WO2013026750A1

WO2013026750A1 - Exposure apparatus and method for the patterned exposure of a light-sensitive layer

Info

Publication number: WO2013026750A1
Application number: PCT/EP2012/065930
Authority: WO
Inventors: Damian Fiolka; Jürgen Baier; Michael Totzeck
Original assignee: Carl Zeiss Smt Gmbh
Priority date: 2011-08-19
Filing date: 2012-08-15
Publication date: 2013-02-28
Also published as: CN103890565B; JP2014526152A; DE102011081247A1; CN103890565A; KR20140056346A; JP6086503B2; KR101986394B1

Abstract

The invention relates to an exposure apparatus (5), comprising: a substrate (6) with a light-sensitive layer (1), a generating device (7) for generating a plurality of exposure rays (3) having an exposure wavelength (λ_B), wherein each exposure ray (3) is assigned to a partial region of the light-sensitive layer (1) and the generating device (7) is designed to generate exposure rays (3) having a maximum intensity that lies above an intensity threshold value for converting the light-sensitive layer (1) from a second state into a first state, a movement device (13) for moving the exposure rays (3) relative to the respectively assigned partial region, and an excitation light source (31) for generating excitation radiation (32) having an excitation wavelength (λ_Α) for converting the light-sensitive layer (1) from the first state into the second state. The invention also relates to an associated exposure method.

Description

Exposure apparatus and method for the patterned exposure of a light- sensitive layer

Cross-reference to Related Applications

This application claims priority under 35 U.S.C. 1 19(a) to German Patent Application No. 10 201 1 081 247.4 filed on August 19, 201 1 , the entire contents of which are hereby incorporated by reference in the disclosure of this application.

Background

The invention relates to an exposure apparatus for the patterned exposure of a light-sensitive layer, and to an assigned exposure method.

Exposure apparatuses for microlithography can expose structures with high precision into a light-sensitive layer formed on a substrate. Such exposure apparatuses generally consist of a light source, an illumination system that processes the light emitted by the light source to form illumination light, an object to be projected, generally called reticle or mask, and also a projection lens, which images an object field onto an image field. The mask or at least a part of the mask is situated in the object field and the substrate (also called wafer hereinafter) or at least a part of the substrate is situated in the image field of the projection lens.

If the mask is situated completely in the region of the object field and the wafer is exposed without a relative movement of wafer and image field, then the lithography apparatus is generally designated as a wafer stepper. If only a part of the mask is situated in the region of the object field and the wafer is exposed during a relative movement of wafer and image field, then the lithography apparatus is generally designated as wafer scanner. The spatial dimension defined by the relative movement of reticle and wafer is generally designated as the scanning direction. An exposure apparatus for near field lithography which is based on the principle of step-and-repeat exposure is described in the article "Near-Field Lithography as Prototype Nano- Fabrication Tool", Microelectronic Engineering 84 (2007) 705-710 by

Yasuhisa Inao et al.

Besides exposure apparatuses wherein a fixedly predefined structure on a mask is imaged onto a light-sensitive layer, there also exist exposure apparatuses which are based on the principle of raster scanning and wherein a plurality of typically parallel exposure rays spaced apart from one another are generated, which are modulated in a manner dependent on a structure to be produced on the light-sensitive layer. In this case, the light-sensitive layer can be displaced transversely with respective to the exposure rays, such that the entire area to be exposed can be patterned. Electron radiation is typically used as exposure radiation in this case, as is illustrated e.g. in the case of the system described in US 7425713 B2.

Object of the Invention

It is an object of the invention to specify exposure apparatuses and associated exposure methods which enable a patterned exposure of a light-sensitive substrate with high resolution.

Subject matter of the Invention

In accordance with one aspect, the invention relates to an exposure apparatus for the patterned exposure of a light-sensitive layer, comprising: a generating device for generating a plurality of, in particular parallel, exposure rays wherein each exposure ray is assigned to a partial region of the light-sensitive layer, a movement device for moving, in particular in scanning fashion, the exposure rays over or relative to the respectively assigned partial region, and a near field optical unit arranged upstream of the light-sensitive layer and serving for converting a respective exposure ray into an evanescent wave for generating a light spot on the light-sensitive layer, the extent of which light spot is smaller than the extent of a respective exposure ray upstream of the near field optical unit.

In the case of such an exposure apparatus, that surface of the light-sensitive layer or of the wafer which is to be exposed is subdivided into a plurality of partial regions in which the exposure takes place simultaneously with a respective exposure ray, i.e. each partial region is assigned an exposure ray. The exposure rays typically proceed from a two-dimensional raster and run parallel, such that a pattern generated by activation or deactivation of the individual exposure rays is transferred to the light-sensitive layer, i.e. a structure to be produced on the light-sensitive layer is defined by the pattern of the exposure rays.

The process of transferring the pattern of the exposure rays to the light- sensitive layer is carried out repeatedly, wherein between successive transfer steps the exposure rays as a whole are in each case displaced with respect to the light-sensitive layer, such that a respective exposure ray progressively reaches each location in the respective partial region and the entire surface to be exposed is microstructured in this way. It goes without saying that for this purpose the exposure rays are manipulated independently of one another, i.e. are switched on or off in particular independently of one another.

In this case, the extent of the partial regions on the light-sensitive layer is typically of the order of magnitude (i.e. approximately 1 to 10-fold) of a diffraction disk (Airy disk) generated by the respective exposure ray on the light- sensitive layer. In this case, the size or the diameter of the diffraction disk is determined by the smallest diaphragm diameter of the exposure apparatus (or of a projection lens used therein), since said diameter limits the resolution capability of the exposure apparatus. In the context of this invention, techniques are described which make it possible to perform the patterning of the light- sensitive layer with an increased resolution relative to this so-called diffraction limit, i.e. techniques are described in which only a part of the extent of a respective diffraction disk contributes to the exposure.

In accordance with a first aspect of the invention, this is achieved by virtue of the fact that a near field optical unit is arranged directly upstream of the light- sensitive layer, which makes it possible to reduce the extent of the exposure rays, such that a light spot is generated on the light-sensitive substrate, the extent or diameter of which light spot is significantly smaller than the extent of the diffraction disk of an exposure ray entering into the near field optical unit.

In one embodiment, a side of the near field optical unit which faces the light- sensitive layer is arranged at a distance from the light-sensitive layer which is smaller than the wavelength of the exposure rays. This is of advantage since the intensity of the evanescent wave formed at the near field optical unit decreases exponentially with the distance from the location of the generation of the evanescent wave. In this case, the used wavelength of the exposure radiation can be in the near UV range, e.g. 193 nm. However, it is also possible to use exposure radiation having a wavelength in the visible wavelength range. The use of an immersion fluid is also possible.

If the light-sensitive layer (resist) is sufficiently robust, the near field optical unit can, if appropriate, at least partly touch the light-sensitive layer. A dose and/or focus control (see below) can also be provided in order to take account of the great distance dependence of the intensity of the exposure rays that is coupled over into the near field, since this may possibly lead to an inhomogeneous illumination of the light-sensitive layer.

In a further embodiment, the exposure apparatus additionally comprises a detector device for detecting the intensity of the exposure rays reflected at the near field optical unit. The intensity of the reflected light can be measured by a suitable spatially resolving detector device (CCD camera or the like) channel by channel, i.e. individually for each exposure ray. In this way, it is possible to measure typically indirectly the energy input of a respective exposure ray or of the evanescent wave generated by the latter in the light-sensitive layer. The less energy is introduced into the light-sensitive layer, the more energy is reflected, and vice versa. By coupling the detector device to the light generating device (or a filter device, see below), it is possible to set the intensity of the individual exposure rays independently of one another such that the light- sensitive layer is exposed (almost) uniformly.

