Method for coating substrate

Abstract

To provide a method for coating a substrate with at least one coating comprising at least one coating material.SOLUTION: A coating material is deposited on a substrate or on a partial coating applied to the substrate, and electrically neutral particles are made available to assist the deposition.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method of coating a substrate with at least one coating comprising at least one coating material, wherein the coating material is deposited on the substrate or on a partial coating applied to the substrate, and to optical elements produced using such a method. [Background technology]

[0002] In particular, in the relatively short-wave ultraviolet wavelength range of approximately 150 nm to 260 nm, also known as DUV (deep ultraviolet) radiation, optical elements are used with optical coatings and / or substrates that have low electrical conductivity compared to metallic materials. With regard to the service life of optical elements, it is advantageous if the porosity of the optical coating is minimized. To reduce the porosity of optical coatings during deposition, deposition can be performed using ion assistance, as disclosed, for example, in German Patent Publication No. 10 2005 017 742. With ion assistance, substrates or coatings applied to substrates with low electrical conductivity can become electrically charged within a very short time, specifically less than one millisecond. Typical substrates are typically glasses, such as fused silica or calcium fluoride. However, even substrates with nominally good electrical conductivity, such as metals, can be affected by this and can become similarly charged if they are coated with a non-electrically conductive coating. Particularly in the case of relatively large optical elements, charging can lead to variations in conditions during layer deposition, possibly for individual layers and over the entire area to be coated, which in turn affect, for example, the optical properties of the grown layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] German Patent Publication No. 10 2005 017 742 Summary of the Invention

[0004] The object of the present invention is to show a method in which the coating conditions remain substantially constant during the deposition of the layer.

[0005] This object is achieved by a method of coating a substrate with at least one optically effective coating comprising at least one coating material, the coating material being deposited on the substrate or on a partial coating applied to the substrate, and electrically neutral particles being available to assist the deposition.

[0006] It has been found that the deposition of layers does not necessarily have to be performed using charged particles, but can instead be performed using neutral particles. This has the advantage that, particularly for substrates and coatings with relatively low electrical conductivity, charging of the substrate undergoing the coating process can be avoided, resulting in a substantially constant coating state during the deposition of the layer. A constant coating state can result in a spatially constant coating across the entire substrate surface to be coated and / or a temporally constant coating during the deposition of the layer. In the case of multiple layers, a constant coating state can also relate to easily reproducible deposition of each individual layer. The resulting coating can be, inter alia, an optical coating, or otherwise a protective coating or coating for withstanding mechanical stress on optical elements.

[0007] Advantageously, neutral particles with energies between 50 eV and 500 eV, preferably between 75 eV and 300 eV, particularly preferably between 100 eV and 200 eV, are available. This approach allows, firstly, an effective densification of the deposited layer, and, secondly, the layer structure to be unduly affected, i.e., sputtering effects on the layer itself or on surfaces in the vicinity of the layer are negligible or may even be completely avoided.

[0008] Preferably, neutral particles with an angle of incidence of at most 60°, preferably at most 45°, particularly preferably at most 30° relative to the surface normal are available. This measure also achieves, firstly, an effective densification of the deposited layer and, secondly, that the layer structure is not excessively affected, i.e., sputtering effects on the layer itself or on surfaces in the vicinity of the layer are negligible or may even be completely avoided.

[0009] It should be pointed out that depending on the combination of coating material and neutral particles used for the support, it is particularly preferred that the particle incidence angle and particle energy are adjusted to one another.

[0010] Preferably, one or more noble gases are used as auxiliary gases, which, being inert, make it possible to ensure that the layer to be deposited is not contaminated by undesired chemical reactions.

[0011] In order to further promote the growth of the desired layer, it has proven advantageous if at least one volatile element of the coating material to be deposited is added to the auxiliary gas.

[0012] In one preferred variant, for example to produce reflective optical elements, an electrically conductive substrate, for example a metal or metal-coated substrate, is coated and a voltage is applied to the substrate, in this way an electric field can be created which deflects charged particles that may be present in the stream of neutral particles away from the substrate to be coated.

