Jang-eun Lee

Influence of freelayer in magnetic tunnel junction on switching of submicrometer magnetoresistive random access memory arrays

As magnetic tunnel junction (MTJ) cells for magnetoresistive random access memory (MRAM) are reduced in size, the presence of a magnetization vortex seriously interferes with switching selectivity. We prepared 0.3 /spl mu/m/spl times/0.8 /spl mu/m, nearly rectangular shape MTJs consisted of PtMn/CoFe/Ru/CoFe/AlOx/NiFe t (t=3,4.5, and 6 nm). Both at-field and remanent state measurements at 0.4 V were conducted to distinguish kinks originating from vortex and domain wall pinning. In addition, we measured samples at various temperatures (from room temperature to 500 K), and with various hard axis fields (from 0 to 90 Oe). As temperature increased, average switching fields decreased, more rapidly for t=6 nm junctions, but kinks were not eliminated completely. When the hard axis field reached about 40-60 Oe, nearly kink-free switching was possible for t=6 nm MTJs.

Plasma charge-induced corrosion of tungsten-plug vias in CMOS devices

Plasma charge-induced corrosion of tungsten plug vias, where part of the via surface is exposed to the chemical solution after metal-2 etch by photolithographic misalignment with upper metal lines, was investigated. Some electrochemical tests and plasma damage monitoring were done to study the corrosion mechanism. The configuration of circuits was also investigated to understand the pattern dependency of the plasma damage and the corrosion. It is believed that the positive charges on the metal lines and P/sup +/ active region of the PMOS, developed during dry etching and ashing, are enhancing the corrosion of tungsten during stripping. The plasma-less O/sub 3/ asher applied to the ashing process reduced the plasma damage and did not produce empty vias on the wafer.

New effect of Ti-capping layer in Co salicide process promising for deep sub-quarter micron technology

A new effect of the titanium (Ti) capping layer on cobalt (Co) silicide formation, which is promising for salicidation applications in deep sub-quarter micron devices, was investigated. TEM, SIMS, and XRD data suggest that Ti on top of the cobalt layer diffuses into the Co/Si interface and dissociates the thin silicon oxide at the interface during RTA. As a result, with a Co/Ti process, the sensitivity of Co salicide processes to surface conditions could be minimized, which gives a larger process window to fabricate deep sub-quarter micron devices.

Switching characteristics in magnetic tunnel junctions with a synthetic antiferromagentic free layer

The properties of sub-micrometer scaled MTJs using various synthetic antiferromagnetic (SAF) free layer were studied using remanent-state measurement. The magnetic tunnel junction device was a structure consisted of TiN/PtMn/CoFe/Ru/CoFe/AlO/NiFe/Ru/NiFe/Ta. It was found that junctions using single free layer showed complex switching behaviors with larger switching field variation while the junction using a specific SAF free layer exhibited kink-free R-H curves with less switching field variation. MR ratio and magnetization moment of the MTJ were also measured