Manufacturing Bits: March 6

Security ICs with multi-beam; silver nanowires; ion litho.


Security ICs with multi-beam
Leti, a research institute of CEA Tech, and Mapper Lithography have developed a new application for its multi-beam, direct-write lithography technology—security.

In 2016, Mapper Lithography introduced the FLX-1200, a direct-write, multi-beam e-beam system. Using a 5-kV acceleration voltage, a beam generator creates an electron beam about 3cm in diameter. Then, a blanker module splits the beam into 65,000 beamlets.

Mapper’s multi-beam architecture (Source: Mapper)

For some time, Mapper and Leti have been jointly developing the technology for a range of applications as part of a program within Leti.

Multi-beam direct-write lithography is an offshoot to traditional direct-write lithography, which directly writes a pattern on the wafer. It doesn’t require a photomask, thereby reducing costs. But direct-write is slow in terms of throughput. Multi-beam direct-write promises to speed up the process. (Multi-beam direct-write lithography is different than multi-beam for photomask applications. One is used for chip production, while a completely different tool is used for photomask writing.)

Regardless, multi-beam direct-write lithography can be used for several applications. For example, using Mapper’s direct-write system, Leti and Mapper have devised a way to encrypt individual chips with a code. This non-falsifiable code is generated by using a unique chip design. The markets for these chips include data security, traceability and combating imports of counterfeit chips.

At the recent SPIE Advanced Lithography conference, Leti and Mapper presented a paper on the development of an N40 via level process for use in security chip applications. The two companies demonstrated a via patterning integration scheme that is compliant with a standard CMOS 40nm process flow.

A 300mm wafer exposed on a FLX-1200 multi-beam tool at 5kV on a N40 BEOL stack. (Source: Leti)

Leti and Mapper are demonstrating the breakthrough for their customers at Leti’s facility in Grenoble, France. “Standard optical exposure tools – optical scanners using masks – repeat the identical design on the entire silicon wafer, and cannot fabricate individualized chips,” said Leti’s Isabelle Servin. “Leti applied its deep multi-beam lithography know-how and Mapper‘s maskless fabrication tools to achieve this differentiating, cyber-security chip.”

Another company, Multibeam, is also developing multi-beam technology for use in developing security chips.

Silver nanowires
Using an electrohydrodynamic (EHD) ink-jet printer, North Carolina State University has developed a process to print silver nanowire circuits on flexible and stretchable electronics.

EHD falls in the category of 3D printing. Unlike conventional inkjet-based 3D printing methods, EHD relies on electrostatic force to eject the ink from the nozzle of a specialized printer.

It is a maskless and non-contact technology, which has better resolutions than conventional systems. It enables high-resolution printing of low-melting-point metal alloys and conductors with sub-50µm resolutions.

Printed features can be controlled by several parameters, such as ink viscosity and printing speed. Patterns can be printed on a range of substrates, such as paper, glass and others. The ink consists of a solvent based on silver nanowires. The nanowires are typically more than 20 micrometers long. They are conductive, flexible and stretchable. The solvent is nontoxic and water-soluble. The solvent can be washed off once the circuit is printed.

Two printed silver nanowire patterns, horseshoe and Peano curve, with high resolution. (Source: NC State)

In the lab, researchers have used the new technique to print silver nanowires on several prototypes. This includes a glove with an internal heater and a wearable electrode for use in electrocardiography. “Our approach uses electrohydrodynamic printing, which relies on electrostatic force to eject the ink from the nozzle and draw it to the appropriate site on the substrate,” said Jingyan Dong, an associate professor in NC State’s Edward P. Fitts Department of Industrial & Systems Engineering. “This approach allows us to use a very wide nozzle–which prevents clogging–while retaining (a) very fine printing resolution.”

Yong Zhu, a professor of mechanical engineering at NC State, added: “Given the technique’s efficiency, direct writing capability, and scalability, we’re optimistic that this can be used to advance the development of flexible, stretchable electronics using silver nanowires – making these devices practical from a manufacturing perspective.”

Ion litho
The National Institute of Standards and Technology (NIST) has demonstrated that an ion-beam technique can be tuned to make structures within the diameter of a single silicon atom.

For years, the industry has used focused ion-beam tools to fix defects in integrated circuits and machine tiny parts in optical and mechanical systems. Meanwhile, NIST has explored several ways of using a focused beam of gallium ions to mill the surfaces of silicon, silicon nitride and silicon dioxide.

With the technology, researchers machined staircase patterns in silicon dioxide. They enclosed them to control the flow of fluid at the nanoscale. In some devices, the researchers machined a staircase with a step size of 1.1nm. Others were patterned with a step size of 0.6nm. “We have tested and advanced what is possible to make and measure below one nanometer,” said NIST researcher Samuel Stavis.

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