TW201734651A - Multilayer reflector, method of manufacturing a multilayer reflector and lithographic apparatus - Google Patents

Abstract

A multilayer reflector for use in EUV lithography, for example, comprises alternating layers of Mo and RbxSiy. The RbxSiyand Mo interface is thermodynamically stable, reducing intermingling of the layers and preventing reduction in reflectivity. The RbxSiylayer can be hydrogenated to form RbSiH3. For the case of Mo/RbSiH3an interlayer of RbH between Mo and RbSiH3layers can be used. An Mo/RbH multilayer mirror is also useful.

Description

Multilayer reflector, method for manufacturing multilayer reflector and lithography device

The present invention relates to multilayer reflectors for EUV or X-ray radiation, methods of making such multilayer reflectors, and lithographic apparatus using such multilayer reflectors.

A lithography apparatus is a machine that is constructed to apply a desired pattern onto a substrate. The lithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). The lithography apparatus can, for example, project a pattern from a patterned device (eg, a mask) onto a layer of radiation-sensitive material (resist) provided on the substrate. The wavelength of the radiation used by the lithography apparatus to project the pattern onto the substrate determines the minimum size of features that can be formed on the substrate. A lithography apparatus using EUV radiation that is electromagnetic radiation having a wavelength in the range of 5 nm to 20 nm, compared to conventional lithography apparatus (which may, for example, use electromagnetic radiation having a wavelength of 193 nm) It can be used to form smaller features on the substrate. It is difficult to collect EUV radiation into a beam; direct it onto a patterned device (eg, a mask) and project a patterned beam onto a substrate, which is not possible due to the fabrication of a refractive optical element for EUV radiation. . Therefore, it is necessary to perform these functions using a reflector (i.e., a mirror). It is even difficult to construct a reflector for EUV radiation. The most useful reflector for EUV radiation is a multilayer reflector (also referred to as a distributed Bragg reflector) comprising a plurality of layers alternating between a relatively high refractive index layer and a relatively low refractive index layer. Each period consisting of a high refractive index layer and a low refractive index layer has a thickness equal to one-half (λ/2) of the wavelength of the radiation to be reflected, so that there is a phase between the reflected radiation at the high to low refractive index boundary. Long interference. This multilayer reflector still does not achieve particularly high reflectivity. The currently available multilayer reflector for EUV using alternating layers of molybdenum (Mo) and yttrium (Si) can theoretically achieve a reflectivity of 74.77% (cycle number = 100, period thickness = 6.9 nm, Mo layer and period thickness) The ratio γ = 0.4). However, in practice, Mo/Si multilayer reflectors are known to suffer from three common defects: intermixing of Si and Mo at their interfaces; formation of a molybdenum telluride interlayer; and Mo/Si interface during the manufacture of multilayer reflectors. Roughening. The combination of these effects reduces the reflectivity of the Mo/Si multilayer reflector to about 70% or less. Since about 10 multilayer reflectors are used in series in the EUV lithography apparatus between the EUV source and the substrate, about 70% of the reflectivity of each multilayer reflector results in less than 3% of the EUV radiation initially produced. The substrate, while the other 97% is absorbed in the multilayer reflector and was wasted. Since it is difficult to increase the power supply power, a low proportion of the power supply output to the substrate actually limits the throughput of the lithography apparatus. The absorption of radiation (including infrared radiation also emitted by the radiation source) causes the temperature of the multilayer reflector to rise, which triggers further intermixing, vapor formation, and roughening at the interface. This occurs because the molybdenum telluride phase is more thermally stable than the elements Si and Mo. Therefore, it is necessary to provide substantial cooling of the multilayer reflector to avoid further degradation of its EUV reflectivity during its operation, and thus its economical useful life.

It is an object of the present invention to provide improved multilayer reflectors. According to the present invention, there is provided a multilayer reflector comprising a plurality of periods, each period comprising a low refractive index layer and a high refractive index layer, wherein: in at least one period, the low refractive index layer comprises Mo and the high refractive index layer comprises a compound, The compound comprises a combination of at least two elements selected from the group consisting of Si, Rb, and H. In accordance with the present invention, a lithography apparatus configured to project a pattern from a patterned device onto a substrate is provided, the apparatus comprising at least one multilayer reflector as described above. According to the present invention, there is provided a method of fabricating a multilayer reflector comprising a plurality of cycles, each cycle comprising a low refractive index layer and a high refractive index layer, the method comprising a physical vapor deposition process to form at least one high refractive index layer, the physics The vapor deposition step uses a vapor deposition target containing Si and Rb.