[0013] In a further preferred variant, for producing a transmissive optical element, a substrate with low electrical conductivity, for example made of fluoride crystals, is coated, and an electrode is arranged on the opposite side of the substrate with respect to the particle flow. In this way, an electric field can be created so as to deflect charged particles that may be present in the flow of neutral particles away from the substrate to be coated. This procedure is particularly advantageous for large substrates.

[0014] In a further preferred variant, at least one electrode is arranged on the side of the substrate facing the particle flow in the direction of the particle flow. In this way, potentially charged particles can be deflected before they strike the substrate surface, so that they instead strike the electrode. It is particularly preferred that at least two electrodes are provided, which are given opposite potentials, so that both negatively and positively charged particles can be removed from the stream of neutral particles.

[0015] In a further aspect, this object is achieved by a method for coating a substrate with at least one coating comprising at least one coating material, the coating material being deposited on the substrate or on a partial coating applied to the substrate, and the substrate being bombarded with electrons due to the fact that a component is used which comprises a filament arranged in a housing and further at least one grid, in an opening provided in the housing, which has a potential difference relative to the filament.

[0016] Generally, it has proven advantageous to carry out deposition using electron beam evaporation or thermal evaporation. Both types of coatings are proven methods for coating materials with low to even non-conductive conductivity. Furthermore, particle-assisted deposition is particularly effective for both methods.

[0017] This object is further achieved by an optical element comprising at least one layer deposited as explained above. Due to the fact that the coating is carried out with the aid of electrically neutral particles or by bombardment with electrons, undesirable charging effects in the optical element being manufactured can be counteracted and more stable coating parameters can be ensured, resulting in more optical elements with a coating that in any case falls within the tolerances of the desired optical properties.

[0018] In a preferred embodiment, at least one oxide layer is applied in this way. Various oxide layer materials are used, particularly for optical elements in the UV wavelength range, for example, for anti-reflection coatings of transmissive optical elements or for high-reflection coatings of reflective optical elements. The oxide layer can extend the service life of the respective optical element.

[0019] Advantageously, the optical element comprises an optically effective coating comprising at least one first layer and at least one second layer on a substrate, the at least one second layer being produced in the manner described, specifically with the aid of electrically neutral particles. In this case, the at least one first layer contains more neutral particles than if the at least one second layer had been deposited without the aid of neutral particles. Neutral particles have a smaller effective cross-section than corresponding charged particles and can therefore penetrate deeper into the surrounding material.

[0020] Alternatively, the optical element may comprise an optically effective coating on a substrate, the coating comprising at least one first layer, a second layer, and a third layer, the at least one third layer being produced in the manner described, specifically with the aid of neutral particles, and the at least one second layer being deposited without the aid of neutral particles. In this case, the at least one second layer is made thicker than if the at least one third layer were deposited without the aid of neutral particles but with the aid of ions. The second layer may prevent neutral particles, which have a greater penetration depth than the corresponding charged particles, from penetrating the first layer, or may prevent the proportion of neutral particles in the corresponding first layer from remaining below a defined threshold.

[0021] The invention will now be described in more detail with reference to preferred exemplary embodiments. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic diagram of a first apparatus for carrying out a coating method. [Figure 2]FIG. 2 is a schematic diagram of a second apparatus for carrying out the coating method. [Figure 3] FIG. 1 is a schematic diagram of a third apparatus for carrying out the coating method. [Figure 4] 1 is a schematic diagram of a first component for carrying out the coating method. [Figure 5a] FIG. 2 is a schematic side view of a second component for carrying out the coating method. [Figure 5b] FIG. 2 is a schematic front view of a second component for carrying out the coating method. [Figure 6] FIG. 10 is a schematic diagram of a fourth apparatus for carrying out the coating method. [Figure 7] FIG. 2 is a schematic diagram of a first optical element. [Figure 8] FIG. 2 is a schematic diagram of a second optical element. [Figure 9] FIG. 1 is a schematic diagram of the depth distribution of auxiliary particles. DETAILED DESCRIPTION OF THE INVENTION

