Scalability of Magnetic Tunnel Junctions Patterned by a Novel Plasma Ribbon Beam Etching Process on 300 mm Wafers

The performance of magnetic tunnel junction (MTJ) over its critical dimension (CD) is critical to the application of spin transfer torque magnetic random access memory. To study the CD scaling effects, we designed a series of MTJ CDs and used a novel plasma ribbon beam etching (PRBE) process to pattern the MTJs. PRBE has constant beam density and beam angle distribution across a 300 mm wafer. The MTJs patterned by PRBE demonstrated low tunneling magnetoresistance degradation from 145% on blanket films to ~130% for MTJ CDs ranging from 100 to 20 nm. At 20 nm, MTJ switching current was down to 20 μA, and the thermal stability factor was still above 40, demonstrating good device scalability.

[1]  Young-Jin Cho,et al.  Etch characteristics of magnetic tunnel junction stack with nanometer-sized patterns for magnetic random access memory , 2008 .

[2]  Seung H. Kang,et al.  Unified embedded non-volatile memory for emerging mobile markets , 2014, 2014 IEEE/ACM International Symposium on Low Power Electronics and Design (ISLPED).

[3]  Sungwoo Chun,et al.  Multi-step ion beam etching of sub-30 nm magnetic tunnel junctions for reducing leakage and MgO barrier damage , 2012 .

[4]  M. Kautzky,et al.  Atomic Layer Deposition Al$_{2}$O $_{3}$ Films for Permanent Magnet Isolation in TMR Read Heads , 2008, IEEE Transactions on Magnetics.

[5]  H. Noguchi,et al.  Progress of STT-MRAM technology and the effect on normally-off computing systems , 2012, 2012 International Electron Devices Meeting.

[6]  M. Gajek,et al.  Spin torque switching of 20 nm magnetic tunnel junctions with perpendicular anisotropy , 2012 .

[7]  J. H. Kim,et al.  Verification on the extreme scalability of STT-MRAM without loss of thermal stability below 15 nm MTJ cell , 2014, 2014 Symposium on VLSI Technology (VLSI-Technology): Digest of Technical Papers.

[8]  M. Yoshikawa,et al.  Ion-Beam-Etched Profile Control of MTJ Cells for Improving the Switching Characteristics of High-Density MRAM , 2006, IEEE Transactions on Magnetics.

[9]  Mahendra Pakala,et al.  A Self-Aligned Two-Step Reactive Ion Etching Process for Nanopatterning Magnetic Tunnel Junctions on 300 mm Wafers , 2014, IEEE Transactions on Magnetics.

[10]  Luan Tran,et al.  45nm low power CMOS logic compatible embedded STT MRAM utilizing a reverse-connection 1T/1MTJ cell , 2009, 2009 IEEE International Electron Devices Meeting (IEDM).

[11]  T. Sugii,et al.  A highly scalable STT-MRAM fabricated by a novel technique for shrinking a magnetic tunnel junction with reducing processing damage , 2014, 2014 Symposium on VLSI Technology (VLSI-Technology): Digest of Technical Papers.

[12]  G. Yeom,et al.  A study on the etching characteristics of magnetic tunneling junction materials using DC pulse-biased inductively coupled plasmas , 2014 .

[13]  H. Ohno,et al.  Perpendicular-anisotropy CoFeB-MgO based magnetic tunnel junctions scaling down to 1X nm , 2014, 2014 IEEE International Electron Devices Meeting.

[14]  Peng Xie,et al.  Post-litho line edge/width roughness smoothing by ion implantations , 2013, Advanced Lithography.

[15]  Yiming Huai,et al.  Spin-Transfer Torque MRAM (STT-MRAM): Challenges and Prospects , 2008 .

[16]  Vasile Paraschiv,et al.  STT MRAM patterning challenges , 2013, Advanced Lithography.

[17]  R. P. Robertazzi,et al.  Effect of subvolume excitation and spin-torque efficiency on magnetic switching , 2011 .