Novellus Systems (NASDAQ:NVLS)
has developed a suite of ashable hardmask (AHM) films that have up to 25 percent
greater etch selectivity compared to similar amorphous carbon films in use by
the industry today. This highly selective and transparent (HST) AHM family of
films has demonstrated die yield improvements as much as 7 percent when coupled
with Novellus' patented integrated edge bevel removal (EBR) technology.
Sub-32nm device design rules require high aspect ratio (AR) patterning for both
logic and memory devices. At these advanced geometries, plasma-enhanced chemical
vapor deposition (PECVD) based amorphous carbon films have higher etch selectivities
and superior mechanical properties than traditional photoresists. Additionally,
films of this nature enable more accurate pattern transfer from the photoresist
to the substrate without complications such as pattern collapse and line bending.
These amorphous carbon films are also used for double patterning schemes, enabling
cost effective, high density patterning.
Figure 1A contrasts the normalized etch selectivity for a conventional amorphous
carbon film deposited at 550°C with a Novellus HST AHM film. While increasing
deposition temperature can be used to increase selectivity, it also has the
negative effect of decreasing the film's transparency. Less transparent films
are more difficult to align during the photo step. With Novellus AHM films,
transparency is not sacrificed, and the selectivity required for high AR patterning
is maintained. Also shown in Figure 1A are critical dimension uniformity (CDU)
maps showing typical etch selectivity performance for conventional amorphous
carbon films and Novellus HST AHM films. The high selectivity and low erosion
rate of the Novellus films demonstrate better within-wafer CDU performance,
which facilitates the patterning of dense, high AR features (Figures 1B and
1C) and is critical to yield enhancement.
The AHM thickness at the wafer's edge impacts the die yield in that region,
requiring a narrow transition zone from full AHM thickness to bare silicon (i.e.,
complete AHM removal). Novellus' VECTOR® PECVD platform features an integrated
EBR capability that provides complete removal of the AHM film within a 1mm transition
zone. This sharp transition ensures that edge die have the required AHM thickness
necessary for excellent CD uniformity control within 2 mm from the wafer's edge.
Because the EBR module is integrated onto the deposition platform, no additional
bevel edge cleaning tools are required. And, since the AHM removal is performed
outside the deposition chamber, better process and particle control can be achieved
as compared to other in-situ edge control techniques.
In addition to enhanced die yield, Novellus' HST AHM films also provide a
wider process window in a high volume manufacturing environment. Conventional
amorphous carbon films deposited at higher temperatures are prone to moisture
absorption at a faster rate. However, the multi-station sequential deposition
(MSSD) architecture of the Novellus VECTOR PECVD platform enables superior hermeticity
performance by incorporating process interfaces, which help to block moisture
uptake.
"Novellus' HST AHM films meet the high density, high aspect ratio patterning
requirements necessary for sub-32 nm devices," said Kevin Jennings, senior
vice president for Novellus' PECVD business unit. "Coupled with the proven
productivity of the VECTOR platform, Novellus' HST AHM solution is the low cost,
high volume manufacturing choice for these advanced optical films."
Posted November 24th, 2009