Device and method for processing a workpiece with an ion beam

Abstract

A device for processing a workpiece (14) with an ion beam (34) comprises a holder (12) for receiving the workpiece (14), an ion source (24) for generating ions, and an extraction grid (28) for accelerating the ions so that a directed ion beam (34) exits the extraction grid (28). Downstream of the extraction grid (28), there is an aperture (36; 36a, 36b) that limits the cross-section of the ion beam (34) and is adjustable such that an adjustment of the aperture (36) changes the angular distribution of the ion beam (34).

Description

[0001] Device and method for machining a workpiece with an ion beam

[0002] BACKGROUND OF THE INVENTION

[0003] 1. Field of the invention

[0004] The invention relates to a device and a method for processing a workpiece with an ion beam that removes material from the workpiece, applies material to the workpiece or introduces material into the workpiece.

[0005] 2. Description of the state of the art

[0006] The surfaces of workpieces are treated in various ways using ion blasting. Ion blasting can be used to remove material from the surface of the workpieces, to apply material to the surface, or to introduce material into the surface.

[0007] Material removal is usually achieved through ion beam etching (IBE) or ion milling, in which accelerated ions are directed at the surface of the workpiece in a high vacuum. The kinetic energy of the ions causes atoms or molecules to be ejected from the surface, partially atomizing it. Ion beam etching is thus similar to sandblasting, except that significantly smaller particles are used instead of sand.

[0008] Ion etching processes include, for example, ion beam figuring (IBF), in which particularly high-quality optical surfaces are post-processed in an ion beam etching system. If the ions interact with the surface not only physically due to their kinetic energy, but also chemically, this is referred to as reactive ion beam etching (RBBE).

[0009] If, however, material is deposited onto the surface by the ion beam, this is called ion beam deposition (IBD), ion beam sputtering, or ion beam sputter deposition (IBS or IBSD). In this process, a broad ion beam strikes the surface of a target, causing atoms or molecules to be ejected from the target. The released particles then land on the surface of the workpiece and form a thin coating. By using different targets in a single process chamber, multiple layers can be produced with very high quality.

[0010] The introduction of ions into the near-surface area of ​​a workpiece is called ion implantation and is used, for example, for doping semiconductors.

[0011] The devices used for workpiece machining often contain a wide-beam source from which a broad ion beam emerges. The diameter of the ion beam in these sources is typically between 5 and 500 mm, most often between 10 and 100 mm, and in Ion Beam Figuring (IBF) even 1 mm or less. The wide-beam source comprises the actual ion source for generating ions and ion optics that shape the generated ions into a beam.

[0012] A Kaufman ion source is frequently used as the ion source, in which free electrons are generated with the aid of a heated cathode and ionize gas atoms or molecules via electron impact ionization. Inductively coupled RF ion sources are also commonly used, in which ionization takes place in a high-frequency alternating magnetic field.

[0013] Ion optics extracts ions from the plasma and forms them into an ion beam. In wide-beam sources, the ion optics typically include an extraction grating to which an accelerating voltage is applied to accelerate the ions generated by the ion source. The extraction grating has numerous openings through which the ions emerge as individual beams, which then superimpose to form a wide beam. Often, several extraction gratings (e.g., screen gratings, accelerating gratings, and retarding gratings) are arranged close together, each subjected to different high voltages, forming a single extraction grating system.

[0014] The ablation effect of the ion beam depends on various parameters. Quantitatively, the ablation effect is often described by the so-called sputtering yield. This is the ratio of the number of ablated particles to the number of incident particles. It is readily apparent that the ablation effect depends on the kinetic energy of the incident particles. There is also a dependence on the mass of the incident particles. For example, heavier gold ions have a stronger ablation effect than lighter silicon ions at the same kinetic energy.

[0015] The abrasive effect is highly dependent on the angle at which the ions strike the surface. A change in angle of just 15° can double the abrasive effect for certain ions. The greatest abrasive effect is generally not achieved when the particles strike the surface perpendicularly, but rather at angles between 60° and 80° relative to the surface. This angle can be influenced by the relative position of the workpiece and the main direction of the ion beam.

[0016] The angular dependence of the material removal rate poses particular difficulties when the ion beam is wide and the workpiece has a curved surface. Even if the ion beam were perfectly collimated, so that all ions propagate in the same direction, the ions would still strike the surface at different angles in this case. The result is uneven material removal across the area being treated by the ion beam. In applications requiring accuracies on the order of a few atoms, such variations in material removal are unacceptable, leading to scrap or costly rework.

[0017] An additional difficulty arises from the fact that the ion beam is generally not perfectly collimated, but rather the propagation directions of the ions are distributed over a certain angular range. This angular distribution of the ion beam further increases the range of possible impact angles.

