DE19827900A1 - Process for coating surfaces - Google Patents

Description

The invention relates to a new method for coating a metallic or semi-metallic surface as well as a structured coated surface.

Surfaces can be functionalized by coating thereby achieving predetermined and desirable properties. The covalent coating of silicon surfaces with organic molecules a carbon-silicon bond is known (M.R. Linford et al., J. At the. Chem. Soc. 115: 12631-12632 (1993); M.R. Linford et al., J. Am. Chem. Soc. 117: 3145-3155 (1995)). These coatings were made by Reaction of hydrogen-terminated Si (111) with 1-alkenes via a radical mechanism using diacyl peroxides as Radical starter manufactured. However, the use of peroxides is disadvantageous because peroxides are extremely reactive, harmful to health and also are not very specific in their reactivity.

Furthermore, it is known to self-assemble monolayers of functionalized organosilyl compounds on hydroxylated Form silicon surfaces (F. Effenberger et al., Synthesis 1995, 1126-1130; K. Bierbaum et al., 1995, Langmuir 11: 512-518; S. Heid et al., Langmuir 12: 2118-2120 (1996); P. Harder et al., Langmuir 13 (1997), 445-454). EP-A-0 664 452 describes the covalent bond of Silicic acid compounds on the OH groups of an oxidized Silicon surface described. However, a disadvantage of these methods is that that the surface is chemically pretreated before coating must and undesirable crosslinking reactions can also take place. In addition, it is advantageous for many applications if the  Coating on a metallic and not on an oxidized Surface is applied.

The present invention was therefore based on the object of a method to provide for the coating of metallic surfaces, which the does not have disadvantages occurring in the prior art.

The object is achieved by a method for Coating a metallic or semi-metallic surface, which is characterized in that coating molecules, the reactive Groups contain covalently to the surface by irradiation with light binds.

Surprisingly, it was found that activation with light an efficient coating of metallic or semi-metallic Surfaces with molecules containing reactive groups can be obtained can. The term "reactive group" means in the context of the present invention that under suitable conditions and at Irradiation with light of a suitable wavelength forms a covalent bond reactive group to a surface.

The binding of the coating molecules to the surface can be done on a direct photoactivation of reactive groups in the coating molecules are based. Furthermore, the bond can also be through Photoactivation of the surface itself if this is reactive, eg. B. groups activated by light, e.g. B. metal or / and Contains semimetal hydride compounds such as silicon hydride. By Light activated groups of the surface are then able to be covalent Enter into bonds with reactive groups of the coating molecules. A combination of both reaction mechanisms, i. H. Photoakti crossing of the coating molecules and photoactivation of the surface, is possible.  

The surfaces to be coated have a metallic or semi-metallic character and can be one or more metals, Semi-metals or / and metallic or semi-metallic compounds include. Examples of suitable elements that have a metallic or form semi-metallic surface, are the metals and semi-metals of Groups 3 to 16 of the periodic table. Particularly preferred examples are silicon, germanium and metallic compounds that contain these elements contain. Examples of surfaces that span more than one element are alloys that are two or more metals and / or semi-metals include. An example of a connection that has a metallic character is gallium arsenide. The surface is particularly preferably one hydrogenated surface, d. H. the metal or / and semimetal atoms of the Surface layers are at least partially bound to hydrogen. A An example of a metal or semimetal hydride is silicon hydride. Both metallic surfaces used according to the invention especially around surfaces that do not contain oxidized elements or Have connections.

According to the invention, the molecules containing reactive groups are covalently bound to the metallic or semi-metallic surface, for example via a surface element-carbon or surface element-oxygen bond. The molecules used can in principle comprise any reactive group, ie a group which can be converted directly or / and due to interactions with the surface into a reactive species, in particular into a radical, by irradiation with light. The reactive group is preferably selected from C = C or C = O double bonds. Examples of such reactive groups are alkene, aldehyde and vinyl ether groups. Aldehyde groups with which surprisingly high degrees of coverage can be obtained are particularly preferred. In the case of aldehyde groups, binding to the surface takes place via oxygen. In contrast to known coating processes on hydroxylated silicon surfaces, in which the thickness of the SiO ₂ layer is indefinite, predetermined, defined and uniform coatings can be obtained with the process according to the invention.

When using alkene groups, the coating molecules bound to the surface via a carbon atom.

