By Ed Korczynski, Sr. Technical Editor
Applied Materials today unveiled the Applied Olympia ALD system, using thermal sequential-ALD technology for the high-volume manufacturing (HVM) of leading-edge 3D memory and logic chips. Strictly speaking this is a mini-batch tool, since four 300mm wafers are loaded onto a turn-table in the chamber that continuously rotates through four gas-isolated modular processing zones. Each zone can be configured to flow any arbitrary ALD precursor or to exposure the surface to Rapid-Thermal-Processing (RTP) illumination, so an extraordinary combination of ALD processes can be run in the tool. “What are the applications that will result from this? We don’t know yet because the world has never before had a tool which could provide these capabilities,” said David Chu, Strategic Marketing, Applied’s Dielectric Systems and Modules group.
Figure 1 shows that in addition to a high-throughput simple ALD process such that wafers would rotate through A-B-A-B precursors in sequence, or zones configured in an A-B-C-B sequence to produce a nano-laminate such as Zirconia-Alumina-Zirconia (ZAZ), almost any combination of pre- and post-treatments can be used. The gas-panel and chemical source sub-systems in the tool allow for the use up to 4 precursors. Consequently, Olympia opens the way to depositing the widest spectrum of next-generation atomic-scale conformal films including advanced patterning films, higher- and lower-k dielectrics, low-temperature films, and nano-laminates.
“The Olympia system overcomes fundamental limitations chipmakers are experiencing with conventional ALD technologies, such as reduced chemistry control of single-wafer solutions and long cycle times of furnaces,” Dr. Mukund Srinivasan, vice president and general manager of Applied’s Dielectric Systems and Modules group. “Because of this, we’re seeing strong market response, with Olympia systems installed at multiple customers to support their move to 10nm and beyond.” Future device structures will need more and more conformal ALD, as new materials will have to coat new 3D features.
When engineering even-smaller structures using ALD, thermal budgets inherently decrease to prevent atomic inter-diffusion. Compared to thermal ALD, Plasma-Enhanced ALD (PEALD) functions at reduced temperatures but tend to induce impurities in the film because of excess energy in the chamber. The ability of Olympia to do RTP for each sequentially deposited atomic-layer leads to final film properties that are inherently superior in defectivity levels to PEALD films at the same thermal budget: alumina, silica, silicon-nitride, titania, and titanium-nitride depositions into high aspect-ratio structures have been shown.
Purging (from the tool) pump-purge
Fab engineers who have to deal with ALD technology—from process to facilities—should be very happy working with Olympia because the precursors flow through the chamber continuously instead of having to use the pump-purge sequences typical of single-wafer and mini-batch ALD tools used for IC fabrication. Pump-purge sequences in ALD tools result in the following wastes:
* Wasted chemistry since tools generally shunt precursor-A past the chamber directly to the pump-line when precursor-B is flowing and vice-versa,
* More wasted chemistry because the entire chamber gets coated along with the wafer,
* Wasted cleaning chemistry during routine chamber and pump preventative-maintenance,
* Wasted downtime to clean the chamber and pump, and
* Wasted device yield because precursors flowing in the same space at different times can accidentally overlap and create defects.
“Today there are chemistries that are more or less compatible with tools,” reminded Chu. “When you try to use less-compatible chemistries, the purge times in single-wafer tools really begin to reduce the productivity of the process. There are chemistries out there today that would be desirable to use that are not pursued due to the limitations of pump-purge chambers.”