| AVS 58th Annual International Symposium and Exhibition | |
| Plasma Science and Technology Division | Thursday Sessions |
| Session PS+SS-ThA |
| Session: | Plasma Surface Interactions (Fundamentals & Applications) II |
| Presenter: | Shin Okamoto, Tokyo Electron Miyagi Ltd., Japan |
| Authors: | S. Okamoto, Tokyo Electron Miyagi Ltd., Japan A. Nakagawa, Tokyo Electron Miyagi Ltd., Japan F. Inoue, Tokyo Electron Miyagi Ltd., Japan H. Oka, Tokyo Electron Miyagi Ltd., Japan H. Mochiki, Tokyo Electron Ltd., Japan K. Yatsuda, Tokyo Electron Ltd., Japan |
| Correspondent: | Click to Email |
Higher aspect ratio of DRAM capacitor is required in order to maintain enough capacitance as the device structure is scaled down. The electrode of DRAM capacitor is generated in mold by metal CVD – typically TiN, and the mold is fabricated by RIE – typically dielectric. Thus, it is necessary to develop new techniques to fabricate higher aspect ratio dielectric mold for further DRAM scaling. RIE challenges for mold fabrication are high dielectric etch selectivity to mask, minimum bowing, and sustainment of enough bottom CD.
Generally speaking, mold etch process is optimized by accurate polymer control. However, conventional polymer control technique became marginal in highly scaled DRAM structure. Even slightly excessive polymer makes bottom CD smaller, and sometimes clogs the top portion of mold. On the other hand, slightly lacking polymer bridges neighboring molds at the top and/or sidewall portion due to lack of etch selectivity to mask and/or bowed etch profile.
In this paper, we suggest DC superimposed capacitively-coupled plasma (CCP) etch technique as a breakthrough of high aspect ratio dielectric etch. High energetic electrons emitted and accelerated by superimposed DC harden the polymer generated on mask and sidewall. This hardening technique works in two roles. The first role is etch selectivity enhancement of undesired etch material. Since polymer is maintained thin enough with good etch selectivity to mask, the top portion of mold is not clogged by polymer. The second role is etch durability enhancement of undesired etch portion. Normally, ultra high aspect ratio dielectric etch needs very high ion energy, which results in bowing etch profile due to incoming angular ions. But, superimposed DC hardens the sidewall polymer, and prevents etch profile from bowing. Bottom CD can be enlarged in the over etch step after etch front reaches etch stop layer. In general, bowing etch profile becomes significant during the over etch step. However, this effect can be avoided with stiff polymer enhanced by superimposed DC.
In conclusion, etch selectivity/durability of the undesired etch material/portion can be enhanced by superimposed DC as long as polymer is generated in the desired area by etch process optimization. Superimposed DC allows us to enhance etch selectivity/durability not with thickness of polymer but stiffness of polymer.