The process according to the invention makes coated metallic or semi-metallic surfaces manufactured for a variety of Applications are suitable, e.g. B. for the production of microelectronic Components, as well as for applications in diagnostics and medicine. Applications for functionalized surfaces by chemical Coupling of coating molecules to the surface were, for. B. in WO 92/10092, Fodor et al. (Nature 364 (1993), 555-556) and Cheng and Stevens (Adv. Mater. 9 (1997), 481-483). According to the invention, these applications are also by photoactivation coated surfaces.

For this purpose, molecules are expediently used for the coating used in addition to one or more reactive groups at least contain another functional group. The other functional group is preferably selected from haptens, biotin, chelation groups, Nucleotides, nucleic acids, nucleic acid analogs, polyethylene glycol, conjugated π systems, charged groups, nonlinear optical Structures, networkable groups, electrically conductive groups, Amino acids, peptides and polypeptides.

Molecules can be used for applications in microelectronics that include conjugated π systems. Especially with such Connections is the activation known in the prior art with Peroxides disadvantageous because the occurrence of undesirable radicals Side reactions are observed. By the radiation according to the invention  with light of a defined wavelength, however, it is possible to be selective those reactive groups that bind to the metallic surface are provided to activate and at the same time other groups, e.g. B. π- Not to influence bonds or conjugated π bonds in the molecule. Organic conjugated π systems are preferred Molecules polyenes, aromatics, e.g. B. polyphenylenes, heterocycles, e.g. B. Polyheteroaryls and / or polyacetylenes are used.

Through crosslinkable groups, such as double bonds, e.g. B. Acrylic esters and / or triple bonds, the coating after the Applied cross-linked to the metallic or semi-metallic surface become. Crosslinking can also take place via oxidation, e.g. B. from sulfur-containing groups such as thiol or thiophene groups.

By using haptens, polypeptides and / or biotin specifically bindable solid phases are formed, for example in diagnostic procedures, e.g. B. immunoassays can be used.

When coating the surface with nucleotides, nucleic acids or Nucleic acid analogs such as peptide nucleic acids Get surfaces that are suitable for nucleic acid Hybridization tests are suitable.

By using polyethylene glycol or other inert molecules can be chemically inert and resistant surfaces as well as biocompatible Surfaces, e.g. B. made for use as implant surfaces become.

Electrically conductive group and certain polypeptides, such as. B. Bacteriorhodopsin are particularly suitable for electronic ones Applications.  

The other functional groups can during the binding of the organic molecules to the surface if necessary Protecting groups are blocked. However, such blocking is often not required if the wavelength used for photoactivation can be selected so that the photoactivatable group is activated the other functional group, however, is in the wavelength range of incident light does not respond.

A metallic or semi-metallic surface is preferably used, the at least one element selected from B, Al, Ga, Si, Ge and As includes. A surface is particularly preferred Silicon hydride surface used. Such a surface can for example by etching oxidized Si (111) with ammonium fluoride (G. J. Pietsch, Appl. Phys. A: Mater. Sci. Process. A 60 (1995) 367-363; G. J. Pietsch, Structure and Chemistry of Technological Silicon surfaces, VDI progress reports series 9, 148, VDI-Verlag, Düsseldorf 1992).

The coating is preferably carried out in an inert gas atmosphere, for example under argon.

The light used for the irradiation in the method according to the invention source must be of sufficient intensity to be sufficient To achieve coating efficiency. Basically is for the coating suitable for any type of light source, e.g. B. lamps such as an HBO lamp. However, the use of lasers has proven to be particularly favorable proven. Preferably, the light source is able to light one defined wavelength or a defined wavelength range to radiate. This can be done by using monochromatic Light sources such as a laser or corresponding filter reached become. When using monochromatic light or a light with a narrow, defined wavelength range, it succeeds in selective  Way, the photoactivatable groups of the coating molecules or / and to excite the surface while others in the coating molecules contained functional groups are not affected.

Light with a wavelength in the range of 350 is preferably used to 400 nm, in particular from 370 to 395 nm. Particularly preferred Light irradiated with a wavelength in the range from 380 to 390 nm.

The duration and intensity of the radiation depend on the desired loading degree of coverage, the metallic or semi-metallic used Surface, the coating molecules used and the Reaction conditions. Usually you get the desired one Results when irradiated for a period of 1 minute to 30 Hours.

