なかのにっき

A high-density surface-wave magnetized argon plasma operated in the very low pressure regime together with a rf biased system is used to study the pure physical etching characteristics of platinum thin films. It is shown that, for a given dc self-bias voltage, the platinum etch rate strongly decreases as the operating pressure increases, which results from a decrease of the ion density at the sheath edge and from enhanced redeposition. It is found that using a high-density plasma in the very low pressure regime yields high etch rates with a good selectivity over resist. Fence-free features can also be achieved at bias voltages that, in contrast with reactive ion etching reactors, are only slightly above the platinum sputtering threshold.

We analyze a real-space expression for the local stress tensor. This tensor rigorously satisfies conservation of linear momentum. From this expression a coarse-grained tensor is obtained for use in atomistic simulations of solids. Our formulation is then validated by considering both a homogeneously strained crystalline solid and one containing an oversized inclusion. In the latter case a direct comparison is made with results from anisotropic elasticity theory. We find that we are able to obtain good agreement with the suitably averaged continuum solutions in the far-field regime. Moreover, the coarse-grained tensor derived here appears to offer superior accuracy as compared to a stress tensor that has been widely used in atomistic analysis.

Based on our previous Monte Carlo simulation model of electron interactions with solids, including cascade secondary electron production, in which an optical dielectric function was used to describe electron energy loss and the associated secondary electron excitation, we have systematically investigated secondary electron generation and emission for 19 metals. The calculated secondary yield curve for primary beam energy ranging from 100 eV to 2 keV was found to correspond with the experimental universal curve. The dependence of the secondary yield on the work function was studied numerically, leading to a remarkable scattered deviation from Baroody's relationship. This deviation shows that the secondary yield relates to different aspects of behavior by electrons in a metal, such as the cascade production process, the stopping power and specific energy loss mechanism for a sample, and the dependence on the electron density of states. The results provide an explanation for the scattered data on the experimental yield versus the work function. The calculations indicate that the characteristic energy loss of primaries may result in a corresponding feature in the energy distribution of secondaries.

The control of reactive sputter processes has been dynamically simulated by integrating the Larsson differential equations. This was done by employing a fast Runge?Kutta step control algorithm, allowing us to simulate sputtering with more than 20-fold real time speed on a pentium 166 Mhz. A simple proportional integral differential (PID) algorithm was implemented to simulate (i) the partial pressure control via reactive gas flow at a fixed current and (ii) the partial pressure control via current at a fixed reactive gas flow. The control cycle time was varied with respect to real life process control. These simulations show that arbitrary setpoints on the stationary s curve resulting from the steady state Larsson equations can be stabilized. However, the cycle time of the PID controller has to be small enough, e.g., less than 600 ms, for a reliable control. The setpoints in the transition mode are highly unstable, so that the process drifts immediately into one of the two corresponding stable steady states (typically within about 3?15 s) after freezing the control. In addition these computations were compared with experimental control results of reactively sputtered TiO2 and Nb2O5 films deposited by the midfrequency technique. In both cases the total s curve was stabilized at a constant oxygen flow. The process stabilization was performed at power densities of up to 5 W/cm2, limited by the generator output. For the oxygen partial pressure measurements a -probe with optimized speed was used.

An expansion of a bicomponent laser plume into a dilute ambient gas is simulated using a combined direct simulation-random trajectory Monte Carlo method. The stoichiometry of thin films deposited from laser-desorbed material on a flat substrate is examined. In the case of energy-dependent particle adsorption probability, the dependencies of deposition rate on the background pressure are shown to be nonmonotonic with maximums at low gas pressure. In addition, an increase in the ratio of light to heavy species was obtained at low pressure. We demonstrate that these results can be attributed to the interplay between the effects of collisions with the background gas on the fluxes of particles arriving at the substrate and on the adsorption probability of the species. The calculation results are consistent with recent experiments. The study is of interest for the optimization of the experimental conditions during pulsed laser deposition of multicomponent materials.