Quoc Toan Le

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.

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.

Effect of Chemical Solution on the Stability of Low-k Films

The compatibility of chemical solutions with different pH is studied on microporous silica-based (SiOCH) and mesoporous methylsilsesquioxane (MSQ) based low-k materials. The surface and bulk properties of as-deposited and O2/CF4 plasma-treated low-k films have been studied after several wet treatments.

UV-Induced Modification of Fluorocarbon Polymer: Effect of Treatment Atmosphere and Aging on Dissolution in Organic Solvent

In back-end of line (BEOL), the use of fluorocarbon-containing plasmas such as CF4 and C4F8 for patterning of low-k dielectrics with k-value ~2.3-2.5 can result in the presence of a highly fluorinated layer, deposited on the sidewalls and bottom of the trenches [1,. This polymer layer must be removed prior to subsequent processing steps to achieve good adhesion and coverage of materials (metals) deposited in the etched features. However, it is known that this type of fluorocarbon polymer is chemically inert to many existing wet clean solutions, including aqueous solutions such as fluoride ion-containing or highly alkaline solutions, and solvent mixtures [2]. Exposure of the polymer to UV irradiation (λ 200 nm) with doses 3 J/cm2 significantly modifies the polymer film, which results in substantial removal ability in a subsequent wet clean process. Polymer film modification was shown to be efficient either by using a narrow band single wavelength source with λ = 254 nm [ or by a broad band UV source with λ~200-300 nm [.

Wet-Chemical Etching of Ruthenium in Acidic Ce4+ Solution

The wet-chemical etching of ruthenium in acidic solutions of cerium (IV) has been investigated using electrochemical methods. Etch rates were determined using Rutherford backscattering spectroscopy (RBS) and post-etching surface roughness was investigated using atomic force microscopy (AFM). Low-k material is compatible with the etchant, however, residues were formed.

Optimization of Post Etch Cobalt Compatible Clean by pH and Oxidizer

The introduction of Co into MOL and BEOL requires a robust wet clean, especially the optimization of the Co rinsing step seems to be critical. The wafer rinsing solutions with a precisely controlled pH and oxidizing additive have been developed to suppress the Co corrosion. In addition, the mechanism of passivation and corrosion of the cobalt surface as well as the passivation stability is discussed.

Effect of Cleaning Chemistries on Cobalt: Surface Chemistries and Electrical Characterization

The etching characteristics of ECD cobalt in different cleaning solutions were characterized using four-point probe, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy. 0.05% HF solution with saturated dissolved oxygen concentration was found to result in a substantial etch of ECD cobalt (~5 nm/min). In contrast, cleaning in the SC1 1:4:100 mixture and the formulated mixture led to a significantly lower etch amount, which could be explained by the formation of a passivation layer at the surface. XPS characterization indicated the formation of a cobalt hydroxide at the surface. The electrical evaluation of the DD structure carried out after cleaning using the formulated chemical mixture and subsequent metallization showed good yield for the 22 nm Kelvin vias, testifying an efficient cleaning of the Co surface at the via bottom.

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.

Characterization of Etch Residues Generated on Damascene Structures

For patterned TiN/silicon oxide/low-k dielectric stack, fluorinated etch residues were detected on the TiN surface, the dielectric sidewall and bottom, regardless of the low-k material used in the stack. XPS results showed that they consisted of polymer-based (CFx) residues deposited on trench sidewall and bottom, and metal-based (TiFx) residues mainly deposited on top surface. In terms of post-etch residue removal, the efficiency of various wet clean solutions can be clearly distinguished for CFx, and TiFx using the same patterned porous low-k stack. These results also demonstrate that the removal of both TiFx and CFx residues generated during the plasma is possible in one step with optimized chemical and process.