1 shows a lithography system including a multilayer reflector in accordance with an embodiment of the present invention. The lithography system comprises a radiation source SO and a lithography device LA. The radiation source SO is configured to produce a far ultraviolet (EUV) radiation beam B. The lithography apparatus LA includes a lighting system IL, a support structure MT configured to support a patterned device MA (eg, a mask), a projection system PS, and a substrate table WT configured to support the substrate W. The illumination system IL is configured to adjust the radiation beam B before the radiation beam B is incident on the patterned device MA. The projection system is configured to project a radiation beam B (now patterned by the mask MA) onto the substrate W. The substrate W may include a previously formed pattern. In this case, the lithography device aligns the patterned radiation beam B with the pattern previously formed on the substrate W. The radiation source SO, the illumination system IL, and the projection system PS can all be constructed and configured such that they can be isolated from the external environment. A gas (e.g., hydrogen) at a pressure below atmospheric pressure may be provided in the radiation source SO. Vacuum can be provided in the illumination system IL and/or the projection system PS. A small amount of gas (eg, hydrogen) at a pressure well below atmospheric pressure may be provided in the illumination system IL and/or the projection system PS. The radiation source SO shown in Figure 1 is of a type that can be referred to as a laser generated plasma (LPP) source. Can be, for example, CO₂ The laser 1 of the laser is configured to deposit energy via a laser beam 2 into a fuel such as tin (Sn) that is supplied from the fuel emitter 3. Although tin is mentioned in the following description, any suitable fuel may be used. The fuel can, for example, be in liquid form and can be, for example, a metal or an alloy. The fuel emitter 3 can include a nozzle configured to direct, for example, tin in the form of droplets along the track toward the plasma forming region 4. The laser beam 2 is incident on the tin at the plasma forming region 4. The deposition of laser energy into the tin produces a plasma 7 at the plasma forming region 4. Radiation including EUV radiation is emitted from the plasma 7 during excitation and recombination of ions of the plasma. The EUV radiation is collected and focused by a near normal incidence radiation collector 5 (sometimes more commonly referred to as a normal incidence radiation collector). The collector 5 can have a multilayer structure (described further below) configured to reflect EUV radiation (eg, EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 can have an elliptical configuration with two elliptical focal points. The first focus may be at the plasma forming zone 4 and the second focus may be at the intermediate focus 6, as discussed below. Laser 1 can be separated from the radiation source SO. In this case, the laser beam 2 can be transmitted from the laser 1 to the radiation source SO by means of a beam delivery system (not shown) comprising, for example, a suitable guiding mirror and/or beam expander and/or other optics. . Laser 1 and the radiation source SO can be considered together as a radiation system. The radiation reflected by the collector 5 forms a radiation beam B. The radiation beam B is focused at point 6 to form an image of the plasma forming region 4 that serves as a virtual radiation source for the illumination system IL. The point 6 at which the radiation beam B is focused may be referred to as an intermediate focus. The radiation source SO is configured such that the intermediate focus 6 is located at or near the opening 8 in the enclosure 9 of the radiation source. The radiation beam B is transmitted from the radiation source SO into the illumination system IL, which is configured to adjust the radiation beam. The illumination system IL can include a faceted field mirror device 10 and a faceted pupil mirror device. The faceted field mirror device 10 and the pupilized pupil mirror device 11 together provide a radiation beam B having a desired cross-sectional shape and a desired angular distribution. The radiation beam B is transmitted from the illumination system IL and is incident on the patterned device MA held by the support structure MT. The patterned device MA reflects and patterns the radiation beam B. The illumination system IL may include other mirrors or devices other than the facetted field mirror device 10 and the pupilized pupil mirror device 11 or not the faceted field mirror device 10 and the pupilized pupil mirror device 11. The faceted field mirror device 10, the pupilized pupil mirror device 11 and other reflectors of the illumination system can have a multilayer structure as further described below. After being reflected from the patterned device MA, the patterned radiation beam B enters the projection system PS. The patterned device can include a reflector having a multilayer structure as described further below. The projection system includes a plurality of mirrors configured to project a radiation beam B onto a substrate W held by a substrate table WT. The projection system PS can apply a reduction factor to the radiation beam to form an image having features that are less than corresponding features on the patterned device MA. For example, a reduction factor of 4 can be applied. Although the projection system PS has two mirrors in Figure 1, the projection system can include any number of mirrors (e.g., six mirrors). Any other reflector of the mirror and projection system PS can have a multilayer structure as further described below. 2 shows a laser generated plasma (LPP) radiation source SO having an alternate configuration of the radiation source shown in FIG. The radiation source SO includes a fuel emitter 3 that is configured to deliver fuel to the plasma forming region 4. The fuel can be, for example, tin, but any suitable fuel can be used. The pre-pulse laser 16 emits a pre-pulsed laser beam 17, which is incident on the fuel. The pre-pulsed laser beam 17 is used to preheat the fuel, thereby altering the properties of the fuel, such as the size and/or shape of the fuel. The main laser 18 emits a main laser beam 19 incident on the fuel after the pre-pulsed laser beam 17. The main laser beam delivers energy to the fuel and thereby converts the fuel into EUV radiation emitting plasma 7. The radiation collector 20, which may be a so-called grazing incidence collector, is configured to collect EUV radiation and focus the EUV radiation at a point 6 that may be referred to as an intermediate focus. Therefore, the image of the radiation-emitting plasma 7 is formed at the intermediate focus 6. The enclosure structure 21 of the radiation source SO includes an opening 22 at or near the intermediate focus 6. The EUV radiation passes through the opening 22 to the illumination system of the lithographic apparatus (e.g., in the form shown schematically in Figure 1). Radiation collector 20 can be a nested collector having a plurality of grazing incidence reflectors 23, 24, and 25 (e.g., as schematically depicted). The grazing incidence reflectors 23, 24, and 25 can be disposed to be axially symmetric about the optical axis O. The illustrated radiation collector 20 is shown by way of example only, and other radiation collectors can be used. A contaminant trap 26 is located between the plasma forming zone 4 and the radiation collector 20. The contaminant trap 26 can be, for example, a rotating foil trap, or can be any other suitable form of contaminant trap. In some embodiments, the contaminant trap 26 can be omitted. The enclosure 21 of the radiation source SO includes a window 27 through which the pre-pulsed laser beam 17 can be passed to the plasma forming region 4, and a window 28 through which the main laser beam 19 can be passed to the plasma formation region. The mirror 29 is used to direct the main laser beam 19 through the opening in the contaminant trap 26 to the plasma forming region 4. The radiation source SO shown in Figures 1 and 2 can include components not illustrated. For example, a spectral filter can be provided in the radiation source. The spectral filter can substantially transmit EUV radiation, but substantially blocks radiation of other wavelengths, such as infrared