Method for coating a substrate

Abstract

A method for 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, is proposed, in which electrically neutral particles are provided to assist the deposition.

Description

[0001] The present invention relates to methods for 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 in the production of which these methods are used.

[0002] Particularly in the shorter ultraviolet wavelength range between approximately 150 nm and 260 nm, also known as DUV (deep ultraviolet) radiation, optical elements are used whose optical coating and / or substrate are not electrically conductive compared to metallic materials. With regard to the service life of the optical elements, it is advantageous if the optical coatings are as little porous as possible. In order to reduce their porosity during deposition, the deposition can be carried out with ion support, as disclosed, for example, in DE 10 2005 017 742 A1. Due to the ion support, a substrate with poor electrical conductivity or the coating applied to it can become electrically charged within a very short time, in particular less than 1 ms. Common substrates are typically glasses such as quartz glass or calcium fluoride. However, even nominally electrically conductive substrates such asMetals can be affected if they are coated with an electrically non-conductive coating, which can become electrically charged. Particularly in larger optical elements, this charging can lead to fluctuating conditions, both from individual layer to individual layer and across the surface to be coated during layer deposition, which in turn can influence, for example, the optical properties of the growing layer.

[0003] It is an object of the present invention to provide a method in which the coating conditions remain substantially constant during layer deposition.

[0004] This object is achieved by a method for coating a substrate with at least one optically active coating which comprises at least one coating material, wherein the coating material is deposited on the substrate or on a partial coating applied to the substrate and wherein electrically neutral particles are provided to assist the deposition.

[0005] It has been found that assisting a layer deposition does not necessarily have to be carried out with charged particles, but can also be done with neutral particles. Especially with less conductive substrates and coatings, this has the advantage that charging of the substrate during the coating process can be avoided and thus the coating conditions remain essentially constant during the layer deposition. Constant coating conditions can be constant locally across the substrate surface to be coated and / or constant over time during the deposition of a layer. With more than one layer, the coating conditions can also be constant with regard to well-reproducible deposition from individual layer to individual layer. The resulting coating can, among other things,It can be an optical coating or a protective coating or a coating against mechanical stress in the optical element.

[0006] Advantageously, neutral particles with an energy between 50 eV and 500 eV, preferably 75 eV to 300 eV, and particularly preferably 100 eV and 200 eV, are provided. This ensures that, on the one hand, the deposited layer is effectively densified, while, on the other hand, the layer structure is not excessively influenced, and sputtering effects on the layer itself or on surfaces in its vicinity remain negligible or even completely avoided.

[0007] Neutral particles are preferably provided at an angle of incidence of up to 60° to the surface normal, preferably up to 45°, and particularly preferably up to 30°. This also ensures that, on the one hand, the deposited layer is effectively densified, while, on the other hand, the layer structure is not excessively influenced, and sputtering effects on the layer itself or on surfaces in its vicinity remain negligible or even completely avoided.

[0008] It should be noted that, depending on the combination of coating material and the neutral particles used for support, the angle of incidence of the particles and their energy are particularly preferably matched to each other.

[0009] One or more noble gases are preferably used as support gases. Since noble gases are inert, this ensures that the layer to be deposited is not contaminated by unwanted chemical reactions.

[0010] It has proven advantageous to add at least one volatile element of the material of the coating to be applied to the support gas in order to further promote the growth of a desired layer.

[0011] In a preferred variant—for example, to produce a reflective optical element—an electrically conductive substrate, such as a metallic or metallically coated substrate, is coated, and a voltage is applied to the substrate. This creates an electric field that deflects any charged particles present in the stream of neutral particles from the substrate to be coated.

[0012] In another preferred variant, a poorly conductive substrate, for example, made of a fluoride crystal, is coated to produce a transmissive optical element, and an electrode is arranged on the side of the substrate opposite the particle flow. In this way, an electric field can be created that deflects any charged particles that would be present in the stream of neutral particles from the substrate to be coated. This procedure is particularly advantageous for large-format substrates.

[0013] In a further preferred variant, at least one electrode is arranged on the side of the substrate facing the particle flow, facing in the direction of the particle flow. In this way, any charged particles can be deflected before they hit the substrate surface, so that they instead hit the electrode. Particularly preferably, at least two electrodes are provided and set to opposite potentials, so that both negatively and positively charged particles can be removed from the stream of neutral particles.

