Optical element including substrate coated with magnesium fluoride by atomic layer deposition

Abstract

To manufacture an optical element whose surface curvature is uniformly coated by a simpler process at a low cost.SOLUTION: Atomic layer deposition methods for coating an optical substrate with magnesium fluoride include two primary processes. The first process includes a step of forming a magnesium oxide layer over a surface of a substrate. The second process includes a step of converting the magnesium oxide layer to a magnesium fluoride layer. These two primary processes may be repeated a plurality of times so as to create multiple magnesium fluoride layers that make up a magnesium fluoride film.SELECTED DRAWING: Figure 1

Description

Priority

[0001] This application claims the benefit of priority under 35 U.S.C. §119(e) from U.S. Provisional Patent Application No. 62 / 880,250, filed July 30, 2019, which is incorporated herein by reference in its entirety, and is a divisional application of Japanese Patent Application No. 2022-505600, filed July 15, 2020. [Technical field]

[0002] The present disclosure relates to atomic layer deposition of antireflective coatings comprising magnesium fluoride. In particular, the present disclosure relates to atomic layer deposition methods for coating optical substrates (e.g., optical lenses) with one or more magnesium fluoride films. [Background technology]

[0003] Anti-reflective (AR) coatings are useful in preventing unwanted reflection of light from the surface of an object. Generally, when light strikes a surface of an object at a large angle of incidence, the light is likely to be reflected from the surface. An object with a surface with a high degree of surface curvature is likely to reflect light directed at the object because at least some of the light strikes the surface at a relatively large angle of incidence.

[0004] Current physical vapor deposition (PVD) processes for AR coatings cannot uniformly coat tight surface curvatures because these processes rely on a roughly linear deposition of particles from a deposition source to a deposition target. To address this uniformity challenge, the process must incorporate complex motion and screening, which increases the process complexity, process cost, and time required to complete the process. Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, there is a need for new methods of depositing antireflective coatings. [Means for solving the problem]

[0006] The present disclosure relates to a method for atomic layer deposition of magnesium fluoride films, which may serve as anti-reflective coating layers for optical substrates, such as optical lenses. The method includes two main process steps. The first process step includes forming a magnesium oxide layer over a surface of a substrate. The first process step is performed by exposing the substrate to a magnesium-containing precursor gas to form a precursor layer, followed by exposing the precursor layer to an oxygen-containing gas, resulting in the formation of a magnesium oxide layer. The second process step includes converting the magnesium oxide layer to a magnesium fluoride layer. The second process step is performed by exposing the magnesium oxide layer to a fluorine-containing source gas to form an intermediate layer, followed by exposing the intermediate layer to an oxygen-containing gas, resulting in the formation of a magnesium fluoride layer. These two main process steps may be repeated multiple times in succession to create multiple magnesium fluoride layers that make up the magnesium fluoride film. By controlling at least the temperature and the type of oxygen-containing gas used, the elemental composition of the magnesium fluoride film can be tailored to produce a film with desired optical properties.

[0007] A first aspect (1) of the present application relates to an atomic layer deposition method for coating an optical lens with a magnesium fluoride layer, the method comprising the steps of: (i) exposing the optical lens to a precursor gas comprising magnesium, thereby forming a magnesium-containing precursor layer over a surface of the lens; (ii) exposing the magnesium-containing precursor layer to a first oxygen-containing gas, thereby forming a magnesium oxide layer; (iii) exposing the magnesium oxide layer to a source gas comprising fluorine, thereby forming an intermediate layer comprising magnesium and fluorine; and (iv) exposing the intermediate layer to a second oxygen-containing gas, thereby forming a magnesium fluoride layer.

[0008] In a second aspect (2), there is provided the atomic layer deposition method according to the first aspect (1), wherein the step of exposing the magnesium-containing precursor layer to the first oxygen-containing gas is carried out at a temperature in the range of 100° C. to 300° C.

[0009] In a third aspect (3), there is provided the atomic layer deposition method according to the first aspect (1), wherein the step of exposing the magnesium-containing precursor layer to the first oxygen-containing gas is carried out at a temperature in the range of 240° C. to 260° C.

[0010] In a fourth aspect (4), there is provided the atomic layer deposition method according to any of aspects (1)-(3), wherein the first oxygen-containing gas comprises a gas selected from the group of water, ozone, hydrogen peroxide, methanol, ethanol, a plasma of oxygen, and a plasma of an oxygen-containing chemical.

[0011] In the fifth embodiment (5), the first oxygen-containing gas is H 2 The atomic layer deposition method according to any one of aspects (1) to (3) is provided, which comprises O.

[0012] In the sixth embodiment (6), the first oxygen-containing gas is H 2 O, and the magnesium-containing precursor layer is heated to a temperature in the range of 240° C. to 260° C. with H 2 The atomic layer deposition method according to any of the aspects (1) to (5) is provided, wherein the substrate is exposed to O.

[0013] In a seventh aspect (7), there is provided an atomic layer deposition method according to any of aspects (1)-(6), wherein the fluorine-containing source gas is an organic source gas.

[0014] In an eighth embodiment (8), the organic source gas is hexafluoroacetylacetone, carbonyl fluoride, chlorine fluoride, chlorine trifluoride, 1-chloro-2,2-difluoroethene, chlorodifluoromethane, 1-chloro-1-fluoroethane, chloropentafluorobenzene, chloropentafluoroethane, chlorotrifluoroethene, chlorotrifluoromethane, dichlorodifluoromethane, 1,2-dichloro-1,1,2,2-tetrafluoroethane, difluoroethane, difluoromethane, fluoropropane, nitrogen trifluoride, In one embodiment, the atomic layer deposition method is provided in which the fluorocarbon fluoride is selected from the group consisting of fluorobenzene, pentafluorobenzene, pentafluoroethane, pentafluorophenol, pentafluorotoluene, perfluorocyclobutane, perfluorocyclohexane, perfluorocyclohexene, perfluoroheptane, perfluoromethylcyclohexane, perfluorotoluene, 1,1,1,2-tetrachloro-2,2-difluoroethane, trichlorofluoromethane, trifluoroacetic acid, trifluoroethane, and trifluoroethanol.

[0015] In a ninth aspect (9), there is provided an atomic layer deposition method according to any of aspects (1)-(8), wherein the magnesium-containing precursor gas is selected from the group of bis(ethylcyclopentadienyl)magnesium, bis(cyclopentadienyl)magnesium(II), bis(2,2,6,6-tetramethyl-3,5-heptanedionato)magnesium, bis(N,N'-di-sec-butylacetamidinato)magnesium, and bis(pentamethylcyclopentadienyl)magnesium.

[0016] In a tenth aspect (10), there is provided an atomic layer deposition method according to any of aspects (1) to (9), comprising repeating steps (i) to (iv) multiple cycles to form a magnesium fluoride film comprising multiple magnesium fluoride layers.

[0017] In an eleventh embodiment (11), there is provided the atomic layer deposition method according to embodiment (10), wherein the magnesium fluoride film has a thickness in the range of 25 nanometers to 75 nanometers.

[0018] In a twelfth embodiment (12), there is provided the atomic layer deposition method according to embodiment (11), wherein the magnesium fluoride film has an optical absorption value of 1% or less for light having a wavelength of 266 nanometers and an angle of incidence of 6 degrees.

[0019] In a thirteenth embodiment (13), there is provided the atomic layer deposition method according to embodiment (11) or embodiment (12), wherein the magnesium fluoride film has an optical transmittance value of 94% or greater for light having a wavelength of 266 nanometers and an angle of incidence of 6 degrees.

[0020] In a fourteenth aspect (14), there is provided the atomic layer deposition method according to any of aspects (11)-(13), wherein the magnesium fluoride film has a surface roughness (Ra) of 1.5 nanometers or less.

[0021] In a fifteenth aspect (15), there is provided the atomic layer deposition method according to any of aspects (11) to (14), wherein the magnesium fluoride film has a refractive index of 1.42 or less for light having a wavelength of 266 nanometers.

[0022] In a sixteenth aspect (16), there is provided the atomic layer deposition method according to any of aspects (11)-(15), wherein the magnesium fluoride film has a carbon content of 1.2 atomic % or less at a depth of 0.02 micrometers as measured using secondary ion mass spectrometry.

[0023] In a seventeenth aspect (17), there is provided an atomic layer deposition method according to any of aspects (11)-(16), wherein the surface of the lens includes a surface bounded by a peripheral edge, and the magnesium fluoride film covers the entire surface bounded by the peripheral edge.

[0024] In an eighteenth embodiment (18), there is provided an atomic layer deposition method according to embodiment (17), wherein the magnesium fluoride film has a thickness variation of 10% or less.

[0025] In a nineteenth aspect (19), there is provided an atomic layer deposition method according to aspect (17), wherein the magnesium fluoride film has a thickness variation of 5% or less.

[0026] In a twentieth aspect (20), there is provided an atomic layer deposition method according to any of aspects (1)-(19), wherein the lens is held substantially stationary during the atomic layer deposition method.

[0027] In a twenty-first embodiment (21), there is provided an atomic layer deposition method according to any of embodiments (1)-(20), wherein step (iii) comprises a remote plasma process.

[0028] A twenty-second aspect (22) of the present application relates to an optical lens having a surface covered with a magnesium fluoride layer deposited by the atomic layer deposition method according to any of the aspects (1) to (21).

[0029] A twenty-third aspect (23) of the present application relates to an optical lens having a magnesium fluoride film coated over a surface of the optical lens, the magnesium fluoride film having a thickness in the range of 25 nanometers to 75 nanometers, an optical absorption value of 1% or less for light having a wavelength of 220 nanometers and an incidence angle of 6 degrees, and a thickness variation of 5% or less.

[0030] In a twenty-fourth embodiment (24), there is provided an optical lens according to embodiment (23), wherein the magnesium fluoride film has an optical transmittance value of 94% or greater for light having a wavelength of 220 nanometers and an angle of incidence of 6 degrees.

[0031] In a twenty-fifth aspect (25), there is provided an optical lens according to aspect (23) or aspect (24), wherein the surface of the lens includes a surface bounded by a peripheral edge, and the magnesium fluoride film covers the entire surface bounded by the peripheral edge.

