DE102004052146A1 - Assembly to focus e.g. a light bundle, for optical lithography and the like, has an evanescent wave generator and amplifier for the seed evanescent fields to give a focus spot - Google Patents

Abstract

The assembly to focus (S) electromagnetic rays e.g. a light bundle (LB) below the diffraction threshold as seed evanescent fields, has an evanescent wave generator (EWE) and diaphragm (B) with an amplifier (EWV) to amplify the seed evanescent waves in close spatial proximity to their point of origin at the EWE. At the same time, the phases of the amplified evanescent fields are matched. The EWE is a semiconductor absorber which can be saturated.

Description

The The invention relates to a method and an arrangement for focusing electromagnetic radiation below the diffraction limit.

The Focusing of light bundles or more generally electromagnetic radiation to an extremely small size area with high energy density is used in a large number of technological Methods or optical instruments needed, such as in optical lithography, optical and magneto-optical Data storage, in laser material processing, in Confocal Scanning microscopy (Scanning Confocal Microscopy), in the integrated Optics and nano-optics, which is the execution of operations in spatial Require dimensions in the size of the wavelength.

One Prominent example is the optical lithography, which is an essential Component in the production of integrated circuits is. at The optical lithography happens by means of optical lenses focused Light or VUV radiation a photomask representing the pattern for the desired optical circuit forms, and is then by a projection lens on a wafer, from the by photochemical processes after a specific processing the integrated circuit is created.

the State of the art according to well-known possibilities for improvement the resolution in optical lithography, of which only the most important to be named.

So there is a possibility in the use of a modified irradiation by dipole and quadrupole-like or annular Dazzle or by partially coherent Light (see, e.g., "Resolution enhancement techniques in optical lithography ", SPIE Press, Bellingham, Washington, 2001, pp. 71-151). The On the other hand, near-field optical lithography uses evanescent fields to increase the resolution limits, being through the tip of a tapered fiber with a Tip diameter in the nanometer range causes a strong field increase will that for a permanent sensitization of the photoresist with a thickness of about 50 nm is sufficient. In the literature were different embodiments of near-field lithography. In a realization (contact lithography) there are alternating layers of absorbers (e.g., chromium) on the surface of the quartz substrate (Appl. Phys. Lett. 69, 3098 (1996)) or embedded within the substrate (conformable embedded-amplitude mask, see e.g. Appl. Phys. Lett. 81, 1315 (2002)). The amplitude mask is therefore in direct contact with contact lithography with the layer of the photoresist. The resolution can with this method be very tall whereas contact lithography is the direct contact of the Photoresist and the mask necessary, thereby reducing the industrial Application considerable problems arise.

A another known variant for increasing the resolution is the optical grid near-field lithography (Scanning Near-Field Lithography), in which modulated light pulses into a conical fiber coupled with a tip and in the near field of structuring Be brought layer. The information to be written takes place here directly over the Modulation of the laser. The disadvantage of this method is the low Transmission of the fiber.

In another embodiment, for example described in US 6,340,813 For example, the end opening of the fiber tip is bonded to a thin layer of saturable dye, whereby the passage of a light beam can only occur if the saturable dye becomes transparent due to the irradiation of the laser due to saturation. As a result, the diameter of the near field diaphragm can be set variably and dependent on the intensity or the temperature.

Another important field of application for focused laser bundles is the optical and magneto-optical data storage, in which information is stored on a data carrier by focusing a laser beam on the smallest possible area (see, for example, TW McDaniel, Handbook of magneto-optical data recording: materials, subsystems, techniques, Noyes Publishing, Westwood (USA), 1997, pp.1-32, 425-547). In optical data storage, physical changes in the medium (especially, for example, structural changes between the crystalline and amorphous states) on this surface are caused by heating. In magneto-optic memory systems, heating causes alignment of magnetic domains along an applied magnetic field. The physical limits in conventional devices for a maximum possible storage density is given here analogously as in lithography due to the diffraction limit by the wavelength of the optical beam. The prior art has examined various possible solutions for increasing the bit rate in optical data storage. In a first variant of optical near-field data storage (Appl. Phys. Lett., 61, 142 (1992)), a scanning Near-Field Microscope with a conical optical fiber with a tip in the near field of the magneto-optical medium for writing and reading the information, whereby structures smaller than 100 nm could be recorded Another solution (see US 2003/035361 and Appl. Phys. Lett., 65, 388 (1994)) uses a solid-immersion lens (SIL) which, due to the high refractive index, can reduce the focused beam radius. The magnetic disk is also located in the near field of the boundary layer of the lens at a distance below the wavelength, whereby Evaneszenzfelder in the near field cause local heating of the magnetic layer. A problem with a practical application of these two techniques, however, is the very difficult under practical conditions to control very small distance of the tip or the solid immersion lens to the disk, whereby only small recording speeds and small recording areas are possible. To avoid these problems was in US 6,226,258 ; US Pat. No. 6,661,745 B1 ; Appl. Phys. Lett. 73, 2078 (1998) used a super-resolution near-field structure (super-RENS) with a material integrated in addition to the magnetic layer, which is located in the near field region of the magnetic layer (GeSbTe). In the super-RENS are created by the incident light due to intensity-dependent processes dazzle-like areas and scattering centers, creating evanescent fields on a smaller area than the spot of the exciting light beam and a near-field recording on the recording layer below the diffraction limit is possible. Modifications of this method can also be used for optical lithography (s. US 6,692,894 and US 6,340,813 ).

