Invited Paper PS-WeM1
The Role and Impact of Metal Hard Masks on BEOL Etch Processes

Wednesday, October 31, 2012, 8:00 am, Room 25

Back-End-of-Line (BEOL) etch processes have undergone a significant transition in recent years as the requirements of advanced technology nodes have shifted the advantage from via-first-trench-last (VFTL) to trench-first-metal-hard-mask (TFMHM) dual damascene patterning schemes throughout the industry. This shift has been primarily driven by the TFMHM scheme’s ability to enable self-aligned vias (SAV), as well as inherently be more multi-patterning friendly through the use of a dissimilar hard mask material. However, typically key advances don’t come without other complexities, and TFMHM is no exception. The role and impact that the metal hard mask material has on all of the etches where it is involved is significant and sometimes very subtle. At a high level, the metal hard mask influences can be split into two areas: patterning of the MHM itself, and etches where the material acts as the hard mask. The patterning of the MHM itself is where all of the challenges associated with multi-patterning come into play. The MHM profile largely determines the overall critical dimension behavior across all patterns, and so pattern control and fidelity in both x and y dimensions are critical. The material properties of the MHM play a significant role in etch profile control and line edge/width roughness (LER/LWR). When considered as a hard mask in the etch, the MHM impacts are far-reaching. First, the selectivity of the MHM material vs. the underlying films must be considered. This is a key focus of etch process optimization when implementing an SAV patterning scheme and often drives all facets of the etch process. Second, the very properties that make it attractive as a hard mask (etch resistivity) can also make it the source of many other issues, typically due to the non-volatile nature of most MHM materials (Ti, TiN, TaN, etc.). Some examples include metal-containing sidewall and/or via hole residues, temperature sensitive profiles, ability to shape the MHM to help metallization, and chamber contamination effects (i.e., non-repeatability or slot-order effects). The MHM material properties have a large influence on these etches, as well, with tradeoffs between etch resistivity (good for SAV) and metal material stress (bad for pattern integrity --> can induce line wiggling). This talk will review some of the benefits of utilizing a metal hard mask, as well as some of the challenges that come hand-in-hand with it and how plasma etch process optimization is advancing in learning how to work with these materials.

This work was performed by the Research Alliance Teams at various IBM Research and Development Facilities.