The present disclosure generally relates to optical components, more specifically, to methods for producing enhanced aluminium mirrors for vacuum ultraviolet (VUV).
Optical technology utilizing ultraviolet light is in wide use in semiconductor manufacturing. Advanced lithography technology enables formation of smaller feature sizes for microelectronics. This technology advancement also demands sensitive optical inspection that allows defect detection down to the nano-scale range. Currently defect inspection is dominated by deep-ultraviolet (DUV) optics, which operate at wavelengths of about 193.4 nm. Next generation optical inspection optics are expected to be dominated by vacuum ultraviolet (VUV) optics (e.g., wavelengths of from 120 nm-190 nm) and extreme ultraviolet (EUV) optics (e.g., wavelengths down to about 13.5 nm). Although the EUV wavelengths are up to 10 times shorter than the VUV wavelengths, many microelectronics defects are optically more sensitive to both the VUV and the EUV wavelengths, compared to DUV optics. As a result, development of VUV and EUV inspection optics is an important focus for the semiconductor industry.
The performance of VUV optical inspection systems depends on VUV mirrors. Aluminium is recognized as the primary material for producing VUV reflective optics, such as VUV mirrors. Aluminium is typically applied to a substrate using physical vapor deposition (PVD) to deposit the aluminium onto the surface of the substrate to create a reflective surface. PVD-Al mirrors can provide a reflectance of greater than 90% over the VUV wavelength range. However, degradation of the PVD-AL coating over time due to oxidation can greatly reduce the reflective performance of the PVD-AL coatings.
Accordingly, an ongoing need exists for enhanced aluminium mirrors and methods for producing enhanced aluminium mirrors for VUV optics, where the methods reduce defects and protect the aluminium reflective coating from degradation caused by oxidation of the aluminium.
According to a first aspect of the present disclosure, a method of making an enhanced aluminium mirror for vacuum ultraviolet (VUV) optics may include depositing a reflective coating comprising aluminium metal to at least one surface of a substrate through physical vapor deposition (PVD) in a PVD system to produce a mirror comprising the substrate and the reflective coating. The method may further include removing aluminium oxides from an outer surface of the reflective coating by conducting Atomic Layer Etching (ALE) in an Atomic Layer Deposition (ALD) system to produce an etched surface of the reflective coating. The method may further include depositing an ALD protective layer onto the etched surface of the reflective coating by conducting atomic layer deposition in the ALD system to produce the enhanced aluminium mirror comprising the substrate, the reflective coating deposited on the substrate, and the ALD protective layer covering the etched surface of the reflective coating.
A second aspect of the present disclosure may include the first aspect, further comprising transferring the substrate comprising the reflective coating from the PVD system to the ALD system, where transferring the substrate having the reflective coating to the ALD system can expose the reflective coating to oxygen resulting in oxidation of aluminium at an outer surface of the reflective coating to form aluminium oxides.
A third aspect of the present disclosure may include either one of the first or second aspects, wherein the atomic layer etching in the ALD system may comprise exposing the substrate and the reflective coating to alternating pulses of a fluorine source and an organometallic compound. Exposing the substrate and reflective coating to a pulse comprising the fluorine source may convert the aluminium oxides to aluminium fluoride to form a thin layer of aluminium fluoride on the outer surface of the reflective coating. Exposing the thin layer of aluminium fluoride to a pulse comprising the organometallic compound may cause the aluminium fluoride to react to form a volatile organometallic compound that may be released from the outer surface of the reflective coating.
A fourth aspect of the present disclosure may include the third aspect, comprising exposing the reflective coating to alternating pulses of the fluorine source and the organometallic compound at a temperature of from 150° C. to 325° C., or from 200° C. to 250° C.
A fifth aspect of the present disclosure may include either one of the third or fourth aspects, comprising exposing the etched surface of the reflective coating to the alternating pulses of the fluorine source and the organometallic compound at from 50 Watts (W) to 600 W.
A sixth aspect of the present disclosure may include any one of the third through fifth aspects, comprising exposing the etched surface of the reflective coating to the fluorine source for an exposure time of from 1 second to 60 seconds.
A seventh aspect of the present disclosure may include the sixth aspect, further comprising, after exposing the etched surface of the reflective coating to the fluorine source for the exposure time, purging an ALD chamber of the ALD system with an inert gas for a purge time sufficient to remove at least 99% of the residual fluorine source and oxygen compounds from the ALD chamber.
An eighth aspect of the present disclosure may include any one of the third through seventh aspects, wherein the fluorine source may comprise sulfur hexafluoride (SF6), nitrogen trifluoride (NF3), trifluoroiodomethane (CF3I), hydrogen fluoride (HF), SF6 plasma, SF6 and argon (Ar) plasma, NF3 plasma, NF3 and Ar plasma, or combinations of these.
A ninth aspect of the present disclosure may include any one of the third through eighth aspects, wherein the fluorine source may comprise SF6, SF6 plasma, or a plasma comprising SF6 and argon (Ar).
A tenth aspect of the present disclosure may include any one of the third through ninth aspects, wherein the organometallic compound may comprise trimethylaluminium (TMA), triethylaluminium (TLA), dimethylaluminium chloride (DMAC), silicon tetrachloride (SiCl4), aluminium hexafluoroacetylacetonate (Al(hfac)3), tri-i-butylaluminium (Al(iBu)3), tin(II) acetylacetonate (Sn(acac)2), tris(2,2,6,6-tetramethyl-3,5-heptanedionato)aluminium (i.e., Al(TMHD)3, or combinations of these.
An eleventh aspect of the present disclosure may include any one of the third through tenth aspects, comprising exposing the thin layer of aluminium fluoride to the organometallic compound for a total exposure time of from 10 milliseconds (ms) to 60,000 ms, or from 10 ms to 30,000 seconds, where the total exposure time is equal to a pulse length of the pulse of the organometallic compound and a shut-in period.
A twelfth aspect of the present disclosure may include any one of the third through eleventh aspects, comprising exposing the thin layer of aluminium fluoride to the organometallic compound at a pressure of from 10 millitorr (1.33 Pa) to 100 torr (13,332 Pa).
A thirteenth aspect of the present disclosure may include any one of the third through twelfth aspects, wherein exposing the thin layer of aluminium fluoride to the pulse comprising the organometallic compound may comprise injecting the organometallic compound into the ALD chamber for a pulse length and closing a throttle valve of the ALD system. Closing the throttle valve may prevent flow of materials into or out of the ALD chamber and may maintain the thin layer of aluminium fluoride in contact with the organometallic compound for a shut in period of from 1 second to 60 seconds, or from 10 seconds to 30 seconds.
A fourteenth aspect of the present disclosure may include the thirteenth aspect, further comprising reopening the throttle valve and purging the ALD chamber with an inert gas to remove at least 99% of the residual organometallic compounds, the volatile organometallic compounds, or both from the ALD chamber.
A fifteenth aspect of the present disclosure may include any one of the third through fourteenth aspects, wherein the atomic layer etching may have an etch rate of 1.1 Angstroms of thickness per cycle, wherein one complete cycle comprises one pulse of the fluorine source and one pulse of the organometallic compound.
A sixteenth aspect of the present disclosure may include any one of the first through fifteenth aspects, wherein the ALD protective layer may comprise a metal fluoride protective coating.
A seventeenth aspect of the present disclosure may include the sixteenth aspect, wherein the metal fluoride protective coating may comprise one or more of aluminium trifluoride (AlF3), magnesium fluoride (MgF2), calcium fluoride (CaF2), lithium fluoride (LiF), lanthanum fluoride (LaF3), gadolinium fluoride (GdF3), or combinations of these.
An eighteenth aspect of the present disclosure may include any one of the first through seventeenth aspects, wherein applying the protective ALD coating on the outer surface of the etched aluminium layer may comprise exposing the etched aluminium layer to alternating pulses of a metal precursor and a fluorine source.
A nineteenth aspect of the present disclosure may include the eighteenth aspect, wherein the fluorine source may comprise sulfur hexafluoride (SF6), nitrogen trifluoride (NF3), trifluoroiodomethane (CF3I), hydrogen fluoride (HF), SF6 plasma, SF6 and argon (Ar) plasma, NF3 plasma, NF3 and Ar plasma, or combinations of these.
A twentieth aspect of the present disclosure may include either one of the eighteenth or nineteenth aspects, wherein the fluorine source may comprise SF6, an SF6 plasma, or a plasma comprising SF6 and argon (Ar).
