Customising Photolithography

A number of recent breakthrough applications for employing contact photolithography mask aligners have demonstrated greatly increased versatility for these proven warhorses in the production of silicon wafers. Once reserved solely for the building of integrated circuits, contact mask aligners are now used to fabricate cutting edge products in diverse industries such as biotech, consumer electronic, aerospace, communications and transportation.

A good idea spreads Contact photolithographic mask aligners have been successfully used for the past twenty years. Over that time, perceptive engineers in industries other than the semiconductor began to recognise the ability of mask aligners to reproduce extremely minute designs on substrates other than silicon wafers.

As a result, this process has recently been harnessed to create a multitude of new products in unexpected markets.

"The secret is out, and CEOs of non-traditional industries are now snapping up mask aligners to help produce millions of new products that incorporate MEMS, LEDs, and biomedical elements," notes Brett Arnold, President of San Jose, California-based Neutronix, Inc., photolithography specialists providing custom engineered contact/proximity and mirror projection mask aligners. "We have to hustle to keep up with the demand."

Arnold's company, Neutronix, focuses on remanufacturing and custom-engineering Canon PLA 501/600 and MPA 600 series mask aligners. These Canon series have been utilised in semiconductor production for almost 25 years, a remarkable feat when compared to other industrial technologies that are now considered obsolete. "These particular mask aligners are a very robust production tool, and no longer limited to silicon wafers," notes Arnold. "Today's new applications represent a good example of the morphing of technology – taking something that was originally intended for one thing and applying it to another to create a new product or even a new market.

The first step in creating new functionality involves dismantling the mask aligner down to the component level. Salvageable parts, such as the castings and guideshaft components, are cleaned and reprocessed. Then all of the consumable items in the machine get replaced with new or re-machined parts. The majority of the optics also undergo replacement, the emphasis is to return the machine to OEM specifications. In-house engineers then go one step further and customise the machine to the particular customer's application.

"We get a very accurate understanding of what the client manufacturer needs the machine to do," explains Arnold. "If a client has a requirement that goes beyond the normal design capability of the machine, then we do the engineering work so that the mask aligner is now capable of handling that requirement. In effect, the machine gets upgraded with additional functionality that it previously did not have when new."

New developments include infrared backside alignment, for example, to allow Canon mask aligners to be used in the MEMS environment. These machines can also be adapted to handle new shapes and sizes of substrates, such as squares and rectangles, which were never even conceived of at the time the machine was originally designed. For manufacturers that require equipment that is more current, automated, or capable of handling larger wafer sizes, companies like Quintel Corp.—in business since 1978 and a sister company to Neutronix—step in to offer the latest proximity contact mask aligners at a reasonable cost of ownership.

Quintel mask aligners are capable of handling wafer sizes of up to 200mm in diameter and providing single and double-sided exposure. The equipment is flexible enough to be modified as required to meet the needs of new applications that might vary from traditional mask sizes and types, as well as types and thicknesses of substrate. "A significant amount of our business is from orders that require some level of custom tooling design," said Jeff Lane, vice president of sales and marketing for Quintel. "The equipment often has to be modified even if slightly to accommodate specific substrate, mask or printing requirements."

Such conversions can be credited for the resurgence of mask aligners, as they account for cost-effective fabricating techniques for manufacturers and researches involved in optoelectronic, microsystem and nanotechnology markets. "Quintel designs precision mask aligners, but the architecture is more ‘open' so it's more conducive to being converted to support these nonsemiconductor type applications," says Lane.

MEMS
Among the most successful derivative technologies that are spring-boarding from the photolithographic process is that of MEMS (miniature electro-mechanical systems). The thick photoresist-based lithography used in micromachining (MEMS) these systems offer the advantage of a high aspect ratio printing for three-dimensionality. Located in Concord, California, BEI Systron Donner is a division of BEI Technologies, Inc., producing mature MEMS sensors and systems that use its proprietary Quartz Angular Rate Sensor technology for integration into OEM applications that include short-term navigation, guidance and control systems, flight testing, robotics, and vehicle instrumentation.