[0018] Similar difficulties can arise during material deposition. Here, it is crucial that the removal rate, i.e., the number of particles ejected from the target per unit of time, remains as constant as possible. If the surface of the target facing the ion source is not perfectly aligned or is no longer flat due to prolonged removal, the removal rate changes, and consequently, so does the amount of material that impacts the workpiece per unit of time. A strong dependence of the implantation rate on the angle of impact is also observed in ion implantation.

[0019] SUMMARY OF THE INVENTION

[0020] The object of the invention is to provide a device and a method for processing a workpiece with an ion beam, in which, in the case of wide ion beams, the angular distribution of the ion beam can be adjusted more precisely.

[0021] With regard to the device, this problem is solved by a device for processing a workpiece with an ion beam, wherein the device comprises a holder for receiving the workpiece and an ion source configured to generate ions. Furthermore, the device includes an extraction grid connected to a voltage source, which is configured to accelerate the ions generated by the ion source such that a directed ion beam emerges from the extraction grid. An aperture limiting the cross-section of the ion beam is arranged behind the extraction grid in the direction of a mean propagation direction of the ions. According to the invention, the aperture is adjustable such that the angular distribution of the ion beam changes when the aperture is adjusted.

[0022] The invention is based on the understanding that, for achieving more homogeneous processing, it is important to be able to influence the angular distribution of the ion beam before it strikes the workpiece. Only when the angular distribution is optimally adapted to the shape and / or orientation of the workpiece surface or – in the case of material deposition – the target surface, can difficulties arising from the angular dependence of the ablation or implantation effect be eliminated or at least reduced to such an extent that less rework or scrap is required. For example, the angular spectrum can be reduced on highly curved surfaces so that the angles at which the ions strike the surface do not vary too much.If the ion beam sweeps across a uniformly inclined section of the workpiece surface, the entire beam can be tilted to achieve a similar machining effect even in the inclined section. A more precisely adjustable angle distribution is not only a prerequisite for particularly homogeneous machining but can also be used for deliberately inhomogeneous machining. For example, to create slanted surface relief gratings, such as those used in augmented reality (AR) glasses for coupling light in and out, the ion beam must strike the surface at a precisely defined angle. Such structures can be homogeneous, meaning they have the same geometry everywhere; however, it is also possible for the inclination angles and etching depth of the grating structures to vary across the surface.This requires inhomogeneous processing, which places particularly high demands on the adjustment of the angular distribution of the ion beam.

[0023] Ions can be easily deflected variably using electric or magnetic fields. However, in processes where ions with different masses are used, mass-dependent deflections occur, which is generally undesirable. Furthermore, undesirable charge redistribution effects occur in ion beam sources under certain operating conditions, causing uncharged particles to mix with the ions; these particles cannot be deflected by electromagnetic fields. Another difficulty with deflection using electric or magnetic fields is that the fields must be homogeneous over a very large area for wide ion beams. Any remaining field inhomogeneities produce additional divergence of the ion beam, which is generally undesirable.

[0024] In contrast, apertures are independent of mass and charge and always result in a reduction of divergence. While apertures inevitably lead to a certain loss of ions for processing, this can be easily compensated for with a more powerful ion source without significant additional costs. Since the effect of apertures can be well simulated, suitable control of the ion source can ensure that the number of ions impacting the workpiece or target remains constant even when the aperture is adjusted. For the purposes of this discussion, an aperture is considered adjustable if the adjustment can be effected by an operator-accessible control element that can be operated without tools, or by an externally driven actuator.

[0025] The angular distribution l(oc) of an ion beam describes how the intensity I of the ion beam is distributed across the angles α at which the individual ions of the beam propagate. The reference direction for the angle measurement is usually given by a mean propagation direction of the ion beam exiting the extraction lattice, which regularly coincides with an axis of symmetry of the extraction lattice. Often, ion beams have a bell-shaped angular distribution upon exiting the extraction lattice, so that most ions propagate along the mean propagation direction. The more the propagation angles deviate from the mean propagation direction, the lower the intensity becomes.

[0026] In the simplest case, the aperture can be adjusted by being positioned so that it can be moved along a linear axis that extends parallel to the mean direction of ion propagation. Even with this very simple measure, it is possible to influence the divergence of the ion beam. The further the aperture is from the extraction grating, the stronger the collimation of the ion beam, because ions can no longer propagate at large angles to the mean direction of propagation.

[0027] In some embodiments, the aperture has a diaphragm opening that is positioned off-center relative to the mean direction of ion propagation. This allows the ion beam to be influenced in a non-rotationally symmetric manner and directed in a specific direction.