A twenty-first aspect of the present disclosure may include any one of the eighteenth through twentieth aspects, wherein the metal precursor may comprise an aluminium precursor selected from one or more of trimethylaluminium (TMA), triethylaluminium (TEA), dimethylaluminium isopropoxide (DMAI), [MeC(NiPr)2]AlEt2, dimethylaluminiumhydride, dimethylethylamine, ethylpiperidine, dimethylaluminium hydride, or combinations of these.
A twenty-second aspect of the present disclosure may include any one of the eighteenth through twenty-first aspects, wherein the metal precursor may comprise a magnesium precursor selected from the group consisting of bis(ethylcyclopentadienyl)magnesium, bis(cyclopentadienyl)magnesium, bis(2,2,6,6-tetramethyl-3,5-heptanedionato)magnesium, bis(N,N′-di-sec-butylacetamidinato) magnesium, bis(pentamethylcyclopentadienyl)magnesium, and combinations of these.
A twenty-third aspect of the present disclosure may include any one of the eighteenth through twenty-second aspects, wherein the ALD may have growth rate of the protective ALD coating of 0.5 Angstroms of thickness per cycle, wherein one complete cycle of the ALD process comprises one pulse of the fluorine source and one pulse of the organometallic compound.
A twenty-fourth aspect of the present disclosure may include any one of the eighteenth through twenty-third aspects, further comprising exposing the surface to a pulse containing an oxygen source after exposing the surface to the pulse comprising the metal precursor and before exposing the surface to the pulse comprising the fluorine source. The metal precursor may form a ligated metal at the outer surface of the article. The oxygen source may cause oxidation of the ligated metal to form a metal oxide. The fluorine source may reduce the metal oxide to form the metal fluoride of the protective ALD coating.
A twenty-fifth aspect of the present disclosure may include the twenty-fourth aspect, wherein the oxygen source may comprise water, water plasma, oxygen, oxygen plasma, ozone, ozone plasma, hydrogen peroxide, hydrogen peroxide plasma, oxygen-containing liquid, oxygen-containing gas, or combinations of these.
A twenty-sixth aspect of the present disclosure may include any one of the first through twenty-fifth aspects, comprising depositing a first ALD protective layer on the etched surface of the reflective coating and depositing a second ALD protective layer on an outer surface of the first ALD protective layer.
A twenty-seventh aspect of the present disclosure may include any one of the first through twenty-sixth aspects, where the ALD protective layer may comprise a high reflective index metal fluoride, wherein the high reflective index metal fluoride may increase the reflectance of the enhanced aluminium mirror relative to a mirror comprising only the reflective coating.
A twenty-eighth aspect of the present disclosure may be directed to an enhanced aluminium mirror for ultraviolet optical systems. The enhanced aluminium mirror may comprise a substrate having a surface, and a reflective coating deposited onto the surface of the substrate, wherein the reflective coating comprises aluminium metal deposited by physical vapor deposition. The enhanced aluminium mirror may further include an ALD protective layer deposited onto an etched surface of the reflective coating. The ALD protective layer may be applied through atomic layer deposition, the reflective coating may reflects light having wavelengths in at least the vacuum ultraviolet wavelength range, and the ALD protective layer may reduce or prevent oxidation of the aluminium of the reflective coating.
A twenty-ninth aspect of the present disclosure may include the twenty-eighth aspect, wherein the reflective coating and the ALD protective layer may contain less than 5 atomic percent oxygen atoms.
A thirtieth aspect of the present disclosure may include either one of the twenty-eighth or twenty-ninth aspects, wherein the enhanced aluminium mirror does not have a layer of aluminium oxide disposed between the reflective coating and the ALD protective layer.
A thirty-first aspect of the present disclosure may include any one of the twenty-eighth through thirtieth aspects, wherein the ALD protective layer may comprise a high reflective index metal fluoride, wherein the high reflective index metal fluoride may increase the reflectance of the enhanced aluminium mirror relative to a mirror comprising only the reflective coating.
A thirty-second aspect of the present disclosure may include the thirty-first aspect, wherein the high reflective index metal fluoride may comprise lanthanum fluoride, gadolinium fluoride, or both.
A thirty-third aspect of the present disclosure may include any one of the twenty-eighth through thirty-second aspects, wherein the ALD protective layer may comprise a first ALD protective layer comprising a first ALD metal fluoride and a second ALD protective layer comprising a second ALD metal fluoride that is different from the first ALD metal fluoride.
Additional features and advantages of the enhanced aluminium mirrors and the methods of producing the enhanced aluminium mirrors described herein will be set forth in the detailed description that follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description that follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.
Reference will now be made in detail to various embodiments of enhanced aluminium mirrors and methods of making the enhanced aluminium mirrors for VUV optics, according to the present disclosure. Examples of the enhanced aluminium mirrors and methods disclosed herein are schematically depicted in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. Referring now to
A method of making the enhanced aluminium mirror 100 can include depositing the reflective coating 110 comprising aluminium metal to at least one mirror surface 104 of the substrate 102 through a PVD process in a PVD system to produce a mirror comprising the substrate 102 and the reflective coating 110. The method can further include removing aluminium oxides from the outer surface of the reflective coating 110 by conducting atomic layer etching (ALE) in an Atomic Layer Deposition (ALD) system to produce the etched surface 122 of the reflective coating 110 and depositing the ALD protective layer 120 onto the etched surface 122 of the reflective coating 110 by conducting an ALD process in the ALD system to produce the enhanced aluminium mirror 100 comprising the substrate 102, the reflective coating 110 deposited on the substrate 102, and the ALD protective layer 120 covering the etched surface 122 of the reflective coating 110.
Various embodiments of the enhanced aluminium mirrors 100 and the methods of making the enhanced aluminium mirrors 100 will be described herein with specific reference to the appended drawings.
As used herein, the term “substantially free” of a constituent may refer to a composition, fiber, or atmosphere that includes less than 0.01 percent by weight or by mole of the constituent. For example, an ALD coating that is substantially free of carbon may include less than 0.01 percent by weight or by mole carbon.
The terms “microns” and “μm” are used interchangeably herein. The terms “nanometers” and “nm” are used interchangeably herein.
As used herein, the term “plasma” refers to a gas of ions that includes positive ions and electrons, and is generated from a starting material through application of heat and an electric current.
As used herein, the term “ppm” means parts per million on a molar basis and represents an atomic concentration. For example, a layer of MgF2 with 1 ppm carbon includes 1 mole of carbon per million moles of MgF2.
As used herein, the term “conformal coating” refers to a coating that conforms to the contours of the surfaces of an article and has generally uniform thickness over all of the surfaces contacted by the coating.
As used herein, the term “passivation” refers to treating or coating a surface of an article to make the surface more passive, meaning to make the surface less reactive with the environment.
As used herein, the term “mirror surface” refers to an outer surface of a substrate to which the reflective coating is applied and is not intended to imply that the outer surface is mirrored prior to depositing the reflective coating.
As previously discussed, the performance of VUV and EUV optics for inspection of microelectronics and semiconductors can depend on the quality and reflectance of mirrors, which are incorporated into the optical inspection systems to direct the VUV and EUV wavelength light along the inspection path. Aluminium is commonly used for coating substrates to produce reflective optics (i.e., mirrors) for VUV and EUV optics systems. Aluminium is typically applied to the surface of a substrate using physical vapor deposition (PVD) to deposit the aluminium onto the surface of the substrate to create a reflective surface. PVD-Al mirrors can provide a reflectance of greater than 90% over the VUV wavelength range.
Referring to
Reflective coatings 110 comprising aluminium applied to the substrate through a PVD process can degrade over time due to oxidation of the aluminium. Oxidation of the aluminium can greatly reduce the reflectivity of the aluminium reflective coating 110. Referring to
Referring now to
To reduce or prevent oxidation of the aluminium of the reflective coating 110, the aluminium of the reflective coating 110 can be coated with a protective layer. In some cases, PVD can be used to apply the protective layer onto the outer surface 112 of the reflective coating 110. The current best practice for aluminium mirrors is to apply PVD based metal fluorides, such as but not limited to PVD magnesium fluoride (PVD-MgF2) or PVD aluminium fluoride (PVD-AlF3), to the outer surface 112 of the reflective coating 110 to form the protective layer. Referring now to
Atomic Layer Deposition (ALD) can provide a protective metal fluoride layer that has a lower oxygen penetration rate compared to PVD coatings and, thus, can improve the passivation behavior of the aluminium mirror. Referring now to
Although the ALD-AlF3 layer applied in step 610 of
Referring now to
The formation of the aluminium oxides in the mirror 300 formed by the hybrid method can reduce the reflectance of the mirror 300 in the VUV wavelength region. Referring now to
As shown in
The present disclosure is directed to enhanced aluminium mirrors and a process for producing the enhanced aluminium mirrors for VUV optics that further reduces the amount of aluminium oxides in the enhanced aluminium mirror and provides one or more ALD protective layers to reduce or prevent oxidation and degradation of the aluminium of the reflective layer during use of the enhanced aluminium mirrors. The methods of the present disclosures solve the problems in the previously discussed methods by incorporating an atomic layer etching (ALE) step after transferring the mirror with the PVD-Al reflective layer from the PVD system to the ALD system. In particular, the methods of the present disclosure include applying the PVD-Al layer to the substrate to produce the reflective layer, transferring the mirror with the reflective layer to an ALD chamber of an ALD system, conducting atomic layer etching (ALE) to remove the aluminium oxides from the outer surface of the reflective layer to produce an etched surface of the reflective layer, and then depositing an ALD protective layer onto the etched surface of the reflective coating. The ALE process removes any metal oxides that may have formed on the outer surface of the aluminium of the reflective coating prior to depositing the ALD protective layer.
