The present invention relates to a method for forming nanolaminate structures, and more particularly, to plating a substrate with nanolayers of a first metal and a second metal, using an electrolytic plating process.
In many fields today, devices are being created from very small components. For example, in the electronics field, the size of integrated circuits and other electronic components is constantly being reduced. To support and interconnect these and other components, as well as to provide small-scale structural components, there is growing need for structural components with desired mechanical characteristics, such as modulus of elasticity, elongation, and/or yield strength, with the required mechanical characteristic dependent on the particular application.
Given the relatively small size of many of today""s electronic components, maintaining reliable electrical contact between components, such as between an integrated circuit and a printed circuit board, has become very difficult. A component providing such connection must be a conductive material, as well as provide a minimum force to maintain the electrical contact. One solution for providing reliable electrical contact between a circuit board and another component is to use an interposer device comprising a plurality of very small metal springs, i.e., microsprings. However, the mechanical properties of individual metals may be inadequate to properly form such microsprings. For example, copper may prove too soft, while nickel may prove too brittle. It has been found that by fabricating such microsprings from a combination of metals, rather than from a single metal, some of the spring properties of the resulting composition are improved. Such an interposer device comprising microsprings formed from multiple layers of metals is disclosed in commonly assigned U.S. patent application Ser. No. 09/454,804, filed Dec. 3, 1999, entitled xe2x80x9cMetallic Microstructure Spring now U.S. Pat. No. 6,442,039.xe2x80x9d
In addition to facilitating the manufacture of extremely small mechanical and electrical components, contemporary integrated circuit fabrication techniques also facilitate the mass production of such devices. Further, photolithographic techniques, such as those commonly used in the fabrication of integrated circuits, readily lend themselves to the mass production of extremely small mechanical and electrical components. According to such contemporary photolithographic techniques, thousands, possibly millions of very small components can be fabricated simultaneously.
Although such photolithographic techniques have proven generally useful for the fabrication of microelectro mechanical system components, such contemporary fabrication techniques suffer from inherent deficiencies. For example, although contemporary photolithographic techniques are well understood and reliable, they utilize comparatively expensive equipment and processes. Further, contemporary photolithographic techniques are not well suited for forming out-of-plane features, such as raised features and depressed features. Although contemporary photolithographic procedures may be utilized to form such out-of-plane structures, the use of such contemporary photolithographic procedures to form such out-of-plane features substantially complicates the process, and thus likewise substantially increases the cost thereof.
Small mechanical features are typically plated or sputtered so as to form components. Typically, printed circuits are made from metal foils which are etched so as to define the desired circuits and/or structures. Generally, nanolaminates are formed via sputtering. However, as those skilled in the art will appreciate, sputtering is an expensive process and currently is only capable of creating nanolaminate structures of a limited size.
Although it is known to use electrolytic plating processes to form nanolaminate materials, only voltage/potential control of the electrolytic plating process has thus far been utilized to create such structures. As those skilled in the art will appreciate, the use of voltage/potential control requires that the electrolytic bath have three separate electrodes, i.e., an anode, a cathode, and a reference electrode. Such a three-electrode electroplating system is primarily only useful in laboratory situations and does not lend itself well to high-volume plating processes. For example, the required presence of the third electrode, and its necessary proximity to the cathode, greatly reduces the size of the materials which may be plated.
Electrolytic plating techniques for forming very thin layers of metals upon a substrate are well known. Such contemporary electrolytic plating techniques are commonly utilized for applying very thin layers of highly conductive materials such as gold, silver and platinum upon less conductive materials such as copper, for example.
In view of the foregoing, it is desirable to provide a method for forming nanolaminate structures utilizing a simple and comparatively inexpensive plating process, wherein structures having comparatively large surface areas can be plated in a reliable and economically feasible manner.
The present invention is directed to a method for forming nanolaminate structures. The method comprises plating a cathode with at least one layer of a first metal, and at least one layer of a second metal, using an electrolytic plating process. The plating current is controlled to maintain the current density at the electrode within a predefined range.