[0032] In a twenty-sixth embodiment (26), there is provided the optical lens according to any of embodiments (23)-(25), wherein the lens further comprises an aluminum oxide layer disposed between the magnesium fluoride film and the surface of the optical lens.

[0033] A twenty-seventh aspect (27) of the present application relates to a semiconductor wafer inspection tool including the optical lens according to any one of aspects (23) to (26).

[0034] A twenty-eighth aspect (28) of the present application relates to an optical element comprising: an optically transparent lens having a first surface having a steepness value in the range of 0.5 to 1.0 and a second surface opposite the first surface, the steepness value being equal to a radius of curvature of the first surface divided by an effective aperture of the optically transparent lens; and an optical film disposed over the first surface and the second surface, the optical film including a first refractive index layer having a first refractive index for light having a wavelength of 550 nanometers, and a second refractive index layer disposed over the first refractive index layer and including a magnesium fluoride film and a low refractive index layer, the second refractive index layer having a second refractive index for light having a wavelength of 550 nanometers, the second refractive index being less than the first refractive index.

[0035] In a twenty-ninth embodiment (29), there is provided the optical element according to embodiment (28), wherein the first refractive index layer is made from a material selected from the group consisting of aluminum oxide, hafnium oxide, gadolinium fluoride, and lanthanum fluoride.

[0036] In a thirtieth embodiment (30), there is provided an optical element according to embodiment (28) or embodiment (29), wherein an optical film is disposed on the first surface and the second surface.

[0037] In a thirty-first embodiment (31), there is provided an optical element according to any of embodiments (28)-(30), wherein the magnesium fluoride film has a thickness in the range of 25 nanometers to 75 nanometers, an optical absorption value of 1% or less for light having a wavelength of 220 nanometers and an angle of incidence of 6 degrees, and a thickness variation of 10% or less.

[0038] In a thirty-second embodiment (32), there is provided an optical element according to any of embodiments (28) to (31), wherein the magnesium fluoride film has an optical transmittance value of 94% or greater for light having a wavelength of 220 nanometers and an angle of incidence of 6 degrees.

[0039] In a thirty-third embodiment (33), there is provided the optical element according to any one of embodiments (28) to (32), wherein the first refractive index is 1.6 or more and the second refractive index is 1.38 or less.

[0040] A thirty-fourth aspect (34) of the present application relates to a semiconductor wafer inspection tool including the optical element according to any one of aspects (28) to (33). [Brief description of the drawings]

[0041] The accompanying drawings contained herein form a part of this specification and illustrate embodiments of the present disclosure. The drawings, together with the description, further serve to explain the principles of the disclosed embodiments and to enable one skilled in the art to make and use the embodiments. These drawings are intended to be illustrative, not limiting. While the disclosure has generally been described in the context of these embodiments, it should be understood that there is no intent to limit the scope of the disclosure to these particular embodiments. In the drawings, like reference numbers indicate identical or functionally similar elements. [Figure 1] Illustrative diagram of an atomic layer deposition method for depositing magnesium fluoride films, according to some embodiments. [Diagram 2] FIG. 1 is an illustration of an optical lens according to some embodiments. [Diagram 3] FIG. 1 is an illustration of an optical instrument according to some embodiments. [Figure 4] 1 is a graph of refractive index, growth rate, and uniformity of magnesium fluoride films as a function of oxygen-containing gas exposure temperature for atomic layer deposition methods according to some embodiments; [Figure 5A] 1 is a graph of optical absorption for magnesium fluoride films deposited by a single-step atomic layer deposition method and a two-step atomic layer deposition method according to some embodiments; [Figure 5B] 1 is a graph of optical transmittance for uncoated silica, magnesium fluoride films deposited by a single-step atomic layer deposition method, and magnesium fluoride films deposited by a two-step atomic layer deposition method according to some embodiments; [Figure 5C] 1 is a graph of optical reflectance for uncoated silica, magnesium fluoride films deposited by a single-step atomic layer deposition method, and magnesium fluoride films deposited by a two-step atomic layer deposition method according to some embodiments; [Figure 6] 1 is a graph of refractive index as a function of light wavelength for magnesium fluoride films deposited by a single-step atomic layer deposition method and for magnesium fluoride films deposited by a two-step atomic layer deposition method according to some embodiments. [Figure 7A] Graph of secondary ion mass spectrometry results for magnesium fluoride films deposited by one-step atomic layer deposition method. [Figure 7B] 1 is a graph of secondary ion mass spectrometry results for magnesium fluoride films deposited by a two-step atomic layer deposition method according to some embodiments; [Figure 8] FIG. 1 is an illustration of an optical lens coated with an optical film according to some embodiments. [Figure 9A] 1 is a graph of light reflectance as a function of incident light angle for example refractive index layers according to some embodiments; [Figure 9B] 1 is a graph of light reflectance as a function of incident light wavelength for example refractive index layers according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] The following examples are illustrative, not limiting, of the present disclosure. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in the art and which would be obvious to those skilled in the art are within the spirit and scope of the disclosure.

[0043] For optical applications, such as optical lenses, reflection and / or absorption of light can be problematic. Reflection and / or absorption of light reduces the amount of light transmitted through the optical lens toward a desired target. The reduction in transmitted light can impair the resolution of an optical system that relies on the optical lens to collect and focus light. Such a reduction in resolution can impair the ability of the optical system to accurately image an object.

[0044] The reflection and / or absorption of light may depend on the wavelength of light utilized by the optical system and the surface curvature of the optical lens utilized to collect the wavelength of light. For example, a high numerical aperture lens (e.g., objective lens) for an optical inspection system may have a tight surface curvature to collect a particular wavelength, or range of wavelengths, of light. If light reflects off such a tight surface, the ability of the inspection system to accurately image the object may be compromised. Accurate imaging of an object is important in many applications, such as semiconductor wafer inspection systems. These systems need to be able to accurately detect any contamination (e.g., debris particles) on the surface of a semiconductor wafer for quality control purposes.

[0045] Due to the importance of accurately imaging the surface, some optical inspection systems, such as semiconductor inspection systems, utilize deep ultraviolet (DUV) laser-based light (i.e., light having wavelengths ranging from 193 nm to 266 nm) or broadband spectrum light (i.e., light having wavelengths ranging from 175 nm to 300 nm). These wavelengths can achieve higher resolution than other wavelengths of light (e.g., visible light ranging from 400 nm to 700 nm). However, the intensity of the light at these wavelengths is relatively low. Low intensity can be problematic as it can reduce the resolution of the inspection system. Therefore, one or more high numerical aperture lenses with tight surface curvatures may be required to focus the light. Proper focusing of DUV or broadband wavelengths increases the intensity of the light in the detection area, thereby achieving adequate detection resolution.

[0046] For inspection systems utilizing DUV or broadband wavelengths, Magnesium Fluoride (MgF 2 ) is a suitable anti-reflective coating material. When properly deposited, magnesium fluoride resists reflection and absorption of light at deep UV and broadband wavelengths, even at large angles of incidence. In other words, when properly deposited, magnesium fluoride can fully transmit a significant amount of deep UV or broadband wavelengths, even at large angles of incidence.

[0047] However, these desirable optical properties depend on the elemental composition and uniformity of the magnesium fluoride film. Therefore, the method utilized to deposit the magnesium fluoride film should be capable of depositing a film with uniform thickness and appropriate elemental composition. Atomic layer deposition of magnesium fluoride films has been demonstrated by Hennessy et al. (hereinafter referred to as "Hennessey et al.") in the article "Atomic Layer Deposition of Magnesium Fluoride Via Bis(ethylcyclopentadienyl)magnesium and anhydrous hydrogen fluoride," Journal of Vacuum Science and Technology A, 33, 01A125 (2015). In this article, a one-step atomic layer deposition process (herein referred to as the "one-step ALD process") is described. In this one-step process, hydrofluoric acid (HF) is utilized as the fluorine source. Hydrofluoric acid is a hazardous material to handle and process.

[0048] Atomic layer deposition methods according to embodiments described herein can deposit magnesium fluoride films having superior optical properties to those deposited by one-step ALD processes. Methods according to embodiments described herein produce magnesium fluoride films having lower optical reflectance, lower optical absorption, and / or higher optical transmittance compared to films deposited by one-step atomic layer deposition processes. Moreover, the methods described herein may achieve these properties without the use of hydrofluoric acid.

[0049] 1 illustrates a method 100 for atomic layer deposition of a magnesium fluoride film (e.g., magnesium fluoride film 210) on a surface 104 of a substrate 102 according to some embodiments. The substrate 102 may be, for example, an optical lens (e.g., optical lens 200). The substrate 102 may be a glass substrate, such as a soda-lime glass, an alkali aluminosilicate glass, an alkali-containing borosilicate glass, or an alkali aluminoborosilicate glass substrate. The surface 104 may be, for example, a first surface 202 and / or a second surface 204 of the lens 200. The method 100 is a multi-step atomic layer deposition process that includes the formation of magnesium oxide and the subsequent conversion of the magnesium oxide to magnesium fluoride.

[0050] In step 110, the substrate 102 is exposed to a precursor gas 112 comprising magnesium, thereby forming a magnesium-containing precursor layer 114 over the surface 104 of the substrate 102. The precursor gas 112 may include, but is not limited to, bis(ethylcyclopentadienyl)magnesium, bis(cyclopentadienyl)magnesium(II), bis(2,2,6,6-tetramethyl-3,5-heptanedionato)magnesium, bis(N,N'-di-sec-butylacetamidinato)magnesium, bis(pentamethylcyclopentadienyl)magnesium, or a combination of two or more of these gases. Step 110 may be performed at a temperature ranging from 100° C. to 300° C., including subranges. For example, step 110 may be performed at a temperature of 100° C., 150° C., 200° C., 210° C., 220° C., 230° C., 240° C., 250° C., 260° C., 270° C., 280° C., 290° C., 300° C., or a temperature range having any two of these values ​​as endpoints. Unless otherwise stated, the temperature or temperature range at which the steps of method 100 are performed is the temperature of substrate 102. For methods utilizing an isothermal reactor, the temperature of the reactor vessel in which substrate 102 is placed is assumed to be the temperature of substrate 102. The temperature of the isothermal reactor vessel may be measured using a thermocouple attached to the vessel wall. For methods utilizing a non-isothermal reactor, the temperature of substrate 102 may be measured using an IR (infrared) temperature probe.