Referring now to
Referring again to
The methods of the present disclosure enable the production of enhanced aluminium mirrors 100 for VUV optics that include a pin-hole free ALD protective layer 120 that reduces or prevents oxidation and degradation of the aluminium of the reflective coating 110 over time. The ALD coating process can enable all of the surfaces of the enhanced aluminium mirror to be coated in a single deposition run with atomic layer precision. In other words, ALD coating processes can enable conformal coating of all surfaces of the enhanced aluminium mirror 100 simultaneously, including non-mirror surfaces of the substrate. The ALD coating process can produce atomically dense, pin-hole-free protective films even at very small thickness, such as thicknesses down to a few nanometers, such as less than or equal to 10 nm. Thus, the ALD coating process can reduce the thickness of protective coatings to less than ⅕ the thickness of PVD-based protective coatings thick enough to provide the same protection. The ALD coating process can reduce coating stress and increase the lifetime of the enhanced aluminium mirrors.
Further, the methods disclosed herein also enable a PVD process to be used for applying the reflective coating 110 and an ALD process to be used to produce the ALD protective layer 120. In particular, the methods disclosed herein remove native aluminium oxides formed at the outer surface of the reflective coating 110 through an ALE process in the ALD chamber before the ALD protective layer is deposited. The strong reducing environment in the ALD chamber of the ALD system prevents further oxidation of the aluminium of the reflective coating 110 during the ALD process. Further, the ALE and ALD processes can be accomplished at similar temperatures, which can reduce delays between the ALE and ALD steps in the method and reduce the chances of further oxidation during heating or cooling steps. The ALE and ALD processes can be conducted using sulphur hexafluoride (SF6) and/or SF6 plasmas, which are better alternatives to hydrogen fluoride-based fluorine sources. Additionally, the ALD protective layer 120 can include a plurality of different layers comprising different metal fluoride materials. For instance, the ALD protective layer 120 can include an aluminium fluoride ALD layer and a magnesium fluoride ALD layer, which can reduce roughness and improve passivation of the enhanced aluminium mirror 100, among other features. In some embodiments, the ALD protective layer 120 comprises ALD-AlF3—MgF2.
Referring again to
The first step in the methods for producing the enhanced aluminium mirrors 100 herein for VUV optics includes forming the reflective coating 110 on the mirror surface 104 of a substrate 102. Referring again to
The reflective coating 110 of the enhanced aluminium mirror 100 can be a PVD-Al layer applied to the mirror surface 104 of the substrate 102. The PVD-Al layer of the reflective coating 110 can be applied to the mirror surface 104 of the substrate 102 through a PVD process at ambient temperature according to known methods in the art. The reflective coating 110 comprising the PVD-AL layer can comprise aluminium metal. Referring to
Referring again to
Referring now to
The ALD system 1000 can further include one or more sources of reaction constituents in fluid communication with the inlet 1006 of the ALD chamber 1002. In particular, the ALD system 1000 can include a fluorine source 1020, a metal precursor source 1030, an oxygen source 1040, or combinations of these. The ALD system 100 can include a fluorine source control valve 1022 disposed between the fluorine source 1020 and the ALD chamber 1002 and operable to control the flow rate of the fluorine source 1020 into the ALD chamber 1002. The ALD system 100 can include a metal precursor source control valve 1032 disposed between the metal precursor source 1030 and the ALD chamber 1002 and operable to control the flow rate of the metal precursor source 1030 into the ALD chamber 1002. The ALD system 100 can include an oxygen source control valve 1042 disposed between the oxygen source 1040 and the ALD chamber 1002 and operable to control the flow rate of the oxygen source 1040 into the ALD chamber 1002. The ALD system 1000 can also include an inert gas source 1050 and an inert gas control valve 1052 operable to control the flow of the inert gas from the inert gas source 1050 into the ALD chamber 1002. Prior to the ALE process, the substrate 102 comprising the reflective coating 110 is placed within the ALD chamber 1002 of the ALD system 1000.
Referring again to
Exposing the reflective coating 110 to the pulse comprising the fluorine source converts aluminium oxides at the outer surface of the reflective coating 110 to aluminium fluoride to form a thin layer of aluminium fluoride on the outer surface of the reflective coating 110. Some aluminium metal can also react with the fluorine source to produce aluminium fluorides at the outer surface 112 of the reflective coating 110. The layer of aluminium fluoride at the outer surface 112 of the reflective coating 110 can be a single molecule in thickness. The oxygen that is replaced can form one or more volatile oxygen species that are released into the ALD chamber 1002. Following the pulse containing the fluorine source, the ALD chamber 1002 can be purged with an inert gas (e.g., Ar, He, Ne, etc.) to remove the volatile oxygen species and any residual fluorine source from the ALD chamber 1002 prior to performing the next pulse of the organometallic compound.
After purging, the methods include exposing the thin layer of aluminium fluoride to a pulse comprising the organometallic compound. Exposing the aluminium fluoride layer to the organometallic compound can cause the aluminium fluoride to react to form volatile organometallic fluoride compounds that are released from the outer surface 112 of the reflective coating 110 and out into the ALD chamber 1002. Referring again to
Each iteration of the ALE process removes about a single molecular layer of aluminium oxide from the surface of the reflective coating 110. The ALE process (e.g., the alternating pulses of the fluorine source and organometallic compound) can be repeated a plurality of times until the aluminium oxides are all removed or to a target depth of from 1 nm to 10 nm, or from 3 nm to 5 nm, from the original outer surface 112 of the reflective layer 110 prior to ALE. In other words, the ALE process can be repeated until from 1 nm to 10 nm or from 3 nm to 5 nm of the material is removed from the outer surface 112 of the reflective layer 110 to produce the etched surface 122 of the reflective layer 110. Following the ALE process, the reflective coating 110 can be substantially free of oxygen containing compounds.
The fluorine source can be derived from a fluorine-containing precursor. The fluorine-containing precursor can be selected from the group consisting of sulfur hexafluoride (SF6), nitrogen trifluoride (NF3), trifluoroiodomethane (CF3I), hydrogen fluoride (HF), and combinations of these. In embodiments, the fluorine source can be a plasma fluorine source derived from a fluorine-containing precursor or a fluorine-containing precursor and argon (Ar) plasma. In embodiments, the fluorine source may be a plasma comprising SF6, SF6 and Ar (SF6/Ar), or NF3 and Ar (NF3/Ar).
HF is commonly used as a fluorine source in ALD systems. However, using HF as the fluorine source requires increasing the temperature of the ALD chamber 1002 in order to promote reduction of the aluminium oxides to form AlF3. The substrate 102 and reflective layer 110 must then be cooled to a lower temperature for the ALD process. Oxidation of the etched surface 122 during this cool down period is a concern that could reduce the effectiveness of removal of the aluminium oxides during the ALE process on the reflectance of the enhanced aluminium mirror 100. Additionally, HF is dangerous to handle and highly corrosive, particularly when contacted with water. Thus, in embodiments, the fluorine source can be a non-HF fluorine source that enables the same process temperature for both ALE and ALD processes and that is significantly safer.