[0014] In a further aspect, the object is achieved by a method for coating a substrate with at least one coating which has at least one coating material, wherein the coating material is deposited on the substrate or on a partial coating applied to the substrate and wherein the substrate is subjected to electrons by using a component which has a filament arranged in a housing, and at least one grid at an opening provided on the housing which has a potential difference with respect to the filament.

[0015] Overall, it has proven advantageous to perform deposition using electron beam evaporation or thermal evaporation. Both coating methods are proven methods, even for poorly or non-conductive coating materials. Furthermore, particle-assisted deposition is particularly effective in both methods.

[0016] Furthermore, the object is achieved by an optical element with at least one layer applied as described above. By coating with the assistance of electrically neutral particles or by applying electrons, undesirable charging effects on the resulting optical element can be counteracted and more consistent coating parameters can be ensured, which can lead to more optical elements whose coatings lie within the tolerance ranges for the desired optical properties.

[0017] In preferred embodiments, at least one oxide layer has been applied in this way. A variety of oxide layer materials are used, particularly for optical elements for the UV wavelength range, for example, in anti-reflection coatings for transmissive optical elements or reflection-enhancing coatings for reflective optical elements. Oxide layers can extend the service life of the respective optical element.

[0018] Advantageously, the optical element comprises an optically effective coating with at least a first and a second layer on a substrate, wherein the at least one second layer was produced by a method as described, in particular by means of support with electrically neutral particles. The at least one first layer comprises more neutral particles than if the at least one second layer had been applied without support from neutral particles. Since neutral particles have a smaller effective cross section than corresponding charged particles, they can penetrate deeper into the surrounding material.

[0019] Advantageously, the optical element alternatively has an optically active coating with at least a first, second and third layer on a substrate, wherein the at least one third layer was produced by a method as described, in particular by means of assistance with neutral particles, and the at least one second layer was applied without assistance from neutral particles. The at least one second layer is thicker than if the at least one third layer had been applied without assistance from neutral particles, but with assistance from ions. The second layer can prevent neutral particles, with their greater penetration depth than corresponding charged particles, from penetrating the first layer or can prevent the proportion of neutral particles in the respective first layer from remaining below a specified threshold.

[0020] The present invention will be explained in more detail with reference to preferred embodiments. Fig. 1 a schematic representation of a first arrangement for carrying out a coating process; Fig. 2 a schematic representation of a second arrangement for carrying out a coating process; Fig. 3 a schematic representation of a third arrangement for carrying out a coating process; Fig. 4 a schematic representation of a first component for carrying out a coating process; Fig. 5a a schematic representation of a second component for carrying out a coating process from the side; Fig. 5b a schematic representation of a second component for carrying out a coating process from the front; Fig. 6 a schematic representation of a first optical element; Fig. 7 a schematic representation of a second optical element; Fig. 8 a schematic representation of the depth distribution of supporting particles; and Fig. 9 a schematic representation of a third arrangement for carrying out a coating process.

[0021] The following examples relate—without limiting their generality—to the production of optical elements for the DUV wavelength range, preferably for useful wavelengths in the range between 150 nm and 260 nm. These can be either transmissive optical elements such as lenses or reflective optical elements such as mirrors. The optical coatings often have oxide and / or fluoride layers. For example, for lenses for a wavelength of approximately 193 nm, substrates made of calcium fluoride can be provided with an optical coating that has oxide layers, e.g., made of silicon dioxide or aluminum oxide, and optionally fluoride layers.

[0022] These materials exhibit low electrical conductivity compared to metallic layers. In conventional ion-assisted coating processes, the resulting optical elements can rapidly charge during coating, which can negatively impact the coating process. To counteract this, measures are proposed here that increase the proportion of electrically neutral particles among the supporting particles to slow down the charging process or provide additional charged particles to at least partially, ideally completely, compensate for the charging process. Ideally, the deposition is also supported only with electrically neutral particles.

[0023] In Fig. 1 schematically shows a first arrangement for carrying out a method for 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 wherein neutral particles are provided to assist the deposition. For this purpose, a substrate 101 to be coated is held in a substrate holder 103. The respective coating material is provided by the material source 109. This can be, in particular, an electron beam evaporator or a thermal evaporator. However, other proven material sources can also be used.Especially when using material sources that emit low-energy particles, it is advantageous to additionally provide higher-energy particles that contribute to the densification of the deposited layer. In the present example, a plasma source 111 is used for this purpose, in which an argon plasma is generated. This produces not only argon ions but also neutral argon atoms. Fig. For clarity, only positive argon ions and neutral argon atoms are shown in Figure 1. Advantageously, even before filtering through an electric field, the proportion of neutral particles among all support particles is at least 10%, preferably more than 20%, particularly preferably more than 30%. Through electrical filtering, the proportion can be increased to more than 80%, preferably more than 90%, particularly preferably more than 95%, and most preferably to virtually 100%.

