Bulletin of the American Physical Society
68th Annual Gaseous Electronics Conference/9th International Conference on Reactive Plasmas/33rd Symposium on Plasma Processing
Volume 60, Number 9
Monday–Friday, October 12–16, 2015; Honolulu, Hawaii
Session TF2: Plasma Etching II |
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Chair: Demetre Economou, University of Houston Room: 308 AB |
Friday, October 16, 2015 10:00AM - 10:30AM |
TF2.00001: Cryogenic Etching for Sub-10 nm Patterning for Bit Patterned Media Fabrication Invited Speaker: Deirdre Olynick Bit patterned media (BPM) is pushing the limits of lithography and plasma etching. In the next 10 years, sub- 10 nm pitch lithography and pattern transfer are required to reach bit densities approaching 10 TB/in$^{2}$. For high throughput manufacturing, nanoimprint lithography will be utilized to pattern the disks. Here, I will discuss low-temperature plasma etching for high-resolution nanoimprint template fabrication using block copolymer lithography and double patterning technologies. The template manufacturing process depends on a multitude of plasma etching steps culminating in quartz etching. Initial dimensions will be determined by the capabilities of block copolymer lithography while the ultimate dimensions will be defined using either double or quadruple patterning. Four to seven plasma etching steps will be required to produce the final template. I will discuss our investigations of cryogenic etching processing for BPM template fabrication. Benefits of cryogenic etching can include enhanced selectivity, better profile control, and novel passivant formation. I will cover applicability of cryoetching in silicon, silicon dioxide, carbon based materials, and chromium. [Preview Abstract] |
Friday, October 16, 2015 10:30AM - 10:45AM |
TF2.00002: Atomic Layer Etch to Escape Aspect Ratio Dependent Etching-Profile-Selectivity Trade-offs in Plasma Etch Alok Ranjan, Mingmei Wang, Sonam Sherpa, Peter Ventzek Minimizing each of aspect ratio dependent etching (ARDE), profile, selectivity, uniformity are met by trading off one requirement against another. The problem of trade-offs is especially critical at \textless\ 10nm technology. Self-limiting processes like atomic layer etching (ALE) promise a way to escape the trade-offs. Industrial implementation of ALE has not occurred due to speed and precision loss from improper balance of self-limiting passivation and its removal. In recent years strides have been made primarily through temporal and/or spatial pulsing. Moderate success has been reported with some of the trade-offs purported to be managed. Difficulty meeting requirements is due to the inability to control ion energy at low and precise values. We overcome many of the practical implementation issues associated with ALE by precise passivation process control. Very low plasma potential, high radical flux and high bombardment flux are indispensable for achieving ALE. We demonstrate that ALE can achieve zero ARDE and infinite selectivity. Experimental results will highlight that careful consideration of surface processes is required to achieve ALE and not simply ``slow etching.'' Profile control will be shown to rely on careful management of the ion energies and angles. Experimental results are compared with simulation results generated using MCFPM [1] and theoretical scaling models to provide context to the work. \\[4pt] [1] M. Wang and M. J. Kushner, J. Appl. Phys., 107, 023308 (2010) [Preview Abstract] |
Friday, October 16, 2015 10:45AM - 11:00AM |
TF2.00003: Low Damage Etching with Atomic Layer Precision L. Dorf, S. Rauf, G. Monroy, K. Ramaswamy, K. Collins, Y. Zhang In this presentation, we describe a Low Damage Etch Chamber (LoDEC) for atomic layer etching (ALE) comprising: (1) an electron beam source (1--2 keV) for generating radical-poor, low electron temperature ($T_{e}$ $\sim$ 0.3 eV) plasma, (2) a remote plasma source (RPS) for supplying radicals to the substrate, and (3) a bias generator for creating the voltage drop (0--50 V) between the substrate and the plasma to accelerate ions over etch-threshold energies. In LoDEC, we reproduced the conventional \textit{Si}-etch ALE cycling scheme: in 1$^{\mathrm{st}}$ part of the cycle, \textit{Cl} atoms are injected by RPS to passivate the surface for $\Delta t=\tau_{p}$, and in 2$^{\mathrm{nd}}$ part, RPS is turned off and etching is done in e-beam \textit{Ar}/$N_{2}$ plasma at low bias power for $\Delta t=\tau_{b}$. As $\tau_{b}$ is increased, we observe saturation in the etch depth per cycle, $\Delta_{c}$, signifying that the entire passivation layer is being removed each cycle, resulting in layer-by-layer etching. In LoDEC, this scheme can be implemented at much lower ion energies, $E_{i}$, than in conventional tools, potentially resulting in lower damage to advanced materials. We also obtained the dependence of $\Delta_{c}$ on ion energy and $\tau_{p}$ for a given \quad $\tau_{b}$. Finally, using LoDEC we developed a novel technique for etching \textit{a-Si} in \textit{Cl} below known threshold energy, at $E_{i}$ $\sim$ 5 -- 7 eV (TEM shows etch rates of $\sim$ 3--4 nm/min). [Preview Abstract] |