One another application example, which is a sharp focusing optical Radiation on a small area requires, laser nano-material processing is the smallest to manufacture Structures and photonic devices in the nanometer range. A variant of this is the use of two-photon photopolymerization by sharply focused laser light in resin or other suitable Media (Opt Lett 22, 132 (1997)) Production of a wide variety of microdevices (see for example Applied Surface Science 208-209, 153 (2003)) and 3D defects in photonic crystals. The spatial resolution is also given by the diffraction limit.

In Optical Near-Field Microscopy is in the configuration in the irradiation mode (illumination mode, I-mode) the object with the from the top of a conical optical Fiber emitted light exiting, with the tip in the near field the sample is located on a substrate. The resulting stray light is through a photomultiplier measured, with resolutions below the diffraction limit are possible. In the configuration In Collective Mode (Collection Mode), the object is replaced by the irradiated on the lower side of the sample, whereby evanescent fields are formed, by a located in the near field of the object itself fiber tip collected and forwarded as a detectable signal.

In Confocal Scanning Microscopy (Scanning Confocal Microscopy) the object is irradiated by a strongly focused light beam and the sample is moved through the focal plane. This method allows already in the conventional version a resolution below the diffraction limit. For However, certain applications is a significantly improved microscopic resolution necessary.

The Focusing light on an extremely small spot below half the wavelength for a reduction the irradiated area as well as an increase the intensity at the same laser power has over the mentioned Areas of application also have a high significance for a multitude of others Processes in other fields of application as well as in basic research, such as. in the integrated optics and nano-optics, the execution of Operations in spatial Dimensions in size or even below the wavelength non-linear optics, in the development of quantum computers and many others.

genügen, wobei λ die Wellenlänge und z die Ausbreitungsrichtung des Bündels ist, bei der Ausbreitung und Fokussierung von Licht in Luft oder im Vakuum verloren geht.The physical limit for the smallest bundle diameter in the focusing of optical or general electromagnetic radiation bundles by lenses or other focusing instruments of conventional optics is due to the diffraction at about half of the wavelength. The reasons for this diffraction limitation are in conventional optics in that a part of the spatial Fourier components E (k _x , k _y , k _Z , ω) (the so-called evanescent components), the condition

where λ is the wavelength and z is the propagation direction of the beam which is lost in the propagation and focusing of light in air or in vacuum.

The prior art discloses photonic crystals as well as other optical media having a negative refractive index. Already in 1968 V. Veselago developed in Sov. Phys. Usp. 10, 509 (1968) hypothesized that materials with a negative refractive index could exist without violating laws of physics. Such a material would allow for a variety of new optical phenomena, such as negative refraction (ie, refraction when moving from the vacuum to a medium away from the solder rather than to the solder as in conventional media). The energy flow in such a medium This would be called "negative-refractive index" and "left-handed media." This topic did not become unexpectedly relevant until some time later, when a negative refractive index for electromagnetic waves with a wavelength in the mm range (described in Phys. Rev. Lett., 84, 4184 (2000) and Appl. Phys., Lett., 77, 2248 (2000)) in a metamaterial composed of a regular array of metallic loops Recently, this phenomenon has been directly experimentally verified (see FIG. Science 292, 77 (2001) and Phys. Rev. Lett. 90, 137401 (2003)).

The size The physical meaning of this topic was especially determined by a theoretical work of Pendry in Phys. Rev. Lett. 85, 3966 (2000) clearly, in which it was shown that a layer of a material with a negative refraction forms a perfect lens that evanescents Strengthen fashions and combined with the radiation modes to form a perfect image below that by the wavelength given resolution leads. artificial However, metamaterials as described above are only for waves in the millimeter to micrometer range applicable. In the year 2000 became in phys. Rev. B 62, 10696 (2000) theoretically predicted that in photonic crystals with specifically chosen parameters an effective Negative refractive index in the optical and infrared range occur can. Later was shown to be photonic crystals under certain conditions also evanescent waves by means of a resonant coupling mechanism to strengthen bound photonic surface states, the crystal a has effective positive refractive index (see, for example, WO 03/088419; WO 03/044897; Phys. Rev. B 68, 045115 (2003) and Phys. Rev. B 68, 245110 (2003)). This phenomenon was named "all-angle negative refraction (AANR) ". The following are both cases short as "negative Refraction ".

Recently became a picture through a thin one Layer of a 2D photonic crystal for long-wave radiation in the Micrometer range experimentally demonstrated (see Nature 426, 404 (2003)).

The latter publications, the the reinforcement of evanescent waves by means of photonic crystals or metamaterials with a negative refractive index are so far only for the picture of structures below the wavelength has been applied.

task The invention is now a method and an arrangement for focusing indicate electromagnetic radiation below the diffraction limit, whereby the physical limit for the smallest bundle diameter overcome in the focusing of electromagnetic radiation and a higher one intensity on a smaller area can be realized.

The The object is achieved by a Method for focusing electromagnetic radiation below the diffraction limit solved, at least comprising the steps of focusing one from a source incident electromagnetic radiation beam by conventional means, generation evanescent wave fields of the electromagnetic to be focused Radiation as seed fields and strengthening of these seed evanescence fields in the immediate spatial Close to her Generation, wherein the phases of the amplified evanescent waves each other are adjusted.

