Steven Lippy

Industrial Challenges of TiN Hard Mask Wet Removal Process for 14nm Technology Node

TiN Hard Mask (TiN-HM) integration scheme has been widely used for BEOL patterning in order to avoid ultra low-k (ULK) damage during plasma-ash process [1]. As the technology node advances, new integration schemes have to be used for the patterning of features below 80 nm pitch with 193 nm immersion lithography. In particular, thicker TiN-HM is necessary in order to ensure Self-Aligned-Via (SAV) integration which resolves via-metal short yield and TDDB issues caused by Litho-Etch-Litho-Etch (LELE) misalignment [2, 3]. The Cu filling process is significantly more difficult if the thick TiN is not removed because of the high aspect ratio of the structures. Moreover, with the use of TiN hard mask, a time-dependent crystal growth (TiCOF) residue may forms between line etch and metal deposition [4, 5], also hindering copper filling. Post-Etch-Treatment after line etching is one solution to the problem but N2 plasma is not efficient enough to suppress the residue completely [6], and the CH4 treatment proposed in [5] may be difficult to implement for 14 nm node, thus an efficient wet strip and clean provides a better solution.

Selective High-Throughput TiN Etching Methods

Titanium nitride (TiN) is widely used as a hard mask film protecting the inter-level dielectric (ILD) before metal or plating seed layer deposition steps. It is common practice to use a wet etch in order to remove residues formed during the ILD dry-etch step, and at the same time to remove some or all of the exposed TiN. From its thermochemical properties, it might be predicted that wet etching of TiN should be easy, since it is quite unstable with respect to both plain and oxidative hydrolysis. For example, in acidic solutions at 25°C [1, :

Selective co growth on Cu for void-free via fill

We report for the first time a highly selective CVD Co deposition on Cu to fill a 45nm diameter 3:1 aspect ratio via in a Cu dual damascene structure. We have achieved void-free Co fill of the via, demonstrating that a selective bottom-up via fill with Co is a potentially viable approach. Defect formation and control in the process and device integration are discussed. This selective process provides an opportunity to reduce via resistance and shrink the minimum metal 1 (M1) area for aggressive standard cell size scaling as needed for 7nm technology.

High Throughput Wet Etch Solution for BEOL TiN Removal

Sub-10 nm technology node manufacturing processes may require the use of thicker and denser TiN hard mask for patterning at the BEOL. The modified TiN, which tends to be more chemically robust, must be removed using a wet etch process, while maintaining typical throughput - no extension of typical wet etch process times. To satisfy these needs, a new TiN etching accelerator was found that enhanced the activity of peroxide-related species in a wet etch chemical formulation that achieved increased TiN etch rate relative to formulation without TiN etch rate accelerator (Sample 1), while also minimizing the damage to ultra-low-k inter layer dielectric (ILD) layer by a strong base, also present in the formulation. We report here the result of a solvent based formulation, which adopted the TiN etching accelerator. The formulation was able to maintain TiN etch rate and remove post-etch residue, while remaining selective to ultra-low-k ILD, Co and Cu. The TiN etch rate of the accelerator enhanced formulation can be further tuned by modifying the process temperature or the hydrogen peroxide to formulation mixing ratio and has the potential capability to process > 400 wafers.

Evaluation of Post Etch Residue Cleaning Solutions for the Removal of TiN Hardmask after Dry Etch of Low-k Dielectric Materials on 45 nm Pitch Interconnects

In the BEOL, as interconnect dimensions shrink and novel materials are used, it has become increasingly difficult for traditional PERR removal chemicals to meet the evolving material compatibility requirements. As a result, formulated cleans that specifically target these unique challenges are required. Two formulated BEOL cleans were evaluated on blanket and patterned wafer coupons for their ability to wet etch titanium nitride (TiN) and clean post-plasma etch residue, while remaining compatible to interconnect metals (Cu and W) and low-k dielectric (k = 2.4). Both, showed an improvement in material compatibility relative to dilute HF, while simultaneously being able to remove the TiN hardmask and post-etch residue, leading > 90% yield on test structures of varying sizes.