Method and device for the spatially resolved introduction of an intensity pattern of electromagnetic radiation into a photosensitive substance and use thereof

Abstract

Method for the spatially resolved introduction of an intensity pattern (5) of electromagnetic radiation by means of an optical imaging system (3) into a photosensitive substance with properties that can be changed by photon irradiation and that comprise a first, liquid and at least one second state, wherein the electromagnetic radiation (4) is guided via the optical imaging system (3) into the photosensitive substance (2) and is imaged there onto predetermined spatial coordinates in order to produce a change in the substance properties at these spatial coordinates or in the areas surrounding them, wherein a surface (6) of an objective lens of the optical imaging system (3), through which the electromagnetic radiation (4) exits therefrom, is immersed in the liquid photosensitive substance (2), characterized in that an optical imaging system (3) is used which has an objective (3) which is designed as an immersion objective, wherein the photosensitive substance (2) serves as an immersion medium, and that the change in the properties of the photosensitive substance (2) is initiated and / or de-excited by a multi-photon process, wherein the intensity pattern (5) is imaged onto an image plane (8) within the photosensitive substance (2).

Description

[0001] The invention relates to a method for the spatially resolved introduction of an intensity pattern of electromagnetic radiation into a photosensitive substance with properties that can be modified by photon irradiation, as well as to a device for carrying out such a method. The present invention can be used in particular for writing, erasing, and rewriting an optical data storage device, as well as for forming micro- and nanoscale structures. These applications and uses are also the subject of the present invention.

[0002] The photosensitive substance used in the present invention has a first, liquid state as its initial state and can change its properties into at least a second state through photon irradiation. These properties are changed by electromagnetic radiation being directed into the substance by means of an optical imaging system and imaged there onto predetermined spatial coordinates in order to produce a change in the substance properties at these spatial coordinates or in regions surrounding these spatial coordinates. The electromagnetic radiation can in particular, without restriction of generality, be a collimated laser beam that is imaged, i.e. focused, by the optical imaging system onto a diffraction-limited volume.The change in the substance's properties can be permanent, for example, a change from a liquid to a solid state. However, for applications such as data storage, the change in the substance's properties can also be temporary and, for example, eliminated by thermal treatment of the substance or can resolve spontaneously. A permanent change can also be reversible or irreversible.

[0003] In the context of the present invention, the first, liquid state of the photosensitive substance used is not only to be understood as a liquid state of aggregation in the true sense, i.e. as the state of a substance in which it offers virtually no resistance to a change in shape or, in the case of a viscous fluid, only a slight resistance, but a quite large resistance to a change in volume, but the photosensitive substance can also be present in its first, liquid state as a paste, i.e. as a solid-liquid mixture or suspension with a high content of solids, which may no longer be flowable but rather spreadable.

[0004] The electromagnetic radiation used in the present invention is normally light in the visible or infrared spectrum. Therefore, for the sake of simplicity of illustration and formulation, the terms "light beam," "light irradiation," and "exposure" are used below only as examples and do not preclude the use of electromagnetic radiation with other wavelengths within the present invention.

[0005] Within the scope of the present invention, the spatially resolved introduction of the electromagnetic radiation is achieved by optical imaging, whereby the radiation is imaged, in particular focused, as an intensity pattern. The term "focusing" used below refers to the introduction of optically imaged intensity patterns of the electromagnetic radiation into the photosensitive substance; since within the scope of the present invention, images of other intensity patterns can also be used in an image plane within the photosensitive substance.

[0006] A method and a device of the present type are generally used for the spatially resolved exposure (hereinafter also: writing) of one-, two- or three-dimensional structures in the photosensitive substance, in particular to store data multidimensionally or to produce multidimensional objects or structures and masks in the nanometer and micrometer range.

[0007] In the field of stereolithography for creating structures in the macro range, for example, DE 10111422 A1 proposes introducing a light beam into a liquid, photosensitive substance and focusing it where the substance is to change from its liquid to a solid state. This change in the substance's properties ideally occurs precisely in the area of ​​the focus. This can be achieved through either a linear or a nonlinear effect: Either the substance reacts linearly but has an intensity threshold below which a change due to light irradiation no longer occurs or does not occur sufficiently, or the substance reacts nonlinearly, which is particularly the case with two- or multi-photon polymerization processes. In the latter process, the probability of a change in the properties of the substance in the focus is increased due to the increased intensity there compared to the surroundings.

