By John Rhea
GAITHERSBURG, Md. - Ultra-large-scale integration - also known as ULSI - is to be the next quantum jump in semiconductor technology.
It will require fabrication methods beyond conventional optical lithography to achieve resolutions of 100 nanometers, 0.1 micron-scale integration, says Karen Brown, director of lithography at SEMATECH in Austin, Texas.
But even nanometer-scale circuit integration will not be good enough for some of the applications that military officials have in mind, points out Noel MacDonald, director of the Electronics Technology Office at the Defense Advanced Research Projects Agency in Arlington, Va.
For heterogeneous devices integrating microelectromechanical systems (MEMS), RF and millimeter-wave components, photonics, and microfluidic systems, Pentagon leaders want another order of magnitude size reduction - to 10 nanometers.
Brown and MacDonald spoke at a conference on characterization and metrology for ULSI, sponsored by the National Institute for Standards and Technology (NIST).
Brown reviewed the accelerating process toward ever-smaller feature size, noting that the 1994 National Technology Roadmap for Semiconductors has consistently fallen short of actual performance. Semiconductor scientists achieved 250 nanometers one year early in 1997, and 180 nanometers is the latest forecast for 1999 - two years ahead of predictions.
Brown says she anticipates 150 nanometers by 2001 and 130 nanometers by 2004 using such techniques as argon-fluorine lasers. To break the 100-nanometers barrier, however, will require such post-optical methods as using synchrotron X-ray sources, extreme ultraviolet lithography, electron or ion projection, or massively parallel electron beam direct write, she says.
MacDonald has a different point of view. He sees the challenge as achieving more three-dimensional monolithic structures. Furthermore, he regards lithography as a "bottleneck" to future progress.
"Heterogeneous integration of MEMS, microfluidics, and microelectronics offers new possibilities for lithography, molecular manipulation, and analytical and medical microinstruments," he says. "Silicon continues to be the substrate of choice for heterogeneous integration."