WO2012140210A1

WO2012140210A1 - Process for producing three-dimensional structures

Info

Publication number: WO2012140210A1
Application number: PCT/EP2012/056803
Authority: WO
Inventors: Heinz Wanzenboeck; Simon WAID; Emmerich Bertagnolli
Original assignee: Technische Universität Wien
Priority date: 2011-04-14
Filing date: 2012-04-13
Publication date: 2012-10-18
Also published as: AT511241B1; EP2697687A1; AT511241A1

Abstract

The invention relates to a process for producing three-dimensional structures (13, 113, 213, 611, 612, 613) on a substrate (10, 100), wherein, in a first process step, a layer having preferred removal properties with respect to at least one subsequent, second process step is produced by local implantation, preferably ion implantation, in particular by irradiating with a focussed ion beam (600), and then, in the at least one subsequent, second process step, the substrate (10, 100) prestructured by the first process step is etched, wherein the etching removal which can be achieved in the second process step is effected depending on the concentration of the implanted ions, and the second process step includes a first etching step (14, 114, 214, 314) of a predefinable first etching duration and with predefinable first process parameters, which is followed by at least a second etching step (15, 115, 215, 315) of a predefinable second etching duration and with predefinable second process parameters, wherein the process conditions of the second etching step (15, 115, 215, 315) differ from the process conditions of the first etching step (14, 114, 214, 314).

Description

Method for producing three-dimensional structures

The invention relates to a method for producing three-dimensional structures on a substrate, wherein in a first method step by local implantation, preferably ion implantation, in particular by irradiation with a focused ion beam (FIB), a layer with preferred removal properties with respect to at least one subsequent second process step is etched, and then in the at least one subsequent second process step, the prestructured by the first process step substrate, wherein the achievable in the second process step Ätzabtrag takes place in dependence on the concentration of the implanted ions.

In the course of the ever-advancing miniaturization of components, the demand for large-scale, cost-effective production methods of structured surfaces is steadily increasing. A common method for the production of structured surfaces is nanoimprint lithography (NIL), in which an imprint of these structures is produced on a substrate by means of impression forms ("stamps") with a structured surface. For this purpose, the surface of the substrate is covered with a positive, usually a polymer layer and impressed the stamp under heating or by means of laser or UV light in the positive. Subsequently, the positive is cured, the stamp removed, and finally etched positive and substrate, with the positive embossed structure in the substrate transmits as a depth profile. The punch required for this purpose is produced either by the same method or by other nanolithography methods. In contrast to other nanostructuring methods, nanoprecipitate lithography does not involve downsizing, which means that the influence of stamping errors has a much greater influence on the final structure on the substrate.

In the context of this disclosure, "substrate" or "substrate surface" or "object" or "object surface" is understood to mean any surface which can be structured by the method according to the invention and is made of a material suitable for this purpose.

An outstanding feature of nanoprint lithography is its suitability for the direct replication of three-dimensional structures with resolutions down to the nanometer range. This feature distinguishes this lithography method over all others and makes it particularly attractive for the manufacture of optical devices. Since the said stamp further should also be used repeatedly, its precise production is essential. In order to exploit the full potential of nanoprecipitation lithography, a patterning process for stamps is required which is capable of producing three dimensions with high resolution and high reproducibility.

In the publication "Three-Dimensional Patterning Using Ultraviolet Nanoimprint Lithography" by M. M. ALKAISI and K. MOHAMED, Lithography, 28, page 571 (2010) describe the production of three-dimensional structures using nanoimprint lithography and subsequent dry etching, in particular Reactive Ion Etching (RIE). However, this method is only suitable for second-generation replication using already three-dimensionally-structured stamps, but not for the primary structure generation of first-generation three-dimensional stamps (eg from electronically present stamp design design data).

The preparation of molds for use in stamp making for nanoimprint lithography is described in the publication "Large Area Mold Fabrication for Nanoimprint Lithography Using Electron Beam Lithography" by CHU J.K. et al., Science China, Vol. 53, pages 248 to 252. In this document, the production of stamps with a small structural width and high accuracy using the electron beam lithography is described, which also allows a multi-stage structuring of the stamp. However, the method is not suitable for the production of stamps with several different height levels, such as those required for lenses or other optical components, because of the many different exposure doses, the total dose to be applied increases greatly, whereby the production time is extremely prolonged so that the production of large-area stamp within economically reasonable process times is impossible. Furthermore, not sufficiently compatible paints are available for this use, whereby the general suitability of the method for structures with several different height levels, as z. B. are required for optical components, is essentially negative.

