Lucile Broussous

Depth-resolved impact of integration process on porosity and solvent diffusion in a SiOCH low-k material

The impact of plasma etching and chemical wet cleaning on solvent diffusion in porous network of a SiOCH low-k dielectric material is studied. Characterization of porosity and pore size distribution by means of ellipso-porosimetry and positron annihilation lifetime spectroscopy are presented. The results are compared with solvent diffusion kinetics, measured using probe molecules of different polarity, surface energies and molecular sizes. Infrared spectroscopy, Doppler broadening of annihilation radiation and time-of-flight secondary ion mass spectrometry measurements are also performed to investigate material modifications causing variations of diffusion kinetics.

Impact of solvent and low k material surface characteristics on pore sealing efficiency and porosity measurement

The penetration kinetics of different solvents having various properties (size, polarity, viscosityl) inside a porous low k SiOCH material modified by plasma treatments were investigated by ellipsometric porosimetry. The solvent penetration rates and durations to reach the saturation strongly depend on both the solvent properties and on the plasma post-treatments performed on the porous low k material. Pore sealing and barrier effect were quantified from the experimental determination of permeability coefficients for sample modified by a NH3 and Fluocarbon based plasma using a permeation model. For these samples, the best barrier effects are observed with toluene and ethanol, respectively. In absence of barrier effect (unmodified material, plasmas He and NH3/N2), the solvent polarity and viscosity influence the time required for the complete saturation of the porous material. The liquid volume fraction fL at saturation is also a function of the used solvent affecting the porosity estimation. All of these results highlight the complexity of the solvent penetration mechanisms.

Impact of Organic Acid and Gas Bubbling on Copper and Copper Oxide Etch-Rates in Diluted HF Solution

In the damascene integration scheme, copper is used as an interconnect material. In a damascene integration scheme, the etch treatment by a plasma process leads to the formation of polymer residues, copper sputtered on the dielectric side wall, copper oxidation at the bottom of the via and copper precipitates at the hard mask surface. In order to remove these impurities, a post-via etch cleaning is mandatory [1]. Several aqueous cleaning solutions constituted of diluted HF and an organic acid were tested. Diluted HF was mainly used to remove the polymer residues and the organic acid to clean the copper surface. These mixtures were already studied and compatible with several porous and dense ULK materials [1]. In this paper, the impact of organic acids and gas bubbling in diluted HF solution on copper and copper oxide-dissolution rate is presented. Firslty the copper oxide and the copper etch-rates and the roughness were obtained from the kinetics of copper dissolution determined by X-ray reflectometry characterization [3]. Secondly, speciation calculations were performed in order to explain the copper etch-rates differences as a function of the solutions and gas bubbling.

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.

Barrier and Copper Seedlayer Wet Etching

This paper summarizes the process development of TiN barrier etching in presence of copper, for a thick copper level in BICMOS technology. In an industrial context, we have chosen to use a SC1 chemistry in a spin etch single wafer tool. The SC1 composition and therefore the pH level allows - the barrier to be etched with no metallic residues, ( if not clear this can be a source for shorts) - control of the selectivity between copper and TiN - control of lateral etching under copper lines, the possible source of open chains by W attack during TiN etch. The electrical results show a robust process according to current specifications, in terms of leakage and via resistance with a fresh chemistry approach. In fact, the recirculation of SC1 is not possible due to substantial concentration changes during processing, high evaporation rate of Ammonia and high decomposition rate of Peroxide in the presence of copper on surface wafer.

Oxygen Control for Wet Clean Process on Single Wafer Platform

Wet processing with low oxygen content may provides some advantages, however, full control to avoid oxygen uptake during wafer processing remains a challenge for short process industrialization on single wafer tool. Inline oxygen concentration monitoring was used for process optimization. Then, cobalt etch in diluted HF solutions was evaluated depending on the recorded oxygen concentration and hardware available options for atmosphere control in the process chamber.

TiN Hard Mask Cleans with SC1 Solutions, for 64nm Pitch BEOL Patterning

Titanium Nitride metal hard mask was first introduced for BEOL patterning at 65 nm [1] and 45 nm nodes [2]. Indeed, in this “Trench First Hard Mask” (TFHM) backend architecture, the dual hard mask stack (SiO2 & TiN) allows a minimized exposure of ULK materials to damaging plasma chemistries, both for line/via etch sequence, and lithography reworks operations. This integration scheme was successfully used for a BEOL pitch down to 90 nm for the 28 nm node, however, for the 14 nm technology node, 64 nm BEOL minimum pitch is required for the first metal levels. Because it is unable to resolve features below 80 nm pitch in a single exposure, conventional 193 nm immersion lithography must be associated with dual patterning schemes, so called Lithography-Etch-Lithography-Etch (LELE) patterning [3] for line levels and self-aligned via (SAV) process [4] for via patterning. In both cases, 2 lithography/etch/clean sequences are necessary to obtain one desired pattern, and associated reworks also become more challenging since first pattern is exposed to resist removal processes (plasma + wet clean). The reference wet cleans that were developed for 65 to 28 nm TiN hardmask patterning, utilizes commonly used chemistry for BEOL post-etch cleans, i.e. diluted hydrofluoric acid (dHF) followed by deionized water Nanospray (DIWNS) on 300 mm single wafer tool.

Electrochemical Behavior of Cobalt in Post-Via Etch Cleaning Solutions

The integration of CoWP and CoWB self-aligned barriers (SAB) for 32 nm technology nodes allows improving copper interconnections reliability [1, 3]. However the introduction of such materials in copper interconnection levels drives new challenges for plasma dry etch and wet clean processes. Indeed, during the post-via-etch cleaning step, cobalt and copper can be altered by corrosion. Moreover, a galvanic coupling between cobalt, the major component of SAB, and copper can thermodynamically occur. In this way, the cleaning solution acts as ionic medium providing a contact between the two metals. Thus, both metals polarize to a mixed potential comprised between the individual open circuit potentials (OCP) of cobalt and copper. As a result, the less noble metal can suffer from accelerated corrosion, and the more noble metal corrodes with slower rate. According to thermodynamic aspects, cobalt in contact with copper is the less noble metal. Consequently, Co is susceptible to undergo galvanic corrosion which may enhance the dissolution of the SAB.

Impact of Plasma and Diluted HF on a CoWP Material

Introduction Self-Aligned Barriers (SAB) are investigated to achieve reliable copper interconnects for the 45 nm technology node and beyond [1][2]. The integration of this material requires the study of the process impacts: plasma etch and ash, and cleaning process. In this study, the impact of several plasma treatments used in the integration and of a cleaning with diluted HF on a CoWP layer with Pd activation process was investigated. Samples were characterized by X-ray reflectometry and X-ray fluorescence spectrometry in order to assess the material modifications in terms of density, thickness and cobalt amount.

Copper Surface Analysis with ToF-SIMS: Spectra Interpretation and Stability Issues

In integrated circuit manufacturing, surface cleanliness is mandatory to achieve high production volumes and device yield. Time-Of-Flight Mass Spectroscopy (ToF-SIMS) is an attractive technique for contamination control since it does provide information about both elemental and molecular species present on essentially any surface and offers high chemical sensitivity associated with sub-micrometer range spatial resolution and short acquisition time. The benefits of this technique to control surfaces after post copper chemical mechanical polishing (Cu-CMP) cleaning [1, 2] and after post via etch cleaning have already been reported.