EP1599763A2

EP1599763A2 - Method for producing an exposed substrate

Info

Publication number: EP1599763A2
Application number: EP04713881A
Authority: EP
Inventors: Wittich Kaule
Original assignee: Giesecke and Devrient GmbH
Current assignee: Giesecke and Devrient GmbH
Priority date: 2003-02-26
Filing date: 2004-02-24
Publication date: 2005-11-30
Also published as: JP2006520010A; DE10308328A1; US20060141385A1; WO2004077493A3; RU2344455C2; RU2005129549A; US7241537B2; WO2004077493A2

Abstract

The invention relates to a method for producing an exposed substrate consisting of at least two different image areas. The inventive substrate is provided with at least two photoresistant layers which are adapted to the image areas to be produced.

Description

Process for producing an exposed substrate

The invention relates to a method for producing an exposed substrate which has at least two image areas. ^' . , ^'' .

To secure security documents such as banknotes, ID cards or the like, optically variable elements are often used, which are made up of diffraction gratings. Such elements are referred to below as grid images. These can be grating images in which the first and higher diffraction arrangement is used for viewing, e.g. with holograms or with such grid images that are composed of grid surfaces. Alternatively, grating images are also used in which the zeroth diffraction order is used, as described, for example, in US Pat. Nos. 892,385 and 4,484,797.

The first-order grating images and the zero-order grating images differ essentially in that in the former the grating constant must be greater than the light wavelength, while in the latter the grating constant is preferably chosen to be smaller than the wavelength, especially if the pure one Wants to observe zero order. While the grid constant is decisive for the color variability and the grid line structure plays a subordinate role in first-order grid images, it is exactly the opposite in the case of zero-order grid images.

The diffraction structures used as security elements are mostly produced as embossed holograms. For this purpose, a photoresist layer applied to a substrate is exposed to laser light or electron beams. Radiation-sensitive, film-forming materials, for example photoresists, are referred to as photoresists, the solubility behavior of which changes as a result of exposure to light or radiation. A distinction is made between positive and negative tending photoresists. The former become easily soluble through irradiation or conversion of functional groups under irradiation, whereas the latter become poorly soluble or insoluble through crosslinking or photopolymerization.

After the photoresist layer has been developed, a structure is formed which has peaks and valleys and can be molded by electroplating. With first-order grating images, the profile structure is preferably sinusoidal, with zero-order grating images box-shaped or trapezoidal. The molded structure can then be duplicated and used to make dies.

Grid images are also known in which several exposure steps have to be combined with one another. There are essentially two methods known for this.

In a first method, partial areas of a photoresist layer are covered with the aid of masks and first the unmasked partial areas of the photoresist layer, e.g. exposed to laser light of a first wavelength to produce a diffraction structure. In further process steps, the parts of the photoresist layer which have already been exposed are covered and the parts of the image which have now been freed from the masks, e.g. exposed with laser light of other wavelengths to produce further diffraction structures.

This method has the disadvantage that it cannot be used if different resist layer thicknesses are required in a lattice image, for example when composing zero-order lattice images. In a further known method, this problem is avoided by producing a plurality of stamping dies by galvanic means from photoresist layers which are exposed independently of one another. Each embossing stamp contains only a part of the overall picture. In order to maintain the overall picture, the dies are embossed side by side in thermoplastic material. However, the seams that occur during side-by-side embossing are disturbing in this process.

On the basis of this prior art, the object of the invention is to provide a method with which the exposure to different types of radiation can be easily accomplished and in which the layer thickness can also be adapted in different areas of the exposure, if necessary.

This object is achieved by a method with the features of the independent claims. Advantageous refinements and developments of the invention are specified in claims dependent thereon.

According to the inventive method for producing a resist master that has at least two different image areas, at least two photoresist layers are used that are adapted to the type of image areas to be produced. This has the advantage that each image area can be produced under optimal conditions and thus shows an optimal optical effect.

For the purposes of the invention, the term “photoresist” denotes a radiation-sensitive material whose chemical properties, in particular its solubility behavior, change due to the action of light or particle radiation. A "positive resist" refers to photoresist materials that become easily soluble through the photochemical degradation or conversion of functional groups. This means that the exposed areas are detached during further treatment, while the unexposed areas remain.

A “negative resist” refers to photoresist materials which become sparingly soluble or insoluble as a result of crosslinking or photopolymerization. This means that the unexposed areas are detached during further treatment, while the exposed areas remain.

The term "grating image" is not limited to grating line images, but encompasses any configuration of diffraction structures. Only if this term is used in contrast to a real hologram is the term to be understood in the narrower sense.

“Substrate” is to be understood to mean any carrier material to which photoresist layers can be applied for an exposure process. Glass plates are often used for this purpose, which may be colored or coated black. However, galvanically molded nickel brains can also be used that already have a A further layer of photoresist is applied to this and exposed and processed with a second grid image in accordance with the photoresist used are.

The “resist master” is the substrate produced according to the invention, which has at least one exposed and developed photoresist layer having. The resist master can be electroplated in further process steps and processed into embossed shims.

