University of Alberta (Canada) researchers have demonstrated a way to extend design features below the 10-nanometer node--off the scale of the current International Technology Roadmap for Semiconductors (ITRS).
Conventional lithographic tools first fabricate a micron-sized data bus, followed by the nanoscale patterning of individual 10-nm-wide wires, which are inserted into the bus using self-assembling block copolymers. Different block copolymers can self-assemble any repeating pattern--from nanowires for interconnections to nanoparticles for ultra-dense flash memories.
"This is the first time we have been able to use self-assembling block copolymers for continuous nanoscale wires," said professor Jillian Buriak of the University of Alberta.
Block copolymers mate two intentionally incompatible polymer-block formulations into double-length string-like molecules. The two polymers, with opposing molecular structures, are covalently bonded at their ends to form the extra-long molecules, which automatically rotate their orientation to form rows. The self-aligned, side-by-side molecules of alternating polymer blocks form perfect rows 10 nm wide.
The researchers had previously demonstrated other periodic lattice structures, but the most recent work represented the first nanoscale metal lines for a bus on a silicon chip.
"We use block copolymers be- cause they are compatible with current silicon manufacturing techniques," said Buriak. "We made as few changes as possible from traditional chip processing."
First, traditional lithography lays down a basic pattern, such as a 30-nm-deep etched trench 1.38 microns wide for a wiring bus. Then the block copolymer self-assembles the individual wires in the bus across the width of the trench. In this case, 10-nm-wide parallel wiring traces are separated into the 30 parallel lines of a bus with its wires spaced 36 nm apart.
After the copolymer self-assembles into the nanoscale lines, a plasma process allows metal atoms to replace the 10-nm-wide copolymer, while the other 36-nm-wide copolymer lines get etched away, leaving the 30 parallel metal lines each 10 nm wide. The bus was 50 microns long, for an aspect ratio of 5,000:1.
"We plan to demonstrate that we can make buses from copper, aluminum and other traditional metals, instead of the gold and platinum we used for our first demonstration," said Buriak.
Her group will look to fit the patterns made by block copolymers into the standard development process for CMOS chips. "Our big- gest obstacle to success is the same obstacle faced by any technology: integration," she said.