The energy distribution of ballistic electrons in a dc/rf hybrid parallel-plate capacitively coupled plasma reactor was measured. Ballistic electrons originated as secondaries produced by ion and electron bombardment of the electrodes. The energy distribution of ballistic electrons peaked at the value of the negative bias applied to the dc electrode. As that bias became more negative, the ballistic electron current on the rf substrate electrode increased dramatically. The ion current on the dc electrode also increased.
One of the most challenging and recurring problems when modeling plasmas is the lack of data on the key atomic and molecular reactions that drive plasma processes. Even when there are data for
Atomic layer etching (ALE) is a promising technique that can solve the challenges associated with continuous or pulsed plasma processes—trade-offs between selectivity, profile, and aspect ratio dependent etching. Compared to silicon, oxide, and other materials, atomic layer etching of silicon nitride has not been extensively reported. In this paper, the authors demonstrate the self-limited etching of silicon nitride in a commercial plasma etch chamber. The process discussed in this paper consists of two sequential steps—surface modification in hydrogen plasma followed by the removal of modified layers in fluorinated plasma. In addition to the ALE characteristics, the authors also demonstrate that the process is anisotropic and the selectivity to oxide is >100. Although the saturated etch rate of one monolayer per cycle could not be attained, self-limited etching of silicon nitride still enables us to incorporate the benefits of atomic layer etching such as an absence of isodense bias and an extremely high selectivity to oxide into practical etch applications.
We
undertake a dielectric breakdown failure analysis of thin hexagonal
boron nitride (h-BN) by conduction atomic force microscopy. The breakdown
field is 21 MV cm–1 for 3 nm-thick h-BN, and the
breakdown voltage statistics follows a tight monomodal Weibull distribution,
indicating the material suitability as a gate dielectric. Breakdown
effects extend over an area of ∼100 nm diameter and evolve
by defect generation in the h-BN, with increasing conductance under
repeated stressing; but the breakdown current–voltage (I–V) curves differ from conventional
ultrathin SiO2 and HfO2 films. Specifically,
there are indications that 2D layering is influencing the breakdown
as follows: (i) Fowler–Nordheim fitting of successive I–V curves after stressing often
proceeds in discrete monolayer thickness values of ∼0.3 nm,
an effect that we propose arises from electrical “shorting”
between adjacent layers, and (ii) the Weibull slope decreases as film
thickness increases, indicating that the defect generation is not
random but occurs preferentially at specific locations.
This study investigates the resistive switching characteristics and underlying mechanism in 2D layered hexagonal boron nitride (h-BN) dielectric films using conductive atomic force microscopy. A combination of bipolar and threshold resistive switching is observed consistently on multi-layer h-BN/Cu stacks in the low power regime with current compliance (Icomp) of less than 100 nA. Standard random telegraph noise signatures were observed in the low resistance state (LRS), similar to the trends in oxygen vacancy-based RRAM devices. While h-BN appears to be a good candidate in terms of switching performance and endurance, it performs poorly in terms of retention lifetime due to the self-recovery of LRS state (similar to recovery of soft breakdown in oxide-based dielectrics) that is consistently observed at all locations without requiring any change in the voltage polarity for Icomp ~1–100 nA.
Atomic-layer
etching (ALE) is a technique that removes thin layers
of material using sequential self-limiting reactions and is considered
to be one of the most promising techniques for achieving the low-process
variability necessary in the imminent atomic-scale era of semiconductor
device fabrication. Here, a theoretical investigation of the ALE of
organic polymer surfaces using oxygen pulses has been performed, by
means of density functional theory calculations. Experimental evidence
shows that ion bombardment of polymer surfaces results in carbon-abundant
layers, which are formed as a competition between two opposite effects,
the breaking of C–H and C–C bonds, which leads to either
structural evolution or sputtering of the polymer surface. Cognizant
of that, we develop appropriate polymer surface models, first, to
investigate whether the adsorption of oxygen on organic surfaces can
be rendered self-limiting, as required in ALE and, second, to establish
the conditions for obtaining controlled, self-limiting etching of
surface carbon atoms. Our results show that, indeed, for large oxygen
flux densities, atomically controlled etching can be obtained in the
form of desorption of different carbonate species. We quantify the
etching process through both the oxygen flux density and the initial
kinetic energy of the impacting oxygen atoms. On the basis of a saturated
carbon surface model, the theoretical maximum etch rate was estimated
to be 0.51 ± 0.05 Å/cycle (4.94 ± 0.1 ng/cm2·cycle), which matches the range of maximum experimental values.
Atomic or layer by layer etching of silicon exploits temporally segregated self-limiting adsorption and material removal steps to mitigate the problems associated with continuous or quasicontinuous (pulsed) plasma processes: selectivity loss, damage, and profile control. Successful implementation of atomic layer etching requires careful choice of the plasma parameters for adsorption and desorption steps. This paper illustrates how process parameters can be arrived at through basic scaling exercises, modeling and simulation, and fundamental experimental tests of their predictions. Using chlorine and argon plasma in a radial line slot antenna plasma source as a platform, the authors illustrate how cycle time, ion energy, and radical to ion ratio can be manipulated to manage the deviation from ideality when cycle times are shortened or purges are incomplete. Cell based Monte Carlo feature scale modeling is used to illustrate profile outcomes. Experimental results of atomic layer etching processes are illustrated on silicon line and space structures such that iso-dense bias and aspect ratio dependent free profiles are produced. Experimental results also illustrate the profile control margin as processes move from atomic layer to multilayer by layer etching. The consequence of not controlling contamination (e.g., oxygen) is shown to result in deposition and roughness generation.
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