[0008] The precise, spatially resolved introduction of a focused light beam into a photosensitive substance is particularly suitable for the creation of a three-dimensional structure when the change in the substance is induced relatively precisely and exclusively at the focal point. Suitable imaging systems, such as piezo stages for moving the substrate or beam-deflecting devices such as galvanomirrors, micromirror actuators, spatial light modulators, or acousto-optical deflectors, allow the focal point to scan a relatively large, three-dimensionally extended writing area in the photosensitive substance.This is not particularly interesting for stereolithographic processes, as known from DE 10111422 A1, but rather for the production of nano- and microscale structures, optical waveguides, or spatially distributed writable optical data storage devices, where the main focus is on the high resolution of the structures and therefore lenses in conjunction with immersion media must be used. To overcome the diffraction limit, the Abbe limit, which depends on the wavelength of the light used, EP 1 616 344 B1 proposes to excite the spatially resolved change in the substance properties with a diffraction-limited signal and simultaneously de-excite this change locally with an offset diffraction-limited signal.

[0009] However, as is the case everywhere in the field of imaging optics, changing the spatial coordinates along the optical axis of the optical imaging system used results in the problem of aberrations, which increase with increasing write depth—that is, with an increasing proportion of material in the optical path with a suboptimally matched refractive index. Therefore, the current technology only allows the creation of three-dimensional structures with a very limited height.

[0010] In the field of two- and multi-photon absorption lithography, a method is already known that attempts to statically compensate for the problem of aberrations by exploiting precompensation. The publication APPLIED OPTICS Volume 27, Number 26 (1998) describes a method that uses two tube lenses movable along the optical axis. The relative deflection of the tube lenses generates aberrations of all orders, which can be selected to partially precompensate the errors of the subsequent optical system. This method only allows for partial compensation of the aberrations and is technically extremely demanding because additional error-prone components must be used and moved. Furthermore, a new relative position of the tube lenses must be set for each exposure plane along the optical axis.Furthermore, the tube lenses shift the image along the optical axis, distorting or compressing the compensated image. Under certain circumstances, the irradiated exposure dose may also change in the compensated image, which has a detrimental effect on the resulting structures.

[0011] WO 90 / 06540 ​​A1 describes a method for producing a three-dimensional workpiece by phototransformation of an organic liquid using a laser beam. To produce the three-dimensional workpiece, the laser beam passes through a neutral volume and then builds up the workpiece, starting from a bottom surface, into successive parallel slices by phototransformation in the organic liquid.

[0012] EP 2 357 186 A1 discloses a method for producing three-dimensional self-supporting and / or substrate-supported molded bodies or structures on surfaces by site-selective solidification of a liquid to pasty, organic or organically modified material within a bath of this material by means of two- or multi-photon polymerization.

[0013] WO 2009 / 108543 A2 describes an exposure system with a light source that emits a beam along an optical axis. The beam is capable of inducing a multiphoton reaction in a resin.

[0014] Based on this prior art, the present invention is based on the object of largely avoiding imaging errors in a method and a device of the present type or of keeping them essentially constant along the optical axis of the imaging system.

[0015] This object is achieved by a method having the features of claim 1 and by a device having the features of claim 14.

[0016] Advantageous developments of the method according to the invention are set out in claims 2 to 10; preferred embodiments of the device according to the invention are set out in claims 15 to 22. Preferred applications of the method according to the invention are set out in claims 11 to 13; inventive uses of the device according to the invention are the subject of claims 23 and 24.

[0017] According to the invention, the given problem is solved by immersing the objective of the optical imaging system or a surface of an objective lens through which the electromagnetic radiation, in particular a light beam, exits the optical imaging system into the liquid photosensitive substance in which the change in the substance properties is to be generated. The photosensitive substance therefore functions as an immersion system, so that the imaging errors can be almost or even completely eliminated by using suitable immersion objectives. Even with non-ideally matched refractive indices of the objective lens and photosensitive substance, the invention leads to much better results than before, because even then the aberrations are constant regardless of the writing depth and the image is identical across the entire writing area.

[0018] A main reason for these effects according to the invention is that the interface(s) between the photosensitive substance and the lens of the optical imaging system, which are always present in the prior art, are essentially eliminated. Such an interface(s) fundamentally lead to imaging errors.

[0019] The method according to the invention thus avoids deviations from an ideal optical image by simultaneously using the photosensitive substance as an immersion medium. A signal, i.e., the focus or other intensity pattern of the electromagnetic radiation radiated via the optical imaging system, such as a light beam, is imaged onto a writing area within the photosensitive substance in such a way that the distance between the objective lens and the image planes of the signals in the writing area assumes a constant value. Aberrations due to a refractive index mismatch of the optical system remain constant along the optical axis (and are ideally constant zero), and the photosensitive substance can be exposed with identical foci or intensity patterns across the entire writing area.

