Previous profile evolution studies of plasma-assisted etch processes have shown that ions scattered from sidewalls can lead to microtrench formation on the bottom of an etched feature [see, for example, Dalton et al., J. Electrochem. Soc. 140, 2395 (1993)]. In these studies, the ions impacting feature surfaces with incident angles above a critical value were assumed to reflect specularly from the surfaces. In the present article, we describe the energy and angle distributions of reflected atoms obtained from molecular dynamics (MD) simulations. We simulated Ar+ and Cl+ ions impacting model silicon surfaces. The ion incident energies Ei were 20, 50, and 100 eV. We varied the ion incident angles θi from 0° to 85° from the surface normal. The model silicon surfaces had chlorine coverages of 0 monolayers (ML) of Cl, 1 ML Cl, and 2.3 ML Cl. We determined the Ar and Cl reflection probabilities, i.e., the fraction of Ar and Cl atoms scattered from the surfaces during the 1–2 ps MD trajectories. For θi⩾75°, we found that the reflection probabilities were greater than 90% in most cases. For these large incident angles, we describe the distributions of energies Er and angles (polar θr and azimuthal φr) for the Ar and Cl atoms reflected from the surfaces. The results of the MD simulations are compared with the assumption of specular scattering. In addition, we compare the average energies of the reflected atoms with the predictions of two simple models based on the binary collision approximation. We discuss the effects of incident ion species, Ei, θi, chlorine surface coverage, and surface roughness on these results.
The trapping probability, or physical adsorption probability, of ethane on a clean Si(100)-(2×1) surface has been measured as a function of the incident translational energy and incident polar angle of the molecule at a surface temperature of 65 K. At all incident angles the trapping probability decreases as the translational energy of the incoming ethane molecule is increased from 0.05 to 1.3 eV. As the incident polar angle, with respect to the surface normal, is increased, the trapping probability decreases. This decrease in trapping probability with increasing polar angle contradicts the idea of normal energy scaling and has been seen in very few cases. Classical molecular dynamics calculations have been employed to study the cause of this unusual angular dependence. This simulation predicts trapping probabilities in good agreement with the experimental data. Analysis of the computed trajectories indicates that the initial site of impact within the unit cell, as well as energy exchange on initial impact with the surface, is important in determining the fate of an incident molecule. Normal momentum of the incident molecule is dissipated during the first impact much more efficiently than is parallel momentum. The simulations also indicate that the observed angular dependence can be explained in terms of parallel momentum accommodation. Large amounts of parallel momentum remaining after initial impact may be converted to normal momentum on subsequent impacts, causing molecules to scatter from the surface. Therefore, molecules that impact the surface at glancing angles and high translational kinetic energies are more likely to scatter from the surface than those at normal incidence or with lower translational kinetic energy.
Back side exposure of variable size through silicon viasDual damascene dielectric etch technology is emerging as a key enabler for advanced integration schemes. Early implementations of copper dual damascene processes favored the trench-first approach. This approach has now been largely superseded by the via-first scheme for technology nodes below 250 nm. Several etch issues typically arise when implementing either of these approaches. The via-first approach can lead to either via veils or excessive faceting problems when the trench is etched. The traditional trench-first approach requires long via overetches and very high selectivity to the underlayer so that allowance can be made for vias that are misaligned or placed outside the trenches. Trench-first lithography employing organic resists often requires patterning over nonplanar surfaces, which can result in narrow process windows. Both the via-first and trench-first approaches increasingly require etching the trench without a stop layer. This places exacting demands on etch uniformity, etch front control, and sidewall profile angle control. Control of these issues is enhanced when the etch mechanisms responsible for driving them are understood. These and other issues as well as the current understanding of the relevant mechanisms are discussed for implementing copper dual damascene structures in plasma enhanced chemical vapor deposition undoped silicate glass or fluorinated silicate glass oxide films.
A better understanding of the surface interactions of energetic atomic and molecular species is needed under conditions relevant to plasma-assisted etching and deposition. In this article we describe the results of molecular dynamics (MDs) simulations of atomic Si and molecular SiFx (x=1–3) species impacting fluorinated silicon surfaces. These impacting species might be sputtered species incident on feature surfaces with energies typically on the order of a few eV, or etch products that are ionized in the plasma and accelerated back towards the substrate surface to attain energies on the order of tens to hundreds of eV. To model both of these cases, the incident energy was varied from 0.1 to 100 eV. We performed the MD simulations to investigate the types of possible events that occur during the picosecond(s) following the impact of these reactive atomic and molecular species. Stillinger–Weber potentials were used to model the interatomic interactions [Phys. Rev. B 31, 5262 (1985); J. Chem. Phys. 88, 5123 (1988); Phys. Rev. Lett. 62, 2144 (1989); J. Chem. Phys. 92, 6239 (1990)]. We observed a variety of events in the simulated trajectories: sticking or reflection of the impacting species, reactions with surface species, sputtering of surface material, and dissociation of the impacting molecular species. The effect of surface coverage and incident angle was studied by simulating impacts onto three silicon surfaces with different amounts [monolayers (MLs)] of fluorine (0 ML F, 1 ML F, 2 ML F), and by varying the incident angle of Si atoms from 0° to 75° from the surface normal. These effects are illustrated for select cases.
We describe the energy and angle distributions of reflected Cl2 molecules and Cl atom fragments obtained from molecular dynamics (MD) simulations of Cl2+ ion impacts onto a chlorinated silicon surface. We simulated Cl2+ ion impacts onto a silicon surface with 1 monolayer (ML) of adsorbed Cl atoms. The ion incident energies Ei were 20, 50, and 100 eV. We varied the ion incident angles θi from 0° to 85° from the surface normal. We report the Cl2 dissociation probability, as well as the scattering probabilities for both the Cl2 molecules and the Cl atom fragments. The effects of Ei and θi on these quantities are discussed. For the 100 eV Cl2+ impacts with θi⩾75°, we describe the distributions of energies Er and angles (polar θr and azimuthal φr) for the reflected Cl2 molecules and Cl atom fragments. In addition, we compare the average energies of the reflected molecules and atoms with the predictions of two simple models based on the binary collision approximation.
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