EP1999498A1

EP1999498A1 - Broadband antireflective optical components with curved surfaces and their production

Info

Publication number: EP1999498A1
Application number: EP07727292A
Authority: EP
Inventors: Konrad Bach; Daniel Gaebler
Original assignee: X Fab Semiconductor Foundries GmbH
Current assignee: X Fab Semiconductor Foundries GmbH
Priority date: 2006-03-24
Filing date: 2007-03-23
Publication date: 2008-12-10
Also published as: DE102006013670A1; US20090180188A1; WO2007110392A1

Abstract

Methods and optical components are proposed which have a nanostructure (4) on a curved surface, so as to achieve broadband antireflection characteristics. The nanostructure is produced with the aid of a self-masking, single-stage etching process from silicon (3) on the curved surface.

Description

Broadband antireflective optical components with curved surfaces and their manufacture

Field of the invention.

The present invention generally relates to manufacturing methods and curved-surface optical components having a refractive power (a positive or negative refractive power for incident light rays). The light is in a given wavelength range, with the invention, an anti-reflection of the optically active surface (the curved surface) is to be achieved.

State of the art.

Antireflective optically effective, curved surfaces, which thus produce a negative or positive bundling effect for light rays impinging on the surface, has been causing problems since the emergence of the first antireflection coatings at the beginning of the 20th century. Antireflective coatings based on the interference phenomena require homogeneous properties of the applied layers, in particular, the thicknesses must be carefully matched. All known processes that produce this type of antireflective coating are affected by this problem. Another problem is the adhesive strength of the applied layers and the effectiveness over an often very limited wavelength range. Only complicated coating systems enable antireflection over a larger wavelength range. Corresponding layer systems, however, make very high demands on the layer homogeneity and tend to reduce the adhesive strength by the combination of the mechanical layer stresses that occur. In addition, layer materials are not suitable for every wavelength range.

Electronic, opto-electronic, sensory or micromechanical components often have as integral components optical components which require curved surfaces for processing optical signals, the overall efficiency of these optical components being very much dependent on the proportion of the radiation component coupled into the surface. Efficient antireflection coating is also important in these cases, whereby the compatibility of the processes for producing the antireflection coatings with the further integration processes is also an important aspect. Frequently, the complex structures of the conventional anti-reflection structures lead to complex and thus costly production steps, whereby a broadband effect of the anti-reflection layers is nevertheless rarely achieved. Overview of the invention.

The invention is based on the object for optical components with curved surfaces, as they occur as components of optoelectronic integrated circuits, as individual components or as purely optical components of devices to specify such an expression of the surface, creating a significantly reduced reflection over a wide (or: wide) wavelength range is achieved.

According to the invention, for this purpose, a layer is produced on a base material with a curved surface, which produces an almost gradual adjustment of the refractive index of the base material into the surrounding medium, at least for the light wavelength range considered, without complex layer systems being required and the desired "globally curved" geometry the surface of the base material is maintained. This is achieved by the use of a self-organizing etching process, which can act directly on the surface when it is composed essentially of silicon, or which can be used to produce a suitable structure in other base materials. In this case, a reactive plasma atmosphere having at most two different gas components with oxygen and a reactive gas for etching silicon is produced by setting process parameters which develop a self-masking effect for producing a nanostructure. The etching takes place without further working gases and is carried out as a one-step process.

After generation of the plasma atmosphere, the silicon surface is exposed to the action of the etching plasma without any further process steps taking place; in particular, no further measures are necessary to achieve a targeted micro-masking of the silicon surface. However, practical "freedom from defects" is achieved, in the sense that substantially no additional defects, such as in the form of etch by-products, are produced by the reactive plasma. Also crystal defects are substantially avoided, whereby the semiconductor properties are not changed by the etching process, if this is important for the further production of the curved surface. These are structural features of the resulting silicon structure which are advantageous for the further steps, in particular if the base of the considered optical component is silicon. If this structure serves as a basis for the production of the surfaces of other base materials, these advantageous properties can also be utilized for the steps required for this purpose. For example, by these properties, the production of a stencil on the basis of microstructuring processes well known for crystalline silicon. An efficient adjustment of the refractive index in the curved surfaces is achieved by adjusting the aspect ratio of the reactive plasma atmosphere resulting needle-like structures to a value of 4 or greater by controlling the process time, wherein a masking of the silicon surface, whether by photoresist or other substances such Aluminum, gold, titanium, polymers, water, or any surface contaminants, etc. is not required.

The needle-like structures produced have a form which is best suited for use on curved surfaces in the visible light and also in the infrared range. The shape of the needle-like structures produced by the self-organized masking of the etching also has a "pyramid-like" shape in addition to the aspect ratio of greater than 4, resulting in a very tapered needle end, whereas at the foot of the above needle-like tapered shape, a relatively flat leaking region is created can be, the shallow ends. The lateral dimensions increase significantly toward the foot. Between the circumscribed pyramid-like structures with needle tip remains a clear distance, at least 50 nm, so that in spite of high needle density too close to each other standing needles are prevented. Such too dense needles would converge to a larger entity and bring the etching process to a halt here.

