For integrated circuit fabrication on 300 mm wafers, copper interconnections cleaning is generally done with single wafer tools. In this study, we focused on the cleaning of aluminum interconnections, on single wafer tool, with a cheap and easy to use chemistry. Aluminum compatibility with diluted HF solutions was first evaluated, then short and efficient cleaning processes were developped for two kind of applications : cleaning after aluminum line etching and cleaning after final dielectric etching over the aluminum pad. It was demonstrated that cleaning efficiency was poor for the shorter process time (20 s), but improved with process time increase, highlighting a lift-off mechanism for polymers removal. Best process was achieved with 40 s of HF 0.2%, that offers a good compromise between polymer removal and lateral recess of the aluminum.

A post-etch residue cleaning formulation, based on balancing the aggressiveness of hydrofluoric acid with its well-known residue removal properties is introduced. In a series of investigations originally motivated by the cleaning challenge provided by high-k dielectric-based residues, a formulation platform is developed that successfully cleans residues resulting from the plasma patterning of tantalum oxide and similar materials while maintaining metal and dielectric compatibility. It is further shown that the fundamental advantages of this solution can be extended to the cleaning of other, more traditional post-etch residues, with no sacrifice in compatibility, as demonstrated by measurements on blanket films and through SEM data.

For 28 nm and beyond, severe specifications in terms of dimensions and materials integrity still drive further cleaning process improvements. As the global “HF budget” drastically decreases with interconnections dimensions, HF solution dilution and process time both decreased stepwise. However, very short recipes with process time shorter than 15s start to suffer from lack of robustness, in particular for the monitoring of inline parameters such as flow-rates and temperature. In this paper, we highlighted that a first matching of silicon oxide consumption was usefull to select temperature and concentration range for the diluted HF solution. High dilution ratio, and “room temperature” (20 °C) were then selected. Variations in cleaning efficiency were analyzed as regard with electrical defects density at three metals levels, then the use of 0.025 %wt. HF, 20 °C, 40 s. was pointed out as the more promising solution for process of record replacement. Process robustness, i.e. inline monitoring data collection and uniformity on wafer should thus be improved thanks to this longer process time and a lower process temperature.

Contact level is the first metal (usually tungsten) connection level between the device and the aluminum or copper interconnects. Depending on the device type (CMOS, memories, photonic device) and technology node, contact patterning is in constant development to improve performance. At the contact cleaning step, we face many new challenges due to the metal or sensitive material exposure with the cleaning chemistry, the decrease of nominal dimensions and the increase of aspect ratio. In particular, new contact clean processes were developed for CMOS devices (28 nm and 14 nm nodes), and photonic devices, in order to be compatible with metal gate or germanium photodiode. In this study, we will compare the efficiency of these new cleaning processes with standard contact clean previously used for CMOS devices from 90 nm down to 45 nm nodes. We will also highlight cleaning efficiency in high aspect ratio structures, and optimized IPA drying capability on a single wafer cleaning tool. (C) 2018 Elsevier B.V. All rights reserved.

This paper investigates the possibility to fine tune a fluorinated solution to dissolve Ta, Zr, or Hf containing residues left after plasma etch, with maximum selectively towards silicon dioxide without corroding Aluminum. In this work amorphous "as dep" HfO2 has been assumed and proven to be a valuable test vehicle to evaluate the chemistry ability to dissolve such residues selectively towards other materials. In solvent/water mixtures, HF doesn't significantly hydrate until water content is predominant in the mixture. Plus, High proton concentration is key to reach a good aluminum protection and significant HfO2 dissolution rate in aqueous fluorinated solutions. By combining these properties an industrial solution has been engineered that achieves good dissolution of Ta, Zr, or Hf based polymers without corroding aluminum.

Porous low-k materials used as insulator for interconnection levels in CMOS devices, are easily damaged during the patterning processes. Pore size characterization after material damage is challenging due to the chemical modification induced by the applied process. Numerical simulation of solvent adsorption on silica and functionalized silica surfaces was used to improve material pore size determination by ellipso-porosimetry, taking into account the modifications of surface/solvent interactions.