[0028] In one embodiment, the aperture has multiple aperture openings. Each aperture opening can correspond to exactly one or more openings in the extraction grating. Ideally, the extraction grating has a first grid of openings, and the aperture has a second grid of aperture openings that corresponds to the first. Visually speaking, there is then exactly one aperture opening behind each opening of the extraction grating in the propagation path. In this way, the individual partial ion beams that emerge from the extraction grating and superimpose to form the ion beam can be directly controlled.

[0029] In the simplest case, this influence is achieved by moving the aperture along a linear axis, as mentioned previously. If all aperture openings are the same size, then the same divergence can be set for each partial ion beam by moving the aperture, so that the ion beam resulting from the superposition of the partial ion beams also has the same divergence as the individual partial ion beams.

[0030] Individual manipulation of the partial ion beams is possible if the dimensions of the aperture openings and / or the distance between adjacent aperture openings are adjustable. This can apply to all existing aperture openings or only to a subset of them. One way to adjust the dimensions of all aperture openings simultaneously is to shift two closely adjacent aperture grids relative to each other. Such an aperture is mechanically more complex, but allows for particularly flexible control of the angular distribution of the ion beam.

[0031] In some embodiments, not just one adjustable aperture is provided, but several apertures, at least one of which is adjustable. In particular, a first aperture and a second aperture may be provided, the latter arranged along the central propagation direction behind the first aperture.

[0032] By combining two apertures, at least one of which is adjustable, the angular distribution can be changed very flexibly. For example, the distance between the first and second apertures can be adjustable along the mean propagation direction, and / or the second aperture can have an aperture opening with adjustable dimensions. Similar to optics, the effect of an aperture depends on its position in the beam path. While an aperture near the extraction grating system primarily affects the spatial distribution of the ion beam, a second aperture located further away from the grating has a stronger influence on the angular distribution of the ion beam. If the second aperture is shifted perpendicular to the mean propagation direction, for example, different angular components are favored. A second aperture is also useful as a clipping aperture when a deflection unit (see below) is used in addition.

[0033] If multiple apertures are used, the aperture openings do not necessarily have to be concentric. For example, the first aperture can have a first aperture opening, and the second aperture can have a second aperture opening that is decentered to the first aperture opening. This asymmetry not only affects the divergence but also the mean direction of propagation of the ion beam, leading to lateral deflection.

[0034] Such lateral deflection can also be generated by a deflection unit designed to deflect the ion beam using electric and / or magnetic forces. As mentioned earlier, the effect of such forces is mass- and charge-dependent. This is often undesirable, but irrelevant if all the ions have the same mass and charge. In conjunction with an aperture positioned behind the deflection unit, this mass- and charge-dependent effect can be advantageously used to create a filtering effect. For example, if an ion beam contains light and heavy ions with the same charge, and the lighter ions are to be filtered out of the beam, the fact that ions with a smaller mass-to-charge ratio are deflected more strongly in a homogeneous electric field than ions with a larger ratio can be exploited.

[0035] It is convenient and sufficient for the filtering described above if the deflection unit is designed to deflect the ion beam by a deflection angle between 5° and 45° and preferably between 15° and 30°.

[0036] The deflection unit can be configured to generate a variable magnetic field and / or a variable electric field to deflect the ion beam by different angles. This variability allows the deflection to be used as an additional parameter for adjusting the angular distribution. For this purpose, it is particularly advantageous to have two apertures and to position the deflection unit between the first and second apertures. If a first deflection unit is positioned in front of the aperture and a second deflection unit behind it, complex deflections and filters can be achieved. If the first and second deflection units have opposing deflection effects, the ion beam can be shifted parallel to itself. This is especially beneficial when the filtering effect is the primary objective.

[0037] It is advantageous if the deflection unit is arranged so that no part of it is directly exposed to the ion beam. If the ion beam can strike parts of the deflection unit, as is the case with the deflection unit known from US 4,381,453 A, ions can be deposited on these parts, leading to contamination that affects the electric field. Furthermore, if the ion beam strikes parts of the deflection unit, the surface of the part can be eroded, potentially destroying it after prolonged exposure.

[0038] To generate a homogeneous electric field, an arrangement similar to a parallel-plate capacitor can be used. Magnetic fields that are largely homogeneous even over a larger volume can be generated, for example, using Helmholtz coils. Even more homogeneous magnetic fields can be generated with cylindrical coils without more than two yokes, as is the case with Maxwell, Braunbeck, or Barker coils.

[0039] It is also possible to incorporate a deflection unit designed to generate electrical and / or magnetic forces that vary at a frequency between 1 Hz and 1 kHz. These rapidly changing forces prevent the ion beam from continuously striking the same area on the surface of the workpiece or target, instead causing it to perform small lateral oscillations. This can be helpful in compensating for inhomogeneities in the ion beam and preventing unwanted "burn-in" of the ion beam at specific locations. Alternatively, such lateral oscillations can be used for the targeted correction of structures with high spatial frequencies.

