Making a good impression: Nanoimprint lithography tests at NIST

Electron micrograph shows a cross-section of a typical SOG microcircuit feature. Nanoporous regions in the interior are lighter. The process forms a dense, stronger skin about 2 nanometers thick on... Click here for more information.

In what should be good news for integrated circuit manufacturers, recent studies by the National Institute of Standards and Technology (NIST) have helped resolve two important questions about an emerging microcircuit manufacturing technology called nanoimprint lithography—yes, it can accurately stamp delicate insulating structures on advanced microchips, and, no, it doesn’t damage them, in fact it makes them better.

An emerging manufacturing technique, nanoimprint lithography (NIL) is basically an embossing process. A stamp with a nanoscale pattern in its surface is pressed into a soft film on the surface of a semiconductor wafer. The film is hardened, usually by heating or exposure to ultraviolet light, and the film retains the impressed pattern from the stamp. The process is astonishingly accurate. NIL has been used to create features as small as ten nanometers across with relatively complex shapes.

NIL is being eyed in particular for building the complexly patterned insulating layers sandwiched between layers of logic devices in future generations of integrated circuits. State-of-the-art semiconductors contain over a billion transistors, packed together into a footprint of silicon that is no bigger than a few square centimeters. Several miles of nanoscale copper wiring are required to connect the devices, and these wires must be separated by a highly efficient insulator. One candidate is a porous glassy material called SOG* that can be applied as a thin fluid film. When heated, SOG turns into a thin glass film laced with nanometer pores that enhance the electrical insulation. But SOG is relatively delicate, and the conventional photoresist etching process used to cut trenches for the wiring can compromise it. NIL, on the other hand, might be able to pattern SOG layers with wiring trenches and eliminate several time-consuming and expensive photolithography steps if it could pattern the film accurately and do so without destroying the delicate nanopore lacework.