According to a first embodiment of the invention, at least two photoresist layers which are optimally adapted to the particular type of radiation to be used are used to produce a resist master which has at least two different image areas, such as a real hologram and a grid image. Laser radiation is usually used for holographic exposure, whereas electron beam is often used for grid generation. With the aid of the invention, such different production variants can thus be combined with one another on a substrate.

Another selection criterion for the photoresist layers in the different image areas can be the profile of the relief structure to be generated. Zero-order grating images require slopes that are as steep as possible, while flat flank angles are preferred for first-order grating images. In particular, sinusoidal profiles are sought. The inventive method can therefore also combine zero-order grating images with any first-order grating images on a substrate.

However, the method according to the invention also makes it possible to provide the different image areas with different zero-order grating images. In this type of grating images, the color variability arises solely from the destructive interference of the radiation reflected on the surfaces of the photoresist. The essential parameter is therefore the profile depth of the relief structure, the profile depth only depending on the layer thickness of the photoresist. This can be set very precisely and is available preferably in the range of approximately 50 to 200 µm. Accordingly, the substrate can also be provided with at least two photoresist layers which consist of the same photoresist material but have different thicknesses.

The photoresist layers according to the invention can already be arranged on the carrier material before the first exposure step. They are preferably applied one above the other, optionally with protective layers in between.

The top layer is optimized for the creation of a first image area, e.g. with regard to a first radiation type, the next layer on the other hand for the generation of a second image area, e.g. with regard to the layer thickness or another type of radiation etc. There may be “stop layers” between the resist layers, which ensure that the layers are only exposed to the correct radiation.

In a preferred embodiment, a positive resist layer suitable for optical holographic exposure is applied over a positive resist layer suitable for electron beam exposure, which is insensitive to the effects of optical radiation.

This layer sequence is first exposed optically in the desired areas, for example with a hologram. This exposure only works in the upper layer, not in the optically insensitive layer underneath. The other areas are optically exposed over their entire surface and additionally subjected to a desired electron beam grating image, as described, for example, in DE 10226 115 or DE 10226112. The optical exposure leads to the deletion of the upper layer in these areas, The electron beam exposure penetrates the upper layer and forms an image in the lower layer. After the resist development, the two image areas are side by side.

According to a further embodiment according to the invention, the individual photoresist layers are only applied to the substrate in a suitable phase of the production process and exposed to the corresponding grating image.

In this way, a first layer of photoresist can first be applied, exposed and developed on the substrate. The quality of this first photoresist layer is adapted to the type of radiation used in the exposure or its layer thickness is optimized for a specific imaging method. In a further process step, a second photoresist layer is applied to the substrate and the first photoresist layer remaining thereon, exposed again and developed. Since the second photoresist layer can be selected independently of the first photoresist layer, a material can be used for the second photoresist layer which is optimized for a second radiation type or whose layer thickness is optimized for a specific imaging method. The method according to the invention therefore makes it possible to produce different image areas lying next to one another, which in some cases may be seamlessly adjacent to one another, all image areas having an optimal quality or layer thickness due to the use of several specially adapted photoresist materials.

In a preferred embodiment, a negative resist layer is applied to the substrate in a first process section and the desired image areas are exposed. The substrate is then developed, wherein the unexposed areas of the negative resist are removed from the substrate. In a further process step, a second negative resist layer is then applied to the substrate and second image areas are exposed.

The areas already exposed in the first negative resist layer in the first process section are not further exposed in the second process section. By developing the second resist layer, the regions of the first resist layer which are filled in by the second resist material are finally exposed again. The result is a substrate with two photoresist layers arranged side by side in the form of mountains and valleys, hereinafter referred to as "relief structure". The relief structures in the first and second photoresist layers are formed at the same height and, depending on the design of the exposed pattern, also merge seamlessly ,

In a further preferred method, a positive resist layer is applied to the substrate instead of a negative resist in a first method section and the desired image areas in the desired design are exposed to suitable radiation. In order to completely remove the positive resist layer in the previously unexposed areas, the exposed areas of the first positive resist layer must be covered with a mask in a subsequent step and the previously unexposed areas must be intensively reexposed. During the development of the positive resist, the patterns exposed in the first step are exposed in the positive resist layer and the areas of the substrate which are subsequently exposed in the second step are completely freed from the positive resist. In addition to the first positive resist layer, this creates space for the application of further photoresist layers. The first positive The resist layer and the subsequent photoresist layers are at the same height.

In the exemplary embodiments described, further method steps can of course be provided in which further photoresist layers are applied and exposed accordingly. Negative resist layers and positive resist layers can also be combined as desired.

Before applying a new photoresist layer, a thin barrier layer can be applied, which ensures that the underneath photoresist layer is not damaged when the new photoresist layer is detached. The barrier layer is preferably made of an inorganic material which is not attacked during the development process. On the other hand, it may be necessary to remove the barrier layer after it has served its purpose if it interferes with subsequent process steps. This removal must be possible without damaging the resist layer. Metal layers fulfill e.g. this condition. They are not attacked by resist developers, but can be removed with acids, alkalis or caustic solutions, which in turn do not attack the resist.

The barrier layer can also perform other functions. If, for example, an electron beam is used for the exposure of one of the photoresist layers, the barrier layer can be designed as a conductive layer in order to derive the electrons after the energy has been released. A chrome layer is preferably used here. With optical exposure, an effectively light-absorbing layer may be required behind the photoresist layer. This is the case, for example, if the substrate or the under the layers lying on the optical photoresist itself do not swallow enough light.