[0040] In one embodiment, the device has a control unit configured to adjust the aperture when the spatial position of a surface of the workpiece being treated by the ion beam changes relative to the device. This allows the angular distribution to be automatically adapted to the spatial position of the surface. To detect this position, a position sensor can be provided, configured to detect the spatial position of the surface of the workpiece being treated by the ion beam relative to the device. The position sensor could, for example, be an optical sensor that measures the surface of the workpiece without contact. However, since the shape and orientation of the surface are often known with sufficient accuracy from design and control data, such a sensor can be omitted in many cases.

[0041] Preferably, at least the parts of the aperture exposed to the ion beam are made of graphite. This material results in particularly low atomization from impacting ions. This counteracts contamination of the extraction grating.

[0042] If the surfaces of the aperture exposed to the ion beam are arranged at a steep inclination, the undesirable abrasive effect can be further reduced. These aperture surfaces can, for example, have a dense arrangement of pyramidal depressions or protrusions. If the inclination of these surfaces to the direction of the incident ions is between 45° and 55°, the amount of aperture material removed can be significantly reduced.

[0043] In one embodiment, the aperture is movable along a linear axis that extends perpendicular to the mean direction of ion propagation. While such lateral adjustment of the aperture generally does not affect the angular distribution of the ion beam, or at least not substantially, this movable feature can be helpful for defining a treatment area of ​​the ion beam on the workpiece. In this way, for example, an area on the workpiece that should not be, or should no longer be, exposed to the ion beam can be protected from the beam very quickly and without moving the workpiece.

[0044] The invention further relates to a method for processing a workpiece with an ion beam comprising the following steps: a) a workpiece is placed in a holder;

[0045] b) an ion source produces ions;

[0046] c) An extraction grid connected to a voltage source accelerates the ions generated by the ion source so that a directed ion beam propagating along a mean direction of propagation emerges from the extraction grid;

[0047] d) the ion beam passes through an aperture which is arranged along the mean direction of propagation behind the extraction grating;

[0048] e) the aperture is adjusted so that the angular distribution of the ion beam is changed as it passes through the aperture; and

[0049] f) The ion beam is directed at the workpiece or at a target where material is atomized and deposited on the workpiece.

[0050] BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. These show:

[0052] Figure 1 shows a machining device according to the invention in a first embodiment in a schematic side section;

[0053] Figure 2 shows the sputtering yield SY as a function of the angle a for an exemplary machining operation;

[0054] Figures 3a and 3b illustrate how the divergence of the ion trajectories can be changed by moving the aperture along the z-direction;

[0055] Figures 4a and 4b illustrate how the variable angle distribution can be used to achieve a more homogeneous material removal on a curved surface; Figure 5 shows a machining device according to a second embodiment in a schematic side section, in which two apertures are provided;

[0056] Figures 6a to 6c show the beam path for different constellations of two apertures;

[0057] Figure 7 shows a machining device according to a third embodiment in a schematic side section, in which two apertures and an electrostatic deflection unit are provided;

[0058] Figure 8 shows a section of the machining device shown in Figure 7 with the deflection unit switched off;

[0059] Figure 9 shows a section of the machining device shown in Figure 8 with the deflection unit switched on;

[0060] Figure 10 shows a machining device according to a fourth embodiment in a schematic side section, in which an aperture and two electrostatic deflection units are provided;

[0061] Figure 10 shows a machining device according to a fifth embodiment in a schematic side section, in which an aperture is arranged to be movable both parallel and perpendicular to the mean direction of propagation;

[0062] Figures 11a and 11b illustrate how the processing area of ​​the ion beam can be changed by moving the aperture along the y-direction without changing the angular distribution of the ions.

[0063] DESCRIPTION OF PREFERRED EXAMPLES

[0064] 1. First embodiment

[0065] Figure 1 shows a schematic, non-scale side section of a machining device according to the invention, designated as 10. The machining device 10 comprises a holder 12 for a workpiece 14, which has a surface 16 from which material is to be removed by means of an ion etching process. The holder 12 is designed as a slide that is movably arranged on a base 18 along the x and y directions. The movability along the y direction is indicated in Figure 1 by a double arrow 20.

[0066] The base 18 is itself pivotable about an axis parallel to the x-direction by means of a pivot joint indicated at 22. This allows the surface 16 of the workpiece 14 to be positioned at different locations and in different orientations. The base 18 can also be pivotable about an orthogonal pivot axis parallel to the x-direction.

