C 2 H 4 -Based Plasma-Assisted CD Shrink and Contact Patterning for RRAM Application
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1249-F04-09
C2H4-Based Plasma-Assisted CD Shrink and Contact Patterning for RRAM Application Alexey P. Milenin, Judit Lisoni, Nico Jossart, Malgorzata Jurczak, Herbert Struyf, Denis Shamiryan, Mohand Brouri2, and Werner Boullart IMEC, Kapeldreef 75, B-3001 Leuven, Belgium 2 Lam Research Corp., Kapeldreef 75, B-3001 Leuven, Belgium
ABSTRACT Critical dimension (CD) shrink and patterning of contact features via plasma etching were studied for typical resistive random access memory (RRAM) stacks. These consist of SiO2 and Si3N4 (total thickness of 65 รท 80 nm) with NiO or pure Ni at the bottom. First, the contact patterning of RRAM stacks was investigated for 90 nm contacts. Thus, a standard high power contact etch recipe was shown to give rise to resist strip challenges due to the incorporation of sputtered Ni in the resist film. Therefore, a low-sputter-yield contact etch recipe based on a CF4/H2/Ar gas chemistry was introduced. The ion sputter efficiency of the recipe was estimated from a blanket SiO2 sputter-yield experiment in Ar plasma for the same recipe settings: this yielded values close to the Ni sputter-yield threshold. Second, plasma-assisted CD shrink was studied in combination with the newly developed patterning scheme to get the contact CD well below the initial 90-nm litho print size. It was shown that a low contact etch power regime could also provide a larger window for contact CD shrink using a C2H4-based chemistry: e.g. the demonstrated CD shrink from 90 nm down to sub-40 nm was shown to be extremely challenging in the case of a high power regime due to polymer instability enhanced with the resulting thickness increase. Perhaps, the relaxation of the polymer film stress, which was measured to be in the range of 1200-1500 MPa, is more easily triggered at higher power settings, which leads to polymer blistering. Finally, the optimization of the plasma-assisted CD shrink step in combination with the low-sputter-yield contact etch recipe was demonstrated to be able to provide CDs as small as 27 nm. The demonstrated approach shows that plasma-assisted CD shrink can provide a robust test vehicle for research programs that require the patterning of small features in the sub-40-nm CD range.
INTRODUCTION Scaling is required for each new generation node. Currently, the design rules are already far beyond the capability of a single print, even for advanced 193-nm immersion lithography. Thus, among developing techniques allowing sub-40-nm patterning for contacts, e.g. EUV, nano-imprint, self-assembled block copolymers, double print, and negative tone development litho, shrink the CD in a plasma reactor is the only one that does not necessarily requires new mask sets and that can be tested directly with relaxed pitch litho masks. From large variety of research activities demanding ever-smaller contact CDs, those that deposit active elements in those holes are in a greater need to get the smallest CD possible. For example, nanowire or RRAM activities need small contacts to grow/put active elements inside of
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