METHOD FOR PRODUCING A SUBSTRATE STRUCTURED BY NANOWIRES, PRODUCED SUBSTRATE, AND USE OF THE SUBSTRATE

Abstract

The invention relates to a method for producing a substrate structured by nanowires, characterized in that no lubricant and no lithographic resist mask is used in the method, and only by moving a donor substrate having nanowires relative to a substrate and by locally tribological properties on the surface of the substrate, a specified number of nanowires is deposited selectively at locally defined points of the substrate. The invention further relates to a substrate that can be produced using the method according to the invention, and which selectively contains a specified number of nanowires on a surface at locally defined points. The invention further relates to the use of the substrate according to the invention in microelectronics, microsystems technology, and/or micro-sensor systems.

Claims

1-14. (canceled)

15. A method for the production of a substrate structured with nanowires, comprising the steps of: a) providing a substrate which, on one surface, comprises at least one first region with first tribological properties and at least one second region with second tribological properties, the first and second tribological properties being different and the first region contacting the second region at least in regions; b) pressing a donor substrate comprising nanowires with a specific contact pressure on the first region of the substrate so that the nanowires contact the first region of the substrate at least in regions; and c) moving the donor substrate relative to the substrate in the direction from the first region over at least the second region at a specific speed; wherein, no lubricant and no lithographical resist mask are utilized in the method and, merely by moving the donor substrate, in step c), and the different tribological properties of the two regions, a specific number of nanowires is deposited selectively at locally defined sites of the first and/or second region.

16. The method according to claim 15, wherein the different tribological properties are achieved via at least one collector structure which the first and/or second region comprises or consists of, or which is applied optionally thereon.

17. The method according to claim 16, wherein the at least one collector structure a) in the first region, comprises a material or consists thereof, which is identical to or different from a material of the second region; b) in the second region, comprises a material or consists thereof, which is identical to or different from a material of the first region; c) in the first region, comprises a topographical structure or consists thereof, which is identical to or different from the topographical structure of the second region; and/or d) in the second region, comprises a topographical structure or consists thereof, which is identical to or different from the topographical structure of the first region.

18. The method according to 16, wherein at least one collector structure comprises a metal, a metal compound, a semimetal, a semimetal compound, a plastic material and/or carbon, or consists thereof.

19. The method according to claim 17, wherein the topographical structure is selected from the group consisting of planar, linear, and point-type topographical structures.

20. The method according to claim 16, wherein the at least one collector structure has a length, width and/or height of 1 nm to 1 mm.

21. The method according to claim 16, wherein the at least one collector structure comprises nanoparticles or consists thereof.

22. The method according to claim 15, wherein the first and/or second region comprises at least two collector structures or consists thereof, or which are applied optionally thereon.

23. The method according to claim 15, wherein the nanowires are deposited on the substrate in a geometry which deviates from linearity.

24. The method according to claim 23, wherein the deposition in a geometry which deviates from linearity is achieved by i) movement of the donor substrate relative to the substrate in different directions relative to the first region and/or second region at a specific speed; and/or ii) movement of the donor substrate over at least one collector structure which the first and/or second region comprises or consists of, or which is applied optionally on the latter.

25. The method according to claim 15, wherein the first region and/or second region or between both regions, at least one groove is produced or disposed.

26. The method according to claim 15, wherein the nanowires i) comprise a metal, semimetal and/or carbon or consist thereof; and/or ii) are produced, before step b), via a vacuum process, or via a dry- or wet-chemical process; and/or iii) have a length of 100 nm to 1 mm; and/or iv) have a diameter of 1 nm to 5 μm; and/or v) have a conical, cylindrical, curved and/or square structure at least in regions; and/or vi) are metallically conducting, p-conducting, n-conducting, intrinsically conducting and/or non-conducting at least in regions or completely.

27. A substrate produced by the method of claim 15 comprising, on one surface, a) at least one first region with first tribological properties; b) at least one second region with second tribological properties, the second region contacting the first region at least in regions; c) at least one nanowire which contacts the first and/or second region at least in regions; wherein the first and second region have different tribological properties and the first and/or second region comprises a specific number of nanowires selectively at locally defined sites.

28. The method of claim 16, wherein the at least one collector structure comprises gold, Pt, Al, Si, Ge, SiO.sub.2, Si.sub.3N.sub.4, diamond, Al.sub.2O.sub.3 and/or TiN, or consists thereof.

29. The method according to claim 16, wherein the at least one collector structure has a length, width and/or height of 2 nm to 500 μm.