Even though the physical problems with an optical mapping of point-like Objects on the one hand and with a focus of light bundles on the other are relatively closely related and have strong analogies exist but characteristic differences and it is by no means a priori Clear that both problems are solved in an analogous way can. In the picture should be as possible undistorted image of an object emerge while focusing from light the bundles the waves are concentrated on a very small area. in the Connection with the solution according to the invention is a particular difference important: while in an image immediately behind the point-like object evanescence fields exist that intensifies can be this at ordinary optical arrangements for focusing of light bundles not the case. Because in the propagation of optical bundles over optical path lengths, the much bigger than the wavelength all evanescent components that may be present are lost, which is why in one of a source incident and to be focused bunch no Evanezzenzwellen exist, which as Seedfelder for example be reinforced by a layer with an effective negative refraction could.

The The invention makes use of the knowledge that focusing is electromagnetic Radiation below the wavelength can be done by suitable means from the incident ray beam Evanescence waves are generated, which are then used as seed fields for amplification disposal stand.

An essential result of the investigations on which the solution according to the invention is based is that the amplification of the relatively weak evanescent components is sufficient for superfocusing and in particular under optimized parameters of the photonic crystal talls and the Evaneszenzwellenerzeugers the phases of the amplified evanescent waves are adjusted, ie caused by the generation and amplification process only small phase differences of all dominant Fourierkomponenten, which essentially give a constructive (and not destructive) superposition. This result is in no way evident from the outset.

In an embodiment The invention is for generating evanescent wave fields of focusing electromagnetic radiation an optical element, a so-called Evaneszenzwellenerzeuger used. This generates Evanescent fields with smaller but sufficient for the subsequent reinforcement greater Amplitude.

In embodiments to Evaneszenzwellenerzeuger is provided, a diaphragm with a size in the range or below the wavelength of to use to focus electromagnetic radiation. It It has been shown that the diameter of a circular assumed aperture not smaller than the wavelength must be, whereby high losses can be avoided. This distinguishes the solution proposed here from other forms of Near-field optics, such as the use of conical fibers, at which a resolution below the diffraction limit much smaller tip diameter require that at the same time lead to a small light transmission. The Aperture can be circular or have another form. In the method according to the invention can for generating the evanescent wave fields also annular diaphragms, Dipole- and quadrupole-like diaphragms or combinations of ring-shaped and quadrupole-type diaphragms are used. The invention is not limited to these forms, since there are a multitude of other possibilities, to open the further optimization variants.

In further embodiments to generate the evanescent wave fields, the marks, in particular consisting of Cr absorbers, in a photomask in the optical Lithography, which assume the function of a diaphragm used.

Also saturable Absorber, for example, semiconductor or semiconductor quantum well layers, in particular ZnS or a compound such as e.g. CdZnSe or CdZnS used for Evaneszenzwellenerzeugung. The saturable absorbers are through saturation only in the spatial area the peak intensity transparent, while the remaining areas are opaque, whereby the effect of a diaphragm with radial variable losses. But it can also be other substances as saturable Absorber can be used, such. Dye molecules. As well can Layers of saturable Absorbers are integrated with the photomask.

For use as Evaneszenzwellenerzeuger also known in the prior art super-resolution near-field layer (super-RENS) is suitable, whereby the solution according to the invention, a further increase in the resolution limits and improved signal / noise ratios can be achieved. When using a super-resolution near-field layer (super-RENS), for example consisting of a Sb film embedded in two SiN layers, or from AgO _x , PtO ₂ or PdO _x , embedded in two ZnS / SiO ₂ layers generates the desired evanescent fields as a result of intensity-dependent nonlinear processes in the near field region of a recording layer or a photoresist. Furthermore, as evanescent wave generator, a solid immersion lens (SIL) or the tip of a conical optical fiber can be used.

Of the following necessary step in the process according to the invention after the production of evanescent wave fields relates to the amplification of the evanescent waves in the immediate spatial Close to her Generation. In embodiments therefor is provided, a thin Layer of a photonic crystal with a thickness in the range the wavelength the electromagnetic radiation to be focused and with a negative refraction of the photonic crystal in the frequency domain to use the electromagnetic radiation to be focused. Preferably, a photonic crystal with a periodic Arrangement of bars with a high refractive index in a hexagonal arrangement or with cylindrical cavities in a periodic square arrangement or with a square one Grid of cruciform arranged cavities of air, which are arranged in a material with a high refractive index, used. Possible are also more complex structures, especially those with a complete bandgap in three dimensions (3D PC), creating a super-focus in both transversal dimensions is possible. Continue to be Metallic photonic crystals with a negative refraction usable.

The inventive arrangement to carry out the method for focusing electromagnetic radiation below The diffraction limit has at least means for generating evanescent Wave fields of the electromagnetic radiation to be focused and means for reinforcement These waves of evanescence in the immediate vicinity of their production, wherein simultaneously adapted the phases of the amplified evanescent waves are and the amplifier is arranged in the near field region of the Evaneszenzwellenerzeugers.