: Wetting efficiency of microstructures or nanostructures patterned on Si wafers is a real challenge in integrated circuits manufacturing. In fact, bad or non-uniform wetting during wet processes limits chemical reactions and can lead to non-complete etching or cleaning inside the patterns and device defectivity. This issue is more and more important with the transistors size shrinkage and concerns mainly high aspect ratio structures. Deep Trench Isolation (DTI) structures enabling pixels’ isolation in imaging devices are subject to this phenomenon. While low-frequency acoustic reflectometry principle is a well-known method for Non Destructive Test applications, we have recently shown that it is also well suited for nanostructures wetting characterization in a higher frequency range. In this paper, we present a high-frequency acoustic reflectometry characterization of DTI wetting through a confrontation of both experimental and modeling results. The acoustic method proposed is based on the evaluation of the reflection of a longitudinal acoustic wave generated by a 100 µm diameter ZnO piezoelectric transducer sputtered on the silicon wafer backside using MEMS technologies. The transducers have been fabricated to work at 5 GHz corresponding to a wavelength of 1.7 µm in silicon. The DTI studied structures, manufactured on the wafer frontside, are crossing trenches of 200 nm wide and 4 µm deep (aspect ratio of 20) etched into a Si wafer frontside. In that case, the acoustic signal reflection occurs at the bottom and at the top of the DTI enabling its characterization by monitoring the electrical reflection coefficient of the transducer. A Finite Difference Time Domain (FDTD) model has been developed to predict the behavior of the emitted wave. The model shows that the separation of the reflected echoes (top and bottom of the DTI) from different acoustic modes is possible at 5 Ghz. A good correspondence between experimental and theoretical signals is observed. The model enables the identification of the different acoustic modes. The evaluation of DTI wetting is then performed by focusing on the first reflected echo obtained through the reflection at Si bottom interface, where wetting efficiency is crucial. The reflection coefficient is measured with different water / ethanol mixtures (tunable surface tension) deposited on the wafer frontside. Two cases are studied: with and without PFTS hydrophobic treatment. In the untreated surface case, acoustic reflection coefficient values with water show that liquid imbibition is partial. In the treated surface case, the acoustic reflection is total with water (no liquid in DTI). The impalement of the liquid occurs for a specific surface tension but it is still partial for pure ethanol. DTI bottom shape and local pattern collapse of the trenches can explain these incomplete wetting phenomena. This high-frequency acoustic method sensitivity coupled with a FDTD propagative model thus enables the local determination of the wetting state of a liquid on real structures. Partial wetting states for non-hydrophobic surfaces or low surface tension liquids are then detectable with this method.

Wetting efficiency of microstructures or nanostructures patterned on Si wafers is a real concern in integrated circuits manufacturing. We present here a high-frequency acoustic method which enables the local determination of the wetting state of a liquid on real DTI and TSV structures. Partial wetting states for non-hydrophobic surfaces or low surface tension liquids are detectable with this method. Filling time of TSV structures has also been measured.

The impact of plasma reactive ion etching on hybrid organic/inorganic polymer materials is investigated in detail regarding chemical (composition) and physical (porosity) aspects. Porous low dielectric constant insulating films are used in integrated circuits and these experience plasma etching before the deposition of conductive copper lines. We show that this induces detrimental changes in the film. Notably, chemical composition modifications were characterized by Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR) and depth-profiled by Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS), whereas fine structural changes were analyzed with 1H, 13C, and 29Si solid-state Nuclear Magnetic Resonance (ssNMR). Evolution of surface properties was measured with Contact Angle (CA) analysis, while porosity variations were probed with Ellipsometric Porosimetry (EP). We show how the complementarity of these techniques enables a thorough description of the impact of the etching process on this low-dielectric constant material, which in turn enables recommendations for the manufacture of microelectronic devices.

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.

Porous low-k materials are now widely used as insulator for Back End of Line interconnection levels in CMOS devices from 45 nm down to 28/14 nm nodes.

Photoresist degradation can occur during wet etching processes due to chemicals diffusion through the polymer. The adhesion of the resist is not guaranteed anymore and damage on the resist / material interface appears. This phenomenon is usually monitored by optical methods. However, invisible resist degradation cannot be detected and the physical nature of the resist / material modification remains unknown. A high-frequency acoustic echography method has been developed to overcome these problems and has been performed to study the apparition of blisters in a deep UV photoresist exposed to a Standard Clean 1 solution. This technique allows the quantitative detection of resist degradation even if blisters cannot be seen in the resist. It has also been found that gas pockets appear during blisters formation.

We show that Derjaguin's theory of adsorption can be used to predict adsorption, on bare and Modified surfaces using parameters available to simple experiments. Using experiment and molecular simulation of adsorption of various gases on hydroxylated, methylated, and trifluoromethylated silica, this simple parametrization of Derjaguin's model allows predicting adsorption on any functionalized surface using a minimum set of parameters such as the heat of vaporization of the adsorbate and the Henry constant of the adsorption isotherm. This general yet simple scheme constitutes a powerful tool as it avoids having to carry out tedious and complex adsorption measurements.

