The present invention relates to the applying of a structured layer to a substrate. Such a layer is for instance applied for the purpose of forming small lenses and other optical elements, gratings and other microstructures such as optical memories and other interfaces between optics and micro-electronics. This technique is per se known in the duplication of CDs, for instance from US-A-4 477 328 and US-A-4 812 34.

According to this prior art the method for applying a structured layer to a substrate comprises the steps of applying a first quantity of curable lacquer to the substrate, placing and pressing a first mould on the substrate and the lacquer in order to form the structure in the first quantity of lacquer between the substrate and the mould, curing the first quantity of lacquer and separating the first mould from the substrate and the first quantity of cured lacquer. The term 'lacquer' is otherwise also understood to mean others resins and plastics.

According to the prior art these steps are carried out at a single location. Pressing of the mould is a slow process particularly, though not exclusively, in the case of thin layers as a result of the great hydrostatic forces. Although the process can be accelerated, this would require presses of particularly heavy form. These heavy presses cannot be combined with means for curing the curable lacquer, these requiring radiation sources, such as heating elements, UV lamps which must also be positioned such that the associated radiation can readily reach the lacquer. In order to nevertheless obtain a sufficiently rapid process the invention proposes a method of the above stated type, wherein applying of the first quantity of curable lacquer to the substrate and placing and pressing of the first mould take place in a first workstation, the assembly of substrate, first quantity of lacquer and first mould is displaced from a first workstation to a second workstation, and curing of the first quantity of lacquer takes place in the second workstation.

This measure separates the station where pressing of the mould is performed from the station where the curable lacquer is exposed, so that both workstations can be optimized for performing the relevant process, albeit at the cost of a displacement of the assembly of substrate, first quantity of lacquer and first mould from the first workstation to the second workstation.

The invention also provides a device for applying a structured layer to a substrate, comprising means for applying a quantity of curable lacquer to the substrate of a form- defining assembly, pressing means for arranging a mould of the form-defining assembly on the combination of the substrate and the quantity of lacquer and pressing thereof in the transverse direction, positioning means for relatively positioning the mould and the substrate in the directions transversely of the transverse direction, and curing means for curing a quantity of lacquer, wherein the lacquer applying means and the pressing means are positioned at a first workstation, the positioning means and the curing means are positioned at a second workstation and the device comprises transport means for transporting the form-defining assembly from the first workstation to the second workstation. It is noted that the lacquer applying means are usually placed in the first station, but that it is likewise possible for the lacquer applying means to be

accommodated elsewhere so that the substrate, optionally on a carrier, is carried already provided with lacquer to the first station.

The method described here is a microtechnique, so that precision is of the greatest importance. According to a preferred embodiment, the first mould is positioned precisely relative to the substrate in the direction of the plane of the substrate prior to curing of the first quantity of lacquer, and this positioning takes place at the location of the second station. The operation defining the accuracy of the product hereby takes place only after the transport of the assembly between the first and the second workstation, so that the chance of the accuracy being adversely affected by the transport is eliminated.

A further optimization of the process results when, after curing of the first quantity of lacquer, the assembly of substrate, cured first quantity of lacquer and first mould is transported to a third workstation and the separation of the first mould from the substrate and the cured first quantity of lacquer takes place in the third workstation. This measure provides the option of optimizing the second and the third workstations in accordance with the operations they are to perform. This results in a further

specialization and optimization potential. According to this embodiment the device comprises a third workstation which is provided with means for separating the first mould from the cured quantity of lacquer, and the transport means are adapted to transport the form-defining assembly from the second workstation to the third workstation.

The distance between the first mould and the substrate is determined during the processing at the first workstation. The whole of substrate, first quantity of lacquer and first mould is then transported to the second workstation. Despite the fact that a great deal of force is required to place the first mould at the correct distance from the substrate, there is a danger of the distance between first mould and substrate changing, which has disastrous consequences for accuracy since means for adjusting this distance are after all no longer present in the second workstation. In order to maintain the correct distance a further preferred embodiment proposes to arrange spacers defining the distance between the first mould and the substrate during placing of the first mould on the substrate. The spacers hereby define the distance between the first mould and the substrate so that the transport can have hardly any effect on this distance. It is noted that the spacers are generally adapted only to limit the smallest distance between the two parts. An increase in the distance is after all always prevented by the hydrostatic pressure of the as yet uncured lacquer.

The same embodiment likewise provides a form-defining assembly for applying a structured layer to a substrate, comprising a substrate and a first mould for defining the form of a quantity of lacquer arranged between the substrate and the first mould, wherein spacers are provided for maintaining the distance between the substrate and the first mould.

In some situations the substrate is placed on a carrier prior to placing of the first mould on the substrate. In such a situation it is attractive for the spacers to be placed between the carrier and the first mould.