30. The method according to claim 16, wherein the at least one collector structure has a length, width and/or height of 5 nm to 50 μm

Description

[0067] The subject according to the invention is intended to be explained in more detail with reference to the subsequent Figures and examples without restricting said subject to the specific embodiments illustrated here.

[0068] FIG. 1 a) and b) show the influence of a step with a height of approx. 80 nm for Si.sub.3N.sub.4. Steps produce a locally greater tribological interaction and hence a locally higher density of deposited nanowires on the raised surfaces. This is irrespective of the direction of movement.

[0069] FIG. 2 shows a contact printing over an SiO.sub.2—Si.sub.3N.sub.4 surface. A purely local deposition of nanowires on the Si.sub.3N.sub.4 is observed here with almost a yield of 100%.

[0070] FIG. 3a) shows that, in the case of a first and second region made of SiO.sub.2 and a step height of approx. 80 nm, no great change in the deposition rate occurs. FIG. 3b) shows a significant difference in the deposition rate in the case where in fact a lower height step, compared with FIG. 3a), prevails between the regions (50 nm instead of 80 nm), but the first and second region are made of a different material (first region Si.sub.3N.sub.4, second region gold).

[0071] FIG. 4a) shows the deposition of nanowires on a substrate, the first region of which consists of SiO.sub.2 and the second region of which has square structures made of gold. It is observed that the nanowires are deposited directly behind the square gold structure (gold structure has a height and hence step of 50 nm). In FIG. 4b), the drastically increased local deposition of nanowires on a substrate is illustrated, the first region of which consists of Si.sub.3N.sub.4 and the second region of which consists of round gold structures (gold nanoparticles). FIG. 4c) shows an REM picture of the surface in the region of the gold nanoparticles. It becomes clear that the nanowires are deposited entirely on the Si.sub.3N.sub.4 and between the gold nanostructures. Also the deviation from linearity during deposition becomes clear here in fact.

[0072] FIG. 5a) shows the specific local deposition of conical nanowires between the gold structures (structure in “+” form) on Si.sub.3N.sub.4. In FIG. 5b), the deposition of a nanowire on a step made of SiO.sub.2 (second region) on Si.sub.3N.sub.4 (first region) is shown in contrast (step height approx. 450 nm). The groove exists as a result of manufacture. Consequently, it becomes clear that the tribological properties of the material SiO.sub.2 which has low affinity with the nanowires used, can lead, by insertion of a topographical structure made of this material with a suitable height, to successful deposition of nanowires. Hence, “low affinity regions” can also become carriers of nanowires by raising the level thereof relative to adjacent regions.

[0073] FIG. 6 shows a functional electrical structure with four integrated nanowires. The nanowires were deposited locally with the help of defined collector structures and subsequently integrated microtechnologically. On chips with 21 functional fields (7×3 matrix), a yield of up to 80% could be achieved in the manufacture of functional nanowire sensors for power microscopy.

[0074] FIG. 7a) shows the basic principle of a collector structure with width filter, i.e. the deposition of nanowires in the intermediate spaces of the collector structures which are designed here as golden rectangles. In FIG. 7b), the influence of the geometric shape of the second region—here a triangle with a height of approx. 50 nm—on the distribution of deposited nanowires is shown, it becoming clear that, with a direction of movement of the donor substrate from the base of the triangle to the tip thereof, nanowires are deposited above all on the tip. In FIG. 7c), the random, non-specifically non-linear deposition of nanowires on a 1 μm high triangular resist structure is illustrated.

[0075] FIG. 8 shows a nanocrystalline diamond layer, in which steps with 1 μm height were produced. In the case of contact printing with Si nanowires, it was shown that, with this material, deposition is effected preferably on lower-lying surfaces. The use of the different tribological properties of first and second regions on one substrate is therefore universally possible and not limited to specific substrates.

EXAMPLE 1—HEIGHT DIFFERENCE AND IDENTICAL MATERIAL OF THE REGIONS

[0076] FIGS. 1a and 1b show, by way of example, the Si.sub.3N.sub.4 system, in which either the first region (FIG. 1b) or the second region (FIG. 1a) made of Si.sub.3N.sub.4 was moved 80 nm downwards. It can hereby be detected clearly that, for this case, a clearly higher nanowire density was deposited on all raised surfaces.

[0077] The direction of movement is characterised respectively in the illustration by an arrow. Whilst in the case of Si.sub.3N.sub.4 a very large influence on the topography is present, this is not to be expected in the case of planar structures made of SiO.sub.2 and also could not be detected.

