Protective coating for aluminum mirrors and method for forming same - Patents.com

Abstract

According to at least one feature of the present disclosure, a method of forming an optical element includes depositing an aluminum layer on a glass substrate by a physical deposition technique, depositing a first fluorine-containing layer on the aluminum layer by a physical deposition technique, depositing a second fluorine-containing layer on the first fluorine-containing layer by a physical deposition technique, and depositing a third fluorine-containing layer on the first fluorine-containing layer by an atomic layer deposition technique.

Description

[Technical field]

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 to U.S. Provisional Application No. 63 / 284,293, filed November 30, 2021, the contents of which are incorporated by reference in their entirety and are hereby incorporated by reference. FIELD OF THE DISCLOSURE This disclosure relates generally to optical elements, and more particularly to protective coatings for aluminum mirrors. [Background technology]

[0002] Improved lithography techniques enable smaller feature sizes for microelectronics. This technological advancement also requires highly sensitive optical inspection capable of defect detection down to the nanoscale. Currently, defect inspection is dominated by deep ultraviolet (DUV) optics (i.e., at 193.4 nm). The next generation of optical inspection optics should be dominated by both vacuum ultraviolet (VUV) optics (i.e., at 120 nm to 190 nm) and extreme ultraviolet (EUV) optics (i.e., at 13.5 nm). Although EUV wavelength is one tenth of VUV, many defects are optically more sensitive to VUV and EUV. As a result, both VUV and EUV inspection optics are essential for the semiconductor industry. VUV inspection performance depends on VUV mirrors. Aluminum has been recognized as the material of choice for VUV reflective optics. Factors affecting the performance of current VUV mirrors include thermally driven wavefront errors of VUV mirrors, high reflectivity of VUV mirrors, and degradation of VUV mirrors. Therefore, new protective coatings for aluminum mirrors, and methods for making the same, would be advantageous. Summary of the Invention

[0003] According to a first embodiment of the present disclosure, a method of forming an optical element includes depositing an aluminum layer on a glass substrate by a physical deposition method, depositing a first fluorine-containing layer on the aluminum layer by a physical deposition method, depositing a second fluorine-containing layer on the first fluorine-containing layer by a physical deposition method, and depositing a third fluorine-containing layer on the first fluorine-containing layer by an atomic layer deposition method. A second embodiment of the present disclosure includes the first embodiment, wherein the first fluorine-containing layer is one of aluminum fluoride (AlF3) or magnesium fluoride (MgF3). A third embodiment of the present disclosure includes the first embodiment, wherein the second fluorine-containing layer is one of aluminum fluoride (AlF3) or magnesium fluoride (MgF3). A fourth embodiment of the present disclosure includes the first embodiment, wherein the third fluorine-containing layer is one of aluminum fluoride (AlF3) or magnesium fluoride (MgF3). A fifth embodiment of the present disclosure includes the first embodiment, wherein the third fluorine-containing layer is a stack of alternating layers of aluminum fluoride (AlF3) and magnesium fluoride (MgF3). A sixth embodiment of the present disclosure includes the fifth embodiment, where the final layer in the stack of alternating layers is aluminum fluoride (AlF3). A seventh embodiment of the present disclosure includes the fifth embodiment, where the final layer in the stack of alternating layers is magnesium fluoride (MgF3).

[0004] According to an eighth embodiment of the present disclosure, a method for forming an optical element includes depositing an aluminum layer on a glass substrate by a physical deposition method; removing aluminum oxide (Al2O3) from a surface of the aluminum layer by an atomic layer etching method; after etching the aluminum layer, depositing a first fluorine-containing layer on the aluminum layer by an atomic layer deposition method without exposing the glass substrate to air; depositing a second fluorine-containing layer on the first fluorine-containing layer by an atomic layer deposition method; and depositing a third fluorine-containing layer on the first fluorine-containing layer by an atomic layer deposition method. A ninth embodiment of the present disclosure includes the eighth embodiment, wherein the first fluorine-containing layer is one of aluminum fluoride (AlF3) or magnesium fluoride (MgF3). A tenth embodiment of the present disclosure includes the eighth embodiment, wherein the second fluorine-containing layer is one of aluminum fluoride (AlF3) or magnesium fluoride (MgF3). An eleventh embodiment of the present disclosure includes the eighth embodiment, wherein the third fluorine-containing layer is one of aluminum fluoride (AlF3) or magnesium fluoride (MgF3).

