NANOSTRUCTURES IN NANOSECONDS
Ultrafast technique imprints patterns directly in silicon chip
A novel method for rapidly imprinting nanostructures in silicon avoids the expensive photolithographic process currently used to fabricate silicon chips.
The new laser-assisted direct imprint (LADI) process uses a XeCl excimer laser with a pulse duration of 20 nanoseconds and a transparent patterned quartz mold to mechanically imprint the molten surface of a silicon wafer. The surface quickly solidifies and, because there is no adhesion between the quartz and silicon, the mold can be removed without damage.
The technique was developed by professor of electrical engineering Stephen Y. Chou and graduate students Chris Keimel and Jian Gu at Princeton University's NanoStructure Laboratory [Nature, 417, 835 (2002)].
The group reports that the technique can be used to imprint 140-nm-wide gratings and other structural features such as rectangles with a resolution better than 10 nm on silicon wafers. The embossing time is less than 250 ns.
"The biggest three advantages of the new method over other nanolithographies are direct patterning without the use of a resist and etching, smaller feature sizes, and high speed and throughput," Chou tells C&EN.
LADI can be extended to large areas, a whole wafer with an 8-inch diameter, for example. It could also be used for imprinting germanium, other semiconducting materials, and dielectric materials such as silicon dioxide, the authors suggest. They add that the technique might well be suited to three-dimensional patterning, which is challenging to achieve by conventional lithography and etching.
The technique is one of the most exciting recent developments in patterning technology, according to R. Fabian Pease, professor of electrical engineering at Stanford University. "On grounds of cost, speed, and resolution, LADI, or some other form of mechanical printing, may displace optical projection as the preferred manufacturing technology for fashioning silicon chips," he writes in the same issue of Nature (page 802).