In embodiments The invention provides that the means for generating evanescent Wave fields of the electromagnetic radiation to be focused a trained as Evaneszenzwellenerzeuger optical element in particular, this can be a circular, annular or dipole and quadrupole type opening, a saturable one Absorber or the structures of a photomask given by the marks, super-resolution Near field structures (super-RENS), solid-state immersion lenses or the tips conical be optical fibers.

to reinforcement the waves of evanescence in the immediate vicinity of their generation and the Simultaneous adaptation of the phase of the evanescent waves is in embodiments the invention a thin Layer of a photonic crystal with one for the frequency the electromagnetic radiation to be focused effective negative refractive index arranged. In this case, the photonic crystal as a periodic Arrangement of bars with formed of a high refractive index in a hexagonal arrangement his or cylindrical cavities in a periodic square arrangement or off a square grid of cross-shaped cavities Air in a material with high refractive index exist. Other realizations are the more complex structures of 3D photonic crystals, metallic photonic crystals or photonic crystals that periodic structures of wires and bars exhibit.

The inventive solution a wide field of application.

So It can be used in lithography for focusing electromagnetic radiation below the diffraction limit to improve the resolution. to Realization of the Evaneszenzwellenerzeugers can on the one hand the brands the etched into the photomask Structures are used. These structures act like a panel and generate the necessary seed evanescence fields, then through the photonic crystal-containing thin layer or by a other material reinforced with an effective negative refractive index, where the distance of the marks is greater than their diameter must be. As already mentioned above and explained in more detail below, can as Evaneszenzwellenerzeuger but also structures of a saturable Absorbers, super-dissolving Near field structures (super-RENS), solid-state immersion lenses or conical optical fibers are used with a needle point. In the versions The prior art has already been described that in the Contact lithography the amplitude mask in direct contact with the Layer of the photoresist must be located. Although this is already one size resolution achieved, however, the direct contact of the photoresist and affects the mask disadvantageous in the industrial application. On the other hand is in the inventive solution this strict requirement avoided or mitigated.

The inventive solution also usable in optical data storage. Also in this application can like it Variants - like already described above in optical lithography - used become. In an industrial application is in previously known Variants of optical or magneto-optical near-field data storage the nanometer-scale control of the distance of the tip a conical optical fiber or the solid immersion lens particularly critical. By means of the solution according to the invention this could Problem can be avoided. A variant of this is the use of built-in saturable Absorbers such as semiconductor or semiconductor quantum well layers to generate the waves of evanescence associated with the photonic crystal and the recording layer can be integrated into a common structure can. In place of the saturable Absorbers can also super-resolving Near field structures (super-RENS) are used. In other embodiments, as with the use of solid immersion lenses or optical conical fibers with a tip for generating the Evanescence waves could the critical requirements regarding the distance to the recording layer attenuated be as the reinforcement the waves of evanescence increase by two to three orders of magnitude Distance allowed. In addition, can by using photonic crystals with effective negative Refractive index as a means of amplification the generated evanescent wave fields improve the resolution and the signal-to-noise ratio and recording speeds, recording areas and storage capacities are increased.

One Another field of application of the solution according to the invention is optical nanomaterial processing, in the known prior art solutions according to the prior art spatial Resolution through the diffraction limit is given. This is contrary to application not the solution of the invention the case, thereby reducing the smallest possible structures to be machined allows becomes.

Also the application in scanning near-field microscopy (SNOM) leaves a increase the resolution and expect an improved signal-to-noise ratio.

Another field of application is confocal scanning microscopy (Scanning Confocal Microscopy), the resolution of which by irradiation of Ob Effect can be increased by means of more focused light below the diffraction limit.

The Invention is intended in the following embodiments closer by means of drawings be explained.

there demonstrate:

1 a schematic diagram of the arrangement according to the invention;

2 a schematic representation of an inventive arrangement with saturable absorber;

3 a schematic representation of another inventive arrangement for optical data storage with a non-linear super-resolution layer (super-RENS);

4 a schematic representation of another arrangement according to the invention for the magneto-optical data storage with a non-linear super-resolution layer (super-RENS);

5 a schematic representation of another inventive arrangement for optical lithography with amplitude mask;

6 a schematic representation of another arrangement according to the invention for the optical scanning lithography, for the near-field optical microscopy and optical nanomaterial processing with conical optical fiber with a peak in the imaging mode;

7 a schematic representation of another inventive arrangement for optical scanning lithography, for near-field optical microscopy and optical nanomaterial processing with a conical fiber with a peak in the collection mode;

8th a schematic representation of another inventive arrangement for optical data processing and optical lithography with a solid immersion lens;

9 Modeling results for an arrangement acc. 1 using the model of effective macroscopic negative refractive index media;

10 Modeling results for a photonic crystal used as a means for amplifying generated evanescent waves, comprising cylindrical tracheas in a square grid;

11 Modeling results for a photonic crystal used as amplification means for generated evanescent waves, comprising GaAs cylindrical rods arranged in a hexagonal lattice in air;

12 Modeling results for a photonic crystal used as amplification means for generated evanescent waves, comprising a square lattice of cross shaped air cavities arranged in Si;

13 schematic arrangement of a square grid of cross-shaped cavities of air, arranged in Si in a photonic crystal.

