DE102018003312A1 - Method for introducing structures or material modifications by means of the top-down method - Google Patents

Abstract

The invention relates to a method for introducing structures or material modifications by means of the top-down method in a region below the diffraction limit of laser beams in the order of the lower three-digit nanometer range in at least one dimension. The object is achieved in that in optically stimulable and detachable material systems having an altered (transient) absorption behavior in the excited state, in a first step, a laser beam excitation in a region (a and b) of the surface to be machined and / or in a predetermined depth of material is carried out, in a second step a de-excitation in the first step excited edge regions (b) takes place wherein the inner region (a) remains excited and in a third step of the so prepared after the first and second step excited inner region (a) irradiation is exposed to a further laser beam in such an expansion and intensity distribution that only in the excited interior region (a) by utilizing the altered (transient) absorption in the interior region (a) by excited state absorption (ESA) such a high energy input by means of a laser beam pulse is caused only indoors (a) a machining effect is achieved, whereas the edge portions (b) remaining after the second step are unchanged, i. without processing effect, remain.

Description

The invention relates to a method for introducing structures or material modifications by means of the top-down method in a range below the diffraction limit of laser beams in the order of the lower three-digit nanometer range and smaller in at least one dimension in optically stimulable and dense material systems that a changed have (transient) excited state absorption behavior (Excited State Absorption).

(N = Anzahl der notwendigen Photonen zur Überwindung der Bandlücke) realisierbar, welche jedoch für typische λ-Werte ebenfalls in der Größenordnung von etwa 200 nm liegen. Zahlreiche Anwendungen auf den Gebieten der Nanotechnologie, Photonik, Plasmonik, Photovoltaik und Optoelektronik erfordern jedoch Strukturgrößen, die nicht durch λ und der damit verbundenen unteren Grenze der Fokussierbarkeit eingeschränkt sind.Both the laser material processing (LMB) and the lithography (LG) by laser in the sense of top-down approach based on a material modification, such as the material removal, reflow processes, etc. Here, the LMB / LG is due to the wide range of radiation sources in many different areas have penetrated. These radiation sources are characterized by a variety of parameters that enable power classes from mW to GW and pulse lengths from fs to cw operation. However, in terms of spatial resolution, the LMB / LG is essentially limited to the bottom due to the focusability of the processing beam, which is largely determined by the beam quality and wavelength. The diffraction-limited structure quantities d _Ls = k · λ / NA (NA = n · sinα Numerical Aperture) that can be realized in this way are taking into account a system-dependent proportionality factor k (k = 0.7-1) with the aid of direct laser structuring / modification and air as surrounding Medium depending on the laser wavelength used λ in the range of about 200 nm (visible) or 100 nm (ultraviolet). Further approaches to spatial constraints, especially in dielectrics and semiconductors, are based on threshold and non-linear multiphoton processes (MPP), in which only the highest-intensity inner part of a Gaussian laser spot in the focus contributes to the processing. Although in this way structure sizes are below the diffraction limit $d_{MPP}=k*\lambda \text{/}\left(\text{N / A}*\sqrt{N}\right)$

(N = number of necessary photons to overcome the band gap) can be realized, which, however, are also on the order of about 200 nm for typical λ values. However, numerous applications in the fields of nanotechnology, photonics, plasmonics, photovoltaics and optoelectronics require feature sizes that are not limited by λ and the associated lower limit of focusability.

Thus, the problem of the LMB / LG in its limited resolution by the diffraction-limited focusability of the laser beam. However, this can not be avoided by currently known methods. In order to generate smaller structures via the top-down approach, the prior art thus uses other material processing methods, such as e.g. Electron or ion beam lithography and UV, EUV, and X-ray lithography usually used. Their disadvantages, however, are the vacuum technology required for this, which makes these methods very expensive and time-consuming and, on the other hand, limits the size of the components to be machined. In addition, especially in UV and EUV lithography mainly only reflective optics can be used, which make these processes technologically highly sophisticated. Furthermore, some of these methods require masks that can be imaged as well as placed directly on the material. However, since these masks are initially also e.g. On the one hand, the effort increases enormously on the one hand, and on the other hand, these methods are very inflexible with respect to changed structures to be introduced, which then require new mask sets.

The same limited resolution problem also existed in optical microscopy, where the Abbe limit d _m = 0.5 * λ / NA was the lower limit of the resolution. Thus, only a maximum resolution of about 200 nm can be achieved in the visible spectral range (at λ = 400 nm). This limit initially also applies to laser scanning microscopy. The overcoming of this limit by optical microscopy was achieved for the first time by the microscopy technique of stimulated emission depletion (STED) [eg: Paper: SW Hell and J. Wichmann, Opt. Lett. 19 (1994) 780-782 . TA Klar and SW Hell, Opt. Lett. 24 (1999) 954-956 , WO 2012069076 A1 . WO002009024529A1 ]. In this case, fluorescence molecules / particles are targeted by means of a Gaussian laser spot and excited by a donut mode, so that the fluorescent and thus considered range can be reduced below the diffraction limit of 200 nm. In this way, a resolution of less than 5 nm is possible. [ E. Rittweger, KY Han, SE Irvine, C. Eggeling, and SW Hell, Nat. Photon. 3 (2009) 144-147 ., D. Wildanger, BR Patton, H. Schill, L. Marseglia, JP Hadden, S. Knauer, A. Schonle, JG Rarity, JL O'Brien, SW Hell, and JM Smith, Adv. Mater. 24 (2012) OP309-OP313 .] However, for LMB / LG this STED microscopy represents a maximum of a nondestructive characterization method, which makes it possible to optically characterize the topography. For the LMB / LG per se, the STED microscopy is not suitable and thus represents a solution of a remote area compared to the present invention area.

Furthermore, in the prior art, a modification of the STED technology for STED lithography [Paper: TA Klar, R. Wollhofen, and J. Jacak, Phys. Scr. T162 (2014) 014049 / WO002011090710A2 . WO002015020814A1 . WO002011089157A2 . US000008432533B2 , US020120092632A1 / Expanding the STED Principle to Multicolor Imaging and Far-Field] Optical Writing. Although this method allows a generative production method for photopolymerizable polymers by means of a BOTTOM-UP approach, which allows the realization of structure sizes in the two-digit nm range, but does not pursue the conventional TOP-DOWN approach of LMB / LG, which removes the material by means of a laser or edited / modified. For this there is currently no approach that allows structuring largely independent of the diffraction limit. In this respect, this solution should only be mentioned here, which with the present invention but otherwise has nothing in common.

The invention is therefore based on the object, a method for introducing structures or material modifications by means of the top-down method in a range below the diffraction limit of laser beams in the order of the lower three-digit nanometer range and smaller in at least one dimension in optically on and abgebregbare Material systems that have an altered (transient) absorption behavior in an excited state (ESA-Excited State Absorption) indicate, which with a considerably low technical effort, compared to the above-cited prior art, manages and which no size limitations of the dimensions in the subject to be processed materials.

The object is solved by the characterizing features of claim 1. Advantageous embodiments are the subject of the respective subsequent claims.