The method according to the invention can be used particularly advantageously in the production of diffraction structures which are used as security features for documents of value or for product security. This is because the method according to the invention makes it possible to produce a diffraction structure with at least two different image areas that were generated with different exposure methods. For example, the diffraction structure can be designed, in part, as a real hologram, while other partial areas are only designed as a grating image, which was produced, for example, by means of electron beam lithography.

For example, a He-Cd laser with a wavelength of 442 nm and a highly sensitive photoresist are well suited for exposing a real hologram. When exposing using the usual holography process, a relief profile with flat flanks is obtained, which can be very easily converted into embossing stamps.

If, however, the same positive resist is used to produce diffraction structures in the electron beam lithography process, rectangular relief profiles are obtained which are not suitable for embossing, since the embossing lacquer remains stuck in the relief profile. In contrast, a low-sensitivity negative resist working with soft gradation and trapezoidal to sinusoidal relief profiles with an appropriately adjusted electron beam focus can be used very well in an embossing process.

However, pure grid images can also be created using different techniques. Depending on the design to be manufactured, it can be useful for Different image areas to use different manufacturing techniques or radiation types in order to produce an optimal image quality and brilliance of the optically variable effect. Different layer thicknesses in different areas can also be advantageous (in the case of first-order grating images) or necessary (in the case of zero-order grating images). The method according to the invention with the method steps described above can also be used here. The individual photoresist layers only have to be applied to the substrate in the desired layer thickness.

According to a further embodiment of the invention, it is also possible to use only one photoresist layer which is exposed to light radiation, such as e.g. Laser radiation, and in at least a further partial area with particle radiation, such as Electron beam, is exposed. This has the advantage that lattice images, which are generated using different recording techniques, can be produced on a substrate and this substrate as a whole can be further processed into an embossing tool. The production of different embossing tools and the problems explained with them are thus eliminated.

The image areas according to the invention can also partially or completely overlap. In this case, a photoresist layer is preferably used, which is at least partially exposed or written to first with one diffraction structure and then in the same area with a second or more diffraction structures.

For the described methods according to the invention, a neutral carrier material, such as a glass plate, is preferably used, onto which the individual photoresist layers are applied and exposed and developed there become. The substrate produced in this way, the so-called “resist master”, is subsequently electroplated and reproduced according to known methods in order to produce an embossing tool, such as an embossing cylinder.

Alternatively, a plastic or metal foil or a galvanic shim that has already been provided with a grid image can also be used instead of the neutral carrier material. The grid image is preferably in the form of a relief structure. A neutral carrier material, such as e.g. a glass plate, coated with a first layer of photoresist and exposed to the corresponding lattice image or parts thereof by means of a laser or electron beam. This resist master is electroplated. Then either the electroplating shim produced in this way or a plastic or metal foil, which was embossed with the grid image using an embossing tool produced from this electroplating shim, is coated with a further photoresist layer. This photoresist layer is also exposed with a lattice image or parts of an entire lattice image or written on by means of an electron beam. Depending on the type of photoresist used, it may be necessary to take further measures after the development of the photoresist to ensure that the first grid image is exposed in the desired image areas.

If, for example, a positive resist is used, this resist layer remains on the entire surface of the carrier material, while the structuring is only present in the exposed area. The unexposed areas must therefore be removed again. For this purpose, for example, the exposed areas can be provided with a metallization using masks or using a so-called washing process. In the washing process, everyone will not exposed areas printed with a preferably water-soluble printing ink and then metallized the support material over the entire surface. When the printing ink is released, the metallization above is also removed, the metallization only remains in the exposed areas. This also protects the exposed areas in the subsequent dissolving process of the photoresist layer, which is only removed in the unexposed areas, for example using acetone. In a final step, the metallization can also be removed. This substrate also forms a resist master, which, as already described, is processed further.

Another alternative provides for the already structured carrier material, i.e. the embossed film or shim, an embossable lacquer layer, e.g. to apply a UV lacquer layer or thermoplastic layer, in which the desired lattice image is embossed with a second embossing tool. This substrate also forms a resist master which, as described, is further processed into an embossing tool. Of course, this process can be repeated any number of times. In addition to the optimal adaptability of the photoresist layers to the type of grid image or the recording method, the procedures described last have the great advantage that an already existing grid image can be supplemented and / or individualized by additional information.

The two procedures described last are suitable, for example, if an optically variable security element is to be produced for a banknote series, which shows in the background a grid image that is identical for all denominations, such as a country symbol, and in the foreground an individual symbol for the respective denomination, like the denomination itself. The embossing tools produced according to the invention can be used to produce security elements which are used to secure documents of value, such as banknotes, checks, identity cards or the like. Embossed diffraction structure elements are also frequently used in the area of product assurance.

With the aid of the method variants according to the invention, zero-order grating images and first-order grating images or with particle radiation and grating images generated by optical exposure can be combined as desired in a resist master.

