Novellus Systems (NASDAQ:
NVLS) announced today that it has developed a new tungsten deposition process,
called LRWxT, that can effectively reduce contact and line resistance at the
3Xnm technology node compared to conventional tungsten chemical vapor deposition
(CVD-W) technology. The new approach uses the company's ALTUS® Max system
for a unique deposition process sequence that results in highly conformal, large
grain size films with lower tungsten bulk resistivity. The new process was developed
and tested on device features provided by NEC Electronics, and the breakthrough
was presented at this year's annual Advanced Metallization Conference in Baltimore.
As semiconductor manufacturing technology approaches 32nm design rules, memory
and logic device manufacturers face challenges in scaling the resistivity of
contacts, vias and bit line interconnects. The thinner tungsten films that are
required to fill the smaller critical dimensions associated with 3Xnm devices
have higher resistivity. This thin-film effect will continue to increase as
these critical dimensions shrink at future nodes. To address the resistance
scaling issue, Novellus developed the LRWxT tungsten deposition process that
enables optimal feature fill while reducing the resistivity of the deposited
bulk tungsten layer.
LRWxT employs the high productivity, multi-station sequential architecture
of the ALTUS Max CVD-W system to deliver a unique, three-step deposition process.
First, a <20Å thick nucleation layer is deposited using Novellus' proprietary
PNL®xT (Pulsed Nucleation Layer) technology. Next, a low-resistivity tungsten
(LRWxT) treatment step is applied to promote growth of the low resistivity bulk
film. Finally, an optimized CVD-W film is deposited for the bulk fill of nanometer-sized
structures.
Figure 1 shows cross-sectional images of 55nm contact features filled with
a) a process using conventional, silane-based nucleation, b) a PNLxT process,
and c) the LRWxT process. The images show that the LRWxT filled features contain
significantly larger tungsten grains as compared to the conventional process,
and moderately larger grains than the PNLxT process. The large grain sizes and
conformal fill are the key differentiating characteristics of the LRWxT process,
and provide the mechanism for lower tungsten bulk resistivity.
"As semiconductor manufacturers advance to smaller technology nodes, minimizing
the resistivity effects from device scaling is critical to improving electrical
performance in logic and memory devices," said Dr. Patrick Lord, senior
vice president for Novellus' Direct Metals, Surface Preparation, and Gapfill
business units. "The ALTUS Max LRWxT process delivers industry-leading
productivity to our customers while improving the speed and efficiency of their
devices."