[0023] The following example relates to the manufacture of optical elements for the DUV wavelength range, without limiting generality, where the wavelengths used are preferably in the range of 150 nm to 260 nm. Optical elements can include both transmissive optical elements, e.g., lens elements, and reflective optical elements, e.g., mirrors. Optical coatings often comprise oxide and / or fluoride layers. For example, a lens element for a wavelength of approximately 193 nm can comprise a substrate, e.g., made of calcium fluoride, provided with an optical coating comprising an oxide layer, e.g., made of silicon dioxide or aluminum oxide, and optionally a fluoride layer.

[0024] These materials have lower electrical conductivity than metal layers. In conventional coating methods using ion assistance, the optical element being fabricated can rapidly become charged during coating, which can have a negative impact on the coating process. To counteract this, a solution is proposed: either increasing the proportion of auxiliary particles composed of electrically neutral particles to slow the charging process, or making additional charged particles available to at least partially, ideally completely, compensate for the charging process. Ideally, deposition is also assisted exclusively by electrically neutral particles.

[0025] FIG. 1 shows a schematic diagram of a first apparatus for carrying out a method for coating a substrate with at least one coating containing at least one coating material, which is deposited on the substrate or on a partial coating attached to the substrate, with neutral particles available to assist the deposition. For this purpose, the substrate 101 to be coated is mounted on a substrate holder 103. The corresponding coating material is provided by a material source 109. This material source may specifically include an electron beam evaporator or a thermal evaporator. However, other proven material sources can also be used. In particular, when using a material source that emits low-energy particles, it is advantageous to also provide high-energy particles that contribute to the densification of the deposited layer. In this example, a plasma source 111 is used for this purpose, in which an argon plasma is generated. In addition to argon ions, neutral argon atoms are also generated in this process. For clarity, only positive argon ions and neutral argon atoms are shown in FIG. 1. Advantageously, before filtering using an electric field, the proportion of neutral particles in all auxiliary particles is already at least 10%, preferably more than 20%, particularly preferably more than 30%. By using electric filtering, this proportion can be increased to more than 80%, preferably more than 90%, particularly preferably more than 95%, and very particularly preferably up to almost 100%.

[0026] 1, an electrode 105 is placed on the opposite side of the substrate 101 from the particle stream using a voltage source 107. The electrode 105 is given a positive potential in this example, so that positive argon ions are deflected away from impinging on the substrate 101 and are thus filtered out of the particle stream.

[0027] 2 shows a schematic diagram of a second apparatus for carrying out a method of coating a substrate with at least one coating containing at least one coating material, the coating material being deposited on the substrate or on a partial coating attached to the substrate, with neutral particles available to assist the deposition. In contrast to the example shown in FIG. 1, here, multiple smaller substrates 201 are inserted into a substrate holder 203 for coating the substrates in parallel with material from a material source 209 and with the assistance of argon particles from a plasma source 211. The substrate holder 203 simultaneously serves as an electrode for generating a field that repels positive argon ions. For this purpose, a positive potential is applied to the substrate holder 203 using a voltage source 207.

[0028] FIG. 3 shows a schematic diagram of a third apparatus for coating with the assistance of neutral particles. In the illustrated example, two electrodes 313, 315 are positioned on the side of a series of substrates 301 facing the particle flow, in the direction of the particle flow. The electrodes 315, 313 are provided with different potentials using a voltage source 307. In the illustrated example, the electrode 315 is at a negative potential and attracts positive argon ions from the plasma source 311. In contrast, the electrode 313 is at a positive potential and attracts electrons originating from the material source 309, configured here as an electron beam evaporator, as well as negative argon ions (not shown). The electrodes 313, 315 are advantageously positioned slightly transverse to the particle flow to deflect charged particles laterally. In a variation of this configuration, if the positive electrode 313 is omitted, the substrates 301 can be neutralized using electrons originating from the electron beam evaporator 309.