[0024] In order to prevent charging of the substrate 101 as much as possible, Fig. In the example shown in Figure 1, an electrode 105 is arranged on the side of the substrate 101 opposite the particle flow. By means of a voltage source 107, the electrode 105 is set to—in this example—a positive potential, so that the positive argon ions are deflected in such a way that they do not impinge on the substrate 101 and are thus filtered out of the particle flow.

[0025] In Fig. 2 schematically shows a second arrangement for carrying out a method for 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 wherein neutral particles are provided to assist the deposition. In contrast to the method shown in Fig. In the example shown in Figure 1, a plurality of smaller substrates 201 are inserted into a substrate holder 203 for parallel coating with material from the material source 209, assisted by argon particles from the plasma source 211. The substrate holder 203 is used as an electrode to generate a field that repels the positive argon ions. For this purpose, the substrate holder 203 is set to a positive potential using a voltage source 207.

[0026] In Fig. Figure 3 schematically shows a third arrangement for coating with the assistance of neutral particles. In the example shown here, two electrodes 313, 315 are arranged in the direction of the particle flow on the side of a row of substrates 301 facing the particle flow. The electrodes 315, 313 are set to different potentials by means of a voltage source 307. In the example shown, the electrode 315 is at a negative potential and attracts the positive argon ions from the plasma source 311. The electrode 313, on the other hand, is at a positive potential and attracts electrons emerging from the material source 309, which is designed here as an electron beam evaporator, as well as negative argon ions (not shown). The electrodes 313, 315 are advantageously arranged slightly to the side of the particle flow in order to deflect charged particles laterally.If, in a variant of this structure, the positive electrode 313 is omitted, the electrons emerging from the electron beam evaporator 309 can be used to neutralize the substrates 301.

[0027] The distance and orientation of the electrode or electrodes relative to the particle stream are generally preferably designed in such a way that secondary sputtering from the electrode(s) and thus contamination of the optical element to be coated is avoided.

[0028] As an alternative or in addition to the coating with the support of neutral particles already described, a coating process is also proposed in which the substrate is specifically exposed to electrons in order to at least partially compensate for a charging of the coated substrate.

[0029] In Fig. Figure 4 schematically shows a first component for carrying out a coating process in which the coated substrate is charged with electrons to compensate for the charge. The component 401 thus serves as a neutralizer, so to speak. It emits low-energy electrons and injects them into a particle stream of ions and neutral particles, such as can come from an ion source, for example. In a housing 403, it has a filament 405, e.g. a simply bent wire, which is heated by a current and releases electrons via thermal thermionic emission. The wire 405 is set to a potential with respect to the surrounding housing 403. The housing 403 is also filled with an inert gas or gas mixture, preferably a noble gas such as argon or krypton.Due to impact ionization with the gas or gas mixture, the number of electrons is significantly increased before they are released through a small opening in the housing 403. Currents of several hundred mA can be achieved, which is sufficient to neutralize typical ion currents during ion-assisted deposition. Components of the device shown in . Fig. 4 have an operating life of up to several tens to hundreds of hours.

[0030] In the Fig. 5a, Fig. 5b schematically shows a second component for carrying out a coating process in which the coated substrate is subjected to electrons to compensate for the charge. The component 501 has a filament 505 wound multiple times like an incandescent filament in a housing 503, which generates electrons via thermionic emission. At least one grid is arranged at an opening provided in the housing 503, which has a potential difference with respect to the filament. In the example shown here, two grids 507, 509 are provided. The grid 507, which is arranged closer to the filament 505, has a positive potential difference with respect to the filament 505 and acts as a control grid, which draws the emitted electrons from the environment of the filament 505. It defines the kinetic energy of the electrons. The grid 509, which is arranged further away from the filament 505, acts as an extraction grid.A negative voltage is applied between grids 507 and 509, accelerating the emitted electrons outward from the area between the two grids 507, 509. In one variant, another grid can be arranged behind grids 507, 509 in the direction of electron movement. This grid is at neutral potential and serves to insulate the acceleration grid 509. For components of the type described in the . Fig. 5a, Fig. In the design shown in Figure 5b, the entire emission current is generated by thermal emission, without recourse to impact ionization. They have an operating life of several days to months. Fig. Fig. 9 schematically shows an arrangement for carrying out a coating of a substrate 901 in a substrate holder 903 with an ion source 909 and a neutralizer 913, which, like the component 501 of Fig. 5a, Fig. 5b and prevents charging of the substrate 901 or the already existing (partial) coating.

