over the peripheral portions of the magnetic layer 506, the reflective multilayer stack 510, the cap layer 520, and the exposed surface of the patterned absorber layer 530P.Figure 7M is in accordance with some embodiments Figure 7K A cross-sectional view of the structure after etching the patterned absorber layer 530P, the cap layer 520, the reflective multilayer stack 510, and the magnetic layer 506 to form the trench 254.

[0101] Referring to Figure 7L and Figure 7M , the trench 554 extends through the patterned absorber layer 530P, the cap layer 520, the reflective multilayer stack 510, and the magnetic layer 506 to expose the surface of the substrate 502. The trench 554 surrounds the patterned region 500A of the EUV mask 500, separating the patterned region 500A from the border region 500B.

[0102] In some embodiments, the patterned absorber layer 530P, the cap layer 520, the reflective multilayer stack 510, and the magnetic layer 506 are etched using a single anisotropic etching process. The anisotropic etching can be a dry etching (e.g., RIE), a wet etching, or a combination thereof, which provides selectivity to the material of the substrate 502 and removes the material of the respective patterned absorber layer 530P, cap layer 520, reflective multilayer stack 510, and magnetic layer 506. In some embodiments, the patterned absorber layer 530P, the cap layer 520, the reflective multilayer stack 510, and the magnetic layer 506 are etched using a plurality of different anisotropic etching processes. Each anisotropic etching can be a dry etching (e.g., RIE), a wet etching, or a combination thereof.

[0103] If not completely consumed during etching the patterned absorber layer 530P, the cap layer 520, the reflective multilayer stack 510, and the magnetic layer 506, the patterned second photoresist layer 570P is removed from the surface of the patterned absorber layer 530P, the cap layer 220, and the magnetic layer 506 after etching, for example, using a wet strip or plasma ashing, thereby providing the EUV mask 500 Figure 5A and 5B ).

[0104] After removing the patterned second photoresist layer 570P, the EUV mask 500 is cleaned to remove any contaminants therein. In some embodiments, the EUV mask 500 is cleaned by immersing the EUV mask 500 in a solution of NH4OH. In some embodiments, the EUV mask 500 is cleaned by immersing the EUV mask 500 in a dilute HF solution.

[0105] The EUV mask 500 is subsequently irradiated with, for example, ultraviolet light having a wavelength of 193 nm, for inspection of any defects in the patterned region 500A. The foreign matter can be detected by diffuse reflection of the light. If contaminants are detected, the EUV mask 500 is further cleaned using an appropriate cleaning process.

[0106] One aspect of the description relates to an EUV mask including a pattern region and a border region. The EUV mask includes: a substrate; a reflective multilayer stack over the substrate; a cap layer over the reflective multilayer stack; a patterned absorber layer over a first portion of the cap layer; and a magnetic layer over a second portion of the cap layer surrounding the first portion.

[0107] Another aspect of the description relates to a method of forming an EUV mask. The method includes: forming a reflective multilayer stack over a substrate; depositing a cap layer over the reflective multilayer stack; depositing an absorber layer over a first portion of the cap layer; depositing a magnetic layer over a second portion of the cap layer surrounding the first portion; and etching the absorber layer to form a plurality of openings therein. The plurality of openings exposes a surface of the cap layer.

[0108] Yet another aspect of the description relates to a method of forming an EUV mask. The method includes: depositing a magnetic layer over a first side of a substrate; forming a reflective multilayer stack over a portion of the magnetic layer, wherein a peripheral portion of the magnetic layer is exposed; depositing a cap layer over the reflective multilayer stack; depositing an absorber layer over the cap layer; and etching the absorber layer to form a patterned absorber layer including a plurality of openings therein, the plurality of openings exposing a surface of the cap layer.

[0109] The foregoing overview has outlined rather broadly the features of several embodiments in order that the detailed description that follows can be better understood with reference to the drawing. It should be appreciated that the conception and specific embodiments disclosed can be readily utilized as a basis for the designing or modifying other processes and structures for carrying out the same purposes and / or for achieving the same advantages of the embodiments presented herein. It should also be realized that these equivalents have graphical and structural equivalents that do not depart from the spirit and scope of the disclosure. It is therefore intended that this disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the present disclosure, but that the present disclosure includes all embodiments falling within the scope of the appended claims.