[0029] The spacing and orientation of the electrode or electrodes relative to the particle stream is preferably configured to generally avoid collateral sputtering of the electrodes and therefore contamination of the optical element to be coated.

[0030] Alternatively or in addition to the neutral particle assisted coating already described, a coating method is also proposed in which electrons are bombarded in a targeted manner onto the substrate in order to at least partially compensate for the charging of the coated substrate.

[0031] FIG. 4 shows a schematic diagram of a first component for implementing a coating method in which electrons bombard the coated substrate to compensate for charging. Component 401 thus functions as a neutralizer, so to speak. This component emits low-energy electrons and injects them into a particle stream of ions and neutral particles, such as those provided by an ion source. This component includes a glow-wire 405, e.g., a bent wire, housed in a housing 403. The glow-wire is heated by an electric current and emits electrons by thermionic emission. The wire 405 is electrically connected to the surrounding housing 403. The housing 403 is further filled with an inert gas or gas mixture, preferably a noble gas such as argon or krypton. Impact ionization by the gas or gas mixture significantly increases the number of electrons, which are then released from the housing 403 through a small opening 402 in the housing. Current strengths of several hundred milliamperes (mA) can be achieved in this case, i.e., sufficient to neutralize the typical ion current during ion-assisted deposition. The components of the design shown in Figure 4 have operational lifetimes of tens to hundreds of hours.

[0032] 5a and 5b show a schematic diagram of a second component for implementing a coating method in which electrons bombard a coated substrate to compensate for charging. The component 501 includes a filament 505 in a housing 503. The filament is wound in multiple layers, like an incandescent filament, and generates electrons by thermionic emission. An opening 504 in the housing 503 houses at least one grid, which has a potential difference relative to the filament. In the example shown, two grids 507 and 509 are provided. The grid 507, located closer to the filament 505, has a positive potential difference relative to the filament 505 and acts as a control grid, removing emitted electrons from the vicinity of the filament 505. This grid determines the kinetic energy of the electrons. The grid 509, located further away from the filament 505, acts as an extraction grid. A negative voltage exists between the grids 507 and 509, accelerating electrons emitted from the region between the two grids 507 and 509 outward. In one variant, another grid can be placed behind grids 507, 509 in the direction of electron movement, this grid being at neutral potential and serving to insulate accelerating grid 509. For components of the design shown in Figures 5a and 5b, the entire emission current is generated by thermionic emission without impact ionization. These components have an operational lifespan of several days to several months.

[0033] Figure 6 shows a schematic diagram of an apparatus for carrying out coating of a substrate 901 in a substrate holder 903, comprising an ion source 909 and a neutralizer 913, which is configured similarly to component 501 of Figures 5a, 5b, to prevent charging of the substrate 901 or any (partial) coating already present.

[0034] Both components 401 and 501 described here as examples can additionally be used for coating with the aid of neutral particles.

[0035] FIG. 7 shows a schematic diagram of a first optical element, in which at least one layer is deposited with the assistance of neutral particles. The optical element 601 shown here is designed for wavelengths between 120 nm and 600 nm, preferably between 150 nm and 260 nm. An optically effective coating is provided on a substrate 603, comprising at least one stack of layers including a first layer 605 and a second layer 607. One, two, three, four, five, or six or more such stacks of layers including a first layer 605 and a second layer 607 can be provided as an optically effective coating on the substrate 603, as shown by the dotted lines. In this example, the at least one second layer 607 is deposited with the assistance of neutral particles. The second layer is an oxide layer deposited using electron beam evaporation with the assistance of neutral particles. The energy of the coating material during electron beam evaporation is typically several hundred meV. This results in a layer with low particle mobility of the coating material and a relatively porous and rough surface. Therefore, neutral particle bombardment assistance is particularly advantageous, since it simultaneously densifies the deposited layer and prevents charging of the optical element being manufactured. The desired densification effect without undesirable sputtering effects in the deposited layer or in areas nearby can be achieved using electrically neutral particles with energies of 50 eV to 500 eV, preferably 75 eV to 300 eV, and particularly preferably 100 eV to 200 eV. Depending on the circumstances, it is possible to further reduce the sputtering rate and increase the densification of the deposited layer by reducing the angle of incidence to a maximum of 60°, preferably a maximum of 45°, and particularly preferably a maximum of 30° relative to the surface normal. The neutral particle dose should be selected so that it is not too low to achieve sufficient densification, but not too high to avoid excessive, possibly undesirable, effects on the layer structure due to the assistance of neutral particles. At the same time, the growth rate should be greater than any sputtering rate that may be present.