In one development, the exposure apparatus comprises a distance determining device for determining a distance and preferably a tilting between the near field optical unit and the light-sensitive layer, in particular on the basis of the detected intensity. On the basis of the intensity detected channel by channel, it is possible to deduce the energy introduced into the light-sensitive layer and thus locally the distance between the near field optical unit and the light- sensitive layer. By determining the distance between near field optical unit and light-sensitive layer at a plurality of locations, it is additionally possible to determine the orientation or the tilting of the near field optical unit relative to the light-sensitive layer. The tilting can be corrected, if appropriate, by manipulators (e.g. in the form of piezo-actuators) provided at the near field optical unit.

Manipulators can also be used to set or to regulate the distance between the near field optical unit and the light-sensitive layer to a desired set point value (focus control or focus regulation). If appropriate, the distance determining device can also be designed to perform a capacitive or ellipsometric

determination of the distance between near field optical unit and light-sensitive substrate.

In a further embodiment, the exposure apparatus comprises a filter device arranged upstream of the near field optical unit and serving for influencing the intensity and/or the polarization of a respective exposure ray. The filter device can be embodied as a neutral (grey) filter or as a polarization filter, for example, which brings about a transmission that can be varied in a location-dependent manner e.g. by applying a voltage, or, respectively, influencing of the

polarization. If the distance between the near field optical unit and the light- sensitive layer varies in a location-dependent manner, the resultant

inhomogeneity of the light distribution on the light-sensitive layer can be compensated for by suitable influencing of the intensity distribution upstream of the near field optical unit. In this case, the intensity of the individual exposure rays can be suitably modulated e.g. by neutral or polarization filters.

In one development, the exposure apparatus additionally comprises a control device for driving the filter device in a manner dependent on the intensity detected by means of the detector device. The control device can be used to set the intensity and the phase (and also, if appropriate, the exposure duration) of the individual exposure rays in a manner dependent on the measured or detected variables, such that these have a desired property at the light- sensitive layer or when impinging on the near field optical unit. In particular, the control device can also be used to minimize the intensity differences between the individual exposure rays impinging on the light-sensitive layer, i.e. to generate an intensity distribution on the light-sensitive layer which is as uniform as possible.

In one embodiment, the near field optical unit has a perforated mask having a plurality of through openings, the diameter of which is preferably smaller than the wavelength of the exposure rays. One possibility for increasing the resolution is to use a perforated mask which is transparent to the exposure rays only within the through openings. In this case, the diameter of the through openings is generally smaller than the diameter of the diffraction disks of the exposure rays, that is to say that the extent of the through openings

transversely with respect to the light propagation direction of the exposure rays is smaller than the wavelength of the exposure radiation. In this case, the distance between the perforated mask and the light-sensitive layer is also generally smaller than the wavelength of the exposure radiation (see above), in order that the exposure radiation as a so-called evanescent wave (in

accordance with the quantum mechanical tunnel effect) can enter into the light- sensitive layer at the location of the through opening and expose the light- sensitive layer ("contactless nano-imprint").

In one development, the perforated mask has a substrate transparent to the exposure rays and a barrier layer facing the light-sensitive substrate, the plurality of through openings being formed at said barrier layer. In this case, the barrier layer having the through openings is applied on the transparent substrate serving as a carrier. By way of example when using radiation in the near UV range, e.g. at approximately 193 nm, a chromium layer can serve as barrier layer, said chromium layer, from a thickness of approximately 50 - 80 nm, no longer being transmissive to exposure rays at said wavelength.

In one development, the transparent substrate is patterned on its side facing the light-sensitive layer and has, in particular, tapering structures. The structuring of the transparent substrate serves as a micro-optical unit, wherein in particular tapering, conical structures have proved to be particularly advantageous. In this case, the through openings in the barrier layer are situated at the cone vertices, which are typically arranged at a distance from the light-sensitive layer which is smaller than the wavelength of the exposure radiation.

In a further embodiment, the light propagation direction of the exposure rays runs at an angle with respect to the near field optical unit (and thus with respect to the light-sensitive layer), wherein the near field optical unit has a dielectric substrate having a plurality of tapering metallic structures embedded into the dielectric substrate. In this case, the incident exposure radiation serves for exciting surface plasmons in the tapering metallic structures. These induce an alternating electric field within the structures, which emerges at the tips in a maximally concentrated fashion as an evanescent wave and is damped exponentially depending on the distance from the light-sensitive layer. In the case of a small distance between a respective tip and the light-sensitive layer (typically smaller than the wavelength of the exposure rays used), the intensity of the evanescent wave suffices to expose the light-sensitive layer in a very small region around the tip.

In order to excite the surface plasmons in the metallic tips, it is necessary to use p-polarized illumination radiation, that is to say that the light propagation direction has to be effected at an angle with respect to the near field optical unit, in order that a plane of incidence (and thus the p-polarization) is actually defined. In order to excite the surface plasmons, the wave number of the exposure radiation used additionally has to be adapted to the plasma frequency of the metal, which is possible via the dielectric, cf. in particular

"http://en.wikipedia.org/wiki/Surface_Plasmon" for more detailed explanations concerning the generation of surface plasmons. When using exposure rays having a wavelength of approximately 193 nm, in this case it is possible, in particular, for aluminum to serve as a plasmon source. If permitted by the mechanical resistance of the light-sensitive layer, the metallic tips can in this case also be in direct contact with the light-sensitive layer.

In a further embodiment, the exposure apparatus comprises a superlens element for imaging evanescent waves emerging from the near field optical unit onto the light-sensitive substrate. The term superlens element, as it is called, denotes an arrangement which makes it possible to transport evanescent waves in an (almost) undamped manner and possibly even to amplify them. This is possible since the superlens element has a negative refractive power for the wavelength of the exposure radiation.

Surface plasmons are excited in the case of the superlens element as well. In the simplest case here the superlens element has a layer stack composed of a first dielectric, a metallic layer and a second dielectric. In this case, the thicknesses of the (planar) layers are typically of the order of magnitude of the wavelength of the exposure radiation. Such a superlens element in which silver serves as the metallic layer is presented in the article "Super-resolution near- field lithography using planar silver lenses" by David O.S. Melville et al. (Invited Poster, MNE-2005 ID 00709, "http://www.mne05.org/3-c_01 .pdf). At wavelengths in the near UV range, e.g. around approximately 193 nm, the use of an aluminum layer has proved to be of advantage. Quartz glass can be used as a dielectric at such wavelengths. The superlens element can be embodied integrally with the near field optical unit.

A further aspect of the invention relates to an exposure apparatus, comprising: a substrate with a light-sensitive layer, a generating device for generating a plurality of, in particular parallel, exposure rays having an (at least one) illumination wavelength, wherein each exposure ray is assigned to a partial region of the light-sensitive layer and the generating device is designed to generate exposure rays having a maximum intensity that lies above an intensity threshold value for converting the light-sensitive layer from a second state into a first state, a movement device for moving, in particular in a scanning fashion, the exposure rays over or relative to the respectively assigned partial region, and an excitation light source for generating excitation radiation having (at least one) excitation wavelength for converting the light-sensitive layer from the first state into the second state.