The company's STD8 Quartz Tuning Fork Sensing Element is manufactured on BEI's highvolume MEMS automotive sensor production line that has produced more than 26 million MEMS sensors at a rate in excess of 35,000 per day. "We use Canon PLA 501 proximity aligners for our patterns for the solid state GyroChip sensors because our smallest line-widths are only about 25 microns, so we don't really need a high end system," says Martin Dewey, pre-production manager for the R&D department of Systron Donner.

"For example, our product just doesn't demand stepper technology, and while projection aligners could work for us, the capital investment was a little too steep to get into them. We believe the Canon machines to be the most cost effective for our purpose. We considered other suppliers like Karl Suss, Electronic Visions Group and Kasper, but we felt that the remanufactured Canon machines from Neutronix were the best value," continues Dewey.

"We're very happy with Neutronix and we continue to buy their equipment. It's easy for the operators to use. It is well supported. Overall, it's a good low cost option."

Biomedical applications
According to a paper entitled "Integrated Fabrication of Polymeric Devices for Biological Applications" by Mark J. Kastantin, et. al. "The use of MEMS in biological research is becoming increasingly common. Micro devices allow easier observation and manipulation of individual cells, proteins, or other biological macromolecules."

The article went on to point out the inherent advantages of producing such micro-devices on equipment once reserved for making ICs.

"Photolithographic-based processes create microchannels in polymeric materials in a matter of hours. Processing these materials requires only a contact aligner for lithography and a few solvents."

Such virtues account for the incorporation of MEMS and microfluidic devices into biomedical applications for capillary electrophoresis, miniature biochemical reaction chambers, microelectrode arrays, and even functional units that include pumps and valves.

"We use our mask aligner in developing microfluidic, lab-on-a-chip type devices for analysing cells, especially from blood, for medical diagnostic and science applications," says Dr. Daniel Irimia, a lead researcher at Harvard Medical School's laboratory at Boston Massachusetts General Hospital. "Within our space we have a clean room, cell culture room and a wet lab with benches and microscopes where we use these photolithography devices for testing and the development of bio-MEMS prototypes."

"We chose the Quintel machines because the newest ones from other manufacturers are prohibitively expensive for starting a lab, especially in our case where we were looking for a machine customised for using plastic masks and substrates of different thicknesses and shapes" continues Irimia.

"After using this mask aligner for almost 10 years we are very happy with the performance and flexibility to the changing needs in a research environment. And this is not a small thing, because by being an NIH [National Institutes of Health] Resource Centre, this lab, in addition to its own research, collaborates with many other NIH investigators, and helps them with their microfabrication needs."

LED applications
Universal Display Corporation (UDC) of Ewing, New Jersey, adapted photolithography mask aligner technology for the purpose of perfecting its innovative organic light emitting device (OLED) technology for use in flat panel displays, lighting and other opto-electronic applications.

An OLED is a monolithic, solid-state device that typically consists of a series of organic thin films sandwiched between two thin-film conductive electrodes. The choice of organic materials and the layer structure determine the device's performance features: emitted colour, operating lifetime and power efficiency. The layer structure is strongly influenced by the use of a mask aligner.

"When we purchased it, the Quintel equipment seemed to have the best combination of product features and cost performance for our needs, and we have been very happy with the technical support," says Janice K. Mahon, vice president of technology commercialisation for UDC.

OLEDs provide desirable advantages such as vibrant colours, high contrast, excellent grayscale, full-motion video, wide viewing angles, a wide range of pixel sizes, low power consumption, a wide operating temperature range, a long operating lifetime, and a thin and lightweight form factor.

Future opportunities
As for UDC and others, many manufacturers stand to gain a competitive edge by utilising mask aligner technology to create cost advantages as well as technical advances. "In many ways, contact proximity mask aligners have helped usher in increased opportunities for those enterprising organisations who find new, unexpected uses for them." sums up Neutronix' Arnold, " Dozens of products will be coming into our lives in the next ten years that rely on the use of this still-valid technology."