The invention is explained below by way of example with reference to the accompanying drawings. Show it:

Fig. La-d successive process steps when using negative resist layers;

2a-f successive method steps when using positive resist layers;

3a-d a further embodiment with two negative resist layers of different layer thickness;

Fig. 4 resist master according to the invention in supervision;

5 template for a holographic exposure;

6 shows an example of a mask; FIG. 7 holographic exposure with the original according to FIG. 5 and mask according to FIG. 6;

8a-f successive method steps of a method in which a positive

Resist is exposed holographically and then a negative resist is exposed using an electron beam;

9a-e show another embodiment of the method according to the invention with photoresist layers lying one above the other;

10 shows a further embodiment;

11a-c show a further embodiment of the invention with a photoresist layer made of positive resist;

12 negative resist exposed using the method according to FIGS. 11a, 11b;

FIGS. 13-15 show different layer structures which can be used in the method shown in FIG. 11;

16-18 further embodiments of the method according to the invention.

1a to 1d show method steps of the method according to the invention, in which a photoresist layer 1 is first applied to a substrate 2. The substrate 2 can be, for example, a glass plate which, if optical holographic exposure is to take place, is preferably colored black in order to avoid reflections. The photoresist layer 1 is applied, for example, by the substrate 2 is given a drop of photoresist material which is distributed uniformly over the substrate 2 in a resist centrifuge, for example a centrifuge. Thereafter, the photoresist layer 1 is cured by heating.

The thickness of the resulting photoresist layer 1 depends on the drop size, the spin speed and spin duration, the temperature, the vapor pressure and other parameters. If optical diffraction structures are to be introduced into the photoresist layer 1, the thickness of the photoresist layer 1 is between 100 and 1000 nanometers.

The method according to the invention is explained below using the example of the production of holographically produced diffraction structures. For this purpose, in the example shown in FIG. 1, a negative resist layer is used as the photoresist layer 1.

After curing, this negative resist layer 1 is exposed to uniform coherent wave fields 3, which interfere in the region of the negative resist layer 1 and form an interference pattern 4, which is indicated by dashed lines in FIG. 1 a, in the negative resist layer 1. The negative resist material and the radiation used are optimally coordinated. The exposure with the wave fields 3 is carried out such that the interference pattern 4 is formed only in the area of a first image area 5, while a second image area 6 remains unexposed. This can be achieved, for example, by using masks. The outlines of the image areas 5 and 6 are each chosen in accordance with the motif represented by the image areas 5 and 6. During development, the unexposed areas of the negative resist layer 1 are dissolved. Corresponding to the interference pattern 4, the negative resist layer 1 now has peaks 7 and valleys 8, which in the example shown are uniformly sinusoidal. Depending on the image to be displayed, the relief structure can also be of any complexity. This is particularly the case with real holograms. In the area of the image area 6, the negative resist layer 1 is completely removed by the development process, so that the substrate 1 is again uncoated in this area.

According to FIG. 1 c, a second negative resist layer 9 is then applied over the entire surface of the substrate 2, so that it also covers the first negative resist layer 1. This second negative resist material 9 is optimally adapted to the type of radiation used for exposure. As indicated in FIG. 1 c, the second negative resist layer 9 is also exposed in the image area 6 with coherent wave fields 10, the wavelength of which, however, is different, for example, from the radiation used for the exposure of the first negative resist 1. Here, too, an interference pattern 11 is formed in the image area 6, which is indicated by dashed lines.

The substrate 2 is developed again. The result is shown in Fig. Id. Since it is a negative resist, the exposed areas of the negative resist layer 9 remain during development. In the areas not exposed by the wave fields 10, the photoresist layer 9 is removed. In particular, the portions of the first photoresist layer 1 which have been clogged up by the second photoresist layer 9 are exposed again. The different image areas 5, 6 directly adjoin one another in the example shown. Of course, they can also be arranged at a distance. If further separate image areas are to be formed in addition to the image areas 5 and 6 shown in FIGS. 1a to d, corresponding areas of the substrate 2 are each left free by non-exposure in the method steps according to FIGS. In further method steps, the procedure is then as shown in FIGS. 1c and 1d.

The method can be carried out not only with negative resist layers, but also with positive resist layers. 2a to 2f show the corresponding method steps of the method according to the invention, using positive resist layers.

In a first method step, as shown in FIG. 2a, the substrate 2 is coated with a positive resist layer 12. In the area of the image area 5, the positive resist layer 12 is then exposed to coherent wave fields 13. These wave fields 13 interfere in the positive resist layer 12 and form an interference pattern 14 shown in broken lines in FIG. 2a. The material of the positive resist layer 12 is adapted to the type of radiation of the wave fields 13.

The exposed areas of the positive resist layer 12 are then covered with a mask, which is formed by a transparent film with areas 15 masked in a light-tight manner (FIG. 2b). Previously unexposed areas of the positive resist layer 12, which are intended for further image areas 6 in subsequent method steps, are intensively overexposed with the aid of radiation 16 according to FIG. 2b.

After the substrate 2 has been developed and the exposed areas have been removed, the relief structure of the positive resist layer 12 shown in FIG. 2 c is obtained. The positive resist layer 12 now has an interface Renzmuster 14 corresponding relief profile with mountains 17 and valleys 18, which is also shown here only for reasons of clarity as a sinusoidal relief structure. In order to provide the image area 6 with a diffraction structure, a second positive resist layer 19 is applied to the substrate 2. The second positive resist layer 19 is acted upon by wave fields 20 which form an interference pattern 21 shown in broken lines in FIG. 2d in the image resistive area 6 in the positive resist layer 19. The material of the positive resist layer 19 is adapted to the radiation type of the wave fields 20.

