Electrolysis: processes – compositions used therein – and methods – Electrolytic erosion of a workpiece for shape or surface... – With irradiation or illumination
Reexamination Certificate
2000-09-01
2002-07-23
Valentine, Donald R. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic erosion of a workpiece for shape or surface...
With irradiation or illumination
C204S290010, C204S22400M
Reexamination Certificate
active
06423207
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method, an electrode and a device according to the preamble to appended claims
1
,
14
and
17
.
2. Description of the Related Art
In wet etching methods, a fluid is usually employed, which comprises an etchant capable of reacting in an etching manner with an etching material. In chemical etching, the etchant reacts spontaneously with the etching material, and in electrolytic etching, the etchant reacts by electrochemical reactions on the surface of the etching material when an etchant, with voltage applied, carries a current.
When the purpose of etching is to provide a structure in the etching material by etching away selected parts thereof, the etching material surface which is not to be etched away is usually coated with an etching preventing layer, a so-called mask or resist, which is insensitive or less sensitive to the etchant than the etching material. Such an etching preventing layer is produced in a multistage operation with an initial coating step and a subsequent step for partially removing the layer.
A common etching preventing layer is a photoresist. When using a photoresist, the surface of the etching material is coated in a first step with the photoresist which is sensitive to light. In a next step, the surface areas of the photoresist where etching is to be carried out are exposed to light, and in a subsequent step, these areas are developed and dissolved, thus uncovering the areas of the etching material that are to be etched. This method is currently used, for instance, when manufacturing printed circuit boards for etching away material to form gaps between conductors. The manufacture of an etching preventing layer in prior-art manner thus is complicated and time-consuming.
In wet etching methods, mainly in chemical etching, so-called underetching takes place owing to the isotropic etching properties, i.e. etching away material under the surface coated with an etching preventing layer. In consequence, it is not possible to make gaps having a greater depth than width by pure chemical etching. Nor is it possible in electrolytic etching to etch, in small dimensions, gaps the depth of which exceeds the width. The possibilities of making narrow gaps, for instance, to arrange conductors close to each other, are thus limited when applying wet etching methods. It is also not possible today to achieve even structures by wet etching methods, for instance, gaps with straight walls whose width or depth is below 1 &mgr;m.
SUMMARY OF THE INVENTION
An object of the present invention is to provide improvements in connection with wet etching, especially when etching in very small dimensions, below 1 mm.
A special object is to provide an improved method of etching selected parts of a surface.
One more object is to permit quicker manufacture of etched patterns in a surface.
According to the invention, these and other objects that will appear from the following specification are now achieved by a method, an electrode and a device which are of the types stated by way of introduction and which, in addition, have the features stated in the characterising clause of claims
1
,
14
and
17
, respectively.
Thus, the invention is based on a new type of electrode for etching selected portions of an etching surface. The electrode has electrically conductive electrode portions in selected portions of an electrode surface. These electrode portions constitute an electrode pattern. When etching according to the invention using such an electrode which is directed towards the etching surface, depressions are made, which form an etching pattern corresponding to the electrode pattern. The etching pattern seen from the electrode will be inverted in relation to the electrode pattern seen from the etching surface.
According to the invention, an etching method for etching selected parts of a surface has thus been provided, without the surface needing to be covered with an etching preventing layer. Such an electrode can be used several times to etch in this manner a plurality of products successively. This enables great improvements in serial etching, both in respect of production times and production costs.
According to a preferred embodiment of the invention, the electrode portions let electromagnetic radiation through. By the electrode portions being permeable to electromagnetic radiation, it is possible to irradiate the etching material through the electrode during etching. The etching material is coated with a passivating layer, which reduces or prevents the capability of the etchant of etching the etching material. The passivating layer is such as to be dissolved in a chemical reaction when exposed to radiation.
According to an alternative embodiment, the passivating layer is exposed to radiation from below through the etching material. The wavelength of the radiation is adapted to the etching material so that the radiation at least partly penetrates the etching material.
It is preferred for the average intensity of the radiation to be so low that the temperature of the passivating layer is kept essentially constant.
According to a preferred embodiment of the present invention, a substance forming a passivating layer on the etching material is added to the etchant. The substance is selected so that the passivating layer is dissolved when exposed to electromagnetic radiation. When the radiation hits the passivating layer, it will be ionised and dissolved.
By providing, according to a preferred embodiment, the substance dissolved in the etchant, the passivating layer will continuously form on the surfaces of the etching material that are not exposed to radiation. As a result, a high anisotropy of the etching is achieved.
According to a preferred embodiment of the invention, the electromagnetic radiation is in the wavelength range 0.01-50 micrometer and preferably in the wavelength range 0.1-10 micrometer. There are a number of light sources that may be used.
In a preferred embodiment, the electrode has electrically insulating portions between the electrode portions. This results in more accurate control of the etching process since distinctly defined electric fields are formed. This is particularly advantageous when etching in small dimensions, below 100 &mgr;m, and yields particularly good conditions for achieving a directed etching effect (anisotropic etching).
Between the electrode portions, the electrode preferably has portions which do not let radiation through. These portions are preferably also electrically insulating portions. Radiation falls only on the portions of the etching surface that are exposed to an electric field. This results in improved anisotropic etching.
The passivating substance can be selected from, for instance, the group consisting of iodine, halide salts, thiosulphates, thiocyanates, ammonia and amines.
In an advantageous embodiment, the insulating portions of the electrode comprise an insulating layer which is applied to the etching surface of the electrode between the electrode portions, which are defined by the insulating layer. This makes it possible to design the electrode in an extremely simple fashion, for instance by an insulating layer being applied directly to a conductive electrode surface. For instance, the layer can be produced in the same manner as a photoresist layer.
According to a special aspect of the invention, use is made of a chemically etching fluid, in which the etchant, which constitutes the active substance, is present in a diluted solution. In this case, extremely good results can be produced, such as exact etchings in small dimensions. This aspect of the invention is based on the surprising discovery that an etching fluid, which has been diluted to have a negligible etching effect, can be used for anisotropic etching under the action of an electric field.
In this connection, etching of an electrically conductive etching material is carried out by means of an etchant, which is present in a solution which is diluted to such an extent that it cannot be p
Heidari Babak
Olsson Lennart
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Obducat AB
Parsons Thomas H.
Valentine Donald R.
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