• - in einem ersten Schritt eine Laserstrahlanregung in einem Bereich (a und b) der zu bearbeitenden Oberfläche und/oder in einer vorgebbaren Materialtiefe vorgenommen wird,
• - in einem zweiten Schritt eine Abregung in nach dem ersten Schritt angeregten Randbereichen (b) erfolgt und
• - in einem dritten Schritt der so nach dem ersten und zweiten Schritt präparierte Innenbereich (a) einer Bestrahlung mit einem weiteren Laserstrahl in einer solchen Ausdehnung und Intensitätsverteilung ausgesetzt wird, dass nur der Innenbereich (a) durch eine angeregte Zustandsabsorption (ESA) zusätzlich selektiv angeregt wird, wodurch ein so hoher Energieeintrag mittels eines Laserstrahlpulses hervorgerufen wird, dass ausschließlich im Innenbereich (a) eine Bearbeitungswirkung erzeugt wird, wohingegen die nach dem zweiten Schritt verbliebenen Randbereiche (b) und darüber hinaus unverändert, d.h. ohne Bearbeitungswirkung, verbleiben,

wobei die zeitliche Abfolge genannter drei Schritte in einem vom zu bearbeitenden Material abhängigen, vorgegebenen Zeitintervall vorgenommen wird, in dem die Wirkungen des ersten und zweiten Schritts sowohl wechselseitig als auch in Bezug auf den dritten Schritt noch hinreichend ausgeprägt im zu bearbeitenden Material vorliegen.The essence of the present invention is that

• in a first step, a laser beam excitation in a region ( a and b ) of the surface to be processed and / or in a predefinable material depth is made,
• in a second step, a de-excitation in edge regions excited after the first step ( b ) takes place and
• in a third step, the interior area thus prepared after the first and second steps ( a ) is exposed to an irradiation with a further laser beam in such an expansion and intensity distribution that only the interior area ( a ) is additionally selectively excited by an excited state absorption (ESA), whereby such a high energy input is caused by means of a laser beam pulse that exclusively in the interior ( a ) a machining effect is produced, whereas the edge areas remaining after the second step (FIG. b ) and, moreover, unchanged, ie without processing effect, remain,

wherein the temporal sequence of said three steps is performed in a predetermined time interval depending on the material to be processed, in which the effects of the first and second steps are mutually and in relation to the third step still sufficiently pronounced in the material to be processed.

The proposal underlying the present invention consists in the targeted utilization of Excited State Absorption (ESA). It is exploited here that excited material regions have a changed (transient) absorption behavior compared to unexcited material regions. This alone would not lead to any overcoming of the diffraction-limited LMB / LG, since this limit is subject to both the necessary excitation and processing laser beam. If one connects this effect of the ESA but now with the STED technology, so can be generated by the LMB / LG structure sizes below the diffraction limit, as found in the present invention, in the form that by the STED technology through the targeted Superimposition of a Gaussian excitation beam and a Abregungsstrahles, for example. In donut mode, the spatial size of the excited region is set specifiable (see. 1a , middle figure B). Due to the changed optical absorption behavior, only this excited region is processed / modified by a further Gaussian laser spot by means of the ESA (cf. 1a , right ). This processing / modification can be done in a predeterminable many ways, for example: melting, evaporation, oxidation, material density changes, etc. Thus, although in principle a LMB / LG takes place in the conventional sense, but the resolution of these known methods is no longer due to the diffraction-limited focusing of all three laser beams (STED: excitation, depletion laser, ESA processing laser), but only through the inner, narrow excited area (area a , see. 1 b ) certainly.

In order to be able to use the method according to the invention, it is first a prerequisite that the materials to be processed are both STED and ESA-capable.
Under STED capability is to be understood that the respective material systems (MS) can be stimulated optically stimulated and optically stimulated. Such material systems may be, for example: all fluorescent materials (fluorescent molecules, polymers, particles, etc.), optically pumped laser materials (rare earth doped crystals or glasses), (direct) semiconductors, semiconductor particles such as quantum dots in a matrix (Glass, dielectrics, semiconductors, polymers), etc., so a variety of technically interesting materials.

The ESA capability of the MS used must be pronounced in such a way that the optical properties in the region of the material which is in the excited state have changed so that a structuring and / or material modification, for example in the sense of: melting , Ablation (evaporation, sublimation), thermally induced refractive index change, density change, change in solubility or etching ability, photochemical reactions, charge transfers, the generation of silver nuclei, etc. are possible. Depending on the MS, the individual mechanisms of the ESA may differ and take place, for example, via: interband, intraband transitions, avalanche effects, Coulomb explosion, level-level transitions, level-band transitions, particle-plasmon polaritons, etc. All these types of ESA processes include all STED-capable materials such as: all fluorescent materials (fluorescence molecules, polymers, particles, etc.), optically pumped laser materials (rare earth doped crystals or glasses), (direct) Semiconductors, semiconductor particles such as quantum dots in a matrix (glass, dielectric, semiconductor, polymer), etc., have an ESA potentially useful for material structuring or material modification.
Thus, it can initially be stated in summary that all material systems which are optically attractable and excitable (STED-capable) and have an ESA are fundamentally suitable for the SDW method (SDW: sub-diffraction writing) proposed here according to the invention.

Since neither pure metals nor optically inactive polymers and optically inactive dielectrics are STED- as well as ESA-capable, they are initially not directly suitable for direct sub-diffraction writing by means of the method according to the invention. However, structuring and material modification of such material classes below the diffraction limit can indirectly, likewise using the present invention, by the structuring / modification of a STED and ESA-capable protective layer with subsequent etching processes or the like. respectively. In addition, e.g. a method known as Dynamic Release Layer Laser Induced Forward Transfer, which transfers these materials to a substrate in feature sizes below the diffraction limit. Here, the "Dynamic Release Layer" is both STED and ESA-capable and thus the actual material system, which can be edited by means of the novel SDW method proposed here. It thus serves as an auxiliary layer to allow transmission of feature sizes independent of the diffraction limit. About this intermediate step so also other materials are accessible to the method according to the invention.

