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This work focuses on capillary-induced collapse of high-aspect-ratio silicon nanopillars. Modification of the surface chemistry is demonstrated to be an efficient approach for reducing capillary forces and consequently reduce pattern collapse. Special effort is spent on determination of the wetting state of chemically modified surfaces as complete structure wetting is of utmost importance in wet processing. In light of this, an ATR-FTIR based method has been developed to unambiguously distinguish between wetting and non-wetting states.

Superhydrophobic surfaces are highly promising for self-cleaning, anti-fouling and anti-corrosion applications. However, accurate assessment of the lifetime and sustainability of super-hydrophobic materials is hindered by the lack of large area characterization of superhydrophobic breakdown. In this work, attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) is explored for a dynamic study of wetting transitions on immersed superhydrophobic arrays of silicon nanopillars. Spontaneous breakdown of the superhydrophobic state is triggered by in-situ modulation of the liquid surface tension. The high surface sensitivity of ATR-FTIR allows for accurate detection of local liquid infiltration. Experimentally determined wetting transition criteria show significant deviations from predictions by classical wetting models. Breakdown kinetics is found to slow down dramatically when the liquid surface tension approaches the transition criterion, which clearly underlines the importance of more accurate wetting analysis on large-area surfaces. Precise actuation of the superhydrophobic breakdown process is demonstrated for the first time through careful modulation of the liquid surface tension around the transition criterion. The developed ATR-FTIR method can be a promising technique to study wetting transitions and associated dynamics on various types of superhydrophobic surfaces. ispartof: SCIENTIFIC REPORTS vol:8 issue:1 ispartof: location:England status: published

In semiconductor manufacturing, potential wetting issues with aqueous chemistries are becoming a concern as feature dimensions are continuously scaled down and novel materials with different wetting properties are introduced in new technology nodes. The wetting behavior of silicon nanopillars with different dimensions and surface modifications has been studied using static contact angle, decoration by etching, and attenuated total reflection infra-red spectroscopy (ATR-FTIR). The contact angle measurements showed a consistent deviation from the classic wetting models for patterned substrates with an hydrophilic surface termination. Under these conditions the decoration and ATR-FTIR studies gave evidence for partial wetting, with residual gas lasting for more than 30 min. It is proposed that this was resulting from the formation of long-lasting surface nanobubbles localized in-between or at the bottom of nanopillars. On the other hand the residual gas volume estimated by ATR-FTIR seemed too small to explain the contact angle deviations. It is proposed that the apparent extension of the superhydrophobic regime to lower contact angles resulted from modifications of the wettability of the surface of nanopillars caused by the manufacturing process. Both the formation of nanobubbles and the extension of the superhydrophobic regime may present challenges for aqueous cleaning in semiconductor manufacturing.

In semiconductor manufacturing, potential wetting issues are becoming a concern as feature dimensions are continuously scaled down and novel materials with different wetting properties are introduced in new technology nodes. The wetting behavior of silicon nanopillars with different dimensions and surface modifications has been studied using static contact angle (θ), attenuated total reflection infra-red spectroscopy (ATR-FTIR), and decoration by etching. The contact angle measurements showed a consistent deviation from the classic wetting models for patterned substrates with an hydrophilic surface termination (60°<θ < 80°). The ATR-FTIR and decoration studies gave evidence for partial wetting under these conditions, resulting from the formation of long-lasting nanobubbles. However the residual gas volumes estimated by ATR-FTIR were too small to explain the contact angle deviations. It is proposed that the apparent extension of the superhydrophobic regime to lower contact angles resulted from modifications caused by the manufacturing process to the wettability of the surface of nanopillars.

In situ characterization of the underwater stability of superhydrophobic micro- and nanostructured surfaces is important for the development of self-cleaning and antifouling materials. In this work, we demonstrate a novel attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy-based method for large-area wetting characterization of silicon nanopillars. When air is present in between the structures, as is characteristic of the Cassie-Baxter state, the relative intensities of the water bands in the absorption spectrum change because of the wavelength-dependent attenuation of the evanescent wave. This phenomenon enables unambiguous identification of the wetting state and assessment of liquid impalement. Using mixtures of isopropanol and water with different concentrations, the breakdown of superhydrophobic states and the wetting hysteresis effects are systematically studied on uniform arrays of silicon nanopillars. A transition from the Cassie-Baxter to Wenzel state is observed when the isopropanol concentration exceeds 2.8 mol %, corresponding to a critical surface tension of 39 mN/m. Spontaneous dewetting does not occur upon decreasing the isopropanol concentration, and pure water can be obtained in a stable Wenzel state on the originally superhydrophobic substrates. The developed ATR-FTIR method can be promising for real-time monitoring of the wetting kinetics on nanostructured surfaces. ispartof: Langmuir vol:33 issue:15 pages:3601-3609 ispartof: location:United States status: published