[0031] Both components described here as examples can be used in addition to the coating with the support of neutral particles.

[0032] In Fig. 6 schematically shows a first optical element in which at least one layer was deposited with the assistance of neutral particles. The optical element 601 shown here as an example is designed for useful wavelengths in the range from 120 nm to 600 nm, preferably useful wavelengths between 150 nm and 260 nm. An optically active coating with at least one stack of a first layer 605 and a second layer 607 is provided on a substrate 603. One, two, three, four, five, six or more such stacks of first and second layers 605, 607 can be provided as an optically active coating on the substrate 603, which is indicated by the dotted line. In the present example, the at least one second layer 607 has been applied with the assistance of neutral particles.This is an oxide layer deposited by electron beam evaporation with the assistance of neutral particles. During electron beam evaporation, the energy of the coating material is typically a few hundred meV. This results in poor mobility of the coating material particles, which in turn leads to relatively porous and rough layers. Therefore, assistance by exposure to neutral particles is particularly advantageous in order to simultaneously densify the deposited layer and prevent charging of the resulting optical element. Desired densification effects without undesired sputtering effects on the deposited layer or its surrounding surfaces can be achieved using electrically neutral particles with an energy between 50 eV and 500 eV, preferably 75 eV to 300 eV, particularly preferably 100 eV and 200 eV.In individual cases, the sputtering rate can be reduced and the densification of the deposited layer increased by reducing the angle of incidence from up to 60° to the surface normal, preferably down to 45°, and particularly preferably down to 30°. The dose of neutral particles should not be too low to achieve sufficient densification, nor too high to avoid excessive and potentially unwanted influence of the supporting neutral particles on the layer structure. At the same time, the growth rate should be higher than any existing sputtering rate.

[0033] Gases containing one or more noble gases are preferred as support gases, preferably argon and / or krypton. Depending on the layer to be deposited, it may be advantageous to add at least one volatile element of the material of the coating to be applied to the support gas in order to compensate for the depletion of the layer due to particle bombardment. Oxygen is suitable for oxide layers. Nitrogen is suitable for nitride-containing layers. The choice of the specific layer material depends on the desired wavelength or wavelength range. For example, aluminum oxide and silicon dioxide are of particular interest as oxide layer materials for the range between 150 nm and 260 nm, and particularly around 193 nm. In the case of silicon dioxide, in particular, the layer structure can be significantly influenced by deposition with the assistance of neutral particles.Fluorides, particularly calcium fluoride, can be used as substrates. In the visible wavelength range, for example, scratch-resistant coatings can be produced using silicon nitride, as proposed here. In principle, coatings can be produced for any desired wavelength, from the X-ray and extreme ultraviolet wavelength ranges, the ultraviolet, the visible, or the infrared wavelength ranges. In addition to optical coatings, these can include, for example, protective coatings for the mechanical or chemical protection of an optical coating or for the protection of the substrate, or coatings to protect against mechanical stresses in the optical element.

[0034] The electrically neutral particles used for support, in this example made of argon, have a smaller cross section with their surroundings than corresponding ions. This results in the neutral particles being able to penetrate further into the layer material already present on the substrate 603 than corresponding charged particles. This can be expressed in the fact that the at least one first layer 605 has more neutral particles than if the at least one second layer 607 had been applied without the support of neutral particles, in particular than if it had been applied with corresponding ion support.

[0035] In particular, the penetration depth profile for layers deposited with the assistance of neutral particles is different from that for layers deposited with the assistance of ions. This is shown schematically in Fig. 8. The number of support atoms in arbitrary units, i.e. the supporting ions or neutral particles penetrated during assisted or assisted coating, is shown logarithmically as a function of the depth in the material towards the substrate, also in arbitrary units. The penetration depth curve is shown for a first layer S1a and an overlying second layer S2a, which was deposited with the assistance of neutral particles. This curve is shown in dashed lines. Another penetration depth curve is shown for a first layer S1b and an overlying second layer S2b, which was deposited with the assistance of ions. This curve is shown in dotted lines. In layer S1b, the number of support atoms decreases more quickly than in layer S1a.