In 1 the arrangement according to the invention is shown schematically having an optical element as Evaneszenzwellenerzeuger EWE, eg a circular diaphragm B, for generating Seedevaneszenzwellen, and an Evaneszenzwellenverstärker EWV, for example a thin layer of a material having an effective negative refractive index, preferably a photonic crystal. As already mentioned, a light beam LB generated by a source is first focused on the diaphragm B by means of conventional methods. Here now evanescent fields in the near field area are generated as a seed field with sufficiently high amplitude. The diaphragm B has a diameter in the range of the wavelength of the light beam, whereby evanescent fields are generated with a smaller but for the amplification sufficiently large amplitude. In the evanescent wave amplifier EWV, which is located directly behind the optical element B in its near field region and has a thickness in the range of the wavelength, the evanescent fields are amplified, wherein their phases are approximately matched under optimized parameters of the photonic crystal and the ERA. The superimposition of all components of the field (both of the radiation components and of the amplified evanescent components) then yields, directly behind the evanescent wave amplifier EWV, a focused beam, a spot S, with an area whose magnitude is below the diffraction limit of λ / 2.

In the 1 The illustrated basic arrangement can be used for applications in which the distance to be controlled in the nm range between the diaphragm and the photonic crystal does not pose great technical difficulties. This could be the case, for example, both for laser nanomaterial processing and for specific variants of optical lithography. For applications such as optical data storage, but also in variants of optical lithography However, typically the use of a near-field aperture with a pitch smaller than the wavelength is typically a critical problem that is technically difficult to solve. To solve this problem are in the 2 to 8th Some embodiments show how the inventive solution for superfocusing can be implemented in these application fields.

2 1 schematically shows an embodiment of the invention without the use of a near-field diaphragm, as it can be used in optical and magneto-optical data storage or also optical nanolithography. Here, a structure having a layer of a saturable absorber SA as an evanescent wave generator, an evanescent wave amplifier EWV such as a photonic crystal having an effective negative refractive index and a recording layer AS in optical data processing or a photoresist PL in optical lithography is integrated. The photosensitization of the recording layer or of the photoresist can take place only in the spatial regions where the saturable absorber SA is made transparent by a laser beam LB, whereby a diaphragm effect with variable losses is produced. The laser beam LB is first focused by means of a lens L onto the layer with a saturable absorber SA. Since the laser beam LB consists of modulated light pulses, the information is transferred to the recording layer or the photoresist at the same time. The diameter of the incident beam LB is already in the region of its wavelength, so that the smaller transparent regions have a spatial extent in which evanescent fields are generated, which are amplified in the evanescent wave amplifier EWY. The focused spot S in the adjacent recording layer AS or the layer of the photoresist PL thereby has an extension below the diffraction limit. As saturable absorber SA can be used, for example, semiconductor layers or semiconductor quantum well absorber with the widest possible band gap, which can be integrated with the recording layer in the optical data processing or the layer of a photoresist. For wavelengths in the range of 400 nm, for example, ZnS or suitable compounds of this material can be used.

A another variant for generating evanescent waves in the near field is the use of super-resolution structures ("super-resolution Near-field structures, super-RENS), as already explained above. In the layers These structures are caused by the incident light as a result of intensity-dependent nonlinear Effect produces small diaphragm-like structures and scattering centers, which cause the formation of near fields. In one embodiment The invention is distinguished from the method described in the literature however, the evanescent waves produced in the super-RENS are not immediate for writing and retrieving data in optical data storage or the optical lithography, but previously by a photonic crystal reinforced with effective negative refractive index. The additional Integration of a deratigen photonic crystal improves the resolution and the signal-to-noise ratio in data storage or optical lithography clearly.

In 3 Fig. 1 schematically shows an arrangement with the use of such a super-RENS layer for the optical data storage by means of phase-changing acquisition layers. The incident light beam LB is focused by a lens L on the super-resolution structure. In this embodiment, the super-resolution structure consists of a layer of the substrate Sub, a protection film SF1, a super-RENS layer RENS, a second protection layer SF2, an evanescent wave amplifier EWV, for example, a photonic crystal having an effective negative refractive index, a dielectric layer DS1 , the structure-changing recording layer SAS, another dielectric layer DS2, a reflective layer RS and another protective layer SF3. In the layer RENS, the seed evanescence waves are generated by the incident radiation and further amplified by the layer EWV, which then cause structure-changing processes in a recording layer SAS by heating, with alternating crystalline and amorphous regions storing the information.

In the 3 arrangement shown for the application of the inventive solution in the optical data storage by means of structure-changing (phase-changing) processes can also be applied in the magneto-optical storage in an analogous manner.

In 4 the corresponding modified arrangement is shown, wherein instead of the structure-changing layer, a magneto-optical layer MOF is inserted and in addition a magnetic field is generated by the magnetic head MK.

Various embodiments of the solution according to the invention can also be used in optical lithography. In 5 is a Vaiante represented in which the marks of the mask itself act as a generator of evanescent fields. In this case, a light beam LB is focused by means of a lens L on the lithography mask LM, the Evaneszenzwellenerzeuger with a mask substrate MaSub, wherein the lithographic mask LM consists of alternating small transparent and opaque surfaces and the template for the inte formed circuit. These structures act like a diaphragm and generate the necessary seed evanescence fields, which are then amplified by the evanescent wave amplifier EWV, again for example a photonic crystal with an effective negative refractive index. The Evaneszenzwellenverstärker EWV is located immediately behind the photomask LM. The photoresist P arranged on a wafer W can thus be exposed with a focused beam whose illumination spot is smaller than the diffraction limit.