[0067] The processing device 10 also includes an ion source 24, which can, for example, be configured as a Kaufman ion source, as is known in the prior art. The ions generated by the ion source, which can be, for example, argon ions, emerge from a window 26 of the ion source 24 and are accelerated by an ion optic designed as an extraction grating system 28. The extraction grating system 28 comprises several extraction gratings arranged in series, for example, a screen grating, an accelerating grating, and a decelerating grating. The extraction gratings of the extraction grating system 28 are connected to a voltage source 30 and accelerate the ions generated by the ion source 26 so that they emerge at high speed through the grating openings of the extraction grating system 28.

[0068] In order to change the relative arrangement between the workpiece 14 on the one hand and the ion source 14 and the extraction grid system 28 on the other hand, the ion source 14 and the extraction grid system 28 can be moved and / or pivoted as an alternative or in addition to the movable and / or pivotable mounting of the holder 14.

[0069] In Figure 1, the trajectories 32 of some ions exiting through the openings of the extraction grid system 28 are schematically indicated by arrows. These ions together form a broad ion beam 34, the diameter of which is between 5 and 500 mm, preferably between 10 and 150 mm, but in the case of the IBF, it can also be only 1 mm or less. In Figure 1, the ions propagate from left to right along a central propagation direction that coincides with the +z direction. An aperture 36 is arranged along this propagation direction behind the extraction grid system 28. This aperture limits the cross-section of the ion beam 34 and also influences its angular distribution, as will be explained in more detail later. The aperture 36 can be moved along the z direction by means of an adjustment device 38, as indicated by double arrows in Figure 1. In this way, the distance between the aperture 36 and the extraction grid system 28 can be varied.

[0070] In the illustrated embodiment, at least the side of the aperture 36 facing the extraction grid system 28 consists of graphite, which absorbs incident ions without causing significant material removal from the aperture 36. If the ion beam contains oxygen, oxides can have more favorable properties than graphite because they do not react with oxygen, or at least react less readily. The side of the aperture 36 facing the extraction grid system 28 can be composed of a multitude of small, flat surface segments, all arranged at an angle to the xy-plane. As can be seen in section C, the deflected ions thus strike the surface segments at such small angles that only a small amount of material is removed from the aperture 36.

[0071] In the illustrated embodiment, the aperture 36 has a grid of aperture openings 40 that corresponds to the grid of openings 44 in the extraction grating system 28. Each aperture opening 40 is therefore assigned an opening 44 in the extraction grating system 28.

[0072] The adjustment device 38 for the aperture 36 is controlled by a control unit 42, which can be part of a higher-level control system for the processing device 10.

[0073] When the ions, propagating along the trajectories 32, encounter the surface 16 of the workpiece 14, their kinetic energy causes atoms or molecules to be ejected from the surface 16, partially sputtering the surface. Often, each impacting ion ejects not just one atom or molecule, but several particles. The ratio of the number of particles removed to the number of particles impacting the surface is usually referred to as the sputtering yield and depends, among other things, on the angle α at which the ions impact the surface 16. Figure 2 shows the sputtering yield SY as a function of the angle α for specific ions and a specific workpiece material. The angle α denotes the direction of the impacting ion relative to the surface normal, i.e., the perpendicular to the surface 16.It can be seen that the highest sputtering yield is not achieved at a perpendicular impact (oc = 0°), but at angles of approximately 65° to 70°. Furthermore, it is evident that the sputtering yield exhibits a strong angle dependency between approximately 30° and 90°.

[0074] When the ions, indicated by their trajectories 32 in Figure 1, strike the curved surface 16 of the workpiece 14, the sputtering yield differs at each point of impact, as the angles of impact range from approximately 45° to 0°. At this angle, the curve shown in Figure 2 already exhibits a significant slope. In this configuration, the material removal on the surface 16 of the workpiece 14 would be highly inhomogeneous, which is generally undesirable.

[0075] Figures 3a and 3b illustrate how the divergence of the trajectories 32 of the ions can be changed by moving the aperture 36 along the z-direction. From each opening 44 in the extraction grating system 28, the ions are extracted with a predetermined divergence, which is primarily determined by the extraction grating system 28 and cannot be arbitrarily reduced.

[0076] In the configuration shown in Figure 3a, the aperture 36 is located close to the extraction grating system 28. Due to this proximity, the ions emerging divergently from the openings 44 can all pass through the aperture openings 40 of the aperture 36. With increasing distance from the aperture 36, the beams emerging from the openings 44 increasingly overlap, resulting in a largely homogeneous ion beam 34a. In the configuration shown in Figure 3a, the divergence of this ion beam 34 is comparatively large.

[0077] To reduce the divergence of the ion beam, the aperture 36 is moved along the +z direction by means of the adjustment device 38 so that the distance of the aperture openings 40 to the extraction grating system 28 increases, as illustrated in Figure 3b. It can be seen that, due to the greater distance, ions exiting at a larger angle to the z-direction are absorbed by the aperture 36. Only ions whose direction of propagation deviates only slightly from the z-direction remain.