The forms specified with the given circumscriptions are not all the same, but in the mean and in the statistical distribution they have regular and individually sharply demarcated forms. Nevertheless, their density distribution results in about 50 "pyramid-like needles" per square micrometer, in any case well below 100 needles per micron ² , with a height of the pyramid-like needles of above 400 nm, especially in the range around 500 nm and at about the same depth of a gap between the pyramid-like needles. Between adjacent such needles of at least 50 nm wide gap remains, the first at the bottom of the pyramid-like course, where the foot area relatively flat, runs down almost shallow, converges. The pyramid should not be understood as having only four pages; even more pages are possible as well, up to a versatile pyramidal shape and towards an approximately round shape in cross section.

In other words, most of the regularly distributed pyramid-like needles above a pointed needle, in the underlying height portion of pyramidal shape and in the foot area laterally wider with a relatively shallow outlet, so different from a pyramidal shape. These pyramid-like needles can be subjected to considerable mechanical stresses so that they can serve directly as a refractive index matching layer or anti-reflection layer, if the silicon also serves as a base material or if further steps are required, such as applying a passivation material, as a nano-template for fabrication needle-like tips in other materials, oxidation processes, and the like. At best, the nanostructures are bent or "smeared" under appropriate load, but not destroyed. Mechanical stresses of the following type do not lead to destruction of the nano-needle structure, resulting in disadvantageous consequences with respect to the reflection of the nanostructure with the pyramid-like needles:

even surface pressure perpendicular to the needles;

AFM in contact mode;

Profilometer.

A profilometer needle of the profilometer exerts a pressure between 0.1 and 10 mg on the sample to be measured (the nano-surface with the pyramidal needles). The profilometer needle is very pointed, but increases in diameter quickly, so that when moving on a sample a 5μm deep well with a width of 1 micron can not be resolved exactly in the measurement image. At a pressure of typically 5 mg and a movement of the profilometer needle at a rate of up to 100 μm / sec on the nanostructure, no adverse effect on the reflection properties of the nanostructure was observed, as would occur if the pyramidal needle structure were destroyed.

Overall, for the resulting (planar) nanostructure, even at a mean length or height of the structures of about 400 nm to 500 nm and below 1000 nm, a very favorable antireflection behavior in the visible range and also up to 3000 nm wavelength or more on curved surfaces of microlenses, for example , etc. are detected.

This property also indirectly describes the structures of the "pyramid-like needles". The (total) reflection is below 0.7% for a wavelength range between 400 nm and about 800 nm (scattered and direct reflection). In an extended range between 180 nm and 3000 nm, the (total) reflection is below 2%, with practically only the scattered reflection contributing. Reflection is a physical property of the nanostructure that is reproducible, measurable, and comparable to another structure. Without intending to limit the invention by the following discussion, studies suggest that efficient self-organized masking (as "self-marking") is achieved by the etching process itself rather than by existing or specially added materials. Corresponding studies based on Auger electron spectroscopy (AES) and energy dispersion X-ray spectroscopy (EDX) indicate that the masking effect is caused by SiO _x , so that a high shielding effect is achieved by the locally formed silicon oxide. Overall, this leads to a moderately low silicon consumption during the production of the needle-like structures with "pyramid-like shape" with simultaneously high aspect ratio and existing gap, so that the inventive method advantageously and efficiently used in semiconductor manufacturing with a high degree of process compatibility in many fields is.

No defects for targeted mask formation are exploited. In place of the targeted masking before an etching process thus occurs the previously described self-organized, caused by the special process conditions masking during the etching process. The combination of the self-masking with the etching during the RIE process thus enables the generation of self-organized pyramid structures in the nanometer range by the plasma. It is thereby possible to convert a smooth silicon surface into a statistically regular, quasi-ordered nanometer-sized needle structure, i. with lateral dimensions in the range below the usual wavelengths of light, for example, to convert the wavelength range of visible light. Overall, therefore, even over a globally curved surface, i.e., the radius of curvature is much greater than the lateral dimensions of the nanostructures, excellent homogeneity of reflectivity is achieved.