The publication "Ga ⁺ Beam Lithography for Nanoscale Silicon Reactive Ion Etching" by MD HENRY et al., Nanotechnology, 21 (2010), 245303, describes the production of three-dimensional structures in silicon, wherein gallium ions are produced by ion beam lithography (Focused Ion Beam , FIB) and the substrate is subsequently etched by means of a one-step dry etching step. In this case, the implanted gallium ions act as an etching mask, with the gallium-enriched silicon in the individual etching process described having a significantly lower etching rate than the untreated silicon. As a result of the ion implantation, regions on the silicon can thus be protected from the etching attack. Due to the different concentrations of im- Planted ions can be achieved a different protection duration. Since the etching parameters are not changed in the described method, a three-dimensional structuring can be defined exclusively via the local concentrations of the implanted ions. Due to the simple etching process, this method is therefore limited in terms of its achievable relative and absolute height resolution, which creates a disadvantage, especially in the production of optical components or stamps for this.

It is therefore an object of this invention to eliminate the drawbacks of the prior art and to provide a method of the type mentioned, which allows the production of three-dimensional structures with high accuracy and small size on a substrate in a rapid and simple manner.

This object is achieved according to the invention in that the second method step has a first etching step with a predeterminable first etching period and predeterminable first process parameters, followed by at least one second etching step with a predefinable second etching period and predeterminable second process parameters, wherein the process conditions of the second etching step are different the process conditions of the first etching step.

According to the invention, a further method step is carried out subsequent to the implantation step in which the doped surface of the substrate is etched, this method step being subdivided into at least two etching steps which differ from one another in at least one of their method parameters, whereby compared to the simple one Etching process a better relative height resolution of the structures is achieved. HENRY et al. describes that the etch rate is in a non-linear relationship with the concentration of implanted gallium ions in the substrate. The Applicants have found, however, that by appropriate choice of the etching gas very well linear relationships are found, which has a higher reproducibility of the inventive method result. Furthermore, structures can be obtained by a specific combination of two or more etching steps with different parameters, which have a curved (convex or concave) surface. This is of particular importance for the production of microlenses.

Furthermore, it is provided that initially a locally high-resolution ion implantation takes place in an object surface, wherein the local implantation dose is related to the desired local structure height in the subsequent etching process. The spatially resolved implantation step is followed by a according to the invention etching process, wherein the doped surface of the substrate is etched.

In a preferred embodiment of the invention, it is provided that, in the first method step, the implantation is carried out with different acceleration voltages for producing implantation structures having different layer thicknesses. Here, the local implantation dose is related to the desired local structure height generated by the subsequent etching step.

The implantation profile is preferably determined on the basis of the structure to be produced and the known properties of the etching processes to be carried out. In this case, the maximum dose of ions per unit area to be applied represents a special characteristic. This variable preferably moves in a range from 1 to 300 pC / μηΊ ² . Values of 40 to 100 pC / μηΊ ² have proven particularly suitable. At higher acceleration voltages of the ion beam, higher values up to 200 pC / μηΊ ^{2 are} possible. In each exposure run, a fixed dose is preferably applied, derived from the maximum dose to be applied and the selected number of exposure runs. Particularly suitable exposure doses per passage between 0.1 and 10 pC / μηΊ ² , for example 4 pC / μηΊ ² . The beam current of the ion beam is preferably between 0.5 pA and 30 nA. Beam currents between 1 and 100 pA have proven to be particularly suitable. The beam profile is preferably Gaussian, but may also be rectangular, circular or otherwise shaped, with Gaussian sloping flanks being preferred in each case. The width of the beam profile at half height preferably ranges between 0.1 and 200 nm. Particularly suitable is a range between 10 and 50 nm has been found.

In a particular embodiment of the implantation process, the implantation mask can be generated by multiple exposures, each with different acceleration energies of the ions, and thus the thickness of the hard mask can be further increased, or the depth distribution of the ions in the implantation zone can be adjusted. Thus, by low acceleration voltages enrichment of the implanted ions near the surface can be carried out, while at high acceleration voltages enrichment in deeper areas below the surface can be achieved. During the implantation process, a single type of ion, a sequential sequence of different ions, or even mixtures of different ions can be used, each of which has a different influence on the etching behavior of the substrate during the second process step. The ion beam used has an energy of 50 eV to 5 MeV, in particular an energy from 200 eV to 30 keV. When using focused ion beam systems (FIB), a variation of the acceleration voltages between 250 eV and 100 keV, but in particular between 10 keV and 50 keV is a useful range. When combined with ion implanters, acceleration voltages between 100 keV and 3 MeV are also possible for the fabrication of the implant masks.

In a further variant of the invention, in the first method step, the layer is produced with preferred removal properties using an additional, removable surface coating, wherein atoms from the surface coating are implanted into the substrate by irradiation with a focused ion beam by atomic impact. Instead of being implanted by the ion beam itself, the implantation layers will be made by atomic mixing by ion beam. For this purpose, the material to be implanted is previously applied as a thin layer on the surface and then the layer only locally mixed by the ion beam in the surface, so that in this way an implantation mask is illustrated. The excess non-implanted material is then removed from the surface and removed. In this way, ions can be implanted into the substrate which can not be implanted into the substrate material by means of an ion beam or only under difficult conditions, but influence the removal properties of the substrate for the subsequent etching step.