[0078] The result is an ion beam 34 with a divergence that is significantly reduced compared to the divergence shown in Figure 3a. In other words, the ion beam 34b shown in Figure 3b has a different, narrower angular distribution than the ion beam 34a from Figure 3a. For ion beam 34b, the critical angle is a g, from which point there are no more ions in ion beam 34b, is smaller than in ion beam 34a. The two angular distributions l(oc) are shown schematically in the graphs to the right of figures 3a and 3b.

[0079] Figures 4a and 4b illustrate how the variable angle distribution can be used to achieve a more homogeneous material removal on the curved surface 16. Only the workpiece 14 and one beam 34a' and one beam 34b are shown.

[0080] 34b', to make the divergence of the ion beam 34 more easily recognizable.

[0081] In the case shown in Figure 4a, the beam 34a' strikes a section of surface 16 that is approximately flat, but whose surface normal runs at an angle of about 65° to the mean direction of propagation R of the beam 34a'. The ions propagate within the beam 34a' at angles of ±2° relative to the mean direction of propagation R. Despite this relatively large divergence, the ions strike the surface with a deviation of only about 2° from the ideal angle of impact of 65°, at which the highest erosion effect is achieved.

[0082] In the orientation shown in Figure 4b, the section of surface 16 onto which the beam of radiation 34b' falls is more strongly curved. If the more divergent beam of radiation 34a' were used here, the deviations from the ideal angle of incidence of 65° would be greater than in the case shown in Figure 4a, with the result that the ablation effect would be significantly more inhomogeneous.

[0083] To prevent this, when the workpiece 14 is oriented as shown in Figure 4b, the aperture 36 is moved to the position shown in Figure 3b, thereby reducing the divergence. The angular deviations of the ion trajectories 32 relative to the mean direction of propagation R are now only 1°. Despite the increased curvature of the surface, the angles of impact then vary by no more than 2°, so that the same homogeneity of material deposition is achieved as in the case shown in Figure 4a.

[0084] To automate these or similar adjustment processes, the surface 16 of the workpiece 14 can be detected using a sensor indicated at 50 in Figure 1, which is preferably an optical measuring device. The control unit 42 for the adjustment device 38 receives data from the sensor 50 about the orientation of the surface 16 in the various travel positions of the holder 12 and the swivel angle of the base 18. From this data, the control unit 42 calculates the optimal divergence of the ion beam 34 and controls the adjustment device 38 accordingly.

[0085] In many cases, the shape of the surface 16 is already known with high accuracy before material is removed using the machining device 10. In these cases, the sensor 50 can be omitted.

[0086] The control unit 42 can also be configured to control the quantity of ions released by the ion source 24 depending on the position of the aperture 36. This ensures that the ion beam 34 has a constant intensity when it strikes the workpiece 14, regardless of the glare reduction effect of the aperture 36.

[0087] 2. Second embodiment

[0088] Figure 5 shows an embodiment based on Figure 1 in which not just one aperture 36, but two apertures 36a, 36b are independently movable along the z-direction. Accordingly, two adjustment devices 38a, 38b are connected to the control unit 42. The two apertures 36a, 36b each have a single continuous aperture opening 40a, 40b, which here also both have the same diameter. The effect of the two apertures 36a, 36b is explained below with reference to Figures 6a to 6c.

[0089] In the configuration shown in Figure 6a, the two apertures 36a and 36b are arranged at a large distance from each other. The first aperture 36a already significantly reduces the divergence of the ion beam 34. The second aperture 36b primarily blocks those ions that propagate along strongly diverging trajectories 32 and could not be blocked by the first aperture 36a. This results in an ion beam 34 that has a relatively uniform and low divergence across its entire cross-section.

[0090] If the second aperture 36b is moved to the left, as indicated in Figure 6b, the divergence of the ion beam 34 increases.

[0091] Figure 6c illustrates the case where the second aperture 36b is not moved along the z-direction, but rather the diameter of the aperture opening 40 is increased or decreased. It can be seen that the effect on the divergence of the ion beam 34 is the same as with the movement illustrated in Figure 6b.

[0092] In addition to or instead of the movement movements described above along the z-direction, in a variant not shown, at least one of the apertures 36a, 36b can be moved in a direction perpendicular to the z-direction, i.e., parallel to the xy-plane. The effects of such movement movements will become clear from the following description of the third embodiment.

[0093] 3. Third example

[0094] Figure 7 illustrates a third embodiment, based on Figure 5, in which an electrostatic deflection unit 52, designed as a plate capacitor, is arranged between the two apertures 36a, 36b. A largely homogeneous electric field is formed between plates 54, 56 of the deflection unit 52, in which the ions are deflected due to electrostatic forces.