Furthermore, in a single etching step, it is possible to significantly reduce the number of contamination defects which are usually caused, for example, by etching byproducts, as well as crystal damage which can be encountered in conventional plasma-assisted processes, or to substantially avoid them within the scope of measurement accuracy. Thus, neither RHEED, CV measurements, TEM or PDS (Photothermal Deflection Spectroscopy) could detect such defects-as a consequence of the etching regime according to the invention. Even a simple photodiode, such as blue light, whose surface was processed by this process, had no peculiarities that indicate increased defect densities. Thus, the fabricated nanostructure can be provided by a single plasma etch step in a quality that does not require further material removal. The structures produced by the method show no edge shading at high edges. It is thus possible, for example, to structure surfaces of a few μm, even if the surface is enclosed by a 5 μm high structure, so that great flexibility results in the production of corresponding curved surfaces of optical components and the positioning of the refractive index matching layer thereon.

The structuring of the silicon is done by the plasma in the RIE process. These structures are deepened by the etching process, resulting in the structures in the nanometer range with enormous aspect ratios.

The structure thus produced has a low-defect nanostructure surface, which can be produced on the base material of the optical component. A height of the free-standing pyramid-like needles is at least 400 nm and a gap of at least 50 nm. The height is between 400 nm and 1000 nm, which can be read from images of the electron beam microscope image, as described in more detail below. The pictorial representation is intended to replace a limited possible structural description of the pyramid-like needles and their environment. For comparison, reference may be made to the John Hancock Center in Chicago, which is about 350m high, slightly pyramid-like, and has a lateral foot measurement (with no shallow, relatively shallow leakage) of about 85m. This structure is constructed in a reduced by a factor of 10 ⁹ form in, for example, silicon, often side by side and difficult to visualize on this scale with the current imaging techniques and clearly described. On the one hand, this task is not simple, but on the other hand, it is essentially fulfilled by measuring and presenting the effects of these structures.

According to the claimed teaching (claim 1 and claims 6, 19 and 27), a layer for adjusting the refractive index of the base material with a curved surface and the surrounding medium is thus produced using the process described therein, which is also already explained above that thus a desired broad-band anti-reflection is achieved.

Claimed is a method for producing an optical component. The production of a globally curved surface takes place in a base material. Due to the (globally) curved shape, rays of light incident on the curved surface are changed in their propagation direction, in the sense of refraction. The rays of light also enter the curved surface.

A refractive index adjusting layer is formed with a nanometer structure in the base material. This preserves the global curvature of the surface. The adaptation layer is formed using the described process. Includes are

Generating a reactive plasma atmosphere based on at most two different gas components.

The gas components are oxygen and a reactive gas for etching silicon, without an intermediate step. In particular, no further gas components are involved.

By setting process parameters, a "self-masking effect" unfolds with the consequence of the generation of a nanometer structure (of such a layer) with needle-like nanostructures.

By controlling the process time to act on the plasma atmosphere, the aspect ratio of the needle-like structures formed in the plasma atmosphere (self-masking) is set to a value of at least four.

The base material of the optical component may be directly silicon (claims 19 to 26, claims 10 to 13), which may be further treated as needed after patterning, e.g. At least partially converted to oxide, or from needle-like silicon structures, layers can be made by molding, so that these structures then allow a gradual refractive index transition in a variety of materials. At the same time, the base material can also simultaneously obtain its global surface curvature by molding (claim 5), thus providing a great flexibility in the selection of materials and an efficient manufacturing method for the antireflection of the curved surfaces.

The surface structure according to the invention for globally curved geometries can therefore be used in a large number of possible components, for example optoelectronic circuits (claim 15, 22, 31), but also in absorption elements for control and measurement purposes (claim 23, 32), whereby almost all incident on the curved surface light intensity can be absorbed and thus detected.

Also, a significant increase in the efficiency of components can be achieved, which are designed for a radiation (claim 33), such as a lens, wherein one or both surfaces can be effectively anti-reflection.

As will be described later, the temperature of the silicon wafer and the ratio of the working gases at the reaction point on the silicon surface are suitably adjusted.

In an advantageous embodiment, the temperature of the silicon surface is set at 27 ° C., preferably in the range ± 5 ° C. Thus, an efficient adjustment of the further process parameters, such as the flow rates specified in the claims and in the following description, can be made, as the temperature, which typically represents a "sensitive" parameter, is specified in a very accurate manner.

Also, the process pressure and plasma power are properly matched as set forth in the following description to obtain the desired aspect ratio while reducing the rate of contamination and low crystal defect density.

In particular, while maintaining an oxygen component in the manner indicated, the ratio of not more than two working gases is adjusted so that etching removal and self-masking balance each other out. This ensures both the structuring and the required freedom from defects (no additional defects due to the etching regime).

In the present method, the absolute parameter values can be efficiently adjusted to the proportion of the open (or free) silicon surface which serves as the basis for the curved surface design. If the Si surface is covered to a high surface area by a mask layer, for example oxide or silicon nitride, since for example only certain areas of the surface or a template should receive a corresponding needle structure, this can be achieved at least by increasing the reactive gas content, for example the SF ₆ share, be compensated, especially if the SF ₆ simultaneous reduction of oxygen content and simultaneous increase of process pressure.