[0110] Example 1. An extreme ultraviolet (EUV) mask including a pattern region and a border region, the EUV mask comprising:

[0111] a substrate;

[0112] a reflective multilayer stack over the substrate;

[0113] a cap layer over the reflective multilayer stack;

[0114] a patterned absorber layer over a first portion of the cap layer; and

[0115] a magnetic layer over a second portion of the cap layer surrounding the first portion.

[0116] Example 2. The EUV mask of example 1, wherein the magnetic layer comprises iron, nickel, cobalt, a combination of the foregoing, or an alloy of the foregoing.

[0117] Example 3. The EUV mask of example 1, wherein the patterned absorber layer comprises a non-magnetic material.

[0118] Example 4. The EUV mask of example 1, wherein the patterned absorber layer comprises chromium (Cr), chromium oxide (CrO), titanium nitride (TiN), tantalum nitride (TaN), tantalum (Ta), titanium (Ti), molybdenum, aluminum copper (AlCu), palladium (Pd), tantalum boron nitride (TaBN), aluminum oxide (AI2O3), or silver oxide (Ag2O).

[0119] Example 5. The EUV mask of example 1, wherein the magnetic layer is located in a border region of the EUV mask.

[0120] Example 6. The EUV mask of example 1, wherein the entire patterned absorber layer is located in a pattern region of the EUV mask.

[0121] Example 7. The EUV mask of example 1, wherein a first portion of the patterned absorber layer is located in a pattern region of the EUV mask, a second portion of the patterned absorber layer is located in a border region of the EUV mask, wherein the first portion of the patterned absorber layer comprises an open pattern.

[0122] Example 8. The EUV mask of example 7, wherein the magnetic layer laterally contacts a sidewall of the second portion of the patterned absorber layer.

[0123] Example 9. A method of forming an extreme ultraviolet (EUV) mask, comprising:

[0124] forming a reflective multilayer stack over a substrate;

[0125] depositing a cap layer over the reflective multilayer stack;

[0126] depositing an absorber layer over a first portion of the cap layer;

[0127] depositing a magnetic layer over a second portion of the cap layer surrounding the first portion; and

[0128] etching the absorber layer to form a plurality of openings in the absorber layer, the plurality of openings exposing a surface of the cap layer.

[0129] Example 10. The method of example 9, wherein depositing the absorber layer comprises:

[0130] positioning a shield between the substrate and a second target comprising a magnetic material, wherein the shield shields the first portion and the second portion of the cap layer is unshielded; and

[0131] sputtering the second target in an argon atmosphere to deposit the magnetic layer over the second portion of the cap layer.

[0132] Example 11. The method of example 9, wherein depositing the magnetic layer comprises:

[0133] positioning a shield between the substrate and a second target comprising a magnetic material, wherein the shield shields the first portion and the second portion of the cap layer is unshielded; and

[0134] sputtering the second target in an argon atmosphere to deposit the magnetic layer over the second portion of the cap layer.

[0135] Example 12. The method of example 9, wherein the magnetic layer comprises iron, nickel, cobalt, a combination of the foregoing, or an alloy of the foregoing.

[0136] Example 13. The method of example 9, further comprising depositing a hard mask layer over the absorber layer and the magnetic layer.

[0137] Example 14. The method of example 13, wherein etching the absorber layer comprises:

[0138] depositing a photoresist layer over the hard mask layer;

[0139] patterning the photoresist layer to form a patterned photoresist layer comprising openings;

[0140] etching the hard mask layer using the patterned photoresist layer as an etch mask to form a patterned hard mask layer; and

[0141] etching the absorber layer using the patterned hard mask layer as an etch mask to form the plurality of openings in the absorber layer.

[0142] Example 15. A method of forming an extreme ultraviolet (EUV) mask, comprising:

[0143] depositing a magnetic layer over a first side of a substrate;

[0144] forming a reflective multilayer stack over a portion of the magnetic layer, wherein a peripheral portion of the magnetic layer is exposed;

[0145] depositing a cap layer over the reflective multilayer stack;

[0146] depositing an absorbing layer over the cap layer; and

[0147] etching the absorbing layer to form a patterned absorbing layer including a plurality of openings therein exposing a surface of the cap layer.

