Emerging Micro-technology Finds Favor with Wafer Producers
10/01/2003
Nickel is presented as an alternative to silicon for next-generation processes.
By Noel Cherowbrier
Tangible progress is being made in the wafer fabrication world and beyond based on new micro-production and replication technology, which presents nickel as a low-cost alternative to silicon for a growing number of next-generation production processes, concepts and applications.
Increasing interest is being displayed by the world's most forward-thinking companies and designers, in the potential of microelectromechanical systems (MEMS) and MOEMS, their optical version. General agreement is that these systems play a significant part in the future micro-technology and microelectronics markets. Until now, silicon has been the only recognized material used in such systems, which have been expensive. One approach to building microstructures, based on nickel rather than silicon, recently has paved the way to lower-cost MEMS and MOEMS applications.
To date, microstructures have been manufactured predominantly in silicon using expensive technology borrowed from the semiconductor industry. The silicon approach has dominated because of its familiarity to designers and the availability of suppliers. However, it is not always the best approach — particularly with regard to cost, application and time-to-market.
Beneficial Contender
This approach has driven the development of an alternative manufacturing process that offers many advantages, including significantly lower cost and turnaround from design to finished product. This technology uses nickel instead of silicon and has the potential to be used with other conductors in due course, such as copper and gold.
 Figure 1. Microstructure parts in nickel can be built in silicon tolerances in a Class 1,000 cleanroom. |
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One company* behind this mi-crostructure technology describes it as a hybrid application building on ideas from the semiconductor, high-volume audio CD and micro-embossing industries. Using this approach, the company has overcome traditional manufacturing obstacles to deliver low-cost micro-metal parts and larger parts with ultra-fine features. The company's in-house specialists have developed photo electroforming production and in-house plating techniques to make such cost-effective accuracy possible.
Representing one of the company's micro-replication capabilities is the continuing development of "imprint patterning," particularly for the electronics industry. This is a high-density circuit formation process involving the production of a fine-pitch metal stamp, or embossed tool foil, that can be used in a traditional laminating press to imprint its image directly onto a malleable substrate, producing ultra-fine impressions. In electronics applications, the impressed circuit traces and connections on the imprinted substrate then are metallized to produce accurate high-density integrated (HDI) circuitry.
Interest in this technology is strong because PCB producers are becoming increasingly aware of the potential of the technology compared to the current problems they encounter, i.e., with the ever-increasing costs of laser drilling systems. Furthermore, pressures such as the need to produce less expensive parts and systems that are smaller, faster and capable of coping with various integral heat-generation and EMC requirements must be addressed, and the new technology does this.
With the exponential rate at which OEMs are buying laser machines, it is only a matter of time as to how quickly the industry is attracted to the potential of imprint technology. There no longer is any need for traditional photoresists or photo tooling for HDI circuit production. Beyond this, the nature of imprint technology will engender mold-breaking design rules so that the sizes of traces, pitches and features will be tighter in tolerance and size, compared to what is currently available.
Wafer Fab Adoption
Tangible acceptance of the technology is being shown by wafer foundries and fabrication houses with the adoption of the technology to produce "families" for replication purposes. These families are being produced through a process that involves electroforming directly onto a 3-D silicon wafer original, generally supplied by the customer, to produce an exact mirror-image replica in nickel. If the original silicon is male or female, defined by the peaks and troughs of its profile, the nickel replica will be the opposite gender. In the case of a female silicon original, for example, the resultant nickel part will be a male, or "father," and vice versa. The process allows this nickel duplicate to be separated from the silicon and used for processing as is, or as a parent part from which mirror-image "offspring" can be produced. These "sons" or "daughters" will have the same form and gender as the original. This allows expensive silicon originals to be kept as perfect masters, from which replicas — in any gender — can be produced at any time and at comparatively low cost.
New-generation Technology
There are three main characteristics that make microstructures an important technological development:
- The systems can be made in a batch process
- Individual features can be made very small and accurate
- Optical elements can be fully integrated.
When cost and real estate savings are factored in, many more applications must be waiting in the wings, representing an untapped source for such solutions.
One advantage to using nickel instead of silicon is that nickel is a less expensive raw material. Physically, it is less brittle, more flexible and offers a good electrical conductivity. Nickel also offers good optical properties and can be made into smooth mirrors suited for use in optical applications.
A frequently asked question is what size wafer companies are working with. In most cases, the wafers are 3" or 6", with some as large as 8" or 12". Using this technology, companies can work with substrates measuring 12 x 12" (300 x 300 mm). Large parts can be manufactured accurately with fine features, or a large number of parts can be manufactured to tight tolerances.
Nickel-based systems also can be produced on a shorter time scale, typically taking less than a month from the initial design to delivered products. This is because they are made in a much simpler way than silicon products, with fewer steps.
Additionally, multi-layered parts are possible with this technique because it allows layer alignment to be less than 1 µm over the 12" square of substrate. Microstructure parts in nickel can be built in silicon tolerances in a Class 1,000 cleanroom.
Application Potential
Nickel-based technology has been used to make products as diverse as sensors, actuators, hearing aids, medical devices, optical instruments, micro-lenses and meshes.
A significant trend in the electronics industry is to make smaller, cheaper, faster devices. The nickel microstructure technology accommodates this trend. Nickel microstructures can be manufactured to an extremely small scale, with features such as apertures, fluidic channels or raised lands down to 1 or 2 µm and tolerances at submicron levels. As they run hotter, the ability to build in fluidic channels raises the possibility of building devices with integrating cooling systems.
Tracks and channels can be fabricated as narrow as 2 µm on a 4 µm pitch, with smooth walls and submicron tolerances. Resultant surface smoothness also is high precision, being sub-wavelength at 600 nm across the surface. Raised areas in the design can be produced with a currently unprecedented aspect ratio of 5:1 — and potentially much higher. These tolerance and accuracy figures are valid across the 12 x 12" (300 x 300 mm) surface area of the substrate, representing a significant alternative over existing silicon techniques.
*Tecan Components Ltd.
NOEL CHEROWBRIER, VP Sales and Marketing, may be contacted at Tecan Components Ltd., Tecan Way, Granby Industrial Estate, Weymouth, Dorset, England DT4 9TU; 44 (0) 1305 765432; Fax: 44 (0) 1305 780194.