Wet etching in photoresist presence is commonly used in MEMS or integrated circuits manufacturing: metal gates [1], or gate oxides patterning [2]. Nonetheless the resist can’t stand a too long exposure to wet chemicals. Indeed, the liquids diffuse through the resist. Then the polymer enters a plasticizing sequence. It swells under the action of polar water and etchant molecules that break the cohesive hydrogen bonds between the polymer chains. The resist stress increases till fractures and blisters appears (figure 1). Hence these phenomena have been characterized by various acoustic means described hereby. First method consists in using a high-frequency echography principle [3]. A ZnO transducer, sputtered on the backside of the silicon wafer emits a 2GHz acoustic wave. The longitudinal wave reflection occurs at the interface between the silicon and the medium on the wafer frontside enabling its characterization by monitoring the transducer electrical impedance (figure 3). In the case of a silicon / air interface, the acoustic wave reflection is total. When air is replaced by water, the reflection is partial and the reflection coefficient value is 0.86. These reflection properties will be modified in the presence of a thin TiN layer coated with a 248nm deep UV resist. As the resist thickness (210 nm) is thin compared with the acoustic wavelengths in the different materials (micrometer range), reflections at each interface cannot be separated (silicon / resist and resist / upper medium) so only one total reflection occurs in the presence of air. Then, the reflection coefficient is measured with water on the resist. Without any resist damage, the reflection coefficient changes from 0.86 to 0.765. This latter value is then modulated by the resist blisters amount due to the modification of the mechanical properties of the silicon / resist interface. Measurements are performed on wafers exposed to SC1 (Standard Clean 1) solutions for different durations (figure 1). The reflection coefficient increases with the blisters apparition (figure 4). By determining the ratio of blisters area on optical microscope images of the resist, the reflection coefficient is theoretically calculated for different blisters mechanical properties (solids, liquids and gas). Experimental and theoretical values perfectly match in the case of gas. This result let us think that gas pockets appeared in the resist during blisters formation. The method sensitivity is excellent and mainly depends on the high contrast between gas and water acoustic impedances. A comparison with two other complementary technics will be made. First, picosecond acoustic will characterize the resist adhesion loss. Its principle is similar to a sonar. The acoustic wave into the sample is supplied by a tunable laser [4], and an echo is generated at each interface enabling its characterization. Finally the scanning acoustic microscopy will monitor the resist blister apparition with a thicker resist. This technic is commonly used to monitor wafer bonding voids in 3D integrated circuits assembly [5]. Conclusion Photoresist degradation occurs during long exposure to wet etching. Resist delamination from substrate and blisters appear after a certain contact duration. This latter is shorter with thin resist, which occurs more and more along the integrated circuits node evolution to maintain photolithography optical requirements. Three acoustic methods have been compared to monitor this degradation. Results show these methods are far better than optical microscopy to detect the resist degradation starting point. References [1] M. Foucaud, solid state phenomena, vol.195, pp58-61 [2] P. Garnier, solid State Phenomena, 2008; 134:71-74 [3] R. Dufour, Langmuir, 2013, 29(43) [4] A.Devos, Ultrasonics Symposium, 2006, pp 564-567 [5] H .Moriceau, Adv. Nat. Sci.: Nanosci. Nanotechnol. 2010 Figure 1

Ellipsometric porosimetry (EP) experiments are performed to obtain the adsorption isotherms of water, methanol, and toluene on pristine and damaged SiOCH porous materials. The use of gaseous adsorbates with different polarities, sizes, and surface tensions enables us to probe their affinity with such organosilica surfaces. Using reference t-curves obtained from Statistical Mechanics molecular simulations, we discuss the ability of the MicroPore analysis (MP) method to accurately estimate micropore sizes from EP measurements by comparing them with the mean pore sizes obtained using positron annihilation lifetime spectroscopy (PALS) and grazing incidence small angle X-ray scattering (GISAXS). We also report accessible microporous volumes estimated from the t-plot method used with the reference t-curves obtained by means of molecular simulation. We show that EP characterization of microporous films combined with the MP and t-plot methods can be improved by taking into account the effect of the chemical nature of the pore surface on the variation of the adsorbed thickness (t-curve).

In this paper, wet cleaning solution compatible with cobalt are investigated to achieve low Co etching rate on blankets film and no film attack on patterned 14nm wafer after line and via etching. Proposed solutions are compared to conventional wet cleaning solutions.

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 N2plasma is not efficient enough to suppress the residue completely [6], and the CH4treatment proposed in [5] may be difficult to implement for 14 nm node, thus an efficient wet strip and clean provides a better solution.

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.

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.