[0036] If the penetration of support particles into the underlying at least one layer is to be avoided, a structure of an optical element as in Fig. 7 may be advantageous. The optical element 701 differs from that used in connection with Fig.6 explained that on the substrate 703, between the at least one randomly applied first layer 705 and the at least one third layer 709 applied with the aid of neutral particles, at least one second, unsupported, second layer 707 is provided. This second layer 707 is made of the same coating material as the assisted third layer 709 and serves as an intermediate layer. Since the second layer 707 is applied without support, it differs from the third layer 709 in its lower density, and it captures the neutral particles that penetrate deeper into the already existing partial coating during the assisted application of the third layer 709.However, in order for the proportion of neutral particles in the first layer 705 to be negligible, the second layer 707 must be thicker than if the at least one third layer 709 had been applied without support by neutral particles, in particular than if it had been applied with corresponding ion support, due to the lower effective cross section of the neutral particles with the surrounding material compared to charged particles.

[0037] It should be noted that deposition by electron beam evaporation was discussed in this example. However, other proven chemical and / or physical vapor-phase deposition methods can also be used, particularly thermal evaporation.

[0038] The optical elements manufactured as proposed can be used, for example, in UV lithography of semiconductor elements or in optical systems for inspecting wafers, imaging masks or optical elements. Reference symbol 101 Substrat 103 substrate holder 105 Electrode 107 Voltage source 109 Material source 111 Plasma source 201 Substrat 203 substrate holder 207 Voltage source 209 Material source 211 Plasma source 301 Substrat 303 substrate holder 307 Voltage source 309 Material source 311 Plasma source 313 Electrode 315 Electrode 401 Component 403 housing 405 filament 501 Component 503 housing 505 filament 507 grids 509 grids 601 optical element 603 Substrat 605 first shift 607 second shift 701 optical element 703 Substrat 705 first shift 707 second shift 709 third layer 901 Substrat 903 substrate holder 909 Ion source 913 Neutralizer QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2005 017 742 A1

[0002]

Claims

[1] A method for 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, characterized by that electrically neutral particles are provided to support the deposition. [2] Method according to claim 1, characterized by that neutral particles with an energy between 50 eV and 500 eV, preferably 75 eV to 300 eV, particularly preferably 100 eV and 200 eV are made available. [3] Method according to claim 1 or 2, characterized by that neutral particles are provided at an angle of incidence of up to 60° to the surface normal, preferably up to 45°, particularly preferably up to 30°. [4] Method according to one of claims 1 to 3, characterized by that one or more noble gases are used as supporting gas. [5] Method according to claim 4, characterized by that at least one volatile element of the material of the coating to be applied is added to the support gas. [6] A method according to any one of claims 1 to 5, wherein a conductive substrate is coated, characterized by that a voltage is applied to the substrate. [7] Method according to one of claims 1 to 6, characterized by that an electrode is arranged on the side of the substrate opposite to a particle flow. [8] Method according to one of claims 1 to 7, characterized by that at least one electrode is arranged in the direction of the particle flow on the side of the substrate facing a particle flow. [9] A method for 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, characterized by that the substrate is subjected to electrons by using a component which has a filament arranged in a housing, and at least one grid at an opening provided on the housing, which grid has a potential difference with respect to the filament. [10] Method according to one of claims 1 to 9, characterized by that the deposition is carried out by electron beam evaporation or thermal evaporation. [11] Optical element comprising at least one layer (607, 709) applied by the method according to one of claims 1 to 10. [12] Optical element according to claim 11, characterized bythat at least one oxide layer (607, 709) was applied by means of the method according to one of claims 1 to 10. [13] Optical element according to claim 11 or 12, comprising a coating comprising at least a first and a second layer (605, 607) on a substrate (603), wherein the at least one second layer (607) was produced by a method according to one of the preceding claims, characterized by that the at least first layer (605) has more electrically neutral particles than if the at least one second layer (607) had been applied without the assistance of neutral particles. [14] An optical element according to claim 11 or 12 comprising a coating comprising at least a first, second and third layer (705, 707, 709) on a substrate (703), wherein the at least one third layer (709) was produced by a method according to the preceding claims and the at least one second layer was applied without assistance by electrically neutral particles, characterized by that the at least one second layer is thicker than if the at least one third layer had been applied without the assistance of neutral particles, but with the assistance of charged particles.

Images