In addition to ion plasma toners, magnetrons and wide beam sources, ions from systems with a focused ion beam are particularly suitable for high-resolution implantation. Further different removal properties of the substrate are obtained if a multi-beam ion beam system is used for the first method step.

Some substrate materials, such as monocrystalline silicon, respond to the implantation with an irregular distribution of the implanted ions and an irregular formation of amorphous and crystalline regions, which are etched irregularly in the subsequent second process step, the etching process. This results in a large surface roughness, undesirable in some applications, due to existing etch selectivities on the order of about 3 nm to 10 nm. In order to avoid this problem, in one variant of the invention, at least one additional coating step preceding the first method step of the local implantation is provided. By applying at least one material which acts as a smoothing layer during the implantation process and the subsequent etching process, the roughening of the surface is reduced by up to 50%. It is preferably provided here that the at least one additional coating step comprises the application of a layer etchable in the second process step. It is particularly preferred that this layer, which is usually only a few nanometers thick, is etchable with that etching medium used in the etching process.

Depending on the thickness of the smoothing layer material and the depth of penetration of the implanted ions, ions may be implanted either either (a) only in the additional uppermost coating layer or (b) in both the uppermost coating layer and the underlying substrate. As a result, with the etching gas gradient according to the invention, slightly different etch selectivities of the upper coating layer and of the underlying substrate-in particular, however, due to the gallium embedding in the materials-can also result in an additional distinction in the etching rates. The additional surface coating and its content of impurities (by the implantation) results in a further option for fine-tuning the cross-sectional profile of the subsequent etching, and in particular further possibility for the design of the edge profile.

Particularly good results in terms of low surface roughness in the final product are obtained if the at least one additional coating step sputtering, vapor deposition, epitaxial coating, chemical vapor deposition, atomic layer deposition, electrodeposition, electrodeless electrochemical deposition, crystallization from the liquid phase, Auffolieren, pressing Metal coatings, lacquers, spin-coating, dip-coating or related methods of applying metals. For substrates of semiconductors of the 4-main group (silicon, germanium), metals and metal alloys, especially from the group of transition metals, in particular vanadium and / or tungsten have proven successful. Vanadium in particular has proven particularly useful as a smoothing material because it provides the desired results, in particular in a dry etching process.

The second method step is an etching method, wherein at least one etching step, preferably all etching steps, are carried out as a preferred physico-chemical dry etching process. Other etching methods such as purely physical or purely chemical or wet-chemical etching or a combination of these methods may also be used.

In a preferred manner, all partial steps take place in a reactive ion etcher (RIE) or a plasma etcher, wherein the etching process or partial processes can also be carried out by means of other etching processes. The temperature during the etching process is between 0 K and 500 K, more preferably between 270 K and 400 K. In the case of using a dry chemical etching process, the gas flow into the etching chamber or into the reaction vessel is preferably between 1 sccm and 1000 sccm per 100 l chamber volume. Preferably during the etching, energy is introduced in the form of electromagnetic waves, or in the form of an alternating electric or magnetic field, or by thermal processes or a combination thereof. The power introduced in this form is preferably in a range between 0 kW and 10 kW. Particularly suitable is a range between 5 W and 800 W, in particular a value of 10 W to 80 W.

During the etching, a particularly aggressive etchant is preferred for the first etching step, which causes a high etch selectivity between implanted regions and native substrate regions. Particularly suitable for silicon substrates in the case of reactive ion etching, the addition of a fluorine-containing species such. B. SF ₆ with a share of at least 20%.

In a preferred embodiment of the method according to the invention, the etching time of the individual etching steps is determined by measuring the etching depth by means of interferometers. In each case etching depths of between 5 nm and 1 mm, but in particular 10 nm and 100 μm, are preferably achieved per etching step. The etching gas composition is preferably changed in the case of burning plasma from process parameter 1 to process parameter 2, wherein the change can be gradual or abrupt.

In a further embodiment, the plasma is deactivated during reactive ion etching (RIE) between the individual etching steps. This is preferably done with the aim of guaranteeing well-defined gas compositions during the individual etching processes, which can thus enable sharper transitions in the structure. Deactivation of the plasma may also be performed for thermal management.

The etching is preferably carried out in a parallel plate reactor. For the ignition of the plasma, the pressure at the beginning of the process is preferably increased in order then to reduce it to the predetermined desired value when the plasma is burning. By means of this ignition process, a first etching step can already result, the influence of which as a function of the parameters is essential for the overall process.

Essential for the etching process according to the invention is a different etch rate for implanted and non-implanted regions. A change of this Selectivity can be achieved by changing the etching parameters, for example by changing the gas composition, but all parameters already mentioned, such as gas flow, pressure, temperature and power, are also suitable for this purpose.