It is possible by the process described above to produce the desired nanometer structures with high, variable aspect ratios in a short time using, for example, a simple RIE system with parallel plate reactor. This is possible over a large area as well as with targeted adaptation of the process parameters even in the smallest areas, so that individual components, such as optically active areas of optoelectronic components, and the like can be provided with a corresponding nanostructure even on demanding geometries with desired curvature without other component areas be adversely affected. Unstructured areas may be simply, e.g. from an oxide mask. Furthermore, due to the low contamination rate and the low crystal defect density, an immediate further processing after the production of the planar nanostructure can take place without the need for complicated preparatory and / or post-processing processes.

Another suitable method comprises generating a reactive plasma atmosphere with oxygen and a reactive gas consisting of a mixture of HCl and BCI3, for etching silicon without further process steps by setting process parameters that have a self-masking effect to produce a nanostructure with needle-like structures unfold. Also in this case, a self-organizing masking effect can be achieved so that the above-described properties (or shapes) of the nanostructures are obtained.

By these methods, there can be provided a nanoscale nanostructure comprising randomly distributed monocrystalline needle-like silicon structures formed on a monocrystalline silicon base layer, wherein the aspect ratio of the needle-like silicon structures is 4 or greater, and the crystal defect density in the silicon structures is not higher is as is in the silicon base layer. These structures may then be further processed as needed, as previously described, to produce the curved surface finish therefrom.

The nanostructure, which thus has silicon structures with lateral dimensions that are typically below the wavelength of visible light, can thus be used efficiently as a layer in devices in which a gradual change in the refractive index between silicon or other base material and a, the medium surrounding the base material is desired. On In this way, an adjustment of the refractive index between the base material and the medium is achieved. As a result, the reflection behavior and / or the transmission behavior of optoelectronic components provided with curved surfaces to achieve the desired optical effect can be significantly improved.

The object of the invention has, inter alia, the advantages that a broadband anti-reflection is achieved with curved silicon surfaces or other optically active surfaces, wherein, if silicon is the base material, no material needs to be applied, but only the surface is modified. There are no adhesion problems, no layer stresses and no restrictions in the optical wavelength range.

The antireflection coating also has the advantage that the direct reflection is significantly lower than the scattered reflection and thus can be suppressed by suitable measures (apertures, dark frames, etc.) in their effects. The excellent homogeneity of the antireflective coating over a large area minimizes the control effort for finished components enormously. For example, for microlens arrays not every lens has to be measured individually.

To generate the nanostructure in the surface, the described RIE silicon etching process is used. The generated structures can be converted by an oxidation of silicon into oxide, whereby the anti-reflection is also applicable to curved oxide surfaces. Other surface processes, such as nitriding or other treatments can be carried out without problems after the generation of the needle-like structure. In addition, the produced silicon or oxide nanostructure in the curved surface can also be transferred by molding to other materials, for example to produce a stamping tool for other materials.

Other embodiments are set forth in the following description. Brief description of the drawings.

The invention will now be explained with reference to embodiments with the aid of the drawing. Show it:

Fig. 1 is an electron micrograph of a RIE etched

Silicon surface in section in an area that is partially covered by an oxide layer,

2 is an electron micrograph with an obliquely incident electron beam, from which the homogeneity of the distribution of the silicon needles and the depth of the spaces between the needles are visible,

3 is a TEM image of the tip of a silicon needle in high-resolution transmission,

FIG. 3 a shows the receptacle from FIG. 3 turned so that the [001] direction is vertical,

FIG. 4 a shows the electron micrograph of FIG. 2 with an obliquely incident electron beam, from which the homogeneity of the distribution of the silicon needles and the depth of the interspaces between the needles are visible, here a left-hand section, FIG.

4b shows the electron micrograph of FIG. 2 with obliquely incident electron beam, from which the homogeneity of the distribution of the silicon needles and the depth of the interspaces between the needles are visible, here an intermediate section,

4c shows the electron micrograph of FIG. 2 with an obliquely incident electron beam, from which the homogeneity of the distribution of the silicon needles and the depth of the interspaces between the needles are visible, here a right section,

5 shows the electron micrograph of FIG. 2 with an obliquely incident electron beam, from which the homogeneity of the distribution of the silicon needles and the depth of the interspaces between the needles are visible, here a front section, 6 shows the electron micrograph of FIG. 2 with obliquely incident electron beam, from which the homogeneity of the distribution of the silicon needles and the depth of the interspaces between the needles are visible, here completely,

FIG. 7 shows corresponding results of reflection of light on a curved surface with an anti-reflection layer, which is produced on the basis of a needle-like structure, as also shown in the preceding figures, FIG.

8a shows an optical component with a curved surface before the formation of a needle-like nanostructure,

FIG. 8b shows the curved-surface optical component after forming a needle-like nanostructure, FIG.