[0051] After forming the magnesium-containing precursor layer 114 in step 110, the magnesium-containing precursor layer 114 is heated in step 120 with an oxygen-containing gas 122 (indicated as “H 2 O or O 3 "). This exposure to oxygen-containing gas 122 results in the formation of magnesium oxide layer 124. The formation of magnesium oxide layer 124 in step 110 reduces carbon impurities in the deposited magnesium fluoride film due to the intentional significant oxide formation prior to fluoride formation in step 130 (see FIGS. 7A and 7B). Less carbon in the film composition may result in less light absorption and / or higher light transmittance in the DUV and / or broadband spectrum compared to a one-step ALD process.

[0052] The oxygen-containing gas 122 may be, but is not limited to, water (H 2 O), ozone (O 3 ), hydrogen peroxide (H 2 O 2 ), methanol (CH 3 OH), ethanol (C 2 H 5 The oxygen-containing gas 122 may be a plasma containing oxygen, a plasma containing an oxygen-containing chemical, or a combination of two or more of these gases. In some embodiments, the oxygen-containing gas 122 may consist essentially of one or more of these gases. In some embodiments, the oxygen-containing gas 122 may consist of one or more of these gases.

[0053] Step 120 may be performed at a temperature in the range of 100° C. to 300° C., including sub-ranges. For example, step 120 may be performed at a temperature of 100° C., 150° C., 200° C., 210° C., 220° C., 230° C., 240° C., 250° C., 260° C., 270° C., 280° C., 290° C., 300° C., or a temperature within a range having any two of these values ​​as endpoints. In some embodiments, step 120 may be performed at about 250° C., for example, at a temperature in the range of 240° C. to 260° C.

[0054] The type of oxygen-containing gas 122 and the temperature at which the magnesium-containing precursor layer 114 is exposed to the oxygen-containing gas 122 may be utilized to control the elemental composition and thickness uniformity of the resulting magnesium fluoride film. A gas 122 that enhances the adsorption of the precursor layer 114 may help maximize ligand removal (e.g., carbon ligand removal) from the precursor layer 114 and / or optimize the nucleation of subsequent layers to achieve the desired amount of oxygen and carbon in the magnesium fluoride film. This results in a film with high optical transmission and low optical absorption. In some embodiments, the oxygen-containing gas 122 is H 2 In some embodiments, the oxygen-containing gas 122 comprises H 2 The magnesium-containing precursor layer 114, which contains O, is exposed to an oxygen-containing gas 122 at a temperature ranging from 240° C. to 260° C. The results discussed herein with respect to FIG. 4 show how desirable properties can be achieved when step 120 is performed at a temperature ranging from 240° C. to 260° C.

[0055] After forming the magnesium oxide layer 124 in step 120, the magnesium oxide layer 124 is exposed to a fluorine-containing source gas 132 (represented as Hhfac in FIG. 1 ) in step 130. This exposure to the source gas 132 forms an intermediate layer 134 that contains magnesium and fluorine. Step 130 may be performed at a temperature in the range of 100° C. to 300° C., including sub-ranges. For example, step 130 may be performed at a temperature of 100° C., 150° C., 200° C., 210° C., 220° C., 230° C., 240° C., 250° C., 260° C., 270° C., 280° C., 290° C., 300° C., or within a range having any two of these values ​​as endpoints.

[0056] In some embodiments, the source gas 132 may include one or more organic source gases, such as, but not limited to, hexafluoroacetylacetone (Hhfac), carbonyl fluoride, chlorine fluoride, chlorine trifluoride, 1-chloro-2,2-difluoroethene, chlorodifluoromethane, 1-chloro-1-fluoroethane, chloropentafluorobenzene, chloropentafluoroethane, chlorotrifluoroethene, chlorotrifluoromethane, dichlorodifluoromethane, 1,2-dichloro-1,1,2,2-tetrafluoroethane, difluoroethane, difluoromethane, and fluoropropane. , nitrogen trifluoride, pentafluorobenzene, pentafluoroethane, pentafluorophenol, pentafluorotoluene, perfluorocyclobutane, perfluorocyclohexane, perfluorocyclohexene, perfluoroheptane, perfluoromethylcyclohexane, perfluorotoluene, 1,1,1,2-tetrachloro-2,2-difluoroethane, trichlorofluoromethane, trifluoroacetic acid, trifluoroethane, trifluoroethanol, or a combination of two or more of these gases. In some embodiments, source gas 132 may consist essentially of one or more of these gases. In some embodiments, source gas 132 may consist of one or more of these gases.

[0057] In some embodiments, step 130 may include a remote plasma process. In such embodiments, the magnesium oxide layer 124 is fluorinated with fluorine by flowing one or more fluorine-containing source gases 132 through a plasma source. This results in the formation of active fluorine radicals in the source gases. These radicals are relatively more active than the original source gases.

[0058] After the intermediate layer 134 is formed in step 130, the intermediate layer 134 is heated in step 140 by the addition of an oxygen-containing gas 142 (in FIG. 1, “OO 2 O 3"). This exposure to oxygen-containing gas 142 results in the formation of a magnesium fluoride layer 144. The type of oxygen-containing gas 122 and the temperature at which intermediate layer 134 is exposed to oxygen-containing gas 142 may be utilized to control the elemental composition and thickness uniformity of the resulting magnesium fluoride film. Carbon monoxide (CO) and CH x Molecules (e.g., CH 3 , C.H. 2 Gas 142, which effectively removes residual compounds such as fluoride, arsenic, fluorine, or CH, helps achieve the desired amount of oxygen and carbon in the magnesium fluoride film, resulting in a film with high light transmission and low light absorption.

[0059] The oxygen-containing gas 142 may be, but is not limited to, water (H 2 O), ozone (O 3 ), hydrogen peroxide (H 2 O 2 ), methanol (CH 3 OH), ethanol (C 2 H 5 The oxygen-containing gas 142 may be an oxygen-containing gas, an oxygen-containing chemical plasma, or a combination of two or more of these gases. In some embodiments, the oxygen-containing gas 142 may consist essentially of one or more of these gases. In some embodiments, the oxygen-containing gas 142 may consist of one or more of these gases. In some embodiments, the oxygen-containing gas 142 utilized in step 140 may be the same as the oxygen-containing gas 122 utilized in step 120. In some embodiments, the oxygen-containing gas 142 utilized in step 140 may be different than the oxygen-containing gas 122 utilized in step 120. In some embodiments, the oxygen-containing gas may be ozone (O 3 ) may be included.

[0060] After forming the magnesium fluoride layer 144 in step 140, steps 110 through 140 may be repeated multiple times in succession to form a magnesium fluoride film (e.g., film 210) having multiple magnesium fluoride layers 144 deposited by method 100. Because atomic layer deposition method 100 is a self-limiting magnesium fluoride layer deposition process, the thickness of film 210 may be precisely and accurately controlled. The self-limiting nature of the atomic layer deposition process promotes consistent and repeatable deposition of a film layer having a uniform thickness across the surface of a substrate, even on substrates having step-like surface curvatures.

[0061] In some embodiments, the substrate 102 may be held substantially stationary during the method 100. Holding the substrate 102 substantially stationary may promote uniform deposition of the magnesium fluoride layer 144, and therefore the magnesium fluoride film. The pressure in the deposition chamber for steps 110, 120, 130, and 140 may range from 1 Torr (about 133 Pa) to 10 Torr (about 1.33 kPa).

[0062] FIG. 2 shows a magnesium fluoride film 210 coated over the first surface 202 of the optical lens 200. In some embodiments, the magnesium fluoride film 210 may be coated on the first surface 202 of the optical lens 200. As used herein, "coated on," "disposed on," or "deposited on" means that a first film / layer / component is in direct contact with a second film / layer / component. A first film / layer / component that is "coated on," "disposed on," or "deposited on" a second film / layer / component may be deposited, formed, placed, or otherwise applied directly on the second film / layer / component. In other words, when a first film / layer / component is "coated on," "disposed on," or "deposited on" a second film / layer / component, there is no film / layer / component disposed between the first film / layer / component and the second film / layer / component. When a first film / layer / component is described as "disposed over," "coated over," or "deposited over" a second film / layer / component, there may or may not be other films / layers / components between the first film / layer / component and the second film / layer / component.

[0063] In some embodiments, the magnesium fluoride film 210 may additionally or alternatively be coated over the second surface 204 of the optical lens 200. In some embodiments, the magnesium fluoride film 210 may additionally or alternatively be coated on the second surface 204 of the optical lens 200. In some embodiments, the magnesium fluoride film 210 may be coated on or over both the first surface 202 and the second surface 204 of the lens simultaneously during the method 100.

[0064] In some embodiments, the magnesium fluoride film 210 on the first side 202 and / or the second side 204 may have a thickness 216, measured between the first side 212 of the film 210 and the second side 214 of the film 210, in the range of 25 nanometers to 100 nanometers, including sub-ranges. For example, the thickness 216 may be 25 nanometers, 30 nanometers, 35 nanometers, 40 nanometers, 45 nanometers, 50 nanometers, 55 nanometers, 60 nanometers, 65 nanometers, 70 nanometers, 75 nanometers, 80 nanometers, 85 nanometers, 90 nanometers, 95 nanometers, 100 nanometers, or a value within a range having any two of these values ​​as endpoints. In some embodiments, the thickness 216 may be in the range of 25 nanometers to 75 nanometers. Unless otherwise noted, thickness 216 values ​​reported herein are determined by fitting data from a variable angle spectroscopic ellipsometer (Woollam M2000®, scanning wavelengths from 190 nm to 1600 nm, incidence angles from 45 to approximately 80 degrees) using CompleteEASE™ software in a Cauchy model.