This aspect of the invention, in order to increase the resolution, makes use of the fact that the light-sensitive layer changes between the second and the first state at an intensity threshold value that lies below the maximum intensity of the exposure ray, which is typically attained in the center of a respective exposure ray. In the case of a reversible state transition, what can thereby be achieved is that the light-sensitive layer, apart from in a partial region which is provided for patterning and which constitutes a sub region of the (diffraction-limited) region covered by an exposure ray impinging on the light-sensitive layer, is converted from the second state to the first state, such that the patterning can be effected only in the partial region provided therefor. By means of the excitation light source, the light-sensitive layer can be converted from the first state to the second state. By contrast, the exposure rays have the opposite effect, that is to say that they serve to convert the light- sensitive layer from the second state to the first state. The excitation can be effected before or during the exposure. It goes without saying that both the excitation radiation and the exposure radiation need not have only a single wavelength, but rather can, if appropriate, cover a respective wavelength range. Since both the excitation light source and the light generating device generally comprise a laser light source, however, the radiation generated by them has, to a good approximation, only a single wavelength.

In one embodiment, the transition from the first state into the second state is reversible and the light-sensitive layer can be converted into a permanently changed chemical state only in the second state. Since the transition between the two states is reversible, the excitation of the light-sensitive layer can be effected before the exposure, wherein the excitation radiation can be applied to the light-sensitive layer in particular homogeneously. In this case, by way of example, it is possible to carry out an exposure method as described in US 2006/0044985 A1 , the entirety of which is incorporated by reference in the subject matter of this application. In the method described therein, the light- sensitive layer is converted from the second state to the first state after excitation with the aid of exposure radiation, wherein a narrowly delimited region is omitted, i.e. the exposure radiation does not impinge thereon, or the intensity of the exposure radiation is minimal there, such that the light-sensitive layer remains in the second state there since the intensity of the exposure rays remains below the intensity threshold there.

In a further embodiment, the partial regions to which the respective exposure rays are assigned at least partly overlap. In order, outside the above-described narrowly delimited region of minimal intensity, to obtain an intensity that is definitely above the intensity threshold, it is of advantage if adjacent partial regions to which a respective exposure ray is assigned partly overlap, such that the intensity distributions of adjacent exposure rays also overlap in their outer regions and are superimposed there to form a total intensity that is above the intensity threshold.

In one development, the exposure apparatus comprises a fixing light source for converting the light-sensitive layer from the second state into the permanently changed chemical state In this case, the light-sensitive layer can be converted into the permanently changed chemical state in the region in which it is in the second state by the fixing light source, and can be patterned in this way. Once a region of the light-sensitive layer has been converted to the permanently changed chemical state, it no longer reacts to the excitation radiation or the exposure rays of subsequent exposures.

In a further embodiment, the excitation light source is designed to generate excitation radiation having an intensity profile that varies in a location- dependent manner on the light-sensitive layer, wherein the excitation radiation preferably has the maximum intensity between two exposure rays impinging in an adjacent fashion on the light-sensitive substrate. By generating a location- dependent intensity profile of the excitation radiation, it is possible to

superimpose the exposure rays with the excitation radiation such that, analogously to an STED ("Stimulated Emission Depletion") microscope, an intensity maximum is formed in a narrowly delimited region and converts the light-sensitive layer into the first state.

In a further embodiment, the transition from the second state to the first state is irreversible, that is to say that the second state already constitutes a state having permanently changed chemical properties. A light-sensitive layer having such properties can be used particularly in the case of the above-described simultaneous use of excitation radiation and exposure radiation. If the combined intensity of excitation radiation and exposure radiation is in this case above the intensity threshold value, the light-sensitive layer attains the first, permanently changed chemical state in the associated region.

Alternatively, the use of excitation radiation can also be completely dispensed with, if appropriate, that is to say that it is possible to use a light-sensitive layer (resist) in which the intensity threshold value is so high (e.g. 80% or 90% of the maximum intensity of the exposure rays) that the light-sensitive layer is irreversibly converted from the second state to the first state only in a small sub region of the intensity distribution amounting to e.g. 30% or less of the area covered by a respective exposure ray. In this case, in the region in which the threshold value of the intensity was not exceeded, the resist should "forget" the exposure as rapidly as possible, that is to say that a so-called Alzheimer resist should be used. Resists of this type are used e.g. for rewritable DVDs and can be embodied e.g. as chalcogenides in which the transition between the two states is effected in particular thermally between an amorphous phase and a crystalline phase.

In other words, the surface region which is intended to be patterned can lie either at the center of a respective exposure ray, if the intensity threshold value is exceeded there, or alternatively at the center of a region in which (almost) no exposure radiation impinges on the light-sensitive layer, i.e. in the region of a minimum of the intensity distribution on the light-sensitive layer. In order to make the respective surface region as small as possible and thus to make the resolution as high as possible, a considerable maximum intensity of the exposure radiation may possibly be required.

In a further embodiment, the light-sensitive layer comprises a switchable organic dye or a switchable chalcogenide. Switchable organic dyes comprise dye molecules which are switchable from a second state to a first state (and vice versa) with the aid of light. As explained further above, in the case of chalcogenides the transition between the two states is typically effected by thermal excitation, to be precise between an amorphous phase and a crystalline phase.

In one development the second state of the switchable organic dye can be converted into the first state of the switchable organic dye by stimulated emission. Here, as in the case of STED microscopy, the dye can be converted from a first, energetically lower state to a second, energetically higher state with the aid of excitation radiation and can be returned from said second state to the first state by stimulated emission with the aid of exposure rays in a suitable wavelength range. In this case, the wavelengths required for exciting the dye into the second state and for exciting the stimulated emission into the ground state typically differ.

The first and second states can also be different structural isomerism states of the switchable organic dye, for example two isomerism states representing a cis-trans transition of the respective dye molecules, as is described for example in US 2006/0044985 A1 cited above. While the dye molecules in the first state (e.g. trans state) can be converted into a permanently changed chemical state by irradiation with fixing light, this is not possible for the second state (e.g. cis state).

Besides the use of fluorescent dyes, in which a transition from an energetically excited state to the ground state can take place by means of stimulated emission, it is also possible, of course, to use light-sensitive layers having other types of (reversible) state transitions in the exposure apparatus, e.g. the abovementioned chalcogenides, in which the transition between amorphous phase and crystalline phase is effected thermally (e.g. excited by an exposure pulse).

In a further embodiment related to both aspects, the generating device has a raster arrangement having a plurality of switchable raster elements, which is designed for switching a respective exposure ray on or off in a manner dependent on a structure to be produced on the light-sensitive layer. With the aid of the raster arrangement, a pattern of light spots corresponding to the activated, i.e. switched-on, raster elements can be generated on the light- sensitive layer.

In one development, the raster elements of the raster arrangement are embodied as switchable diaphragms for a respective exposure ray. In this case, the raster arrangement transmits exposure radiation only in those regions in which the raster elements are activated, i.e. in which the latter do not act as diaphragms. By contrast, the illumination radiation is blocked in the regions in which the raster elements are switched off.

In one development, the raster arrangement is embodied as an LCD array, as a laser diode array or as an OLED array. In the first case, an illumination device is required which illuminates the LCD array on its side facing away from the light-sensitive substrate. When a laser diode array or an OLED array is used, each raster element has a dedicated light source that can be activated individually for generating a respective exposure ray. Both LCD arrays and laser diode or OLED arrays are commercially available in which the raster elements are small enough to achieve a very high resolution. In particular the switching times of commercially available OLED arrays are short enough to ensure a high throughput during the exposure.

In an alternative embodiment, the raster elements are embodied as switchable reflectors for a respective exposure ray. In this case, the raster elements, in a first, active switching position, can deflect the exposure radiation onto the light- sensitive layer, whereas in a second, deactivated switching position they do not deflect the exposure radiation onto the light-sensitive layer, but rather into a different spatial region.

In one development, the raster arrangement is embodied as a micro-mirror array (MMA). The raster elements of MMAs are very small and have sufficiently short switching times of the switchable reflectors to enable a high throughput during the exposure.