Preferably, at least one predefinable threshold value is provided which characterizes the transition from the first etching step to the second etching step. This threshold value represents a change in the process conditions between the first (previous) and the second (subsequent) etching step. In preferred applications, more than two, further etching steps and also more than two further threshold values can be provided, which are independent of one another or repeat cyclically. In no case is the inventive method limited to only two etching steps.

The threshold value may depend on the process progress (eg etch depth) or independent of feedback parameters (eg already elapsed process time). The threshold value relates to a change in the etching parameters, for example the composition and / or the concentration of the etching medium during the transition between the first and subsequent second etching step; For example, it may also relate to the concentration of the etching medium and / or the temperature, the pressure or, in the case of a dry etching process, the energy input during the etching process. Of course, the change can also affect other process parameters not listed here.

The transition between the first and second, and any further etching steps can be continuous or discontinuous, this change can be done, for example, continuously gradual, stepwise, pulsed or periodic.

The change of the process parameters of the etching process according to the invention can be carried out on the basis of the threshold value, time-dependent or under the control of a suitable control system.

In a preferred embodiment of the invention, it is provided that the threshold value is detected by means of a process-accompanying control system. In this case, the etching process is monitored by a suitably designed control system, which preferably processes sensor data that provide information about the etching progress, and preferably at least partially specifies the process parameters for the etching process. Through the use of a control system, parameter fluctuations throughout the process can be minimized, allowing a better absolute height resolution of the structures can be achieved. Thus, the reproducibility of structuring can be increased. Preferably, a control system is used which adjusts or controls the process parameters of the etching process on the basis of measurement data, in particular those which provide information about the progress of the etching or the surface condition of the substrate. In particular, a control system is preferred which compares the measurement data or quantities derived therefrom with values of the desired altitude profile or values derived therefrom.

The monitoring of the etching progress is preferably carried out within at least one implanted area, but is by no means limited thereto. The monitored area is preferably designed specifically for this purpose. In particular, suitable patterns with at least one, but preferably at least four different implantation doses are used.

The measurement data available to the control system are preferably supplied by suitably developed sensors. Particularly suitable are sensors which detect the etching progress on the substrate to be etched or another reference object provided for this purpose. These include, in particular, sensors which permit spatially resolved monitoring of the etching progress. Preferably, optical, electron-optical or mechanical scanning or a combination thereof are used.

For this purpose, the control system is particularly preferably based on an optical method, in particular interferometry or reflectometry, or an electron-optical method, in particular scanning electron microscopy, or on a scanning probe technique, in particular Atomic Force Microscope (AFM).

In one embodiment, the etching progress is monitored by means of an interferometer camera consisting of a coherent light source, preferably a laser, an interferometer, preferably a Michelson interferometer, and a camera or at least one of these components.

Alternatively, the etch progress control system may consist of a broadband light source, a white light interferometer and a spectrometer or at least one of these components.

In a further embodiment, the monitoring system consists of a quartz crystal, which is mechanically coupled to the substrate. The monitoring of the Ätzfortschrittes carried out by measuring the oscillation frequency of the quartz (quartz microbalance). As already described, the etching rate in the second method step is dependent on the concentration of ions implanted in the substrate by the ion beam and on the composition of the etchant. These implanted ions are preferably atomic ions or inorganic cluster ions, which are produced in technical systems for generating an ion beam.

Suitable ions are all ions from non-noble gases, in particular the ions from the group of metal ions from the II, III, IV, V and VI main group, here preferably ions from that group, gallium, indium, silicon, arsenic or selenium includes, selected. Furthermore, ions from the group of secondary group metals, the lanthanides or actinides, in particular gold, platinum or other noble metals are chosen, those ions which do not react with halogens being particularly suitable.

It is preferably provided that a halogen-containing gas is used as the etching medium. Particularly preferred is at least one fluorine-containing gas, in particular F ₂ , XeF ₂ , SF ₆ , CF ₄ , C ₂ F ₆ , C ₃ F ₈ , CHF ₃ , HF or SiF ₄ and / or at least one chlorine-containing gas, in particular Cl ₂ , SOCl ₂ , CCI ₄ , CH ₃ Cl, CH ₂ Cl ₂ , CHCl ₃ , C ₂ Cl ₆ , C ₃ Cl ₈ , HCl or SiCl ₄ . The etching medium may be a single etching gas or a mixture of different components. Likewise, the use of chlorine-containing gases, such as SiCl ₄ alone or in combination with fluorine-containing gases is provided in order to influence the selectivity of the etching process can.

In addition to the use of a halogen-containing gas-in particular of a fluorine-containing gas-the etching rate of the substrate during the etching process can be influenced by further gases, in which case non-halogen-containing gases, in particular oxygen- or nitrogen-containing gases, such as, for example, nitrous oxide (N ₂ O), Ammonia (NH ₃ ), pure nitrogen or pure oxygen can be used. In a further embodiment, the etching properties of the gas mixture are changed by adding additional, additional etching gases. In particular, in this way the roughness of the resulting surface can be influenced. This can be achieved in particular by the addition of oxygen- or nitrogen-containing gases.