8c an optical component with a curved surface during

Forming a needle-like nanostructure by molding a nanostructure made of silicon, and

9a,

Fig. 9b,

Fig. 9c,

9d Examples in which the curved surface (with a needle-like nanostructure) has been changed by a treatment in its material composition, for example by oxidation. Only one narrow lateral section is shown in each case.

Detailed description.

FIG. 1 shows a silicon-containing component 1 with a nanostructure 2 which has a monocrystalline silicon base layer 3 on which needle-like silicon structures 4 are formed. In this application, needle-like silicon structures are to be understood as "pyramid-like" structures that have a tip with lateral dimensions of a few nanometers, wherein the tip increases significantly downwards in its lateral dimension, so that in the lower part of the structure has a lateral dimension of some ten nanometers or up to 100 nm is achieved. The silicon base layer 3 is limited in this embodiment by a mask layer 5, which may be composed of silicon dioxide, silicon nitride or the like, wherein the needle-like silicon structures 4 are formed up to an edge region 5 a of the mask layer 5. In the embodiment shown, the silicon base layer 3 is a part of a 6 inch diameter silicon wafer with a (100) surface orientation that has a p-type doping giving a resistivity of 10 ohm.cm.

However, as previously stated, the base layer 3 may have any desired crystal orientation with any predoping. In alternative examples, the base layer 3 may be formed substantially of amorphous or polycrystalline silicon.

FIG. 2 shows an enlarged section of the nanostructure 2, wherein the angle of incidence of the probing electron beam is irradiated with an inclination angle of approximately 17 ° in order to more clearly show the size relationships in the lateral direction and in the height or thickness direction of the pyramidal structures 4. As can be seen from FIGS. 1 and 2, the silicon structures 4 have a height which is on average about 1000 nm, so that in some embodiments a height is reached which is greater than the wavelengths of visible light. In the scale with 2 microns 10 scale parts are plotted in Figure 2. In Figure 1, it is 500 nm per scale part.

Due to the tilted electron beam of 17 °, the height entered as a measure in FIG. 2 is to be converted from 603 nm to the real height. It is also possible to convert the vertical extent by up to 60% for lower pyramid-like needles, which achieve their effects from about 400 nm. This is done by compression of Figure 2 in the height direction to 40% of the height shown. But also pyramid-like structures 4 with a mean height in the range of 400 nm show excellent optical properties in many applications. Thus, for example, for an average height of 400 nm, excellent antireflection in the visible wavelength range and up to 3000 nm was observed.

As can be seen from FIG. 1, a mean maximum height of the silicon structures 4 can also be substantially 1000 nm.

On the other hand, FIGS. 1 and 2 show that the lateral dimension of the silicon structures (at the foot) is less than 100 nm or a few tens of nanometers (significantly less), so that on average an aspect ratio of height to lateral dimension of 4 or higher is achieved becomes.

The results shown in Figures 1 and 2, which relate to a 6-ZoII (100) Si disk with p-type doping, a 10 ohm resistance and a surface area of the oxide mask of greater than 90% (to substantially 93%) produced in a single step plasma etching process in a system with parallel plate reactor type STS 320 with the following parameters:

SF ₆ gas flow: 100 sccm

O ₂ gas flow: 20 sccm

Gas pressure: 70 mTorr

Si slice temperature: 27 degrees Celsius Plasma power: 100 W

Etching time: 2 min

Self-adjusting BIAS (DC potential between the plasma atmosphere and the surface to be etched): varies by 350 V.

In alternative examples, comparable results were obtained for the nanostructured surface. Output parameters and process parameters are given below. For an area fraction of 0.1% silicon and 99.9% oxide mask, with the following parameters.

150 sccm SF ₆

20 sccm O2

91 mTorr

27 ⁰ C

100 watts

4 minutes etching time (process time)

For 100% silicon surface, ie a bare silicon wafer

65 sccm SF ₆

23 sccm O2

50 mTorr

27 ⁰ C

100 watts

10 min to 20 min etching time (process time).

For bare silicon wafers, process time of up to 20 min is also useful. Then the process results in an extremely high-quality antireflective coating of the surface nanostructured with the needles.

In other embodiments, gas flow rates were between 50 sccm for the reactive gas, so SF _6, C _n F _m or HCl / BCl 3 provided to 150 bar. For oxygen gas flow rates of 20 to 200 sccm are provided. Further, in some embodiments, the temperature of the substrate, and thus the base layer 3, is set to a range of 27 ° C ± 5 ° C.

The 6 "(inch, inch) disk was mounted on an 8" disk in the RIE STS 320 system, and the plasma can also act next to the 8 "disk.A power density can be approximated as follows: The plasma power can be in the range of 100 W can be set to 300 W, which corresponds to a power density of about 4 W / cm ² to 12 W / cm ² for a 6-inch disk.