[0078] Since with SiO.sub.2, despite an increase in the bearing weight of 60 g to 200 g with respect to 0.45 cm.sup.2 as surface area, in general hardly any removal could be noted, a reduction in the effective surface area by step formation hardly leads to a significant increase in the deposition rate (see FIG. 3a). Here, typical surface damage for SiO.sub.2 with 200 g bearing weight occurs in addition.

[0079] The case of a combination of the materials gold and Si.sub.3N.sub.4 with a step behaves differently. If a step made of gold is applied on Si.sub.3N.sub.4, then now a preferred deposition on the higher-lying gold is effected whilst lower-lying Si.sub.3N.sub.4 has only a very low nanowire density (see FIG. 3b).

[0080] A significant reduction in the surface area of raised surface structures is in principle accompanied by an increase in the local bearing force, which can lead to an increased nanowire density on raised portions. This effect is particularly pronounced for the system with silicon nanowires on the Si.sub.3N.sub.4 substrate used here.

EXAMPLE 2—HEIGHT DIFFERENCE AND DIFFERENT MATERIAL OF THE REGIONS

[0081] Additional degrees of freedom can be generated by the use of regions made of different materials (heterostructures such as e.g. Si.sub.3N.sub.4/SiO.sub.2) and also by a reduction in the lateral structural size of the functional regions. Critical orders of magnitude of the structural geometries are thereby intrinsically the length and the diameter of the nanowires. In addition to the pure increase in the bearing force, also the dynamic interaction plays a large role, which appears in particular if the lateral dimension of the structure becomes smaller than the length of the nanowires. If a nanowire covers a raised structure only with part of the length thereof, then the nanowires are nevertheless effectively decoupled from the underlayer. A friction force at a critical level can hence hardly arise, only a mechanical deformation of the nanowires according to the model of a tensioned spring.

[0082] In general there applies that the smaller the lateral extension of the structure and the smaller the tribological activity of the step material, the more improbable is deposition of nanowires on the step. If the nanowire leaves a locally delimited increase by sliding off laterally or after complete covering, then the short vertical movement, induced by release of the deformation energy, seems to lead to a greater tribological interaction than with pure sliding friction. The critical friction value is exceeded and the nanowire is deposited behind or next to the raised portion with increased probability. This mechanism is extremely efficient and even results in a local/selective deposition on SiO.sub.2. Nanowires can hereby be deposited in a significant quantity behind gold structures of different geometries on the approx. 50 nm lower-lying SiO.sub.2, which is otherwise rather unsuitable for deposition.

[0083] Also for other underlayers, such as e.g. Si.sub.3N.sub.4, a greater deposition is produced behind the gold structures, however also a pronounced deposition in the lower area should be expected, as for the material Si.sub.3N.sub.4.

[0084] What is crucial for the general mechanism, in particular the height of the step, but not the lateral dimension thereof, is represented in FIGS. 4a and 4b. Gold nanoparticles with a diameter of approx. 50 nm were hereby applied in a local area on the surface of Si.sub.3N.sub.4. After the contact printing, the increasing effect of such a nanoparticle raised portion at a locally significantly increased density of nanowires becomes clear exactly in the area of the gold nanoparticles (FIG. 4b). By means of electron microscopy, it is shown that the nanowires are however not deposited on the gold or remain attached thereon but rather are deposited between the structures, also non-linearly (FIG. 4c). This effect is also observed in the case of microtechnologically produced structures, irrespective of the nanowire morphology (FIG. 5a).

[0085] In order to extend the general applicability of the principles presented here, regions made of SiO.sub.2, including an SiO.sub.2 step, were produced lithographically in an area with Si.sub.3N.sub.4. In contrast to the previous steps of 50 to 100 nm, these steps were however 400 nm to 500 nm high. As was to be expected, a change in the contact printing was observed in these regions. The nanowires hereby remain attached on the high step so that the nanowires were deposited preferably on the SiO.sub.2 step (FIG. 5b).

EXAMPLE 3—HEIGHT DIFFERENCE DUE TO SPECIAL STEP SHAPE

[0086] Furthermore, an influence on the lateral geometry itself also exists. The shape of the structure can hereby crucially influence the local probability of a nanowire deposition. This is shown particularly clearly in the case of triangular structures (see FIG. 4a).