According to this embodiment the form-defining assembly comprises a carrier carrying the substrate, and the spacers are placed between the carrier and the first mould. The above elucidated embodiments relate in the first instance to making a single-sided structure, as is relevant in manufacturing digital information carriers and some optical elements. For other products such as optical elements, both optical surfaces of which are curved, it is important that a structure is applied to both sides. In order to also enable manufacture of such products, a preferred embodiment provides the measure that, after curing of the first quantity of lacquer, the combination of the first quantity of cured lacquer, substrate and first mould is turned over and transported to the first workstation, a second quantity of curable lacquer is applied to the substrate, a second mould for forming the structure in the second quantity of lacquer is placed on the substrate and the second quantity of lacquer, the thus obtained assembly is transported to the second workstation, the second quantity of lacquer is cured and the two moulds are separated from the substrate and the cured quantities of lacquer.

The precision of placing of the two moulds is if possible of even greater importance than in the case of the single-sided structure. A further embodiment provides for this purpose the measure that, prior to curing of the second quantity of lacquer, the second mould is positioned precisely relative to the second mould in the direction of the main plane of the substrate, and that this positioning takes place at the location of the second workstation. The positioning relative to the first mould automatically also results in positioning relative to the substrate.

This embodiment also provides a form-defining assembly comprising a second mould, wherein the spacers are placed between the two moulds. In order to here also maintain sufficient precision in transverse direction of the finished product, this being important particularly, though not exclusively, in the case of optical elements, a further embodiment provides the measure that, prior to curing of the second quantity of lacquer, the second mould is positioned precisely relative to the substrate in the direction of the main plane of the substrate, and that this positioning takes place at the location of the second workstation.

Most lacquers have the property that they contract during curing. In the case of rigid spacers this could possibly result in a deformed structure, particularly in a concave structure. There are different possibilities for preventing this deformation. It is thus possible to give the press used for pressing a concave profile, which compensates the lacquer contraction. This results in a convex lacquer layer which compensates the contraction of the lacquer. It is however also possible to provide the second workstation with reference surfaces with a vacuum profile which pull the mould into a concave form. During curing the vacuum can be removed so that the mould can co-displace.

It is also possible to remove the spacers, wherein control of the thickness takes place by means of a claw which is adapted to engage the mould and the position of which can be controlled.

According to an alternative option, the dimension of the spacers defining the distance between the first mould and the substrate is adjusted prior to and during curing of the quantities of lacquer. This requires spacers which are adapted to adjust the respective dimension. This dimension can be varied by applying for instance piezoelectric, magnetostrictive or electromagnetic elements, although other types of actuator are not precluded.

This embodiment thus also provides the measure that the spacers are adapted to controllably change their dimension defining the distance between the mould and the substrate.

The same problem can likewise be solved in that the stiffness of the spacers in the direction defining the distance between the first mould and the substrate is adjusted prior to and during curing of the quantities of lacquer. An example is formed by a magnetically biased air bearing. When the pressure is removed, there is a great decreases in the stiffness of the bearing.

This embodiment further results in spacers which are adapted to controllably change their stiffness in the direction defining the distance between the first mould and the substrate.

Finally, it is possible to adjust the position of the spacers in the direction of the main plane of the substrate prior to or during curing of the quantities of lacquer. These parts can hereby be placed so far from the substrate that they have hardly any further effect. This embodiment also results in a form-defining assembly of the above stated type, wherein the spacers are adapted to be displaced in the direction away from the main plane of the substrate. The present invention will be elucidated hereinbelow with reference to the

accompanying figures, in which:

Figure 1 shows a block diagram of the device according to the invention;

Figure 2 is a schematic cross-sectional view of a first embodiment of an assembly according to the invention;

Figure 3 is a schematic cross-sectional view of a second embodiment of an assembly according to the invention;

Figure 4 shows a series of schematic cross-sectional views of the first and second embodiment during various steps of the method according to the invention;

Figure 5 is a schematic view of the assembly shown in figure 2, wherein an effect to be compensated is shown in exaggerated manner;

Figure 6 is a schematic view of a first embodiment of a support element for use in the invention; and

Figure 7 is a schematic view of the second embodiment of a support element for use in the invention.

