Papers by Keyword: BEOL

Abstract: Cleaning of semi-damascene structures after direct metal etch (DME) are becoming more challenging as the size of features are getting smaller and number of materials increase in advanced nodes. Typical DME residues in-between Ru lines, generated during/after semi-damascene patterning by DME, mainly consist of Ti-based residues whereas there are TiN layers present as etch stop layer (ESL) below the SiN HM and underneath Ru lines. Wet cleaning of Ti-based residues selective to TiN and Ru in a decent process time is necessary. Undercut of TiN during wet cleaning results in collapsing of the SiN HM and/or Ru lines. We present a novel FOTOPUR^® R solution designed to clean Ti-based residues selective to Ru and TiN. Moreover, the new chemistry can further extend the process window without collapsing the Ru lines.

Abstract: Particle removal from BEOL low-k structures is studied using a novel particle removal technique, called Nanolift which removes particles from the substrate by forming a thin polymer film on the surface and removing the polymer film together with the particles. It was confirmed that Nanolift is capable to remove TiF_x particles successfully which are generated during the low-k dry etch process for dual damascene structure formation for BEOL interconnect fabrication. Pattern collapse of the fragile low-k structure was confirmed to be prevented by Nanolift in comparison with conventional dual fluid spray cleaning method. FTIR results show that Nanolift leaves no residual polymer remain in low-k films and K-value shift by the Nanolift process was negligible and comparable with the conventional formulated chemistry cleaning process. From these results, Nanolift can be concluded as a suitable cleaning process for advanced BEOL fabrication process.

Abstract: In this paper we demonstrate an effective process control mechanism to significantly improve on the process performance of a BEOL post-etch cleaning process with an integrated partial or complete removal of the TiN HM (hard mask) layer by so called formulated chemistries on a single wafer processing tool. The novel process control mechanism enables a 50% reduction in chemical consumption while achieving an at least equivalent TiN etch uniformity.

Abstract: 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.

Abstract: The impact of dissolved oxygen (O₂) on cobalt (Co) corrosion in dilute HF (dHF) solution was studied. It was confirmed that Co etch rate was enhanced as the amount of dissolved O₂ in the HF solution increased. The Co etch rate was also found to increase radially outward when performed on a single-wafer spin process in atmospheric air due to the uptake of O₂ during the dispense process. The galvanic corrosion of Co was investigated with two types of structures with a Co/Cu interface in different dissolved O₂ concentrations, i.e. (1) Co bump structures on Cu and (2) Cu lines with a Co/TaN liner/barrier structure. By controlling both the dissolved and the atmospheric O₂ levels, galvanic corrosion prevention at the Co/Cu interface was achieved.

Abstract: For advanced technology nodes TiN hard mask integration into Cu/low-k via/trench DD process requires the mask to be fully stripped after DD etching. The one-step H₂O₂ containing wet chemical clean aiming to removing TiN mask often failed to simultaneously clean etch residue. We developed more reliable two-step wet chemical process combining a solvent-based post-etch residue clean followed by a solvent/H₂O₂ mixture strip for TiN mask removal. Bath lifetime optimization was also demonstrated.

Abstract: Wafer charging has become an issue since single-wafer wet clean has been introduced and multiple aspects could be potential root causes. In chemistry and DIW process factors, typical process parameters; flow rate and time were re-evaluated. As an alternative solution, dilute NH₄OH could reduce the wafer surface charging. Hardware parts were also investigated and wafer holding chuck-pin material was revealed to become a risk of discharging failure at edge of wafer. Ionizer has been known to discharge wafer surface; however, it is not enough to remove pre-existing charge from post DIW rinsed wafer. Soft X-ray is challenged to remove pre-existing charge and obtained initial positive result.

Abstract: 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.

Abstract: A possible way to realize a 22.5 nm 1⁄2 pitch and beyond BEOL interconnect structures within the low-k material is the partial-trench via first with self-aligned double patterning (SADP) integration approach. A scheme of this BEOL integration stack with the different materials used after patterning is described in Figure 1. In BEOL processing, fluorocarbon-containing plasma is commonly used to pattern silica-based dielectric layers. During the patterning of the low-k dielectric layer, a thin layer of fluoropolymer (CFx-type residues) is intentionally deposited on the dielectric sidewalls and TiN hardmask to ensure anisotropic etching and prevent/minimize dielectric degradation. This polymer layer must be removed from the sidewall and the via bottom prior to the subsequent processing steps to achieve good adhesion and coverage of materials deposited in the etched features. The compatibility requirement is even more stringent for advanced low-k dielectrics, i.e. materials with lower k-value and higher porosity. The post etch residue (PER) amount and properties are specific and depend on the stack structure and the plasma that is used for patterning. The low-k materials and hardmasks that are used in this work are respectively an organo-silicate glass (OSG) type of low-k material with k = 2.4 (~20 % open porosity) and low-stress TiN. Recent results clearly showed the presence of a highly fluorinated layer deposited on the trench sidewalls during the plasma etch based on a fluorocarbon plasma [1-3]. Commodity aqueous cleaning solutions, such as diluted HF, do not efficiently remove the sidewall polymers without etching the underlying layer (lift-off). Therefore, there is a need for commercially available chemicals that can be easily tuned to deal with the different requirements. This study focuses on the use of FOTOPUR® R 2300 mixed with H2O2 for polymer residue removal selectively to other materials (presented in the stack) such as MHM, metals (Cu, W), and porous low-k dielectrics. We will show that TiN etch can be easily tuned by changing the concentration of H2O2.

Abstract: Back end of the line processing requires removal of deposited polymers resulting from etch processes. These polymers typically exist on the whole of the pattern including the dielectric sidewalls and can be removed by wet cleans or a combination of wet cleans and plasma treatments. When a porous dielectric is present these residues cannot be efficiently removed using plasma or certain wet cleans without potentially damaging the underlying porous dielectric layer. Therefore there exists a need for a one-step wet clean that can completely remove the residues without damaging the porous dielectric. Previous work has shown that a combination of a UV pretreatment followed by a wet clean can remove these residues [1]. These residues are composed of CF, -CF₂, and CF₃ groups as described by X-ray photoelectron spectroscopy (XPS). In an effort to improve the manufacturing viability of such a process we have undertaken a study to develop a one-step wet clean for fluoropolymer removal. Utilizing a blanket checkerboard pattern with a model fluoropolymer deposited on a porous low-κ substrate we have demonstrated the one-step wet clean of the aforementioned fluoropolymer while maintaining compatibility with the pristine and etch processed porous low-k dielectric.