In a further process step shown in FIG. 2e, the areas of the positive resist layer 19 exposed to the wave fields 20 are in turn covered with a mask 22 and the image area 5 and any further image areas (not shown) are intensively exposed to radiation 23.

Finally, the substrate 2 is developed and the exposed areas are removed, so that the relief structures shown in FIG. 2f result on the substrate 2.

With the methods described here with reference to FIGS. 1a to 1d and 2a to 2f, one obtains side by side at the same height, i.e. photoresist layers 1, 9, 12, 19 lying directly on the substrate, the material for the photoresist layers being selected in each case with regard to the radiation used for exposure, so that optimal results are achieved.

It should be noted that the positive and negative resist layers can also be combined with one another. For example, the procedure ^{'Rensschritte} of FIG. La and ld 2d connect in FIGS. 2f shown to further method steps.

In certain embodiments, it may be useful to have a thin barrier or auxiliary layer, e.g. made of metal, an oxide or the like, which ensures that when the new photoresist layer is removed, the underlying photoresist layer is not damaged. The barrier layer is preferably made of inorganic material which is not attacked in the development process.

The auxiliary layer can also perform other functions. If an electron beam is used for the exposure of one of the photoresist layers, it is preferably formed as a conductive layer in order to derive the electrons after the energy has been released. In this case, the barrier layer is preferably a chrome layer. In contrast, in the case of interference exposure, it can be designed as a highly absorbent thin layer.

The invention is also not restricted to methods in which the exposure is combined by means of light radiation and particle radiation. For example, different wavelengths can also be used for the exposures.

Any types of grid images, such as first-order and zero-order grid images, can also be combined with one another.

3a to 3d show an embodiment of the invention in which the substrate is provided with two different image areas which are distinguished by different profile depths. This is for example at Zero-order grating images that show different optical effects. For this purpose, in a first step, as shown in FIG. 3a, a glass plate 60 is provided with a first negative resist layer 61. Since the profile depth depends solely on the resist layer thickness, the resist layer thickness must be set exactly. In the example shown, the resist layer thickness can be 200 nm. If an electron beam is used for the exposure to the radiation 62, the glass plate 60 can be sputtered with a chromium layer before the negative resist layer is applied. The thickness of this layer is approximately 20 nm. The negative resist layer 61 is finally exposed to the radiation 62 in such a way that trapezoidal exposed areas 63 are formed.

The negative resist 61 is then developed, the unexposed areas being detached and only the exposed areas 63 remaining on the glass plate 60, as shown in FIG. 3b. A second negative resist layer 64 is then applied to the glass plate 60. The layer thickness d _{2 of} this second negative resist layer 64 is 150 nm. This layer is finally exposed to the same radiation 62, preferably an electron beam. The exposure takes place in the areas 65 adjacent to the areas 63. This negative resist 64 is also subsequently developed, the unexposed areas being detached, so that only the exposed areas 63 and 65 remain on the glass plate 60. The regions 63, 65 are distinguished by different profile depth di, d ₂ , which leads to different optical effects, in particular in the case of zero-order diffraction gratings.

This method can of course also be carried out using positive resist layers or a mixture of positive and negative resist layers, as already explained with reference to the previous FIG. was tert. It is also possible to arrange any first-order grid image in one of the image areas.

FIG. 4 schematically shows a resist master 110 according to the invention for an embossed hologram, which has a first image area 100 which is exposed to light radiation and a second image area 101 which is exposed to particle radiation. In the example shown, the optically exposed image area 100 has a real hologram which represents a field of letters arranged in the background. The image area 101 generated with particle radiation is formed by a letter “A” which appears to pulsate when the image is tilted and which is produced by means of electron beam lithography. The motifs can of course be chosen as desired. The different image areas can also be interleaved as desired his.

The holographic, i.e. Letter field 100 generated by superimposing coherent light radiation is interrupted in area 101 or has a gap 101 there. In this gap 101 there is a letter “A” generated with particle radiation, in particular electron beam, which is composed of different band-shaped lattice structures, which is shown schematically by the different hatching.

Various method variants are described below with which such a resist master 110 according to the invention can be produced.

According to a first method, a template 102, as shown in FIG. 5, is used for producing the holographic background. This template 102 is optically exposed in a photoresist layer, wherein a mask 103 in the form of a letter "A" is used. The mask 103 is shown schematically in FIG. 6. The mask 103 prevents the holographic exposure of the photoresist layer in the region 101 and only the background is exposed with the letter field 100. This is shown in FIG 7. The lattice structure shown in Fig. 4 is then written into the recessed, unexposed area 101 by means of an electron beam. The sequence of the exposure steps can of course be interchanged. As will be explained in detail below, one or several layers of photoresist can be used.

