Etching a substrate: processes – Nongaseous phase etching of substrate – Etching inorganic substrate
Reexamination Certificate
1999-07-13
2002-07-02
Goudreau, George (Department: 1763)
Etching a substrate: processes
Nongaseous phase etching of substrate
Etching inorganic substrate
C204S157150, C204S471000, C204S478000, C204S479000, C205S123000, C205S157000, C205S091000, C205S092000, C205S131000
Reexamination Certificate
active
06413440
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention involves a process for manufacturing an electrode, in which a surface structure, with at least one electrically conducting projection having at least a tip or edge, is produced on a substrate.
A process of this type is already known from German published patent application DE 44 22 049 A1. There, a three-dimensional surface structure is first created on a silicon substrate using an anisotropic or isotropic etching process. The surface structure has a number of pyramidal or cone-shaped projections arranged adjacent to each other, each of which has a tip. Then, the substrate is dipped into a polymer solution, or a polymer solution is sprayed onto or poured onto the substrate. On the tips of the projections a film outline thereby occurs which is controlled, in that the surface structure having the projections is exposed to the vapor of a solvent. By the film outline, it should be achieved that the tips remain for the most part free of the polymer solution, while the surface areas surrounding the tips of the projections are covered with the polymer solution, which forms an electrically insulating layer after curing.
The previously known process, however, has proven to be problematic in practice, since the film outline is a statistical process, which does not always progress the same way in the individual projections of the substrate. In particular, different flow behavior of the polymer solution can occur on the individual projections of the surface structure. In addition, it is unfavorable that the polymer solution contains a solvent which is released during the curing of the lacquer layer. Also, the lacquer layer can contain toxic materials, which is especially disadvantageous when the electrodes manufactured according to the process are to be used to examine living biological cells, which react very sensitively to toxic materials. An influencing of the cells can also occur thereby, and thus lead to measurement errors. Moreover, it is disadvantageous that by having the lacquer layer arranged in the intermediate spaces located between the pyramidal or cone-shaped projections, the height of the projections, i.e. the distance between the furthest projecting position of a projection and the furthest set back position of the lacquer layer adjacent to it, is reduced. The electrode area located on the tip of the projection cannot be positioned very well by this, for example, through a cell membrane to the interior of the cell, in order to examine it with the electrode tip. Also, the electrode tip can only be poorly stuck into another soft material to be investigated.
SUMMARY OF THE INVENTION
Therefore, an object of the invention is to create a process of the type mentioned at the beginning, with which a micro-electrode having on its surface an electrically conducting tip or edge surrounded by an electrically insulating surface area can be manufactured while avoiding a lacquer layer that remains in the area of the tip or edge.
The solution of this object consists in that a supply channel is made in the substrate, which opens in close proximity to the tip or edge that is to be mounted on the surface of the substrate, and that through the supply channel a chemical is supplied which emerges at the tip or edge, and which upon irradiation with electromagnetic and/or particle radiation precipitates an electrically conducting material, in particular a metal, and that the chemical is irradiated with electromagnetic and/or particle radiation in the area of the tip or edge in order to precipitate the electrically conducting material at the tip or edge.
The tip or edge can, for example, be created using a traditional structuring process such as anisotropic etching, underetching of a lacquer layer or vapor deposition of the substrate surface through an opening located in a mask arranged near the substrate surface. Through the supply channel the chemical preferably reaches the area of the tip or edge of the substrate, so that the electrically conducting material precipitated out of the chemical with the aid of the electromagnetic and/or particle radiation preferably is deposited there. By an electromagnetic and/or particle radiation is understood here a radiation that supplies energy to the chemical, for example optical radiation, such as light, infrared or ultraviolet radiation, X-ray radiation, or particle radiation, such as alpha, beta or gamma radiation.
Expediently, the supply speed of the chemical emerging in the area of the tip or edge is selected such that it is disposed in the area of the tip or edge during the entire switched-off period of the electrically conducting material. In this way, a possible precipitation of the conducting material outside of the area of the tip or edge is prevented. The electrode manufactured according to the process is thus only conducting on the part of its surface that is located in the area of the tip or edge, while the remaining surface areas are electrically insulating. This can be achieved, for example, in that as a substrate an electrical insulator is used or that an electrically conducting substrate is provided with an insulating surface layer before the switch-off of the electrode material. On the whole, a partially conducting electrode having a micro-electrode tip or edge, which allows a locationally resolved measurement of electric signals, thus results while avoiding a lacquer mask surrounding the electrode layer. The electrode is suitable especially for an examination or treatment of biological cells deposited on the surface of the electrode. The supply channel can, for example, be applied by laser drilling or plasma etching into the substrate. Optionally, the penetration of the supply channel can be done from the rear side of the substrate, which faces away from the tip or edge. For this purpose, for example, an etch-resistant mask can be applied on the rear side of the substrate.
An advantageous embodiment of the process provides that the electromagnetic and/or particle radiation is beamed through the supply channel into the area of the tip or edge. For this purpose, for example, on the end of the supply channel that faces away from the tip or edge, a laser beam can be coupled into the supply channel. The optical radiation can thereby be positioned in a simple way on the tip or edge. Since the electromagnetic and/or particle radiation becomes interspersed in the chemical located in the supply channel, the electrically conducting material is also precipitated out in the supply channel and can deposit on its wall. The wall of the supply channel then forms an electrically conducting bond to the electrode tip or edge. In the electrode manufactured according to the process, an electrical voltage can, for example, be applied via this bond conductor to the electrode tip, or a measurement signal on the electrode tip can be measured. In an advantageous manner, the electrically conducting material applied to the wall of the supply channel also forms, however, a hollow electrode which, in comparison to its dimensions in the surface plane of the substrate, has a relatively large area. The electrode manufactured according to the process therefore allows, in spite of a high locational resolution, a good electrical contact to a medium to be examined or treated.
The previously mentioned object can also be achieved in that the surface structure is manufactured from an electrically conducting material, in that in the area of the tip or edge at least one electrically conducting electrode layer is galvanized and/or applied by electrostatic powder coating onto this material, and in that a surface area of the substrate surrounding the electrode layer located on the tip or edge is then converted by a chemical reaction into an insulating layer or provided with such an insulating layer.
The invention makes use of the discovery that upon application of an electric voltage on the substrate or its surface structure in the area of the tip or edge, an especially high electrical field strength occurs. The electrode material to be galva
Akin Gump Strauss Hauer & Feld L.L.P.
Goudreau George
Micronas GmbH
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