[0036] A gas containing one or more noble gases, preferably argon and / or krypton, is preferably used as the auxiliary gas. Depending on the layer to be deposited, it may be advantageous to add at least one volatile element of the coating material to be applied to the auxiliary gas to compensate for layer wear due to particle bombardment. For oxide layers, oxygen is preferred. For nitride-containing layers, nitrogen is preferred. The choice of specific layer material depends on the desired wavelength or wavelength range to be used. In this regard, for example, in the range of 150 nm to 260 nm, specifically around 193 nm, aluminum oxide and silicon dioxide are particularly relevant oxide layer materials. Neutral particle-assisted deposition can significantly affect the layer structure, especially in the case of silicon dioxide. For example, fluorides, specifically calcium fluoride, can be used as the substrate. In the visible wavelength range, the proposed scratch-resistant layer can be produced using, for example, silicon nitride. In principle, coatings for any desired wavelength of use can be produced from the X-ray and extreme ultraviolet wavelength ranges, ultraviolet, visible, or infrared wavelength ranges. The coatings can be optical coatings as well as protective coatings, for example for mechanical or chemical protection of the optical coating or for protection of the substrate or coating to withstand mechanical stresses of the optical element.

[0037] The electrically neutral particles used for the assistance, which in this example consist of argon, have a smaller effective cross-sectional area, including the periphery of the neutral particles, than the corresponding ions. This has the effect that the neutral particles can penetrate further than the corresponding charged particles into the layer material already present on the substrate 603. This can be manifested in the fact that the at least one first layer 605 contains more neutral particles than if the at least one second layer 607 had been deposited without the assistance of neutral particles, in particular than if the second layer had been deposited with the assistance of the corresponding ions.

[0038] Specifically, the penetration depth profile of layers deposited with the assistance of neutral particles differs from that of layers deposited with the assistance of ions. This is shown schematically in FIG. 9. The number of auxiliary atoms, in arbitrary units, i.e., the number of auxiliary ions or neutral particles that penetrated into the assisted or assisted coating, is presented logarithmically as a function of the depth of the material, also in arbitrary units, specifically toward the substrate. A penetration depth profile is shown for a first layer S1a and the overlying second layer S2a, deposited with the assistance of neutral particles. This profile is shown by the dashed line. Another penetration depth profile is shown for a first layer S1b and the overlying second layer S2b, deposited with the assistance of ions. This profile is shown by the dotted line. The number of auxiliary atoms decreases more rapidly in layer S1b than in layer S1a.

[0039] When it is intended to avoid penetration of auxiliary particles into at least one underlying layer, the structure of the optical element as shown in Figure 8 may be advantageous. The optical element 701 differs from the optical element described in connection with Figure 6 in that at least one unassisted deposited second layer 707 is provided on the substrate 703 between at least one optionally deposited first layer 705 and at least one neutral particle-assisted deposited third layer 709, the second layer being made of the same coating material as the unassisted deposited third layer 709 and functioning as an intermediate layer. Because the second layer 707 is unassisted, it differs from the third layer 709 by being less dense, and traps neutral particles that penetrate deeper into the already existing partial coating during the assisted deposition of the third layer 709. However, since the effective cross-sectional area of ​​neutral particles, including surrounding material, is small compared to charged particles, in order to make the proportion of neutral particles in the first layer 705 negligible, the second layer 707 must be thicker than if at least one third layer 709 were deposited without the assistance of neutral particles, specifically than if it were deposited with corresponding ion assistance.