SF6 fluorine precursor is significantly safer to use compared to HF and enables similar temperature ranges to be used for both the ALE and ALD processes. In embodiments, the fluorine source may comprise SF6 or a plasma derived from SF6 (i.e., SF6-based plasma). In embodiments, the fluorine source may comprise, consist of, or consist essentially of an SF6-based fluorine source, such as SF6 or an SF6-based plasma. In embodiments, the fluorine source may comprise, consist of, or consist essentially of a plasma derived from SF6 and Ar (i.e., SF6/Ar plasma) or SF6 and other inert gases. When the fluorine source comprises an SF6/Ar plasma, a flow rate ratio of the Ar to SF6 may be from 0.1:1 to 10:1, from 0.1:1 to 5:1, from 0.1:1 to 2:1, from 0.5:1 to 10:1, from 0.5:1 to 5:1, from 0.5:1 to 2:1, from 1:1 to 10:1, from 1:1 to 5:1, from 1:1 to 2:1, from 2:1 to 10:1, from 2:1 to 5:1, or about 2:1, where flow rate is a volumetric flow rate expressed in units of sccm (standard cubic centimeters per minute).
The fluorine source may be converted into a plasma by heating a fluorine precursor, such as but not limited to SF6, and subjecting the heated fluorine precursor to an electric current or a strong electromagnetic field. Argon (Ar) can be added to create an SF6/Ar plasma. The materials (e.g., fluorine precursor, Ar, or combinations of these) can be heated to the ALD process temperature and subjected to an electric current sufficient to convert the materials into a plasma. In embodiments, converting the materials (e.g., fluorine precursor, Ar, or combinations of these) into a plasma may comprise heating the materials to a temperature of from 100° C. to 325° C., or from 120° C. to 250° C., and applying an electric current having a power of from 50 Watts (W) to 600 W, or from 100 Watts (W) to 300 W.
The methods may include exposing the reflective coating 110 comprising the PVD-Al layer to the pulse comprising the fluorine source at the ALE temperature of from 150° C. to 325° C., such as from 200° C. to 250° C. The methods can include exposing the reflective coating 110 comprising the PVD-Al layer to the pulse comprising the fluorine source at a power of from 50 W to 600 W, from 50 W to 300 W, from 100 W to 600 W, or even from 100 W to 300 W. The methods can include exposing the reflective coating 110 comprising the PVD-Al layer to the pulse comprising the fluorine source for a fluorine pulse duration that is sufficient to react all the aluminium oxide molecules on the very outer surface of the PVD-Al layer with the fluorine source to produce a single molecule layer of aluminium fluoride. In embodiments, the fluorine pulse duration can be from 1 second to 30 seconds, or about 7 seconds. As previously discussed, after exposing the outer surface of the reflective layer 110 to the fluorine source for the exposure time, the ALD chamber can be purged with an inert gas for a purge time sufficient to remove at least 99% of the residual fluorine source and oxides from the ALD chamber.
Following exposure to the fluorine source and purging, the ALE process can include exposing the aluminium fluoride layer to a pulse comprising the organometallic compound. The organometallic compound can include one or more of trimethylaluminium (TMA), triethylaluminium (TEA), dimethylaluminium chloride (DMAC), silicon tetrachloride (SiCl4), aluminium hexafluoroacetylacetonate (Al(hfac)3), Tri-i-butylaluminium (Al(iBu)3), tin(II) acetylacetonate (Sn(acac)2), tris(2,2,6,6-tetramethyl-3,5-heptanedionato)aluminium (i.e., Al(TMHD)3, or combinations of these. In embodiments, the organometallic compound can be an organoaluminium compound selected from the group consisting of TMA, YEA, DMAC, aluminium hexafluoroacetylacetonate, Tri-i-butylaluminium (Al(iBu)3), tris(2,2,6,6-tetramethyl-3,5-heptanedionato)aluminium (i.e., Al(TMHD)3, and combinations of these. In embodiments, the organometallic compound can be TMA, and exposure of the thin layer of aluminium fluoride on the surface of the reflective layer to the TMA causes reaction between the TMA and the aluminium fluoride to form AlF(CH3)2 gas. The AlF(CH3)2 is released from the outer surface of the reflective coating 110 and into the ALD chamber.
Referring again to
The method may include exposing the thin layer of aluminium fluoride to the organometallic compound at a temperature and pressure sufficient for the organometallic compound to react with the aluminium fluoride to produce the volatile organometallic compound. In embodiments, the method can include exposing the thin layer of aluminium fluoride to the organometallic compound at the ALE temperature of from 150° C. to 325° C. The method may include exposing the thin layer of aluminium fluoride to the organometallic compound at a pressure of from 10 millitorr (1.33 Pa) to 100 torr (13,332 Pa).
Referring again to
The ALE steps of exposing the outer surface 112 of the reflective layer 110 to the pulse comprising the fluorine source to produce the thin layer of aluminium fluoride, purging, contacting the thin layer of aluminium fluoride with the organometallic compound to convert the aluminium fluoride to a volatile organometallic compound, and purging can be performed a plurality of times. The etch rate of the ALE process can be about 1.1 Angstroms of thickness per cycle (A/cycle) at an ALE temperature of 225° C. One complete cycle of the ALE process comprises one pulse of the fluorine source and one pulse of the organometallic compound with the accompanying purge steps therebetween. The ALE process can be continued for a plurality of cycles necessary to remove all of the aluminium oxides from the surface of the reflective coating.
Referring again to
Following the ALE process to etch away the aluminium oxides from the surface of the reflective layer 110, the ALD protective layer 120 is then deposited on top of the etched surface 122 of the reflective coating 110. The ALD protective layer 120 and ALD process for producing the ALD protective layer 120 will now be described with reference to the enhanced aluminium mirror 100 in
The ALD protective layer 120 can comprise a metal fluoride. In embodiments, the ALD protective layer 120 can be aluminium fluoride (AlF3), magnesium fluoride (MgF2), lithium fluoride (LiF), calcium fluoride (CaF2), or combinations thereof. Additionally or alternatively, in embodiments, the ALD protective layer 120 may comprise other metal fluorides, such as but not limited to, lanthanum fluoride (LaF3) ALD coatings or gadolinium fluoride (GdF3) ALD coatings. In some embodiments, the ALD protective layer 120 comprises AlF3 and MgF2. The ALD protective layer 120 can be coupled directly to the etched surface 122 of the reflective coating 110. As used herein, the term “coupled directly to” means that the ALD protective layer 120 contacts and is bonded to the etched surface of the reflective coating 110 without any intervening coating or layer disposed between the ALD protective layer 120 and the etched surface 122 of the reflective coating 110. Referring now to
Referring again to
In embodiments, the ALD process may be a direct reduction ALD process, during which the metal precursor is deposited onto the etched surface 122 of the reflective coating 110 or other surfaces of the substrate 102 and then directly reduced using a reducing agent, such as the fluorine source, to produce the ALD protective layer 120. In embodiments, the ALD process for applying the ALD protective layer 120 may include exposing at least the etched surface 122 of the reflective coating 110 to alternating pulses of a metal precursor and a fluorine source. Referring to
The process for deposing the ALD protective layer 120 has a similar chemistry to the ALE process, except that the order of the steps is in reverse. In the ALD process, the reflective coating 110 is exposed to the metal precursor pulse first, followed by exposure to the fluorine source pulse. For the ALD process, the duration of exposure to the metal precursor pulse is much less compared to the total contact time between the organometallic compound and the aluminium fluoride in the ALE process. Additionally, in the ALD process, the throttle valve 1010 of the ALD system 1000 (
In embodiments, the ALD protective layer 120 can be a metal fluoride coating, and the ALD process can include exposing the etched surface 122 of the reflective coating 110 to the pulse containing the metal precursor, purging the ALD chamber after the metal precursor pulse with an inert gas, and exposing the etched surface 122 of the reflective coating 110 to a subsequent pulse of the fluorine source. During the pulse of the metal precursor, the metal precursor, in vapour, plasma, or atomized liquid form, may be injected into the ALD chamber containing the substrate 102 with the reflective coating 110 that has been etched through the ALE process. The ALD process may further include heating the metal precursor (e.g., aluminium precursor, magnesium precursor, lithium precursor, calcium precursor, lanthanum precursor, gadolinium precursor, etc.) to a temperature greater than or equal to 95° C. prior to introducing the metal precursor to the ALD chamber. Exposing the etched surface 122 of the reflective coating 110 to the pulse containing the metal precursor may cause the metal precursor to react with the aluminium at the etched surface 122 of the reflective coating 110 to bond a single layer of ligated metal onto the etched surface 122 of the reflective coating 110.
The single layer of ligated metal bonded to the surface may have a thickness approximately equal to a size of a single molecule of the ligated metal. For pulses of the metal precursor subsequent to depositing the initial ALD metal fluoride layer directly bonded to the etched surface 122, the metal precursor may react with the previously deposited metal fluoride to bond a subsequent single layer of ligated metal to the outer surface of the previously deposited ALD metal fluoride layer. After depositing and bonding the single layer of ligated metal to the surface (e.g., etched surface 122 or surface of previously deposited ALD metal fluoride layer), the ALD process may further include ceasing exposure of the mirror to the metal precursor. Ceasing exposure of the mirror to the metal precursor may include stopping the flow of the metal precursor into the ALD chamber.