[0065] The method 100 facilitates the deposition of a magnesium fluoride film 210 having one or more of the following seven properties: In some embodiments, the magnesium fluoride film 210 may have two or more of the seven properties. In some embodiments, the magnesium fluoride film 210 may have three or more of the seven properties. In some embodiments, the magnesium fluoride film 210 may have four or more of the seven properties. In some embodiments, the magnesium fluoride film 210 may have five or more of the seven properties. In some embodiments, the magnesium fluoride film 210 may have six or more of the seven properties. In some embodiments, the magnesium fluoride film 210 may have all seven properties.

[0066] In some embodiments, the magnesium fluoride film 210 may have one or more of the seven properties at a thickness 216 in the range of 25 nanometers to 75 nanometers. In some embodiments, the magnesium fluoride film 210 may have two or more of the seven properties at a thickness 216 in the range of 25 nanometers to 75 nanometers. In some embodiments, the magnesium fluoride film 210 may have three or more of the seven properties at a thickness 216 in the range of 25 nanometers to 75 nanometers. In some embodiments, the magnesium fluoride film 210 may have four or more of the seven properties at a thickness 216 in the range of 25 nanometers to 75 nanometers. In some embodiments, the magnesium fluoride film 210 may have five or more of the seven properties at a thickness 216 in the range of 25 nanometers to 75 nanometers. In some embodiments, the magnesium fluoride film 210 may have six or more of the seven properties at a thickness 216 in the range of 25 nanometers to 75 nanometers. In some embodiments, the magnesium fluoride film 210 may have all seven properties at a thickness 216 ranging from 25 nanometers to 75 nanometers.

[0067] (1) An optical absorption value of 1% or less for light having a wavelength in the DUV and / or broadband wavelength range and an angle of incidence (θ) of 6 degrees (shown in FIG. 2 by line 220). In other words, the magnesium fluoride film 210 may have an optical absorption value ranging from 0% to 1% for light having a wavelength in the DUV and / or broadband wavelength range and an angle of incidence (θ) of 6 degrees. For example, the magnesium fluoride film 210 may have an optical absorption value of 1% or less for light having a wavelength of 266 nanometers and an angle of incidence of 6 degrees. In other words, the magnesium fluoride film 210 may have an optical absorption value of 0% to 1% for light having a wavelength of 266 nanometers and an angle of incidence of 6 degrees. In some embodiments, the magnesium fluoride film 210 may have an optical absorption value of 1% or less for light having a wavelength of 220 nanometers and an angle of incidence of 6 degrees. In other words, the magnesium fluoride film 210 may have a light absorption value ranging from 0% to 1% for light having a wavelength of 220 nanometers and an angle of incidence of 6 degrees.

[0068] "Light absorption value" is the percentage of light absorbed by a layer or film of material for a given wavelength of light and a given angle of incidence (θ) of light. Light absorption means that photons of light are neither reflected nor transmitted from the layer or film, but are instead accepted by the layer or film and released as energy, usually in the form of heat. The given wavelength of light can be a specific wavelength value or a range of wavelength values. For a range of wavelength values, the light absorption is calculated by averaging the light absorption of each integer wavelength within the wavelength range. The angle of incidence (θ) is the angle at which light strikes the surface of a layer or film of material, measured with respect to a line perpendicular to the surface at the point of incidence. Light absorption values ​​can be measured using a spectrometer.

[0069] Unless otherwise stated, the optical absorption values ​​reported herein are measured according to the following procedure: A film of the material to be tested was deposited on an 8655 fused silica substrate. A film of the material was deposited on both sides of the fused silica substrate to determine the total optical absorption through the film on both sides of the substrate. Optical transmittance and reflectance values ​​were measured using an Agilent Cary5000 UV-Vis-NIR Spectrophotometer with a wavelength range of 400 nm to 200 nm. The following instrument parameters were used: (i) angle of incidence: 6 degrees, (ii) data interval: 1 nm, 150 nm / min, and (iii) average measurement time: 0.4 seconds. No polarizer was used. The measured transmittance and reflectance values ​​were related to the corresponding ratios of the true surface reflectance and transmittance of 8655 fused silica to the measured surface reflectance and transmittance. For this correlation, the standard Fresnel equations for the reflected intensity of s and p polarized light were used. Equation: %A=100-%T-%R The light absorption was calculated using the formula: where %A equals light absorption, %T equals the percentage of transmitted light, and %R equals the percentage of reflected light.

[0070] (2) An optical transmittance value of 94% or more for light having a wavelength in the DUV and / or broadband wavelength range and an angle of incidence (θ) of 6 degrees. In other words, the magnesium fluoride film 210 may have an optical absorption value ranging from 94% to 100% for light having a wavelength in the DUV and / or broadband wavelength range and an angle of incidence (θ) of 6 degrees. For example, the magnesium fluoride film 210 may have an optical absorption value of 94% or more for light having a wavelength of 266 nanometers and an angle of incidence (θ) of 6 degrees. In other words, the magnesium fluoride film 210 may have an optical absorption value ranging from 94% to 100% for light having a wavelength of 266 nanometers and an angle of incidence (θ) of 6 degrees. In some embodiments, the magnesium fluoride film 210 may have an optical absorption value of 94% or more for light having a wavelength of 220 nanometers and an angle of incidence (θ) of 6 degrees. In other words, the magnesium fluoride film 210 may have a light absorption value ranging from 94% to 100% for light having a wavelength of 220 nanometers and an angle of incidence of 6 degrees.

[0071] An "optical transmittance value" is the percentage of light that is transmitted through a layer or film of material for a given wavelength of light and a given angle of incidence (θ) of the light. The given wavelength of light can be a specific wavelength value or a range of wavelength values. For a range of wavelength values, the optical transmittance is calculated by averaging the optical transmittance for each integer wavelength within the wavelength range. Optical transmittance values ​​can be measured using a spectrometer.

[0072] Unless otherwise stated, the optical transmittance values ​​reported herein were measured according to the following procedure: A film of the material to be tested was deposited on an 8655 fused silica substrate. A film of the material was deposited on both sides of the fused silica substrate, and the total optical transmittance through the film on both sides of the substrate was determined. Optical transmittance and reflectance values ​​were measured using an Agilent Cary5000 UV-Vis-NIR Spectrophotometer with a wavelength range of 400 nm to 200 nm. The following instrument parameters were used: (i) angle of incidence: 6 degrees, (ii) data interval: 1 nm, 150 nm / min, and (iii) average measurement time: 0.4 seconds. No polarizer was used. The measured transmittance values ​​were related to the corresponding ratio of the true surface transmittance of 8655 fused silica to the measured surface transmittance. The standard Fresnel equations for the reflected intensity of s- and p-polarized light were used for this correlation.

[0073] (3) An optical reflectance value of 5% or less for light having a wavelength in the DUV and / or broadband wavelength range and an angle of incidence (θ) of 6 degrees. In other words, the magnesium fluoride film 210 may have an optical reflectance value ranging from 0% to 5% for light having a wavelength in the DUV and / or broadband wavelength range and an angle of incidence (θ) of 6 degrees. For example, the magnesium fluoride film 210 may have an optical reflectance value of 5% or less for light having a wavelength of 266 nanometers and an angle of incidence (θ) of 6 degrees. In other words, the magnesium fluoride film 210 may have an optical reflectance value ranging from 0% to 5% for light having a wavelength of 266 nanometers and an angle of incidence (θ) of 6 degrees. In some embodiments, the magnesium fluoride film 210 may have an optical reflectance value of 4% or less for light having a wavelength of 220 nanometers and an angle of incidence (θ) of 6 degrees. In other words, the magnesium fluoride film 210 may have an optical reflectance value ranging from 0% to 4% for light having a wavelength of 220 nanometers and an angle of incidence of 6 degrees.

[0074] An "optical reflectance value" is the percentage of light that is reflected by a layer or film of material for a given wavelength of light and a given angle of incidence (θ) of the light. The given wavelength of light can be a specific wavelength value or a range of wavelength values. For a range of wavelength values, the optical reflectance is calculated by averaging the optical reflectance for each integer wavelength within the wavelength range. Optical reflectance values ​​can be measured using a spectrometer.

[0075] Unless otherwise stated, the optical reflectance values ​​reported herein were measured according to the following procedure: A film of the material to be tested was deposited on an 8655 fused silica substrate. A film of the material was deposited on both sides of the fused silica substrate, and the total optical reflectance through the film on both sides of the substrate was determined. Optical transmittance and reflectance values ​​were measured using an Agilent Cary5000 UV-Vis-NIR Spectrophotometer with a wavelength range of 400 nm to 200 nm. The following instrument parameters were used: (i) angle of incidence: 6 degrees, (ii) data interval: 1 nm, 150 nm / min, and (iii) average measurement time: 0.4 seconds. No polarizer was used. Reflectance measurements were correlated to the corresponding ratio of the true surface reflectance of 8655 fused silica to the measured surface reflectance. Standard Fresnel equations for the reflected intensity of s- and p-polarized light were used for this correlation.

[0076] (4) Surface roughness (Ra) of 1.5 nanometers or less. In some embodiments, the magnesium fluoride film 210 may have a surface roughness (Ra) of 1.5 nanometers to 1 nanometer. The Ra surface roughness may be measured using atomic force microscopy. Unless otherwise specified, the Ra (arithmetic mean roughness) values ​​reported herein are the surface roughness of a surface profile obtained by measuring a 2 micrometer by 2 micrometer square area with an atomic force microscope having a resolution of 512 by 512 pixels.

[0077] (5) A refractive index of 1.42 or less for light having a wavelength of 266 nanometers. In some embodiments, the magnesium fluoride film 210 may have a refractive index in the range of 1.42 to 1.38 for light having a wavelength of 266 nanometers. Unless otherwise noted, the refractive index values ​​listed herein are measured by fitting data from a variable angle spectroscopic ellipsometer ("Woollam M2000", scanning wavelengths from 190 nm to 1600 nm, angles of incidence from 45 to about 80 degrees) using Cauchy model "CompleteEASE" software.

[0078] (6) A carbon content of 1.2 atomic % or less at a depth of 0.02 micrometers as measured using secondary ion mass spectrometry. In some embodiments, the magnesium fluoride film 210 may have a carbon content ranging from 0.01 atomic % to 1.2 atomic % at a depth of 0.02 micrometers as measured using secondary ion mass spectrometry. In some embodiments, the magnesium fluoride film 210 may have a carbon content of 1 atomic % or less at a depth of 0.02 micrometers as measured using secondary ion mass spectrometry. In some embodiments, the magnesium fluoride film 210 may have a carbon content ranging from 0.01 atomic % to 1 atomic % at a depth of 0.02 micrometers as measured using secondary ion mass spectrometry.