Certain conditions are also bound to the lasers used in the proposed method. In general, it can first be stated that for the SDW method described here, the different laser beams (startup and de-excitation as well as ESA processing) can be operated predominantly only pulsed and in a wavelength, pulse length, and pulse spacing relationship adapted to the material. The only sub-process and thus also the laser operation, which under certain conditions can be carried out with continuous cw irradiation, is that of the de-excitation (referred to as a second step in the context of the invention).
Furthermore, in order to overcome the diffraction limit in the method proposed according to the invention, the sequence of individual pulses must be regarded as a pulse ensemble which only enables an increased resolution of the LMB / LG if, depending on the material system to be processed, in a very specific time and intensity and wavelength dependent relationship applies to each other. These individual parameters will be explained in more detail below:

The individual wavelengths must be adapted to the respective material system (MS) both for the arrival and the de-excitation. In this case, it is true that in the majority of cases the de-excitation wavelength is longer than the excitation wavelength, so far no excitation takes place via multiphoton processes. The tables below give examples of different wavelength ranges of excitation (single-photon excitation, no multiphoton excitation) and de-excitation as well as ESA processing for different material systems. MS1: direct semiconductors, MS2: semiconductor nanoparticle precipitates in a matrix, MS3: rare earth doped crystals or glasses and MS4: dyes as polymer or in a polymer matrix MS1 MS2 Al _x Ga _1-x As In _x Ga _1-x N GaAs PbS CdSe λ _an [nm] <λ _Ab <λ _Ab <λ _Ab <λ _Ab <λ _Ab λ _Ab [nm] 606-873 370-1240 400-816 496-3024 344-717 λ _ESA [nm] > λ _Ab > λ _Ab > λ _Ab > λ _Ab > λ _Ab MS3 Nd ³⁺ Yb ³⁺ He ³⁺ Ce ³⁺ Ti ³⁺ λ _an [nm] 750 942 940 248-353, 500 490 809 967-981 λ _Ab [nm] 900, 946, 1050-1410 1009-1042 850, 1540, 2700-2900 280-333, 550 790, 650-1180 λ _ESA [nm] ≠ λ _Ab , λ _An ≠ λ _From λ _An ≠ λ _Ab , λ _An ≠ λ _Ab , λ _An ≠ λ _Ab , λ _An MS4 Red Perylimide Dye Rhodamine 6G λ _an [nm] 500-550 525-545 λ _Ab [nm] 600-650 625-645 λ _ESA [nm] ≠ λ _Ab , λ _An (eg:> 650) ≠ λ _Ab , λ _An , (eg: 1055)

The above tables are not a limitation of the invention only to the material classes listed there, since the exact choice of the expertise and specific uses and needs of the average person skilled in subject. Thus, under certain circumstances, the de-excitation wavelength can be selected in the same wavelength as that of the excitation. In addition, utilizing multiphoton processes, the excitation wavelength may be greater than the de-excitation wavelength. Above all, this plays a decisive role in a LMB or material modification in the volume of the material to be processed. The ESA machining wavelength must be selected so that it is not or only minimally absorbed by the optically unexcited area of the material. Since the ESA processing pulse is responsible for the actual material processing / modification, it has a relatively high intensity. Secondary effects such as multiphoton absorption in the optically unexcited or optically excited region (see area II and III in 1b ) of the MS, it often makes sense to choose the wavelength of the ESA processing laser greater than the wavelength of the excitation laser (see the tables above). However, this does not apply to all MS or the respective process used for the ESA, such as interband, level-level, level-band transitions, particle-plasmon polaritons, etc. Nevertheless, in the unexcited as well again depressed area of the MS (area III and II 1 b ) no linear and no non-linear (eg via Mehrphotonenabsorption) absorption of the ESA laser machining done to the extent that an undesirable material processing in just these areas is made possible. However, this does not exclude that the ESA machining wavelength can not also correspond to the de-excitation wavelength. The exact choice is again subject to the average knowledge of the expert using the proposed method.

wie sie bereits in [ S. W. Hell, K. Willig, M. Dyba, S. Jakobs, L. Kastrup, and V. Westphal, in Handbook of biological confocal microscopy, edited by J. B. Pawley (Springer, New York, 2006), p. 571 - 579 .] angegeben wird. Das heißt, dass die räumliche Ausdehnung des angeregten Innenbereiches (a) durch die Variation der Intensität der Abregung gemäß Schritt 2, gemäß vorliegender Erfindung, in Verbindung mit dessen Pulslänge (bei gepulstem Schritt 2), Strahlformung, Strahlfokussierung und Pulsabstand zu Schritt 1 sowie unter Berücksichtigung der materialspezifischen Sättigungsintensität ISAT und der Anregung gemäß Schritt 1 gezielt eingestellt wird und somit die räumliche Ausdehnung der Materialmodifikation unter Berücksichtigung von Schritt 3 vorgenommen wird. Die Intensität des ESA-Bearbeitungspulses ist hingegen so zu wählen, dass ausschließlich eine Materialbearbeitung/-modifikation im optisch angeregten Bereich (vgl. Bereich a 1 b) mittels ESA und möglichen sekundären Prozessen (Coulomb-Explosion, Avalanche-Prozesse usw.) erfolgt, jedoch nicht im optisch nicht angeregten bzw. wieder abgeregten Bereich (vgl. Bereiche III und II 1 b), und zwar weder durch lineare, noch durch Mehrphotonenprozesse mit anschließenden Sekundärprozessen.Another prerequisite for the successful application of the method according to the invention relates to the respective intensities of the lasers used for the stimulation and de-excitation, which are to be chosen so that, although an optical effect takes place, just the arrival or de-excitation, but no material processing / modification in terms of: melting, ablation (evaporation, sublimation), (thermally-induced) refractive index change, density change, change of solubility or etching ability, photochemical reactions, charge transfers, the generation of silver nuclei etc. are possible, not even Mehrphotonenprozesse. However, the intensity of the excitation must be chosen so high that subsequent ESA processing in the optically excited center (cf. a 1 b ) of the spatially superimposed laser beam spots is possible. Furthermore, for the magnitude of the intensity of the excitation beam (pulse) I _STED (in relation to the material-specific saturation intensity I _SAT ), it must be so strong that its size can be used to determine the spatial extent of the inner excited region, according to Relationship: $$d_{STeD}=\frac{0.5*\lambda }{NA*\sqrt{1+\raisebox{1ex}{$I_{STeD}$}\!\left/ \!\raisebox{-1ex}{$I_{SAT}$}\right.}}$$

as already stated in [ SW Hell, K. Willig, M. Dyba, S. Jakobs, L. Kastrup, and V. Westphal, in Handbook of biological confocal microscopy, edited by JB Pawley (Springer, New York, 2006), p. 571 - 579 .]. This means that the spatial extent of the excited interior ( a ) by the variation of the intensity of the de-excitation according to step 2, according to the present invention, in conjunction with its pulse length (at pulsed step 2), beam shaping, beam focusing and pulse distance to step 1 and taking into account the material-specific saturation intensity ISAT and the excitation according to step 1 targeted is set and thus the spatial extent of the material modification is made taking into account step 3. The intensity of the ESA machining pulse, on the other hand, should be selected so that only material processing / modification in the optically excited region (cf. a 1 b ) by means of ESA and possible secondary processes (Coulomb explosion, avalanche processes, etc.), but not in the optically unexcited or re-excited region (cf. III and II 1 b ), neither by linear nor by multiphoton processes with subsequent secondary processes.