[0005] A twelfth embodiment of the present disclosure includes the eighth embodiment, wherein the third fluorine-containing layer is a stack of alternating layers of aluminum fluoride (AlF3) and magnesium fluoride (MgF3). A thirteenth embodiment of the present disclosure includes the twelfth embodiment, wherein the last layer in the stack of alternating layers is aluminum fluoride (AlF3). A fourteenth embodiment of the present disclosure includes the twelfth embodiment, wherein the last layer in the stack of alternating layers is magnesium fluoride (MgF3). According to a fifteenth embodiment of the present disclosure, an optical element includes a glass substrate, an aluminum layer on the glass substrate, a first fluorine-containing layer on the aluminum layer, a second fluorine-containing layer on the first fluorine-containing layer, and a third fluorine-containing layer on the first fluorine-containing layer. A sixteenth embodiment of the present disclosure includes the fifteenth embodiment, wherein the first fluorine-containing layer is one of aluminum fluoride (AlF3) or magnesium fluoride (MgF3).

[0006] A seventeenth embodiment of the present disclosure includes the fifteenth embodiment, wherein the second fluorine-containing layer is one of aluminum fluoride (AlF3) or magnesium fluoride (MgF3). An eighteenth embodiment of the present disclosure includes the fifteenth embodiment, wherein the third fluorine-containing layer is one of aluminum fluoride (AlF3) or magnesium fluoride (MgF3). A nineteenth embodiment of the present disclosure includes the fifteenth embodiment, wherein the third fluorine-containing layer is a stack of alternating layers of aluminum fluoride (AlF3) and magnesium fluoride (MgF3). A twentieth embodiment of the present disclosure includes the nineteenth embodiment, wherein the last layer in the stack of alternating layers is aluminum fluoride (AlF3). A twenty-first embodiment of the present disclosure includes the nineteenth embodiment, wherein the last layer in the stack of alternating layers is magnesium fluoride (MgF3). These and other features, advantages, and objectives of the present disclosure will be further understood and appreciated by those skilled in the art from a review of the following specification, claims, and accompanying drawings. The following is a description of the figures in the accompanying drawings, which are not necessarily to scale and certain features and aspects of the figures may be exaggerated in scale or shown in schematic form for clarity and conciseness. [Brief description of the drawings]

[0007] [Figure 1] 1 is a flowchart of an exemplary method of forming an optical element according to an embodiment of the present disclosure. [Diagram 2] 1 is an exemplary optical element according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Additional features and advantages of the invention will be set forth in the following detailed description, and will be apparent to those skilled in the art from the specification, or may be learned by practicing the invention as described in the following description, taken in conjunction with the claims and the accompanying drawings. As used herein, the term "and / or," when used in a list of two or more items, means that any one of the listed items may be used alone, or any combination of two or more of the listed items may be used. For example, if a composition is described as containing components A, B, and / or C, the composition may contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.

[0009] In this document, relationship terms, such as first and second, upper and lower, and the like, are used only to distinguish one element or action from another element or action, without necessarily requiring or implying any such actual relationship or order between such elements or actions. It will be understood by those of skill in the art that the compositions and other components of the disclosure described are not limited to any particular material, and other exemplary embodiments of the disclosure disclosed herein may be formed from a variety of materials, unless otherwise noted herein. For purposes of this disclosure, the term "coupled" (in all of its forms: coupled, connecting, coupled, etc.) generally means connecting two components (electrical or mechanical) directly or indirectly to one another. Such a connection may be fixed or movable. Such a connection may be achieved by the two components (electrical or mechanical) and any additional intermediate members integrally formed with one another or with the two components as a single, unitary body. Unless otherwise specified, such a connection may be permanent or removable or releasable.

[0010] As used herein, the term "about" means that amounts, sizes, formulations, variables, and other quantities and characteristics are not and need not be exact, but may be approximate and / or larger or smaller, as desired, to reflect tolerances, conversion factors, approximations, measurement errors, and the like, as well as other factors known to those skilled in the art. When the term "about" is used to describe a value or an endpoint of a range, the disclosure should be understood to include the specific value or endpoint mentioned. Regardless of whether a numerical value or an endpoint of a range in the specification is described as "about," the endpoint of the numerical value or range is intended to include two embodiments: those modified by "about" and those not modified by "about." It is further understood that each endpoint of a range is significant relative to the other endpoint and independently of the other endpoint. The terms "substantial", "substantially", and variations thereof, as used herein, are intended to note that a described feature is equal or approximately equal to a value or description. For example, a "substantially planar" surface is intended to refer to a flat or approximately planar surface. Additionally, "substantially" is intended to refer to two values ​​being equal or approximately equal. In some embodiments, "substantially" may refer to values ​​within about 10% of each other.