A first embodiment, in which two photoresist layers are used, is explained in more detail with reference to FIGS. 8a to 8f. Here, a black-colored glass plate serving as substrate 2 is coated with a positive resist layer 24 made of the positive resist material A-RP 3040 with a layer thickness of approximately 0.50 micrometers. In a conventional holographic apparatus with, for example, He-Cd laser, the positive resist layer 24 is exposed in the background 25 in the usual rainbow hologram Hl / H2 experience, while for the foreground 26, i.e. the electron beam grid image, intended areas remain unexposed. 8a, this apparatus is only indicated by laser radiation 27. It is also pointed out that, for reasons of clarity, only a small partial section of the substrate is shown.

According to FIG. 8b, a mask, as shown for example in FIG. 6, is now brought into contact with the substrate 2. The mask is a transparent film 29 with light-tightly masked parts 15, which covers the image parts intended for the background 25 and those for the foreground 26 intended areas. The substrate 2 is now post-exposed with homogeneous UV light 30.

After the substrate 2 has been developed in the developer AR 300-35, the relief profile 24 shown schematically in FIG. 8c results. In the following, a 30 nanometer thick chrome layer 31 is vapor-deposited, as shown in FIG. 8d. A negative resist layer 32 made of the negative resist material X AR-N 7720/25 with a thickness of 300 nm is then applied to the chrome layer 31 in accordance with FIG. 8e. In the area 26 provided for this purpose, the foreground is written as a grid image 101 with electron beam lithography, as shown in FIG. 8e. An electron beam 33 is guided along the grid lines provided. The electron beam 33 inserts the grid lines into the negative resist layer 32, so to speak. The fully exposed substrate 2 is developed in the developer AR 300-48. This results in the relief profile 32 shown in FIG. 8f.

FIG. 9 shows an example in which the layers are not applied alternately with the work steps, but in which all layers are already present at the beginning of the process and the exposures can be carried out in succession without further coating processes.

A chrome layer 41 is applied to a glass plate 40, preferably a ground quartz glass plate. A dark-colored positive resist 42 which is largely insensitive to optical radiation and which is suitable for exposure to an electron beam and has a layer thickness of, for example, 200 nm desired for electron beam exposure is applied to this. A layer of positive resist 43, which is 400 nm thick, is applied over it, making it highly sensitive. Has light radiation, for example for light from an He-Cd laser with a wavelength of 442 nm. The plate is now ready for exposure (FIG. 9a). , _{, ,} ^'''''■; .- 7 _.

The order of the exposure steps now required is arbitrary. In the example shown, the optical; Exposure started. The area 431 provided for this purpose is holographically exposed with a He-Cd laser 44. The area 431 thus exposed now contains the latent holographic image, which is indicated in FIG. 9b by a dashed sine curve.

The photoresist area 421 underneath is not damaged because of its optical insensitivity and, because of its dark color, serves as an absorption layer in order to avoid undesired light reflections. The region 431 which is optically exposed in this way is now covered by a mask 45 and the region intended for electron beam exposure is first completely exposed with blue light 46 in order to make the upper photoresist layer in the region 432 detachable. Because of the light-insensitivity of the photoresist layer 42, the ^" blue light effect 46 has no effect on the underlying photoresist layer area 422 (FIG. 9c). The electron beam exposure 47 then takes place in this area (FIG. 9d).

The electron beam penetrates the upper photoresist layer 43 and exposes the underlying electron beam resist layer 42 with the desired grid image. The damage caused by the electron beam in the upper photoresist layer 43 is irrelevant, since this layer is ultimately removed in this area. This completes the exposure. During development, mountain and valley profiles (Fig. 9e) emerge from the latent images, as determined by the exposure. Area 431 shows a holographic image, area 421 is undamaged because it was not exposed. The area 432 is removed because it was exposed over the entire area and there is an electron beam grating image in the area 422.

FIG. 10 shows an alternative construction which is treated in the same way as FIG. 9. The difference is that instead of the chrome layer 41, a conductive polymer layer 51 is applied and a black-colored glass substrate 50 is used. This structure brings an even better suppression of reflections for the optical exposure than the structure according to FIG. 9.

The diffraction structure pattern shown in FIG. 4 and already explained, consisting of a holographic exposure 100 and a lattice structure 101 generated by means of an electron beam, can also be produced by exposure of only one photoresist layer. This case is shown in FIGS. Ha to 11c. Before the exposure, the substrate 2 is provided with a metal layer 70, a dark absorption layer 73 and a photoresist layer 71 are applied over it. For the holographic exposure of the background pattern 100, this photoresist layer 71 is partially covered with a mask 72. The mask 72 shown schematically in FIG. Ha has, for example, the shape shown in FIG. 6. The area of the photoresist layer 71 that is not covered by the mask 72 is now exposed, as shown in FIG. Ha, by the superimposition of two coherent light beams 75, 76. The object beam 76 carries the information of the letter field 102, which is shown in FIG. 5. By superimposing the object beam 76 with the reference beam 75, the holographic diffraction structure 77 is formed in the photoresist layer 71 in the form of the letter field 100, which, as shown in FIG. 7, has a gap in the area 101. This gap will 101 covered by mask 72 and is therefore not yet exposed at this point in the process. Subsequently, the mask 72 is removed and the lattice structure 79 is written into this area of the photoresist layer which has not yet been exposed with an electron beam 78. Hb shows this method step. The metal layer 70 ensures that the electrons of the electron beam 78 are derived in this method step. The dark absorption layer 73, on the other hand, ensures that no disturbing light reflections occur during the holographic exposure. If the photoresist layer 71 used in the method steps Ha and 11b is a positive resist, the photoresist layer 71 after development has the relief structure shown in FIG. 11c.

