Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating selected area
Patent
1992-04-24
1993-03-02
Tufariello, T. M.
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating selected area
205125, C25D 502
Patent
active
051906376
DESCRIPTION:
BRIEF SUMMARY
n occur over both of these materials. The photoresist is then removed. At this point, if only two layers are desired, the secondary metal can be removed with an etchant which differentially etches the secondary metal and not the primary metal to leave the isolated two layer primary metal structure on the substrate. If this structure is to be freed from the substrate, the plating base is then patterned and removed around the structure and the sacrificial layer under the plating base is then dissolved to free the structure.
Alternatively, the first layer of secondary metal may be left in place and a second layer of secondary metal deposited over both the second layer of the primary metal and the first layer of the secondary metal. After electroplating, the exposed surface may then be machined down to reduce the overall height of the multilayer structure to a desired level and to expose the second layer of the primary metal. At this point, the process described above can be repeated, i.e., casting of the photoresist, exposure of the photoresist, removal of the exposed photoresist, and deposit of the third layer of the primary metal. The process can be repeated for as many layers as appropriate.
Complex structures, such as hollow tubes and bridge structures, can be readily formed by having the second layer of the primary metal bridge a secondary metal between two or more structures formed of the first layer of the primary metal.
Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIGS. 1-9 are schematic views illustrating steps in the process of the invention for forming a multi-layer structure fixed to a substrate.
FIGS. 10-17 are schematic views illustrating steps in the process of the invention for forming a tubular structure fixed to a substrate.
FIGS. 18-23 are schematic views illustrating steps in the process of the invention for forming a structure which can be freed from the substrate by removal of a sacrificial layer.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, microstructures can be formed on a variety of substrates, including silicon, germanium, metals, ceramic, glass, and so forth. Such substrates can include semiconductor substrates on which electronic devices have been formed utilizing conventional planar processes. Although the present invention utilizes deep exposures of a photoresist to radiation, such as by X-ray exposure with synchrotron radiation, portions of the substrate on which no structures are to be formed can be masked off so that they are not exposed to substantial radiation. Moreover, minor radiation damage can be annealed out after exposure. Thus, the present process is compatible with microelectronic manufacture, allowing for the integration of mechanical structures onto microelectronic semiconductor substrates.
The basic process of the invention is illustrated with respect to the views of FIGS. 1-9. With reference to FIG. 1, the initial substrate 30 may, as noted above, comprise a variety of materials, including semiconductors, insulators and so forth. The substrate 30 could be composed of a conductive metal. In such a case, no plating base may be necessary. However, in general, a plating base 31 will be deposited onto the top surface of the substrate 30, such as by sputtering, and then the photoresist 33, for example, polymethylmethacrylate (PMMA), may be cast on to the desired thickness. The next step, as shown in FIG. 2, involves X-ray exposure and dissolving of the photoresist in a desired pattern, and the electroplating of a primary layer of a first metal 34, for example nickel. Depending on the type of radiation used, the depth of exposure, and the properties of available photoresists, it is apparent that positive or negative photoresists may be used. Next, as illustrated in FIG. 3, the photoresist 33 is removed, and a secondary metal 36 is electroplated over the first layer of
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Tufariello T. M.
Wisconsin Alumni Research Foundation
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