ES2935471T3 - Procedure for smoothing surfaces - Google Patents

Abstract

The present invention relates to a method for smoothing surfaces (12), with which surfaces (12) can be smoothed more efficiently than before and can also be smoothed in a direct machining method. Above all, the surfaces (12) of metal optics, in particular aluminum-based optics (10), can be smoothed more effectively than before. The optical properties (refractive index and absorption coefficient) of the surfaces (24) smoothed in this way remain substantially unchanged. In addition, the smoothed surfaces (24) have high long-term stability in terms of their chemical and/or mechanical resistance and their geometric and/or optical properties. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Procedure for smoothing surfaces

The present invention relates to a process for smoothing surfaces according to the preamble of claim 1.

Surface smoothing is used as a finishing process for numerous products, as disclosed, for example, in patent documents CN106683998 A, CN108385110A and CN5922083 A.

Above all, in optical applications sufficiently smooth surfaces are required. The lower the wavelength of light incident on the surface, the more critical it is to avoid surface roughness in the range 10 3 1/pm to 35 1/pm. Above all, the undulations can lead in this case to grating-like structures, which have a negative effect on the optical properties of the surface.

A large field of application, in particular in the area of the production of integrated, reproduction mirror optics, have surfaces of optical elements made of aluminum. These surfaces are generated at least mechanically, for example by means of diamond turning. In this case, however, the smallest grooves occur, which lead to surface roughness and undulations.

A pure mechanical polishing is not possible on such aluminum surfaces, since aluminum occurs in polycrystalline form and (chemically supported) mechanical polishing would lead to increased roughness and waviness.

However, to smooth these surfaces it is already known to smooth the surface by wet chemical coating. For example, an amorphous nickel-phosphorus coating is applied, in which the phosphorus content is adjusted to approximately 5 atomic %, so that in a subsequent malleabilization stage a complete relaxation of the compressive layer stress against the material is performed. in volume of aluminum and the hardness of the layer and the adhesion of the layer are raised.

A disadvantage here is that the wet chemical coating step and the subsequent malleabilization step are costly additional steps in order to allow a sufficient polishability of the optical surface for applications in the visible and UV spectral region. The degree of reflection for nickel-phosphorus is significantly below the degree of reflection for aluminum, so that subsequent metallization is often required. Such generated mirror optics are used, for example, for use in laser technology or illumination technology, as well as in the area of astronomy, where high requirements are placed on the surface quality, i.e. shape fidelity and low roughness. , and optics in terms of thermal load. The nickel-phosphorus coating in this case leads to deformation of the optical surface due to the bimetallic effect and can become brittle and peel off under continuous load.

It is also possible to work with an amorphous silicon coating, for example applied by sputtering instead of the nickel-phosphorus coating. However, there is also a high thermal maladaptation between silicon and aluminum in this case, so that deformation of the optical surface can also occur due to the bimetallic effect and the silicon coating can become brittle and peel off under continuous load.

Therefore, the object of the present invention is to provide a process for smoothing surfaces that eliminates at least one of the aforementioned drawbacks. Preferably, the method should smooth surfaces of metallic optical systems, in particular based on aluminium, better than hitherto. Preferably, the optical properties (refractive index and absorption coefficient) of such smoothed surfaces should not be altered. In particular, the generated surfaces must have high long-term stability in terms of their geometric and/or optical properties.

This object is solved by the method according to claim 1. Advantageous improvements are indicated in the dependent claims and the description.

From the inventive point of view it was recognized that the stated objective can be surprisingly solved with the combination of two different ion beam etching processes. For this purpose, a sacrificial layer is applied to the surface and this sacrificial layer is abraded in a first stage of ion beam etching. While this first etching process leads in most cases only to improvements in surface roughness and waviness <2.0 1/pm, by means of a second etching process, possibly in contact with a direct smoothing by ion beam ("direct smoothing" exists when the sacrificial layer has essentially been worn away already in the first stage of ion beam etching and therefore in the second stage of etching there is a direct interaction between the original surface and the beam ions), the microroughness of surfaces >2.0 1/pm can be further reduced. In this case, the sacrificial layer is preferably matched in its etching speed in the first etching process to the etching speed of the surface material in such a way that with the parameters selected etchings in the first etching process, a shape-saving transfer is made to the shape of the surface.

