Novellus Systems (NASDAQ:NVLS)
announced today that it has developed an advanced Hollow Cathode Magnetron (HCM®)
IONX(TM) PVD copper seed process that will enable copper interconnects below
the 2xnm technology node. The breakthrough will allow the company's highly-productive
and proven HCM PVD technology on the INOVA® platform to continue to be used
for barrier and seed thin film deposition, avoiding the migration to less-productive
and costly ALD or CVD approaches.
PVD seed thickness requirement for the 2xnm technology node.
For the past ten years, PVD copper barrier/seed and copper electrochemical deposition
have been the dominant technologies used in building logic devices. Memory manufacturers
are now transitioning to copper interconnects as well, for reasons driven by
technology and cost. In terms of technology, the lower RC interconnect delay
gained when using copper equates to higher speed memory chips. From the cost
perspective, copper DRAM and Flash devices are more manufacturable than their
aluminum counterparts since the copper damascene process flow requires fewer
production steps and utilizes deposition equipment with higher throughputs.
As the critical dimensions (CD) of via and trench structures decrease with advanced
technology nodes, PVD deposition technology becomes limited by its lack of conformality.
Copper seed requirements generally call for at least 100 Angstroms of film thickness
in the field to minimize the electroplating terminal effect, as well as >20
Angstroms of continuous film within the structure to ensure void-free copper
fill. With 2xnm devices already limiting the top CD to approximately 220 Angstroms,
obtaining sufficient step coverage using conventional and even ionized PVD copper
seed will be a challenge. Excessive overhang at the top of the feature will
lead to a reduction in the size of the opening, also known as "pinch-off,". This constriction in the copper seed layer leads to insufficient
copper fill of these extremely small structures, resulting in voiding and poor
device reliability. Extending PVD copper seed to 2xnm nodes and beyond requires
a new approach that is not constrained by typical step coverage performance.
Working with leading logic and memory customers, Novellus has developed innovative
plasma confinement and focusing magnetics for the INOVA HCM sputtering source
that enable simultaneous control of PVD overhang, step coverage, and bottom-up
fill. By matching the proper balance of ion density and ion energy, Novellus'
advanced copper seed process operates in a regime that results in bottom-up
feature fill versus conformal deposition. This advanced copper seed approach
reduces the pre-plating aspect ratio and increases the process window for subsequent
void-free copper fill. Alternative ALD or CVD seed and adhesion layer technologies,
such as cobalt, increase this pre-plating copper fill aspect ratio and the propensity
for micro-voiding. Adding adhesion layers into the barrier-seed stack also results
in an increase in line resistance, negatively impacting device speed.
"This latest innovation in HCM technology will extend PVD copper seed
to the 22nm node and beyond," said Dr. Wai-Fan Yau, general manager for
Novellus' Integrated Metals Business Unit. "Our advanced copper seed offers
the ability to fill ultra-small features, resulting in increased device reliability,
without having to introduce more complicated and costly CVD or ALD processes
into the manufacturing sequence."