The process according to the invention makes one over the coating area laterally homogeneous layer of coating molecules, preferably a monolayer. A single species of Coating molecules but also a mixture of several species of Coating molecules are used. In a preferred one Embodiment of the method according to the invention is a mixture different coating molecules used, one species of Coating molecules specifically with a free reactant bindable group, e.g. B. biotin, hapten, polypeptide, nucleic acid etc., contains, while another species of the coating molecules none contains such a functional group and thus as a "diluent molecule" works. The molar ratio of functional coating molecules to Diluent is preferably from 1: 100 to 100: 1.

A major advantage of the method according to the invention is that it is possible to selectively and precisely define certain areas of a surface coat. For example, by using suitable optics  or through the use of laser technology a metallic or semi-metallic surface selectively in the smallest spatial areas up to be coated in the micrometer range. For example, Beschich tion molecules that contain electrically conductive groups at desired Locations are applied by radiation, so that one in the Microelectronic usable circuit arises. Of course it is also possible to coat a surface over a large area. In addition to the Using lasers and / or focusing optics can be a problem structured coating also through the use of masks or / and optical gratings are applied. That way it is possible, coated metallic surfaces with any to generate predetermined patterns. The method according to the invention is particularly suitable for the production of array structures that used for example in diagnostics for the production of biosensors can be.

By applying molecules to the specifically bindable groups have, such as haptens, biotins, nucleobases, nucleic acids, Nucleic acid analogs, polypeptides and the like can be used on coated surfaces for diagnostics. By using biocompatible organic molecules it is possible to create surfaces that are made of one material exist, which is rejected by the body, biocompatible do.

Another object of the invention is a coated object comprising a carrier with a metallic or semi-metallic surface and coating molecules covalently bonded thereto, which is characterized in that the surface has an arrangement of coated and uncoated areas. The coated areas are preferably miniaturized, ie they have an area of 1 μm ² to 10 mm ² , particularly preferably 10 μm ² to 1 mm ² . In contrast to methods known in the prior art for coating metallic surfaces by chemical activation, in which only full-area coating was possible, a structured coated surface can be obtained with the method according to the invention. A surface with a defined coating pattern can be produced, in which the coating is applied only in predetermined areas of the surface. The surface preferably has an array structure. Suitable focusing optics and / or laser techniques make it possible to selectively coat precise, locally delimited areas. The surface preferably comprises coating molecules which contain at least one further functional group, or mixtures of functional coating molecules with inert diluent molecules. Depending on the application, suitable functional groups can be used as described above.

The invention is illustrated by the accompanying figures and the following Examples further explained.

Fig. 1 shows the connections 1 to 3, which were used for coating metal surfaces. Compounds 1a, 1b and 1c are alkenes, compound 2 is a vinyl ether and compounds 3a and 3b are each an aldehyde.

Fig. 2 shows schematically the formation of a layer of octadecanal 3a to an H-terminated Si (111) surface.

Fig. 3 shows the dependence of the degree of coverage of a tetradecanal layer on an Si surface of the irradiated wavelength.

Fig. 4 shows the dependence of the degree of coverage of an octadecene-layer on an Si surface of the irradiated wavelength.

Examples example 1 Coating an H-terminated silicon surface with Alkenes and vinyl ethers

An Si-H surface was formed by etching oxidized Si (111) wafers Ammonium fluoride produced by known methods (G. J. Pietsch, Appl. Phys. A: Mater. Sci. Process. A 60 (1995) 347-363; G. J. Pietsch, Structure and chemistry of technological silicon surfaces, VDI Progress reports, series 9, 148, VDI-Verlag, Düsseldorf 1992). The Silicon wafers (Si (111) p-type) were manufactured by Wacker-Chemitronic GmbH and Siltronix.

The H-terminated silicon surface etched with fluoride ions was added to the pure compounds 1, 2 and 3 (cf. FIG. 1) in a glass cuvette and irradiated for 20 to 24 hours in an inert gas atmosphere. Under the test conditions used here, an optimal reaction time of 20 to 24 hours was found, with shorter or longer reaction times resulting in reduced coverage. The formation of self-assembling monolayers was initiated by irradiating an HBO lamp (150 W). Then the silicon substrate was taken out, rinsed several times with dichloromethane and wiped with cotton to remove physically adsorbed material.

For comparison, the formation of monolayers with 1-octadecene (1a) on an H-terminated Si (111) surface by dioctadecanoyl peroxide initiated according to the prior art (M.R. Linford et al., J. Am. Chem. Soc. 117: 3145-3155 (1995)). The results are shown in Table 1.  

As can be seen from Table 1, the inventive Process approximately the same degree of coating for alkenes can be achieved as with the method known in the prior art using Peroxides, being careful of these dangerous and unspecific chemical reagents can be dispensed with.