[0079] Unless otherwise stated, the carbon content of the films is measured using a Cs microbeam ion gun with the following parameters: (i) energy (volts): 1000, (ii) scan size-X: 400.0 micrometers (μm), (iii) scan size-Y: 400.0 micrometers (μm), (iv) beam current: 20 nanoamperes (nA), (v) primary beam angle: 45 degrees, and (vi) sputter rate: 2.9 × 10 -5 Micrometers per second. Data were normalized based on a standard with controlled carbon concentration.

[0080] (7) Thickness variation of 10% or less. In some embodiments, magnesium fluoride film 210 may have a thickness variation in the range of 0% to 10%, including sub-ranges. For example, magnesium fluoride film 210 may have a thickness variation of 0%, 0.1%, 1%, 2%, 3%, 4%, 5%, 10%, or a range having any two of these values ​​as endpoints. In some embodiments, magnesium fluoride film 210 may have a thickness variation of 5% or less. In some embodiments, magnesium fluoride film 210 may have a thickness variation of 3% or less.

[0081] The "thickness variation" for a layer or film of material is determined by the following formula: T=SD / A×100 where T is equal to the thickness variation, SD is equal to the standard deviation of the representative set of thickness measurements, and A is equal to the mean of the representative set of thickness measurements. The thickness variation is defined by the thickness variation for the entire surface area of ​​a film or layer disposed over a surface bounded by a peripheral edge, as represented by the set of thickness measurements. For example, the first surface 202 of the lens 200 is bounded by a peripheral edge 206. In some embodiments, the magnesium fluoride film 210 may cover the entire first surface 202 of the lens 200 bounded by the peripheral edge 206. In such embodiments, the thickness variation of the film 210 is defined by the thickness variation of the film 210 disposed over the entire first surface 202, and not just a portion of the film 210. Similarly, for a magnesium fluoride film 210 covering the entire second surface 204 of the lens 200 bounded by the peripheral edge 206, the thickness variation of the film 210 is defined by the thickness variation of the film 210 disposed over the entire second surface 204, and not just a portion of the film 210.

[0082] The thickness values ​​of the film can be measured by a spectroscopic ellipsometer. A representative set of thickness measurements includes at least three measurements. For purposes of selecting the points of thickness measurements, the points should be spaced to provide a representation of the entire film being measured, and should not all be located in one area of ​​the film (i.e., all at the edge of the film).

[0083] The optical lens 200 coated in one or more magnesium fluoride films 210 may be utilized in a variety of optical applications. For example, the coated optical lens 200 may be utilized in optical inspection tools, microscopes, and dark field polarized scatterometers. In particular, the coated optical lens 200 may be utilized in optical applications in which collection, transmission, and / or collection of deep UV light and / or light in a broadband spectrum is desirable. For example, the coated optical lens 200 may be utilized in a semiconductor inspection tool 300 shown in FIG. 3. The semiconductor inspection tool 300 may include an optical element 310 including one or more coated lenses 200 to collect incident light 220 having wavelengths in the deep UV light spectrum or the broadband light spectrum.

[0084] The lens 200, with or without the coating 210, may be optically transparent. As used herein, the term "optically transparent" means a transmission or average transmission of 90% or greater for a particular wavelength or range of wavelengths through a 1.0 mm thick strip of material. In some embodiments, an optically transparent material may have a transmission or average transmission of 95% or greater, or 98% or greater, for a particular wavelength or range of wavelengths. The average transmission for a range of wavelengths is calculated by measuring the transmission of all integer wavelengths in the range and averaging the measurements. In some embodiments, the wavelength may be any integer wavelength in the range of 193 nm to 266 nm. In some embodiments, the wavelength range may be 193 nm to 266 nm. In some embodiments, the wavelength may be any integer wavelength in the range of 400 nm to 700 nm. In some embodiments, the wavelength range may be 400 nm to 700 nm.

[0085] In some embodiments, one or more of the coated lenses 200 can have a first surface 202 with a steepness value in the range of 0.5 to 1.0, where the steepness value is equal to the radius of curvature of the first surface 202 divided by the effective aperture of the coated lens 200. A steepness value in this range facilitates focusing of DUV and / or broadband spectrum light to an intensity suitable for precise detection resolution in an optical inspection system (e.g., an inspection system that includes the semiconductor inspection tool 300).

[0086] "Effective aperture" is the diameter of a lens through which light passes during intended use of the lens. In some cases, the "effective aperture" may be the diameter of the entire lens measured between opposite points on the peripheral edge of the lens. In some cases, the "effective aperture" may be smaller than the diameter of the entire lens, for example, when the lens is surrounded by a frame that ends over the peripheral edge of the lens. For non-circular lenses, the "effective aperture" is the maximum outer cross-sectional dimension of the lens shape through which light passes during intended use of the lens. The steepness value of a lens is determined by the following formula: S=R / # where S is the steepness value, R is the radius of curvature of the lens surface, and # is the effective aperture of the lens.

[0087] In some embodiments, the magnesium fluoride film 210 may be disposed over or on a first surface 202 of a lens in the inspection tool 300. As used herein, the "first surface" of a lens may be the surface of a lens where incident light enters the lens 200 during intended use. In some embodiments, the magnesium fluoride film 210 may be disposed over or on a second surface 204 of a lens 200 in the inspection tool 300. As used herein, the "second surface" of a lens may be the surface of a lens where incident light exits the lens 200 during intended use. In some embodiments, the magnesium fluoride film 210 may be disposed over or on both the first surface 202 and the second surface 204 of a lens 200 in the inspection tool 300. In some embodiments, the second surface 204 can be a curved surface having a steepness value in the range of 0.5 to 1.0, where the steepness value is equal to the radius of curvature of the second surface 204 divided by the effective aperture 230 of the coating lens 200.

[0088] In some embodiments, one or more lenses 200 of optical element 310 may be coated with an optical film (e.g., optical film 802) that includes one or more magnesium fluoride films 210. In such embodiments, the optical film may be disposed over or on the first surface 202, over or on the second surface 204, or both.

[0089] The following tests demonstrate the effectiveness of magnesium fluoride films 210 deposited in accordance with embodiments of the present invention. Specifically, the tests illustrate the superior compositional, structural, and optical properties of magnesium fluoride films 210 deposited in accordance with embodiments of the present invention as compared to a one-step ALD process.

[0090] 4 shows a graph 400 illustrating how step 120 of method 100 can be used to control and optimize the refractive index, growth rate, and uniformity of magnesium fluoride films. The results shown in graph 400 are for three magnesium fluoride films having a thickness of 50 nanometers deposited on an optical lens by method 100. Each film 210 was prepared by (i) exposing the optical lens to bis(ethylcyclopentadienyl)magnesium gas at a temperature of 250° C. to form a magnesium-containing precursor layer, (ii) converting the magnesium-containing precursor layer into H 2 (iii) exposing the magnesium oxide layer to Hhfac gas at a temperature of 250° C. to form an intermediate layer, and (iv) exposing the intermediate layer to ozone gas at a temperature of 250° C. to form a magnesium fluoride layer, repeating steps (i)-(iv) multiple times to achieve a film thickness of 50 nanometers. 2 The O gas exposure temperature was 200° C., and the H 2 The O gas exposure temperature was 250° C., and the H 2 The O gas exposure temperature was 300°C.

[0091] As shown in graph 400, the refractive index at 550 nanometers is 2 The refractive index decreases as the O2 gas exposure temperature increases from 200°C to 300°C. The first, second and third films had refractive indices at 550 nanometers in the range of 1.4 to 1.2. Without being bound by theory, it is believed that the higher processing temperature in step (ii) results in more carbon in the magnesium fluoride film due to thermal decomposition of ligands present in the magnesium-containing precursor layer. This higher carbon content can be seen by the decrease in refractive index across the first, second and third films.

[0092] Regarding the growth rate, graph 400 shows the growth rate of H at about 250°C. 2It is shown that the O gas exposure temperature increases the growth rate per cycle (one cycle = one repetition of steps (i)-(iv)). The growth rate peaks at about 0.6 angstroms (Å) / cycle for a temperature of about 250° C. and decreases slightly as the temperature increases toward 300° C. The growth rate of 0.6 Å / cycle is about 50% faster than the growth rate of about 0.4 Å / cycle for a one-step ALD process performed at 200° C.

[0093] Regarding uniformity, graph 400 shows the H 2 It is shown that the O2 gas exposure temperature results in the best thickness uniformity (i.e., the lowest amount of "thickness variation"). The second film had a thickness uniformity of about 10%, which is less than half that for the first and third films. Both the first and third films have a thickness uniformity of over 20%. This is significant because the thickness uniformity of the magnesium fluoride film affects the optical properties of the film. For example, non-uniformity can locally increase light absorption and / or locally decrease light transmittance.

[0094] Taken as a whole, graph 400 illustrates that the exposure temperature of step 120 in method 100 can be used to control and optimize magnesium fluoride film properties. A one-step ALD process does not include step 120, and therefore cannot control and optimize magnesium fluoride film properties in this manner. Specifically, graph 400 illustrates that in some embodiments, an exposure temperature in the range of 240° C. to 260° C. for step 120 can be used to optimize magnesium fluoride film properties. Graph 400 also illustrates that in some embodiments, an exposure temperature in the range of 240° C. to 260° C. for step 120 can be used to optimize magnesium fluoride film properties. 2 We show that the O gas exposure temperature can be used to optimize the properties of magnesium fluoride films.

[0095] To evaluate the effect of different oxygen-containing gases in step 120 of method 100, H was used instead of ozone gas. 2A magnesium fluoride film was deposited on the optical lens using the same process parameters as those used for the second film in graph 400, except that O gas was used. 2 The film deposited using O gas (i.e., the second film in graph 400) showed lower thickness variation and a higher refractive index at 550 nanometers compared to that deposited using ozone gas in step 120. This higher refractive index means higher oxide density and less carbon in the film. Thus, the composition of the oxygen-containing gas in step 120 can also be used to control and optimize the magnesium fluoride film properties. Again, one-step ALD processes do not include step 120 and therefore cannot control and optimize the magnesium fluoride film properties in this manner.