[0095] In contrast to the embodiment shown in Figure 5, the two apertures 36a, 36b are not identical in construction, but differ both in the diameter of the aperture openings 40a, 40b and in their arrangement. The second aperture opening 40b has a smaller diameter than the first aperture opening 40a and is arranged off-center relative to the first aperture opening 40a. The axes of symmetry of the round aperture openings are therefore not coaxial, but parallel and offset. With the aid of the adjustment devices 38a, 38b, the ends 36a, 36b can be moved not only along the z-direction (see double arrow in Figure 7), but also perpendicular to it. Figure 8 shows a section of the processing device 10 shown in Figure 7, with the deflection unit 52 switched off. It can be seen that the off-center arrangement of the second aperture opening 40b leads to a tilting of the ion beam 34.In this way, for example, alignment errors of the workpiece 14 in the holder 12 can be corrected. Furthermore, it is possible to dispense with the pivoting capability of the base 18. If the second aperture 36b can additionally be rotated about an axis parallel to the z-direction or moved perpendicular to the z-direction as described above, the azimuth of the ion beam 34 on the workpiece 16 can be freely selected.

[0096] Figure 9 shows the arrangement shown in Figure 8 with the deflection unit 52 switched on. The field lines E extending between the plates 54, 56 are indicated by dashed lines. When the ions exiting the first aperture 36a penetrate the electric field E, they are deflected. If the ions are positively charged, the electric force acts in the direction of the field lines, which in Figure 9 causes a downward deflection.

[0097] The combination of downward deflection and the upwardly decentered arrangement of the second aperture 40b causes the ion beam 34 to acquire an asymmetrical angular distribution, corresponding to a slight downward tilt. The deflection effected by the deflection unit 52 represents a further parameter that, in addition to adjusting the apertures 36a and 36b, can be used to influence the angular distribution of the ion beam. Since deflection and aperture have different effects on the angular distribution, the combination of these two measures allows for a very flexible adaptation of the angular distribution to the requirements of the ablation process.

[0098] If the deflection unit 52 is controlled such that the electric field is varied at a frequency between 1 Hz and 1 kHz, for example by varying the electric field strength, switching the field completely on and off, or even reversing its direction, the deflection effect varies accordingly. Particularly through small changes in the electric field strength, the ion beam 34 can be made to oscillate laterally back and forth on the surface 16 of the workpiece 14. This allows, for example, inhomogeneities in the ion beam 34 to be compensated for. Furthermore, unwanted "burn-in" of the ion beam can be prevented without having to move the workpiece 14. Alternatively, such lateral oscillation movements can be used for the targeted correction of structures with high spatial frequencies.

[0099] 4. Fourth embodiment

[0100] Figure 10 shows, in a representation based on Figures 8 and 9, parts of a processing device 10, in which a first deflection unit 52a with plates 54a, 56a is arranged in front of a (single) aperture 36, which is arranged off-center to the mean direction of propagation, and a second deflection unit 52b with plates 54b, 56b is arranged behind the aperture 36. The two deflection units 52a, 52b are oppositely polarized.

[0101] This allows the deflection caused by the second deflection unit 52b to compensate in the opposite direction for the deflection caused by the first deflection unit 52a, so that the ion beam 34 is offset in parallel, but not tilted.

[0102] The processing device 10 shown in Figure 10 allows ions with a smaller mass-to-charge ratio to be filtered out of the ion beam. Such ions are deflected more strongly in the electric field than ions with a larger mass-to-charge ratio.

[0103] In Figure 10, the trajectory of an ion with a small mass-to-charge ratio is indicated by a dashed line 32'. It can be seen that this ion is deflected so strongly in the electric field E generated by the first deflection unit 52a that it is blocked by the aperture 36 and thus cannot strike the workpiece 14.

[0104] In the illustrated embodiment, deflection occurs only parallel to the Zury direction. Preferably, two or more additional deflection units are provided, which are oriented perpendicular to the deflection units 52a, 52b and cause a variable deflection of the ions parallel to the x-direction.

[0105] 5. Fifth example

[0106] Figure 11 shows a processing device 10 in a representation based on Figure 1, in which the aperture 36 is not only arranged parallel to the mean direction of propagation (z-direction) of the ion beam 34, but is also arranged to be movable perpendicular to it, as indicated in Figure 11 by two double arrows.

[0107] Figures 12a and 12 illustrate the effect of a movement of the aperture 36 along the y-direction. In Figure 12a, it is assumed that the aperture 36 is in a y-position in which the aperture 36 is centered relative to the extraction grating system 28.