The inventive solution can also be used to increase the resolution and improvement of other known methods for optical raster lithography or for near-field optical microscopy (NOM). An arrangement in the "illumination mode" is in 6 shown in which a substrate Sub is irradiated with a surface structure OS. Here, a light beam LB is coupled into a conical optical fiber OF with a metallized tip MS tip. In contrast to the prior art is located at the end of the tip, which can have a diameter in the nm range significantly smaller than the wavelength and acts as a diaphragm, and an evanescent wave amplifier EWV, such as a photonic crystal with an effective negative refractive index. The evanescent wave amplifier EWV amplifies the evanescent waves, which improves resolution and signal-to-noise performance. The use of solid immersion lenses in optical data storage or optical lithography by means of the solution according to the invention can also be improved in an analogous manner.

7 shows a schematic representation of another arrangement according to the invention for optical scanning lithography, optical near-field microscopy and optical nano-material processing in the "collection mode" by irradiation of a substrate Sub with a surface structure OS as a means for generating evanescent A photonic crystal is provided as a means for amplifying the evanescent waves EWV The recording tip AFS of a measuring arrangement in the collection mode of a near-field microscope interacts with the amplified evanescent waves, which are converted into far-field radiation and for detection by means of photodetectors be used.

In 8th an arrangement is shown, wherein a light beam LB is coupled into a solid immersion lens FIL. As a result of their high refractive index, the spatial spectrum of the bundle LB within the lens FIL is substantially widened, so that evanescent waves penetrate the lower boundary of the solid-state immersion lens FIL and are amplified by the evanescent wave amplifier EWV in the immediate vicinity. This improves the resolution and the signal-to-noise ratio of a solid-state immersion lens.

To demonstrate the mode of action of the solution according to the invention, as described in 1 In its basic version, the diffraction of a spatial beam through a circular aperture is first calculated by means of the exact diffraction theory (for example described in Ann. Phys. 7, 157 (1950)). For the material of the panel, the two limiting cases of an ideally conducting and a perfectly absorbing surface were considered. To understand the mechanism of superfocusing, the medium with a negative refractive index in the context of an effective macroscopic model is first described as a homogeneous medium with an effective dielectric permeability ε and magnetic permeability μ. In the case of a photonic crystal, these parameters can be determined from the band structure of the crystal. Such a description in the range of negative refractive index is possible because of the isotropic shape of the surfaces of the same frequency in k-space. An optimal amplification of the evanescent fields is realized in the case when the effective media parameters satisfy the condition ε = μ = n = -1 or have only small deviations from this condition. The propagation coefficients for S- and P-polarized waves, respectively, can be obtained by applying the ordinary electric and magnetic field boundary conditions at a boundary layer with different effective ε and μ (see, for example, Appl. Phys. Lett., 82, 1506 (2003) )). The electric field after passing through the layer with negative refractive index can be calculated exactly by a spatial Fourier transformation. The modeling results are in 9 shown. The amplitudes of the Fourier components after passing through the aperture are in 9 (a) shown. The evanescence fields are those components that are outside the circle with the radius 2π / λμm the coordinate origin k = 0. As can be seen, these components have a very small but finite amplitude of the order of 10 ^-2 after passing through the aperture. The gain of these components by a factor of about 10 ² through the negative refractive index layer is in 9 (b) shown. By inverse Fourier transform it can be calculated from the transverse distribution of the spatial beam after passing through the layer with negative refractive index, which in 9 (c) is shown. As can be seen, the arrangement considered here focusses the radiation onto a spot with a diameter (FWHM) of approximately 0.15λ, ie below the diffraction limit. The dependence of the By of the focused output beam of the layer length for a diaphragm with a diameter of 1.0 λ is in 9 (d) shown. Due to the different boundary conditions for the S and P components, different spot diameters result in the direction parallel (filled circles) and perpendicular (filled triangles) to the incident electric field. The curves were calculated for the parameters ε = -1 + 10 ^-4 (i-1) and μ = -1 + 10 ^-4 (i-1), the smallest bundle diameter being 0.12 λ in the x-direction and 0 , 16 λ in the y direction, this corresponds to an area of the beam of 0.019 λ ² . With a 100 times greater deviation of the parameters ε and μ from the ideal value -1, with ε = -1 + 10 ^-2 (i-1) and μ = -1 + 10 ^-2 (i-1), a superfocusing with something larger spot diameter of 0.23 λ and 0.33 λ achieved, as in the curve with the open triangles or circles in 9 (d) is shown.

The Description of a microstructured material system, as described for physical realization of a negative refractive index necessary is, by a homogeneous medium with negative refractive index is one Approximation method that certain restrictions requires and through an analysis of concrete potential real materials added should be. As already explained, have photonic crystals with certain geometric structures and parameters the properties of a negative refraction, where the possible Frequency range can be extended to the optical range. The chosen one Frequency must be below the lowest band gap. You can also continue Photonic crystals with an effective positive refractive index due to resonances to bound photonic surface states amplify evanescent fields.

• (i) zylindrische Luftröhren (ε = 1) mit einem Radius von 0,35 a, die in einem Material aus Silizium (ε = 12 im IR-Bereich), in quadratischen Gitter mit der Gitterkonstante a angeordnet sind,
• (ii) zylindrische Stäbe aus Galliumarsenid (ε = 12,96) und einem Radius von 0,35a, die in einem hexagonalen Gitter mit dem Gitterabstand a in Luft angeordnet sind,
• (iii) quadratische Gitter von „+" -geformten Hohlräumen aus Luft, die in Silizium eingebracht sind und geometrische Parameter besitzen, wie sie 13(b) zu entnehmen sind.