It is therefore particularly preferable that, in addition to the fluorine-containing or chlorine-containing gas, another non-fluorine-containing gas, especially an oxygen-containing gas such as N ₂ O or pure oxygen, or a nitrogen-containing gas such as NH ₃ or pure nitrogen, and / or a noble gas, in particular helium, argon, xenon or else a hydrogenating gas, in particular hydrogen or N ₂ H _{4 is} used. Particularly good results have been obtained even with the use of chemically inert gases, especially with noble gases, in particular argon in conjunction with the above-mentioned gases. With chemically inert gases that do not chemically react with either the substrate or the implanted material, low selectivity in chemical-physical etching can be achieved (while high selectivity is achieved with etch gases that preferentially react with the substrate). In the context of this disclosure, the selectivity of the etching process is understood to be the context in which the etching rate of the implanted / doped region of a substrate is related to its undoped region.

In a preferred embodiment, the selectivity of the etching process is achieved by changing the mixing ratio of a Hauptätzgases to a Nebenätzgas. In particular, this relates to admixtures of chlorine-containing gases to fluorine-containing gases, of fluorine-containing gases to chlorine-containing gases, the admixture of oxidizing gases to chlorine or fluorine-containing gases, and the addition of inert gases to chlorine or fluorine-containing gases.

In a further embodiment, the etching gas during an RIE process consists of two or more etching gases, which may be designed to optimize surface properties such. B. to achieve low surface roughness, as well as one or more additional gases, which set the selectivity between implanted and unimplanted areas. Preferably, several parameters are adapted during the etching process in such a way that not only the selectivity of the individual regions is changed, but also the properties of the basic composition, such as, for example, B. be maintained or remain optimized surface properties.

A significant advantage of the method according to the invention is that it can be carried out both on planar and non-planar, in particular on curved or stepped substrate surfaces. In particular, in the production of stamps for nanoimprint lithography, which are intended for use on large areas, there are efforts to produce roller-like die, which are rolled over a suitably prepared substrate surface to create a depth profile here. Also, the nanostructuring of spherical substrates (eg a dirt-repellent coating of reflection optics) is possible with specially prepared complementary impression forms with nano-surfaces produced according to the invention. The processing of such curved surfaces is difficult to implement with the usual methods. By contrast, the method according to the invention is particularly suitable for this purpose, since the curved surface of the substrate is processed particularly precisely by the sequence of different etching steps. In a further embodiment of the invention, it is provided that the substrate has a three-dimensional structure on at least one surface, which is additionally further structured according to the method according to the invention by ion implantation and subsequent etching. Thus, it is particularly preferred that these "primary" three-dimensional structures have an order of magnitude in the millimeter or micrometer range, while smaller three-dimensional structures in the micrometer or submicrometer range, preferably <10 m, are produced by subsequent processing by the methods according to the invention.

The method according to the invention has proven particularly useful in the production of stamps for nanoprint lithography. Likewise, its use for the production of microlenses, as well as three-dimensional structures (for example dirt-repellent surfaces or flow-optimized surfaces) is generally particularly suitable. Furthermore, the method is outstandingly suitable for the production of microfluidic structures.

The invention is explained in more detail below with reference to non-limiting exemplary embodiments with associated figures.

Example 1: Production of a lenticular structure

1st step: implantation

In an optionally pre-doped silicon substrate 10 (with the crystal orientation <100>), starting from digital data, in particular from a grayscale image according to FIG. 1, gallium ions are implanted by means of FIB, wherein the ion beam is passed over the substrate surface in ten passes. The exposure of the respective area (each pixel) of the substrate surface occurs depending on the blackening of the respective pixel in the gray scale image and results in a gradual graded implantation mask. 40 pC / pm ^{2 is} defined as the maximum required ion dose, 4 pC / μηΊ ^{2 being} implanted / applied in each of the ten exposure runs. Based on a predetermined threshold dose, it is decided whether or not to expose a pixel in the respective pass. The beam current is 1.3 pA, the beam profile is approximately Gaussian with a width of 25 nm to 50 nm at half height. In this case, the implantation is carried out using a special ion beam system (for example a Zeiss Neon X-beam system), with acceleration voltages of 10 kV to 30 kV being used.

If smoother transitions are to be achieved, the division into a higher number of exposure passes, for example 20 to 50, can take place. In contrast, by reducing the exposure passes, for example, way to less than five exposure passes, a step-like flank structure achieved. To produce larger structures with lower fineness requirements, ion beams with higher beam currents and larger beam widths can also be used.

FIG. 2A shows the linear implantation profile 11 into the silicon substrate 10, wherein in the diagram of FIG. 2B the implantation profile 12 corresponding to the dose of gallium ions within the substrate 10 is shown along the line A-A in FIG. 2A.