The pulse of the metal precursor may have a pulse duration sufficient for the metal precursor to react with at least 90%, at least 95%, at least 98%, at least 99%, or at least 99.9% of the reactive aluminium sites at the etched surface 122 of the reflective coating 110 or of the reactive metal fluoride sites at the outer surface of the previous applied ALD metal fluoride layer. In embodiments, the pulse of the metal precursor may have a pulse duration of from 10 milliseconds (ms) to 10 seconds (s), or for about 1 second. Factors influencing the pulse duration include the vapor pressure of the metal precursor, flow rate of the metal precursor, reactivity of the metal precursor with the surface, volume of the ALD chamber, and dimensions of the substrate 102. In embodiments, the pulse duration of the metal precursor can be set to achieve coverage, preferably conformal coverage, of at least 90%, or at least 95%, or at least 98%, or at least 99%, or at least 99.9% of the area of the etched surface 122 of the reflective coating 110 and optionally all of the other surfaces of the substrate 102. Referring again to
After purging the chamber, the mirror may be exposed to the pulse comprising the fluorine source. During the fluorine source pulse, the fluorine source may be injected into the ALD chamber containing the mirror. The fluorine source pulse may include the fluorine source or the fluorine source in combination with an inert gas, such as any of the inert gases discussed herein. Exposing the layer of ligated metal bonded to the surfaces of the mirror to the subsequent pulse containing the fluorine source may cause the fluorine source to react with the ligated metal to reduce the ligated metal to form the metal fluoride (e.g., undergo a chemical reduction reaction between the fluorine source and ligated metal to replace the ligand with fluorine to produce the metal fluoride of the ALD protective layer 120). Injection of the fluorine source may be ceased at the end of the pulse, when at least 90%, at least 95%, at least 98%, at least 99%, or even at least 99.9% of the ligated metal at the surface of the mirror has reacted with the fluorine source to form the metal fluoride. In embodiments, the fluorine source pulse may have a pulse duration of from 10 ms to 30 s, such as from 10 ms to 20 s, from 10 ms to 10 s, from 1 s to 30 s, from 1 s to 20 s, from 1 s to 10 s, from 3 s to 30 s, from 3 s to 20 s, or from 3 s to 10 s. The fluorine source pulse may be ceased by stopping the flow of the fluorine source into the ALD chamber. The ALD process may be repeated a plurality of times through a sequence of alternating pulses of metal precursor and fluorine source to add further ALD metal fluoride layers to increase the thickness of the ALD protective layer 120.
In embodiments, the ALD protective layer 120 can include an ALD aluminium fluoride (ALD-AlF3) layer. When the ALD protective layer 120 includes an ALD-AlF3 layer, the metal precursor can be a metal ligand complex comprising aluminium. In embodiments, the metal precursor may can include one or more of TMA, TEA, dimethylaluminium isopropoxide (DMAI), dimethylaluminium hydride: dimethylethylamine, ethylpiperidine:dimethylaluminium hydride, dimethylaluminium chloride (DMAC), aluminium hexafluoroacetylacetonate (Al(hfac)3), tri-i-butylaluminium (Al(i-Bu)3), tris(2,2,6,6-tetramethyl-3,5-heptanedionato)aluminium (Al(TMHD)3, or combinations thereof. Other aluminium compounds may also be suitable for use as the metal precursor. In embodiments, the ALD protective layer 120 can include an ALD magnesium fluoride (ALD-MgF2) layer. In the case of an ALD-MgF2 layer, the metal precursor may be a metal ligand complex comprising magnesium as the metal. In embodiments, the metal precursor may be 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, bis(pentamethylcyclopentadienyl)magnesium, and combinations of these. Other magnesium-containing compounds may also be suitable as the metal precursor for forming the MgF2 ALD layer.
In embodiments, the ALD protective layer 120 can be a metal fluoride having a metal other than aluminium or magnesium. In these cases, similar metal ligand complexes may be used where the metal is different from aluminium or magnesium. For instance, in embodiments, the metal of the metal precursor may be calcium (Ca), lithium (Li), or combinations thereof. In embodiments, the ALD protective layer 120 can include an ALD calcium fluoride (ALD-CaF2) layer. When the ALD protective layer 120 is an ALD-CaF2 layer, the metal precursor may be selected from the group consisting of Ca(2,2,6,6-tetramethyl-3,5-heptanedionato)2, Bis(N,N′-diisopropylformamidinato)calcium(II), bis(N,N′-diisopropylacetamidinato)calcium(II), [Ca3(2,2,6,6-tetramethyl-3,5-heptanedionate)6], Ca(1,2,4-triisopropylcyclopentadienyl)2], and combinations thereof. In embodiments, the ALD protective layer 120 can include an ALD lithium fluoride (ALD-LiF) coating. When the ALD protective layer 120 includes the ALD-LiF layer, the metal precursor may be selected from the group consisting of lithium tert-butoxide, lithium 2,2,6,6-tetramethyl-3,5-heptanedionate, and combinations thereof.
In embodiments, the ALD protective layer 120 can include a high reflective index fluoride ALD layer, such as but not limited to lanthanum fluoride (LaF3), gadolinium fluoride (GdF3), or combinations of these. When the ALD protective layer 120 includes the ALD-LaF3 layer, the metal precursor can be one or more lanthanum precursors selected from the group consisting of tris(N,N′-diisopropylformamidinato) lanthanum, tris [N,N-bis(trimethylsilyl)amide]lanthanum(III), (2,2,6,6-tetramethyl-3,5-heptanedione) lanthanum, tris(tetramethylcyclopentadienyl) lanthanum(III), LANA™ brand lanthanum precursor from Air Liquide, and combinations thereof. When the ALD protective layer 120 includes the ALD-GdF3 layer, the metal precursor can be one or more gadolinium precursors selected from the group consisting of gadolinium tris(N,N′-isopropylacetamidinate), tris(isopropyl-cyclopentadienyl) gadolinium(III) (Gd(iPrCp)3), tris(OCMe2CH2OMe) gadolinium(III) (Gd(mmp)3), tris(2,3-dimethyl-2-butoxy) gadolinium(III) (Gd(DMB)3), tris(2,2,6,6-tetramethyl-3,5-heptanedionato) gadolinium(III) (Gd(thd)3), GANBETTA™ brand gadolinium precursor available from Air Liquide, GAUDI™ brand gadolinium precursor available from Air Liquide, and combinations thereof.
The metal precursor may be in vapor, plasma, liquid, or atomized liquid form. The metal precursor pulse may include the metal precursor or a mixture of the metal precursor and an inert gas, which may be any of the inert gases previously discussed herein. The inert gas may be used as a carrier gas to transport the metal precursor into the ALD chamber.
In embodiments, the ALD protective layer 120 may be a metal fluoride compound comprising a plurality of different metals. In embodiments, the ALD protective layer 120 may have the general formula AXMYFZ; where A is a first metal selected from the group consisting of Mg, Ca, Li, and Al; M is a second metal different from the first metal A, where M is selected from the group consisting of Mg, Ca, Li, and Al; X is the number of moles of the first metal A; Y is the number of moles of the second metal M; and Y is the number of moles of fluorine (F). In embodiments, the ALD protective layer 120 may be LiXAlYFZ or CaXAlYFZ, in which X is the number of moles of Li or Ca, respectively; Y is the number of moles of Al, and Z is the number of moles of F. Other metal fluorides comprising a mixture of different metals are contemplated. Metal fluoride ALD coatings comprising a plurality of different metals may be made by exposing the optical component to a metal precursor pulse having a plurality of different metal precursors, each of the different metal precursors having a different metal.
The fluorine source can be derived from a fluorine-containing precursor selected from the group consisting of sulfur hexafluoride (SF6), nitrogen trifluoride (NF3), ammonium fluoride (NH4F), trifluoroiodomethane (CF3I), hydrogen fluoride (HF), and combinations thereof. In embodiments, the ALD process can be a plasma-assisted ALD process in which the fluorine source is a plasma fluorine source derived from a fluorine-containing precursor or a fluorine-containing precursor and argon (Ar) plasma. In embodiments, the fluorine source can be a plasma comprising SF6, SF6 and Ar (SF6/Ar), or NF3 and Ar (NF3/Ar). In embodiments, the fluorine source can be derived from one or more organic fluorine sources, such as but not limited to hexafluoroacetylacetone or other fluorine-containing organic compounds. However, organic fluorine sources may require additional pulse steps in the ALD process, such as a long ozone pulse, to remove the carbon compounds, which are contributed by the organic fluorine source, from the ALD coating.
