By William Glime, Swagelok Company, USA, and Thomas Seidel, Genus, Inc., USA

ABSTRACT

High-productivity Atomic Layer Deposition (ALD) processes are being driven by semiconductor applications (e.g., capacitor, gate and interconnects) requiring ultra-thin films or conformal coatings with precise thickness control. ALD is particularly effective on surfaces with high aspect ratios or where graded compositions (i.e., where one layer consists of one material and the next layer of another) are required.  Future memory devices referenced in the International Technology Roadmap for Semiconductors (ITRS) - such as Magnetic RAM (MRAM) and Phase Change Memories, Nanofloating Gates, Single-Electron and Molecular Memories - may initially employ topologies with relatively relaxed aspect ratios, as compared to today’s DRAM devices. However, they all require ultra-thin films, and eventually, they will all migrate toward moderate, if not extreme, aspect ratios. The ITRS projects that DRAM capacitor deep trenches made circa 2010 will require step coverage on high aspect ratios approaching 100:1 at 45nm sizes. The active area would be 20× the planar silicon. The challenge to provide conformal coating on such high-density structures will depend on significant advances over conventional ALD, including advances in ALD chemical precursors, delivery systems, and operating systems.