[0096] 5A-5C show the effect of the incident angle on the wavelength of a magnesium fluoride film ("Two-Step: MgF") deposited according to an embodiment of the present invention. 2 ") and magnesium fluoride films deposited according to a one-step ALD process (referred to as "One-step: MgF 2 5B and 5C are graphs comparing the optical properties of the coated silica (referred to as "coated silica"). For reference, Figures 5B and 5C also show the optical properties for uncoated silica. The incidence angle was 6 degrees.

[0097] Second stage: MgF 2 The film was prepared using a process temperature of 250° C., bis(ethylcyclopentadienyl)magnesium as the precursor gas 112, and H as the oxygen-containing gas 122. 2 O, Hhfac as the source gas 132, and O as the oxygen-containing gas 142 3 The mixture was deposited using method 100 using MgF. 2 The films were deposited using the method described in Hennessy et al., with a process temperature of 150° C. and HF as the source gas.

[0098] As shown in graph 500 of FIG. 5A, two stages: MgF 2The films have appreciably lower optical absorption for wavelengths between 200 and 300 nanometers. For example, the two-stage: MgF 2 The film exhibited less than 1% optical absorption for wavelengths as small as about 210 nanometers. 2 The film achieved less than 1% optical absorption at a wavelength of about 254 nanometers. Thus, graph 500 shows a two-stage: MgF 2 The membrane is one-stage: MgF 2 The films show less optical absorption in the DUV and / or broadband optical wavelength ranges compared to the two-step films, which is believed to be a result of less carbon in the two-step film composition (see FIGS. 7A and 7B).

[0099] In that regard, as shown in graph 520 of FIG. 5B, two stages: MgF 2 The films have appreciably higher optical transmittance for wavelengths between 200 and 250 nanometers. For example, the two-stage: MgF 2 The film exhibited optical transmittance of over 94% for wavelengths as small as about 210 nanometers. 2 The film achieved greater than 94% light transmission at a wavelength of about 255 nanometers. Thus, graph 520 shows a two-stage: MgF 2 The membrane is one-stage: MgF 2 These results show that, compared to the ZnO-based ZnO films, greater optical transmittance can be achieved at shorter wavelengths in the DUV and / or broadband light spectrum, which is believed to be a result of less carbon in the two-step film composition (see Figures 7A and 7B).

[0100] As shown in graph 540 of FIG. 5C, two stages: MgF 2 The films also have appreciably lower optical reflectance for wavelengths less than 250 nanometers. 2 The film exhibited an optical reflectance of about 4% for wavelengths ranging from 200 nanometers to 250 nanometers. 2 The film achieved an optical reflectance of less than 4% at a wavelength of about 240 nanometers. Thus, graph 540 shows a two-stage: MgF 2The membrane is one-stage: MgF 2 This shows that lower optical reflectance can be achieved at shorter wavelengths in the DUV and / or broadband light spectrum compared to the two-step film, which again is believed to be a result of less carbon in the two-step film composition (see Figures 7A and 7B).

[0101] As can be seen in graphs 500, 520, and 540, there are two stages: MgF 2 The film covers the entire DUV light spectrum (i.e., wavelengths between 193 nm and 266 nm) in one step: MgF 2 However, the two-stage MgF 2 The films were deposited without the use of HF, which is a relatively hazardous material, so a deposition method that does not require HF would be beneficial.

[0102] The graph of FIG. 6 shows the effect of the incident angle on the luminance of a magnesium fluoride film ("Two-Step: MgF 2 ") and magnesium fluoride films (referred to as "HF MgF 2 As shown in graph 600, a two-stage: MgF 2 The film had a lower refractive index. This lower refractive index was achieved in two stages: MgF 2 It is believed to be caused by a lower amount of carbon in the film.

[0103] Secondary ion mass spectrometry (SIMS) was used to analyze the compositional differences between magnesium fluoride films deposited according to embodiments of the invention and films deposited using a one-step ALD process. 2 FIG. 7B shows a graph 700 of SIMS results for the film. 2 A graph 750 of the SIMS results for the film is shown.

[0104] The average normalized carbon ion intensity and average normalized oxygen ion intensity for the one-step ALD film in graph 700 are about 1.66 atomic % and about 0.0041 atomic %, respectively. In contrast, the two-step MgF 2 The average normalized carbon ionic strength and average normalized oxygen ionic strength for the film are about 1 atomic % and about 0.019 atomic %, respectively. Therefore, the two-stage MgF 2 The films contained approximately 40% fewer carbon ions and significantly more oxygen ions. For example, at an approximate depth of 0.02 micrometers, the two-stage MgF 2 The films had a carbon content of about 1 atomic %, and the one-step ALD films had a carbon content of about 1.66 atomic %. As mentioned previously, the two-step MgF 2 The lower amount of carbon in the film improves the optical properties of the film for use in optical applications in the DUV and / or broadband light spectrum.

[0105] In some embodiments, the magnesium fluoride film 210 may be layered with other optical layers to produce an optical film having desired properties. FIG. 8 illustrates an optical film 802 disposed over a surface 804 of an optical lens 800, according to some embodiments. In some embodiments, the optical film 802 may be disposed on the surface 804. The surface 804 may be a first side of the optical lens (e.g., first side 202) or a second side of the optical lens (e.g., second side 204). In some embodiments, the optical film 802 may be disposed on or over opposing sides of the optical lens (e.g., first side 202 and second side 204).

[0106] The optical film 802 includes a refractive index layer 810 and a refractive index layer 820. The refractive index layer 820 is disposed over the refractive index layer 810 and includes at least one magnesium fluoride film 210. In some embodiments, the optical film 802 may include multiple refractive index layers 810 and / or multiple refractive index layers 820. In some embodiments, the optical film 802 may include multiple refractive index layers 810 and / or multiple magnesium fluoride films 210. In some embodiments, the optical film 802 may include multiple refractive index layers 810 and multiple magnesium fluoride films 210 in an alternating arrangement.

[0107] In some embodiments, the refractive index layer 820 may include at least one low refractive index layer 822. The low refractive index layer 822 may be the outermost layer of the optical film 802 that is exposed to the atmosphere surrounding the lens 800 during use.

[0108] The refractive index of the low refractive index layer 810 and / or the low refractive index layer 822 may help minimize the amount of light that reflects off of the optical lens 800. Optical lenses, typically made from silica, generally have a refractive index of about 1.5 for light having a wavelength of 550 nanometers. Generally, to provide desirable anti-reflective properties, anti-reflective coatings are designed to have a refractive index of about 1.2 for light having a wavelength of 550 nanometers. However, magnesium fluoride films according to embodiments of the present application may have a refractive index of 1.42 to 1.38 for light having a wavelength of 550 nanometers.

[0109] The use of refractive index layer 810 with a relatively high refractive index increases the equivalent refractive index of lens 800. This aids in the use of magnesium fluoride films with a relatively high refractive index, greater than about 1.2. Low refractive index layer 822 reduces the refractive index mismatch between the atmosphere and the magnesium fluoride film with a relatively high refractive index, greater than about 1.2. This helps prevent reflection of light as it enters optical film 802.

[0110] The refractive index layer 810 has a first refractive index for light having a wavelength of 550 nanometers, and the refractive index layer 820 has a second refractive index for light having a wavelength of 550 nanometers that is less than the first refractive index. In some embodiments, the first refractive index may be 1.6 or greater. For example, in some embodiments, the first refractive index may be in the range of 1.6 to 2.0. In some embodiments, the second refractive index may be 1.38 or less. For example, in some embodiments, the second refractive index may be in the range of 1.2 to 1.38. For a refractive index layer 820 including a magnesium fluoride film 210 and a low refractive index layer 822, the refractive index of the refractive index layer 820 is the average of the refractive index of the magnesium fluoride film 210 and the refractive index of the low refractive index layer 822.

[0111] The refractive index layer 810 may include a material selected from the group of aluminum oxide, hafnium oxide, gadolinium fluoride, lanthanum fluoride, or combinations thereof. In some embodiments, the refractive index layer 810 may be disposed on the surface 804. In some embodiments, the refractive index layer 810 may consist essentially of one or more of these materials. In some embodiments, the refractive index layer 810 may consist of one or more of these materials. In some embodiments, the refractive index layer 810 may have a thickness in the range of 25 nanometers to 100 nanometers, including sub-ranges. For example, the refractive index layer 810 may have a thickness of 25 nanometers, 30 nanometers, 35 nanometers, 40 nanometers, 45 nanometers, 50 nanometers, 55 nanometers, 60 nanometers, 65 nanometers, 70 nanometers, 75 nanometers, 80 nanometers, 85 nanometers, 90 nanometers, 95 nanometers, 100 nanometers, or a value in a range having any two of these values ​​as endpoints.

[0112] The low index layer 822 may include a material selected from the group of magnesium fluoride, aluminum fluoride, calcium fluoride, or lithium fluoride, or a combination thereof. In some embodiments, the low index layer 822 may consist essentially of one or more of these materials. In some embodiments, the low index layer 822 may consist of one or more of these materials. In some embodiments, the low index layer 822 may have a thickness in the range of 25 nanometers to 100 nanometers, including sub-ranges. For example, the low index layer 822 may have a thickness of 25 nanometers, 30 nanometers, 35 nanometers, 40 nanometers, 45 nanometers, 50 nanometers, 55 nanometers, 60 nanometers, 65 nanometers, 70 nanometers, 75 nanometers, 80 nanometers, 85 nanometers, 90 nanometers, 95 nanometers, 100 nanometers, or a value in a range having any two of these values ​​as endpoints.

[0113] Desired optical properties can be achieved by layering one or more magnesium fluoride films 210 and one or more refractive index layers 810. Graph 900 in Figure 9A shows modeled optical reflectance for light having a wavelength of 226 nanometers as a function of incidence angle for (i) a bilayer optical film 802 including a refractive index layer 810 and a magnesium fluoride film 210 according to some embodiments, and (ii) a four-layer optical film 802 including two magnesium fluoride films 210 and two refractive index layers 810. Graph 950 in Figure 9B shows modeled optical reflectance for the same two exemplary optical films as a function of wavelength for light having a normal incidence angle (i.e., an incidence angle equal to zero).