In the following, three types of photonic crystals are considered:

• (i) cylindrical tracheas (ε = 1) with a radius of 0.35 a, which are arranged in a material of silicon (ε = 12 in the IR range), in square lattices with the lattice constant a,
• (ii) cylindrical rods of gallium arsenide (ε = 12.96) and a radius of 0.35a arranged in a hexagonal lattice with the lattice spacing a in air,
• (iii) square lattices of "+" shaped voids of air, introduced into silicon and possessing geometric parameters such as 13 (b) are to be taken.

First is to note that these photonic crystals have a bandgap in only have two dimensions (2D photonic crystals) while at the spread along the third dimension no effects caused by band gaps will be able to occur. Accordingly, a negative refractive index occurs only along this Directions on. That's why here is only the 2D propagation problem considered superfocusing only along the one transverse Direction, but not in the other direction. That focused bunch then shows a diameter only in a transverse direction below the wavelength. 3D photonic crystals with negative refraction (see, for example Appl. Phys. Lett. 81, 2352 (2002)) have already been successful demonstrated. It is expected that when using such crystals completely analogous, as it is here for the 2D crystals are shown, a super-focusing below the diffraction limit with respect to both transverse directions he follows. Furthermore, metallic photonic 3D crystals exist with a negative refraction in all three spatial dimensions.

First, the passage through an aperture whose material is assumed to be completely absorbent is calculated again. The electromagnetic field in the aperture can therefore be assumed equal to the incident field according to the Kirchhoff condition. The propagation through the 2D photonic crystal is calculated using the "corrected plane-wave expansion method" (described, for example, in "Optical properties of photonic crystals", Springer, 2001, pp. 81-90), where, due to the high contrast of the electric permeability in the photonic crystal a large number of coefficients of the plane waves (up to 10 ⁴ ) must be considered. The spatial structure of the focused beam at the output surface of the photonic crystal can then be obtained by the inverse Fourier transform.

The results for the three different structures (i), (ii) and (iii) are given in the 10 . 11 and 12 shown. Superfocusing is achieved in all three cases, as can be seen in the panels (b) and (c) of these figures. The smallest bundle diameter is 0.29λ for the structure (i); 0.25λ for (ii) and 0.25λ for (iii). An increase in intensity is only in the case of 11 (c) to recognize. In the other two cases, the reduction in intensity, despite the appearance of superfocusing, is explained by the strong reflection at the air - photonic crystal and photonic crystal - air interfaces. For interfaces of homogeneous air-silicon layers, the intensity reflection coefficient is 0.32. This explains the reduction in intensity at the output surface in the case of 10 (c) and 11 (C). The amplitudes (solid curves) and phases (dashed curves) of the Fourier components of the transverse distributions are in the

10 (B) 11 (Federation 12 (b) shown. In all cases, the significant contribution of the evanescent components in the spectrum with λk _x > 2π can be clearly seen. The spectrum is widest in the world Trap of the hexagonal lattice in 11 but has some noticeable side peaks in the spatial distribution due to the uncompensated phases ( 11 (C)). For structures (i) and (iii) in 10 and 12 the presence of strong side peaks in the spatial spectrum due to resonances in the transmission affects the spatial structure of the beam, the resonances affecting the superfocusing to approximately the same degree as the part of the evanescent components. In 10 (A) 11 (A) 12 (a) shows the transmission function for transition to the 0. Bragg order demonstrating the significant enhancement of the evanescent components by the photonic crystal layer with an effective negative refraction. 10 (D) 11 (d) and 12 (d) represent the dependence of the bundle diameters (FWHM) on the bundle diameter.

For the structure (iii) of a photonic crystal - shown in 13 (b) - is the spatial structure of the field during propagation through this photonic crystal in 13 (a) shown. As can be seen, the field penetrates from the top of the figure into the photonic crystal and undergoes a complex spatial redistribution within the crystal. Immediately at the backside of the crystal the radiation is focused on a bundle diameter of 0.3 λ (see 13 (A)). As can be seen, with the subsequent propagation of the bundle by air behind the photonic crystal, the evanescent components are lost again, whereby the transverse distribution widens again.

Claims (46)