The surface coverage was determined using equation 1:

y = 0.007.x - 0.03429 (x = the number of CH ₂ groups)

calculated from a linear regression analysis of the diagram areas of the v _as (CH ₂ ) and v _s (CH ₂ ) bands of seven alkyltrichlorosilanes (wafer data) depending on their chain length (8, 10, 12, 14, 16, 18 and 20 CH ₂ Groups) was obtained (S. Heit et al., Langmuir 12 (1996) 2118-2120). Coverage is obtained by dividing the areas of the bands of V _as (CH ₂ ) and v _s (CH ₂ ) by y.

In addition to the terminally unsubstituted 1-alkene 1a, the mono Layer formation also with the pure ω-thienyl-substituted 1-alkenes 1b and c and with the hexadecyl vinyl ether 2 by irradiation under comparable conditions examined. It was also found that even a slight dilution of the 1-alkenes with an alkane as Solvent the formation of the self-assembling monolayer clearly affects what results in less coverage. The usage a mixture comprising nine parts of compound 1a and one part For example, hexadecane has a coverage of only 20%.

Example 2 Coating an H-terminated silicon surface with Aldehydes

The experiment described in Example 1 was carried out under the same conditions as described for compound 1a, except that pure 1-octadecanal (3a) (R. Redcliff et al., J. Org. Chem. 35 (1970), 4000) was used as the coating molecule -4002) was used. It was determined by high-resolution AFM images (50 × 50 nm ² ) that a homogeneous self-assembling monolayer with a high degree of coverage of 97% based on 100% coverage with octa-decyltrichlorosilane (OTS) was obtained. FIG. 2 schematically shows a monolayer of the connection 3a. An average inclination angle of 12 ° for the molecules in the monolayer relative to the substrate can be derived from the dichromatic ratio D = 0.54 (A. Ulman, An Introduction to Ultrathin Organic Films, Academic Press, London 1991). This result agrees with the literature data from OTS films (MR Linford et al., J) Am. Chem. Soc. 117 (1995) 3145-3155).

Example 3 Formation of a self-assembling monolayer under Use of different wavelengths

Pure tetradecanal (compound 3b) was applied as described in Example 1 to an Si (111) -H surface at 40 ° C. at different radiation wavelengths. An XBO lamp (450 W) and a double monochromator (Jarrell Ash Co. mod. 82-440) with a half-width of 1.3 nm were used as the light source in this experiment. The results are summarized in Table 2 and Fig. 3.

As can be seen from Table 2 and Fig. 3, the maximum degree of coverage was obtained with light of a wavelength of 385 nm.

The dependency of the degree of coverage on the wavelength was investigated analogously with pure octadecene (compound 1a). Here, too, a maximum coverage was obtained at 385 nm (see Fig. 4).

Example 4 Formation of a self-assembling monolayer of Aldehydes as a function of the irradiation time

The rate of formation of self-assembling monolayers was with pure octadecanal (compound 3a) on a Si (111) -H- Surface examined. The influence of the irradiation time Degree of coverage and orientation of the monolayers formed is in Table 3 summarized.

Table 3

The H-terminated Si surface prepared as in Example 1 was cleaned Put octadecanal (compound 3a) in a glass cuvette. She was on Heated to 70 ° C and for the time periods specified in Table 3 polychromatic light of 385 nm wavelength irradiated. The surface was removed and cleaned as described in Example 1.

After one minute of irradiation, a degree of coverage of 39% was found and the position of the u _s (CH ₂ ) band at 2922 cm ^-1 indicates a low order of the monolayer. The degree of coverage was increased to 80% after 3 minutes of irradiation. An optimal coverage of 103% could be obtained with an irradiation time of 5 minutes. The u _as (CH ₂ ) band at 2917 cm ^-1 indicates the formation of a perfectly ordered self-assembling monolayer of compound 3a.

Example 5 Manufacture of laterally structured coated surfaces

Previous investigations into the construction of self-assembly Monolayers (Ulman, Chem. Rev. 96 (1996), 1533-1554 and others Literature quotes therein; Xia and Whitesides, Angew. Chem. Int. Ed. Engl. 37 (1998), 550-575; Effenberger and Heid, Synthesis 1995, 1126-1130; Bierbaum et al., 1995, Langmuir 11: 512-518; Heid et al., Langmuir 12 (1996), 2118-2120; Harder et al., Langmuir 13 (1997), 445-454) was one direct lateral structuring of the surfaces is not possible because of chemically uniform surfaces and the subsequent chemical reaction with the layer-forming substrates as well was done uniformly.