The process according to the invention for smoothing surfaces is characterized in that a sacrificial layer is applied to the surface and the surface coated with the sacrificial layer is treated by means of ion beam etching, whereby in the context of ion beam etching For ions, at least two different etching steps are used. The surface contains at least one substance, for example aluminium, when this is an aluminum-containing body that has a surface to be smoothed. The sacrificial layer fills in the surface roughness of the surface, the sacrificial layer having a very smooth surface that can be transferred to the original surface by the first post-etching step.

In an advantageous development it is provided that there is at least a first etching step, in which nitrogen ions and/or fluorine ions are used. Fluorine ions can be supplied, for example, via fluorine-containing compounds (eg trifluoromethane, tetrafluoromethane, nitrogen trifluoride). In addition, it can be provided that oxygen ions and/or inert gas ions (for example ions of atomic noble gases or ions of noble gas groups (for example argon, neon)) are used, so that they are formed given the oxides case. As a result, a surface layer comprising nitride and/or fluoride and optionally oxide is formed in situ , which enables very good smoothing. This is because the strong ionic-covalent chemical bond (Phillips ionicity of approx. 0.44 in the case of nitride) effectively inhibits surface diffusion. In addition, inhomogeneities in the structure matrix (for example, a polycrystalline grain structure with heterogeneous composition with aluminium) are passivated by the surface layer formed on the surface. The surface layer therefore acts as the dynamic progressive etch front, where the surface structure is largely preserved through chemical bonding and the passivation property.

It is provided that a surface-modified layer is formed on the surface by the first etching step, ie a layer that contains at least one of the substances contained in the original surface and has at least one other substance from the first etching step, preferably from a working gas of the first etching stage. As a result, a protection of the surface takes place, since this modified surface layer is on the one hand passivating and even amorphous. By this a progressive etch front is formed which prevents exposed parts of the surface from becoming rough.

It is provided that a surface layer with a thickness of at least 10 nm, preferably at least 12 nm, in particular at least 15 nm, is generated. This forms a particularly good engraving front.

In an advantageous development, provision is made for the sacrificial layer to be completely worn away by the first etching step. "Wearing" in this context also includes the complete chemical conversion of the sacrificial layer into a new layer. As a result, negative influences on the optical properties of the material can be avoided by the sacrificial layer. A preferred method according to the invention therefore consists in applying a sacrificial layer to the surface and completely abrading this sacrificial layer in the first step of ion beam etching and thus transferring its smooth surface to the original surface, so that so that it adopts in its roughness the improved properties of the sacrificial layer.

In an advantageous development, provision is made for the ions in the first etching step to have an energy of more than 10 eV per atomic component, preferably at least 800 eV, preferably at least 1000 eV, very preferably at least 1200 eV, in particular when minus 1500 eV and still more up to 5000 eV per atomic constituent part. The total ionic energy in this connection generally does not exceed 5000 eV. As a result, a particularly homogeneous surface layer is formed with a relatively large layer thickness. "Energy per atomic constituent part" means in this sense that polyatomic ions, such as CF4 ions, or cluster ions have a total energy that corresponds to the energy of the sum of the atomic constituent parts (in this case, with CF4 one carbon atom and 4 fluorine atoms). When the CF4 ion therefore has an energy of 2000 eV, the individual atomic constituent parts have an energy of 400 eV. Cluster ions themselves have from 100 to some 1000 atomic constituent parts.

In an advantageous development it is provided that the surface is coated at least twice with a sacrificial layer and after the respective coating with the sacrificial layer is treated with the first etching step. As a result, the undulation can be further reduced. The first two etching stages, which are used for the wearing away of the respective sacrificial layer, can also be differentiated from one another, where for example the energies, the geometry of the ion beams, the irradiation angles on the surface and/or or the ions used may be different. Also the sacrificial layers can differ from each other in their chemical composition and/or thickness. In this way, a particularly good adaptation can take place.

In an advantageous development it is provided that there is at least one second etching step, in which inert gas ions, fluorine ions and/or oxygen ions are used, the second etching step preferably taking place after one or more cycles of the coating with the sacrificial layer and the first stage of subsequent etching. As a result, the surface layer after the first etching step is effectively removed and the microroughness can be further reduced, so that the surface has almost optical properties. invariable compared to an aluminum surface not treated with natural oxide. Above all, when oxygen is used, the surface layer with possibly still contained constituent parts of the sacrificial layer is effectively removed.