[0114] Both the two-layer optical coating 802 and the four-layer optical coating 802 were modeled as coated on an optical lens. The two-layer optical coating 802 included (i) a 49 nanometer thick aluminum oxide layer coated on the lens, and (ii) a 42 nanometer thick magnesium fluoride film coated on the aluminum oxide layer. The four-layer optical coating 802 included (i) a 70 nanometer thick aluminum oxide layer coated on the lens, (ii) an 82 nanometer thick magnesium fluoride film coated on the 70 nanometer thick aluminum oxide layer, (iii) a 34 nanometer thick aluminum oxide layer coated on the 82 nanometer thick magnesium fluoride film, and (iv) a 50 nanometer thick magnesium fluoride film coated on the 34 nanometer thick aluminum oxide layer.

[0115] As shown in graph 900, both the two-layer and four-layer optical films 802 had light reflectances of less than 0.2% for angles of incidence less than 25 degrees. At angles of incidence greater than 25 degrees, the four-layer optical film 802 had a lower light reflectance. However, both optical films 802 had light reflectances of 2% or less for angles of incidence less than 50 degrees. As shown in graph 950, the two-layer optical film 802 generally had a lower light reflectance at smaller wavelengths, and the four-layer optical film 802 generally had a lower light reflectance at larger wavelengths. However, both optical films 802 had light reflectances of 2% or less for wavelengths between 230 degrees and 330 degrees.

[0116] Although various embodiments have been described herein, they are presented by way of example, not limitation. Based on the teaching and guidance presented herein, it will be apparent that adaptations and modifications are intended to be within the scope and meaning of equivalents of the disclosed embodiments. Thus, it will be apparent to those skilled in the art that various changes in form and detail can be made to the embodiments disclosed herein without departing from the spirit and scope of the present disclosure. Elements of the embodiments presented herein are not necessarily mutually exclusive and may be interchanged under various circumstances, as will be recognized by those skilled in the art.

[0117] Embodiments of the present disclosure are described in detail herein with reference to the embodiments thereof as illustrated in the accompanying drawings, in which like reference numerals are used to indicate identical or functionally similar elements. References to "one embodiment," "an embodiment," "several embodiments," "particular embodiments," and the like indicate that the described embodiments may include a particular feature, structure, or characteristic, but not all embodiments may necessarily include that feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Moreover, when a particular feature, structure, or characteristic is described with respect to one embodiment, it is believed to be within the knowledge of one of ordinary skill in the art that such feature, structure, or characteristic may be affected with respect to other embodiments, whether or not expressly described.

[0118] The examples are illustrative, not limiting, of the disclosure. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in the art and which would be obvious to those skilled in the art are within the spirit and scope of the disclosure.

[0119] As used herein, the term "or" is inclusive; more specifically, the phrase "A or B" means "A, B, or both A and B." Exclusive "or" is specified herein by terms such as "either A or B" and "one of A or B."

[0120] The indefinite articles "a" and "an" to describe elements or components mean that there is one or at least one of those elements or components. Although these articles are conventionally used to indicate that the modified noun is a singular noun, as used herein, the articles "a" and "an" also include plurals, unless stated otherwise in a specific instance. Similarly, as used herein, the definite article "the" again indicates that the modified noun may be singular or plural, unless stated otherwise in a specific instance.

[0121] As used in the claims, "comprising" is an open-ended transitional phrase. A list of elements following the transitional phrase "comprising" is a non-exclusive list, and thus elements in addition to those specifically recited in the list may be present. As used in the claims, "consisting essentially of" or "consisting essentially of" limits the composition of a material to the specified materials and those that do not materially affect the basic and novel characteristics of the material. As used in the claims, "consisting of" or "consisting entirely of" limits the composition of a material to the specified materials and excludes any materials not specified.

[0122] The term "herein" is used as an open-ended transitional phrase to introduce the description of a series of features of a structure.

[0123] When a range of numerical values, including upper and lower limits, is recited herein, unless otherwise stated in the specific context, the range is intended to include its endpoints, as well as all integers and fractions within the range. The scope of the claims is not intended to be limited to the specific values ​​recited when defining the range. Furthermore, when an amount, concentration, or other value or parameter is given as a range, one or more preferred ranges, or a list of a preferred upper value and a preferred lower value, this should be understood to specifically disclose all ranges formed from any pair of any upper range or preferred value with any lower range or preferred value, whether or not such pairs are separately disclosed. Finally, when the term "about" is used in describing a value or an endpoint of a range, the disclosure should be understood to include the specific value or endpoint referred to. Whether or not a numerical value or an endpoint of a range is accompanied by "about," the numerical value or endpoint of the range is intended to include two embodiments: those modified by "about" and those not modified by "about."

[0124] As used herein, the term "about" means that amounts, sizes, formulations, parameters, and other quantities and characteristics are not, and need not be, exact but may be approximate and / or larger or smaller, as appropriate, to reflect tolerances, conversion factors, rounding, measurement errors and the like, as well as other factors known to those of ordinary skill in the art.

[0125] As used herein, the terms "substantially," "substantially," and variations thereof are intended to indicate that a described feature is equal or approximately equal to a value or description. For example, a "substantially flat" surface is intended to indicate a flat or nearly flat surface. Additionally, "substantially" is intended to indicate that two values ​​are equal or approximately equal. In some embodiments, "substantially" may indicate values ​​within about 10% of each other, such as within about 5% of each other, or within about 2% of each other.

[0126] The embodiments of the present invention have been described above using functional components that illustrate the implementation of certain functions and relationships thereof. The boundaries of these functional components have been arbitrarily defined herein for convenience of description. Alternative boundaries may be defined so long as the certain functions and relationships thereof are appropriately performed.

[0127] It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. The breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined in accordance with the following claims and their equivalents.

[0128] Preferred embodiments of the present invention will be described below in detail.

[0129] EMBODIMENT 1 1. An atomic layer deposition method for coating an optical lens with a magnesium fluoride layer, comprising the steps of: (i) exposing an optical lens to a precursor gas comprising magnesium, thereby forming a magnesium-containing precursor layer over a surface of said lens; (ii) exposing the magnesium-containing precursor layer to a first oxygen-containing gas, thereby forming a magnesium oxide layer; (iii) exposing the magnesium oxide layer to a source gas comprising fluorine, thereby forming an intermediate layer comprising magnesium and fluorine; and (iv) exposing the intermediate layer to a second oxygen-containing gas, thereby forming a magnesium fluoride layer; The method comprising:

[0130] EMBODIMENT 2 2. The method of embodiment 1, wherein exposing the magnesium-containing precursor layer to a first oxygen-containing gas is performed at a temperature in the range of 100° C. to 300° C.

[0131] EMBODIMENT 3 3. The method of claim 1 or 2, wherein exposing the magnesium-containing precursor layer to a first oxygen-containing gas is carried out at a temperature in the range of 240° C. to 260° C.

[0132] EMBODIMENT 4 4. The method of any one of claims 1 to 3, wherein the first oxygen-containing gas comprises a gas selected from the group consisting of water, ozone, hydrogen peroxide, methanol, ethanol, a plasma with oxygen, and a plasma with an oxygen-containing chemical.

[0133] EMBODIMENT 5 The first oxygen-containing gas is H 2 The method of any one of embodiments 1 to 4, comprising O.

[0134] EMBODIMENT 6 The first oxygen-containing gas is H 2 O, and the magnesium-containing precursor layer is heated to a temperature in the range of 240° C. to 260° C. with H 2 6. The method of any one of embodiments 1 to 5, wherein the subject is exposed to O.

[0135] EMBODIMENT 7 7. The method of any one of the preceding embodiments, wherein the fluorine-containing source gas is an organic source gas.

[0136] EMBODIMENT 8 8. The method of embodiment 7, wherein the organic source gas is selected from the group consisting of hexafluoroacetylacetone, carbonyl fluoride, chlorine fluoride, chlorine trifluoride, 1-chloro-2,2-difluoroethene, chlorodifluoromethane, 1-chloro-1-fluoroethane, chloropentafluorobenzene, chloropentafluoroethane, chlorotrifluoroethene, chlorotrifluoromethane, dichlorodifluoromethane, 1,2-dichloro-1,1,2,2-tetrafluoroethane, difluoroethane, difluoromethane, fluoropropane, nitrogen trifluoride, pentafluorobenzene, pentafluoroethane, pentafluorophenol, pentafluorotoluene, perfluorocyclobutane, perfluorocyclohexane, perfluorocyclohexene, perfluoroheptane, perfluoromethylcyclohexane, perfluorotoluene, 1,1,1,2-tetrachloro-2,2-difluoroethane, trichlorofluoromethane, trifluoroacetic acid, trifluoroethane, and trifluoroethanol.

[0137] EMBODIMENT 9 9. The method of any one of the preceding claims, wherein the magnesium-containing precursor gas is selected from the group consisting of bis(ethylcyclopentadienyl)magnesium, bis(cyclopentadienyl)magnesium(II), bis(2,2,6,6-tetramethyl-3,5-heptanedionato)magnesium, bis(N,N'-di-sec-butylacetamidinato)magnesium, and bis(pentamethylcyclopentadienyl)magnesium.

[0138] EMBODIMENT 10 10. The method of any one of the preceding embodiments, further comprising repeating steps (i)-(iv) for multiple cycles to form a magnesium fluoride film comprising multiple magnesium fluoride layers.

[0139] EMBODIMENT 11 11. The method of embodiment 10, wherein the magnesium fluoride film has a thickness in the range of 25 nanometers to 75 nanometers.

[0140] EMBODIMENT 12 12. The method of claim 11, wherein the magnesium fluoride film has an optical absorption value of 1% or less for light having a wavelength of 266 nanometers and an angle of incidence of 6 degrees.

[0141] EMBODIMENT 13 13. The method of claim 11 or 12, wherein the magnesium fluoride film has an optical transmittance value of 94% or greater for light having a wavelength of 266 nanometers and an angle of incidence of 6 degrees.