HF is commonly used as a fluorine source in ALD coating operations. However, HF is dangerous to handle and highly corrosive, particularly when contacted with water. Therefore, safer alternatives to HF are desired. SF6 fluorine precursor is significantly safer to use compared to HF and is more productive than organic fluorine sources, which require a four-step process and a long ozone pulse to form the metal fluoride ALD protective layer. In embodiments, the fluorine source may comprise SF6 or a plasma derived from SF6 (i.e., SF6-based plasma). In embodiments, the fluorine source may comprise, consist of, or consist essentially of an SF6-based fluorine source, such as SF6 or an SF6-based plasma. In embodiments, the fluorine source may comprise, consist of, or consist essentially of a plasma derived from SF6 and Ar (i.e., SF6/Ar plasma) or SF6 and other inert gas. When the fluorine source comprises an SF6/Ar plasma, a flow rate ratio of the Ar to SF6 may be from 0.1:1 to 10:1, from 0.1:1 to 5:1, from 0.1:1 to 2:1, from 0.5:1 to 10:1, from 0.5:1 to 5:1, from 0.5:1 to 2:1, from 1:1 to 10:1, from 1:1 to 5:1, from 1:1 to 2:1, from 2:1 to 10:1, from 2:1 to 5:1, or about 2:1, where flow rate is a volumetric flow rate expressed in units of sccm (standard cubic centimeters per minute).
As previously discussed, the ALD process can be a direct reduction process in which deposition of the ALD protective layer 120 is accomplished by bonding the ligated metal to the surface of the optical component and then directly reducing the ligated metal with the fluorine source to produce the ALD metal fluoride layer. However, when SF6, SF6 plasma, or SF6/Ar plasma is used as the fluorine source, the resulting ALD coating can have a high concentration of carbon impurities originating from the ligands of the ligated metal. Not intending to be bound by any particular theory, it is believed that the sulphur from the SF6 may react with the ligands to damage or break apart the ligands during the reaction of the ligated metal with the fluorine source to produce the metal fluoride, thus, causing carbon or carbon-containing fragments of the ligands to remain in the ALD protective layer.
When SF6 is used to provide the fluorine source, the concentration of carbon deposits in the ALD protective layer 120 can be reduced or eliminated by conducting an oxide formation step between the metal precursor pulse and the fluorine source pulse. The oxide formation step can include exposing the mirror having the layer of ligated metal deposited on the surfaces thereof to an oxygen source for a pulse duration sufficient to oxidize or convert the ligated metal to a metal oxide. Exposure of the ligated metal to the pulse containing the oxygen source may cause the ligand of the ligated metal to react with oxygen of the oxygen source to replace the ligand with oxygen, which becomes bonded to the metal (e.g., the ligated metal undergoes an oxidation reaction to convert the ligated metal layer into a metal oxide layer). Following the metal oxide formation, the ALD chamber may be purged of any residual oxygen source. The mirror with the layer of metal oxide on the outermost surfaces can then be exposed to the pulse containing the fluorine source. Exposure of the metal oxides to the fluorine source converts the metal oxide into the metal fluoride of the ALD protective layer 120. The oxygen source can include water (H2O), H2O plasma, ozone (O3), O3 plasma, oxygen (O2), O2 plasma, hydrogen peroxide, other oxygen-containing gases, other oxygen-containing liquids, or combinations thereof. The oxygen source can be in a liquid state, gaseous state, or plasma state. In embodiments, the oxygen source pulse can include the oxygen source or the oxygen source in combination with one or more inert gases, which may be any of the inert gases previously described herein.
When an SF6-based fluorine source is used, the ALD process comprising first converting the metal ligand to the metal oxide with the oxygen source pulse and then converting the metal oxide to metal fluoride with the fluorine source pulse may produce an ALD protective layer having a lesser concentration of carbon compared to direct reduction of the metal ligand with the fluorine source. Not intending to be bound by any particular theory, it is believed that oxidation of the ligands of the ligated metal may wholly remove the ligands from the metal without decomposing the ligand, thereby eliminating or greatly reducing the fragments of organic (carbon-containing) constituents that remain attached to the metal or that otherwise remain present in the ALD protective layer 120.
In embodiments, the methods disclosed herein can include exposing the etched surface 122 of the reflective layer 110 of the mirror to the pulse containing the metal precursor to produce a metal ligand layer, exposing the metal ligand layer a pulse containing an oxygen source to produce a metal oxide layer, and then exposing the metal oxide layer to the pulse containing the fluorine source to convert the metal oxides to the metal fluoride of the ALD protective layer 120. The ALD process of the methods disclosed herein can first comprise exposing the mirror to the metal precursor. During the pulse of the metal precursor, the metal precursor, in vapour, plasma, or atomized liquid form, can be introduced, such as through injection, into the ALD chamber containing the mirror (i.e., substrate 102 comprising the reflective layer 110 after atomic layer etching). Exposing the surfaces of the mirror to the pulse containing the metal precursor may cause the metal precursor to react with the aluminium at the etched surface 122 of the reflective coating 110 of the mirror to bond a single layer (monolayer) of ligated metal onto the etched surface 122 of the reflective coating 110. The metal precursor may be any of the metal precursors previously described herein. The metal precursor pulse may have a duration sufficient to cause the metal precursor to react with at least 90%, at least 95%, at least 98%, at least 99%, or even at least 99.9% of the reactive aluminium sites on the etched surface 122 of the reflective layer 110. The metal precursor pulse may have a pulse duration of from 10 ms to 10 seconds, or about 1 second. The single layer of ligated metal bonded to the surface may have a thickness equivalent to a size of a single molecule of the metal ligand. For pulses of the metal precursor subsequent to the initial ALD metal fluoride layer, the metal precursor may react with the previously deposited ALD metal fluoride layer to bond a subsequent single layer of ligated metal to the outer surface of the ALD metal fluoride layer. After depositing and bonding the single layer of ligated metal to the outer surface of the mirror (e.g., etched surface 122 or outer surface of the previously deposited ALD metal fluoride layer), the ALD coating process may further include ceasing exposure of the mirror to the metal precursor. Ceasing exposure of the mirror to the metal precursor may include stopping the flow of the metal precursor into the ALD chamber. The ALD chamber may then be purged with an inert gas to remove any residual metal precursor from the ALD chamber before continuing with the ALD process.
After ceasing exposure of the optical component to the metal precursor and purging the ALD chamber, the ALD process part of the methods disclosed herein can include exposing the mirror having the layer of ligated metal bonded thereto to an oxygen source. The oxygen source can include water, water plasma, oxygen, oxygen plasma, ozone, ozone plasma, hydrogen peroxide, hydrogen peroxide plasma, oxygen-containing liquid, oxygen-containing gas, or combinations of these. The oxygen source may be in a liquid state, gaseous state, or plasma state. Exposing the ligated metal layer on the surface of the mirror to the oxygen source may comprise introducing a pulse containing the oxygen source into the ALD chamber containing the mirror. In embodiments, the oxygen source pulse may include the oxygen source or the oxygen source in combination with one or more inert gases, which may be any of the inert gases previously described herein. Exposing the mirror to the oxygen-containing pulse may cause oxidation of the ligated metal to form the metal oxide on the surfaces of the mirror. The oxygen source pulse may have a pulse duration sufficient to cause the oxygen source to react with at least 90%, at least 95%, at least 98%, at least 99%, or even at least 99.9% of the ligated metal bonded to the surfaces of the mirror. The oxygen source pulse may have a pulse duration of from 0.1 seconds to 1 second, or about 0.3 seconds. The ALD process may further include ceasing exposure of the mirror to the oxygen source pulse, such as by stopping the flow of the oxygen source into the ALD chamber at the end of the oxygen source pulse. In embodiments, the ALD chamber may then be purged with an inert gas after the oxygen source pulse, which may remove any residual oxygen and organic compounds from the ALD chamber.