If, on the other hand, a negative resist is used for the method steps according to FIGS. Ha and 11b, this has the relief structure shown in FIG. 12 after development.

FIGS. 13 to 15 show different layer sequences that can be arranged on the substrate 2 and that can be used in the methods shown in FIG. 11. For example, the dark absorption layer 73 can be dispensed with if a dark-colored glass is used as the substrate layer 2. A conductive polymer 80 can also be used instead of the metal layer 30 (FIG. 13). It is also possible to use the metal layer 70 simultaneously as a dissipation layer and as a mask. FIG. 14 shows this case. A dark colored glass can also be used here as substrate 2. According to a further alternative (FIG. 15), the mask 72 can also be constructed in multiple layers and consist of a glass plate or plastic film 81, to which the masking metal layer 82 is applied in a separate method step. The structuring of the metal layer 82 can be carried out using known washing or Etching processes are carried out. This mask 72 is placed on the photoresist layer 71. It may be helpful to arrange a glycerine layer between the mask 72 and the photoresist layer 71 in order to avoid reflections on the surface of the photoresist layer. Instead of glycerin, a suitable other substance can also be used, which has approximately the same refractive index as the photoresist layer 71 and the glass layer 81.

An alternative method for producing the resist master 110 according to FIG. 4 is shown in FIGS. 16a to 16d. Here, the use of masks is dispensed with, so that the diffraction structures 100, 101 generated overlap. That is, the diffraction structure 101 forming the foreground is arranged above the letter field 100 and replaces the letter field forming the background in this image area.

16a, a substrate 2 coated with a photoresist 1 is exposed to coherent radiation 195 such that a latent lattice image 196 is formed in the resist 1. Then the resist 1 is developed. An intermediate product results, as shown in FIG. 16b. The grid image 196 represents the letter field 100. A photoresist layer 197 is now applied to this intermediate product, which, because of its consistency and the greater layer thickness, pours in and levels the previously applied structure, as shown in FIG. 16c. A latent image 199 is generated in the layer 197 with an electron beam 198, the exposure taking place in such a way that the layer is not exposed through to the bottom. 16d shows the result after development. The diffraction structure 101 overlaps and replaces the diffraction structure of the letter field 100. In this way, a uniform diffraction structure can easily be provided with additional, preferably individualizing information. 17a to 17c show a further variant in which two different types of radiation are exposed in a photoresist layer, in this case the images produced by the exposures overlap. 17a, a substrate 2 coated with photoresist 1 is exposed to radiation 3 (for example laser light) in such a way that a latent grid image 196 is formed in the photoresist. Thereafter, as shown in FIG. 17b, another type of radiation 190, such as electron radiation, is exposed again, so that a further grating image 191 is superimposed on the first grating image 196. 17c shows the result of the procedure after the development of the photoresist layer 1. The final lattice structure 194 accordingly consists of a superimposition of the lattice images 196 and 191.

In the manner shown in FIG. 17, a photoresist 1 is required which is equally suitable for both types of radiation, which is not feasible for all types of radiation. 18a to 18d show a method which can be used for all types of radiation. In FIG. 18a, a substrate 2 coated with photoresist 1 is again exposed to radiation 3, such as laser light, in such a way that a latent lattice image 196 is formed in photoresist 1. The photoresist 1 is then developed. An intermediate product results, as shown in FIG. 18b. A further photoresist layer 192 is now applied to this intermediate product, the layer thickness and sensitivity of the exposure to radiation type 190, for example electron radiation, being optimally adapted. As shown in FIG. 18c, exposure to radiation type 190 results in latent image 193 in layer 192. FIG. 18d shows the result after photoresist development. Here too, the final grid structure 194 consists of a superimposition of the grid images 196 and 193. Of course, any other layer structures can also be used for the method according to the invention. Under certain circumstances, it may make sense to arrange the reflection-preventing absorption layer on the underside of the substrate 2, so that the photoresist layer and the absorption layer are arranged on different surfaces of the substrate.

Furthermore, substrates that are already provided with a diffraction structure, such as e.g. Electroplated shims, embossed plastic or metal foils. In some circumstances, however, it is sufficient to merely provide these special substrates with a further photoresist layer and to expose them using the methods described.

All of the described process variants can be combined with one another as desired. The methods explained in connection with the resist master according to FIG. 4 can also be used for the production or combination of other different grating images.

The relief structures or exposed substrates can be processed as resist masters in the usual way as in optical holography. In the following, a thin silver layer is therefore applied by vapor deposition or chemical precipitation and a nickel impression is made in the electroplating bath. The nickel molding can be multiplied and used as an embossing tool for embossing an embossing layer. The embossing layer is finally applied to the final substrate, e.g. a banknote, credit card or packaging material, transferred with or without a shiny metallic reflective layer.

Claims

Patent claims

1. A method for producing a resist master which has at least two different image areas, wherein at least two photoresist layers are used in the manufacture of the resist master, which are matched to the type of image areas to be produced.