EXAMPLE 4—GROOVE STRUCTURE BETWEEN THE REGIONS

[0087] It is possible with the method according to the invention to span groove structures in the substrate with nanowires. It was found that a groove can still be spanned when the latter is already equal in its width to half the length of the nanowires (e.g. nanowire length 40 μm, groove width 20 μm). It is hereby not absolutely necessary that both groove sides are orientated in a planar manner.

EXAMPLE 5—COMPETITION OF HEIGHT DIFFERENCE AND DIFFERENT MATERIALS

[0088] A step defined previously in the substrate can be quasi overwritten by use of further functional structures, e.g. a raised step can be weakened and even neutralised in the tribological interaction thereof by adding a further step of greater height. The same applies for a lowered step. For example, a lowered step which, under specific conditions, effects no deposition of nanowires can, by applying nanoparticles with a large diameter, become a step on which nanowires are deposited. By means of this (temporary) modification of the step, the latter is quasi “overwritten” in the original effect thereof.

[0089] This fact can be used technically-procedurally, as a result of which additional degrees of freedom in the design of structures for surface-controlled contact printing are produced.

EXAMPLE 6—COLLECTOR STRUCTURES ON THE SUBSTRATE

[0090] Collector structures permit specific and directed local deposition of a nanowire. The collector structures hereby represent for example microtechnologically-produced gold structures, between which, during the process for contact printing of nanowires, specific deposition of nanowires takes place (see e.g. FIG. 5a).

[0091] Also locally delimited regions of local roughness changes (here gold nanoparticles) and lateral geometries (e.g. triangular structures) can fall in the region of the collector structures. Collector structures consequently comprise all locally predefined structures which consist of a different material and/or have a different topography/geometry and hence lead to a local change in the tribological properties of the substrate and hence to a locally changed deposition probability of the nanowires.

[0092] As an application example, the provision of sensors for power microscopy with a nanowire in the region of the sensor tip is illustrated in FIG. 6. 3×7 sensors were hereby manufactured in parallel by conventional photolithography. For a functional sensor, it is necessary that a nanowire is deposited in a narrow, locally defined region in order that all structures can be contacted electrically subsequently in parallel without individual adaptation. For this special application, the requirement exists in addition that the nanowire extends beyond the structure. In tests, a yield of up to 80% was achieved with respect to the 21 sensors.

[0093] According to the design of the material system, a differentiation can be made between positive and negative collectors. In the case of a negative collector structure, the nanowire deposition is effected preferably on the underlayer between the structures (e.g. gold on Si.sub.3N.sub.4, FIG. 7a), the nanowire deposition, in contrast thereto, being effected on the structure in the case of a positive collector structure (e.g. Si.sub.3N.sub.4 on SiO.sub.2, FIG. 2). Furthermore, there are also neutral structures, in which both properties can be observed (gold on SiO.sub.2, FIG. 4a).

[0094] From the presentation of the model of a critical interaction length or surface area, it results consequently that the surface-controlled contact printing method includes the possibility of “filtering” of nanowires with respect to length and diameter (width) during contact printing. In order to be able to deposit nanowires of a specific predefined width or length, preferably locally, structures can be used as collectors vertically or laterally relative to the direction of movement, the spacing of the opposite structures determining the width or length which is to be deposited preferentially (see FIG. 7a).

[0095] Also steps of a different height, variations in the density of nanoparticles, the geometry of the collector structures etc. can be used for filtering of the length and the width. A further possibility is influencing the distribution of the deposited nanowires by the geometry of the collector structure shape (e.g. a raised triangle; see FIG. 7b)).

[0096] In addition to linear deposition, nanowires can also in principle be deposited in other forms. This is possible, on the one hand, by effective coupling of the tribological interaction with a variation in the stripping direction (e.g. x-y instead of only x component in the speed vector), but also by geometrical or tribological “guide rails” on the surface, i.e. positive and negative collector structures placed specifically on the substrate surface (see FIG. 7c)). Also in FIG. 4c), it can already be detected for the upper nanowire that the latter was deposited orientated non-linearly on the gold nanoparticles.

EXAMPLE 7—DIAMOND AS SUBSTRATE

[0097] If a depression of 1 μm is etched into a nanocrystalline diamond layer (NCD) by means of oxygen plasma, then no deposition of the nanowires is effected on the raised portion (as with Si.sub.3N.sub.4) but on the lower-lying regions (i.e. the base of the recess). By means of the etching process, e.g. the tribological interaction of the etched surfaces can be significantly increased (e.g. roughness), which can again be exploited for local deposition (see FIG. 8).