The ALD process may further include, after the oxygen source pulse, exposing the mirror having the layer of metal oxide deposited on surfaces thereof to the fluorine source. Exposing the mirror to the fluorine source may comprise introducing a pulse containing the fluorine source to the ALD chamber containing the mirror. The fluorine source may be any of the compositions previously described herein for the fluorine source. In embodiments, the fluorine source is an SF6-based fluorine source, such as but not limited to SF6, SF6 plasma, SF6/Ar plasma, or combinations of these. The fluorine from the fluorine source may reduce the metal oxides to form the metal fluoride of the ALD protective layer 120 on the surfaces of the mirror to produce the enhanced aluminium mirror 100. The fluorine source pulse may have a duration sufficient to cause the fluorine to react with at least 90%, at least 95%, at least 98%, at least 99%, or even at least 99.9% of the metal oxide at the surfaces of the mirror to produce the enhanced aluminium mirror 100. The fluorine source pulse may have a pulse duration of from 10 ms to 30 s, such as from 10 ms to 20 s, from 10 ms to 10 s, from 1 s to 30 s, from 1 s to 20 s, from 1 s to 10 s, from 3 s to 30 s, from 3 s to 20 s, or from 3 s to 10 s. The process may further include ceasing exposure of the enhanced aluminium mirror 100 to the fluorine source, such as by stopping the flow of the fluorine source into the ALD chamber at the end of the fluorine source pulse. As previously discussed, exposing the optical component to the oxygen source after exposure to the metal precursor and before exposure to the fluorine source may reduce the concentration of carbon in the ALD protective layer 120 applied to the reflective coating 110 of the enhanced aluminium mirror 100 compared to alternating pulses of the metal precursor and the fluorine source without the pulse containing the oxygen source.
The mirror comprising the substrate 102 and the reflective coating 110 may be contacted with or exposed to the metal precursor and fluorine source or metal precursor, oxygen source, and fluorine source at operating conditions sufficient to cause the metal precursor, fluorine source, oxygen source, or combinations of these to undergo chemical reactions at the surfaces of the mirror to deposit the ALD protective layer 120 on top of the reflective coating 110. The ALD process may be conducted at a process temperature sufficient to cause the metal precursor, oxygen source, fluorine source, or combinations of these to undergo reactions at the surface of the optical component. In embodiments, the ALD process may include depositing the ALD coating on the surfaces of the optical component at a process temperature of from 120° C. to 250° C.
In embodiments, the ALD process can be a plasma-assisted ALD process, in which plasma materials are utilized for one or more of the metal precursor pulse, oxygen source pulse, fluorine source pulse, or combinations of these. The metal precursor, oxygen source, fluorine source, or combinations of these may be converted into a plasma by heating the materials and subjecting the materials to an electric current or a strong electromagnetic field. The materials (e.g., metal precursor, oxygen source, fluorine source, or combinations of these) may be heated to the ALD process temperature and subjected to an electric current sufficient to convert the materials into a plasma. In embodiments, converting the materials (e.g., metal precursor, oxygen source, fluorine source, or combinations thereof) into a plasma may comprise heating the materials to a temperature of from 100° C. to 325° C., or from 120° C. to 250° C., and applying an electric current having a power of from 100 Watts (W) to 300 W, or about 200 W.
The ALD process may be repeated a plurality of times to build up the thickness of the ALD protective layer 120. Each iteration of the ALD process may add another molecular layer of the ALD metal fluoride to the ALD protective layer 120. The thickness of the ALD protective layer 120 can be controlled by controlling the number of iterations of the ALD process, thus, controlling the number of molecular layers of ALD metal fluoride are present in the ALD protective layer 120. The growth rate of the ALD process for producing the ALD protective layer 120 can be about 0.5 Angstroms per cycle, where a cycle comprises one sequence of metal precursor followed by fluorine source, or one complete sequence of metal precursor-oxygen source-fluorine source.
In embodiments, the ALD protective layer 120 may comprise a stack of different ALD metal fluoride layers, wherein each of the different ALD metal fluoride layers comprises a metal fluoride having a different metal from the metal fluorides in adjacent layers in the stack. In embodiments, the ALD protective layer 120 may comprise a stack of metal fluorides comprising an amorphous ALD-AlF3 layer disposed between layers of polycrystalline ALD metal fluoride layers, such as but not limited to ALD-CaF2, ALD-MgF2, or ALD-LiF 2 layers. Other combinations of different metal fluoride layers formed into a stack are also contemplated.
Referring again to
In embodiments, the ALD protective layer 120 may be an ALD metal fluoride and may include sulfur in addition to the metal fluoride. In embodiments, the ALD protective layer may comprise an ALD metal fluoride layer and may have a sulfur content in the ALD metal fluoride layer of greater than zero parts per million (ppm), such as from greater than zero ppm to 300 ppm, or from greater than 1 ppm to 250 ppm, or from greater than 5 ppm to 200 ppm, or from greater than 10 ppm to 150 ppm, or from greater than 25 ppm to 125 ppm.
In embodiments, the ALD protective layer 120 may comprise the ALD metal fluoride and may be substantially free of carbon. In embodiments, the ALD protective layer 120 may have a concentration of carbon of less than or equal to 10,000 ppm, or less than or equal to 5,000 ppm, or less than or equal to 1,000 ppm, or less than 500 ppm in the ALD protective layer 120. In embodiments, the reflective coating 110, the ALD protective layer 120, or both have less than 5 atomic percent (at %) oxygen, such as less than or equal to 4 at %, less than or equal to 3 at %, less than or equal to 2 at %, or even less than or equal to 1 at % oxygen, where atomic percent of oxygen is the number of oxygen atoms in a structure divided by the total number of atoms in the structure. In embodiments, the reflective coating 110, the ALD protective layer 120, or both can have from at % to about 5 at % oxygen atoms.
Referring to
The ALD protective layer 120 may be a conformal coating having a uniform thickness across all coated surfaces. In embodiments, the ALD protective layer 120 may have a thickness that varies by less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, or even less than or equal to 0.5% from an average thickness of the ALD protective layer 120. The average thickness of the ALD protective layer 120 is the total thickness tALD of the ALD protective layer 120 averaged over all of the surface area of the surfaces in contact with the ALD protective layer 120.
The enhanced aluminium mirror 100 may have a reflectance of light in the wavelength range of from 110 nm to 180 nm (or from 150 nm to 180 nm) that is greater than or equal to 77%, greater than or equal to 80%, greater than or equal to 81%, or even greater than or equal to 82%. The reflectance was measured by using a commercial VUV spectrophotometer. In embodiments, the enhanced aluminium mirror 100 can include a high reflective index ALD layer, such as but not limited to a lanthanum fluoride ALD layer, a gadolinium fluoride ALD layer, or other high reflective index layer. When the ALD protective layer 120 includes a high reflective index ALD layer, the enhanced aluminium mirror 100 can have a reflectance of VUV wavelength light greater than the reflectance of the substrate with the pure aluminium reflective coating, such as a reflectance greater than 90%, or even greater than 92%.
Referring to
Referring now to
The enhanced aluminium mirror 100 comprising a plurality of ALD protective layers 120 can be prepared by depositing the aluminium reflective layer 110 to the mirror surface 104 of the substrate using a PVD process, etching the outer surface 112 of the reflective layer 110 by the ALE process to produce the etched surface 122 of the reflective layer 110, depositing the first ALD protective layer 140 to the etched surface 122 of the reflective layer 110, and then depositing the second ALD protective layer 150 onto the outer surface of the first ALD protective layer 140. The first ALD protective layer 140 is then disposed between the reflective layer 110 and the second ALD protective layer 150. After depositing the second ALD protective layer 150, subsequent ALD protective layers can be applied until the desired ALD coating structure is attained. The first ALD protective layer 140, the second ALD protective layer 150, and any other subsequent ALD protective layers may be deposited onto one or more surfaces of the enhanced aluminium mirror 100 according any of the ALD processes previously discussed herein.
In embodiments, the enhanced aluminium mirror 100 can include the substrate 102, the reflective layer 110 comprising PVD-Al, a first ALD protective layer 140 comprising ALD-AlF3 deposed on an etched surface 122 of the reflective layer 110, and a second ALD protective layer 150 comprising ALD-MgF2 deposited on the outer surface of the first ALD protective layer. In embodiments, the first ALD protective layer 140 comprising the ALD-AlF3 can have a thickness of from 5 to 25, and the second ALD protective layer 150 comprising ALD-MgF2 can have a thickness of from 5 nm to 25 nm. In embodiments, the enhanced aluminium mirror 100 can comprise the first ALD protective layer 140 comprising the ALD-AlF3 having a thickness of 5 nm and the second ALD protective layer 150 comprising ALD-MgF2 having a thickness of 23 nm.
