FILTER SUBSTRATE FOR FILTERING AND OPTICALLY CHARACTERIZING MICROPARTICLES, METHOD FOR PRODUCING THE FILTER SUBSTRATE, AND USE OF THE FILTER SUBSTRATE

Abstract

The present invention relates to a filter substrate for filtering and optically characterizing microparticles. The filter substrate comprises a wafer having a thickness of at least 100 pm and a transmittance of at least 10% for radiation in the wavelength range of 2500 nm to 15000 nm. Furthermore, the surface of the front side and/or the surface of the rear side of the wafer is completely or partially provided with an antireflective layer, which prevents the optical reflection of radiation in the wavelength range of 200 nm to 10000 nm. Moreover, the wafer has, at least in some regions, filter holes having a diameter of 1 pm to 5 mm. With the filter substrate according to the invention, microparticles can be filtered and the microparticles on the filter substrate can be subsequently optically characterized with very high measurement quality. The present invention further relates to a method for producing the filter substrate according to the invention and to the use of the filter substrate according to the invention.

Claims

1-13. (canceled)

14. A filter substrate for filtering and optical characterization of microparticles, comprising a wafer with a thickness of at least 100 μm and a transmission degree of at least 10% for radiation in the wavelength range of 2,500 nm to 15,000 nm, the surface of the front-side and/or the surface of the rear-side of the wafer being provided, completely or in regions, with an antireflection layer which prevents an optical reflection of radiation in the wavelength range of 200 nm to 10,000 nm, and the wafer having, at least in regions, filter holes with a diameter of 1 μm to 5 mm.

15. The filter substrate according to claim 14, wherein the antireflection layer is a nanostructure which is introduced in the surface of the wafer or a nanostructured coating which is applied on the surface of the wafer.

16. The filter substrate according to claim 14, wherein the wafer has a thickness greater than 100 μm.

17. The filter substrate according to claim 16, wherein the wafer has a thickness greater 250 μm.

18. The filter substrate according to claim 14, wherein the filter substrate has a reinforcing structure for mechanical stabilization of the wafer.

19. The filter substrate according to claim 14, wherein the wafer is a silicon wafer.

20. The filter substrate according to claim 19, which has a doping degree of max. 10.sup.18 atoms/cm.sup.3.

21. The filter substrate according to claim 14, wherein the number of filter holes is at least 100.

22. The filter substrate according to claim 21, wherein the number of filter holes is at least 10,000.

23. The filter substrate according to claim 14, wherein the filter holes are introduced by laser boring, and/or form respectively a straight channel which extends perpendicular to the front-side and to the rear-side of the wafer, and/or have a diameter of 1 μm to 4,000 μm, and/or are disposed, at least in regions, with a density of 1 filter hole per cm.sup.2 to 1,000,000 filter holes per cm.sup.2, in the filter substrate, and/or all have the same diameter and/or the same geometry.

24. A method for the production of a filter substrate according to claim 14, in which, in a wafer with a thickness of at least 100 μm and a transmission degree of at least 10% for radiation in the wavelength range of 2,500 nm to 15,000 nm, filter holes with a diameter of at least 1 μm are introduced at least in regions, and the surface of the front-side and/or the surface of the rear-side of the wafer is provided, completely or in regions, with an antireflection layer which prevents an optical reflection of radiation in the wavelength range of 200 nm to 10,000 nm.

25. The method according to claim 24, the filter holes are introduced by laser boring.

26. The method according to claim 24, wherein the front side and/or the rear side of the wafer is provided with the antireflection layer by a nanostructure being introduced into the surface of the wafer or a nanostructured coating being applied on the surface of the wafer.

27. The method according to claim 24, wherein the production of the antireflection layer is effected before or after the introduction of the filter holes.

28. The method according to claim 24, wherein the wafer is provided with a reinforcing structure for the mechanical reinforcement thereof.

29. A method of filtering microparticles comprising utilizing the filter substrate according to claim 14 for filtering the microparticles and subsequently optically characterizing the filtered microparticles by transmission spectroscopy and/or reflection spectroscopy.

