| AVS 58th Annual International Symposium and Exhibition | |
| Plasma Science and Technology Division | Tuesday Sessions |
| Session PS1-TuA |
| Session: | Advanced BEOL / Interconnect Etching II |
| Presenter: | Eric A. Hudson, Lam Research Corp. |
| Authors: | E.A. Hudson, Lam Research Corp. T. Choi, Lam Research Corp. K. Takeshita, Lam Research Corp. S. Sirard, Lam Research Corp. B. Ji, Lam Research Corp. M. Kato, Lam Research Corp. M. Moravej, Lam Research Corp. O. Turmel, Lam Research Corp. G.A. Delgadino, Lam Research Corp. S. Heo, Lam Research Corp. A.D. Bailey III, Lam Research Corp. |
| Correspondent: | Click to Email |
Integration of materials with low dielectric constant into microelectronics interconnect structures has presented significant challenges for several years. As structures and materials have evolved, there has been a consistent concern that plasma processing damages the low-k material, especially during process steps intended to strip organic mask films. For efficiency, it is convenient to remove organic films in situ, as part of a sequence of etch steps in the etch reactor. But plasma strip conditions may remove carbon from the dielectric film, causing an increase in dielectric constant and other issues. This is an increasing concern as the target dielectric constant is reduced with successive device generations, and the films become more sensitive.
For via-first integration schemes which use an embedded metal hard mask to define the trench pattern, organic mask stripping is required only after the vias are partially defined in the dielectric. This approach protects the trench sidewall by eliminating the post-trench strip, but may lead to localized regions of dielectric damage in the final structure, corresponding to the remaining material which was exposed to post-via strip.
For in situ plasma strip processes based upon CO2 gas, damage to the dielectric film is mainly induced by reactive neutral species at the via sidewall. There are several strategies to reduce this damage while maintaining the ability to strip the targeted organic mask layer. One is to minimize the radical to ion ratio, in order to reduce the damage rate while preserving strip rate. Another method is the “hybrid strip” in which a protective layer of polymer is deposited on the via sidewall prior to strip. This barrier reduces the influence of strip plasma species on the underlying dielectric film. Damage reduction is achieved using passivation based either upon hydrocarbon or fluorine-containing polymers.
Because the strip plasma tends to remove the passivation from the sidewall, and because the damage rate increases in the final part of the strip process, better results can be achieved if the protective films is periodically re-applied. A cyclic process which alternates between passivation and strip conditions minimizes the strip-induced damage at the via sidewall. To facilitate an efficient hybrid strip process, the etch reactor design can be optimized for rapid switching between the two different plasma conditions. This requires minimization of both the gas exchange time and the RF coupling stabilization time.