radiation. FIG. 3 depicts a multilayer reflector 30 in accordance with an embodiment of the present invention. The multilayer reflector 30 includes a plurality of alternating high refractive index layers 32 (sometimes referred to as spacer layers) and a low refractive index layer 34 (sometimes referred to as a refractive layer). A pair of adjacent layers is referred to herein as a cycle. The thickness of the period is approximately one-half (λ/2) (eg, 6.9 nm) of the wavelength of the radiation that needs to be reflected to reflect EUV radiation at 13.5 nm. The multilayer reflector acts as a distributed Bragg reflector with constructive interference between the radiation reflected at each boundary between the high refractive index layer and the low refractive index layer. The multilayer reflector can be formed on the substrate 38 and can be provided with a cap layer 36. The cover layer 36 can be formed from a variety of known materials and helps protect the multilayer reflector from chemical and physical damage. In an embodiment of the invention, the low refractive index layer is Mo and the high refractive index layer is germanium, wherein at least one high refractive index layer has been added with antimony (Rb). Desirably, at least 50%, at least 80%, at least 90%, or all of the high refractive index layers have been added with ruthenium. In embodiments where not all of the high refractive index layers have germanium, the layers having germanium are preferably those closest to the incident surface. Compared to conventional Mo/Si multilayer reflectors, the addition of Rb increases both the reflectivity and thermal stability of the multilayer reflector. Therefore, the present invention replaces the ruthenium layer by ruthenium telluride and the resulting multilayer reflector has Mo/Rb_x Si_y The general structure. The use of Rb produces four notable advantages. First, the solubility of Rb in Mo is predicted to be defect controlled and can be assumed to be almost zero (see W. Moffatt, The Handbook of Binary Phase Diagrams, Genium Pub, USA, 1984). On the other hand, Rb is extremely reactive and forms a strong bond with Si. The formation of RbSi has not been reported in the literature at the time of writing, but for the closely related compound RbGe (which has a zintl crystal structure similar to RbSi), the value is -100 kJ/mole (see J. Sangster and ADPelton, Journal of Phase Equilibria 18 (1997) 298). It should be noted that the energy formed here is expressed in kilojoules per mole of RbSi (or RbGe) "molecule". It is known that the alkali metal chalcantide is slightly more stable than its telluride counterpart (see E. Hohman, Z. Anorg. Allg. Chem. 257 (1948) 113). In addition, the free energy of formation of bismuth telluride (which also has a Qinte crystal structure) has been reported to be about 80% of bismuth telluride (see H. Peng et al., Physics Letters A 374 (2010) 3797). Therefore, it is safe to predict the formation energy of RbSi to be -80 kJ/mole. There are three known molybdenum molybdenum phases having the following formation enthalpy (H. Fujiwara, Y. Ueda, J. Alloys Compd. 441 (2007) 168): 1/4 Si + 3/4 Mo → 1/4 Mo₃ Si ΔH⁰ _r = 1/4 ΔH⁰ _f (Mo₃ Si) = 1/4 (-122.1 kJ/m) = -30.5 kJ/Mo_x Si_y Medium Atom Molar 3/8 Si + 5/8 Mo → 1/8 Mo₅ Si₃ ΔH⁰ _r = 1/8 ΔH⁰ _f (Mo₅ Si₃ ) = 1/8 (-313.5 kJ/m) = -39.2 kJ/Mo_x Si_y Medium atom Mohr 2/3 Si + 1/3 Mo → 1/3 MoSi₂ ΔH⁰ _r = 1/3 ΔH⁰ _f (MoSi₂ ) = 1/3 (-135.8 kJ/m) = -45.3 kJ/Mo_x Si_y The atomic mole selects the molar coefficient such that there is one mole of atoms at either side of each reaction equation, and thus the reaction enthalpy is pressed here._x Si_y In the atomic representation of each mole. The negative enthalpy shows that all three molybdenum molybdenum phases are more stable than their elemental components. MoSi₂ The highest negative enthalpy of formation of atoms per mole, and this is also the predominant and most stable telluride phase formed in the Mo/Si multilayer reflector, resulting in significant sharpness loss at the Mo/Si interface. However, if we replace Si with RbSi, the reaction enthalpy used to form the molybdenum telluride phase changes drastically: 1/4 RbSi + 3/4 Mo → 1/4 Mo₃ Si + 1/4 Rb ΔH⁰ _r = 1/4 (-122.1) - 1/4 (-80.0) = -10.5 kJ/Mo_x Si_y Medium atomic molar (65% reduction) 3/8 RbSi + 5/8 Mo → 1/8 Mo₅ Si₃ + 3/8 Rb ΔH⁰ _r = 1/8 (-313.5) - 3/8 (-80.0) = -9.2 kJ/Mo_x Si_y Medium atomic molar (76% reduction) 2/3 RbSi + 1/3 Mo → 1/3 MoSi₂ + 2/3 Rb ΔH⁰ _r = 1/3 (-135.8) - 2/3 (-80.0) = +8.0 kJ/Mo_x Si_y Medium atomic mole (complete suppression). These data show that the presence of Rb in the Si layer should inhibit both the intermixing of Si and Mo and the formation of the molybdenum molybdenum phase at each Si/Mo interface. More specifically, Mo in Mo/RbSi multilayer reflectors₃ Si and Mo₅ Si₃ The driving force behind the formation will be 65% and 76% lower than the Mo/Si system. At the same time, due to the positive reaction, most of the problematic tellurides (ie, MoSi) will be completely suppressed.₂ The formation of). In other words, the presence of Rb will thermally improve and protect Mo/Rb_x Si_y The sharpness of the interface (and therefore the reflectivity). This will also imply a significant increase in thermal/chemical stability and thus a significant increase in the useful life of the multilayer reflector. Secondly, for reflective EUV light, the element Rb has superior optical properties compared to Si. This is mainly due to the lower spectral absorption of Rb compared to Si for 13.5 nm light, as shown in Figure 4. In theory, Mo/Rb multilayer reflectors can achieve EUV reflectivity greater than 77%. Unfortunately, the Mo/Rb multilayer reflector cannot be used in practice because Rb has a melting point of only 39.3 °C. However, all phases of bismuth telluride are expected to have a melting point above 600 °C (see the Sangster et al. reference cited above). In the EUV spectrum, the optical properties of the compound (exactly, the refractive index n) can be estimated as a linear function of the individual components (see D. L. Windt, Computers in Physics 12 (1998) 360):Where ρ is the density,f ₁ andf ₂ For the atomic scattering factor, the sum includes each of the chemical elements constituting the compound,x _j For the relative concentration of each element, andA _j For the associated atomic density;e ,m _e ,c andN _a They are electronic charge, electron mass, speed of light, and Avogadro's number. Therefore, Rb_x Si_y The refractive index of the phase will depend on its stoichiometric ratio and density. To give an example, the reflectivity of the Mo/RbSi multilayer reflector is predicted to be higher than 72.9% (double layer number = 100, double layer thickness = 6.9 nm, Mo layer to double layer thickness ratio γ = 1/3, interface roughness) =4 Å, RbSi density = 2.72 gr/cm³ - See H. G. von Schnering et al., Z. Kristallogr. NCS 220 (2005) 525). It should be noted that this value is lower than the maximum theoretical reflectance (74.77%) of a conventional Mo/Si multilayer reflector. However, as previously mentioned, the thermal instability of the Mo/Si system results in a loss of interface sharpness and thus a loss of reflectance of about 70%. In contrast, Mo/Rb_x Si_y The thermal stability should protect the sharpness of the interface and prevent the loss of reflectivity. It should be noted that since we have assumed a roughness/diffusion of 4 Å at all interfaces (about 3 monolayers), the calculation of the 72.9% reflectivity mentioned above for the Mo/RbSi multilayer reflector is Based on a moderate estimate of the sharpness of the interface. Third, the reflectivity of the multilayer reflector is improved by "chemical shift". Chemical bonds are known to displace the electron energy levels of atoms. This effect is often referred to as "chemical shift" (CS). Figure 5 shows the refractive index difference (contrast) between Mo and Si (solid line), the sum of the spectral absorptances (dotted lines) and the reflectivity of the Mo/Si multilayer mirror with a period of 6.9 nm and γ = 0.4 (shadow) Area). Qualitatively, the higher contrast and lower absorption of a multilayer reflector for 13.5 nm wavelength light will result in a higher reflectivity of the multilayer reflector for this wavelength. For lower energy radiation (toward the L₃ The absorption edge (positioned at about 99 eV)), the sum of the absorption