Emanuel I. Cooper

Wet Selective SiGe Etch to Enable Ge Nanowire Formation

For the Ge nanowire formation in a gate-all-around (GAA) integration scheme, a selective etch of Si0.5Ge0.5 or Si0.3Ge0.7 selective to Ge is considered. Two wet process approaches were evaluated: a boiling TMAH as a commodity chemistry is compared with a formulated chemistry using a multi-stack SiGe/Ge layer as a test vehicle. The boiling TMAH exhibits an anisotropic etch of the SiGe whereas the formulated semi-aqueous chemistry removes the sacrificial SiGe by an isotropic etch which makes the process suitable for a Ge nanowire release process.

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.

Titanium Nitride Hard Mask Removal with Selectivity to Tungsten in FEOL

This paper describes etching of titanium nitride (TiN) highly selective to tungsten (W), where the TiN etch rate (E/R) was about 100 Å/min and W E/R was less than 1 Å/min at 60°C. The formulation concept was adapted from the Entegris TK-10 series, but it was modified to fit the criteria for front-end application. No damage to tantalum nitride (TaN) was required during the etching process but silicon oxide compatibility requirement was relaxed. By replacing W inhibitors with more suitable ones, W loss was well controlled, while the particle issue previously found in the scale up lots was also solved.

Selective Etching of Silicon Oxide versus Nitride with Low Oxide Etching Rate

This paper describes both aqueous and solvent-based formulations aimed at etching silicon oxide (SiOx) with etching rates (E/R) of the order of 10-20 A/min with selectivity greater than 5 with respect to silicon nitride (SiNx) . Diluted hydrofluoric acid (dHF) with very low pH was tried first but the selectivity was found to increase only with higher SiOx E/R. Solvent-based formulations derived from previous work also behaved in a similar way, however its SiOx E/R could be reduced by modifying the total fluoride concentration inside formulation. Finally, we found that low SiOx E/R could also be implemented in the diluted buffer-oxide etch (BOE) solution and the selectivity could be adjusted by addition of a specific surfactant at a very low concentration level.

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.

Selective Nitride Etch by Using Fluorides in High Boiling Point Solvent

Conventional wet etching techniques for selectively removing silicon nitride (Si3N4) have utilized hot (approximately 145-180°C) aqueous phosphoric acid (H3PO4) solutions (often referred to as hot phos). The typical Si3N4:SiO2 selectivity is about 40:1 when using 85% fresh hot phosphoric acid. Advantageously, as the nitride layer is removed, hydrated silicon oxide forms and dissolves in the etchant. Consistent with Le Chatelier principle, this inhibits the additional removal of silicon oxide from the device surface; thus selectivity gradually increases with use [.