Process for coating a substrate

Details Process for coating a substrate Process for coating a substrate

1999-06-25

2001-09-25

Beck, Shrive P. (Department: 1762)

Coating processes

Nonuniform coating

Applying superposed diverse coatings or coating a coated base

C427S261000, C427S266000, C427S269000, C427S270000, C427S271000, C427S287000, C427S397700

Reexamination Certificate

active

06294218

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention involves a process for coating a substrate, in particular for manufacturing a sensor, wherein on a portion of the surface of the substrate, at least one texture is created on which a layer that is to be applied on the surface of the substrate, adheres better than on a surface area of the substrate located outside of the texture, wherein the layer is applied after creating the texture on the surface of the substrate and areas of the layer which overhang laterally beyond the texture are removed mechanically, and wherein the material of the texture contains at least one chemical element or a chemical compound, which the layer applied on the texture does not have or has only in a smaller concentration than the material of the texture.
From German published patent application DE 196 41 777 A1, it is already known to use such a process for the manufacture of a sensor with a metal electrode in a MOS-arrangement. This process has thus proven itself to be advantageous in practice, since it makes possible a textured coating of a substrate, without the coating applied to the substrate having to be textured for this using a photolithographic process and/or an etching process. A contamination of the manufacturing facilities used for the MOS semiconductor manufacture by the metallic electrode material to be applied to the substrate is thus avoided. A contamination of this sort can occur, for example, in photolithographic texturing processes when stripping the photoresist or when etching the metallic layer to be textured. Metallic contaminations of the manufacturing facilities are therefore especially undesirable, since they reduce the puncture resistance of gate oxides and thus reduce the reliability of the semiconductors manufactured with the manufacturing facilities.
A disadvantage of the previously known coating process consists, however, in that the layer may only be applied with a relatively small thickness, since the areas of the layer overhanging laterally beyond the texture can otherwise not be removed by mechanical mechanisms. The layers manufactured according to the process mentioned at the beginning therefore have only a comparatively small resistance to temperature, that is, the chemical compounds or elements located in the textured area of the substrate, such as silicon, can diffuse out of the substrate into the layer that is applied onto it, and possibly reach the surface of this layer. In the process, it is even possible that the substances diffused out of the substrate into the layer enter into a chemical bond with the materials contained in the layer and/or mix with them and change their chemical and/or physical properties, for example the resistance to corrosion. Such an undesired diffusion of materials out of the substrate into the layer applied on it occurs especially at higher temperatures, for example above 100° C. Such temperatures are, however, unavoidable in the manufacture of semiconductors and can, for example, occur during a temperature treatment for curing (hardening) on a lacquer coat located on the substrate or when applying a bonding compound on the substrate.
SUMMARY OF THE INVENTION
Therefore, an object of the invention is to create a process of the type mentioned at the beginning, in which the chemical and/or physical properties are largely stable with respect a temperature treatment of the substrate in an area near the surface of a layer applied on the substrate.
The solution of this object consists in that on the first layer applied to the surface, at least one second layer is applied, and that the second layer does not have the chemical element or chemical compound contained in the material of the texture, or has it only in a concentration smaller than that of the material of the texture.
In an apparently unnecessary manner, a second layer connected with the already textured first layer is thus applied onto the already textured first layer and has the same texture as the first layer. In this way, on the one hand, a larger layer thickness is achieved so that the chemical elements or compounds located in the substrate have to travel a larger distance, in order to reach the surface of the topmost layer, and on the other hand, however, a boundary surface is also created between the first and the second layer, which possibly makes more difficult the diffusion of materials out of the substrate into the second layer. The process according to the invention thus allows, without the use of photolithography or etching processes, and thus while avoiding a cross-contamination of the manufacturing facilities used for the manufacture of a sensor by chemical elements or compounds contained in the coating, the application of a textured layer onto a portion of the surface of a substrate, wherein the layer is, at least in an area near the surface, to the greatest extent stable in its chemical composition and physical properties, with respect to temperatures occurring during a temperature treatment. Optionally, at least one additional layer can be applied onto this layer.
One embodiment of the invention provides that the areas of the first layer projecting laterally beyond the texture are removed prior to the application of the second layer, in particular by using ultrasound. The second layer is thus applied in a later manufacturing step than the first layer so that chemical elements or compounds, which diffuse out of the substrate into the first layer during a temperature treatment occurring between the application of the first and the second layer, can then not progress beyond the surface of the first layer. The concentration of the chemical elements or compounds diffused out of the substrate which is reached on the surface of the first layer, which is smaller than the concentration of these elements or compounds in the substrate, then forms, after the application of the second layer, the starting point for a possible additional diffusion of these elements or compounds at the surface of this layer, so that the elements or compounds can reach there only at a correspondingly smaller concentration.
The areas of the first layer projecting laterally beyond the texture are removed, preferably using ultrasound, wherein due to the better adherence properties of the texture in comparison to the untextured substrate surface, it is achieved that the first layer only remains adhering to the texture, while the areas of this layer projecting beyond the texture detach from the substrate. The projecting areas of the first layer can, however, also be removed using other mechanical processing procedures, for example by brushing.
It is advantageous if the second layer is applied onto the electrically conducting first layer by galvanic or external currentless deposition of a metal, in particular a noble metal. The deposition of the metal is preferably performed in an external currentless manner.
A preferred embodiment of the invention provides that the second layer is applied on the surface of the substrate after the areas of the first layer projecting laterally beyond the texture have been removed, that the adherence properties of the second layer are so chosen that the second layer adheres better to the first layer than to a surface area of the substrate that does not have the first layer, and that after the application of the second layer, areas of the second layer projecting laterally beyond the first layer are mechanically removed, particularly by using ultrasound. For this purpose, the adherence properties of the second layer can be achieved by a suitable shaping of the surface of the first layer, for example a micro-roughness, and/or by a chemical property of the layer, such as the presence of unsaturated chemical bonds. Surprisingly, it is also possible to apply a second layer on the first layer by a suitable selection of the adherence properties of the first layer, and to texture it also by mechanically removing its areas that project laterally beyond the texture or the edge of the first layer. Thus, on the whole, a coating can be

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