In a further embodiment, the movement device has at least one displacement unit for displacing the raster arrangement relative to the light-sensitive layer, preferably synchronously with the near field optical unit. In order to displace the exposure rays in the respective partial regions, it is advantageous to displace the raster arrangement in a plane parallel to the light-sensitive layer. For this purpose, the movement device can comprise two linear displacement units, which displace the raster arrangement in two, preferably mutually

perpendicular, directions in said plane. In this way, the partial regions of the light-sensitive layer can be scanned in order to pattern the latter over the whole area. It goes without saying that alternatively, if appropriate, the raster arrangement can remain stationary and the light-sensitive layer or the substrate can be displaced. Of course, it is also possible for substrate and raster arrangement to move simultaneously, if appropriate in opposite directions.

In a further embodiment, the generating device comprises an illumination device for, in particular homogeneously, illuminating the raster arrangement. In this case, the illumination radiation impinges on the raster arrangement over the whole area and the individual exposure rays are generated at the raster elements of the raster arrangement which are switched into an active state, while they are not transmitted to the light-sensitive layer by the other

(deactivated) raster elements.

In a further embodiment, the exposure apparatus comprises a lens for the reducing imaging of the raster arrangement onto the light-sensitive layer or onto the near field optical unit. The reducing imaging, e.g. by a factor of 10, increases the resolution during the exposure of the light-sensitive layer. If the exposure apparatus comprises a near field optical unit, the imaging is typically effected onto said near field optical unit or onto that side thereof which faces away from the light-sensitive layer, i.e. it forms the image plane of the lens. The invention also relates to a method, associated with the first aspect, for the patterned exposure of a light-sensitive layer, comprising: generating a plurality of, in particular parallel, exposure rays, wherein each exposure ray is assigned to a partial region of the light-sensitive layer, moving the exposure rays over or relative to the respectively assigned partial region, and arranging a near field optical unit upstream of the light-sensitive layer for converting a respective exposure ray into an evanescent wave for generating a light spot on the light- sensitive layer, the extent of which light spot is smaller than the extent of the exposure ray upstream of the near field optical unit.

As explained above, the exposure of the light-sensitive layer is parallelized as far as possible by virtue of a multiplicity of exposure rays being emitted simultaneously onto the layer to be exposed, which respectively impinge on the light-sensitive layer in a partial region which is of the order of magnitude of a diffraction disk. The near field optical unit serves for increasing the resolution beyond the diffraction limit, that is to say that the exposure ray is reduced to a light spot whose extent can be e.g. an order of magnitude below the diffraction limit, such that, for patterning the entire light-sensitive layer, the exposure rays are guided, in particular in scanning fashion, over the light-sensitive layer or the corresponding partial region.

A method, assigned to the second aspect, for the patterned exposure of a light- sensitive layer comprises: generating a plurality of, in particular parallel, exposure rays, wherein each exposure ray is assigned to a partial region of the light-sensitive layer, and moving the exposure rays over or relative to the respectively assigned partial region, wherein the exposure rays are generated with a maximum intensity that is greater than an intensity threshold value for converting the light-sensitive layer from a second state into a first state, exciting the light-sensitive layer with excitation radiation for converting the light-sensitive layer from the first state into the second state, and returning the light-sensitive layer from the second state into the first state in a region not provided for patterning.

As explained further above, the second aspect uses a light-sensitive layer having a defined intensity switching threshold, such that, with a suitable choice of the intensity of the exposure rays, the resolution can be increased beyond the diffraction limit. In this case, the light-sensitive layer can be converted reversibly from the first state to the second state by the excitation radiation and can be returned to the first state by means of the exposure rays in a region not provided for patterning. It is only in the region to be patterned, in which the exposure radiation has a minimum (or a maximum, see above), that the light- sensitive layer is not converted into the first state and can therefore be converted into a permanently chemically changed state, e.g. using fixing radiation.

Further features and advantages of the invention are evident from the following description of exemplary embodiments of the invention, with reference to the figures of the drawing, which show details essential to the invention, and from the claims. The individual features can be realized in each case individually by themselves or as a plurality in any desired combination in a variant of the invention.

Drawing

Exemplary embodiments are illustrated in the schematic drawing and are explained in the description below. In the figures:

Figure 1 shows a detail of a light-sensitive layer having a plurality of partial regions, to each of which an exposure ray is assigned, Figure 2 shows a schematic illustration of an exposure apparatus for simultaneously generating a plurality of exposure rays, and comprising a near field optical unit,

Figures 3a-d show schematic illustrations of different exemplary embodiments of a near field optical unit,

Figure 4 shows a schematic illustration of an exposure apparatus

comprising a raster arrangement in the form of an LCD array,

Figure 5 shows a schematic illustration of an exposure apparatus

comprising a raster arrangement in the form of a light emitting diode array,

Figure 6 shows a schematic illustration of a location-dependent intensity distribution of the exposure radiation and of an intensity threshold of the light-sensitive layer,

Figure 7 shows an illustration analogous to figure 6 with an intensity

minimum below the intensity threshold,

Figure 8 shows a schematic illustration of an intensity distribution

generated by the superimposition of the exposure radiation with excitation radiation,

Figure 9 shows a schematic illustration of an exposure apparatus

comprising an excitation light source and a fixing light source and an LED array, and

Figure 10 shows a schematic illustration analogous to figure 9 with an OLED array and an illumination system. Fig. 1 schematically shows a detail of a light-sensitive layer 1 having a plurality of square partial regions 2a-h, to each of which an exposure ray 3 is assigned. As can be discerned in figure 1 , the extent of a respective partial region 2a-h is of the order of magnitude of the extent 4 - represented by a dashed circle - of a respective exposure ray 3, i.e. in the present case is approximately ten times as large as the extent 4 of an exposure ray 3. The light-sensitive layer 1 is exposed simultaneously with a plurality of exposure rays 3, which are

individually switched on or off depending on a structure to be produced on the light-sensitive substrate 1 , as is explained below with reference to Figure 2.

Figure 2 shows an exposure apparatus 5 for exposing the light-sensitive layer 1 applied on a substrate 6 (wafer). The exposure apparatus 5 comprises a light generating device 7. The latter comprises a light source 7a in the form of a laser for generating exposure radiation having a wavelength of e.g. 193 nm or 157 nm. The light source 7a serves for illuminating a raster arrangement 8 over the whole area, said raster arrangement being embodied as a micro-mirror array (MMA). The micro-mirror array comprises a multiplicity of individually drivable raster elements 9 in the form of mirror elements. In this case, the micro-mirror array 8 can have e.g. a matrix arrangement of approximately 4000 x 2000 raster elements 9, wherein one raster element 9 (hereinafter: individual mirror) can have e.g. an area of approximately 16 m x 16 pm. Commercially available MMAs have switching frequencies in the range of approximately 5 kHz in order to move an individual mirror 9 from an (active) basic position, in which the individual mirror 9 is arranged in a plane 10 parallel to the plane of the light- sensitive layer 1 , into a tilted position, which is shown only for a single individual mirror 9 for the sake of simplification in figure 2. The throughput of the wafers 6 to be exposed is approximately 100 wafers per hour given a switching frequency of approximately 5 kHz.

Since the individual mirrors 9 of the MMA 8 are in each case separated from one another by non-reflective regions, a multiplicity of exposure rays 3 arise at the MMA 8, said exposure rays being deflected to the light-sensitive layer 1 or into a spatial region alongside the latter, depending on the position of a respective individual mirror 9. The respective switching position of the individual mirrors 9 and thus the pattern generated by the MMA 8 are dependent on the structure to be produced on the light-sensitive layer 1 . A control device 1 1 serves for driving the MMA 8 in a manner dependent on the predefined structure to be produced on the light-sensitive layer 1 .