[0108] If the aperture 36, and thus also its aperture opening 40, is moved from this centered position along the positive y-direction, which corresponds to an upward movement in Figure 12b, it remains fully exposed to the ion beam 34 in the illustrated embodiment. A comparison of Figures 12a and 12b shows that the angular distribution of the ion beam 34 does not change due to this displacement of the aperture opening 40. Rather, the portion of the ion beam 34 incident on the workpiece 14 is merely shifted laterally, i.e., perpendicular to the mean direction of propagation, without changing its magnitude.

[0109] Such a displacement can be used to define the processing area of ​​the ion beam 34 on the workpiece 14. In this way, for example, an area 58 on the workpiece 14, indicated by dashed lines in Figure 12b, which should not or should no longer be exposed to the ion beam 34, can be protected from processing very quickly and without moving the workpiece 14.

[0110] If the aperture 40 moves out of the ion beam 34 during the displacement, the y-dimension of the ion beam 34 behind the aperture 36 also decreases. This can be advantageous, for example, if only a small area on the workpiece 14 is to be machined. If the aperture is also moved along the x-direction in a similar manner, the x-dimension of the ion beam 34 behind the aperture 36 can also be reduced.

Claims

- 22 - PATENT CLAIMS 1. Device for machining a workpiece (14) with an ion beam (34), with a holder (12) for receiving the workpiece (14), an ion source (24) which is configured to generate ions, an extraction grid (28) connected to a voltage source (30), which is configured to accelerate the ions generated by the ion source (24) in such a way that a directed ion beam (34) emerges from the extraction grid (28), an aperture (36; 36a, 36b) arranged along a mean propagation direction (R) of the ions behind the extraction grid (28), which limits the cross-section of the ion beam (34), characterized by the fact that the aperture (36) is adjustable such that when the aperture (36) is adjusted, the angular distribution of the ion beam (34) changes.

2. Device according to claim 1, characterized in that the aperture (34) is arranged to be movable along a linear axis which extends parallel to the mean direction of propagation (R) of the ions.

3. Device according to claim 1 or 2, characterized in that the aperture (34) has an aperture opening (40) which is arranged decentered to the mean direction of propagation (R) of the ions.

4. Device according to claim 1 or 2, characterized in that the aperture (34) has several aperture openings (40).

5. Device according to claim 4, characterized in that the extraction grid (28) has a first grid of openings (44) and the aperture (36) has a second grid of aperture openings (40) corresponding to the first grid.

6. Device according to any one of the preceding claims, characterized by a first aperture (36a) and a second aperture (36b) arranged along the central propagation direction behind the first aperture (36a).

7. Device according to claim 6, characterized in that the distance between the first aperture (36a) and the second aperture (36b) is adjustable along the mean propagation direction (R).

8. Device according to claim 6 or 7, characterized in that the first aperture (36a) has a first aperture opening (40a) and the second aperture (36b) has a second aperture opening (40b) which is arranged decentered to the first aperture opening (40a).

9. Device according to one of the preceding claims, characterized by a deflection unit (52; 52a, 52b) which is configured to deflect the ion beam (34) using electrical and / or magnetic forces.

10. Device according to claim 9 with reference to one of claims 6 to 8, characterized in that the deflection unit (52) is arranged between the first aperture (36a) and the second aperture (36b).

11. Device according to claim 9 or 10, characterized in that a first deflection unit (52a) is arranged in front of the aperture (36; 36a, 36b) and a second deflection unit (52b) is arranged behind the aperture (36; 36a, 36b).

12. Device according to claim 11, characterized in that the first deflection unit (52a) and the second deflection unit (52b) have opposing deflection effects, so that the ion beam (34) is displaced in parallel.

13. Device according to one of claims 9 to 12, characterized by a deflection unit (52) configured to generate electrical and / or magnetic forces that vary at a frequency between 1 Hz and 1 kHz.

14. Device according to one of the preceding claims, characterized by a control device which is configured to adjust the aperture (36; 36a, 36b) when the spatial position of a surface (16) of the workpiece (14) to be processed by the ion beam changes relative to the device (10).

15. Device according to one of the preceding claims, characterized in that the aperture (36) is arranged to define a processing area along a linear axis which extends perpendicular to the mean direction of propagation (R) of the ions.

16. Method for machining a workpiece (14) with an ion beam (34) comprising the following steps: g) the workpiece (14) is placed in a holder (12); h) an ion source (24) produces ions; i) an extraction grid (28) connected to a voltage source (30) accelerates the ions generated by the ion source (24) such that a directed ion beam (34) propagating along a mean direction of propagation (R) emerges from the extraction grid (28); j) the ion beam (34) passes through an aperture (36; 36a, 36b) which is arranged along the mean propagation direction (R) behind the extraction grating (28); k) the aperture (36; 36a, 36b) is adjusted so that the angular distribution of the ion beam is changed as it passes through the aperture; and l) The ion beam (34) is directed at the workpiece (14) or at a target on which material is atomized, which is deposited on the workpiece (14).

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