The present invention relates generally to soft-lithographic techniques, which are based on physical contact of a reactant with a substrate.
The present invention relates in particular to a structured, elastic stamp device for producing the physical contact of the reactant with the substrate. More specifically, the invention relates to a stamp device for carrying out soft-lithographic processes which comprises a base, which is produced from a polymer material, and at least one structured stamp surface of the base, which has a definable surface relief, the stamp surface being structured by means of an impression of a master element which has a defined primary surface relief.
For reasons including the deformability of the stamp device, soft-lithographic methods can only be used to a restricted extent with regard to the sizes of structures. One reason for this is that such a stamp is exposed to high mechanical loads. On the one hand, the material used must have a high degree of elasticity, i.e. be “soft”, in order to permit adequately good contact with the substrate, on the other hand, it is required that deformation of the defined surface relief is avoided.
To suppress deformations of conventional stamp devices in a soft-lithographic process, “ideal” aspect ratios must be maintained in the lithography, i.e. aspect ratios in the range from 0.9 to 1.1. In a disadvantageous way, such restrictions on setting the aspect ratio have the effect that conventional soft-lithographic processes using conventional stamp devices cannot be used with sufficient reproduction accuracy for small structures, i.e. structures with a structure width of less than 1 μm (micrometer).
To solve these problems, it has been proposed to use stamp devices made of a polymer material with a high degree of crosslinking and/or incorporated silicate particles. In the publication “H. Schmid, B. Michel, Macromolecules 2000, 33, 3042-3049”, such polymers with a high degree of crosslinking are described as conventional polymers. They allow structures in the range of about 100 nm (nanometers) to be produced.
However, one disadvantage of such use of polymer material with a high degree of crosslinking in soft-lithographic processes according to the prior art is that the greater hardness of the polymer material brought about by the increased degree of crosslinking leads to increased material brittleness. Such brittleness inexpediently allows cracks, structure defects, etc. to occur or the stamp device has cracks and/or fractures.
In a conventional way, as the polymer material from which the base of the stamp device is formed is produced from polydimethyl siloxane (PDMS). Such siloxanes and their use for producing the base for stamp devices are familiar to a person skilled in the art, as described for example in the publication “A. Star, J. F. Stoddart, D. Steuermann, M. Diehl, A. Boukai, E. W. Wong, X. Yang, S.-W. Chung, H. Choi, J. R. Heath, Angew. Chem. Int. Ed. 2001, 40, 1721-1725”.
Consequently, adequate strength of the base, and consequently production of small structures, is not possible.
It is therefore an object of the present invention to provide a stamp device for use in soft lithography which has a base with a greater strength than stamp devices according to the prior art.
This object is achieved according to the invention by a device with the features of patent claim 1.
Furthermore, the object is achieved by a method specified in patent claim 11. Further refinements of the invention emerge from the subclaims.
A central idea of the invention is that a polymer material in which nanoelements are incorporated is used for the base of the stamp device. As a main advantage concerning the above object, nanoelements, such as for example nanotubes or carbon nanotubes, have a high mechanical strength. A further advantage of incorporating nanoelements in the polymer material forming the base of the stamp device is that a higher degree of elasticity of the material of the base can be achieved in comparison with known, more highly crosslinked polymer materials. This leads in an advantageous way to avoidance of fractures, cracks, structure defects, etc., since brittleness of the material can be avoided.
In particular, the present invention has the advantage that, with the stamp device according to the invention, structures can be created in the nanometer range by means of soft-lithographic processes. Since a high degree of elasticity of the stamp device can be provided by the incorporation of, for example, carbon nanotubes (CNT) in the polymer material of the base, a high level of durability of the stamp device is achieved.
Even when the stamp device is used repeatedly in soft-lithographic processes, there are expediently no changes in the interfacial properties of the stamp material.
It is advantageous in this respect that reusability of the stamp device is ensured on account of increased mechanical strength in comparison with conventional stamp devices.
The stamp device according to the invention for use in soft lithography substantially comprises:
Furthermore, the method according to the invention for producing a stamp device for use in soft lithography substantially comprises the following steps:
Advantageous developments and improvements of the respective subject matter of the invention can be found in the subclaims.
According to a preferred development of the present invention, the nanoelements are provided as nanotubes and/or as nanowires. The nanotubes are preferably formed on a carbon basis, i.e. in such a way that the nanoelements are provided as carbon nanotubes (CNT).
According to a further preferred development of the present invention, the polymer material from which the base of the stamp device is formed comprises siloxanes.
According to a still further preferred development of the present invention, the polymer material has such an elasticity that it can be peeled from the master element which has a defined primary surface relief, the surface relief of the structured stamp surface of the base being provided as a negative imprint of the defined primary surface relief of the master element.
According to a still further preferred development of the present invention, the polymer material which contains the nanoelements is prepared from polydimethyl siloxane (PDMS).
According to a still further preferred development of the present invention, the nanoelements are formed as silicon, germanium, boron-nitride, gallium-nitride and/or cadmium-sulfide nanowires.
According to a still further preferred development of the present invention, the proportion of the nanoelements contained in the polymer material of the base of the stamp device is between 0.001 and 0.00001% by weight.
According to a still further preferred development of the present invention, the master element is prepared from a silicon material.
According to a still further preferred development of the present invention, the defined primary surface relief of the master element has an aspect ratio in a range between 5 and 0.5.
