Solid State Phenomena Vol. 187

Abstract: Light emission in sound-irradiated liquids, known as Sonoluminescence (SL), is associated with the phenomenon of cavitation that affects wafer damage during megasonic processing of wafers. It has been shown that the intensity of SL can be substantially decreased through the dissolution of carbon dioxide in deionized water. However, such dissolution decreases the pH to roughly 4.0, which is not very desirable for the removal of contaminant particles. This paper reports two chemical systems that are capable of taking advantage of the effect of CO₂ while allowing the use of slightly higher pH values. Specifically, NH₄OH/CO₂ and NH₄HCO₃/dilute HCl systems have been shown to be capable of well controlled reduction in SL at pH 5.7 or 7.0. In order to test whether the free radical scavenging ability of CO₂ may be responsible for its strong SL-inhibitory effect, the effect of a well known free radical scavenger, dimethyl sulfoxide (DMSO), on SL produced in DI water has been investigated.

Abstract: When fabricating flat panel displays (FPDs), cleaning process is important in the preparation of next steps. A megasonic system for cleaning FPD which can remove smaller particles with lower power and lower consumptions of chemical and UPW was designed and manufactured. The anti-resonance frequency of the lead zirconate titanate (PZT) actuator was measured, and the value was 992 kHz. The impedance graph of the cleaning system was analyzed using commercial finite element method (FEM) analysis software Ansys, and the obtained value was 992 kHz. This agreed well with the measured value of 989 kHz. The performance of the developed system was evaluated by comparing the acoustic pressures with the conventional product. As a result, the acoustic pressures of the developed system were three times larger than that of the commercial system (conventional type: 13.9 kPa, the developed one: 43.1 kPa). In addtion, the PRE test was performed and the 83% particles were removed using 64% reduced power and 80% reduced chemical consumptions.

Abstract: An important problem in megasonic cleaning is the nucleation process of bubbles, which act as the cleaning agents. A fundamental understanding of this nucleation process will help to optimize the cleaning parameters for future applications to achieve damage free cleaning. In this work, we use quantitative stroboscopic Schlieren imaging to study the interaction of nucleating bubbles with a travelling acoustic wave. The advantage of this method is that it is non-interfering, meaning that it does not disturb the bubble nucleation. It is revealed that nucleation mechanism is a 2 step process, where a regime of slow bubble growth due to rectified diffusion is subsequently followed by a transient cavitation cycle, where bubbles grow explosively. The latter is accompanied by broadband acoustic emission and enhanced thermal dissipation, leading to the occurrence of thermal convection visible in the Schlieren images.

Abstract: For the 45 nm interconnect technology node, porous dielectric materials (p-SiOCH) have been introduced, leading to complex integration issues due to their high sensitivity upon FC etching and ashing plasma exposure [1, 2]. Thanks to Metallic hard mask (MHM) integration high selectivities towards dielectric materials (>100:1) can be reached and minimizes exposure of p-SiOCH films to ashing plasmas. However MHM such as TiN generates other issues such as i) metal contamination in the patterned structures and ii) growth of metal based residues on the top of the hard mask [3, 4, 5]. The residues growth, which is air exposure time dependent, directly impacts the yield performance with the generation of via and line opens [.

Abstract: Atomic force microscope (AFM) with inclined sample measurement and hydrophobic functionalized AFM probe was used to visualize the sidewall of low-k pattern and allowed to characterize the hydrophobic characteristics on the sidewall after low-k etch. To functionalized the AFM probe, 1H,1H,2H,2H-Perfluorodecyltrichlorosilane (FDTS) as a hydrophobic film was coated on an AFM probe. Because of the magnitude of the phobic-phobic interaction force and the tip forced to make a phase shift. Using this technique the visualization and characterization of the etch residue on the low-k sidewall can be successfully performed. It is shown that the investigation toward an effective chemical clean for the etch residue removal could be applicable.

Abstract: Wet chemical plasma etch residue removal is a promising alternative to low-k dielectric degrading plasma cleaning processes. With decreasing feature dimensions the wetting behavior of the liquid on low energetic surfaces present after dielectric patterning will be an important issue in developing wet cleaning solutions. High surface energy liquids may not only be unable to wet low energetic surfaces, but can also cause nonwetting of small structures or pattern collapse. The improvement of the wetting behavior of a cleaning liquid by lowering its surface energy by the addition of surfactants is the strategy followed in this study. We show that with choosing the appropriate rinsing solution a wet chemical process using surfactant aided cleaning solutions compatible to the materials used in BEOL (porous low-k, copper, barriers) can be found. The results show a distinct improvement of the wetting behavior of the modified solutions on several low energetic solid surfaces like copper or polymers deposited during dry etching.

Abstract: In back-end of line processing, the polymer deposited on the dielectric sidewalls during the etch 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 short plasma treatment and 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 efficiently remove this residue. Furthermore, aqueous cleaning solutions is not efficient to achieve a complete removal without etching the underlying layer. Hence appropriate wet clean chemistries are needed to dissolve/decompose these polymers without etching the dielectric. On the other hand, analytical techniques available for direct characterization of sidewall polymer are limited. For a fast screening of potential chemistries capable of dissolving/removing polymer residues generated during the low-k etch, a fluoropolymer deposited on a blanket, checkerboard low-k substrate was used as a model polymer. In our recent study [, using X-ray photoelectron spectroscopy (XPS), it was shown that the polymer was composed of CF, CF₂, and CF₃ groups. This model polymer was found to be very similar to the polymer residue generated during the etch of the low-k stack using similar plasma. The present study mainly focused on the effect of UV treatment and the concentration of active component in wet clean solution on the structure change of the polymer and the enhancement of polymer removal.

Abstract: For the 32nm logic technology and beyond, more stringent specifications in terms of dimensions and materials integrity continue to drive the cleaning process improvements. In this paper, post-etch wet cleaning was optimized in order to address CD loss issues and metal hard mask cleaning improvement in a Trench First Hard Mask (TFHM) backend architecture. Based on materials compatibility tests and electrical results, this wet clean process should also be fully compatible with a Via First Trench Last (VFTL) architecture.

Abstract: In this paper we review the effects of the plasma descum steps used in current process flows for the fabrication of Cu interconnects embedded in polymer, paying particular attention to polymer residues that are not easily removed in a gentle oxygen only plasma.

Abstract: All-wet processes are gaining a renewed interest for the removal of post-etch photoresist (PR) and Bottom AntiReflective Coating (BARC) in the back-end-of-line (BEOL) semiconductor manufacturing, as plasma ash, traditionally used to remove the PR and BARC layer after etch, cause damage to the low-k dielectric. This study investigates the modification of 193 nm post-etch PR and BARC layer by UV irradiation, that can be used as an intermediate step to enhance PR and BARC wet strip by O₃/H₂O.