Els Kesters

The thermal conversion reaction of sulphonyl substituted poly( para-xylylene): evidence for the formation of PPV structures

Abstract The thermal elimination of the n -octyl-sulphonyl group from poly[1,4 phenylene (1- n -octyl-sulphonyl)-1,2-ethylene] and the phenyl-sulphonyl group from poly[1,4 phenylene (1-phenyl-sulphonyl)-1,2-ethylene] is evaluated by different analytical techniques: thermal gravimetric analysis, direct insert probe mass spectrometry, in situ ultraviolet–visible spectroscopy and in situ Fourier transform infra red spectroscopy. This thermal treatment yields PPV with improved optical properties compared to the conventional PPV concerning UV-absorption and photoluminescence efficiencies. The results obtained are consistent with the formation of a PPV with a more or less restricted conjugation length compared to the PPV material obtained from the conversion of a sulphinyl precursor polymer.

Alternative Photoresist Removal Process to Minimize Damage of Low-k Material Induced by Ash Plasma

Dry ashing of photoresist (PR) using oxygen-containing plasma applied subsequently to an etch plasma leads to degradation of porous low-k material. The surface region is substantially depleted in carbon. The low-k film becomes more hydrophilic after being subjected to plasma etch and especially ash process as evidenced by water absorption results. The amount of absorbed water into a 30% porosity film at moisture saturation is estimated to be about 15% of the film volume, which corresponds to 50% of the total pores in the low-k film. A wet, alternative means for PR removal based on dissolution of PR in organic solvents combined with physical forces is presented. Under certain conditions, megasonic cleaning resulted in complete removal of the PR layer without damaging of the dielectric lines. These results suggest that the PR crust is permeable to these solvents and that out-diffusion of dissolved bulk PR also occurred through the crust. Dissolution of bulk PR in organic solvents first makes the PR structure more fragile, then the physical energy helps to remove the remaining crust mechanically without dissolving it. Compared to plasma ashing, solvent strip shows no carbon depletion and no significant increase in k-value.

All-Wet Strip Approaches for Post-Etch Photoresist Layers After Low-K Patterning

Plasma chemistries, applied during low-k patterning processes in back-end of line (BEOL) applications, modify the photoresist (PR) layer present on top of the etched structures. The remaining resist layer after plasma etch is resilient towards most organic solvents and aqueous solutions. Conventionally, the layer is removed before copper deposition using an oxidizing plasma process. This approach is not acceptable anymore due to damage of the dielectric, i.e. k-value degradation and chemical modifications [1,2]. In order to obtain less damaging photoresist removal processes for post low-k etch, the use of wet-only methods is under investigation.

Characterization of Modification of 193-nm Photoresist by HBr Plasma

[Vereecke, G.; Claes, M.; Le, Q. T.; Kesters, E.; Struyf, H.] IMEC, B-3001 Heverlee, Belgium. [Carleer, R.; Adriaensens, P.] Univ Hasselt, IMO Div Chem, B-3590 Diepenbeek, Belgium. guy.vereecke@imec.be

Study of the conversion process of sulfinyl-OC1C10-PPV precursor polymers with different analytical techniques

Abstract The use of sulfinyl groups as thermally eliminable groups in precursor routes towards conjugated systems, like OC1C10-PPV, is evaluated by different techniques: Fourier Transform Infrared Spectroscopy (FT-IR), Ultraviolet Visible Spectroscopy (UV-Vis), X-ray Photoelectron Spectroscopy, Electron Spin Resonance (ESR) and Raman Spectroscopy. In-situ FT-IR and UV-Vis, allows determination of the temperature range where elimination takes place. XPS was performed on the surfaces of the polymer films.

Modification of photoresist by UV for post-etch wet strip applications

In Back-End-of-Line processing, the remaining photoresist layer after plasma etch is traditionally removed using a plasma process. Plasma process was reported to induce damage to porous dielectric [1-3]. To minimize damage to low-k material, wet alternative methods of removal of photoresist layer on porous low-k dielectrics are gaining a renewed interest [4]. However, the presence of a “crust” generated by etch plasma at the photoresist surface makes it impossible to completely remove by a pure organic solvent. Indeed, the crust, most likely composed of crosslinked polymer, is not soluble in organic solvents [5]. For this reason, a UV pre-treatment is investigated to break cross-links in the crust or to modify the crust to enhance removal efficiency with solvent stripping in more advanced generations.

Wet Removal of Post-Etch Residues by a Combination of UV Irradiation and a SC1 Process

In back-end of line processing (BEOL), the polymer deposited on the dielectric sidewalls during the etch process must be removed prior to subsequent processing steps to achieve high adhesion and good coverage of materials deposited in the etched features [1, . Typically, this is done by a combination of a short plasma treatment and a diluted wet clean, or by wet cleans alone. On the one hand, for porous dielectric stacks, a mild plasma treatment that preserves the integrity of the low-k dielectrics would not be sufficient to effectively remove this residue. With regard to wet clean, diluted aqueous solutions (e.g. HF-based) are not efficient for polymer removal without etching the underlying dielectric to lift off the polymer, leading to unacceptable critical dimension (CD) loss. In addition, analytical techniques available for direct characterization of sidewall residues are limited. For a fast screening of potential chemistries capable of dissolving/removing polymer residues generated during the low-k etch, a model fluoropolymer was deposited on a blanket, checkerboard low-k substrate. The present study mainly focused on the characterization of model polymer after deposition (as-deposited) and after immersion in aqueous and solvent-based cleaning solutions. The polymer removal efficiency was influenced/ improved by UV treatments prior to wet clean processes. In the second part of the study, selected UV treatment conditions and cleaning solutions were applied to low-k patterned structures using Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) to characterize the dielectric sidewall before and after UV modification and the subsequent cleaning process.

Photoresist Characterization and Wet Strip after Low-k Dry Etch

[Claes, M.; Le, Q. T.; Kesters, E.; Lux, M.; Franquet, A.; Vereecke, G.; Mertens, P. W.] IMEC VZW, B-3001 Louvain, Belgium.

Impact of Dissolved Oxygen in Dilute HF Solution on Material Etch

Using diluted HF (0.05-0.1%) as cleaning solutions, experimental results showed that the etching behavior of Cu strongly depended on the dissolved oxygen (DO) concentration and the chamber atmosphere conditions. On the contrary, the Cu etch rate was not affected by the HF concentration. A complete reverse trend was observed for plasma-treated OSG2.4. The etching behavior of plasma-treated OSG2.4 was not affected by DO concentration and chamber atmosphere conditions, but was strongly dependent on the HF concentration. The etch rate determined on patterned structure with low-k exposed, using CD measurements, confirmed the results obtained on blanket plasma-treated OSG2.4 material.

Modifications of Porous Low-k by Plasma Treatments and Wet Cleans

With the implementation of Cu and low-κ dielectrics in back-end-of-line (BEOL), issues arise in every process step that must be addressed. One of the challenges is the susceptibility of Cu and low-κ materials to attack during residue removal (polymer) after low-κ etch and resist strip. This work focuses on the influence of the plasma etch and ash processes on compatibility of porous low-κ dielectrics with a selection of wet chemistries that are used for BEOL polymer removal.