The fluorine ions can themselves be supplied, for example, via fluorine-containing compounds (eg trifluoromethane, tetrafluoromethane, nitrogen trifluoride). As inert gas ions, atomic noble gas ions or noble gas cluster ions (eg argon, neon) can be used.

In the case of formation of a nitride surface layer after the first etching stage, inert gas ions, fluorine ions and/or oxygen ions can be used in the second etching stage, so that they can be effectively removed the nitride layer and the microroughness can be further reduced.

If a fluoride surface layer forms in the context of the first etching step, then inert gas ions and/or oxygen ions can be used in the second etching step, so that the fluoride layer can be effectively removed. fluoride and microroughness can be further reduced.

In an advantageous development, provision is made for the surface layer modified by the first etching step to be completely worn away by the second etching step. As a result, smoothing can be further improved.

In an advantageous development, provision is made for the second etching step to be carried out in such a way that the surface has a surface layer comprising oxide and/or fluoride. As a result, a protective layer is formed on the surface.

In an advantageous development, it is provided that the second etching step is carried out in such a way that the surface has a surface layer with a layer thickness of at least 10 nm, preferably at least 12 nm, in particular at least 15 nm. While normal contact of a surface with oxygen forms a natural oxide layer with approx. 5 nm thick, a greater thickness is preferred in this case, since this improves the long-term stability of the surface, in particular with thermally loaded applications.

By using pure inert gas (e.g. noble gas) as process gas in the second etching stage, on the other hand, an aluminum surface without a surface layer is produced, whereby a natural oxide layer is instantly formed by subsequent contact with air.

In an advantageous further development, provision is made for the ions in the second etching step to have an energy of more than 10 eV per atomic component, preferably at least 800 eV, preferably at least 1000 eV, very preferably at least 1200 eV, in particular when minus 1500 eV and still more up to 5000 eV per atomic constituent part. The total ionic energy in this connection generally does not exceed 5000 eV. In particular when using inert gas (eg noble gas) as process gas, the nitride and/or fluoride layer is eroded particularly carefully in this connection.

In an advantageous development, it is provided that the ions of the second etching step have at least initially, preferably at least until the wear of a surface layer formed by the first etching step, an energy of more than 10 eV per atomic component, preferably at most 700 eV, preferably at most 500 eV. Due to the reduced ionic energy, the surface layer is abraded very carefully and particularly thoroughly. In the following, it is provided in particular that the ions of the second etching step subsequently have a higher energy of at least 750 eV, preferably at least 900 eV, in particular at least 1500 eV. The total ionic energy in this connection generally does not exceed 5000 eV. When the second etching step is performed using oxygen ions, then a relatively thick oxide-comprising surface layer is generated thereby.

In an advantageous development, it is provided that oxygen ions are used in the context of a third etching step, which is carried out after the second etching step. As a result, the fluorine- and/or nitrogen-containing surface layers of the second etching stage can be abraded very gently.

When the ions of the third etching step have an energy of at least 750 eV, preferably at least 900 eV, in particular at least 1500 eV, a relatively thick surface oxide layer is generated. In advance, however, for a particularly gentle wear of the surface layer of the second etching step, the ions of the third etching step can present at least initially, preferably at least until the wear of the surface layer formed by the second etching step, an energy greater than 10 eV per atomic constituent part, preferably at most 700 eV, preferably at most 500 eV.

In an advantageous further development, provision is made for the surface to be the surface of a metal, preferably at least one metal from the group comprising aluminum, as well as alloys thereof, in particular Al6061, AI905, AI501, AI708. These metals and alloys can preferably be found in a microcrystalline finish or in coarse grain finish For such surfaces the smoothing process according to the invention is particularly effective. In this connection, in the context of the present invention, "metals" are understood to mean both individual compounds and also alloys based on at least one individual metal compound. Alternatively or additionally the following substances can also be used: silicon carbide, tungsten carbide, steel, ceramics, elemental metals or alloys with copper, beryllium, gold, silver, titanium, magnesium.

In an advantageous development, it is provided that the surface is subjected to a mechanical surface treatment step before the sacrificial layer is applied. The smoothing process according to the invention is particularly effective for smoothing surface roughness which is produced by mechanical surface treatment. In an advantageous development, provision is made for the surface to be part of an optical element, for example a mirror or a molding tool for the mass production of optical elements. For such optical elements, the smoothing process according to the invention is particularly effective.