[0142] EMBODIMENT 14 14. The method of any one of claims 11 to 13, wherein the magnesium fluoride film has a surface roughness (Ra) of 1.5 nanometers or less.

[0143] EMBODIMENT 15 15. The method of any one of claims 11 to 14, wherein the magnesium fluoride film has a refractive index of 1.42 or less for light having a wavelength of 266 nanometers.

[0144] EMBODIMENT 16 16. The method of any one of claims 11 to 15, wherein the magnesium fluoride film has a carbon content of 1.2 atomic % or less at a depth of 0.02 micrometers as measured using secondary ion mass spectrometry.

[0145] EMBODIMENT 17 17. The method of any one of claims 11 to 16, wherein the surface of the lens includes a surface bounded by a peripheral edge, and the magnesium fluoride film covers the entire surface bounded by the peripheral edge.

[0146] EMBODIMENT 18 18. The method of embodiment 17, wherein the magnesium fluoride film has a thickness variation of 10% or less.

[0147] EMBODIMENT 19 18. The method of embodiment 17, wherein the magnesium fluoride film has a thickness variation of 5% or less.

[0148] EMBODIMENT 20 20. The method of any one of the preceding claims, wherein the lens is held substantially stationary during the atomic layer deposition method.

[0149] EMBODIMENT 21 21. The method of any one of the preceding claims, wherein step (iii) comprises a remote plasma process.

[0150] EMBODIMENT 22 22. An optical lens having a surface coated with a magnesium fluoride layer deposited according to the method according to any one of embodiments 1 to 21.

[0151] EMBODIMENT 23 In optical lenses, A coating is applied over the surface of the optical lens, thickness ranging from 25 nanometers to 75 nanometers, An optical absorption value of 1% or less for light having a wavelength of 220 nanometers and an angle of incidence of 6 degrees; and Thickness variation of less than 5% A magnesium fluoride film having An optical lens comprising:

[0152] EMBODIMENT 24 24. The optical lens of embodiment 23, wherein the magnesium fluoride film has a light transmittance value of 94% or greater for light having a wavelength of 220 nanometers and an angle of incidence of 6 degrees.

[0153] EMBODIMENT 25 25. The optical lens of embodiment 23 or 24, wherein the surface of the lens includes a surface bounded by a peripheral edge, and the magnesium fluoride film covers the entire surface bounded by the peripheral edge.

[0154] EMBODIMENT 26 26. The optical lens of any one of embodiments 23 to 25, further comprising an aluminum oxide layer disposed between the magnesium fluoride film and the surface of the optical lens.

[0155] EMBODIMENT 27 A semiconductor wafer inspection tool comprising an optical lens according to any one of embodiments 23 to 26.

[0156] EMBODIMENT 28 In the optical element, an optically transparent lens having a first surface having a steepness value in the range of 0.5 to 1.0 and a second surface opposite the first surface, the steepness value being equal to a radius of curvature of the first surface divided by an effective aperture of the optically transparent lens; an optical film disposed over the first surface and the second surface, a first refractive index layer having a first refractive index for light having a wavelength of 550 nanometers; a second refractive index layer disposed over the first refractive index layer, the second refractive index layer including a magnesium fluoride film and a low refractive index layer, the second refractive index layer having a second refractive index for light having a wavelength of 550 nanometers, the second refractive index being less than the first refractive index; An optical film comprising: An optical element comprising:

[0157] EMBODIMENT 29 29. The optical element of embodiment 28, wherein the first refractive index layer is made from a material selected from the group consisting of aluminum oxide, hafnium oxide, gadolinium fluoride, and lanthanum fluoride.

[0158] EMBODIMENT 30 30. The optical element of embodiment 28 or 29, wherein the optical film is disposed on the first surface and the second surface.

[0159] EMBODIMENT 31 31. An optical element according to any one of embodiments 28 to 30, wherein the magnesium fluoride film has a thickness in the range of 25 nanometers to 75 nanometers, an optical absorption value of 1% or less for light having a wavelength of 220 nanometers and an incidence angle of 6 degrees, and a thickness variation of 10% or less.

[0160] EMBODIMENT 32 32. The optical element of any one of embodiments 28 to 31, wherein the magnesium fluoride film has an optical transmittance value of 94% or greater for light having a wavelength of 220 nanometers and an angle of incidence of 6 degrees.

[0161] EMBODIMENT 33 33. The optical element according to any one of embodiments 28 to 32, wherein the first refractive index is 1.6 or more and the second refractive index is 1.38 or less.

[0162] EMBODIMENT 34 A semiconductor wafer inspection tool comprising an optical element according to any one of embodiments 28 to 33. EMBODIMENT 35 1. An atomic layer deposition method for coating an optical lens with a magnesium fluoride layer, comprising the steps of: (i) exposing an optical lens to a precursor gas comprising magnesium, thereby forming a magnesium-containing precursor layer over a surface of said lens; (ii) exposing the magnesium-containing precursor layer to a first oxygen-containing gas, thereby forming a magnesium oxide layer; (iii) exposing the magnesium oxide layer to a source gas comprising fluorine, thereby forming an intermediate layer comprising magnesium and fluorine; and (iv) exposing the intermediate layer to a second oxygen-containing gas, thereby forming a magnesium fluoride layer; The method comprising:

[0163] EMBODIMENT 36 36. The method of embodiment 35, wherein the exposing the magnesium-containing precursor layer to a first oxygen-containing gas is performed at a temperature in the range of 240° C. to 260° C.

[0164] EMBODIMENT 37 The first oxygen-containing gas is H 2 The method of embodiment 35 or 36, comprising O.

[0165] EMBODIMENT 38 The first oxygen-containing gas is H 2 O, and the magnesium-containing precursor layer is heated to a temperature in the range of 240° C. to 260° C. with H 2 36. The method of embodiment 35, wherein the subject is exposed to O.

[0166] EMBODIMENT 39 39. The method of any one of embodiments 35 to 38, wherein the fluorine-containing source gas is an organic source gas.

[0167] EMBODIMENT 40 40. The method of any one of embodiments 35 to 39, further comprising repeating steps (i)-(iv) for multiple cycles to form a magnesium fluoride film comprising multiple magnesium fluoride layers.

[0168] EMBODIMENT 41 41. The method of embodiment 40, wherein the magnesium fluoride film has a thickness in the range of 25 nanometers to 75 nanometers.

[0169] EMBODIMENT 42 42. The method of embodiment 41, wherein the magnesium fluoride film has an optical absorption value of 1% or less for light having a wavelength of 266 nanometers and an angle of incidence of 6 degrees.

[0170] EMBODIMENT 43 43. The method of any one of embodiments 35 to 42, wherein the lens is held substantially stationary during the atomic layer deposition method.

[0171] EMBODIMENT 44 In optical lenses, A coating is applied over the surface of the optical lens, thickness ranging from 25 nanometers to 75 nanometers, An optical absorption value of 1% or less for light having a wavelength of 220 nanometers and an angle of incidence of 6 degrees; and Thickness variation of less than 5% A magnesium fluoride film having An optical lens comprising: [Explanation of symbols]

[0172] 100 ways 102 Base 104 Surface 112 Magnesium-containing precursor gas 114 Magnesium-containing precursor layer 122, 142 Oxygen-containing gases 124 Magnesium oxide layer 132 Fluorine-containing source gases 134 Intermediate layer 144 Magnesium Fluoride Layer 200, 800 Optical Lenses 202 First surface of optical lens 204 Second surface of optical lens 206 Peripheral Edge 210 Magnesium fluoride film 212 First surface of magnesium fluoride membrane 214 Second side of magnesium fluoride membrane 220 Incident light 300 Semiconductor inspection equipment 310 Optical Elements 802 Optical film 810, 820 Refractive index layer 822 Low refractive index layer

Claims

1. In the optical element, an optically transparent lens having a first surface having a steepness value in the range of 0.5 to 1.0 and a second surface opposite the first surface, the steepness value being equal to a radius of curvature of the first surface divided by an effective aperture of the optically transparent lens; an optical film disposed over at least one of the first surface and the second surface, a first refractive index layer having a first refractive index for light having a wavelength of 550 nanometers; a second refractive index layer disposed over the first refractive index layer, the second refractive index layer including a magnesium fluoride film and a low refractive index layer, the second refractive index layer having a second refractive index for light having a wavelength of 550 nanometers, the second refractive index being less than the first refractive index; An optical film comprising: An optical element comprising:

2. The optical element according to claim 1 , wherein the optical film includes a plurality of the first refractive index layers and a plurality of the second refractive index layers.

3. 2. The optical element of claim 1, wherein the first refractive index layer is an innermost layer of the optical film in contact with the optically transparent lens, and the low refractive index layer is an outermost layer of the optical film.

4. The optical element of claim 1 , wherein the first refractive index is greater than or equal to about 1.6 for light having a wavelength of 550 nanometers.

5. The optical element of claim 1 , wherein the second refractive index is less than or equal to about 1.38 for light having a wavelength of 550 nanometers.

6. 2. The optical element of claim 1, wherein the first refractive index is in the range of about 1.6 to about 2.0 for light having a wavelength of 550 nanometers, and the second refractive index is in the range of about 1.2 to about 1.38 for light having a wavelength of 550 nanometers.

7. 7. The optical element of claim 1, wherein the magnesium fluoride film has a refractive index in the range of about 1.42 to about 1.38 for light having a wavelength of 266 nanometers.

8. The optical element of claim 1 , wherein the first refractive index layer comprises aluminum oxide, hafnium oxide, gadolinium fluoride, lanthanum fluoride, or a combination thereof.

9. The optical element of claim 1 , wherein the first refractive index layer has a thickness in the range of about 250 nanometers to about 100 nanometers.

10. The optical element of claim 1 , wherein the low refractive index layer comprises magnesium fluoride, aluminum fluoride, calcium fluoride, lithium fluoride, or a combination thereof.

11. The optical element of claim 1 , wherein the low refractive index layer has a thickness in the range of about 25 nanometers to about 100 nanometers.

12. The optical element of claim 1 , wherein the magnesium fluoride film has a thickness in the range of about 25 nanometers to about 100 nanometers.

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