rates of Mo and Si (dotted line) decreased. This seems to imply that the closer to L₃ The light energy at the edge, the higher the reflectivity of the Mo/Si multilayer reflector. Unfortunately, this is not the case, because the Mo/Si contrast (solid line) is closer to L₃ The light energy at the edges is also reduced. However, by₃ Edge (corresponding to Si2p ^{2 / 3} The electronic orbital domain shifts to a lower energy level, which increases the refractive index difference for the 13.5 nm wavelength while keeping the total absorption rate almost constant (see Figure 6, which corresponds to Figure 5 but with Si2p Imagination of the orbital domain - 4 eV chemical shift). This will result in a higher reflectivity for 13.5 nm radiation. Since Rb has one of the lowest electronegativity values in the periodic table, Rb_x Si_y The germanium atoms in the matrix (which is an ionic solid) become negatively charged. This should promote the electronic energy level of 矽 (including Si2p Track domain) towards lower bonding energy. The expected level of change will be reflected at least to some extent in L₃ The downward displacement of the absorption edge. This situation stems from the orbital domain with higher bonding energy (here, closer to the core Si)2p The chemical shift of the orbital region is generally greater than the chemical shift of the orbital domain (here, the unoccupied orbital domain) with lower bonding energy. L₃ The displacement of the edge should increase the refractive index of Si in the telluride (the real part), while its absorption rate remains almost constant. The effective complex refractive index calculated by Equation 1 does not consider Si caused by the formation of a compound by Rb2p The beneficial effect of this chemical shift of the energy level. Si2p The chemical shift of the orbital domain will depend on Rb_x Si_y The oxidation state of Si and the lattice structure of the telluride phase. X-ray photoelectron spectroscopy or density function theoretical calculations are required to determine the specific Rb_x Si_y Membrane Si2p The exact value of the energy level CS and L₃ The resulting displacement of the absorption edge. The exact quantification of the Si L-edge displacement depends on the nature of the arrangement and boundaries of the atoms in the telluride. Qualitatively, the chemical shift of the absorption edge is proportional to the effective charge of the absorbed ion (see MNGhatikar, BDPadalia and RMNayak, "Chemical shifts and effective charges in ternary and complex systems", J. Phys. C: Solid State Phys. , 10 (1977) 4173 to 4180). Expected for Rb_n Si_m The negative charge transfer to Si is stronger because Rb has one of the lowest electronegativity values in the periodic table. The rule of thumb of Suche approximates the effective charge of ions in binary compounds.q ,Such as:among themz ,r andn Indicates the total number of electrons, the ionic radius, and the oxidation state of the ions. Here,a andc Subscripts indicate anions and cations. For RbSi, the predicted effective charge of Rb (,Å,) and Si (,Å,) for each atomandelectronic. Here, forand, already using Rb^{+ 1} And Si^{- 1} Pauling ionic radius (see Inorganic Chemistry: Principles of Structure and Reactivity, 4th edition, HarperCollins, USA, New York, 1993 JE Huheey, EAKeiter and RL Keiter; JE Huheey, Inorganic Chemistry: Principles of structure And reactivity, 3rd edition, Harper International, New York, 1983, ISBN 0-06-042987-9). From SiC, Si₃ N₄ SiO₂ And SiF₄ Experimental L-edge absorption data (see I. Waki and Y. Hirai, "The silicon L-edge photoabsorption spectrum of silicon carbide", J. Phys.: Condens. Matter 1 (1989) 6755 to 6762), L- The scaling factor between the edge chemical shift and the effective charge is estimated to be 1.24 eV per atom per atom (for linear fit,R ² =0.12). This implies a chemical shift of about -1.0 eV for the Si L-edge in RbSi. Can be calculated, compared to current state of the art (ie, Mo/B₄ C/Si/B₄ C. 70.15% reflectivity of the multilayer reflector), this chemical shift should improve the integral reflectivity of a single multilayer reflector in the range of 12.5 nm to 14.5 nm by an additional amount of approximately 0.27% and an integral reflectance of a series of 10 mirrors Improved by 0.58%. Therefore, in the case of the same EUV optical power supply, but using a Mo/RbSi multilayer reflector instead of a Mo/Si multilayer reflector, the EUV lithography apparatus can increase the throughput by 60% or more. Fourth, the addition of Rb allows for further optimization of the multilayer reflector. For the Mo layer and uniform Rb_x Si_y Multilayer reflector with a combination of layers, overall reflectivity and thermal/chemical stability for Rb_x Si_y Stoichiometric and telluride phases (for example, Rb₄ Si₄ , Rb₆ Si₄₆ A function of the crystal structure. The telluride phase can be amorphous and consist of any stoichiometric ratio between Rb and Si. An additional possibility that can be optimized for maximum reflectivity and stability is the use of multiple telluride phases in multilayer reflectors, such as {Mo/Rb₄ Si₄ /Rb₆ Si₄₆ /Rb₄ Si₄ }_n , {Mo/Rb₄ Si₄ /Si/Rb₄ Si₄ }_n , {Mo/Rb₆ Si₄₆ /Si/Rb₆ Si₄₆ }_n Etc. (where {.../.../.../...}_n Indicates the layer of the period, n is the number of cycles). In this embodiment, the high Rb content telluride interlayer acts as a diffusion barrier to protect the core ruthenium layer or core ruthenium layer having a lower Rb content from direct contact with Mo. This strategy can be practical because Rb with a higher Rb content, despite being combined with Mo_x Si_y The phase will have higher stability, but compared to pure tantalum or a halide with a lower Rb content, Rb_x Si_y Phases also tend to have higher densities. Therefore, by sandwiching a Si (or low Rb concentration telluride) layer between the high Rb concentration telluride interlayers, it is possible to obtain a multilayer reflector having an even better combination of reflectance and stability. To give an example, have the structure {Mo[22.6 Å]/B₄ C[3.0 Å]/Si[40.40 Å]/B₄ C[3.0 Å]}₁₀₀ The multilayer reflector has a predicted maximum theoretical reflectance of 13.5 nm for light greater than 74.75% (assuming all interfaces are extremely sharp and flat). However, by using Rb₄ Si₄ Replace B₄ C diffusion barrier, the reflectivity can rise above 75.35%, which reflects Rb₄ Si₄ Compared to B₄ Excellent optical properties of C. This reflectivity is even higher than {Mo[22 Å]/Rb₄ Si₄ [46 Å]}₁₀₀ The maximum theoretical reflectivity of the multilayer reflector is 74.74% (again assumed that all interfaces are extremely sharp and flat and ignore chemical shifts). Still, expectation {Mo/Rb₄ Si₄ /Si/Rb₄ Si₄ } compared to {Mo/Rb₄ Si₄ } has a slightly lower thermal stability due to Rb₄ Si₄ Rb in the interlayer can diffuse into the Si core layer, which will give the remaining Si in the interlayer diffusion toward Mo and form MoSi₂ chance. In summary, the effects of adding a Si layer to a Mo/Si multilayer reflector include: 1 - thermally improving and protecting the sharpness of the multilayer reflector interface. This results in: a - by suppressing the intermixing between Si and Mo and by suppressing MoSi₂ The formation at the interface increases the reflectivity of the multilayer reflector. B- attributed to Mo/Rb_x Si_y The enhanced thermal and chemical stability of the system increases the life of the multilayer reflector at elevated temperatures. 