[0020] A further major advantage of the present invention is that the extent of the imageable spatial coordinates in the direction of the optical axis of the imaging system is no longer limited by the working distance of the lens. This is because, according to the invention, the lens is immersed directly into the photosensitive substance during imaging, particularly focusing the light beam onto the predetermined spatial coordinates. This allows three-dimensional structures to be written into the photosensitive substance whose extent in the direction of the optical axis is much larger and thus much higher than the structures producible using the prior art, while potentially maintaining the highest spatial resolution.

[0021] The method according to the invention and the corresponding device are preferably used to produce one-, two- and / or three-dimensional structures in a writing area within the photosensitive substance.

[0022] In a preferred variant of the novel process, the write signal or signals (multiple signals may be required, for example, in the case of STED lithography described above with reference to DE 101 11 422 A1) consist of radiation from the visible or near-infrared electromagnetic spectrum. The light source can be, for example, a pulsed laser or a continuous-wave laser. Electromagnetic radiation from the UV range or the mid- or far-infrared range can also be selected. Furthermore, the exposure mechanism can be, for example, (photo-)chemical and / or thermal.

[0023] With the present invention, an optical system can be used to produce optical data storage devices with constant or no aberrations and with particularly few imaging errors. By selecting a suitable photosensitive substance, such an optical data storage device can be written, erased, and rewritten.

[0024] Likewise, micro- and nanostructures can be produced with otherwise unattainable precision across the entire writing area within a photosensitive substance.

[0025] By building up the one-, two-, and / or three-dimensional structure to be created in the photosensitive substance layer by layer, it is possible to avoid exposing or writing through pre-structured material. This is because the refractive index of the photosensitive substance generally changes when it changes due to photon irradiation. This can lead to further imaging errors if the light beam is focused or imaged through altered material into the photosensitive substance.

[0026] Preferably, the liquid photosensitive substance is applied to a solid substrate, such as a glass plate or other arbitrarily shaped, possibly opaque, body, and then the optical imaging system is immersed in the liquid photosensitive substance. The substrate is thus not located between the photosensitive substance and the optical imaging system, thus avoiding further imaging errors caused by interfaces, and the height of the structures to be written is not limited by the working distance of the imaging system's lens.

[0027] According to a further development of this variant of the invention, a transparent, disc- or plate-shaped solid is used as the substrate, which carries a liquid photosensitive substance on both sides. On the side of the substrate facing the optical imaging system, the photosensitive substance then serves according to the invention as an immersion medium, whereby the light beam can be focused not only into this photosensitive substance, which also functions as an immersion medium, but, if necessary, also through this substance and the substrate into the photosensitive substance applied to the substrate on the opposite side. The alignment of structures on both sides of the substrate is possible much more precisely according to the invention than in the previous prior art, since structuring can be carried out directly on both sides of the substrate in a single step. The rotating and aligning of the substrate, as required in the prior art, is no longer necessary.

[0028] For the present invention, a laser, in particular a continuous-wave laser or pulsed laser in the electromagnetic spectrum of UV, visible light, or near-infrared, is preferably used as the radiation source for the electromagnetic radiation or as the light source. Within the scope of the present invention, the liquid photosensitive substance can be locally modified by photon irradiation through physical, thermal, and / or chemical means.

[0029] According to the invention, the change in the substance properties of the photosensitive substance is initiated and / or de-excited by a multi-photon process.

[0030] As already mentioned, the device and method according to the invention can be used particularly and advantageously for writing to and / or erasing data storage devices, as well as for creating micro- or nanoscale structures. In the latter case, the points or regions of the photosensitive substance altered by photon absorption can subsequently be exposed or removed by a selective development process.

[0031] The present invention is based on the finding that the intensity pattern of the electromagnetic radiation imaged into the photosensitive substance, in particular a light beam focus, collects imaging errors with increasing writing depth, i.e. increasing penetration depth into the photosensitive substance with a mismatched refractive index along the optical axis of the imaging system, and thus no longer permits precise spatial resolution. The imaging errors are all the more pronounced the greater the difference in the refractive indices between the photosensitive substance and the air or a substrate when irradiated through such a substrate. According to the invention, the imaging errors are not necessarily eliminated, but are merely kept constant or at least essentially constant within a writing area along the optical axis of the imaging system, so that highly precise spatial resolution can be achieved within the photosensitive substance.