From the above indications, corresponding parameter values for other etching systems and other degrees of coverage of the silicon base layer 3 to be structured with the pyramidal structures can be determined. For example, a lower coverage of the silicon base layer due to a lower gas flow rate of the reactive gas.

If no mask is given, the reactive gas content is low, and vice versa.

With the above settings, the Si needles 4 having a height of about 1000 nm were generally randomly distributed at the areas not masked by the mask layer 5.

As the mask layer 5, e.g. Silicon oxides or silicon nitrides.

Machined disks with similar structures (without oxide mask) become completely black and showed a reflection of less than 0.4% for the wavelength range of 400 nm to 1000 nm, at the same time excellent homogeneity of this property over the entire wafer (disk). In particular, in a wavelength range extending in both directions beyond 180 nm to 3000 nm wavelength, the investigations showed a still excellent anti-reflection behavior with reflections below 2%. The reflections recorded here (practically only) the reflections in all solid angles.

Furthermore, the crystal damage caused by the plasma-assisted single-stage structuring process and the contamination are very low and are below the detection limit in the exemplary embodiments shown. No residual substances could be detected after the plasma structuring process and the crystal quality of the silicon structures is almost identical to the crystal quality of the silicon base layer before the etching process.

As can be seen in FIG. 3, the needle sections of the pyramid-like needles are almost atomically pointed at their end 4a. The lateral dimensions of the end 4a are only a few nanometers. Furthermore, individual network planes (111) of the monocrystalline needle section can be clearly seen without crystal defects caused by the etching being recognizable.

FIG. 3 shows, from a pyramid-like needle 4, a single tip 4a or an end region with this tip 4a. As can be clearly seen, the needles are almost atomically pointed at their end 4a, ie, the lateral dimensions of the end 4a are only a few nanometers and are thus smaller than 10 nm. In the illustration of FIG. 3, the crystal direction is also perpendicular to Surface of the silicon base layer 3 registered. This direction corresponds to a [001] direction, since for the shown Embodiment, the surface orientation is a (100) orientation. As can be seen, the end region extends with the pointed end 4a substantially along the [001] direction with only a slight deviation of less than 10 °, so that the structural elements are nearly perpendicular with only a few degrees deviation from the normal to the surface of the base layer 3 are aligned.

FIG. 3a is the direction [001] oriented vertically. With the figures 3, 3a, the inclination of the side wall of a pyramid-like needle can be roughly determined. It is about 4 ° to the normal [001].

In the individual lattice planes of the monocrystalline needle, no crystal defects caused by the etching are recognizable. In the base layer configuration shown, the appearing lattice planes correspond to the (111) planes.

The surface, which is severely rugged after the process, significantly increases their surface area, which significantly alters their properties. The increased surface area offers a much larger attack surface for attaching molecules and can thus significantly increase the sensitivity of sensors.

For example, it has been found that gases remain localized in the structure for quite a long time. In the optical region, the pyramidal structures 4 are interesting in that they are smaller in lateral size than the wavelength of light (VIS / NIR) and by their needle shape, ie by the small lateral dimension of the end region 4a and the relatively large dimension at the foot pyramidal structure, and the high aspect ratios give a nearly perfect gradient layer. The refractive index gradually changes from the refractive index of the silicon to the refractive index of the medium surrounding the nanostructure 2, for example, air, so that a corresponding layer having the structures 4 can be referred to as a refractive index matching layer between two media.

The nanostructure 2 thus allows an impedance matching or refractive index matching, which leads to an excellent broadband reflection suppression.

This results in a broad field for the use of the nanostructure 4 in many microdevices and also in other fields, such as solar cells, sensors and the like, in which in particular curved surfaces with improved optical behavior are required, such as microlenses, arrays of microlenses, and the like , The examples thus provide methods and structures in which silicon structures with large and adjustable aspect ratio occur, whereby due to the (special) parameter setting in the self-masking plasma etching process in a single etching step contamination and formation plasma-related crystal defects is kept low With little effort for the one-step patterning process, the resulting structure can be used immediately without the need for further post-processing steps when needle-like silicon structures in a high monocrystalline form are required.

Furthermore, no elaborate surface preparations or additional measures to produce a micro-masking are required. A prior conditioning or conditioning can be omitted.

By means of a standard RIE etching process for silicon, without any additional structuring measures (e-beam, interference lithography, or the like), a multiplicity of virtually crystal-defect-free, needle-shaped structures with, inter alia, high aspect ratio and nanodimensions are produced on the surface of a silicon wafer a broadband anti-reflection is achievable, thus allowing an application to curved surfaces.

Figure 8a shows schematically in cross section an optical component 8, which is shown here as a micro lens system (Microlinsenarray). The component 8 may be an integral part of a complex microstructure, such as an opto-electronic circuit in which optical and electrical signals are processed. Also, mechanical components may be provided to obtain the desired function. For the sake of simplicity, corresponding further components are not shown.

