Method for applying selectively a layer to a structured substrate by the usage of a temperature gradient in the substrate
A semiconductor wafer ( 10 ) is structured such that fine structures ( 3 ), such as membranes, bridges or tongues, with a thickness d<<D are formed, wherein D designates the thickness of the semiconductor wafer ( 10 ). Then particles of a desired material are applied. A temporal or spatial temperature gradient is generated in the semiconductor wafer ( 10 ), e.g. by progressive heating. In such a heating process the fine structures heat up more quickly and become hotter than the remaining wafer because they have a smaller heat capacity per area and cannot carry off heat as quickly. In this manner, the fine structures can be heated to a temperature that allows a sintering of the particles. For coating the semiconductor wafer ( 10 ) is brought into a reactor ( 11 ). A precursor compound of a metal is provided and fed to the reactor ( 11 ), where a reaction takes place during which the metal is transformed to a final compound and is deposited in the form of particles on the semiconductor wafer ( 10 ).
1. A method for applying a structured layer of a material on a substrate having a thickness D, comprising:
forming structures of a thickness d in or on the substrate, wherein d is less than D, and
applying particles of the material to said substrate and heating the substrate for generating a spatial or temporal temperature gradient in the substrate such that the structures reach a higher temperature T than non-structured regions of the substrate, wherein the material is synthesized in a flame during a flame pyrolysis process and the substrate is heated by said flame.
2. The method of claim 1 wherein the particles are sintered at the temperature T.
3. The method of claim 2 wherein a temperature T′ in a region of non-structured regions of the substrate remains smaller than a sintering temperature of the particles.
4. The method of claim 1 wherein each structure comprises at least two free surfaces a distance between which corresponds at most to the thickness d.
5. The method of claim 1 wherein the structures are arranged at openings extending through the substrate.
6. The method of claim 1 wherein said structures are membranes, tongues or bridges.
7. The method of claim 1 wherein the substrate is heated by means of electromagnetic radiation.
8. The method of claim 1 wherein the particles are applied from a first side to the substrate, and the substrate is heated from a second side opposite the first side.
9. The method of claim 1 wherein a temporal temperature gradient is generated within the substrate by changing the temperature of the substrate.
10. The method of claim 1 wherein the substrate is provided with a coating in the region of the structures, which coating allows for a deposition of the particles at a temperature reigning during deposition and/or that the substrate is provided with a coating outside the structures, which coating hinders a deposition of the particles.
11. The method of claim 1 wherein the particles have a diameter of not more than 100 nm, in particular not more than 10 nm.
12. The method of claim 1 wherein the layer on the substrate is at least partially polarized by applying an electric or magnetic field.
13. The method of claim 1 wherein the substrate comprises integrated heaters, which are heated during deposition, and in particular wherein the integrated heaters are arranged in or at the structures.
14. The method of claim 1 wherein the substrate is heated by means of heated particles and/or by means of a gas and/or plasma and/or a flame.
15. The method of claim 1 wherein the substrate is brought into contact with a cooling device.
16. The method of claim 1 wherein said substrate is a semiconductor wafer.
17. The method of claim 1 further comprising the step of manufacturing one or more sensors, in particular substance sensors, from said substrate.
18. The method of claim 1 comprising the step of applying a mask over said substrate for structuring said layer.
19. The method of claim 1 comprising the steps of applying several layers on said substrate.
20. A method for applying a structured layer of a material on a substrate having a thickness D, comprising:
forming structures of a thickness d in or on the substrate, wherein d is less than D, and
applying particles of the material to said substrate and heating the substrate for generating a spatial or temporal temperature gradient in the substrate such that the structures reach a higher temperature T than non-structured regions of the substrate, wherein the substrate is brought into contact with a cooling device, wherein, the structures are not in direct contact with the cooling device.
21. The method of claim 20 wherein the structures on a first side of the substrate are arranged over openings and the openings extend to a second side of the substrate, wherein the second side of the substrate is brought into contact with the cooling device.