2nd step: etching process

The etching of the silicon surface 10 takes place in a parallel plate reactor in a three-stage process with the following parameters:

1st etching step:

Temperature: 30 ° C

Working pressure: 20 mbar

Process gases: argon: 5 sccm

SF ₆ : 25 sccm

RF power: 50W

Etching depth (total) 150 nm

2nd etching step:

Temperature: 30 ° C

Working pressure: 20 mbar

Process gases: argon: 15 sccm

SF6: 15 sccm

RF power: 50W

Etching depth (total) 225 nm

3rd etching step:

Temperature: 30 ° C

Working pressure: 20 mbar

Process gases: Argon: 29 sccm

SF6: 1 sccm

RF power: 50W

Etching depth (total) 300 nm To ignite the plasma within the reactor, the pressure in the plasma chamber is first increased to 50 pbar and lowered to the predetermined working pressure after ignition has taken place (recognizable by a sudden increase in pressure). In each individual etching step, the plasma can be ignited again or remain switched on.

The above-described etching process has the variation of an etching parameter, namely the etching gas composition, between the individual threshold values. In this embodiment, three etching steps are shown, the first etching step a) a high selectivity for etching the substrate, the second etching step b) a lower selectivity for etching the silicon substrate and the third etching step c) no significant selectivity between substrate and implanted areas more represents. In this way, a different geometric result can be achieved with a defined implantation dose depending on the etching parameter.

FIG. 3A shows the lens-like structure 13 obtained by the etching process, wherein in the diagram according to FIG. 3B the etching profile is shown in the substrate 10 along the line B-B from FIG. 3A. It can clearly be seen here that the first etching step 14 results in a high edge steepness of the etching profile, which flattenes in the two subsequent etching steps 15, 16. FIG. 4 shows an atomic force microscope image of the structure 13 obtained according to example 1.

In this way, a lens-like structure 13 is obtained by the method according to the invention, whose profile can be varied by changing the different parameters of the etching process.

Example 2: Production of another lenticular structure

1st step: implantation

This step is the same as in Example 1.

2nd step: etching process

The etching of the silicon surface 10 takes place in a parallel plate reactor with the following process parameters: a) 1st etching step:

Temperature: 44 ° C

Working pressure: 13 pbar Process gases: 5 sccm

25 sccm

RF power: 50 W b) 2nd etching step:

The total flow of the etching gases is successively replaced after reaching 120 of the predetermined threshold, in the present case a predetermined etch depth after the first etching step, by argon. As a result, the etching selectivity between implanted and non-implanted regions of the substrate 10 is changed. FIG. 5 shows the flow of the etching gases SF ₆ , N ₂ and Ar. The transition 120 between the first etching step 114 and the second etching step 115 is in this case continuous.

The etched profile of the lenticular structure 113 obtained with this process can be seen in FIG. By continuously changing the etching gas composition during the etching step, more rounded and smoother structures are obtained compared to the structure 13 (Figure 3B) of Example 1. A similar effect is also achieved when using oxygen rather than nitrogen.

Example 3: Production of an irregular surface structure

In the implantation of gallium ions, in this embodiment of the invention, as an alternative to the implantation method described in Example 1, a three-dimensional pixel or vector image guiding the implantation beam is used (FIG. 7). The implantation beam is also rasterized only once over the silicon surface 10, remaining on each pixel until the desired implantation dose is achieved. This allows a temporal shortening of the implantation step, and continuous doping profiles 212 are obtained.

Subsequent dry etching according to the RIE method with two different etching steps 214, 215, in which the etching gas composition was again changed, results in a structure 213 according to FIG. 8, which substantially corresponds to the implantation profile 212 of FIG.

Example 4: Preparation of an irregular surface structure with reduced surface roughness _{Λ r}

- 16 -

Beschichtunqsschritt:

On a silicon wafer as substrate 10 (surface roughness <0.3 nm RMS) was sputtered with 25-100 W (especially 50 W) at an argon process gas pressure of 8xl0 ^"3 mbar of a vanadium target (purity> 99.9 Of course, the thickness of the additional coating may preferably vary between 5 nm and 150 nm.

1st step: implantation

This step is basically the same as that of Example 1. The pattern to be etched was implanted into the vanadium-coated silicon by implantation of gallium ions using FIB. The implantation took place with a dose of 1 mC / cm ² . A 10 pA gallium ion beam with an acceleration voltage of 30 kV was used. FIG. 10 shows a schematic representation of the layer structure of the substrate 10 after implantation. In the vanadium layer 20, gallium-doped island-like regions 21 are provided which are less than the thickness of the vanadium layer 20.

2nd step: etching process

Temperature: 60 ° C

Working pressure: 13 pbar

Process gases: Ar: 5 sccm

SF ₆ : 25 sccm

RF power: 50 W b) 2nd etching step:

The total composition of the etching gas is successively changed after reaching the predetermined threshold value, in the present case a predetermined etching depth after the first etching step, by increasing the flow of argon while simultaneously reducing the SF ₆ Ätzgasflusses. The altered etching gas composition changes the etch selectivity between implanted and non-implanted regions of the substrate 10. The surface structure obtained with this process has a lower surface roughness compared to Example 3.

