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Fabrication of Magnetic Nanostructures for MRAM using Electron Beam and Focused Ion Beam Exposure of HSQ

Published online by Cambridge University Press:  01 February 2011

Chen Chen ,
Michael J Cabral ,
Robert Hull  and
Lloyd R Harriott
Chen Chen
Affiliation:
[email protected], University of Virginia, Electrical and computer engineering, 126A Appletree rd, Charlottesville, VA, 22903, United States, 434-825-2203
Michael J Cabral
Affiliation:
[email protected], University of Virginia, Electrical and computer engineering, 351 Mccormick road, Charlottesville, VA, 22904, United States
Robert Hull
Affiliation:
[email protected], University of Virginia, Material Science and Engineering, Charlottesville, VA, 22903, United States
Lloyd R Harriott
Affiliation:
[email protected], University of Virginia, Electrical and computer engineering, 351 Mccormick road, Charlottesville, VA, 22904, United States
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Abstract

Giant magnetoresistive (GMR) materials-based magnetic random access memory (MRAM) has become attractive due to non-volatility, speed and density1. The vertical MRAM (VMRAM) design model shows good signal level and high speed and density potential. The memory cell for the VMRAM model is a ring shaped magnetic material multilayer, which ensures high repeatability and low switching energy. This GMR structure, however, is difficult to pattern as it contains materials such as Ni, Fe, Co, and Cu, which are difficult to dry etch because they lack volatile etch products. This work shows that it is possible to overcome the difficulties associated with etching GMR materials by using hydrogen silsesquioxane (HSQ) as an etch mask. We have used HSQ in a direct-write electron-beam lithography system with a dose of 600 μC/cm2, and in a Ga+ ion focused ion beam (FIB) system with a dose of 12 μC/cm2. Both are followed by development and an argon plasma etch at 10mTorr and 100W RIE power. The HSQ layer provides high resolution as well as good etching resistance. Electron-beam exposed HSQ shows a 1:1.5 selectivity over the GMR film stack and the FIB exposed HSQ showed an improved etch selectivity of 1:1. Ring shaped GMR structures with a 75/225 nm (ID/OD) have been fabricated, which corresponds to a memory density of 4Gb/in2.

Keywords

magnetoresistance (magnetic)ion-beam processingelectron irradiation
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 961: Symposium O – Nanostructured and Patterned Materials for Information Storage , 2006 , 0961-O09-05-P02-05
Copyright
Copyright © Materials Research Society 2007

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References

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