The exposure rays 3 which are deflected to the light-sensitive layer 1 at the MMA 8 are oriented parallel to one another and their propagation direction runs perpendicular to the light-sensitive layer 1. A lens 12 serves for the reducing imaging (e.g. by a factor of 10) of the exposure rays 3 or of the plane 10 with the MMA 8 onto the light-sensitive layer 1.

As can be discerned in figure 1 , a respective exposure ray 3 covers only a part of the surface of a partial region 2a-2h assigned to it. For the whole-area patterning of the light-sensitive layer 1 in a region to be patterned, the exposure apparatus 5 therefore comprises a movement device 13, which comprises a linear movement unit 14 for displacing the MMA 8 along the X-direction of an XYZ coordinate system shown in figure 2. A corresponding linear movement unit (not shown) serves for displacing the MMA in the Y-direction. With the aid of the movement device 13, the MMA 8 can be displaced in the X-direction and in the Y-direction over a distance corresponding approximately to the edge length of a respective partial region 2a-2h, in order to pattern the entire light- sensitive layer 1 in a desired region. In this case, the control device 1 1 is coupled to the linear movement unit 14 in order to control the displacement thereof in the X-direction (and of the further linear movement unit in the Y- direction). It goes without saying that a multiplicity of adjacent regions are formed on the wafer 6, which regions can be patterned in the manner described above by virtue of the movement device 13 suitably controlling the movement of the MMA 8 (and if appropriate of the wafer 6). The exposure apparatus 5 additionally comprises a near field optical unit 15, which is arranged in direct proximity to the light-sensitive layer 1 . A further linear movement unit 14a is coupled to the control device 1 in order to displace the latter synchronously with the MMA 8 in the X-direction. There is also a corresponding coupling to a further linear displacement unit (not shown) for displacing the near field optical unit 15 in the Y-direction.

The near field optical unit 1 5 serves for converting a respective exposure ray 3 into an evanescent wave. In this way, the extent of the exposure ray 3 can be reduced to the size of a light spot 16 (cf. figure 1 ), which is significantly smaller than the (diffraction-limited) extent 4 of the exposure ray 3 upstream of the near field optical unit 15. Consequently, the resolution of the exposure apparatus 5 can be increased beyond the diffraction limit by means of the near field optical unit 15.

Several exemplary embodiments of the near field optical unit 1 5 are described in greater detail below with reference to Figures 3a-d. What is common to the exemplary embodiments shown therein is that a distance a between the side of the near field optical unit 1 5 at which the evanescent wave emerges is of the order of magnitude of the wavelength λβ of the exposure radiation, and is smaller than said wavelength AB in figures 3a-c.

This is of advantage since the intensity of an evanescent wave 17 respectively emerging from the near field optical unit 15 decreases exponentially with the distance "a" from the emergence, that is to say that the following holds true: l(a) = lo x Exp (- k *a), wherein l₀ denotes the intensity at the emergence and k denotes a proportionality constant. Therefore, if the near field optical unit 15 is too far away from the light-sensitive layer 1 , the intensity of the evanescent wave is too low to expose the light-sensitive layer 1 .

In the example shown in figure 3a, the near field optical unit 15 is embodied as a perforated mask and comprises a substrate 18 as a carrier, said substrate being transparent to the exposure rays 3, and a planar barrier layer 19 facing the light-sensitive substrate 1 and composed of chromium with a plurality of through openings 20, the diameter D of which is smaller than the used wavelength λ_Β of the exposure rays 3. The barrier layer 19 has a thickness of approximately 80 nm and is no longer transmissive to the exposure rays 3 at the used wavelength λ_Β of 193 nm. The diffraction-limited extent (Airy disk) 4 - caused by the lens 12 - of the exposure rays 3 when entering into the near field optical unit 15 is reduced by means of the barrier layer 19 or the through openings 20 to the extent of the light spot 16 as illustrated in figure 1.

Figure 3b shows an exemplary embodiment of the near field optical unit 15 wherein the transparent substrate 19 has a surface structure in the form of conical tips 21 serving as a micro-optical unit. In this case, the through openings 20 in the barrier layer 19 are situated at the outermost end of the conical tips 21 , which is arranged at a distance a from the light-sensitive layer 1 that is smaller than the wavelength λβ of the exposure radiation.

In two examples shown in figures 3c, 3d, the light propagation direction of the exposure rays 3 runs at an angle a with respect to the near field optical unit 15 or with respect to the light-sensitive substrate 1 . This can be achieved in the exposure apparatus 5 from figure 2, for example, by departing from the parallel orientation of the A 8 with respect to the light-sensitive layer 1. In this case, the exposure rays 3 are polarized parallel to the plane of incidence,

corresponding to the plane of the drawing. The exposure rays 3 can be polarized by suitable polarization filters (not shown). Since the laser light source 7 (cf. figure 2) typically generates linearly polarized exposure radiation anyway, a polarization filter can be dispensed with, if appropriate, given suitable orientation of the laser light source 7 relative to the light-sensitive layer 1.

In the example shown in figure 3c, the near field optical unit comprises a dielectric substrate 22 with a plurality of metal tips 23 which are embedded into the dielectric substrate 22 and which are electrically insulated from one another. In this case, the incident exposure rays 3 serve for exciting surface plasmons in a respective metal tip 23 and induce there an alternating electric field which is maximally concentrated at the tapering end of the metal tips 23 and emerges from the latter as an evanescent wave 17. Given a small distance a between a respective tip 23 and the light-sensitive layer 1 , the intensity of the evanescent wave 17 is sufficient to expose the light-sensitive layer 1 in a very small region around the metal tip 23. If permitted by the mechanical resistance of the light- sensitive layer , the metal tips 23 can also be in direct contact with said layer.

In order to excite the surface plasmons, the wave number of the exposure rays 3 used additionally has to be adapted to the plasma frequency of the metal used, which can be effected via the dielectric substrate 22. In the present example, in which the exposure rays 3 have a wavelength λ_Β of approximately 193 nm, aluminum, for example, is suitable as material for the metallic tips 23.

In the exemplary embodiment shown in figure 3d, the near field optical unit 15 from figure 3c is extended by a so-called superlens element 24. The superlens element 24 is mounted on that side of the near field optical unit 15 which faces the light-sensitive layer 1 , and consists of a first dielectric layer 24a and a second dielectric layer 24c, between which a metallic layer 24b is arranged. Surface plasmons are excited in the case of the superlens element 24 as well. Said surface plasmons make it possible to image the evanescent waves 17 emerging from the near field optical unit 15 onto the light-sensitive substrate 1 , wherein the evanescent waves 17 are transported in an almost undamped manner. This is possible since the superlens element 24 has a negative refractive index for the wavelength λβ of the exposure rays 3. In this case, the thicknesses of the (planar) layers 24a-c are typically of the order of magnitude of the wavelength λ_Β of the exposure rays 3. In the present example of a wavelength λ_Β of approximately 193 nm, the use of a metallic layer 24b composed of aluminum has proved to be of advantage. In this case, quartz glass layers, for example, can be used as dielectric layers 24a, c. As can likewise be discerned in figure 3d, the distance a between the emergence of the evanescent waves 17 and the light-sensitive substrate 1 can be chosen to be greater than in the examples described in figures 3a-c. It goes without saying that a superlens element 24 can also be used in the near field optical units shown in figures 3a-c.

As is shown in figure 3c, the exposure apparatus 5 can additionally comprise a detector device 25 for the spatially resolved detection of the intensity of the exposure rays 3 reflected at the dielectric substrate 22 of the near field optical unit 15. The intensity of the reflected light can be measured by such a spatially resolving detector device 25, e.g. in the form of a CCD camera or the like, channel by channel, i.e. individually for each exposure ray 3. In this way, it is possible to measure indirectly the energy input of a respective exposure ray 3 or of the evanescent wave 17 generated by the latter in the light-sensitive layer 1 , since the less energy is introduced into the light-sensitive layer 1 , the more energy is reflected, and vice versa.