In an advantageous development, provision is made for the sacrificial layer to be a polymer layer, preferably a photolacquer. Such polymer layers can be used particularly well as a sacrificial layer and their etch rates can be matched to the etch rates of the surface. Alternatively, oxides or amorphous materials can also be used as the sacrificial layer, however polymers are preferred. The application of the sacrificial layer is preferably carried out by conventional methods of microsystems art such as spraying, spray coating or dip coating; alternatively physical and chemical deposition methods are used, such as evaporation, sputtering, gas phase chemical deposition (thermally or plasma supported).

The characteristics and other advantages of the present invention will become apparent below through the description of two preferred embodiments in connection with the figures. In this regard it shows in a purely schematic way:

figure 1 scheme of the method according to the invention,

Figure 2 shows the waviness and microroughness of a first specific embodiment for an Al905 material,

figure 3 the average isotropic spectral power density in relation to spatial frequency for the first particular embodiment,

figure 4 the height profiling for the first specific embodiment example,

figure 5 the depth profiles of the chemical composition for aluminum oxide (AlO), carbon (C) and aluminum nitride (AlN) for the first concrete embodiment example,

figure 6 the depth profiles of the chemical composition for aluminum oxide (AlO) as well as the impurities nickel (Ni) and copper (Cu) for the first specific embodiment example,

figure 7 the reflectivity for the first concrete embodiment example,

figure 8 the waviness and microroughness of a second specific embodiment for an Al6061 material,

Figure 9 the average isotropic spectral power density in relation to spatial frequency for the second particular embodiment,

Figure 10 the height profiling for the second specific embodiment.

In FIG. 1 the method according to the invention is represented in a block diagram.

It can be distinguished that an optical element 10 (for example a mirror) with a surface 12, which has surface roughness, has been coated with a polymer as a sacrificial layer 14 for example by means of spray coating. As a result, a very flat outer surface 16 is formed, which evens out the surface roughness of the surface 12 of the optical element 10.

This outer surface 16 is now treated with an ion beam 18. Both the parameters of the ion beam 18 (composition of the working gas, energy of ion acceleration, geometry of the ion beam 18 and angle of impact on the outer surface 16) as well as the parameters of the sacrificial layer 14 have been set relative to each other and to the material of the optical element 10 in such a way that the selectivity of the etching process is as close as possible to 1. This selectivity is It is determined in this regard by the etching speed of the material of the optical element 10 in relation to the etching speed of the sacrificial layer 14.

In the first concrete exemplary embodiment, aluminum of the type AI905 is used as the material of the optical element 10, which had a diameter of 50 mm and was provided with a flat mirror surface 12 by means of diamond turning (monograin diamond turning technique). . A novolak-based photoresist was used as the sacrificial layer 14 .

In the context of ion beam etching of the first etching stage, nitrogen is used as working gas with an energy of 1200 eV. As a result, with a selectivity of 1, the shape of the outer surface 16 is transferred to the material of the optical element 10, whereby the sacrificial layer 14 wears away completely and an aluminum nitride layer 19 is formed, which acts as a front of dynamic progressive etching, wherein the surface structure of the outer surface 16 is largely preserved through the chemical bond formation and passivation property of the nitride layer 19.

As a result, the optical element 10 is formed with a modified surface 20. In this connection, the modification consists on the one hand of a chemical modification by formation of a nitride layer 19 and on the other hand of planarization.

This process of applying the sacrificial layer 14 and the subsequent ion beam etching 18 as the first etching step can then be repeated as often as desired with another sacrificial layer 14a and a new ion beam etching 18a, where preferred. a single repeat, so that a further modified surface 20a is formed. The parameters of the ion beam etching 18a can be preserved in this connection or can also be changed, where preservation is preferred. Also in this repetition step, the sacrificial layer 14a has been completely removed and an aluminum nitride layer 19a with a thickness of 10 nm to 15 nm has been formed.

Next, the ion beam process 18b is modified so that oxygen is used as the process gas. As a result, the nitride layer 19a is worn away to a large extent and an aluminum oxide layer 22 is formed. This second etching step is preferably carried out in two parts so that oxygen ions in the range of energy below 500 eV up to 700 eV maximum, so that the nitride layer 19a is very carefully removed, and then after removal of the nitride layer 19a oxygen ions in the energy range of at least 750 eV to above 1500 eV, so that a very stable oxide layer 22 is formed. As a result, the oxide layer 22 with a thickness of 10 nm to 15 nm is formed, which has excellent long-term stability even in applications with high thermal load.