[0032] An exemplary embodiment of a device according to the invention and test results for a method carried out according to the invention are described and explained in more detail below with reference to the accompanying drawings. They show: Fig. 1 a schematic representation of an arrangement of device parts essential to the invention; Fig. 2 shows an image of a three-dimensional microstructure produced by the method according to the invention; Fig. 3 an illustration of a three-dimensional microstructure produced according to the state of the art using the same template as Fig. 3; Fig. 4 shows a further illustration of a microstructure produced by the method according to the invention; Fig. 5 shows a further illustration of a microstructure produced by the method according to the invention.

[0033] Fig. Figure 1 is a schematic representation of the core of the present invention: On a substrate 1 there is a liquid photosensitive substance 2, which here consists of a liquid photoresist system known from lithography technology with a refractive index between n ~ 1.3 and n ~ 1.7. A light source (not shown), here a pulsed laser in the near-infrared range, is imaged into the photosensitive substance 2 via an optical imaging system, for example a microscope, with an objective 3, indicated here by a light beam 4, and focused at a focus 5 in an image plane 8 in order to cause the change in the properties of the photosensitive substance 2 in the region of the focus 5. The light beam 4 emerges from a surface 6 of an objective lens of the objective 3, wherein, according to the invention, this surface 6 is immersed in the photosensitive substance 2 in order to avoid any interfaces therebetween.

[0034] Objective 3 is an immersion objective; such objectives are typically used for the refractive indices of oils (n ~ 1.5-1.7), glycerol (n ~ 1.47) or water (n ~1.3). If, in this configuration, the lens is adapted to the refractive index of the photoresist 2, the image plane 8 can, in principle, be shifted along the optical axis 7 and imaged and structured with constant aberrations. The image can, in particular, be a Gaussian focus. In the normal case of a small difference between the refractive index, for which the lens 3 functions ideally, and the refractive index of the photosensitive substance 2, structuring cannot be carried out without aberration errors. However, this error is constant over the entire writing depth along an optical axis 7, which leads to significant improvements in writing quality compared to the state of the art, even with an imperfectly adapted system. This is demonstrated using the following Fig. 2 and Fig. 3 clearly.

[0035] Fig. Figure 2 shows a three-dimensional structure arranged in accordance with Fig. 1 was created by writing in IP-L and subsequent development of the photosensitive substance. An oil lens was used for the refractive index n ~ 1.52 and a photoresist with the refractive index n ~ 1.48 was used. The model, as can be clearly seen, was the Statue of Liberty in New York, which was inscribed into the photosensitive substance at a total size of approximately 300 µm.

[0036] The structure that is Fig. 3, the model was the Statue of Liberty with a total height of approximately 300 µm; however, since a state-of-the-art process was used, this could not be imaged into the photosensitive substance with the required accuracy.

[0037] Fig. 4 again shows the image of a three-dimensional structure which, in an arrangement designed according to the invention, is shown in Fig. 1. As already mentioned in Fig. 2, the Statue of Liberty in New York was also exposed as a three-dimensional structure. However, as the scale in Fig. 4 shows, a much larger structure is written: The Statue of Liberty is opposite Fig. 2 unchanged high resolution and correspondingly high detail, much larger; their total height is about 1 mm. In this example, which is shown in Fig. As shown in Figure 4, it is clear that the present invention can be used to write three-dimensional structures into the photosensitive substance whose extension in the direction of the optical axis is greater than the working distance of the lens used for writing or exposure. And, as can be seen, this can be achieved with the highest spatial resolution.

[0038] Fig.5 finally shows a further example of a photolithographically produced three-dimensional structure using the method according to the invention, this structure having a total height of approximately 200 µm and, despite this total height, a previously unattainable level of detail in the spatial resolution.

