Abstract
The effects of plasma and precursors during low-temperature silicon nitride (LT-SiN) film deposition on the magnetic properties of a CoFeB alloy layer, which is one magnetic material in a magnetic tunnel junction (MTJ) in magnetoresistive random access memory (MRAM), were investigated. The NH3 plasma exposure was found to nitride the CoFeB alloy layer, resulting in degradation of the magnetic properties of the CoFeB alloy layer. To suppress this degradation, NH3-free LT-SiN films deposited using silane and nitrogen source gases with helium or argon dilution in a conventional plasma enhanced chemical vapor deposition (PECVD) apparatus were evaluated. The LT-SiN film deposited under conditions of a highly dilute helium flow in the SiH4–N2–He gas mixture exhibited high density, sufficient moisture-blocking ability, and low leakage current. On the other hand, the film deposited at the SiH4–N2–Ar gas mixture exhibited poor film qualities. It is revealed that helium gas has enhanced the generation of N2 radicals and the decomposition of silane gas during the deposition of the SiH4–N2–He gas mixture. Finally, we demonstrated that the electrical properties of 8-kbit MRAM arrays have been improved by using the optimized NH3-free LT-SiN film for the MTJ-protection layer.
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