[0011] It is also important to note that the composition and configuration of the elements of the present disclosure shown in the exemplary embodiments are merely exemplary. Although only a few embodiments of the present invention are described in detail in this disclosure, those skilled in the art who evaluate this disclosure will readily recognize that many modifications are possible (e.g., changes in size, dimensions, configuration, shape and proportion of various elements, values ​​of variables, mounting configurations, use of materials, colors, orientations, etc.) without substantially departing from the novel teachings and advantages of the described subject matter. For example, elements shown to be integrally formed may be composed of multiple parts, or elements shown as multiple parts may be integrally formed, interface behavior may be reversed or otherwise varied, the length or width of structures and / or members, or connectors, or other elements of the mechanism may be varied, and the nature or number of adjustment positions provided between elements may be varied. It should be noted that the elements and / or assemblies of the mechanism may be composed of any of a variety of materials that provide sufficient strength or durability in any of a variety of colors, textures, and combinations. Thus, any such modifications are intended to be included within the scope of the present invention. Other substitutions, modifications, changes, and omissions may be made to the design, operating conditions, and configuration of other exemplary embodiments as desired without departing from the spirit of the present invention.

[0012] FIG. 1A shows a flow chart of a method 100 for forming an optical element, such as the exemplary optical element 200 shown in FIG. 2. The method 100 begins at 102 by depositing an aluminum layer 204 on a glass substrate 202. In an embodiment, the glass substrate 202 is ULE glass available from Corning Incorporated. The aluminum layer 204 is deposited on the glass substrate 202 by physical vapor deposition. In an embodiment, the aluminum layer 204 has a thickness of about 100 nm. The thickness of the aluminum layer 204 and the subsequent layers described herein may vary depending on the specifications required for the final optical element. Next, at 104, a first fluorine-containing layer 206 is deposited on the aluminum layer 204 by physical vapor deposition. In an embodiment, the first fluorine-containing layer 206 is one of aluminum fluoride (AlF3) or magnesium fluoride (MgF3). In an embodiment, the first fluorine-containing layer 206 has a thickness of about 5 nm. Next, at 106, a second fluorine-containing layer 208 is deposited on the first fluorine-containing layer 206 by physical deposition. In an embodiment, the second fluorine-containing layer 208 is one of aluminum fluoride (AlF3) or magnesium fluoride (MgF3). In an embodiment, the second fluorine-containing layer 208 has a thickness of about 10 nm. Next, at 108, a third fluorine-containing layer 210 is deposited on the second fluorine-containing layer 208 by atomic layer deposition. In an embodiment, the third fluorine-containing layer 210 is one of aluminum fluoride (AlF3) or magnesium fluoride (MgF3). In an embodiment, the third fluorine-containing layer 210 is a stack of alternating layers of aluminum fluoride (AlF3) and magnesium fluoride (MgF3). In an embodiment, the last layer in the stack of alternating layers is aluminum fluoride (AlF3). In an embodiment, the last layer in the stack of alternating layers is magnesium fluoride (MgF3). The third fluorine-containing layer 210 provides protection from oxidation of the aluminum layer 204 by forming a pinhole-free film. Table 1 below shows exemplary embodiments of suitable optical elements formed by the methods described herein.

[0013] [Table 1]

[0014] [Table 2]