The examples given above are to be understood in a non-limiting manner. Thus, more than three different etching steps may also be provided, wherein, for example, in each etching step 314, 315, 316, 317, 318, the composition of the etching gases 20, 21, 22 (FIG. 9) changes.

Regardless of the gas composition, the changes in the individual etching steps may also relate to temperature, working pressure, RF power of the RIE process, or the total flow rate of gases, which variations may refer to a single or multiple parameters.

FIG. 11 schematically shows a control system 400 for monitoring and controlling the etching parameters, in particular the corresponding threshold values. It is preferably used to compensate for deviations or inaccuracies in the etching process by adjusting the etching parameters. For this purpose, a self-contained control loop 401, 402 is provided in this embodiment of the control system 400, which is equipped with a sensor system 403, the sensors of which supply measured data to an evaluation / control units 404, 405. Particularly suitable here are sensors which detect the etching progress on the substrate 10 to be etched in the reactor 500. These include, in particular, sensors which permit spatially resolved monitoring of the etching progress. Preferably, optical, electron-optical or mechanical scanning methods or a combination thereof are used. Instead of the etching substrate 10, the monitoring of a reference object can be provided, from whose data corresponding data can be derived to the substrate.

In this embodiment of the control system, the etching progress is monitored by the analysis of the substrate surface 10, which preferably serves as a feedback input 406, 407 for the process parameters of the subsequent further etching step.

In the variant of the invention shown in FIG. 12, the etching progress is monitored by optical scanning 410, 411 of a preferably specially designed zone 110 of the substrate 10, which has been doped according to a suitable pattern. This pattern has regions 111, 112, 113, 114, 115, 116 with different doping doses, the number of which can be between 2 and 20. The measured values obtained by the scanning 410, 411 allow direct conclusions to be drawn about the etching progress on the entire substrate 10. Example 5: Production of Different Structures on a Substrate Surface

In Figs. Figures 13A-13B illustrate the progress in fabricating structures on a surface 10 after each etching step. In FIG. 13A, the implantation step is shown schematically, wherein structures 601, 602, 603 with different local implantation doses are generated by means of ion beam 600 into a substrate surface 10 according to one of the implantation methods described above. After a first etching step 614 (FIG. 13B), the first regions are exposed with a higher implantation dose, while after reaching the desired etching depth according to FIG. 13C after the second etching step, the structures 611, 612, 613 are in their desired different heights according to the implanted in the first method step Ion concentration on the substrate surface 10 are arranged.

The process according to the invention can be used to produce a wide variety of structures. Thus, FIG. 14 shows a substrate 100 in which a micro-fluid channel 101 has been etched in the manner described above.

A more complex structure is shown in FIG. 15, in which a regularly repeating three-dimensional structure 102 has been etched into a substrate surface 100 ("grating"). The production of repetitive structures is of particular interest for the production of NIL punches, which are constructed in the form of rollers and are thus able to impress uniform structures on large-area substrates.

FIG. 16 shows an optical waveguide which was also produced by the method according to the invention, wherein a waveguide 150 with a filter element 151 is arranged in the substrate 100.

It is understood that the invention is not limited to the above-mentioned embodiments. By a suitable combination of corresponding implantation and etching steps, a multiplicity of very different structures can be produced on substrate surfaces made of a very wide variety of materials.

Claims

PATENT APPLICATIONS

1. A method for producing three-dimensional structures (13, 113, 213, 611, 612, 613) on a substrate (10, 100), wherein in a first method step by local implantation, preferably ion implantation, in particular by irradiation with a focused ion beam (600 In the at least one subsequent second method step, the substrate (10, 100) prestructured by the first method step is subsequently etched, the etching removal achievable in the second method step being etched into the substrate Dependent on the concentration of the implanted ions, characterized in that the second method step comprises a first etching step (14, 114, 214, 314) having a predeterminable first etching duration and predeterminable first process parameters, to which at least one second etching step (15, 115, 215, 315) with a vorgeb followed by the second etching time and predetermined second process parameters, wherein the process conditions of the second etching step (15, 115, 215, 315) are different from the process conditions of the first etching step (14, 114, 214, 314).

2. The method according to claim 1, characterized in that in the first method step, the implantation with different acceleration voltages for the production of implantation structures (111, 112, 113, 114, 115, 116) is carried out with different layer thicknesses.

3. The method according to claim 1, characterized in that in the first method step, the formation of the layer (111, 112, 113, 114, 115, 116) is carried out with preferred Abtragseigenschaften using an additional, removable surface coating, wherein by irradiation with a focused Ion beam (FIB) atoms from the surface coating are implanted into the substrate (10, 100) by atomic impact.