The resulting surface 24 of the optical element 10 produced in this way has a substantially improved undulation and roughness with at least not worsened microroughness.

In figure 2, for a surface 12 made of aluminum AL905, which has been mechanically treated by means of diamond turning, the waviness/roughness and microroughness for the untreated (non-machined) optical element 10 are compared for the first passage of application of the sacrificial layer 14 of photoresist and ion beam etching 18 with nitrogen (after 1st planarization), the second application step of the sacrificial layer 14a of photoresist and ion beam etching 18a with nitrogen (after 2nd planarization) and the second etch stage 18b with oxygen (after final machining with O2). In this connection, the AFM recordings for 35 pm and 3 pm edge lengths of the surfaces 12, 20, 20a, 24 under study have been shown in each case. The corresponding measurement values are given in Tables 1 for Rq (rms) and 2 for the maximum amplitude of the ripple amplitude.

Table 1: (Al905)

Table 2: (Al905)

It can be seen that the waviness of the modified surface 20 after the first performance of the first etching step (after 1st planarization) is reduced from 9.5 nm to 5.9 nm and the microroughness increases from 2.2 nm to 3 .2 nm. The maximum amplitude is reduced in this respect from 11.8 nm to 4.0 nm. After the second execution of the first etching step (after 2nd planarization), the ripple of the additionally modified surface 20a can be reduced to 5.1 nm, while the microroughness at 3.3 nm remains approximately the same and the maximum amplitude is reduced to 2.2 nm. After the second etching step (after final machining with O2) the resulting surface undulation 24 with 5.2 nm remains approximately the same, while the microroughness can be reduced again to the original value of 2.2 and the maximum amplitude is of approximately 3.3 nm.

These results are also reflected in Figure 3, where the average isotropic power spectral density (average isotropic PSD) is indicated for spatial frequencies from about 10-3 pm'1 to about 100 pm-1. In this respect it can be distinguished that the waviness in the area of the striations (turning marks) produced by the mechanical treatment by diamond turning could be clearly reduced by a factor of 2, while the long wave waviness (fault in the frequency range average spatial) remains almost uninfluenced. Almost no changes are made in the microroughness area either.

The height profiling shown in figure 4 shows a clear reduction by factor 4 for the flutes for the second execution of the first etching stage (after 1st planarization) and the second etching stage (after final machining with O2). compared to the untreated surface 12.

As a result, turning flute structures with a period of 3 pm, i.e. with a spatial frequency of 0.33 pm-1, as well as superstructures resulting from the special shape of the turning tool could thus be reduced. with spatial frequency of 0.69 pm-1, 1.0 pm-1 and 1.4 pm-1 from an initial value of approx.

24 nm maximum structure height up to approx. 7nm.

In figures 5 and 6 are shown depth profiles determined by means of secondary ion mass spectrometry of the chemical composition on the modified surface 20a and the resulting surface 24 for aluminum oxide (AlO), carbon (C) and aluminum nitride. aluminum (AlN) in figure 5 and for aluminum oxide (AlO) as well as the impurities nickel (Ni) and copper (Cu) in figure 6.

It can be seen that the nitrogen content in the resulting surface 24 has been reduced by 2 orders of magnitude. However, due to impurities in the second etching stage, the carbon content was increased. For this purpose, the nickel and copper impurities were reduced in the first 5 nm depth of the resulting surface 24 and the aluminum oxide layer 22 has a thickness of approximately 15 nm.

In FIG. 7, the reflectivity of the surfaces 12, 22, 24 for three different measurement points is compared with one another.

It can be seen that the reflectivity of the surface 22 after the second carrying out of the first etching step (after 2nd planarization) over the entire measured spectral region from 400 nm to 800 nm has clearly decreased, which is due to the layer surface nitride.

The second oxygen etching step wore away the nitride layer and created an oxide layer, so that the reflectivity over the entire measured spectral region essentially increases again, although it does not quite reach the starting surface values. 12 not treated. One reason for this is considered the ingress of carbon and the possibly associated carbide formation in the context of oxygen etching, which had to be prevented by suitable measures, such as adaptation of the materials used in the ion source.