[0148] Example 16. The method of example 15, wherein depositing the magnetic layer comprises depositing iron, nickel, cobalt, a combination of the foregoing, or an alloy of the foregoing.

[0149] Example 17. The method of example 15, further comprising forming a conductive layer over a second side of the substrate opposite the first side.

[0150] Example 18. The method of example 15, further comprising forming a trench extending through the patterned absorbing layer, the cap layer, the reflective multilayer stack, and the magnetic layer, wherein the trench exposes the first side of the substrate.

[0151] Example 19. The method of example 15, further comprising forming a trench extending through the magnetic layer, wherein the trench exposes a surface of the substrate.

[0152] Example 20. The method of example 15, wherein forming the reflective multilayer stack comprises depositing alternating layers of a high refractive index material and a low refractive index material over portions of the magnetic layer not shielded by a shield plate.

Claims

1. An extreme ultraviolet (EUV) mask, comprising a patterned region and a boundary region, wherein the EUV mask comprises: Substrate; A magnetic layer is located on the front surface of the substrate; A reflective multilayer stack is located on top of a portion of the magnetic layer, wherein the peripheral portion of the magnetic layer is exposed; A cap layer, located on top of the reflective multilayer stack; and A patterned absorbent layer is located above the cap layer and includes a plurality of openings that expose the surface of the cap layer.

2. The extreme ultraviolet (EUV) mask according to claim 1, wherein, The magnetic layer comprises iron, nickel, cobalt, a combination of the foregoing, or an alloy of the foregoing.

3. The extreme ultraviolet (EUV) mask according to claim 1, wherein, The patterned absorption layer comprises a non-magnetic material.

4. The extreme ultraviolet (EUV) mask according to claim 1, wherein, The patterned absorption layer includes chromium (Cr), chromium oxide (CrO), titanium nitride (TiN), tantalum nitride (TaN), tantalum (Ta), titanium (Ti), molybdenum, aluminum copper (AlCu), palladium (Pd), boron tantalum nitride (TaBN), aluminum oxide (Al2O3), or silver oxide (Ag2O).

5. The extreme ultraviolet (EUV) mask according to claim 1, wherein, A portion of the magnetic layer is located in the boundary region of the extreme ultraviolet (EUV) mask.

6. The extreme ultraviolet (EUV) mask according to claim 1, wherein, The entire patterned absorption layer is located within the patterned region of the extreme ultraviolet (EUV) mask.

7. The extreme ultraviolet (EUV) mask according to claim 1, wherein, The first portion of the patterned absorption layer is located in the patterned region of the extreme ultraviolet (EUV) mask, and the second portion of the patterned absorption layer is located in the boundary region of the EUV mask, wherein the first portion of the patterned absorption layer includes an open pattern.

8. A method for forming an extreme ultraviolet (EUV) mask, comprising: A magnetic layer is deposited on the first side of the substrate; A reflective multilayer stack is formed on a portion of the magnetic layer, wherein the peripheral portion of the magnetic layer is exposed; A capping layer is deposited on the reflective multilayer stack; An absorber layer is deposited on the cap layer; and The absorbent layer is etched to form a patterned absorbent layer, the patterned absorbent layer including a plurality of openings that expose the surface of the cap layer.

9. The method according to claim 8, wherein, Depositing the magnetic layer includes depositing iron, nickel, cobalt, a combination of the foregoing, or an alloy of the foregoing.

10. The method of claim 8, further comprising forming a conductive layer on a second side of the substrate opposite to the first side.

11. The method of claim 8, further comprising forming a trench extending through the patterned absorption layer, the capping layer, the reflective multilayer stack, and the magnetic layer, wherein, The trench exposes the first side of the substrate.

12. The method of claim 8, further comprising forming a trench extending through the magnetic layer, wherein, The trench exposes the surface of the substrate.

13. The method according to claim 8, wherein, Forming the reflective multilayer stack involves depositing alternating layers of high-refractive-index and low-refractive-index materials on the unshielded portions of the magnetic layer.

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