The component 8 has a base material 8a, which is suitable for the production and the function of the component, or can be converted into a suitable material in a later phase. For example, the base material is silicon, although it may also serve as a surface material or at least be converted to a suitable material, for example, oxide, as described in more detail below. The base material 8 has at least one, preferably a plurality of curved surface (s) 8b, 8b ', the curvature being understood as a global curvature in the sense that the radius of curvature is substantially greater than any dimensions of nanostructures, for example the nanostructures 4 to be formed in the surface 8b. The "global" curvature of the surface 8b is defined by dimensions that are larger are at least microns, with structuring with nanostructures 4 not resulting in any significant change in global curvature.

As shown in Fig. 8a, a maximum thickness of the base material 8a is given by the value x.

FIG. 8b shows the component 8 (the microlens array) after an etching process, as described in detail above, so that a layer 8c is formed which has corresponding needle-like nanostructures, for example in the form of the structures 4, and thus an adjustment of the refractive index of the base material 8a to the surrounding medium, such as air or other material, causes, as previously explained. The one-step etching with the properties described above gives the layer 8c with a pronounced homogeneity with respect to the properties of the nanostructures formed therein as well as with regard to the layer thickness, without the global curvature leading to a significant geometry-dependent influence. The overall dimensions x of the component 8 also remain substantially the same, since the etching process can be adjusted so that undesirable silicon consumption is low, since the corresponding self-masking effect can start immediately at the beginning of the etching, as explained above.

The layer 8c can thus be produced while avoiding the application of other material layers, whereby further post-processing can be dispensed with if the base material 8a in the form of silicon is suitable for the application of the optical component 8. In this way, stresses in the component are avoided, which can occur conventionally, if several layers are to be applied for anti-reflection.

Figure 7 shows a corresponding measurement of the direct and scattered reflections typically achieved. It can be seen that in a range from about 400 nm to 800 nm, the total reflection is dominated by the scattered reflection and is very low. For this wavelength range, the total reflection is 0.7% or even less.

FIG. 8c shows the component 8 in a further embodiment, wherein the base material 8a is made of a different material, which in the embodiment shown is provided in a deformable state. For example, a variety of polymeric materials may be applied or transferred into a deformable state by appropriate treatment to allow subsequent surface structuring. This has a Template 9 a single or multiple curved surface 9b, which is a template material 9a formed. The surface 9b has a layer 9c with a nanostructure which has the geometric properties as described above in connection with the nanostructure 4. For example, the template 9 may be a silicon carrier, in which in addition to the surface 9b and the layer 9c is incorporated.

Of course, the template 9 can also be made of a different material, which in turn has been patterned on the basis of a silicon-based support material, in a similar manner as described below. In addition, let it be assumed that the template 9 or at least the layer 9c is made of a silicon-containing material.

The stencil 9 can then be brought into contact with the deformable base material 8a, so that the structure of the layer 9c is first transferred into the surface 8b "and then into the base material 8a, whereby nanostructures are also formed therein corresponding to the molding process, the global curvature is simultaneously formed in the surface 8b (and the base material 8a), which is formed as a negative in the template 9.

FIGS. 9a to 9d show narrow lateral cut-outs or cut-outs of the curved surfaces 8b, 8b 'or 9b of an optical component 8 or a template 9, whereby a different material composition for the layer 8c, 9c is created starting from a silicon nanostructure.

FIG. 9a shows the layer 8c, 9c, as it results from the etching process described above, in a lateral section.

FIG. 9b shows the layer 8c, 9c after a certain duration of a surface modification, which in a second embodiment comprises an oxidation process, so that an oxidized section 9d is formed, which extends into the depth. Again, only one section represents the entire curved surface.

FIG. 9c shows the layer 8c, 9c when the individual needle-like structures are completely oxidized as 9d ', as a further example.

FIG. 9d shows the layer 8c, 9c, when the oxidized region 9d "extends further into the base material 8a, 9a, as yet another example. In this way, materials other than silicon can be fabricated directly in curved surfaces of optical devices, for example, when the optical or electrical properties of silicon are not suitable for the application. Accordingly, corresponding stencils can also be formed on the basis of other materials, such as silicon dioxide, which allows great flexibility in the production of templates for antireflection coatings, since proven manufacturing processes from microelectronics, such as selective etching processes, and the like in combination with silicon oxides, nitrided Silicon, and the like can be applied.

In the embodiments shown, components with a curved optically active surface were shown. Of course, one or more further surfaces, flat or curved, can be provided and provided with the layer 8c, 9c in order to achieve improved optical properties.