In addition to a reduction in roughness and microroughness in the spatial frequency range of 0.015 pm-1 to 34.6 pm-1, especially periodic turning groove structures, which result from the above single grain diamond turning technique in the spatial frequency range of 0.2 pm-1 to 2.0 pm-1. This allows for the future use of aluminum optics 10 in the shortwave spectral region (UV/VIS), where the aluminum surface 24 itself can take on the role of the optically active surface. In this respect, the topography of the surface 12 stamped on the optical element 10 is preserved.

The second concrete embodiment differs from the first concrete embodiment only in that Al6061 is now used instead of Al905. All other procedural parameters had been selected identically, so it is not addressed again.

In FIG. 8, for a corresponding surface 12 made of aluminum AL6061, which has been mechanically treated by means of diamond turning, the waviness/roughness and microroughness for the untreated (untreated) optical element 10 are compared for the first passage. sacrificial layer 14 of photoresist and ion beam etching 18 with nitrogen (after 1st planarization), the second application step of sacrificial layer 14a of photoresist and ion beam etching 18a with nitrogen (after 2nd planarization) and the second etch stage 18b with oxygen (after final machining with O2). In this connection, the AFM recordings for 35 pm and 3 pm edge lengths of the surfaces 12, 20, 20a, 24 under study have been shown in each case. The corresponding measurement values are given in Tables 3 for Rq (rms) and 4 for the maximum amplitude of the ripple amplitude.

Table 3: (AI6061)

Table 4: (AI6061)

It can be seen that the waviness of the modified surface 20 after the first performance of the first etching step (after 1st planarization) is reduced from 4.7 nm to 4.2 nm and the microroughness increases from 1.3 nm to 2 0.6 nm. The maximum amplitude is reduced in this case from 1.5 nm to 0.9 nm. After the second execution of the first etching step (after 2nd planarization), the ripple of the additionally modified surface 20a can be reduced to 3.2 nm, while the microroughness at 2.5 nm remains approximately the same and the maximum amplitude down to below 0.5 nm. After the second etching step (after final machining with O2) the resulting surface undulation 24 with 3.3 nm remains approximately the same, while the microroughness can be reduced again to the original value of 1.4 and the maximum amplitude is more less than 0.5 nm.

These results are also reflected in Figure 9, where again the average isotropic power spectral density (average isotropic PSD) is indicated for spatial frequencies from about 10 -3 pm'1 to about 100 pm -1 . In this respect it can be distinguished that the waviness in the area of the striations (turning marks) produced by the mechanical treatment by diamond turning could be clearly reduced by a factor of 1.5, while the long wave waviness (failure in the interval average spatial frequency) remains almost uninfluenced. Almost no changes are made in the microroughness area either.

The height profiling shown in figure 10 shows a clear reduction by factor 3 for the flutes for the second execution of the first etching stage (after 1st planarization) and the second etching stage (after final machining with O2). compared to the untreated surface 12.

As a result, turning flute structures with a period of 1.3 pm, i.e. with a spatial frequency of 0.8 pm-1, as well as superstructures resulting from the special shape of the tool could therefore be reduced. of turning with a spatial frequency of 1.4 pm-1 and 1.9 pm-1 from approx. 3 nm originally from maximum structure height to below 1 nm.

The results for the chemical composition and for the reflectivity were very similar, as this is represented in Figures 5 to 7, so this is not addressed separately.

Although the invention has been described in question by means of exemplary embodiments with aluminum and a photoresist as well as a first etching step with nitrogen and a second etching step with oxygen, the invention is not limited to this, but can be other materials can also be used, for example elemental metals or alloys with copper, beryllium, gold, silver, titanium, magnesium; Silicium carbide; tungsten carbide; steel; ceramics, particularly those with low thermal expansion, and other ions. An advantage of the described ion beam technology is precisely also the high range of application for different material systems, in particular for the application in optics.

From the above description it has become apparent that with the present invention a method for surface smoothing is provided as a direct machining method, with which surfaces 12 can be smoothed better than hitherto. Especially surfaces 12 of optical systems 10 made of metal, in particular those based on aluminium, can be smoothed better than hitherto. In this regard, the optical properties (refractive index and absorption coefficient) of such smoothed surfaces 24 remain essentially unchanged. In addition, the smoothed surfaces 24 have a high long-term stability in terms of their chemical and/or mechanical stability as well as their geometric and/or optical properties.