ergeben sich z.B. für Gläser oder Al₂O₃ als Matrixmaterialien bei einer Pulslänge τ von 3-5 ns Wärmeeinflusszonen in der Größe von Lth < 120 nm bzw. L_th < 450 nm. Somit sind vor allem für den ESA-Bearbeitungspuls möglichst kurze Pulslängen von Vorteil, da unterhalb 1 ps eine Wärmeleitung während der Wechselwirkungszeit vernachlässigt werden kann. Da der Abregungslaserstrahl bei verschiedenen MS sowohl gepulst, als auch cw betrieben werden kann, ist die Pulslänge hier eher von untergeordneter Bedeutung. Dennoch muss auch hier berücksichtigt werden: sollte der Abregungslaser gepulst betrieben werden, so muss der Puls im Zusammenspiel mit der Intensität so lang sein, dass eine stimulierte Abregung in gewünschter Höhe erfolgt. Darüber hinaus ist ein cw-Betrieb des Abregungsstrahles kaum möglich, wenn Ab- und Anregungspuls die gleiche Wellenlänge besitzen, insofern die Anregung nicht über Mehrphotonenprozesse erfolgt. Denn bei einer Anregung über Mehrphotonenprozesse kann unter Umständen auch eine cw-Abregung bei gleicher Wellenlänge erfolgen.Likewise, the used laser pulse lengths are within the scope of the invention to be complied with proviso, which is dependent on the material to be processed and based on this material specification. The pulse length plays a crucial role, especially in the excitation and ESA processing pulse. Thus, the excitation pulse should be on the order of magnitude or shorter than the lifetime of the optically excited state of the respective MS. Since an optical excitation due to the Stokes shift is always associated with a certain heat input into the material, even if the essential energy release occurs following excitation via photons (fluorescence), its length must be adapted to the respective MS. Thus, the excitation pulse must be chosen so short that an excessive heat input is avoided in the surrounding material. In addition, secondary effects such as charge carrier diffusion must be prevented from increasing the excited region beyond the spatial intensity distribution of the excitation pulse. The decisive influence with its pulse length has the ESA processing pulse used according to the invention. Since this pulse is responsible for the actual material processing / modification and thus for the greatest energy input into the workpiece or MS, the shortness of the ESA processing pulse must prevent that by heat conduction and other secondary effects (charge carrier diffusion) actually through the STED process limited machining area is inadvertently increased. Thus, the ESA machining pulse should be long enough, in combination with the strength of the ESA and the laser beam intensity, to result in material processing / modification in the STED area (d _STED ) (see 1b Area I ). In general, the ESA pulse length should also be of the order of magnitude or shorter than the lifetime of the excited states, in order to avoid unnecessary material stress, for example due to heat conduction. With ${\text{L}}_{\text{th}}=2\sqrt{{\text{k}}_{\text{w}}\cdot \mathrm{\tau }}$

result for example for glasses or Al ₂ O ₃ as matrix materials at a pulse length τ of 3-5 ns heat affected zones in the size of Lth <120 nm and L _th <450 nm. Thus, especially for the ESA processing pulse pulse lengths are as short as possible advantageous because below 1 ps, heat conduction during the interaction time can be neglected. Since the Abregungslaserstrahl in different MS both pulsed, and cw can be operated, the pulse length is here rather of minor importance. Nevertheless, it must also be taken into account here: should the depletion laser be operated pulsed, the pulse in conjunction with the intensity must be so long that a stimulated de-excitation occurs at the desired level. In addition, a cw operation of the Abregungsstrahles is hardly possible if Ab- and excitation pulse have the same wavelength, insofar as the excitation does not take place via Mehrphotonenprozesse. For excitation via multiphoton processes under certain circumstances, a cw-depletion can take place at the same wavelength.

The following table shows examples of the parameter range of the laser pulses used with regard to pulse energy, pulse duration and wavelength in pure STED microscopy and pure processing without prior STED excitation. technology Pulse energy [nJ] Pulse length [ps] Wavelength λ [nm] STED excitation 0.039-2075 0.1-7.5 · 10 ⁶ 480, 780, 800, 810, 820 STED de-excitation 0.5-1.25 50-250 375, 532, 800, 500-600 processing 10 ¹ -10 ⁶ 0.1-10 ⁶ 200-10600

If the pulse ensemble consists of three individual pulses, the following pulse sequence must be ensured in the context of the present invention: first pulse: excitation pulse, second pulse: de-excitation pulse, third pulse: ESA processing pulse. Although a certain temporal overlap of the pulses is possible, their temporal intensity focuses must be temporarily shifted from each other. In this case, it is also necessary that the time interval between the pulses is chosen so that the excited region after relaxation processes on the one hand again can be de-energized and on the other hand, the time interval between excitation and processing pulse is not too large, so that even one ESA is possible. This means that the time interval between arrival and ESA processing pulse is within the life of each optically excited MS. This can be very different for the respective MS, as illustrated by the following two tables with different examples. ion matrix material Excitation [nm] Emission [nm] Lifetime [ms] levels Nd ³⁺ YAG, glass, YVO ₄ 809, 750 900, 946, 1053, 1064, 1330, 1050-1410 0.1-0.34 4 He ³⁺ YAG, YAlO ₃ , YSGG, glass 940 850, 1540, 2700-2900 0.12, 5.3, 1.2 3 Yb ³⁺ YAG, glass 942, 960, 967-981 1009-1042 0.951, 1.54 3 Ce ³⁺ LaF ₃ , CaF ₂ , LiCaAIF ₆ , YAG, glass 248-353, 500 280-333, 550 (20-65) · 10 ^-5 4 Cr ³⁺ Ruby (Al ₂ O ₃ ), BeAl ₂ O ₄ , LiSrAlF, glass 410.590 693, 694, 780-920, 701-818 3 3 Ti ³⁺ Sapphire (Al ₂ O ₃ ) 490 790, 650-1180 0,003 4

In the above table, lifetimes and other properties of various rare earth ions in different matrix materials and in the following table the different bulk semiconductors and their nanoparticle precipitations are exemplified. semiconductor Band gap E _g (bulk) Band gap E _g (quantum dot) D _P lifespan [Ev] [Nm] [Ev] [Nm] [Nm] [Ns] CdS 2.42 512 2.7 to 4.6 270-459 0.5 to 2.6 10 CdSe 1.73 717 1.9-3.6 344-653 0.5 to 5.3 25 CdTe 1.44 861 1.65 to 2.2 564-751 1.6 to 4.6 2-7 GaAs 1.52 816 2.25 to 3.1 400-551 1.85 to 3.85 0.1-1 PbSe 0.28 4428 0.35 to 1.2 1033-3542 0.8 to 16.9 200-800 PbS 0.41 3024 0.5-2.5 496-2480 1.5 to 13.0 600-1000

Aufgrund dessen, dass der Abregungslaser auch cw betrieben werden kann, muss in diesem Fall nur die zeitliche Zuordnung, dass zuerst der Anregungspuls und dann der ESA-Bearbeitungspuls folgen eingehalten werden. In Anbetracht dessen ist es bei einem zeitlich langen Abregungspuls auch möglich, dass nur der Anregungspuls oder der ESA-Bearbeitungspuls sowie die Abfolge von zuerst Anregungs- und dann ESA-Bearbeitungspuls innerhalb dieses Abregungspulses liegt, der somit als „quasi-cw Puls“ wirkt.In addition, the time between pulses should be so short that excessive charge carrier diffusion and heat conduction is prevented. Because these would destroy the spatial restriction on the excitation area defined by the STED technology. In contrast to the excited systems / ions in rare earth ions and crystalline precipitation (due to their reduced size), which are predominantly spatially localized, an excessive charge carrier diffusion has to be considered, especially for bulk semiconductors (diffusion lengths> 1μm). The effect of heat affected zones must be taken into account by a timely pulse spacing in combination with the pulse length for all MSs $\left({\text{L}}_{\text{th}}=2\sqrt{{\text{k}}_{\text{w}}\cdot \mathrm{\tau }}\right),$

Due to the fact that the depletion laser can also be operated cw, in this case, only the temporal assignment that first follows the excitation pulse and then the ESA processing pulse must be observed. In view of this, it is also possible for a time-long excitation pulse that only the excitation pulse or the ESA processing pulse and the sequence of first excitation and then ESA processing pulse lies within this de-excitation pulse, which thus acts as a "quasi-cw pulse".