In contrast to the near field optical units 15 in the form of perforated masks as shown in figures 3a, b, the energy transfer is more efficient when surface plasmons are excited, since the plasmons absorb the light energy "over a large area" and can release it again essentially via the metallic tips 23. In the exemplary embodiments described in figures 3a, b, the geometrical ratio between the diameter D of the through openings 20 and the total area of the perforated mask is crucial.

Since the intensity coupled over into the light-sensitive layer 1 in the near field is greatly distance-dependent, it is possible, as shown in figure 3c, to arrange a distance determining device 26 for determining distance between the near field optical unit 15 and the light-sensitive substrate 1 in the exposure apparatus 5. The distance determining device 26 can determine the local distance a and, in particular, a possible tilting of the near field optical unit 15 with respect to the light-sensitive substrate 1 on the basis of the intensity picked up by the detector device 25. By determining the distance a at a plurality of locations, it is possible to deduce a tilting of the near field optical unit 15, which can be compensated for, if appropriate, by means of manipulators (not shown), e.g. in the form of piezo-actuators. The distance a determined with the aid of the distance determining device 26 can be set or regulated to a desired distance in order to enable focus control or focus position regulation.

If the distance a between the conical tips 21 and the light-sensitive layer 1 varies locally differently, the exponential dependence of the tunneling efficiency on the distance a can be used to compensate for the resultant inhomogeneity of the light distribution on the light-sensitive layer 1 by suitable influencing of the intensity distribution upstream of the near field optical unit 15.

For this purpose, the detector device 25 and also, if appropriate, the distance determining device 26 are connected to the control device 1 1 (cf. figure 2), which evaluates the detected or measured data and, in a manner dependent thereon, drives a neutral filter 27 arranged upstream of the lens 12, which filter allows channel by channel, i.e. individual, modulation of the intensity of each individual exposure ray 3. In this case, the control device 1 1 modulates the intensity of the exposure rays 3 in such a way that an intensity of the exposure rays 3 that is as uniform as possible is obtained on the light-sensitive layer 1. It goes without saying that in addition or as an alternative to the setting of the intensity, it is also possible to provide further measures for modulating the exposure rays 3, e.g. influencing of the polarization of the exposure rays 3 with the aid of polarizer devices that effect modulation channel by channel, i.e. individually.

Figure 4 and Figure 5 show two further examples of exposure apparatuses 5 wherein the light generating device 7 in each case differs from that shown in figure 2. The light generating device 7 from figure 4 has an illumination system 7b, which expands the laser radiation emerging from the laser radiation source 7a and homogeneously illuminates a matrix arrangement in the form of an LCD array 8a. The individual raster elements 9a (pixels) of the LCD array 8a can be switched on or off depending on the structure to be produced on the light- sensitive layer 1 , such that a desired pattern of exposure rays 3 is obtained. In this case, the raster elements 9a can have e.g. an extent of 2.9 μιη x 2.9 μιη given a size of 100 mm x 100 mm, as is the case e.g. for the LCD array having VGA resolution as described at "http://www.lgblog.de/2009/06/15/kleinstes-lcd- displa -der-welt-mit-vga-auflosung/".

The light distribution of the exposure rays 3 that is generated by the LCD array 8a is transmitted by the lens 2, which has a numerical aperture NA=1 as in figure 2, onto the image plane with the light-sensitive layer 1 in a manner reduced at least by a factor of 10, such that there arises on the latter an image of the pattern of the active raster elements 9a of the LCD array 8a e.g. with a size of 10 mm x 10 mm. In this case, the extent of each exposure ray 3 on the light-sensitive layer 1 corresponds to the resolution (according to Abbe) of the lens 12 used.

If a numerical aperture NA=1 , a k factor of 0.5 (for example produced by an annulus diaphragm in the pupil plane of the lens 12), and a wavelength λ_Β of the exposure rays 3 of 193 nm are assumed for the lens 12, then the formula for the possible distance that can still be resolved between two light points (d = k x λ_Β / NA) yields d = 0.5 x 193 nm / 1 , i.e. approximately 100 nm. If the resolution actually achieved by suitable measures (see above and below) is fixed at 10 nm, then the area of 100 nm x 100 nm formed on the light-sensitive layer 1 by an impinging exposure ray 3 has to be scanned in at least 20 x 20 = 400 sub steps.

For this purpose, the LCD array 8a can be moved with the aid of the movement device 13 or a linear movement unit 14 step by step in 5 nm steps or continuously (at constant speed) in the Z-direction, the movement being synchronized with the exposure, that is to say that the switchable raster elements 9a are switched on or off depending on the structure to be produced in each case. It goes without saying that a second linear displacement unit (not shown) serves for displacing the LCD array 8a in the Y-direction. It furthermore goes without saying that additionally or alternatively the wafer 6 can also be displaced by means of suitable displacement devices in the plane in which the light-sensitive layer 1 is arranged.

If it is assumed that the LCD array 8a operates with a switching frequency of 500 Hz, the 10 mm x 10 mm field on the wafer 6 can be exposed in

approximately 0.8 second. A commercially available wafer 6 has approximately 700 of such 10 mm x 10 mm cells and could therefore be exposed after approximately 560 seconds, resulting in a throughput of approximately 8 wafers per hour. In this case, primarily the switching frequency of the raster elements 9a (pixels) of the LCD array 8a (switching time approximately 2 ns) has a limiting effect on the exposure rate. It goes without saying that in the case of LCD arrays that will be developed in the future, the switching frequencies will possibly be increased or the switching times will be able to be improved by adapting LCD arrays to the present application (only on/off), thus making it possible to increase the throughput achievable with the exposure apparatus 5 shown in figure 4.

A significant reduction of the switching times is possible in the case of the exposure apparatus 5 shown in figure 5, wherein the light generating unit 7 has a raster arrangement in the form of a laser diode array 8b having a plurality of switchable laser diodes 9b as light sources, the number of which substantially corresponds to that of the LCD array 8a shown in figure 4. In the case of such a laser diode array 8b, the switching times can turn out to be shorter by approximately a factor of 2000, with the result that a theoretical throughput of approximately 16000 wafers is possible, that is to say that the switching times in this case do not have a limiting effect provided that enough exposure radiation is present. Instead of the laser diodes 9b, OLEDs can also be used, but they only generate a power of approximately 10 mW/cm² on the light- sensitive substrate 1 , while the power that can be generated by a conventional 193 nm laser is approximately 100 W/cm², i.e. approximately 10000 times greater. On account of the low light intensity available, possibly likewise only approximately 5 wafers per hour can be exposed with an OLED array.

Moreover, OLEDs operate with visible light, and so the extent of the exposure rays 3 respectively impinging on the light-sensitive layer 1 is comparatively large.

The exposure apparatuses 5 shown in figure 4 and figure 5 can be combined with the near field optical unit 15 shown in figure 2 and in figures 3a-d, respectively, in order to achieve the desired increase in resolution. Instead of the above-described use of a near field optical unit 15 for increasing the resolution, it is also possible to use the properties of the light-sensitive layer 1 to achieve an increase in resolution.

In order to elucidate this procedure, Figure 6 shows the intensity I of three adjacent exposure rays 3, each having a central intensity maximum I MAX, said intensity impinging on the light-sensitive layer 1 as a function of the position P (in the X-direction). The light-sensitive layer 1 has an intensity threshold value Is, which is approximately 10% of the maximum intensity IMAX in the present case. In this case, the intensity threshold value Is defines that intensity at which the light-sensitive layer 1 undergoes transition from a second state B to a first state A. The second state B is assumed here if the intensity I lies below the threshold value Is; the first state A is assumed if the intensity I lies above the threshold value Is- In this case, the maximum intensity l_MAx of the exposure rays 3 was chosen such that it lies above the intensity threshold value l_s.