2. The method according to claim 1, characterized in that the photoresist layers are applied in the image areas in different layer thickness.

3. The method according to claim 2, characterized in that the photoresist layers consist of the same material.

4. The method according to at least one of claims 1 to 3, characterized in that the photoresist layers are adapted to the type of the relief profile to be produced.

5. The method according to at least one of claims 1 to 4, characterized in that the photoresist layers on different

Radiation types are adjusted.

6. The method according to at least one of claims 1 to 5, characterized in that the photoresist layers are arranged one above the other or next to one another.

7. The method according to at least one of claims 1 to 6, characterized in that the different image areas at least partially overlap.

8. The method according to claim 7, characterized in that the overlapping image areas are exposed in a photoresist layer.

9. The method according to claim 7, characterized in that the overlapping image areas are exposed in superimposed photoresist layers.

10. The method according to at least one of claims 1 to 7 with the following steps:

Coating the substrate with a first photoresist, exposing the first photoresist to radiation of a first radiation type in the first image area, developing the first photoresist, applying a second photoresist layer to the substrate,

Exposing the second photoresist to radiation of a second radiation type in the second image area, developing the second photoresist.

11. The method according to at least one of claims 1 to 9 with the following steps:

Coating the substrate with a first photoresist first

Film thickness,

Exposing the first photoresist to radiation in the first image area,

Developing the first photoresist,

Applying a second photoresist layer of second layer thickness to the substrate, Exposing the second photoresist to radiation in the second

Image area,

Develop the second photoresist.

12. The method according to any one of claims 1 to 11, characterized in that a positive or a negative resist is selected for the first photoresist layer (1, 12, 24) and for the second photoresist layer (9, 19, 32) ,

13. The method according to any one of claims 1 to 11, characterized in that a negative resist (1, 19, 32) is used for the first photoresist layer and a positive resist (12, 19, 24) for the second photoresist layer or vice versa ,

14. The method according to claim 12 or 13, characterized in that in the case of a positive resist (12, 19, 24), the associated image area is first exposed and then, using a mask (15, 22), the surrounding area with radiation (16 , 23, 30) is applied.

15. The method according to any one of claims 1 to 14, characterized in that a barrier layer (31) is applied between the first photoresist layer (1, 12, 24) and the second photoresist layer (9, 19, 24).

16. The method according to claim 15, characterized in that a metal or oxide layer (31) is selected for the barrier layer.

17. The method according to any one of claims 1 to 16, characterized in that a particle radiation or electromagnetic radiation is selected for the radiation (3, 10, 13, 20, 33) of the first and second radiation type.

18. The method according to claim 17, characterized in that an electron beam or laser is selected for the radiation (3, 10, 13, 20, 33) of the first or second radiation type.

19. The method according to at least one of claims 1 to 18, characterized in that diffraction structures are exposed or written into the first and / or second photoresist layer.

20. The method according to at least one of claims 1 to 19, characterized in that a real one in at least one of the image areas

Hologram is exposed.

21. The method according to at least one of claims 1 to 20, characterized in that a grid image is written or exposed in at least one of the image areas.

22. The method according to at least one of claims 1 to 21, characterized in that a zero-order grid image is written or exposed in at least one of the image areas.

23. The method according to at least one of claims 1 to 21, characterized in that more than two image areas are generated.

24. The method according to at least one of claims 1 to 23, characterized in that at least one of the photoresist layers is applied to a glass plate, an embossed plastic or metal foil or a galvanic shim and exposed there.

25. A method for producing a resist master which has at least two different image areas, the substrate being provided with a photoresist layer, and the photoresist layer being exposed to light radiation in one image area and with particle radiation in the other image area.

26. The method according to claim 25, characterized in that the different image areas at least partially overlap.

27. A method for producing a resist master which has at least two different image areas, a photoresist layer being applied to a substrate which is provided with a diffraction structure in the form of a relief structure, and the photoresist layer being exposed in one of the image areas, and not exposed areas of the photoresist layer are removed, so that the relief structure underneath is exposed and forms the second image area.

28. The method according to claim 27, characterized in that an electroplating brain or an embossed plastic or metal foil is used as the substrate.

29. Resist master, produced by a method according to at least one of claims 1 to 28.

30. Resist master with at least one photoresist layer which has a first image area which is exposed to light radiation and a second image area which is exposed to particle radiation.

31. Resist master with at least two photoresist layers, each photoresist layer being exposed in at least one image area, and the image areas in the two photoresist layers being exposed to different types of radiation.

32. Resist master with at least one photoresist layer which has a first image area which has a first image area which is exposed to a zero order grating image and a second image area which is exposed to a first order grating image.

33. Resist master with at least two photoresist layers, each photoresist layer being exposed in at least one image area, and the photoresist layers having different layer thicknesses.

34. Resist master according to claim 33, characterized in that a zero-order grating image is exposed in each photoresist layer.

35. Resist master according to at least one of claims 30 to 34, characterized in that the image areas at least partially overlap.

36. Security element produced with a resist master according to at least one of claims 29 to 35.

37. Use of the resist master according to one of claims 29 to 36 for the production of embossing tools, in particular embossing cylinders.

38. Method for producing a resist master, wherein an embossable lacquer layer is applied to an already structured carrier material, into which a lattice image is embossed.