With the above instructions and suggestions the expert is thus given all provisos that he can apply the inventive method to his concrete material systems to be processed without further inventive step. Nevertheless, the inventive method will be explained in more detail with reference to the following exemplary embodiments for various exemplary applications.

• 1a die grundsätzliche Abfolge der einzelnen Verfahrensschritte zur Durchführung eines Sub-Diffraction-Writings vorliegender Erfindung;
• 1b die resultierenden Bereiche in der wirksamen Bearbeitungszone;
• 2 eine beispielhafte Anordnung zur Anwendung des erfindungsgemäßen Verfahrens für ein Innen-Sub-Diffraction-Writing;
• 3 eine beispielhafte Anordnung zur Anwendung des erfindungsgemäßen Verfahrens für ein Außen-Sub-Diffraction-Writing und
• 4 eine beispielhafte Anordnung zur Anwendung des erfindungsgemäßen Verfahrens für ein Opferschicht-Sub-Diffraction-Writing.

Show it:

• 1a the basic sequence of the individual method steps for carrying out a sub-diffraction writing of the present invention;
• 1b the resulting regions in the effective processing zone;
• 2 an exemplary arrangement for applying the method according to the invention for an inner sub-diffraction writing;
• 3 an exemplary arrangement for applying the method according to the invention for an external sub-diffraction writing and
• 4 an exemplary arrangement for applying the method according to the invention for a sacrificial layer sub-diffraction writing.

In 1a The three basic laser beam processing steps for the introduction of structures or material modifications are shown using the top-down method. You can see in the upper part of 1a in plan view the different areas: excitation area A , Abregation area B and ESA editing area C , which can be achieved by the three claimed laser processing steps in the sequence symbolized by arrows and in the lower half of the 1a by way of example the three different excitation states thus generated (in each case S ₀ and S ₁ ). 1b shows the resulting three resulting regions of the effective processing zone, namely inner region I , stimulated emission range II and border area III , In this case, in a first step, a laser beam excitation in an area ( a and b ) of the surface to be processed and / or made in a predeterminable material depth, in a second step there is a de-excitation in after the first step excited edge regions II ( b ) and in the actual third processing step, the (excited) interior area thus prepared after the first and second steps becomes a an irradiation with another laser beam (cf outer, continuous Gaussian profile, 1a . 1b ) subjected with such an expansion and intensity distribution that only this excited interior a excited state absorption (ESA) is further such that such a high energy input into this interior a is caused by the third laser beam pulse that a processing effect takes place, whereas remaining after the second step (depressed) edge areas b and beyond that in the fields III areas remain unchanged, ie without processing effect, remain. It clarifies 1b that only in a very narrow range a a material processing / modification takes place, which is substantially below the beam cross section of the processing laser in the third step and thus the object of the present invention is achieved to introduce structures in a range below the diffraction limit of laser beams in the order of the lower three-digit nanometer range and smaller in at least one dimension or to effect material modifications.

Based on 2 schematically illustrating an exemplary arrangement for implementing the method according to the invention for an inner sub-diffraction writing, the potential of the proposed method with respect to a 3D material modification inside a solid example by Ce ³⁺ doped YAG crystals (possible in the context of the invention of course also other crystals or glasses) are represented, since with these crystals already an ESA was proven (see Jacobs, Ralph R., William F. Krupke, and Marvin J. Weber. "Measurement of excited-state- absorption loss for Ce3 + in Y3Al5O12 and implications for tunable 5 d → 4 f rareearth lasers. " Applied Physics Letters 33.5 (1978): 410-412 ). In principle, this material modification in the interior of a whole range of materials that are suitable in principle according to the present invention, expand, but especially those who have the requirements for a 4-level laser system or in a 3-level system, at that the stimulated emission takes place between levels 3 and 2. However, other possibilities are also within the scope of the invention. According to the present invention, the time sequence of the respective pulses (time length of the pulse ensemble as sum of pulse lengths and pulse intervals) must be in the lower single-digit ns range, because of the fluorescence lifetime of the 5d band. To an excessive heat input over the spatially restricted area a out (see 1b ), a fs laser pulse should be used here for the material modification by means of ESA. In order to achieve a 3D material modification, the excitation in the volume of the crystal to be modified must be via a multi-photon absorption. In the example shown here, this is done by a 3-photon absorption in the focus range of an exciting fs pulse of a Nd: YAG laser 1 with a wavelength of 1064 nm. The low probability of such Non-linear transition causes a high pulse peak power, which is ideally provided by, as in the illustrated case, an fs laser. For de-excitation, according to the second step of the invention, the second harmonic (SHG unit 3, 532 nm) of a Nd: YAG cw laser 2 with a wavelength of 1064 nm is used in the example with the aid of a second-harmonic generation (SHG). This simplifies in the case shown, the timing of the pulses to each other, since the cw radiation is present continuously and thus requires no timing. The according to Jacobs et al. for an ESA-capable required wavelength range around 610 nm is by a subgroup in the structure of the arrangement according to 2 realized the construction of a dye laser 5 like. Here, the adapted dye, eg Rhodamine 6G, is pumped with the second harmonic of the 1064 nm pulse, including an SHG unit 3 is used, whereby an ESA processing pulse in the time range of the pump pulse and thus, as mentioned above, is generated in the desired fs range. The temporal assignment of the excitation, and ESA processing pulse via a delay unit 6 , By changing the optical path length Ax the excitation pulse, the time interval .delta.t be set between excitation and subsequent ESA processing pulse. It should be noted that the maximum time interval for the implementation of the present invention within the life of the optically excited state (several 10 ns) is, but also at least as long that a complete stimulated de-excitation of the areas b through the cw-depletion laser 2 is done. Thus, advantageously a temporal offset in the range of 10 ns is desired. The respective pulse energies should, as already explained above, be adapted to the respective processes. Thus, for the excitation pulse, due to the low probability of nonlinear 3-photon absorption, the intensity / power of the excitation pulse must be sufficiently high, but not too high, so that no processing based on even higher nonlinear effects (4-5) is required. Photon absorption and higher). Due to the shortness of the fs pulse, pulse energies in the range of pJ to nJ should be sufficient for multiphoton excitation. For the most complete possible de-excitation of the area b the time delay between excitation and ESA processing pulse, which is in the range of 10 ns, must be taken into account. Thus, the cw power of the laser must be 2 be adjusted so that it, in terms of the time offset, in the energy range from pJ to nJ. This means that the cw power is chosen so large that you are in the range b a maximum, most complete stimulated detuning receives, but not so large that caused by the cw Abregungslaser a material modification. In addition, there is targeted de-energizing of the area b the variation of the intensity profile of the cw excitation laser 2 in a donut mode using a spacial light modulator 4 , The responsible for the material modification ESA machining pulse, however, should be chosen so large that a material modification based on ESA and thus only in the field a occurs. But again not so great that a material modification caused by multiphoton processes is initiated. Thus, due to the shortness of the fs-pulses, the pulse energy in the range from pJ to nJ should not exceed a few μJ. For combined ensemble processing, consisting of targeted stimulation and de-excitation as well as ESA processing, the individual pulses or the cw irradiation must, with the aid of beam guiding and shaping elements 8, beam splitters 10 , Flipping 11 as well as wavelength-selective mirrors 12 spatially superimposed. Subsequently, a scanner unit allows 7 a deflection of the beam ensemble in the XY plane, which in combination with a Z-deflection of the workpiece to be machined 13 relative to the focal plane (eg by piezo actuators or stepper motors) for a 3D machining / material modification in the workpiece 13 leads. Thus, in the illustrated example, a difference in refractive index in the spatially restricted range a achieve what can be used for example for photonic crystals. The spatially perfectly superimposed Gaussian profiles of the excitation and ESA processing pulse and of the donut-shaped cw excitation beam are subsequently produced by means of a focusing unit / optics 9 (eg: HCX PL APO, aperture of up to 1.4 when using oil) usually focused diffraction-limited, with the focal plane in the workpiece to be machined 13 lies.