There are various possibilities with regard to the two states A, B of the light- sensitive layer 1 : by way of example, the transition from the second state B to the first state A can be irreversible. In this case, after the intensity threshold value Is has been exceeded, the light-sensitive layer 1 can no longer return to the second state B and remains in the permanently chemically changed state A or is converted into a further, permanently chemically changed state during subsequent fixing (so-called Alzheimer resist). In the case of such a resist it may be necessary to carry out a thermal treatment between two successive exposures, which thermal treatment brings about a type of "de-exposure" of the previously weakly exposed regions. In particular, resists which react highly nonlinearly to the exposure can be used as light-sensitive layers in this case.

With the use of a light-sensitive layer (resist) having such an irreversible transition, the intensity of the exposure rays 3 is typically chosen differently from the case illustrated in figure 6 such that the intensity threshold value Is is comparatively close to the intensity maximum I_MAX, e.g. I_s = 0.9 x I_MAX can be chosen. In this way, the light-sensitive layer is converted from the second state B to the first state A only in a comparatively small surface region 16 (cf. figure 1 ) of e.g. less than 20% or less than 10% of the surface region 4 of a

respectively impinging exposure ray 3, as a result of which the desired increase in resolution can be realized.

As an alternative to the use of a light-sensitive layer 1 which can be switched irreversibly from a second state B to a first state A by means of the exposure rays 3, it is also possible to use a light-sensitive layer 1 in which the transition from the second state B to the first state A (and vice versa) takes place in a reversible manner. In this case, the light-sensitive layer 1 can be embodied such that it can be converted into a permanently changed chemical state only in the second state B, but not in the first state A.

A light-sensitive layer 1 having such properties can be realized by specific switchable molecules, in particular in the form of switchable organic dyes. In this case, the switching of the molecules between the two states A, B can be brought about by light, wherein the wavelength of the light which serves for switching from the second state B to the first state A differs from the

wavelength of the light which is used for switching from the first state A to the second state B. In the case of fluorescent organic dyes, the transition from the second, excited state B to the first state A can be effected e.g. by stimulated emission. If, firstly, the entire light-sensitive layer is converted from the first state A to the second state B and, subsequently, the light-sensitive layer 1 is illuminated inhomogeneously in the manner shown in figure 6, then said layer remains in the second state B only in a comparatively narrow intensity range and can be converted from said state to a permanently chemically changed state C. In this way, it is likewise possible to increase the resolution during the exposure.

An exposure apparatus 5 designed for this purpose is illustrated in figure 9. The exposure apparatus 5 corresponds to that from figure 4 and is supplemented by an additional light generating unit 30, which comprises an excitation light source 31 for generating excitation radiation 32 and a fixing light source 34 for generating fixing radiation 33 for converting the light-sensitive layer 1 from the second state B to the permanently changed chemical state C.

During exposure with the exposure apparatus 5, firstly, the light-sensitive layer 1 is irradiated with the excitation radiation 32 over a large area and

homogeneously, for which purpose a partly transmissive mirror 36 is used, which deflects the excitation radiation 32 onto the light-sensitive layer 1 . In this case, the excitation radiation 32 has an excitation wavelength λ_Α, which, in the present example, wherein the light-sensitive layer 1 is formed from an organic dye (e.g. RH414), can be in the range of between 400 nm and 650 nm and can be e.g. at a wavelength of λ_Α = approximately 500 nm. The light-sensitive layer 1 is converted from the first state A to the second state B by the excitation radiation 32. In a subsequent step, the light generating unit 7 is used to radiate the exposure rays 3 onto the light-sensitive layer 1 , the wavelength of which is λ_Β = 745 nm in the present case.

The exposure rays 3 generate at the light-sensitive layer 1 an intensity profile which can be embodied e.g. as shown in Figure 7. In this case, the individual exposure rays 3 overlap and are superimposed to form a substantially homogeneous intensity I_HO , which is interrupted only in a small region 37, where it falls almost to zero. The exposure ray 3 associated with the omitted region 37 or an associated raster element 9a is switched off in this case. The intensity IHOM outside the omitted region 37 is greater than the intensity threshold Is and thus suffices to convert the light-sensitive layer 1 from the second state B to the first state A.

It is only in the omitted region 37 that the intensity I remains below the intensity switching threshold Is along a distance d_min, with the result that the light- sensitive layer 1 remains in the second state B along this section. If, in a subsequent step, with the aid of the fixing light source 34, fixing radiation 33 is applied to the light-sensitive layer 1 over a large area, then said layer is converted into the permanently changed chemical state C only in the omitted region 37. As can likewise be discerned in figure 7, the distance d_min is smaller than the distance d corresponding to the extent of an exposure ray 3, such that, by means of the measures described above, the resolution of the exposure apparatus 5 can likewise be increased beyond the diffraction limit or the maximum resolvable distance d.

With the use of a wavelength λβ of approximately 500 nm, a k factor of 0.5 and a numerical aperture NA = 1 , the maximum resolvable distance is d = 0.5 x 500 nm /1 = 250 nm. By contrast, if the resolution d_min is fixed as 10 nm, the corresponding partial region of approximately 250 nm x 250 nm has to be scanned at least in 25 x 25 = 625 steps, wherein in this case, too, if appropriate a continuous movement at constant speed can be performed instead of a plurality of discrete steps. In this case, the three successive steps of excitation, exposure and fixing have to be coordinated with the respective displacement by the control device 1 1 .

In the exemplary embodiment of the exposure apparatus 5 as shown in figure 9, as in figure 4 the throughput is limited by the switching speed of the LCD array 8a of approximately 500 Hz, with the result that a throughput of

approximately four wafers per hour is possible. Alternatively, an exposure apparatus 5 analogous to figure 5 can be used, as is illustrated in Figure 10. The exposure apparatus 5 from figure 10 differs from that from figure 5 firstly in that an OLED array 8c having a plurality of OLEDs 9c is used instead of a laser diode array. In this case, the excitation light source 31 and the fixing light source 34 are embodied as in figure 9 and the excitation, exposure and fixing, which has to be performed in each scanning step, is likewise coordinated or synchronized by means of the control device 1 1 .

With the use of the OLED array 8c, it is possible, as described above in connection with figure 5, to increase the switching speed by approximately a factor of 2000. A throughput of approximately 8000 wafers per hour would accordingly be possible. In this case, the excitation light source 31 and the fixing light source 34 should operate in the MHz range, which is possible without any problems, however, when using laser light sources having wavelengths λ_Α, hp in the visible range. In this case, the OLED array 8c can be displaced by means of the movement device 13 at a constant synchronized speed of e.g. approximately 0.1 m/sec.

The above-described procedure wherein the minimum of the respective exposure rays is used as "write signal" makes possible a particularly high resolution, since no imaging-relevant secondary radiation as a result of fluorescence photons takes place here.

As an alternative to the above-described procedure, it is also possible to carry out, with the aid of the exposure apparatuses 5 shown in figure 9 and figure 10, an exposure in which the excitation radiation 32 does not impinge

homogeneously on the light-sensitive layer 1 , e.g. by virtue of the excitation light source 31 being provided with a suitable illumination system and, if appropriate, a further raster arrangement (not shown) or a (neutral) filter. If the excitation radiation 32 having a location-dependent intensity l_A impinges on the light-sensitive layer 1 simultaneously with the exposure rays 3 having a likewise location-dependent intensity IB, then upon the superimposition of the two intensity distributions - as known from STED microscopy - this results in an intensity distribution _B = U X Exp(-I_B) (cf. figure 8), which, in contrast to the intensity distribution shown in figure 7, instead of a minimum restricted to a very small spatial region, has a maximum limited to a very small spatial region (peak having an extent in the nm range).