[0015] In an embodiment, after depositing the aluminum layer 204 in step 104, a natural aluminum oxide (Al2O3) layer may be formed on the aluminum layer 204. The aluminum oxide (Al2O3) is removed from the surface of the aluminum layer 204 by an atomic layer etching process. In an exemplary atomic layer etching process, the aluminum oxide (Al2O3) is removed by sequential exposure to trimethylaluminum (TMA) and hydrogen fluoride (HF) or other fluorine-containing compounds, such as SF6, at a temperature of about 225°C to 325°C. In an embodiment, the aluminum oxide (Al2O3) is exposed to a remote plasma of Ar / SF6 for about 1 second to 10 seconds, and then exposed to TMA for more than 100 milliseconds. The exposure time may be adjusted based on the volume of the reactor. In embodiments, suitable aluminum precursors used in the atomic layer deposition of aluminum layers include: trimethylaluminum (TMA), triethylaluminum (TEA), or dimethylaluminum isopropoxide (DMAI), or [MeC(NiPr)2]AlEt2, or dimethylaluminum hydride:dimethylethylamine, or ethylpiperidine:dimethylaluminum hydride. In embodiments, suitable fluorine sources used in the deposition of fluorine-containing layers include: hydrogen fluoride (HF), and a plasma having a mixture of sulfur hexafluoride (SF6) and argon, or a mixture of nitrogen trifluoride (NF3) and argon, or SF6, NF3, or CF4. In embodiments, suitable Mg precursors include: bis(ethylcyclopentadienyl)magnesium, MgCp2, Mg(thd)2; bis(2,2,6,6-tetramethyl-3,5-heptanedionato)magnesium, bis(N,N'-di-sec-butylacetamidinato)magnesium, bis(pentamethylcyclopentadienyl)magnesium.

[0016] Modifications of the disclosure will occur to those skilled in the art and to those who make or use the disclosure. Thus, it is understood that the embodiments shown in the drawings and described above are for illustrative purposes only and are not intended to limit the scope of the disclosure, which is defined by the following claims, which are to be interpreted in accordance with the principles of patent law, including the doctrine of equivalents. It will be understood by those of skill in the art that the compositions and other components of the disclosure described are not limited to any particular material, and other exemplary embodiments of the disclosure disclosed herein may be formed from a variety of materials, unless otherwise noted herein.

[0017] It is understood that any described method, or steps within a described method, may be combined with other disclosed methods or steps to form structures within the scope of the present disclosure. The exemplary structures and methods disclosed herein are for illustrative purposes and should not be construed as limiting. It is also to be understood that changes and modifications may be made to the structures and methods described above without departing from the concepts of the present disclosure, and that such concepts are intended to be within the scope of the following claims, unless those claims specifically state otherwise by their language.

Claims

1. 1. A method of forming an optical element, comprising: depositing an aluminum layer on a glass substrate by physical deposition; depositing a first fluorine-containing layer over the aluminum layer by physical deposition; depositing a second fluorine-containing layer on the first fluorine-containing layer by physical deposition; and depositing a third fluorine-containing layer on the first fluorine-containing layer by atomic layer deposition; A method comprising:

2. 1. A method of forming an optical element, comprising: depositing an aluminum layer on a glass substrate by physical deposition; The aluminum oxide (Al) was removed from the surface of the aluminum layer by atomic layer etching. 2 O 3 ) removing the depositing a first fluorine-containing layer on the aluminum layer by atomic layer deposition without exposing the glass substrate to air after etching the aluminum layer; depositing a second fluorine-containing layer on the first fluorine-containing layer by atomic layer deposition; and depositing a third fluorine-containing layer on the first fluorine-containing layer by atomic layer deposition; A method comprising:

3. At least one of the first, second, or third fluorine-containing layers is aluminum fluoride (AlF 3 3. The method according to claim 1, wherein the fluoride is one of magnesium fluoride (MgF2).

4. The third fluorine-containing layer is aluminum fluoride (AlF 3 3. The method according to claim 1, wherein the layer is a stack of alternating layers of magnesium fluoride (MgF2).

5. Glass substrate, an aluminum layer on the glass substrate; a first fluorine-containing layer on said aluminum layer; a second fluorine-containing layer on the first fluorine-containing layer; and a third fluorine-containing layer on the first fluorine-containing layer; An optical element comprising:

6. The at least one fluorine-containing layer of the first or second layer is aluminum fluoride (AlF 3 6. The optical element of claim 5, wherein the fluoride is one of magnesium fluoride (MgF2).

7. The third fluorine-containing layer is aluminum fluoride (AlF 3 7. The optical element according to claim 5, wherein the material is one of magnesium fluoride (MgF2) and magnesium fluoride (MgF2).

8. The third fluorine-containing layer is aluminum fluoride (AlF 3 7. The optical element according to claim 5, wherein the optical element is a stack of alternating layers of fluoride (MgF2) and magnesium fluoride (MgF2).

9. The last layer in the stack of alternating layers is aluminum fluoride (AlF 3 9. The optical element according to claim 8, wherein

10. 9. The optical element of claim 8, wherein the last layer in the stack of alternating layers is magnesium fluoride (MgF2).

Images