Reference list

10 Optical element, mirror

12 Optical element surface 10

14, 14a Sacrificial layer, polymer, photoresist

Outer surface, sacrificial layer surface 14, 14a, 18a, 18b Ion beam etching

, 19a Nitride layer, aluminum nitride layer

modified surface

a Additionally modified surface

Oxide layer, aluminum oxide layer

resulting surface

Claims (14)

Yo. Method for smoothing surfaces (12), characterized in that a sacrificial layer (14, 14a) is applied to the surface (12) and the surface (12) coated with the sacrificial layer (14, 14a) is treated by means of ion beam etching (18, 18a, 18b), wherein in the context of ion beam etching (18, 18a, 18b) at least two different etching steps (18, 18a, 18b) are used, wherein by means of the first etching step, the sacrificial layer (14, 14a) is abraded and a surface-modified layer (19, 19a) is formed on the surface (20, 20a), wherein the surface-modified layer (19, 19a) it is generated with a thickness of at least 10 nm and contains at least one of the substances contained in the original surface and has at least one other substance from the first etching step. Method according to claim 1, characterized in that there is at least a first etching step (18a, 18b), in which nitrogen ions and/or fluorine ions are used and preferably additionally oxygen ions and/or inert gas ions. Method according to claim 2, characterized in that the modified surface layer (19, 19a) is a surface layer comprising nitride (19, 19a) and/or fluoride and optionally oxide. Method according to claim 3, characterized in that the surface-modified layer (19, 19a) is produced with a thickness of at least 12 nm, in particular at least 15 nm. Method according to one of Claims 2 to 4, characterized in that the ions in the first etching step have an energy of more than 10 eV per atomic constituent part, preferably at least 800 eV, preferably at least 1000 eV, most preferably at least 1200 eV, in particular at least 1500 eV and still more up to 5000 eV per atomic constituent part. Method according to one of Claims 2 to 5, characterized in that the surface (12) is coated at least twice with a sacrificial layer (14, 14a) and after the respective coating with the sacrificial layer (14, 14a) is deals with the first stage of engraving (18, 18a). Method according to one of the preceding claims, characterized in that there is at least one second etching stage (18b), in which inert gas ions, fluorine ions and/or oxygen ions are used, wherein the second stage Etching (18b) is preferably carried out after one or more cycles of coating with the sacrificial layer (14, 14a) and the first subsequent etching stage (18, 18a). Method according to claim 7 in conjunction with claim 3 or 4, characterized in that the surface layer (19, 19a) modified by the first etching step is completely abraded by the second etching step. Method according to claim 7 or 8, characterized in that the second etching step (18b) is carried out in such a way that i) the surface (24) has a surface layer comprising oxide (22) and/or fluoride and/or ii) the surface (24) has a surface layer (22) with at least 10 nm, preferably at least 12 nm, in particular at least 15 nm layer thickness and/or iii) the surface does not have any surface layer. Method according to one of Claims 7 to 9, characterized in that the ions of the second etching step have an energy of more than 10 eV per atomic constituent part, preferably at least 800 eV, preferably at least 1000 eV, most preferably at least 1200 eV, in particular at least 1500 eV and still more up to 5000 eV per atomic constituent part. Method according to one of Claims 7 to 10, characterized in that the ions of the second etching step (18b) exhibit at least initially, preferably at least until wear, a surface layer (19, 19a) formed by the first etching step (18, 18a), an energy of more than 10 eV per atomic constituent part, preferably not more than 700 eV, preferably not more than 500 eV, where in particular it is provided that the ions of the second etching step ( 18b) then have a higher energy of at least 750 eV, preferably at least 900 eV, in particular at least 1500 eV. Method according to one of the preceding claims, characterized because the surface (12) is the surface of a metal, preferably at least one metal from the group comprising aluminum as well as alloys thereof, in particular Al6061, Al905, Al501, Al708, where the metal can preferably be in the form microcrystalline or coarse-grained and/or because the surface (12) is the surface of a substance from the group: silicon carbide, tungsten carbide, steel, ceramics, elemental metals or alloys with copper, beryllium, gold, silver, titanium, magnesium. Method according to one of the preceding claims, characterized iv) because the surface (12) before the application of the sacrificial layer (14, 14a) was subjected to a stage of mechanical surface treatment and/or v) because the surface (12) is part of an optical element (10), for example a mirror, or a molding tool for the mass production of optical elements. Method according to one of the preceding claims, characterized in that the sacrificial layer (14, 14a) is a polymer layer, preferably a photolacquer.