With the downscaling of devices, due to device geometry shrinkage, the total number of cleaning steps has increased dramatically. As a result, the number of drying cycles after cleaning has increased as well. As the device shrinks with the integration density increase, it is noteworthy that a perfect drying efficiency is mandatory to obtain a high performance device [. Basically, the mechanism of wafer drying in semiconductor industry can be explained as: first reducing the amount of liquid on the wafer surface by mechanical forces. There are some approaches for removing the liquid such as spinning, high pressure gas blowing by nozzle or air-jet, vertical withdrawal from the liquid bath, using surface gradient tension and so on [2]. Second: if the mechanical forces in the liquid removal part are not sufficient for drying and some droplets or a thin liquid layer remain on the wafer surface, complete drying will be achieved by evaporation of the remaining layer on the wafer. After this evaporation step, known as state transformation, the wafers will be completely dried. Evaporation of the remaining liquid layer is the main mechanism for generating drying defects (watermarks, residues, particles, and etc.)[3]. In this study, we propose a new methodology for semiconductor wafer drying based on a high-pressure gas flow. In comparison to conventional drying tools, the new drying set up combines high speed drying (wafer drying time down to 2 sec at 150mm.s-1) and a low number of added drying defects.

Following Moores scaling law, the transistor source and drain area become shallower and higher doped regions. As a consequence the limitations of substrate and dopant loss during cleaning become more stringent. For a better understanding, highly B, As and P doped blanket substrates, either prepared by ion implantation or by EPI growth, are studied. Substrate and dopant loss as a function of time and different HF etching conditions is monitored by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and additional techniques like Spectroscopic Ellipsometry (SE), .... It is shown that in general, the Si etching is dependent of the position of the Fermi level. More remarkably, the junction (4 nm) of a non-annealed heavily As or P doped substrate is completely removed after less than 20 min of etching in HF. This process is related to enhanced etch rates because of the amorphization of the substrate.

Single-wafer cleaning based on megasonic nozzle systems can be used for removing nano-particles. An optimized cleaning process must deliver a high degree of cleaning uniformity with a minimal amount of structural damage. However, the cleaning liquid is confined to a sonicated liquid jet, which is ejected by the nozzle. As a result, a high degree of complexity is introduced to the cleaning process due to the strong interdependencies between acoustic, electric and hydrodynamic characteristics of such systems. In the present work, the influence of the gas content of the cleaning liquid on the performance of a 1 MHz nozzle system is investigated and related to the intrinsic properties of the water jet. Cleaning tests are performed and the cleaning results are correlated to the electrical responses of the driving transducer. The electrical response depends both on the gasification of the liquid and the occurrence of acoustic reflections. Furthermore, Schlieren- and Sonoluminescence-imaging of the cleaning system are performed. The imaging techniques can identify the impact of bubbles on the propagation of acoustic waves and the resonant excitation of cleaning cavitation throughout the liquid column.

Cleaning of nano-particles is becoming a major challenge in semiconductor manufacturing as efficient particle removal must be achieved without substrate loss and without damage to fragile structures. In this work cleaning performance and structural damage by a mixed fluid-jet technique were evaluated and directly compared to the performance of several megasonic systems. The test vehicles were hydrophilic Si wafers contaminated with 78-nm SiO2 particles and 70-nm poly-gatestack line patterned wafers. The results showed a broader process window for particle removal without damaging for the mixed fluid-jet technique compared to the megasonic systems.

In this paper, a single wafer linear IPA vapour based vertical drying technique is presented. Using salt residue tests the performance of this technique is evaluated and compared to spin drying. The equivalent film thickness of evaporating liquid is below 0.05µm for blanket wafers, which is two orders of magnitude less than with spin drying. It is also shown that the presence of surface topography (200nm high TEOS features on Si covered with a chemical oxide) does not significantly influence the drying performance. A study of the process window shows that for the setup evaluated in this work best performance is achieved when the IPA/N2 flow rate is above 20 liters per minute and the drying speed is below 8 mm/s. With a manual prototype already very good particle performance is demonstrated.

This study focuses on the analysis of the forces and moments acting on a particle to reveal the particle-removal mechanisms during a scrubbing process. The brush-asperities/substrate contact geometry during scrubbing is first investigated. The forces and moments under different lubrication modes are then determined by means of a mixed theoretical-experimental method. Finally, the analysis of the forces and moments is used to explain the experimental results and to find out the particle-removal mechanisms.