In order to obtain the intensity profile U_B from figure 8 with the pronounced peak, the intensity of the excitation radiation 32 is chosen such that the latter has, between two adjacent exposure rays 3, a maximum I_MAX at which the total intensity I_AB also becomes a maximum. As in the case of the exposure processes described in connection with figure 6 and figure 7, the excitation radiation 32 brings about a transition from a first state A to a second state B, whereas the exposure rays 3 cause the opposite effect, i.e. a transition from the second state B to the first state A by stimulated emission. It is only in the region of the peak that the light-sensitive layer 1 remains in the second state B and can be converted to a permanently changed chemical state C with the aid of the fixing light source 34. It goes without saying that the use of fixing light can be dispensed with if the transition between the first state A and the second state B is irreversible.

The procedure described in connection with figure 8 in this case represents the application of the principle of STED microscopy to lithography. With the use of organic dyes as light-sensitive layer 1 , said dyes remain excited only in the region of the peak and can chemically convert and thus fix the adjacent molecules of the light-sensitive layer 1 e.g. by means of Forster resonance energy transfer (dipole-dipole interaction) or by means of Dexter energy transfer (exchange of electrons). A "secondary emission" as a result of fluorescence photons, which would lead to expansion, does not take place in this case either.

In STED microscopy, a light-sensitive layer 1 consisting of a switchable organic dye is typically used, wherein the second, fluorescent state B can be returned to the first state A of the switchable organic dye by stimulated emission. Dyes that can be used for this purpose are available in large numbers, cf. e.g.

"http://www.mpibpc.mpg.de/groups/hell/STED_Dyes.html". If necessary, it may also be possible to produce new organic dyes that are optimized with regard to the chemical properties respectively required.

It goes without saying that the exposure described above is not restricted to the use of fluorescent dyes in which the return from the second state B to the first state A takes place on the basis of stimulated emission. Rather, the two states can e.g. also be different structural isomerism states (e.g. cis-trans isomers) of a switchable organic dye, of which a first state is a state capable of

fluorescence, while this is not the case for the second state. This principle is used, for example, in so-called RESOLFT (Reversible Saturable Optical Fluorescence Transitions) microscopy, where e.g. switchable proteins can also be used alongside organic dyes. The use of such materials for the light- sensitive layer has the advantage that the intensity required for overcoming the intensity threshold is lower than is typically the case for transitions as a result of stimulated emission.

Other types of light-sensitive layers can also be used, if appropriate, for the exposure processes described here. All that is essential in this case is that the light-sensitive layer has molecules having at least two states between which a changeover can be made in a reversible manner.

To summarize, in the manner described above it is possible to carry out a parallel exposure of a wafer in a plurality of partial regions, the extent of which is in each case of the order of magnitude of the diffraction limit. By means of the measures described above it is possible to increase the resolution beyond the diffraction limit, thereby enabling patterning within the respective partial regions by means of scanning exposure. An effective and cost-effective exposure of light-sensitive layers with high resolution can be achieved in this way.

Claims

1 . Exposure apparatus (5), comprising:

a substrate (6) with a light-sensitive layer (1 ),

a generating device (7) for generating a plurality of exposure rays (3) having an exposure wavelength (λ_Β), wherein each exposure ray (3) is assigned to a partial region (2a-2h) of the light-sensitive layer (1 ) and the generating device (7) is designed to generate exposure rays (3) having a maximum intensity (I MAX) that lies above an intensity threshold value (Is) for converting the light-sensitive layer (1 ) from a second state (B) into a first state (A), a movement device (13) for moving the exposure rays (3) relative to the respectively assigned partial region (2a-2f), and

an excitation light source (31 ) for generating excitation radiation (32) having an excitation wavelength (λ_Α) for converting the light-sensitive layer (1 ) from the first state (A) into the second state (B).

2. Exposure apparatus according to claim , wherein the transition from the first state (A) into the second state (B) is reversible and the light-sensitive layer (1 ) can be converted into a permanently changed chemical state (C) only in the second state (B).

3. Exposure apparatus according to claim 2, further comprising: a fixing light source (34) for converting the light-sensitive layer (1 ) from the second state (B) into the permanently changed chemical state (C).

4. Exposure apparatus according to any of the preceding claims, wherein the partial regions (2a-2h) to which the respective exposure rays (3) are assigned at least partly overlap.

5. Exposure apparatus according to any of the preceding claims, wherein the excitation light source (30) is designed to generate excitation radiation (32) having an intensity profile ( ) that varies in a location-dependent manner on the light-sensitive layer (1 ), wherein the excitation radiation (32) preferably has a maximum intensity (I AX) between two exposure rays (3) impinging in an adjacent fashion on the light-sensitive substrate.

6. Exposure apparatus according to any of the preceding claims, wherein the transition from the second state (B) into the first state (A) is irreversible.

7. Exposure apparatus according to any of the preceding claims, wherein the light-sensitive layer (1 ) comprises a switchable organic dye or a switchable chalcogenide.

8. Exposure apparatus according to claim 7, wherein the second state (B) of the switchable organic dye can be converted into the first state (A) of the switchable organic dye by stimulated emission.

9. Exposure apparatus according to claim 7 or 8, wherein the first and second states (A, B) are different structural isomerism states of the switchable organic dye.

10. Exposure apparatus according to any of the preceding claims, wherein the generating device (7) has a raster arrangement (8, 8a-8c) having a plurality of switchable raster elements (9, 9a-9c), which is designed for switching a respective exposure ray (3) on or off in a manner dependent on a structure to be produced on the light-sensitive layer (1 ).

1 1 . Exposure apparatus according to claim 10, wherein the raster elements (8a- 8c) of the raster arrangement (9a-9c) are embodied as switchable diaphragms for a respective exposure ray (3).

12. Exposure apparatus according to either of claims 10 and 1 1 , wherein the raster arrangement is embodied as an LCD array (9a), as a laser diode array (9b) or as an OLED array (9c).

13. Exposure apparatus according to claim 12, wherein the raster elements are embodied as switchable reflectors (9) for a respective exposure ray (3).

14. Exposure apparatus according to claim 13, wherein the raster arrangement is embodied as a micro-mirror array (8).

15. Exposure apparatus according to any of claims 10 to 14, wherein the

movement device (13) has at least one displacement unit (14) for displacing the raster arrangement (8, 8a-8c) relative to the light-sensitive layer (1 ).

16. Exposure apparatus according to any of claims 10 to 15, wherein the

generating device (7) has an illumination device (7b) for illuminating the raster arrangement (8a).

17. Exposure apparatus according to any of claims 10 to 16, further comprising: a lens (12) for the reducing imaging of the raster arrangement (8, 8a-c) onto the light-sensitive layer (1 ).

18. Method for the patterned exposure of a light-sensitive layer (1 ), comprising: generating a plurality of exposure rays (3), wherein each exposure ray (3) is assigned to a partial region (2a-2h) of the light-sensitive layer (1 ), and moving the exposure rays (3) relative to the respectively assigned partial region (2a-2h),

wherein the exposure rays (3) are generated with a maximum intensity (I MAX) that is greater than an intensity threshold value (Is) for converting the light- sensitive layer (1 ) from a second state (B) into a first state (A),

exciting the light-sensitive layer with excitation radiation (32) for converting the light-sensitive layer (1 ) from the first state (A) into the second state (B), and returning the light-sensitive layer (1 ) from the second state (B) into the first state (A) in a region not provided for patterning.