In embodiments, the enhanced aluminium mirror 100 can comprise the ALD protective layer 120 that includes a plurality of alternating ALD-AlF3 and ALD-MgF2 layers. In embodiments, the enhanced aluminium mirror can include a first ALD protective layer comprising nm of ALD-AlF3, a second ALD protective layer comprising 9 nm of ALD-MgF2, a third ALD protective layer comprising 5 nm of ALD-AlF3, and a fourth ALD protective layer comprising 9 nm of ALD-MgF2. In embodiments, the enhanced aluminium mirror 100 can include a first ALD protective layer comprising 5 nm of ALD-AlF3, a second ALD protective layer comprising 2 nm of ALD-MgF2, a third ALD protective layer comprising 5 nm of ALD-AlF3, a fourth ALD protective layer comprising 2 nm of ALD-MgF2, a fifth ALD protective layer comprising 5 nm of ALD-AlF3, and a sixth ALD protective layer comprising 2 nm of ALD-MgF2. Other combinations of ALD materials, numbers of ALD protective layers, and layer thickness are contemplated.
In embodiments, the enhanced aluminium mirror 100 can include the substrate 102, the reflective coating 110, the first ALD protective layer 140, and the second ALD protective layer 150, where the second ALD protective layer 150 comprises a high reflective index metal fluoride that can improve the reflectance of the enhanced aluminium mirror 100 compared to aluminium mirrors without the high reflective index metal fluoride. In embodiments, the ALD protective layer 120 of the enhanced aluminium mirror 100 can include the first ALD protective layer comprising ALD-AlF3 and the second ALD protective layer 150 comprising lanthanum fluoride (LaF3), gadolinium fluoride (GdF3), or other high reflective index metal fluoride. In embodiments, the enhanced aluminium mirror 100 can include the aluminium reflective layer 110 having a thickness of from 70 nm to 100 nm, the first ALD protective layer 140 comprising from 10 nm to 30 nm ALD-AlF3, and the second ALD protective layer 150 comprising from 5 nm to 20 nm ALD-LaF3.
The enhanced aluminium mirrors 100 of the present disclosure having the reflective coating 110 comprising PVD-Al and the ALD protective layer 120 comprising ALD metal fluoride coatings can be used as mirrors in various VUV or EUV applications, such as VUV or EUV lithography or inspection systems for making and/or inspecting microelectronics. The enhanced aluminium mirrors 100 can be used with lasers having wavelength in the VUV range such as but not limited to beams having wavelengths of from 110 nm to 180 nm. In embodiments, the enhanced aluminium mirrors 100 can be used with beams having wavelengths of greater than 180 nm.
The embodiments of coated optical components and ALD process for producing the coated optical components described herein will be further clarified by the following examples.
In Example 1, an enhanced aluminium mirror was prepared according to the methods disclosed herein and represented in the flow chart in
Following ALE, the etched surface of the reflective layer was coated with an ALD protective layer comprising 4 nm of AlF3. The ALD process was conducted by exposing the etched surface of the protective layer to alternating pulses of the metal precursor (TMA) and fluorine source, starting with the pulse of the TMA. The ALD process was conducted at a temperature of 225° C. For the TMA pulse, the exposure time was 40 ms and the throttle valve was maintained in the open position during the TMA pulse. The fluorine pulse was conducted with an exposure time and power that were the same as for the ALE process. The growth rate of the ALD protective layer was 0.5 Angstroms per cycle. The resulting enhanced aluminium mirror included the substrate, the aluminium metal reflective layer having a thickness of 96 nm, and the ALD protective layer comprising AlF3 having a thickness of 4 nm.
For Comparative Example 2, an aluminium mirror was prepared by depositing the aluminium reflective coating through a PVD process and then passivating the reflective coating by depositing a low-density PVD-AlF3 layer and a dense PVD-AlF3 layer according to the method represented in the flow chart of
For Comparative Example 3, an aluminium mirror was prepared according to the hybrid method represented in the flow chart of
In Example 4, the reflectance of the enhanced aluminium mirror of Example 1 and the aluminium mirrors of Comparative Examples 2 and 3 were evaluated according to the methods disclosed herein. In Example 4, the reflectance was measured by using a commercial VUV spectrophotometer. Referring again to
As shown in
For Example 5, an enhanced aluminium mirror was prepared having a first ALD protective layer comprising ALD-AlF3 and a second ALD protective layer comprising ALD-MgF2. The aluminium reflective coating having a thickness of 100 nm was deposited using the PVD process. Following PVD, mirror was transferred to the ALD chamber of the ALD process and the ALE process was conducted to remove 4 nm of the reflective coating. The ALE process steps, materials, and conditions were the same as those previously described in Example 1. The final thickness of the reflective coating after etching was 96 nm. The first ALD protective layer comprising ALD-AlF3 was deposited according to the process described in Example 1. The thickness of the first ALD protective layer was 12 nm.
The second ALD protective layer was then deposited onto the first ALD protective layer. For the second ALD protective layer, the ALD chamber was cooled down to a temperature of 150° C. The magnesium precursor was (EtCp)2Mg (i.e., bis(ethylcyclopentadienyl) magnesium). The bubbler temperature was set to 92° C. and the ICP plasma power was 200 W. The metal precursor pulse comprising the (EtCp)2Mg had a pulse duration of 1 second followed by a purge with inert gas for 9 seconds. Following the metal precursor pulse and purge, a water pulse having a duration of 40 milliseconds was conducted followed by purging for 8 seconds with inert gas. After the water pulse and purge, the optical component was subjected to a fluorine source pulse comprising a mixture of SF6 and Argon. The SF6/Argon flow ratio was 30/15, and the fluorine source pulse had a duration of 7 seconds. The fluorine source pulse was followed by a purge pulse. The sequence of metal precursor pulse/water pulse/fluorine source pulse was repeated until the thickness of the MgF2 ALD coating attained a thickness of 9 nm.
For Example 6, the enhanced aluminium mirrors of Examples 1 and 5 and the aluminium mirrors of Comparative Examples 2 and 3 were analyzed using secondary ion mass spectrometry (SIMS) to evaluate the relative amounts of aluminium, aluminium fluoride, oxygen, carbon, hydrogen in the various coating layers. The secondary ion mass spectrometry analysis was performed using a secondary ion mass spectrometer. The SIMS analysis was conducted by sputtering the surface of the mirror with cesium ions (Cs+) having a kinetic energy of 2 kV and conducting analysis in positive mode with 30 kV Bi3+ ions. In
Referring now to
As shown in
Referring now to
Referring now to
Referring now to
In Example 7, the enhanced aluminium mirror of Example 1 and a PVD-only aluminium mirror comprising a PVD-AlF3 passivation layer were subjected to UV ozone to evaluate the effectiveness of the protective layers for reducing or preventing oxidation of the reflective layer. As previously indicated, the enhanced aluminium mirror of Example 1 had an ALD protective layer comprising ALD-AlF3 and having a thickness of 4 nm. The PVD-only aluminium mirror had a protective layer comprising PVD-AlF3 and having a thickness of 18 nm. The exposure time was increased from 0 to 99 minutes to 2×99 minutes to 3×99 minutes.
Referring now to
As shown in
In Example 8, a prophetic example of an enhanced aluminium mirror can include a first ALD protective layer and a second ALD protective layer comprising a high reflective index fluoride. For Example 8, the high reflective index fluoride is lanthanum fluoride (LaF3). The aluminium reflective coating is a PVD aluminium coating and has a thickness of 100 nm. The first ALD protective layer comprises ALD-AlF3 and has a thickness of 28 nm. The second ALD protective layer comprises the ALD-LaF3. The ALD-LaF3 of the second ALD protective layer can be prepared by subjecting the mirror to an ALD process comprising alternating pulses of a lanthanum precursor and a fluorine source. The ALD process for depositing the ALD-LaF3 can be conducted at a temperature in the range of from 250° C. to 350° C. The lanthanum precursor can be any of the lanthanum precursors disclosed herein, such as but not limited to tris(N,N′-diisopropylformamidinato) lanthanum, and each of the lanthanum precursor pulses can have a pulse duration of about 2 seconds. The fluorine pulses can be conducted as previously discussed herein. The thickness of the second ALD protective layer comprising the ALD-LaF3 is 10 nm.
The theoretical reflectance of the enhanced aluminium mirror of Example 8 is calculated based on the properties of the materials in each layer of the reflective coating and ALD protective layers of the enhanced aluminium mirror of Example 8. For comparison, a theoretical reflectance of an aluminium mirror comprising only the reflective coating comprising the PVD-Al as a function of wavelength is also calculated. Referring now to
Humidity Test
With reference again to
It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.
This application claims the benefit of priority under 35 U.S.C § 120 of U.S. Provisional Application Ser. No. 63/354,257 filed on Jun. 22, 2022, the content of which is relied upon and incorporated herein by reference in its entirety.
Number | Date | Country | |
---|---|---|---|
63354257 | Jun 2022 | US |