4. The method according to any one of claims 1 to 3, characterized in that a multi-beam ion beam system is used for the first method step.

5. The method according to any one of claims 1 to 4, characterized in that at least one preceded by the first step of the local implantation additional coating step is provided.

6. The method according to claim 5, characterized in that the at least one additional coating step comprises the application of an etchable layer.

7. The method according to claim 5 or 6, characterized in that the at least one additional coating step sputtering, vapor deposition, epitaxial coating, chemical vapor deposition, atomic layer deposition, electrodeposition, electrodeless electrochemical deposition, crystallization from the liquid phase, Auffolieren, pressing metal layers , Lacquering, spin-coating, dip-coating or related processes of metals or metal alloys.

8. The method according to any one of claims 5 to 7, characterized in that the at least one additional coating step comprises the application of metals or metal alloys, which are preferably selected from the group of transition metals, in particular vanadium and / or tungsten.

9. The method according to any one of claims 1 to 8, characterized in that the penetration depth of the ions to be implanted is adjusted by means of the acceleration voltage, wherein the thickness of the implanted zones is selected such that the thickness of the additional coating layer is exceeded or undershot.

10. The method according to any one of claims 1 to 9, characterized in that in the second process step at least one etching step (14, 114, 214, 314), preferably all the etching steps (14, 114, 214, 314, 15, 115, 215, 315 , 16, 316, 317, 318) as a dry etching process.

11. The method according to any one of claims 1 to 10, characterized in that at least one predetermined threshold value is provided, the transition (120) from the first etching step (14, 114, 214, 314) to the second etching step (15, 115, 215, 315).

12. The method according to claim 11, characterized in that upon reaching the at least one threshold value, a change in the etching parameters, in particular the composition and / or the concentration of the etching medium and / or the flow rate of the etching medium and / or the temperature and / or pressure and / or the energy input during the second process step takes place.

13. The method according to claim 12, characterized in that the change of the Ätzparameter takes place continuously or discontinuously, in particular stepwise, pulsed or periodically.

14. The method according to any one of claims 11 to 13, characterized in that the threshold value is detected by means of a process-accompanying control system (400).

15. Method according to claim 14, characterized in that the control system is based on an optical method, in particular interferometry or reflectometry, or an electron-optical method, in particular scanning electron microscopy, or on a scanning probe technique, in particular AFM.

16. The method according to any one of claims 1 to 15, characterized in that during the first process step in the substrate (10, 100) implanted ions from the group of non-noble gases, in particular from the group of metal ions from II, III, IV, V and VI main group, preferably ions selected from the group comprising gallium, indium, silicon, arsenic or selenium.

17. The method according to any one of claims 1 to 16, characterized in that during the first process step in the substrate (10, 100) implanted ions from the group of secondary group metals, the lanthanoid or actinides, in particular gold, platinum or other precious metals are selected.

18. The method according to any one of claims 1 to 17, characterized in that during the first process step in the substrate (10, 100) implanted ions of elements which show no reactions with halogens exist.

19. The method according to any one of claims 1 to 18, characterized in that during the implantation process, a single type of ion, or a sequential sequence of different ions, or mixtures of different ions are used.

20. The method according to any one of claims 1 to 19, characterized in that the etching medium at least one fluorine containing gas, in particular F _2, XeF _2, SF _6, CF _4, C ₂ F _6, C ₃ F _8, CHF _3, HF or SiF ₄ or a mixture of at least two of the aforementioned gases is used.

21. The method according to any one of claims 1 to 19, characterized in that the etching medium at least one chlorine-containing gas, in particular Cl _2, SOCI _2, CCI _4, CH ₃ CI, CH ₂ Cl _2, CHCl 3, C ₂ Cl _6, C ₃ CI ₈ , HCl, or SiCl ₄ or a mixture of at least two of the aforementioned gases is used.

22. The method according to claim 20 or 21, characterized in that in addition to the fluorine-containing or chlorine-containing gas, another non-volatile gas, in particular an oxygen-containing gas, such as N ₂ 0 or pure oxygen, or a nitrogen-containing gas, such as NH ₃ or pure nitrogen, and / or a noble gas, in particular He, Ar, Xe, or else a hydrogenating gas, in particular H ₂ or N ₂ H _{4 is} used.

23. The method according to any one of claims 1 to 22, characterized in that the surface of the substrate (10, 100) is planar or non-planar, in particular curved.

24. The method according to any one of claims 1 to 23, characterized in that the substrate (10, 100) before performing the method on at least one surface has a three-dimensional structure (13, 113, 213).

25. Use of a method according to any one of claims 1 to 24 for the production of three-dimensional structures (13, 113, 213) with dimensions <10 μηι.

26. Use according to claim 25 for the production of master stamps for three-dimensional nanoimprint lithography (3D-NIL).

27. Use according to claim 25 for the production of microlenses.

28. Use according to claim 25 for the production of microfluidic structures.