Claims

Claims:

1. A method for producing an optical component with the steps

Forming a globally curved surface (8b) in a base material (8a, 9a) to change rays of light incident (and entering) on the curved surface in the direction;

Producing a refractive index adjustment layer (8c, 9c; 4) by forming a nanometer structure (2; 4a) in the base material while maintaining the global curvature of the surface, wherein the matching layer (8c, 9c; 4) is made using a process, which includes

Producing a reactive plasma atmosphere on the basis of at most two different gas components containing oxygen and a reactive gas for etching silicon (3) without an intermediate step, by setting process parameters which have a self-masking effect for generating the nanometer structure (2) deploy with needle-like structures (4,4a);

Setting an aspect ratio of the needle-like structures (4, 4a) formed in the plasma atmosphere to a value of four or more by controlling a process time of the action of the plasma atmosphere.

2. The method of claim 1, wherein the base material comprises silicon and the process is applied directly to the base material for patterning the curved surface.

3. The method of claim 2, wherein the process further comprises an oxidation process after the preparation of the nanostructures to at least partially oxidize them.

4. The method of claim 1, wherein forming the refractive index-adjusting layer comprises: forming a template by the process and using the template to mold the nanostructure contained therein into the base material.

5. The method of claim 4, wherein the template generates the curved surface in the base material in addition to the nanostructure.

6. An optical component having an optically effective curved surface for light in the range of substantially 400 nm to 800 nm, wherein a refractive index matching layer (8c) for broadband anti-reflection at least in the range of

400 nm to 800 nm is provided, the matching layer of needle-like nanostructures

(2, 4,4a), and has the property of producing a total reflection of 0.7% or less.

7. An optical device according to claim 6, wherein the nanostructures in the refractive index matching layer are randomly distributed and have an aspect ratio of four or more.

8. An optical device according to claim 6 or 7, wherein a layer thickness of the refractive index matching layer is about 500 to 1000 nanometers.

The optical device according to any one of claims 6 to 8, wherein an average density of the nanometer structures in the refractive index matching layer is 100 per square micrometer or less.

10. An optical device according to any one of claims 6 to 9, wherein the nanostructures comprise silicon.

11. The optical component according to claim 10, wherein the nanostructures are made of silicon.

12. The optical component according to claim 10, wherein the nanostructures are made of silicon oxide.

13. An optical device according to claim 10, wherein the needle-like structures consist of silica-coated silicon.

14. An optical device according to any one of claims 6 to 9, wherein the nanostructures are made of a deformable by embossing techniques material.

15. An optical device according to any one of claims 6 to 14, wherein the device represents a part or more parts of an optoelectronic circuit.

16. Optical component according to one of claims 6 to 15, wherein it is a suitable for continuous light device.

17. An optical device according to claim 16, wherein a second surface is provided, which is provided with a second refractive index matching layer with nanostructures.

18. Optical component according to one of claims 6 to 15, wherein it is an absorber component for control or measurement purposes.

19. An optical component (8) with a curved surface, the - for broadband anti-reflection - made of silicon-containing material constructed needle-like structures with nanometer dimensions with an aspect ratio greater than four to one.

20. The optical component according to claim 19, wherein the needle-like structures are produced or producible by a single-stage self-masking etching process.

21. An optical device according to claim 19 or 20, wherein an average density of the needle-like structures of the curved surface is between 50 and 100 needles per square micrometer.

22. An optical device according to any one of claims 19 to 21, wherein it is a part or more parts of an optoelectronic circuit.

23. Optical component according to claim 19, wherein it is an absorber component for control or measurement purposes.

24. Optical component according to one of claims 19 to 23, wherein the needle-like structures consist of silicon.

25. An optical device according to any one of claims 19 to 23, wherein the needle-like structures are made of silicon dioxide.

26. An optical device according to any one of claims 19 to 23, wherein the needle-like structures consist of silicon dioxide coated with silicon.

27. An optical component with a curved surface, which consists for broadband anti-reflection of needle-like structures with nanometer dimensions with an aspect ratio greater than 4 to 1 and the material of the needle-like structures has substantially no silicon.

28. An optical device according to claim 27, wherein the needle-like structures are equivalent in configuration to silicon structures producible by silicon in a self-masking single-stage plasma etching process.

29. An optical component according to claim 27 or 28, wherein the needle-like structures are contained in a material layer which is structured by molding a corresponding silicon or silicon dioxide layer with a needle-like structure.

30. An optical device according to any one of claims 27 to 29, wherein an average density of the needle-like structures of the curved surface is between 50 and 100 needles per square micrometer.

31. An optical device according to any one of claims 27 to 30, wherein it is a part or more parts of an optoelectronic circuit.

32. Optical component according to one of claims 27 to 31, wherein it is an absorber component for control or measurement purposes.

33. Optical component according to one of claims 27 to 31, wherein it is a suitable part for continuous light part, wherein the surface of one side or the surfaces of both sides are non-reflective.

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