2 - by Si due to formation of a compound with Rb2p The negative chemical shift of the rail region increases the refractive index of Si in the RbSi layer and increases the reflectivity of the Mo/Si multilayer reflector. By using the ruthenium additive in the Mo/Si multilayer reflector, the intensity of the EUV light transferred from the source to the substrate and thus the throughput of the EUV lithography apparatus can be improved by at least 45%. (Compare Mo/B₄ C/Si/B₄ 70.15% of C reported world recorded reflectance and 72.9% predicted reflectivity of Mo/RbSi/Mo multilayer mirror, assuming double layer number = 100, double layer thickness = 6.9 nm, Mo layer to double layer thickness ratio γ =1/3, interface roughness/diffusion = 4 Å, RbSi density = 2.72 gr/cm³ ) such as B₄ Different layers of C and carbon have been used as diffusion barriers between the Si layer and the Mo layer to dynamically prevent MoSi₂ Formation. In this approach, MoSi₂ It still tends to form but only forms at slower speeds. The invention thermally prevents MoSi₂ The formation is excellent in the sense. Therefore, there is no MoSi₂ The driving force for formation. In contrast to Rb, which has superior optical properties compared to Si, both B and C result in a slight degradation in the optical properties of the Si layer. The presence of Rb in the Si layer also alters the optical properties of the Si layer to cause higher reflectivity in addition to the beneficial, thermodynamic effects described above. According to another embodiment of the invention, hydrogen is included in the high refractive index layer. Introducing hydrogen into the high refractive index layer reduces its density and increases the reflectivity of the multilayer reflector. The presence of Rb in the Si layer can significantly stimulate the hydrogen uptake of the Si layer. At room temperature, RbSi can absorb hydrogen at concentrations up to 60 at% (atomic %). This is achieved by simply exposing RbSi to hydrogen at a pressure of only 40 mbar. The resulting RbSiH₃ The phase has only 1.84 gr/cm which is 20% smaller than the density of pure Si.³ Density (see W.S. Tang, J.-N Chotard, P. Raybaud, R. Janot, J. Phys. Chem. C, 118 (2014) 3409). This reduction in density (along with other benefits of Rb) can result in a single Mo/RbSiH₃ The reflectivity of the multilayer reflector is increased to 76.1% (double layer = 100, double layer thickness = 6.9 nm, Mo layer to double layer thickness ratio γ = 1/3, interface roughness / diffusivity = 4 Å). Figure 7 shows RbSi and RbSiH as a function of temperature and hydrogen pressure.₃ The phase boundary between the phases. At room temperature, only 40 mbar of hydrogen pressure is sufficient to make RbSi into RbSiH₃ And stabilize the hydride phase. This also implies that if Mo/RbSiH₃ There are voids or cracks in the structure, and the segregation and release of hydrogen into the voids can result in a hydrogen pressure of only 40 mbar inside the void. This corresponds to a 4.0 KPa stress that is much smaller than the typical fracture strength of the solid material involved and its interface, which is in the range of MPa to GPa. Therefore, although implanted hydrogen with 30 at.% H is prone to H segregation and foaming, RbSiH with 60 at.% H₃ Medium H₂ The steady state pressure is too low to cause nucleation and/or growth of the voids and cause foaming damage. Mo/RbSi or Mo/RbSiH in a specific EUV lithography device₃ Whether a multilayer reflector is suitable depends on the operating temperature and the activity of the H radicals surrounding the multilayer reflector in the device. If an H radical generator is provided in a lithography apparatus (for example, for Sn cleaning purposes), it is expected that enhanced H activity will stabilize RbSiH.₃ phase. This would be beneficial due to Mo/RbSiH₃ The multilayer reflector will have significantly higher reflectivity (76.1% compared to 72.9% and 70.15%, respectively) compared to both Mo/RbSi and Mo/Si multilayer reflectors. Therefore, Mo/RbSiH is used in the lithography apparatus.₃ Substituting a multilayer reflector for 10 Mo/Si multilayer reflectors would result in an increase in the intensity of EUV light on the substrate of more than 125%. Mo/RbSiH for reflecting 13.5 nm EUV light according to an embodiment of the present invention₃ Multilayer reflectors have several advantages over conventional Mo/Si multilayer reflectors. As discussed above, the presence of Rb increases the reflectivity of the Mo/Si multilayer reflector from 70.15% to 72.9% due to: 1) as a spacer atom between the Mo layers in the multilayer reflector, the added Rb atoms are excellent. Optical properties of the optical properties of Si; 2) the presence of Rb due to Si2p Negative chemical shift in the orbital domain to increase the refractive index of Si in the RbSi layer; and 3) formation of antimony telluride suppresses intermixing between Si and Mo and MoSi₂ It forms, and thus protects, the sharpness of all interfaces in the multilayer reflector. The latter nature will also be attributed to Mo/Rb_x Si_y The system has an expected increase in the life of the multilayer reflector at elevated temperatures compared to the enhanced thermal and chemical stability of Mo/Si. Three additional benefits can be realized attributable to reducing the density of the high refractive index layer by hydrogen absorption. First, the presence of Rb in the Si high refractive index layer via RbSiH₃ Spontaneous formation of the phase stimulates hydrogen uptake to 60 at.%. The density of this hydride phase is about 20% lower than the density of pure Si, which increases the reflectivity of the entire multilayer reflector up to 76.1%. This is a significant improvement over the alternative approach to H implantation of the Si layer, which can result in a 7% density reduction, but is known not to increase the reflectivity, most likely due to ion bombardment induced interface roughening (V Rigato et al., Surf. Coat. Tech. 174 to 175 (2003) 40). Second, hydrogen uptake of up to 60 at.% of the RbSi phase can be achieved by simply exposing RbSi to hydrogen at relatively low pressure. For pure conditions, the solubility of hydrogen is only 3 to 4 at.%. The only way to achieve a higher H content in pure helium is to force the H atoms into the Si layer using the hydrogen ion implants mentioned above with intractable results. Third, unlike the Si layer implanted with H (which is supersaturated and thermally unstable), RbSiH₃ The phase is stable at room temperature under a hydrogen pressure of only 40 mbar. This translates into a potential void in the multilayer reflector structure and a low inside of the crack of only 4.0 KPa.₂ The pressure, which will be too low to cause blistering damage in the multilayer reflector. Another aspect of the invention provides a multilayer mirror comprising a multilayer stack of Mo/RbH. The reaction of the element Rb with hydrogen results in the formation of a RbH phase (NaCl crystal structure type) having 2.60 gr·cm^{- 3} (2600 kg/m³ The density and the decomposition temperature of 443 K. Similar to RbSi, RbH reacts strongly when in contact with air (see D. R. Lide, Handbook of Chemistry and Physics (version 87), Boca Raton, FL: CRC Press, (1998) pages 4 to 79).Here,andThey are the standard enthalpy of reaction and entropy (298.15 K, 101.3 kPa). The entropy term in this reaction cannot be ignored because it involves a change in the form of hydrogen intercalation from the molecular form of hydrogen in the gas phase to the solid phase. Standard Moir entropy from Rb and RbH (ie,andCalculate the standard entropy that forms RbH. The error on the thermal data of RbH was not reported. For the sake of safety, we have assumed that the error is 10% of the standard 熵 and entropy. In order to check the compatibility of RbH for EUV MLM applications, it is critical to check the steady-state hydrogen pressure of RbH as a function of temperature. Each material inevitably has multiple cavities or microcracks. Steady state H at a given temperature₂ The pressure is higher than the stress (breaking strength) required for the growth of the crack, then H₂ The release of gas into these voids can lead to foaming and MLM failure. Using the standard enthalpy and entropy that form RbH, it is possible to calculate with temperature (T And change the steady state pressure of hydrogen ():Here,R Is a gas constant, andk For the reaction in H₂ Mohr coefficient. For the temperature range associated with EUVL,Less than 1E-6 Pa. This value is much lower than the typical breaking strength of the solid (the range of MPa to GPa). Therefore, from this aspect, the application of RbH in MLM seems to be safe. Furthermore, Mo/RbH MLM is not expected to undergo any intermixing, since neither Rb nor H forms any compound with Mo, and its solubility in Mo is negligible. For this reason, it is expected that the intermixing at the Mo/RbH interface and the thermal sharpness of the interface will be sufficiently suppressed. This implies that the σ of the interface can be assumed to be at its smallest possible value (ie, 2.0 Å). This can be confirmed by calculating the reflectance value of Mo/RbH MLM with σ = 4.5 Å (corresponding to a 50% reduction of the mismix). The results are presented in Table 3, and Table 3 gives the presence and absence of B.