Enhancement of STT-RAM Characteristics by Wet Clean Treatment after MTJ Etch Process
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Enhancement of STT-RAM Characteristics by Wet Clean Treatment after MTJ Etch Process Jung Nam Kim1, Choon Kun Ryu, Hong Ju Suh, Bo Kyung Jung, Soon Ju Lee, Chang Hyup Shin, Won Joon Choi, Jae Sung Roh, Sung Ki Park. 1 R&D Division, SK hynix Semiconductor Incorporated, Icheon-si, Kyoungki-do, 467-701, Korea ABSTRACT The effect of wet chemical treatment on the magnetic tunneling junction (MTJ) was examined. The tunneling magneto-resistance (TMR) increased and the resistance of anti-parallel state and parallel state decreased when a wet cleaning treatment was carried out after a reactive ion etching process. Furthermore, the exfoliation between the capping layer and Inter layer Dielectric (ILD) was prevented. Presumably, these were due to the elimination of the damaged layer and the residues. This investigation showed that the wet treatment after the MTJ patterning using RIE process could improve the MTJ properties without degradation of Hc, such as TMR and Rlow. INTRODUCTION The conventional memories, NAND and DRAM, have been faced with the limitations of scalability. And may semiconductor manufacturers and university research groups have been investigating the alternatives. Among many candidates, spin torque transfer RAM (STT RAM) has an unlimited endurance, the highest reliability of any other non-volatile memories and high speed. Furthermore, the STT write operation could give us better scalability than conventional field switching. On the other hand, there are some issues to be overcome, such as high cell current drivability, high cost and thermal stability of magnetic tunnel junction. Even though, STT RAM is the most promising candidate which can substitute for DRAM and NAND. [1] After Reactive Ion Etching (RIE) process for patterning MTJ stack, the side of MTJ stacks could be damaged slightly and be covered by the etch residues. These residues could cause the poor adhesion between the ILD oxide and the encapsulating layer (normally Si3N4). Moreover, the edge of the MTJ stack was damaged during the etching process. Especially, the damage of MgO and a free layer could cause the increase of Rlow and the decrease of TMR. After the RIE process, post treatments should be applied for removing the residues and recuperating the damaged area of the MTJ stack. In this paper, we present the research results regarding the enhancement of STT-RAM characteristics by the wet cleaning after the MTJ etch. EXPERIMENT In this work, we used the in-plane type MTJ structure and TiN as a bottom electrode and a low resistance W as a top electrode. The Reactive Ion Etch (RIE) process was employed for the MTJ patterning. As listed in Table 1, the post wet treatments were carried out after the MTJ stack patterning by using various chemicals. The chemicals were divided to two groups, fluoridegroup and amine- group. As shown in figure 1, two kinds of cleaning machines were used; single
and batch type. The schematic structure of the STT RAM and key process flow were shown in figure 2. The resistance-magnetic field (R-H) curves were obtained
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