by Debra Vogler, senior technical editor, Solid State Technology
June 1, 2009 – Applied Materials says its new Endura CuBS RFX PVD system, qualified for copper barrier/seed deposition technology at 32nm and 22nm for production of logic and flash memory, provides a lower cost/wafer than competing technologies, including CVD alternatives, by as much as 40% — calculating a normalized COO of the 130Å Ta + 450Å RFX Cu process (CuBS) at $1/wafer, according to Marek Radko, the firm’s BEOL GPM manager.
Effective barrier and seed layer deposition is critical to assuring the speed and reliability of copper interconnects as it prevents copper diffusion and provides a quality nucleation layer for subsequent bulk copper fill. The main issues with copper gap fill at 32/22nm, Radko told SST, are overhang and sidewall coverage, along with asymmetry at the wafer’s edge. There are three key considerations for the new process technology: a flux optimizer, universal magnet motion (UMM), and high-energy copper ion resputter (ratio of ions falling on the wafer vs. ions/atoms redistributed inside the feature).
The flux optimizer, made of copper and positioned between the target and the wafer, acts as a kind of directional lens for the ions. By improving the directionality of the ions, bottom coverage is improved and overhang minimized. When the flux optimizer is used in conjunction with the UMM — the new magnet design, a multidirectional magnet that allows movement up and down — the entire surface area of the target can be used and compensation for target erosion is achieved, Radko explained. (The angle of ion deposition in the new chamber design is not distorted to the extent it is in conventional technologies). Furthermore, the flux optimizer minimizes the area where plasma condensation occurs; the plasma is directed to an area right above the wafer. Optimized magnetron trajectories in the UMM change the wear pattern — the tool operator can multiplex different types of motions of the magnet.
Figure 1. Gap fill on 2x node trench. (Source: Applied Materials)
"With the baseline process, i.e., a straight, directional copper ion deposition, the process window was very small and the bias and resputter ratio were very small," said Radko. "As we increased the resputter ratio, we found a regime where the process window is very large and all aspects of good deposition — sidewall coverage, bottom coverage, and top opening — are extremely compatible with ECP without defects and voids."
Figure 2.Post-CMP data (MTC trench: 25nm). (Source: Applied Materials)
The company believes it has an advantage in this application sector because the technology has been production-proven over the years (the original Endura CuBS PVD tool was launched in 1997), making it less risky for chip manufacturers to introduce. Furthermore, the new process is extendible to the next two nodes. — D.V.
Figure 3.Top: Long via-chain RC (1.38M vias). Bottom: SM 168hr/250C (1.38M vias) (Source: Applied Materials)