₄ Mo/RbA in the case of a C-protective interlayer (A=Si, H and SiH)₃ The calculated reflectance value (normal incidence angle, 13.5 nm wavelength light) of MLM compared to Mo/Si. Consider the effect of intermixing at the interface. For each Mo/Rb_n A_m MLM, exhibiting two sets of reflectance values: one set of reflectance values with a low σ value, the suppression of the intermixed driving force for its self-heating analysis; and another set of reflectance values with a higher σ value, where Inhibition is only one-half of the inhibition of the first group. Optimized for each MLMd andΓ Combine to achieve the highest possible peak reflectance at 13.5 nm. For all conditions, N = 100 and the sigma of both the assumed substrate and the top surface is 2.0 Å. For Mo/Si without inter-layer (according to its normalized other integral reflectance values), the integral reflectance of a single mirror and 10 continuous mirrors in the range of 12.5 nm to 14.5 nm is 37.6 and 0.584 [% nm], respectively. See the graph of peak reflectance in the supplemental information. Although for Mo/RbSi, Mo/RbH and Mo/RbSiH₃ MLM, reflectivity values have an increasing order, but their thermal stability is in descending order because RbSi, RbH, and RbSiH₃ Decomposed under 623, 443, and 401 K [34], respectively. In the context of the EUVL machine, RbH and RbSiH are expected₃ Both phases are relatively stable relative to the Rb and RbSi phases. Use RbSiH in MLM₃ Or the RbH layer, rather than Si, can reduce or eliminate the hydrogen blistering problem common to current Mo/Si MLMs. RbH and RbSiH₃ Steady state H (at the appropriate service temperature)₂ The pressure is quite low and the H diffusion in these phases is expected to be high (especially for RbSiH₃ , due to the high concentration of H atoms, low hydrogenation free energy and its open crystal structure). This is an additional advantage because it creates an excess of H in the MLM crack.₂ Pressure or extra H atoms (which are forced into the MLM by H+ bombardment) via RbSiH₃ The layer is effectively discharged outside the MLM, thus preventing the possibility of occurrence of foaming. On the other hand, for a pure Si layer, low H solubility and diffusion coefficient result in the accumulation of hydrogen and eventually foaming. According to an embodiment of the present invention, it is proposed to add an RbH interlayer to a multilayer mirror having a high refractive layer comprising Si and Rb. Such interlayer suppression thermally drives the inter-layer mixing. The RbH interlayer may have a thickness ranging from 0.1 nm to 0.4 nm, desirably about 0.2 nm. By implementing the proposed Mo/RbSi, Mo/RbH and Mo/RbSiH₃ (The latter has an RbH interlayer) MLM or a combination thereof, the total EUV throughput can be increased by up to 2 times compared to current Mo/Si MLM solutions. In addition, use RbH or RbSiH₃ Phases create new possibilities to reduce or eliminate hydrogen blistering problems common to current Mo/Si MLM. In an embodiment of the invention, the multilayer reflector is a reflective mask for patterning EUV beams. A reflective mask for EUV comprises a multilayer reflector as described above, wherein a patterned absorber layer is provided on the incident surface. The patterned absorber layer is designed to expose the radiation sensitive layer in a manner such that the desired pattern can be transferred to the substrate. The pattern in the absorber layer does not necessarily correspond directly to the pattern transferred to the substrate. The pattern in the absorber layer can include changes in non-printing optical proximity correction (OPC) features and/or feature sizes (eg, line width) to compensate for the effects of the development and pattern transfer steps. A multilayer reflector in accordance with an embodiment of the present invention can be fabricated using conventional techniques known for fabricating Mo/Si multilayer reflectors. There is no change in the process of forming the Mo layer. In order to form a Si layer containing Rb, a deposition technique such as pulsed laser deposition or sputtering deposition using a target having an appropriate ratio of Si and Rb may be used. In order to hydrogenate Rb_x Si_y The layer can be deposited under a hydrogen atmosphere. In general, no specific measures are required to ensure the Mo layer and Rb_x Si_y Adhesion between layers; Van Valli is sufficient. In an embodiment, the invention may form part of a mask detection device. The mask detection device can use EUV radiation to illuminate the mask and an imaging sensor to monitor the radiation reflected from the mask. The image received by the imaging sensor is used to determine if there is a defect in the mask. The mask detection device can include a multilayer reflector of the type described above configured to receive EUV radiation from an EUV radiation source and to form EUV radiation as a radiation beam to be guided. The mask detecting device may further comprise a multilayer reflector of the type described above configured to collect EUV radiation reflected from the mask and form an image of the mask at the imaging sensor. The mask detection device can include a processor configured to analyze the image of the mask at the imaging sensor and determine from the analysis whether there are any defects on the mask. The processor can be further configured to determine whether a mask defect detected when the mask is used by the lithography apparatus will cause unacceptable defects in the image projected onto the substrate. In an embodiment, the invention may form part of a metrology device. The metrology device can be used to measure the alignment of the projected pattern in the resist formed on the substrate relative to the pattern already present on the substrate. This measurement of relative alignment can be referred to as a stack. The metrology device can, for example, be positioned proximate to the lithography device and can be used to measure the overlay before the substrate (and resist) has been processed. The metrology device can use EUV radiation for improved resolution and thus a multilayer reflector of the type described above can be used to form and direct the EUV radiation beam. Although embodiments of the invention in the context of the content of a lithographic apparatus may be specifically referenced herein, embodiments of the invention may be utilized in other apparatus. Embodiments of the invention may form part of a mask detection device, a metrology device, or any device that measures or processes an article such as a wafer (or other substrate) or a mask (or other patterned device). Such devices may be commonly referred to as lithography tools. This lithography tool can use vacuum conditions or environmental (non-vacuum) conditions. The invention is also applicable to multilayer reflectors used in fields other than EUV lithography (e.g., in X-ray optics for astronomical applications). The term "EUV radiation" can be considered to encompass electromagnetic radiation having a wavelength in the range of 5 nm to 20 nm (eg, in the range of 13 nm to 14 nm). The EUV radiation can have a wavelength of less than 10 nm, for example, a wavelength in the range of 5 nm to 10 nm (such as 6.7 nm or 6.8 nm). Although FIGS. 1 and 2 depict the radiation source SO as a laser-generated plasma LPP source, any suitable source can be used to generate EUV radiation. For example, an EUV emitting plasma can be produced by using a discharge to convert a fuel (eg, tin) to a plasma state. This type of radiation source can be referred to as a discharge generated plasma (DPP) source. The discharge may be generated by a power supply that may form part of the radiation source or may be a separate entity that is connected to the radiation source SO via an electrical connection. Although reference may be made herein specifically to the use of lithographic apparatus in IC fabrication, it should be understood that the lithographic apparatus described herein may have other applications. Other possible applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like. Although the specific embodiments of the invention have been described above, it will be understood that the invention may be practiced otherwise. The above description is intended to be illustrative, and not restrictive. Therefore, it will be apparent to those skilled in the art that the present invention may be modified without departing from the scope of the appended claims.