Based on 3 , which is intended to show an exemplary arrangement for applying the method according to the invention for an external sub-diffraction writing, a direct material modification in the sense of a direct material removal is exemplified for a semiconductor or a material (surface) with semiconductor precipitates. In addition, it is shown that the spatial restriction of the area a not necessarily radial (such as Gaussian or Donutmode), but, depending on the beam shaping, can be arbitrarily shaped. This is exemplified here by means of a line shape, ie an intensity distribution extended in a spatial direction, by longer bar fields after the spacial light modulators 4 , The semiconductors which are suitable for the proposed method must be optically attractable and excitable. This applies, as already mentioned, for direct semiconductors, which also have an intracavity transient an ESA in the sense of the present invention. Since the fluorescence lifetimes of these materials are in the lower ns range, and sometimes considerable diffusion lengths of the excited charge carriers in this short lifetime of up to several microns may occur, the overall sequence of the pulse ensemble (consisting of the claimed three steps: excitation , Depletion and ESA processing pulses) are in the ps range, again suggesting the use of fs lasers 1a. In addition, will thereby preventing an increased heat input during the material modification based on the ESA. Nevertheless, it has to be taken into account that after excitation relaxation of the excited charge carriers must take place (for the electrons at the lower edge of the conduction band and for the holes at the upper edge of the valence band) in order to be able to stimulate stimulation in accordance with the second step of the invention. Since this relaxation time can last up to ps, there should be a time lag Δt ₁ between excitation and de-excitation pulse in the range of one hundred (s) ps, which is a variation of the optical path Δx ₁ with the help of a delay unit 6 is realized. After the de-excitation takes place with the help of the third pulse, the material modification, according to step three present claim 1, in the spatially restricted area a , Its temporal offset Δt ₂ with respect to the de-excitation pulse should also be in the hundred (e) ps range, so that a total duration of the pulse ensemble is no longer than the (fluorescence) life and the previously spatially restricted area a is not extended by charge carrier diffusion. This is also done here again via an adjustment of the optical path Δx ₂ by means of a delay unit 6 , Since no material modification without prior excitation is to take place by the ESA machining pulse per se, multiphoton absorption effects must be prevented. This is achieved in the exemplary embodiment illustrated here, in which the direct semiconductor In _x Ga _{1 -x} N (workpiece 13 ) having a composition giving a bandgap of 2.4 eV by using an fs laser 1a having a wavelength of 1560 nm for ESA processing. Thus, a 2-and largely a 3-photon absorption are prevented as a disturbing secondary effect. The excitation pulse in the embodiment shown here is generated by generating the 4th harmonic (390 nm) of the output wavelength 1560 nm of the laser 1a generated by means of an FHG (Fourth Harmonic Generation) unit 3b. As a de-excitation pulse, the 3rd harmonic (520 nm) of the output wavelength, which is generated by means of a THG (Third Harmonic Generation) unit 3a, is used. The excitation pulse based on linear absorption should also be in the pJ to nJ range in this exemplary embodiment. This also applies to the relaxation pulse. The ESA processing pulse, on the other hand, should be in the higher pJ or nJ up to μJ, so that although a material modification based on excited state absorption in the range a takes place, but not in the already depressed area b and beyond (cf. 1a , there the areas III ) by multiphoton absorption. In order to produce a spatially restricted line shape as a material modification by a pulse ensemble, all three pulses must in their intensity profile, for example, by a spacial light modulator 4 be modulated. In this case, the Gaussian shape of the excitation pulse and of the ESA processing pulse and the donut shape of the de-excitation pulse are stretched in a spatial direction. For combined ensemble processing, consisting of targeted stimulation and de-excitation as well as ESA processing, the individual pulses have to be generated with the aid of beam guiding and shaping elements 8th , Beam splitters 10 , Flipping 11 as well as wavelength-selective mirrors 12 spatially superimposed. Subsequently, the pulses are using a focusing / objective 9 according to the temporal sequence mentioned above (firstly: excitation pulse, secondly: excitation pulse, third: ESA processing pulse) on the material surface of the crystal or the crystalline precipitates in a matrix (workpiece 13 ) focused. By means of a specific relative movement between the focused pulse ensembles in combination with the limited line shape as material modification per pulse ensemble, any desired material modification, such as material removal, can take place in its spatial form.