As stated in the preamble, the invention relates to a method, assembly and device for applying a structured layer to a substrate. The invention relates particularly to the allocation of the steps among different locations or workstations so that the means to be provided at the workstations can be optimized according to the operations to be performed. Figure 1 thus shows a block diagram representing three workstations, i.e. a first workstation 1 in which first operations are carried out, a second workstation 2 in which second operations are carried out, and a third workstation 3 in which third operations are carried out. Figure 2 shows an assembly designated as a whole with 4, which is provided with a carrier 5, on which a substrate 6 is placed. This substrate 6 must be provided with a structured layer 7 with a form which is defined by a first mould 8 placed with its structured side toward the structured layer to be formed. In order to maintain the distance between carrier 5 and first mould 8, and thereby the distance between substrate 6 and first mould 8, and therefore the thickness of structured layer 7, two spacers 9 are placed between carrier 5 and mould 8. It will be apparent that the form of spacers 9 will depend on the form of carrier 5 and substrate 6; in the case the substrate has a rectangular form two elongate carriers 9 are preferably applied, while in the case substrate 6 has a round form three spacers 9 can for instance be used. It is of course possible to apply other numbers or forms of spacer, such as for instance round spacers. It is noted that it is also possible, in the absence of spacers 5, to place spacers 9 directly onto the substrate. It is also possible to integrate the spacers into the carrier. As shown in figure 4, the substrate or carrier 5 with substrate 6 is initially arranged in the first workstation 1 and a quantity of curable lacquer is applied to the substrate. Spacers 9 are then placed, although earlier placing of the spacers cannot be precluded. Finally, mould 8 is placed on spacers 9, wherein the structured side of mould 8 comes into contact with the as yet uncured lacquer. In order to be able to precisely determine the thickness of the layer of lacquer, use is made of a press for pressing the mould 8 onto spacers 9. It is noted that, given the usually small thickness of the layer, the pressing forces required are considerable, this requiring the presence of a heavy press in the first workstation 1. Once the first mould has been placed on the spacers and the lacquer, this distance is properly fixed as a result of the small layer thickness and the presence of the spacers.

The thus obtained assembly is then transported to the second workstation 2. It is important here that the thickness of the layer of lacquer is precisely maintained. In the second workstation the mould 8 is positioned precisely relative to the carrier and, more particularly, precisely relative to the substrate. The thickness of layer 7 is preserved here. Second station 2 is therefore adapted to carry out this precise positioning. After this positioning the lacquer 7 is allowed to cure. The second station is provided with means for this purpose, such as a UV light source. This assumes that the lacquer can be cured by means of U V light. When use is made of other types of curable lacquer, such as heat-curable lacquer, second station 2 can be provided with heating means.

Finally, the assembly is transported from the second station to the final, third station 3. Third station 3 is adapted to separate the first mould 8 from the lacquer layer 7 which has meanwhile cured and been provided with a structure, for which purpose the third station is provided with appropriate means. A substrate thus results which is provided with a single structured layer.

For a number of applications, and particularly for optical applications, the substrate must however be provided with two structured layers. It is here important that the structures present on either side are properly positioned relative to each other. Use is made initially of a structure as shown in figure 2. After passing through the first and the second station the assembly is not separated in third station 3 as in the above discussed single embodiment, but the thus obtained whole 4 is turned over and carrier 5 is removed together with spacers 9 and transported to first station 1. In the first station a layer of curable lacquer 10 is once again applied to the side of substrate 5 thus made available, other larger spacers 12 are placed and a second mould 1 1 is placed on lacquer layer 10 and spacers 12. Second mould 1 1 is provided on its underside with the negative of the structure which must be applied to the second side of substrate 6. After placing of second mould 1 1 the whole is pressed by the press present at first station 1. Pressing here also takes place until lacquer layer 10 has the required thickness and second mould 1 1 rests on spacers 12. The assembly is then obtained as shown in figure 3. The various steps are also shown in figure 4. The thus obtained whole 13 is then moved to second station 2 and in second station 2 the second mould 1 1 is positioned precisely relative to first mould 8, and thereby relative to the structure already arranged in the lower, cured lacquer layer 7. Once the correct position has been obtained, the second lacquer layer 10 is cured by the appropriate means.

Finally, assembly 13 is transported to third station 3, wherein the first and second moulds 8, 11 are removed together with the spacers and the substrate 6 provided on either side with a structure 7, 10 remains. Contraction occurs during curing of most lacquers or resins. This can be taken into account per se in the dimensioning of the various components. In the present case however the problem occurs that, as a result of the small layer thickness, the contraction results in the mould becoming concave. This is shown in highly exaggerated manner in figure 5. The thickness of the cured lacquer layer is thus much smaller in the centre than at the edges. This effect can be compensated in different ways.

One possibility is to reduce the thickness of the spacers during the process of curing the lacquer. It is hereby possible to decrease the distance between the mould and the substrate, and thereby the thickness of the structured layer over the whole surface, whereby the parallelism and flatness of these parts is ensured, and no deformation of the structures occurs. Figure 6 shows a spacer 20 which is provided with a piezoelectric layer 21. Arranged on either side of piezoelectric layer 21 are respective electrodes 22, 23 with which an electrical field can be applied to the piezoelectric layer and with which the thickness of this layer can be controlled. Figure 7 shows an alternative construction of a spacer 24 which is provided with material having a high degree of magnetostriction, i.e. the material contracts or expands under the influence of a magnetic field. Arranged for this purpose around the spacer is a coil 25 which generates an axial magnetic field when an electric current passes therethrough. The length of the spacer can vary under the influence of this axial magnetic field.

It will be apparent that other physical mechanisms can also be used to change the dimensions of the spacers, and that other types of actuator can be used. The spacers can also be moved outward during the curing process, and thereby during the contracting process. Although the curvature of the mould does not hereby come to equal zero, it does become exceptionally small.