A dramatic increase in the Al2O3 atomic layer etching (ALE) rate versus time was demonstrated using sequential, self-limiting exposures of hydrogen fluoride (HF) and trimethylaluminum (TMA) as the reactants with no purging. The normal purging expected to be required to prevent chemical vapor etching or chemical vapor deposition (CVD) is not necessary during the Al2O3 ALE. This purgeless, rapid atomic layer etching (R-ALE) was studied from 250 to 325 °C using various techniques. In situ quartz crystal microbalance (QCM) measurements monitored Al2O3 R-ALE at 300 °C. The Al2O3 R-ALE process produced linear etching versus number of R-ALE cycles. Each HF exposure fluorinates the Al2O3 substrate to produce an AlF3 surface layer. Each subsequent dose of TMA then undergoes a ligand-exchange transmetalation reaction with the AlF3 surface layer to yield volatile products. Using reactant partial pressures of HF = 320 mTorr and TMA = 160 mTorr, the fluorination and ligand-exchange reactions produced a mass change per cycle (MCPC) of −32.1 ng/(cm2 cycle) using sequential, 1 s exposures for both HF and TMA with no purging. This MCPC equates to a thickness loss of 0.99 Å/cycle or 0.49 Å/s. Comparison experiments using the same reactant exposures and purge times of 30 s yielded nearly identical MCPC values. These results indicate that the etch rates for Al2O3 R-ALE are much faster than for normal Al2O3 ALE because of shorter cycle times with no purging. Smaller MCPC values were also observed at lower reactant pressures for both Al2O3 R-ALE and Al2O3 ALE. The QCM studies showed that the Al2O3 R-ALE process was self-limiting versus reactant exposure. Ex situ spectroscopic ellipsometry and x-ray reflectivity (XRR) measurements revealed temperature-dependent etch rates from 0.02 Å/cycle at 270 °C to 1.12 Å/cycle at 325 °C. At lower temperatures, AlF3 growth was the dominant mechanism and led to an AlF3 atomic layer deposition (ALD) growth rate of 0.33 Å/cycle at 250 °C. The transition temperature between AlF3 growth and Al2O3 etching occurred at ∼270 °C. XRR scans showed that the Al2O3 ALD films were smoothed by Al2O3 R-ALE at temperatures ≥270 °C. Additionally, patterned wafers were used to compare Al2O3 R-ALE and normal Al2O3 ALE in high aspect ratio structures. Scanning electron microscope images revealed that the etching was uniform for both processes and yielded comparable etch rates per cycle in the high aspect ratio structures and on flat wafers. The HF and TMA precursors were also intentionally overlapped to explore the behavior when both precursors were present at the same time. Similar to ALD, where precursor overlap produces CVD, precursor overlap during Al2O3 ALE leads to AlF3 CVD. However, any AlF3 CVD growth that occurs during precursor overlap is removed by spontaneous AlF3 etching during the subsequent TMA exposure. This spontaneous AlF3 etching explains why no purging is necessary during R-ALE. R-ALE represents an important advancement in the field of thermal ALE by producing rapid etching speeds that will facilitate many ALE applications.

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The growth mechanism of the passivation layer in the cryogenic process used for silicon deep etching is explored experimentally in an inductively coupled plasma reactor. In particular, the role of SiF4 etching by-products on the SiOxFy layer deposition is investigated. The deposition of a SiOxFy layer using SiF4 and O2 gases is studied by in situ ellipsometric spectroscopy in different experimental configurations to devise the deposition mechanism: SiF4/O2 plasma mixture, alternation of SiF4 plasma and O2 plasma steps and alternation of SiF4 flow without plasma and O2 plasma steps. The refractive index and the thickness of the deposited layer are measured for different substrate temperatures, from −125 °C to 20 °C. Although some of the passivation layer is removed during the wafer warm up, a residual amount remains at the surface. The deposited SiOxFy layer forms more efficiently at low temperature with an optimal temperature of −100 °C in our experimental conditions. The passivation layer was etched by a SF6 plasma without bias versus the deposition temperature, to evaluate its resistance to plasma etching steps. The passivation layer was analyzed by ex situ EDX and XPS. We investigated the role of SiF4 low temperature physisorption in the formation of the passivation layer on the sidewalls of the features that are being etched, which are not submitted to ion bombardment. It is shown that physisorption of SiFx species play an important role because their residence time at the surface is longer, thus increasing the probability of reaction with oxygen.

Dielectrophoretic (DEP) phenomena have been explored to great success for various applications like particle sorting and separation. To elucidate the underlying mechanism and quantify the DEP force experienced by particles, the point-dipole and Maxwell Stress Tensor (MST) methods are commonly used. However, both methods exhibit their own limitations. For example, the point-dipole method is unable to fully capture the essence of particle-particle interactions and the MST method is not suitable for particles of non-homogeneous property. Moreover, both methods fare poorly when it comes to explaining DEP phenomena such as the dependence of crossover frequency on medium conductivity. To address these limitations, the authors have developed a new method, termed volumetric-integration method, with the aid of computational implementation, to reexamine the DEP phenomena, elucidate the governing mechanism, and quantify the DEP force. The effect of an electric double layer (EDL) on particles' crossover behavior is dealt with through consideration of the EDL structure along with surface ionic/molecular adsorption, unlike in other methods, where the EDL is accounted for through simply assigning a surface conductance value to the particles. For validation, by comparing with literature experimental data, the authors show that the new method can quantify the DEP force on not only homogeneous particles but also non-homogeneous ones, and predict particle-particle interactions fairly accurately. Moreover, the authors also show that the predicted dependence of crossover frequency on medium conductivity and particle size agrees very well with experimental measurements.

including nanotechnology, optoelectronics, photonics, microfluidics, sensing, biotechnology, and separations. [8][9][10][11][12][13][14][15][16] Among the different CVD techniques to deposit polymer thin films, initiatedchemical vapor deposition (iCVD) involves the vapor phase delivery of at least two precursors (a free radical initiator and a monomer) into a vacuum chamber. [17] The vapor flow direction can either be parallel (most of the works published in the literature uses this configuration) or perpendicular to the substrate. iCVD operates according to a free radical polymerization carried out in absence of solvent. The activation of the initiator occurs selectively through an array of heated filaments typically in the temperature range of 200-400 °C producing the primary radicals. The monomers are believed to be preserved from thermal degradation and are condensed on a cooled substrate, usually kept at a temperature lower than 50 °C to promote their adsorption, where they react to generate a polymer. This reaction pathway leads ultimately to the simultaneous formation of welldefined polymer chains and polymeric thin films that can be extremely conformal to the surface of the substrate. iCVD has been extremely successful in depositing a wide variety of polymers including those that are not easily soluble in solvents and can thus be only deposited using this technique. [18,19] Several studies were devoted to the determination of the growth mechanisms during an iCVD process, especially to understand the impact of process parameters on the growth Polymer Thin Films Initiated-chemical vapor deposition (iCVD) is a very promising technique whichhas demonstrated the ability to deposit a large variety of polymers that can be integrated in micro-nanotechnology applications. However, studies on the underlying growth mechanisms responsible for the formation of these thin films remain scarce in the literature. This work shows that the iCVD growth follows surprisingly two regimes: in the first stage of the growth, the deposition rate is relatively slow then increases with the deposition time until a linear growth is reached. The presence of these two growth regimes can be interpreted by taking into account, as the iCVD growth progresses, that the synthesized polymer chains help the monomer adsorption on the substrate which locally increases the concentration of monomers available for the polymerization and thus the growth rate. This increase of the local concentration of monomer consistently correlates with the formation of polymer chains with higher molar mass.