[0040] It should be noted that in this example deposition using electron beam evaporation is discussed, however other proven chemical and / or physical vapor deposition methods can also be used, specifically thermal evaporation.

[0041] Optical elements manufactured as proposed can be used, for example, in UV lithography of semiconductor elements or in optical systems for inspection of wafers, imaging masks or optical elements. [Explanation of symbols]

[0042] 101 Base material 103 Substrate holder 105 Electrode 107 Voltage Source 109 Material sources 111 Plasma Source 201 Base material 203 Substrate holder 207 Voltage Source 209 Material sources 211 Plasma Source 301 Base material 303 Substrate holder 307 Voltage Source 309 Material sources 311 Plasma Source 313 Electrode 315 Electrode 401 Components 402 Opening 403 Case 405 Glow Wire 501 Components 503 Case 504 Opening 505 filament 507 Grid 509 Grid 601 Optical Elements 603 Base material 605 First Layer 607 Second Layer 701 Optical Elements 703 Base material 705 First Layer 707 Second Layer 709 Third Layer 901 Base material 903 Substrate holder 909 Ion Source 913 Neutralization device

Claims

1. 1. A method of coating a substrate with at least one coating comprising at least one coating material, wherein the coating material is deposited on the substrate or on a partial coating applied to the substrate; A method wherein electrically neutral particles are made available to assist said deposition.

2. 2. The method according to claim 1, wherein neutral particles having an energy of 50 eV to 500 eV, preferably 75 eV to 300 eV, particularly preferably 100 eV to 200 eV, are made available.

3. 3. The method according to claim 1, wherein neutral particles are available with an angle of incidence of at most 60°, preferably at most 45°, particularly preferably at most 30° relative to the surface normal.

4. 4. The method according to claim 1, wherein one or more noble gases are used as auxiliary gases.

5. 5. The method of claim 4, wherein at least one volatile element of the material of the coating to be deposited is added to the auxiliary gas.

6. The conductive substrate is coated, The method according to any one of claims 1 to 5, characterized in that a voltage is applied to the substrate.

7. 7. The method according to claim 1, wherein an electrode is arranged on the opposite side of the substrate relative to the particle flow.

8. 8. The method according to claim 1, wherein at least one electrode is arranged on the side of the substrate facing the particle flow in the direction of the particle flow.

9. 1. A method of coating a substrate with at least one coating comprising at least one coating material, wherein the coating material is deposited on the substrate or on a partial coating applied to the substrate; A method characterized in that the bombardment of the substrate with electrons is due to the fact that a component is used which comprises a filament arranged in a housing and further comprising at least one grid, in an opening provided in the housing, which has a potential difference with respect to the filament.

10. A method according to any one of claims 1 to 9, characterized in that the deposition is carried out by means of electron beam evaporation or thermal evaporation.

11. An optical element comprising at least one layer (607, 709) deposited using the method according to any one of claims 1 to 10.

12. Optical element according to claim 11, characterized in that at least one oxide layer (607, 709) is deposited using a method according to any one of claims 1 to 10.

13. A coating comprising at least one first layer (605) and at least one second layer (607) on a substrate (603), wherein the at least one second layer (607) is produced by the method according to any one of claims 1 to 12, 13. The optical element according to claim 11 or 12, characterized in that the at least first layer (605) contains more electrically neutral particles than if the at least one second layer (607) were deposited without the aid of neutral particles.

14. A coating comprising at least one first layer (705), a second layer (707) and a third layer (709) on a substrate (703), wherein the at least one third layer (709) is produced by the method according to claims 1 to 13, and the at least one second layer is deposited without the aid of electrically neutral particles, 13. The optical element according to claim 11 or 12, characterized in that the at least one second layer is thicker than when the at least one third layer is deposited without the aid of neutral particles but with the aid of charged particles.

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