Ill. - A new dielectric material, developed by researchers
at the University of Illinois at Urbana-Champaign,
could facilitate the use of copper circuitry at the
chip level. The thermally stable aromatic polymer
has a low dielectric constant of 1.85, good mechanical
properties and excellent adhesion.
aluminum with copper as the multilayer interconnect
structure in microelectronic devices could enhance
both miniaturization and performance. Copper offers
much higher electrical and thermal conductivity than
aluminum. Placing narrow copper lines close together,
however, requires a good dielectric to reduce cross
talk between wires. Unfortunately, existing dielectric
insulators can't withstand the rigors of the aggressive
chemical-mechanical polishing step used to produce
a smooth copper surface.
developed an aromatic thermosetting polymer for use
as an insulating material in copper chip technology,"
said James Economy, a professor of materials science
and engineering at Illinois. "The material has
a high thermal stability, low moisture pick-up and
can withstand chemical-mechanical polishing."
material that Economy and former graduate student
Youngqing Huang (now at DuPont) started with had a
dielectric constant of 2.7. By adding porogens - materials
that leave tiny holes when they evaporate
- the researchers lowered the dielectric constant
to 1.85, while maintaining an acceptably high level
of hardness and stiffness.
pores are closed and about 5 nanometers in size,"
"They are formed when heat is applied to low
molecular weight porogens dispersed through the film.
The porogens break down into small gas molecules that
can diffuse through the polymer structure.
The resulting microporosity does not significantly
reduce the mechanical integrity of the foamed material."
new dielectric can withstand temperatures up to 400
degrees Celsius, is easily applied in solution phase
to form a submicron thin film, and adheres to substrates
better than other candidate materials.
feel we have identified the critical problems confronting
the development of a dielectric material to facilitate
the use of copper chip interconnections," Economy
said, "and we have solved every one of them."
will describe the new material at the spring meeting
of the Materials Research Society, to be held in San
Francisco, March 28 through April 1. The researchers
have applied for a patent.
James E. Kloeppel, Physical Sciences Editor 217-244-1073;