Method for focusing electromagnetic Radiation below the diffraction limit, at least comprising the steps - Focus an electromagnetic radiation beam incident from a source by conventional means, - Generation evanescent wave fields of the electromagnetic to be focused Radiation as sea evanescence fields and - Reinforcement of these Seedevaneszenzwellen in the immediate spatial Close to her Generation, wherein the phases of the reinforced Evaneszenzfelder each other are adjusted. The method of claim 1, wherein an optical Element for generating evanescent wave fields of the to be focused electromagnetic radiation, here as Evaneszenzwellenerzeuger is used. A method according to claim 2, wherein said evanescent wave generator a panel with a size in the range or below the wavelength the electromagnetic radiation to be focused is used. The method of claim 3, wherein a circular aperture is used. The method of claim 3, wherein a square Aperture is used. A method according to claim 2, wherein said evanescent wave generator an annular Aperture with an outer radius in the range or below the wavelength of the radiation to be focused is used. A method according to claim 2, wherein said evanescent wave generator a double or quadruple aperture with a mutual distance in the range or below the wavelength of the radiation to be focused is used. A method according to claim 2, wherein said evanescent wave generator a saturable Absorber is used. A method according to claim 8, wherein said saturable Absorber a semiconductor layer is used. A method according to claim 8, wherein said saturable Absorber a semiconductor quantum well structure is used. The method of claim 9 or 10, wherein as the semiconductor material ZnS or a compound of this material, such as CdZnSe or CdZnS, is used. A method according to claim 2, wherein said evanescent wave generator a super-resolution near field structure (super-RENS) is used. The method of claim 12, wherein the super-resolution near-field structure consists of an Sb film embedded in two SiN layers, or AgO _x , PtO ₂ or PdO _x embedded in two ZnS / SiO ₂ layers. A method according to claim 2, wherein said evanescent wave generator Marks are used in the structures of a photomask. The method of claim 14, wherein the marks Cr absorbers exist. A method according to claim 9 or 10 and 14, wherein as Evaneszenzwellenerzeuger semiconductor layers with the brands a photomask are combined. A method according to claim 2, wherein said evanescent wave generator a tip of a conical optical fiber is used. A method according to claim 2, wherein said evanescent wave generator a solid immersion lens is used. Method according to Claim 1, in which the amplifier is the Evanescence waves in the immediate vicinity of their generation a thin layer of a photonic crystal having a thickness in the wavelength range of to be focused electromagnetic radiation and an effective negative refraction in the range of the frequency to be focused electromagnetic radiation is used. The method of claim 19, wherein a photonic Crystal with a periodic arrangement of rods with a high refractive index is used in a hexagonal arrangement. The method of claim 19, wherein a photonic Crystal with cylindrical cavities is used in a periodic square arrangement. 22 The method of claim 19, wherein a photonic crystal comprising a square grid of cross-shaped cavities Air arranged in a material of high refractive index, is used. The method of claim 19, wherein a photonic Crystal, the whole bandgaps in three dimensions is used. The method of claim 19 and 23, wherein a metallic photonic crystal is used. Arrangement for carrying out the method according to claim 1 for focusing electromagnetic radiation below the diffraction limit, at least comprising means for generating evanescent wave fields of to be focused electromagnetic radiation as Seedevaneszenzfelder - one Evanescence Wave Generator (EWE) - and Means for reinforcement These Seedevaneszenzwellen (EWV) in the immediate vicinity of their Generation, where at the same time the phases of the enhanced evanescent fields and the means to enhance the evanescent fields (ERA) in the near field region of the Evaneszenzwellenerzeugers (EWE) arranged is. An assembly according to claim 25, wherein the evanescent wave generator (EWE) a diaphragm (B) of a size in the range or below the wavelength is to be focused electromagnetic radiation. Arrangement according to claim 26, wherein the aperture is circular is. Arrangement according to claim 26, wherein the aperture is square is trained. Arrangement according to claim 26, wherein the diaphragm is annular with an outer radius formed in the region or below the radiation to be focused is. Arrangement according to Claim 26, in which the diaphragm is designed as Double or quadruple aperture with a mutual distance in the Range or below the wavelength of the radiation to be focused is trained. An assembly according to claim 25, wherein the evanescent wave generator (EWE) a saturable absorber (SA) is. Arrangement according to claim 31, wherein the saturable Absorber (SA) consists of a semiconductor layer. Arrangement according to claim 31, wherein the saturable Absorber (SA) consists of a semiconductor quantum well structure. Arrangement according to claim 32 and 33, wherein the semiconductor material ZnS or ZnSe or compounds thereof. An assembly according to claim 25, wherein the evanescent wave generator (EWE) a super-resolution Near field structure (super RENS) is. The device of claim 35, wherein the super-resolution near-field structure is formed of a Sb film embedded in two SiN layers, or AgO _x , PtO _2, or PdO _x embedded in two ZnS / SiO ₂ layers. An assembly according to claim 25, wherein the evanescent wave generator from marks of a mask (LM) is formed. Arrangement according to claim 37, in which the marks are made Cr absorbers are formed. Arrangement according to claim 32 or 33 and 37, wherein the evanescence wave generator of a semiconductor layer and the Marks a photomask is formed. An assembly according to claim 25, wherein the evanescent wave generator is a tip (MS) of a conical optical fiber (OF). Arrangement according to claim 25, wherein the Evaneszenzwellenerzeuger is a solid immersion list (FIL). Arrangement according to Claim 25, in which the means for reinforcing the Evanescence waves (ERA) in the immediate vicinity of their generation a thin layer of a photonic crystal having a thickness in the wavelength range of to be focused electromagnetic radiation and an effective negative refraction in the range of the frequency to be focused electromagnetic radiation is. Arrangement according to claim 42, wherein the photonic Crystal a periodic array of rods with a high refractive index in a hexagonal arrangement. Arrangement according to claim 42, wherein the photonic Crystal cylindrical cavities in a periodic square arrangement. Arrangement according to claim 42, wherein the photonic Crystal a square grid of cross-shaped cavities Air, which is arranged in a material with high refractive index are. Arrangement according to claim 42, wherein the photonic Crystal complete bandgaps in all three dimensions. Arrangement according to claim 42 and 46, wherein the photonic Crystal is a metallic one.