Establishing a cost-effective technology for the metallization of through-Si vias (TSV) is an important factor in the realization and volume manufacturing of 3D-stacked integrated circuits (3D-SIC). Cu electroplating, which is the preferred technique, should provide not only a void-free TSV fill, but also short filling time and small overburden. The duration of the plating process is a significant contributor to the overall 3D process cost, and thus needs to be minimized. The overburden, the thickness of the material deposited on the top surface of the wafer, has to be limited for compatibility with the following processing steps (e.g. chemical mechanical polishing, CMP). In this paper we report on Cu plating of TSV-s with a thin Ta film on the field. The thin Ta film is sputtered on top of the Ta barrier/Cu seed, and inhibits Cu plating outside the TSV-s. We show that the use of this Ta-cap and in situ electrochemical monitoring techniques leads to significant savings in plating and polishing time, and thus savings in manufacturing costs of 3D-stacked integrated circuits.

Publisher Summary In this chapter, the performance of several drying techniques commonly used in the semiconductor manufacturing industry is evaluated. This is done by measuring the residues on a wafer onto which a solution containing metal salts acting as tracer elements has been dispensed and dried. To correctly interpret the experimental data, the results are compared with predictions from a theoretical model. This model assumes two distinct mechanisms for deposition: adsorption and evaporative deposition. The first mechanism is a result of attractive interactions between the contaminant and the wafer surface, while the second mechanism is due to liquid evaporation during drying. For the latter case, the evaporated film thickness is introduced as a figure of merit for the drying process under study. In the tests, tests, spin drying was compared with two types of Marangoni based drying: on a vertically moving wafer and on a horizontally rotating wafer. The results show that for spin drying two consecutive phases occur: during the first seconds of spinning convective removal of liquid is the dominant mechanism, followed by a phase where evaporation takes over. This behavior is confirmed by models reported in the literature describing photo-resist coating. The amount of liquid evaporating during spin drying is inversely proportional to the square root of the rotation speed. This suggests that entrainment of liquid by the gas flow over the wafer surface is the dominant mechanism for evaporation. This finding is in agreement with fluid dynamics models describing the flow of gas entrained with a rotating substrate.

A novel fast drying method for single wafer wet cleaning is proposed. The water-mark free drying method is based on an efficient interaction between Marangoni forces and rotational forces. The method is shown to yield excellent particle performance.

Dynamics of the evaporative drying of ultrapure water (UPW) droplets on a hydrophobic Si surface in a controlled ambient is studied. A quantitative study of the watermarks (WM) residue volume and mass is performed from low to high ambient humidity. The effects of oxygen in the gas phase and dissolved O2 concentration in UPW are investigated for different levels of ambient humidity. The shape of the drying residue on surface is studied to estimate the mechanism of residual colloids/particles deposition in presence of different ambient conditions. Our quantitative study on WM formation in different ambient humidity showed a linear increase in drying residue mass as a function of the initial UPW droplet volume.

In this work a methodology and metrology for the Si substrate loss characterization during cleaning and etching of Si semiconductor substrate has been developed. Using this methodology, the substrate loss in different HF based cleaning solutions can be investigated, both in situ and ex situ. The etching mechanism in different HF mixtures is studied, where the effect of dissolved O2, illumination, free F-ions and additives can be explored. Etch rates are determined ex situ by measuring the Si concentration as function of time with Inductively Coupled Plasma - Mass Spectrometry (ICP-MS). By combining both electrochemical and ICP-MS data, the number of electrons n involved in the electron transfer reaction are determined both in darkness and illumination. Results confirm the existing Si etching mechanism under illumination, with n=2. It is shown that in darkness a low etch rate is observed, and even under deoxygenated HF conditions pointing to some chemical etching mechanism.

To ensure high device yields, wafer surface contamination and defects must be monitored and controlled during the entire process of semiconductor manufacturing. Particle surface concentrations on the wafers, mostly related to chemical mechanical polishing (CMP) processes, must be kept at the lowest possible levels. Brush scrubber cleaning has the potential to achieve this goal. However, the particle removal mechanisms are still under discussion especially the removal of nano-sized particles. This paper investigates the interactions between the particle, the brush and the wafer surface and explores the potential and limitations of the brush scrubbing technique. Furthermore the effect of the various brush/wafer parameters on the particle removal efficiency (PRE) is studied. From a mechanistic viewpoint it is shown that brush scrubbing acts in a mixed lubrication regime. From an extensive analysis of the relevant forces and moments it can be concluded that in the hydrodynamic lubrication regime, particles ar...

Brush scrubbers are among the most commonly used instruments for wafer-cleaning applications nowadays. However, the removal mechanisms of nanosized particles are far from clear, especially because no direct experimental data are available to backup theoretical models in the literature. This study combines a theoretical approach based on a force analysis with an experimental study of the removal of nanosized slurry particles. In the theoretical part, all forces affecting the adhesion and the removal of particles are evaluated to determine which are dominant in two extreme removal mechanisms: lifting and rolling. In the experimental part, the removal efficiency of 34nm SiO2 particles is investigated by using the haze approach. Based on a study of the aging of contaminated wafers, conditions are selected where no chemical bonds are formed between a particle and a substrate. Force analysis and experimental observations both show that nanosized particles cannot be lifted directly by a brush. Instead, rolling s...