Finally shows 4 an exemplary arrangement for applying the method according to the invention for a sacrificial layer sub-diffraction writing. Since, as mentioned at the beginning, not all materials to be structured have a usable ESA capability, they should also be structured by the top-down method in a range below the diffraction limit of laser beams on the order of the lower three-digit nanometer range via the detour described below and be made less accessible.
For this purpose, in the exemplary embodiment, first a, in the sense of the present invention, SDW-capable sacrificial layer 16 on the actual material surface to be processed 13 , applied and used as a lithographic assistant. The ability of the as a sacrificial layer generated in the sense of the present invention 16 used paints or polymers can be done, for example, by additionally introduced dyes or by fluorescent polymers per se. These are in principle suitable for the SWD method presented according to the present invention by virtue of their ability to excite and de-excite as well as the excited state absorption. According to the invention, the time sequence of the respective pulses (temporal length of the pulse ensemble as sum of pulse length and pulse intervals) must take place in the one-digit ns range (fluorescence lifetime of the state S1 , see. 1a bottom half). The use of such a short pulse sequence additionally offers the advantage that secondary effects, such as the occupation of triplet levels, which cause an additionally changed optical absorption behavior, are prevented. For the transitions from singlet to triplet states are in the higher single-digit to double-digit ns range, so that they can not occur, because before everything is again de-energized (see section b in 1b ) or processed by ESA (see area a in 1b ) has been. From the variety of existing dyes (polyphenyl 1 , Styles 3 Coumarin 30 , Rhodamnin 6G Oyridin 2 etc.), as used for example in tunable dye lasers should be used in the illustrated embodiment "Red Perylimide Dye" (RPD), since this already the proof of an ESA has been done within a PMMA matrix (see: Reisfeld, R., R. Gvishi, and Z. Burshtein. "Photostability and loss mechanism of solid-state red perylimide dye lasers." Journal of Sol-Gel Science and Technology 4.1 (1995): 49-55 ). In the 4 Illustrated exemplary embodiment is based on the 2 , Harmonic (532 nm) of an Nd: YAG laser pulse in the ps range, generated by a ps-Nd: YAG laser 1b with 1064 nm wavelength in combination with an SHG unit 3 , Part of the pulse is used directly for optical stimulation of the RPD. However, the far greater residual power component of the pulse is needed to generate the de-excitation or ESA processing pulse and thus indirectly serves for optical de-excitation as well as ESA processing. This is done through two subassemblies, each of which builds a titanium sapphire laser 2 B same. As a result, the wavelength range for depletion (here in the range 620-670 nm, depending on the dye) and the wavelength range for ESA processing for the dye used (here greater than 700 nm, see Reisfeld et al.) Can be set separately. Since the total duration of the pulse ensemble consisting of excitation, de-excitation and ESA processing pulse according to the present invention may not be longer than the lifetime of the excited material, this must be determined by the temporal displacement of the pulses ( Δt ₁ . Δt ₂ ) using two optical delay units 6 ( Δx ₁ . Δx ₂ ) respectively. Thus, for the RPD used here, it must be part of the sacrificial layer 16 a total duration of the pulse ensemble in the range around 1 ns can be estimated as the maximum length. This has the consequence that the pulses are shifted from each other by a distance of 0.5 ns, which may also be lower. The respective pulse energies should be in the pJ to nJ range for the starting and de-excitation. By contrast, the ESA machining pulse responsible for material modification should be on the order of nJ, μJ, and possibly beyond. For easier adjustment, the excitation and de-excitation pulse were in this embodiment using various optical elements (beam guiding and -formungselementen 8th , Mirror 11 , wavelength-selective mirrors 12 , Beam splitter 10 etc.) first superimposed and then into a single-mode optical fiber 14 (single mode fiber) coupled. The glass fiber 14 transmits only the central Gaussian mode of the two pulses and these leave the fiber perfectly spatially superimposed. Due to the wavelength-selective effect of the segmented phase plate used 15 If only the intensity profile of the de-excitation pulse is converted into a donut-shaped intensity profile, the Gaussian mode of the excitation pulse remains largely unchanged. Subsequently, the ESA processing pulse is spatially superimposed and all three pulses are in their timing to each other on the sacrificial layer 16 consisting of RPD focused in PMMA. This should be diffraction limited with a maximum aperture of the focusing unit / lens used 9 (eg: HCX PL APO, aperture of up to 1.4 when using oil). Under certain circumstances, ie depending on the wavelengths used and the segmented phase plate 15 , is also a coupling of all three pulses in the monomode fiber for spatial superposition possible, in which case only the de-excitation pulse, due to the adapted to its wavelength phase plate 15 is converted into a donut-shaped intensity profile and the other two remain in the Gaussian mode.
Such a structurable sacrificial layer can then, after corresponding further, belonging to the prior art treatment steps such as dissolving, etching, as a finely structured mask for further structuring of the actually machined workpiece 13 be used. In addition, it can be used, for example, as a positive or negative varnish for further, already belonging to the prior art lithographic steps.

Basically, this applies to all special applications of the invention, the choice of wavelength for the laser used for the first and second step depends on the material to be processed. Thus, the de-excitation wavelength of the laser used in the second step can be selected to be greater than the excitation wavelength of the laser used in the first step. This applies, for example, for single-photon excitation by linear absorption in, for example: direct semiconductors, semiconductor precipitates, glasses or crystals doped with laser-active ions (eg rare earths), laser materials, fluorescent dyes in which the depletion takes place via single-photon processes.
Likewise, the de-excitation wavelength of the laser used in the second step can be selected smaller than the excitation wavelength of the laser used in the first step. This applies, for example, to multiphoton excitation by nonlinear absorption in, for example: direct semiconductors, semiconductor precipitates, glasses or crystals doped with laser-active ions (eg rare earths), laser materials, fluorescent dyes. This applies, for example, to a 3D interior inscription, where the depletion takes place via single-photon processes.
It is also possible that the de-excitation wavelength of the laser used in the second step is chosen to be equal to the excitation wavelength of the laser used in the first step. This applies, for example, for single-photon excitation by linear absorption in, for example, direct semiconductors, semiconductor precipitates, glasses or crystals doped with laser-active ions (eg rare earths), laser materials, fluorescent dyes, where the depletion takes place via single-photon processes.

The respective specific choice of wavelengths used is incumbent on the expertise of the average person skilled in the art, which he can determine without inventive step, or can easily determine, based on the properties of the material to be processed.
Furthermore, the temporal adaptation of the pulses with one another with sufficiently long pulse intervals ( Δt ₁ . Δt ₂ ) also be carried out electronically, for example by means of a delay station or by other, also suitable steps. Furthermore, the modulations of the beam profiles of the excitation, degeneration and ESA machining beam are not limited to the Spacial Light Mudulator (SLM) and phase plates, but can also be modified by further elements belonging to the prior art, such as Diffractive Optical Elements (FIG. DOE), set specifically.

On the basis of previously performed experiments, it was possible to determine that, for example, with the Nd: YAG laser (wavelength: 1064 nm) for ESA processing (third step) with a diffraction-limited focus, structures of the order of magnitude of 150 nm could be introduced, which is clearly below that optical diffraction limit and thus the requirement for structure generation by a device technically cheaper top-down method, as in the prior art (see., The above-described prior art) usual, which are in the lower three-digit nanometer range corresponds.