According to a still further preferred development of the present invention, curing of the polymer material in which a stamp surface of the stamp device is structured in a way corresponding to the defined primary surface relief of the master element is carried out by means of baking of the polymer material. The baking of the polymer material is preferably performed at a temperature of 120° C. for a time period of 12 hours.
According to a still further preferred development of the present invention, the fluid which contains a polymer material for the base of the stamp device is prepared by dispersing the nanoelements in a solvent, in order to obtain a dispersion solution, and by mixing the dispersion solution obtained with a siloxane solution.
According to a still further preferred development of the present invention, the dispersion solution obtained is carried out with the siloxane solution at room temperature.
According to a still further preferred development of the present invention, the solvent in which the nanoelements are dispersed is prepared from dichloromethane.
According to a still further preferred development of the present invention, the fluid is shaken before curing of the polymer material. The fluid is preferably shaken for a time period of 60 minutes at room temperature before the curing of the polymer material.
Exemplary embodiments of the invention are represented in the drawings and described in more detail in the description which follows.
In the drawings:
In the figures, the same reference numerals designate components or steps which are the same or functionally the same.
In the process step shown in
In the exemplary embodiment of the present invention, polydimethyl siloxane (PDMS) is used as a preferred polymer material. The incorporation of the nanoelements in the form of preferably carbon nanotubes allows the mechanical properties of the polymer material to be significantly changed in such a way that a resultant base 101 (see
Furthermore, it is advantageous that a great elasticity of the polymer material is retained, any occurrence of fractures and/or cracks and/or structure defects being prevented by avoiding brittleness.
FIGS. 2(d) and 2(e) schematically show the use of the stamp device according to the invention in a soft-lithographic method. For this purpose, the surface relief 103 of the base 101, which contains the nanoelements 102, is wetted for example with ink, as shown in
Subsequently, the wetted stamp is pressed onto a substrate 201, which is provided with a substrate coating 202, in the direction indicated by the arrows of
At the raised locations of the surface relief 103 of the structured stamp surface 104 of the base 101 there is consequently a stamp wetting 203, as shown in
After etching of the structure shown in
In an advantageous way, on account of the high strength of the stamp device 100 according to the invention, substrate structures 205 in the nanometer range can be created by means of soft-lithographic processes. Since a high degree of elasticity of the stamp device 100 is retained, the stamp is not destroyed, even in the case of repeated use, nor are interfacial properties of the stamp material changed. Therefore, good reusability of the stamp device is obtained, which leads to a considerable reduction in the cost of soft-lithographic processes.
To produce the base 101, which has the defined surface relief 103, a polymer material 106 is used, preferably prepared as a polydimethyl siloxane (PDMS), such as for example Sylgard 184 produced by Dow Corning.
After curing of the polymer material 106, the cured polymer material 106 is peeled from the master element 105, in order to separate the base 101 of the stamp device 100. The curing of the polymer material is preferably carried out by means of baking. In the preferred exemplary embodiment of the present invention, the baking of the polymer material 106 is carried out at a temperature of 120° C. for a time period of 12 hours.
To produce the fluid, which contains the polymer material 106, nanoelements 102, which are prepared for example from carbon nanotubes (CNT), are dispersed in a solvent in such a way that a dispersion solution is obtained. Subsequently, the dispersion solution obtained is mixed with a siloxane solution.
The mixing of the obtained dispersion solution with the siloxane solution is preferably carried out at room temperature. Furthermore, it is expedient that the fluid is shaken before curing of the polymer material 106, in order to achieve a uniform distribution of the nanoelements 102 in the polymer material. After the curing of the polymer material 106 containing the nanoelements 102, an elastic base 101 of the stamp device 100 that has an adequate mechanical strength is obtained.
It should be pointed out that the proportion of the nanoelements 102 in the polymer material can be varied by variation of the nanoelements 102 in the fluid. In the preferred exemplary embodiment according to the present invention, the proportion of nanoelements is varied between 0.001 and 0.00001% by weight, related to the polymer material 106.
The high mechanical strength of the base 101, combined with adequate elasticity, makes it possible to provide master elements 105 which have an aspect ratio in a range between 5 and 0.5. The surface relief 103 of the structured stamp surface 104 of the base 101 is thereby obtained as an exact negative impression of the defined primary surface relief 107 of the master element 105. Dichloromethane is preferably used as a solvent for dispersing the nanoelements 102, in order to obtain a dispersion solution which is then mixed with the siloxane solution in the further process step, described above.
Although the present invention has been described above on the basis of preferred exemplary embodiments, it is not restricted to these but can be modified in various ways.
The invention is also not restricted to the stated application possibilities.
The substrate may be coated (gold), but also for example consist only of silicon. A natural oxide film would suffice here in order to create a structuring by means of soft-lithographic processes.
In the figures, the same reference numerals designate components or steps which are the same or functionally the same.
Number | Date | Country | Kind |
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10344777 6 | Sep 2003 | DE | national |
This application is a continuation of PCT patent application number PCT/EP2004/010082, filed Sep. 9, 2004, which claims priority to German patent application number 10344777.6 filed Sep. 26, 2003, the disclosures of each of which are incorporated herein by reference in their entirety.
Number | Date | Country | |
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Parent | PCT/EP04/10082 | Sep 2004 | US |
Child | 11363751 | Feb 2006 | US |