1‧‧ ‧ laser
2‧‧‧Laser beam
3‧‧‧fuel emitter
4‧‧‧ Plasma formation area
5‧‧‧ Collector
6‧‧‧Intermediate focus/point
7‧‧‧ Plasma
8‧‧‧ openings
9‧‧‧Enclosed structure
10‧‧‧琢面面镜镜装置
11‧‧‧ Faceted Optic Mirror Device
16‧‧‧Pre-pulse laser
17‧‧‧Pre-pulse laser beam
18‧‧‧Main laser
19‧‧‧Main laser beam
20‧‧‧radiation collector
21‧‧‧Enclosed structure
22‧‧‧ openings
23‧‧‧ grazing incident reflector
24‧‧‧ grazing incident reflector
25‧‧‧grazing incident reflector
26‧‧‧Contaminant trap
27‧‧‧ window
28‧‧‧ window
29‧‧‧Mirror
30‧‧‧Multilayer reflector
32‧‧‧High refractive index layer
34‧‧‧Low refractive index layer
36‧‧‧ Cover layer
38‧‧‧Substrate
B‧‧‧radiation beam
IL‧‧‧Lighting System
LA‧‧‧ lithography device
MA‧‧‧patterned device
MT‧‧‧Support structure
O‧‧‧ optical axis
PS‧‧‧Projection System
SO‧‧‧radiation source
W‧‧‧Substrate
WT‧‧‧ substrate table

