Bulletin of the American Physical Society
65th Annual Gaseous Electronics Conference
Volume 57, Number 8
Monday–Friday, October 22–26, 2012; Austin, Texas
Session HW2: Plasma Etching I |
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Chair: Makoto Sekine, Nagoya University, Japan Room: Classroom 203 |
Wednesday, October 24, 2012 8:00AM - 8:30AM |
HW2.00001: Time-Multiplexed Deep Silicon Etching Invited Speaker: Lawrence Overzet There is continuing interest in Time Multiplexed Deep Silicon Etch (TMDSE) processes to enable the fabrication of MEMS devices as well as through wafer vias. Yet, current knowledge of these processes is not comprehensive and has often emerged from designed experiments conducted to create/control feature profiles. The presented research helps to fill some of the gaps in our understanding. Experiments were conducted to understand the mechanisms that function during the deposition and etch steps of TMDSE. In our deposition step studies, we first etched trenches of various aspect ratios and subsequently deposited a thick passivation layer using the standard deposition step settings of the TMDSE process. The characteristics of the deposited layers were found to be very instructive. Contrary to typical assumptions, the experiments and analysis indicate that the contribution of ions is much more critical than the contributions of neutral molecules. This leads to large deposition rates in regions where it is NOT wanted and tiny deposition rates in regions where it IS wanted/needed! We relate this to the progression of feature undercut. In our etch studies, we began with standard trenches again and examined either the results of an extended etch step, or the results of both an extended deposition and etch steps. The experimental evidence suggests that the etchant species at higher aspect ratios become something besides the commonly assumed atomic fluorine. It may be that the primary etchant becomes molecular fluorine. (The etch profile characteristics appear consistent with molecular fluorine.) Our analysis was facilitated by a feature scale model. [Preview Abstract] |
Wednesday, October 24, 2012 8:30AM - 8:45AM |
HW2.00002: Formation Mechanisms of Surface Roughening and Rippling during Plasma Etching and Sputtering of Silicon Hirotaka Tsuda, Yoshinori Takao, Koji Eriguchi, Kouichi Ono For the prediction of the atomic-scale surface roughness on feature bottom and sidewalls, we have developed our own three-dimensional atomic-scale cellular model (ASCeM-3D) and feature profile simulation. In this study, emphasis is placed on a better understanding of the formation mechanisms of nanoscale surface roughening and rippling during plasma etching and sputtering of Si with different ion incidence angles and ion incident energies. Numerical results indicated that surfaces are randomly roughened in the case of Cl$_{2}$ plasma etching for normal incidence of ions. For increased incident angles, ripples are formed perpendicular to the direction of ion incidence, while parallel to that of ion incidence for further increased incident angle. Numerical results also implied that the spatial dispersion of ion scattering and focusing on etched surfaces triggers the local difference in etch yield, and leads to the surface roughening and rippling during plasma etching and sputtering. [Preview Abstract] |
Wednesday, October 24, 2012 8:45AM - 9:00AM |
HW2.00003: Ion Energy Distribution Control Using Ion Mass Ratios in Inductively Coupled Plasmas With a Pulsed DC Bias on the Substrate Michael D. Logue, Mark J. Kushner In many applications requiring energetic ion bombardment, such as plasma etching, gas mixtures containing several ion species are used. In cases where two ions have significantly different masses, it may be feasible to selectively control the ion energy distributions (IEDs) by preferentially extracting the lighter ion mass with a controllable energy. In this work, we investigate the possibility of using a pulsed DC substrate bias in an inductively coupled plasma (ICP) to obtain this control. Pulsing of the substrate bias in the afterglow of a pulsed ICP plasma should allow for shifting of the IED peak energy by an amount approximately equal to the applied bias. If short enough pulses are used it may be possible to obtain a higher flux at high energy of the lower mass ion compared to the higher mass ion. A computational investigation of IEDs in low pressure (a few to 100 mTorr) ICPs sustained in gas mixtures such as Ar/H$_{2}$ or Xe/H$_{2 }$(having large mass differences) was conducted as a proof of principle. The model is the Hybrid Plasma Equipment Model with which electron energy distributions (EEDs) and IEDs as a function of position and time are obtained using Monte Carlo simulations. We have found a selective ability to mass and energy discriminate ion fluxes when using sufficiently short bias pulses. Results from the model for plasmas densities, electron temperatures, EEDs and IEDs will be discussed. [Preview Abstract] |
Wednesday, October 24, 2012 9:00AM - 9:15AM |
HW2.00004: Multi-scale approach for simulation of deep silicon etching under ICP SF6/Ar plasma mixture Amand Pateau, Ahmed Rhallabi, Marie Claude Fernandez, Fabrice Roqueta, Mohamed Boufnichel Deep etching of silicon represents a new challenge in the silicon semi-conductor manufacturing. Indeed, deep silicon etching is used to form through-silicon vias and connect stacked dies or wafers in 3D integration. In this context, computer simulation of plasma etching can contribute to the optimization of the etching process. In this study, we have developed a silicon etching simulator under ICP SF6/Ar plasma discharge. Such model is composed of three modules permitting to predict the 2D etched silicon morphology versus the operating conditions: plasma kinetic model, sheath model and etching model. The plasma kinetic model is based on the 0D global approach which allows the calculation of the average densities and fluxes of neutral and ion species as well as the electron density and temperature versus the ICP machine parameters. Such output parameters are introduced as input parameters in the sheath model and silicon etching model. Cellular Monte-Carlo method is used to describe the plasma surface interactions in a probabilistic way for silicon etching trough the mask. The aim of this work is to validate the set of simulation and show the influence of some input parameters (Rf power, pressure, gas flow rate and bias voltage) on the etching processes. [Preview Abstract] |
Wednesday, October 24, 2012 9:15AM - 9:30AM |
HW2.00005: Molecular Dynamics Analysis of Physical and Chemical Behavior of Etch Products Desorbed during Si Etching in Cl- and Br-based Plasmas Nobuya Nakazaki, Yoshinori Takao, Koji Eriguchi, Kouichi Ono Profile anomalies and surface roughness are critical issues to be resolved in plasma etching of nanometer-scale microelectronic devices, which in turn requires a better understanding of the effects of ion incident energy and angle on surface reaction kinetics. This paper presents a classical molecular dynamics (MD) simulation of Si etching by energetic Cl$^{+}$ and Br$^{+}$ ion beams with different incident energies ($E_{i}$ = 20--300 eV) and angles (\textit{$\theta $}$_{i}$ = 0--85$^{\circ}$), and low-energy neutral Cl and Br radicals with different neutral radical-to-ion flux ratios ($\Gamma _{n}$/$\Gamma _{i}$ = 0--100), where the improved Stillinger-Weber interatomic potential is used for Si/Cl and Si/Br systems. Emphasis is placed not only on the etch yield and stoichiometry, but also on the energy and angular distributions of etch products desorbed. Numerical results indicated that as $\Gamma _{n}$/$\Gamma _{i}$ is increased at high $E_{i} >$ 100 eV, the Si etch yield and the amount of products containing more halogen atoms increase, where the energy distribution of desorbed etch products peaks at lower energies. In addition, the desorption angle of etch products, which is measured from the surface normal on substrates, become slightly smaller with increasing $\Gamma _{n}$/$\Gamma _{i}$, which is more clearly observed in the case of oblique ion incidence. [Preview Abstract] |
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