Claims

[1] Method for the spatially resolved introduction of an intensity pattern (5) of electromagnetic radiation by means of an optical imaging system (3) into a photosensitive substance with properties that can be changed by photon irradiation and that comprise a first, liquid and at least one second state, wherein the electromagnetic radiation (4) is guided via the optical imaging system (3) into the photosensitive substance (2) and is imaged there onto predetermined spatial coordinates in order to produce a change in the substance properties at these spatial coordinates or in the areas surrounding them, wherein a surface (6) of an objective lens of the optical imaging system (3), through which the electromagnetic radiation (4) exits therefrom, is immersed in the liquid photosensitive substance (2), characterized bythat an optical imaging system (3) is used which has an objective (3) which is designed as an immersion objective, wherein the photosensitive substance (2) serves as an immersion medium, and that the change in the properties of the photosensitive substance (2) is initiated and / or de-excited by a multi-photon process, wherein the intensity pattern (5) is imaged onto an image plane (8) within the photosensitive substance (2). [2] Method according to claim 1 characterized by that one-, two- and / or three-dimensional structures are written into the photosensitive substance (2) using the imaged intensity pattern of the electromagnetic radiation (4). [3] Method according to claim 2, characterized by that the one-, two- and / or three-dimensional structures are written with several imaged intensity patterns. [4] Method according to one of claims 2 or 3; characterized bythat the writing direction is chosen in such a way that writing is not carried out through substance material that has already been altered. [5] Method according to at least one of claims 1 to 4, characterized by that the liquid photosensitive substance (2) is applied to a solid body used as a substrate (1) and then the optical imaging system (3) is immersed in the liquid photosensitive substance (2). [6] Method according to claim 5, characterized by that a transparent, disc- or plate-shaped solid body is used as substrate (1) and a liquid photosensitive substance (2) is applied to both sides of the substrate (1). [7] Method according to at least one of claims 1 to 6, characterized by that a laser, in particular a continuous wave laser or pulsed laser in the electromagnetic spectrum of UV, visible light or near infrared is used as the source for the electromagnetic radiation (4). [8] Method according to at least one of claims 1 to 7, characterized by that the intensity pattern is imaged by focusing the electromagnetic radiation onto the predetermined spatial coordinates. [9] Method according to at least one of claims 1 to 8, characterized by that several intensity patterns are imaged simultaneously and one or more optical imaging systems are used for this purpose. [10] Method according to at least one of claims 1 to 9, characterized by that the liquid photosensitive substance (2) is locally modified by photon irradiation in a physical, thermal and / or chemical manner. [11] Application of a method according to at least one of claims 1 to 10 for writing and / or erasing and / or rewriting data memories. [12] Application of a method according to at least one of claims 1 to 11 for producing micro- or nanoscale structures. [13] Application according to claim 12, characterized by that the points or areas of the photosensitive substance (2) altered by photon irradiation are subsequently exposed or removed by a selective development process. [14] Device for the spatially resolved introduction of an intensity pattern (5) of electromagnetic radiation into a photosensitive substance (2) with properties that can be changed by photon irradiation, comprising a photosensitive substance (2) whose properties can be changed by photon irradiation between a first, liquid and at least one second state, and a radiation source and an optical imaging system (3) for introducing electromagnetic radiation (4) originating from the radiation source into the photosensitive substance (2) and for imaging the electromagnetic radiation (4) in the photosensitive substance (2) onto predetermined spatial coordinates (5) in order to produce a change in the substance properties at these spatial coordinates or in the areas surrounding them, wherein the device is designed such that a surface (6) of an objective lens of the optical imaging system (3), through which the electromagnetic radiation (4) exits therefrom, is immersed in the photosensitive substance (2) for introducing the electromagnetic radiation (4) into the latter, characterized by that the optical imaging system (3) has an objective (3) which is designed as an immersion objective, wherein the photosensitive substance (2) serves as an immersion medium, and that the change in the properties of the photosensitive substance (2) is initiated and / or de-excited by a multi-photon process, and that the intensity pattern (5) is imaged onto an image plane (8) within the photosensitive substance (2). [15] Device according to claim 14, wherein the objective (3) is designed as an immersion objective for a refractive index of oils in the range of 1.5 to 1.

7. [16] Device according to claim 14, wherein the objective (3) is designed as an immersion objective for a refractive index of glycerol equal to 1.

47. [17] Device according to claim 14, wherein the objective (3) is designed as an immersion objective for a refractive index of water equal to 1.

3. [18] Device according to claim 14, wherein the objective (3) is designed as an immersion objective which is adapted to the refractive index n of the photosensitive (2) substance. [19] Device according to claim 14, characterized bythat several optical imaging systems (3) are present in order to image several intensity patterns (4) into the photosensitive substance (2). [20] Device according to one of claims 14 to 19, characterized by that the photosensitive substance (2) is applied to a solid body used as substrate (1). [21] Device according to claim 20, characterized by that the photosensitive substance (2) is applied on both sides to a disc-shaped or plate-shaped, transparent solid used as substrate (1). [22] Device according to at least one of claims 14 to 21, characterized by that the radiation source for the electromagnetic radiation is a laser, in particular a continuous wave laser or pulsed laser in the electromagnetic spectrum of UV, visible light or near-infrared. [23] Use of a device according to at least one of claims 14 to 22 for writing and / or erasing and / or rewriting data memories. [24] Use of a device according to at least one of claims 14 to 22 for producing micro- or nanoscale structures.

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