72 nm Pitch Hexagonal MTJ Array on DRAM Platform for High-Density MRAM

Abstract

Well isolated 72 nm pitch hexagonal honeycomb magnetic tunneling junction (MTJ) array with about 45 nm MgO CD was successfully fabricated on a DRAM platform by using mature DRAM array patterning solution with self-aligned double patterning technology and proposed triple hard mask scheme. The 72 nm pitch MTJ array had an equivalent cell size as small as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.0044~\mu \text{m}$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the world’s smallest pitch size and cell size for industrial MTJ array to our knowledge. The hexagonal array geometry offered considerably merit for storage density enhancement and MTJ etch convenience. A reactive ion etch (RIE) and ion beam etch (IBE) combined MTJ etching solution was adopted to optimize pillar isolation and mitigate metallic re-deposition and etch damage. Perpendicular magnetic anisotropy was maintained in MTJ array; however, free layer coercivity was smaller than expected, indicating the existence of etch damage or fringe magnetic field interaction. Potential challenges for the chip integration of high-density hexagonal MTJ array are also discussed.