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 depicts a micro-shaving device and a radiation source in accordance with an embodiment of the present invention. Figure 2 depicts a radiation source in accordance with an embodiment of the present invention; - Figure 3 depicts a multilayer reflector in accordance with one embodiment of the present invention; - Figure 4 shows the refractive index as a function of wavelength for 铷 and 矽And the graph of the absorptivity; - Figure 5 depicts the difference in refractive index and spectral absorptance of Mo and Si; - Figure 6 depicts the difference in refractive index and spectral absorptance of Mo and Si in the case of chemical shift; 7 is a graph showing the phase boundary between RbSi and RbSiH ₃ phases as a function of temperature and hydrogen pressure; - Figure 8 is a calculated reflectance of a multilayer mirror of various compositions of composition A as Mo/Rb _n A _m A plot of values versus wavelength; and - Figure 9 is a plot of calculated reflectance values versus wavelength for 10 multilayer mirrors of a series of different compositions of composition A, Mo/Rb _n A _m .

30‧‧‧Multilayer reflector

32‧‧‧High refractive index layer

34‧‧‧Low refractive index layer

36‧‧‧ Cover layer

38‧‧‧Substrate

Claims (20)

A multilayer reflector comprising a plurality of periods, each period comprising a low refractive index layer and a high refractive index layer, wherein: in at least one period, the low refractive index layer comprises Mo and the high refractive index layer comprises a compound The compound comprises a combination of at least two elements selected from the group consisting of Si, Rb, and H. The multilayer reflector of claim 1, wherein the high refractive index layer of at least one period comprises RbSi. The multilayer reflector of claim 1, wherein the high refractive index layer of at least one of the cycles comprises Rb ₆ Si ₄₆ . A multilayer reflector of 2 or 3, wherein the high refractive index layer of at least one cycle further comprises ruthenium hydride. The multilayer reflector of claim 4, wherein the high refractive index layer of at least one period comprises RbSiH ₃ . The multilayer reflector of claim 4, further comprising an inter-RbH interlayer between the low refractive index layer and the high refractive index layer. A multilayer reflector of 2 or 3 wherein the high refractive index layer is amorphous. The multilayer reflector of claim 2, wherein the high refractive index layer is in a Qin phase. a multilayer reflector of 2 or 3, wherein the high refractive index layer of at least one period comprises a first sublayer, a second sublayer and a third sublayer in order, wherein the first sublayer and the third sub The layer has a higher Rb content than the second sub-layer. The multilayer reflector of claim 1, wherein the high refractive index layer comprises RbH. A multilayer reflector of 2 or 3 wherein all of said high refractive index layers of said periods have substantially the same composition. A multilayer reflector of 2 or 3, further comprising at least one cap layer on one of the radiation receiving surfaces of the multilayer reflector. A lithography apparatus configured to project a pattern from a patterned device onto a substrate, the apparatus comprising at least one multilayer reflector of any one of claims 1 to 12. A lithography tool comprising at least one multilayer reflector according to any one of claims 1 to 12. A mask for use in a lithography apparatus, the mask comprising at least one multilayer reflector and a patterned absorber layer of any one of claims 1 to 12. A method comprising projecting a patterned beam of radiation onto a substrate, wherein the patterned beam is guided or patterned using at least one multilayer reflector as claimed in any one of claims 1 to 12. A method of fabricating a multilayer reflector comprising a plurality of cycles, each cycle comprising a low refractive index layer and a high refractive index layer, the method comprising a physical vapor deposition process to form at least one high refractive index layer, The physical vapor deposition step uses a vapor deposition target comprising one of Si and Rb. The method of claim 17, wherein the physical vapor deposition process comprises pulsed laser deposition. The method of claim 17, wherein the physical vapor deposition process comprises sputter deposition. The method of claim 17, 18 or 19, wherein the physical vapor deposition process is performed in a hydrogen atmosphere.