The light-induced production of self-assembly according to the invention However, monolayers allow one when using suitable masks direct structuring of surfaces. Particularly suitable as a mask are films that are used in the manufacture of circuit boards.  

The structures of the masks were created using the Freehand computer program 5.0 drawn and directly with a laser-assisted photo typesetting system (Linotronic 530, Linotype-Hell, resolution 2540 dots / inch) on polymer films (Fuji laser recorder film F100) printed. Then the SiH substrate was with covered the mask, added octadecanal and melted. The Monolayer formation and cleaning was carried out as previously described.

On the basis of IR spectra, it was possible to demonstrate that with coverage part of the Si (111) -H surface only the uncovered area one SAM layer results. In addition, it was found that the unexposed part of the SiH surface is still fully reactive.

Due to the different wettability of the coated or Uncoated silicon can be used to structure the silicon surface Also visible for viewing with the naked eye or in a microscope do. For this purpose, the was provided with a structured coating Substrate under a microscope (Carl Zeiss, 20x magnification) with a few drops of a mixture of 2-propanol and universal oil (Lubricant Consult GmbH). That trained after a few seconds Pattern was photographed.

Claims (25)

1. A method for coating a metallic or semi-metallic surface, characterized in that coating molecules containing reactive groups are covalently bound to the surface by irradiation with light. 2. The method according to claim 1, characterized in that the binding of the coating molecules to the surface

• (a) photoactivation of reactive groups in the coating molecules,
• (b) photoactivation of reactive groups on the surface or
• (c) a combination of (a) and (b) takes place.

3. The method according to claim 1 or 2, characterized, that the reactive groups of the coating molecules from C = C- or C = O double bonds can be selected. 4. The method according to claim 3, characterized, that the coating molecules reactive alkene, aldehyde or / and Contain vinyl ether groups. 5. The method according to any one of the preceding claims, characterized, that the coating molecules in addition to reactive groups at least contain another functional group.   6. The method according to claim 5, characterized, that the further functional group is selected from haptens, Biotin, chelation groups, nucleotides, nucleic acids, Nucleic acid analogs, polyethylene glycol, conjugated π systems, charged groups, nonlinear optical groups, networkable Groups, electrically conductive groups, amino acids, peptides and Polypeptides. 7. The method according to claim 6, characterized, that the coating molecules as further functional groups contain conjugated π systems. 8. The method according to claim 7, characterized, that the coating molecules polyene, aryl, heteroaryl or / and Contain polyacetylene groups. 9. The method according to claim 7 or 8, characterized, that the other functional groups during binding to the Surface can be blocked by protective groups. 10. The method according to any one of the preceding claims, characterized, that the surface has at least one element selected from B, Al, Ga, Si, Ge and As includes.   11. The method according to any one of the preceding claims, characterized, that the surface has at least one metal or / and Semi-metal hydride compound. 12. The method according to claim 11, characterized, that the surface comprises silicon hydride. 13. The method according to any one of the preceding claims, characterized, that the coating is carried out in an inert gas atmosphere. 14. The method according to any one of the preceding claims, characterized, that light with wavelengths in the range of 370-395 nm shines in. 15. The method according to claim 14, characterized, that you shine in monochromatic light. 16. The method according to any one of the preceding claims, characterized, that a mixture of different species of Coating molecules used. 17. The method according to claim 16, characterized, that one species of coating molecule another functional group and another species of Coating molecules no further functional group.   18. The method according to any one of the preceding claims, characterized, that you can get a structured coating by using Masks and / or optical grids. 19. The method according to claim 17, characterized, that you apply array structures. 20. The method according to any one of the preceding claims, characterized, that a coated surface for use in the Microelectronics manufactures binding molecules that are electrical have conductive groups. 21. The method according to any one of claims 1-19, characterized, that you produce a coated surface for diagnostics, whereby binding molecules are applied, the specifically bindable Has groups. 22. The method according to any one of claims 1-19, characterized, that you apply a biocompatible coating. 23. A coated article comprising a support with a metallic or semi-metallic surface and covalent to it bound coating molecules, characterized, that the surface is an arrangement of coated and uncoated has layered areas, the coated areas are miniaturized.   24. The article of claim 23, characterized, that it is a biosensor that has an array structure. 25. The article of claim 23, characterized, that the coating molecules at least one other functional Contain group or mixtures of coating molecules with or without other functional groups.