The novel invention presented here thus represents an innovative, flexible and cost-effective technology in the far-reaching field of "sub-diffraction-writing". However, for the first time not only direct material structuring / modification based on a direct laser writing process up to Structure sizes in the single-digit nanometer range on the surface of materials, but also in their interior allows. Thus, while the material structuring / modification of the surface is much more flexible in terms of its spatial and temporal configuration compared to previously known methods, such as EUV, X-ray and electron beam lithography, it also makes it possible for the first time for larger areas and moreover faster and more cost-effectively Material structuring / modification in the sense of the TOP-DOWN approach in the single-digit nanometer range, to the specific modification of individual atoms / ions (eg rare earths in glasses, doping, color centers, etc.) or their electron system in the bulk material by laser radiation ,
Thus, the presented invention not only has the potential to drastically reduce the enormous costs of writing the structures of the latest computer chips in the range of below 13 nm (EUV, XUV ..), because they have to work in vacuum with reflective high-precision optics, but also in many other fields that require surface finishing, such as mask fabrication for lithography, direct surface structuring / modification, and sacrificial layer indirect, Laser Induced Forward Transfer, Laser Induced Forward Transfer with Dynamic Release Layer, etc.
In addition, structures / modifications by laser processing are made possible in the material for the first time, for example, are smaller than the Bragg gratings based on laser beam interference, for example in fibers. Since the technology described here is no longer limited by diffraction or interference patterns, the spatial configuration of 3D interior structuring / modification thus finds potential use in many areas, such as: photonic crystals, metamaterials, holography, quantum computer, integrated Photonic Quantum Computing, Photosensitive Materials, Photo-Thermo-Refractive Materials, etc.

All in the description, the embodiments and the drawings recognizable features may be essential to the invention both individually, as well as in any combination.

LIST OF REFERENCE NUMBERS

A -

stimulation

B -

deexcitation

C -

ESA-processing step

1 -

fs-Nd: YAG laser 1 with 1064 nm wavelength

1a -

fs laser 1560 nm wavelength

1b -

ps-Nd: YAG laser 1064 nm wavelength

2 -

cw Nd: YAG laser 1064 nm wavelength

2 B -

Assemblies such as titanium sapphire laser

3 -

SHG unit for generating the 2 .Harmonischen

3a -

GHG unit for the production of 3 , harmonious

3b -

FHG unit for the production of 4 , harmonious

4 -

Spacial light modulator

5 -

SHG (532 nm) pumped dye laser

6 -

Delay unit, delay station

7 -

scanner unit

8th -

Beam guide, beam shaping elements, intensity attenuator

9 -

Focusing / lens

10 -

beamsplitter

11 -

mirror

12 -

wavelength-selective mirrors

13 -

workpiece to be machined

14 -

Single-mode optical fiber

15 -

segmented phase plate

16 -

sacrificial layer

a -

lively interior

b -

agitated border area

Δx -

Variation of the optical path length of the excitation pulse

Δt -

time offset between excitation and ESA processing pulse

Δx ₁ -

Variation of the optical path length of the de-excitation pulse

Δt ₁ -

time offset between excitation and de-excitation pulse

Δx ₂ -

Variation of the optical path length of the ESA machining pulse

Δt ₂ -

time lag between de-excitation and ESA processing pulse

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

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• US 000008432533 B2 [0005]

Cited non-patent literature

• Paper: S.W. Hell and J. Wichmann, Opt. Lett. 19 (1994) 780-782 [0004]
• T.A. Clear and S.W. Hell, Opt. Lett. 24 (1999) 954-956 [0004]
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• D. Wildanger, B.R. Patton, H. Schill, L. Marseglia, J.P. Hadden, S. Knauer, A. Schonle, J.G. Rarity, J.L. O'Brien, S.W. Hell, and J.M. Smith, Adv. Mater. 24 (2012) OP309-OP313 [0004]
• T. A. Klar, R. Wollhofen, and J. Jacak, Phys. Scr. T162 (2014) 014049 [0005]
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Claims (11)

Method for introducing structures or material modifications by means of the top-down method in a range below the diffraction limit of laser beams in the order of the lower three-digit nanometer range and smaller in at least one dimension in optically stimulable and dense material systems that have a modified (transient) absorption behavior in the excited state (ESA Excited State Absorption), characterized in that - in a first step, a laser beam excitation in a region (a and b) of the surface to be machined and / or in a predeterminable material depth is made - in a second step a de-excitation in edge regions (b) excited after the first step takes place while the inner region (a) remains excited and, in a third step, the excited inner region (a) prepared after the first and second steps of irradiation with a further laser beam in one Extension and intensity vert Exposure is exposed to the fact that only in the excited interior (a) taking advantage of the altered (transient) absorption in the interior (a) by excited state absorption (ESA) such a high energy input by means of a laser beam pulse is caused that only in the interior (a) a machining effect whereas the marginal areas (b) remaining after the second step remain unchanged, ie without any processing effect, the time sequence of said three steps being carried out in a predeterminable time interval depending on the material to be processed, in which the effects of the first and second Step both mutually and in relation to the third step still sufficiently pronounced in the material to be processed. Method according to Claim 1 , characterized in that the laser irradiation is pulsed in the first and third steps, wherein the laser irradiation in the second step both pulsed, then followed in time to the first step of the second step and then the third step of the laser irradiation, as well as in the continuous Mode (cw) and quasi-cw mode, in which the pulse length of the second step is so long as to include the first step or the first and third step or the third step in time. Method according to Claim 1 , characterized in that the Abregungswellenlänge of the laser used in the second step is greater than the excitation wavelength of the laser used in the first step is selected. Method according to Claim 1 , characterized in that the de-excitation wavelength of the laser used in the second step is chosen to be smaller than the excitation wavelength of the laser used in the first step. Method according to Claim 1 , characterized in that both Abregungswellenlänge of the laser used in the second step and the excitation wavelength of the laser used in the first step are the same size. Method according to one of Claims 1 to 5 , characterized in that the intensities of the laser radiation used for the first and second steps are chosen so small that caused by this still no material changes of the material to be processed, wherein the intensity of the selected laser for the first step but in cooperation with the intensity the intensity chosen for the second step is selected to be high enough to ensure sufficient excitation for the third actual material processing step in the interior area (a). Method according to Claim 1 characterized in that the spatial extent of the excited inner region (a) by the variation of the intensity of the de-excitation according to step 2 in conjunction with its pulse length (at pulsed step 2), beam shaping, beam focusing and pulse distance to step 1 and taking into account the material-specific saturation intensity I _SAT and the excitation according to step 1 is set specifically and thus the spatial extent of the material modification is made taking into account step 3. Method according to Claim 1 or 6 characterized in that the laser selected for the third step is pulsed with such short pulse lengths (intrapulse effects) and has an intensity such that the effects of the stimulation and de-excitation of the regions produced after the first and second steps are retained and only one Material processing / modification in the interior (a) carried out and a spatial expansion by secondary effects, such as heat conduction and carrier diffusion is prevented. Method according to Claim 1 characterized in that the temporal pulse spacing between the third and the first step (interpulse distances) is selected to be shorter than the lifetime of the material states (fluorescence lifetime) which are specifically excited after step one and two. Method according to Claim 1 , characterized in that the temporal sequence of the three steps (Interpulsabstände) is such that a spatial extension of the excited inner region (a) by material-specific, intrinsic secondary effects, such as charge carrier diffusion, heat conduction, is prevented. Method according to one of the preceding claims, characterized in that the wavelength of the laser used in the third step in combination with the pulse spacing, pulse length and pulse intensity exclusively in the excited inner region (a) and thus not in the abggenten edge region (b) to a material processing / modification , due to the altered (transient) excited state absorption behavior (ESA-Excited State Absorption), leads.

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