Description

EMBODIMENTS

[0047] In FIG. 1, a first embodiment of the filter substrate according to the invention and also the use thereof is illustrated schematically. The filter substrate comprises a wafer 1 with a thickness of at least 100 μm and a transmission degree of at least 10% for radiation in the wavelength range of 2,500 nm to 15,000 nm. The wafer 1 concerns a silicon wafer which has a doping degree of max. 10.sup.17 atoms/cm.sup.3. The surface of the front-side of the wafer 1 is provided in regions with an antireflection layer 2 which prevents optical reflection of radiation in the wavelength range of 200 nm to 10,000 nm. Of concern hereby is an antireflection layer which prevents the optical reflection by more than 99% of the radiation impinging thereon in the wavelength range of 200 nm to 10,000 nm. The wafer 1 has, at least in regions, filter holes 3 with a diameter of 1 μm to 5 mm. The filter holes 3 are introduced by means of laser boring and respectively form a straight channel which extends perpendicular to the front-side and to the rear-side of the wafer 1.

[0048] During the filter process, the medium 4 to be filtered (liquid or gas) can pass through the filter holes 3, the microparticles 5 contained in the medium remaining suspended on the front-side of the filter substrate.

[0049] After the filter process, the optical characterisation of the microparticles can be effected directly on the filter substrate, the microparticles 5 being irradiated with light 6. In the region or the regions of the filter substrate without an antireflection layer (region A), the optical characterisation can be effected by means of transmission measurement (e.g. FTIR). Because of the high transmission degree of the wafer, a large part of the light can be transmitted through the wafer. The transmitted light 7 can then be analysed. From the high transmission degree of the wafer, a very good measuring quality results.

[0050] In the region or the regions of the filter substrate with an antireflection layer 2 (region B), the optical characterisation can be effected in addition also by means of reflection measurements (e.g. Raman). The incident light 6 impinges on the microparticles 5 and is reflected. The reflected light 8 can then be analysed. Because of the antireflection layer 2, a very good signal-to-noise ratio is obtained, from which a very good measuring quality results.

[0051] In FIG. 2, a second embodiment of the filter substrate according to the invention and also the use thereof is illustrated schematically. This second embodiment differs from the previously described first embodiment merely by the surface of the front-side of the wafer 1 being provided completely with the antireflection layer 2. Otherwise, the filter substrates of both embodiments are identical.

[0052] As a result of the fact that the entire surface of the front-side of the filter substrate is provided with the antireflection layer 2, the optical characterisation can be effected at any place of the wafer 1 or of the filter substrate by means of reflection measurements (e.g. Raman). The incident light 6 impinges on the microparticles 5 and is reflected. The reflected light 8 can then be analysed. Because of the antireflection layer 2, a very good signal-to-noise ratio is obtained, from which a very good measuring quality results.

[0053] In addition, the optical characterisation can be effected in principle also by means of transmission measurement (e.g. FTIR) (not illustrated in FIG. 2). In order to achieve a very high measuring quality even with these transmission measurements, the antireflection layer should however have a transmission degree of at least 10% for radiation in the wavelength range of 2,500 nm to 15,000 nm.

[0054] In the following, a variant, given by way of example, of the method according to the invention for producing the filter substrate according to the invention is described.

[0055] Firstly, Si filter substrates (thickness 150 μm) were produced by laser boring in polished silicon wafers. A laser process with the following parameters was used: wavelength 532 nm, pulse duration 8 ns, repetition rate 50 kHz, power 3 W. As a function of the required filter properties (particle size and throughflow), variable hole structures with diameters in the range of a few millimetres to approx. 50 μm can be achieved with an ns laser (see FIG. 3). Smaller filter holes were already produced by ultrashort pulse lasers and/or electrochemical etching processes.

[0056] In this context, FIG. 3 shows in a) an incident-light microscopic image of an Si filter for the particle size class 3,000 μm (all particles greater than 3,000 μm are collected in this filter). In b), a transmitted-light microscopic image of a filter for the particle size class 30 μm is shown.

[0057] In addition, an antireflection layer can be produced on the silicon wafers simply by sputtering deposition processes. For example, an SiN.sub.x layer is deposited with the optical layer thickness λ/4 which leads by interference to a reduced reflection in the range of the wavelength λ. Optionally broadband antireflection layers can be produced by a nanostructuring (black silicon) with plasma etching processes. The layer deposition can be effected before or after introduction of the filter holes in the Si wafer. The process sequence of layer deposition/laser boring depends upon the required precision of the hole diameters and upon the respective deposition process. In the case of conformal deposition methods and small hole diameters, an antireflection layer production leads to more precise hole geometries.