Friday, October 16, 2015 11:00AM - 11:15AM |
TF2.00004: Layer by layer etching of LaAlSiOx Mitsuhiro Omura, Kazuhito Furumoto, Kazuhisa Matsuda, Toshiyuki Sasaki, Itsuko Sakai, Hisataka Hayashi In order to fabricate a gate transistor with high-k oxide materials, removal of high-k oxide films after gate electrode etching is necessary for the formation of ohmic contacts on source and drain regions. It is crucial that the removal process of high-k oxide film by dry etching is highly selective to and low in damage to the Si substrate in order to avoid the degradation of device performances. Sasaki et al. have achieved a high LaAlSiOx-to-Si selectivity of 6.7 using C4F8/Ar/H2 plasma [1]. A sequential layer by layer etching could realize low damage etching, similar to atomic layer etching. Therefore, a sequential LaAlSiOx etching process using a H2 surface modification step followed by a removal step using C4F8/Ar plasma is investigated. The etched amount of LaAlSiOx by the C4F8/Ar plasma step doubles with H2 modification. It is confirmed that when the C4F8/Ar plasma treatment time is sufficient to remove the surface modification layer, a self-limiting reaction is realized. Furthermore, it is confirmed that the etched amount per step can be controlled by control of the ion energy of H2 plasma. \\[4pt] [1] T. Sasaki, K. Matsuda, M. Omura, I. Sakai, and H. Hayashi: Jpn. J. Appl. Phys. 54 (2015) 06GB03. [Preview Abstract] |
Friday, October 16, 2015 11:15AM - 11:30AM |
TF2.00005: Cryogenic etching of Si with SF$_{6}$/O$_{2}$: a modeling and experimental study Stefan Tinck, Erik C. Neyts, Thomas Tillocher, Remi Dussart, Annemie Bogaerts Cryogenic etching, although already proposed in 1988, has recently seen an immense increase in popularity in microchip development, due to its very promising ability to reduce plasma induced damage of ultra-small features. Here, we wish to obtain a fundamental understanding of the SF$_{6}$/O$_{2}$ plasma behavior and its interaction with the surface to improve cryogenic etching. We apply numerical models and experiments to describe the plasma behavior and plasma-surface interactions. SF$_{6}$/O$_{2}$ low-pressure plasmas are investigated at different wafer temperatures ranging between conventional 293 K and cryogenic 173 K. Cryogenic etch rates are slightly higher due to local cooling of the gas above the wafer, resulting in a slightly higher reactive neutral density. Fundamental surface reactions are also investigated with MD simulations. It is found that the probabilities for chemisorption (i.e., sticking) are insignificantly affected by the wafer temperature. However, surface diffusion and thermal desorption occur much slower at cryogenic conditions and, as a result, it is found that a thick layer of physisorbed species is formed during cryoetching, which is absent at room temperature etching, and which facilitates the formation of an oxygen-based passivation layer. [Preview Abstract] |
Friday, October 16, 2015 11:30AM - 11:45AM |
TF2.00006: Etching of GaAs materials by chlorine neutral beam for quantum nanodisks fabrication Cedric Thomas, Akio Higo, Takeru Okada, Seiji Samukawa Quantum dots (QD) fabrication is still challenging, either from bottom-up or top-down approaches. We have combined a Bio-Nano-Process (BNP) and a Neutral Beam Etching (NBE) process to make nanopillars, embedding GaAs quantum nanodisks. Using BNP, a self-assembled monolayer array of nanoparticle is deposited on the GaAs surface to form a nanometer size etching mask array. NBE by chlorine neutrals of GaAs is subsequently performed, enabling low-damage etching of nanodisks. During the fabrication process, insights of NBE mechanisms were investigated. It has been found that NBE was really sensitive to the surface oxide, so the nanopillars fabrication needed a good control of surface oxide and NBE parameters. By studying NBE of GaAs with respect to substrate temperature, it was found that NBE has a low activation energy. In the case of RIE within the same condition, a lower activation energy was estimated. It is assumed that the residual oxide on the surface is the main cause for such behavior. Tuning steps prior etching such as hydrogen radical treatment, have been successful for the fabrication of nanopillars. NBE and RIE have shown same order characteristics, however NBE process enables low-damage nanostructures compared to RIE, which is promising for next generation QD devices. [Preview Abstract] |
Friday, October 16, 2015 11:45AM - 12:00PM |
TF2.00007: Etching of Magnetic Tunneling Junctions Materials using a Reactive Ion Beam Kyung Chae Yang, Sung Woo Park, Min Hwan Jeon, Geun Young Yeom The etching of magnetic tunneling junctions (MTJs) was investigated using a reactive ion beam (RIB) system with gases such as Ar, NF$_{\mathrm{3}}$, CH$_{\mathrm{3}}$OH and CO/NH$_{\mathrm{3}}$. Improved etch characteristics were observed with CH$_{\mathrm{3}}$OH or CO/NH$_{\mathrm{3\thinspace }}$in comparison with Ar or NF$_{\mathrm{3}}$, possibly due to the enhanced volatile product formation of CH$_{\mathrm{3}}$OH or CO/NH$_{\mathrm{3\thinspace }}$with MTJ materials by showing lower sidewall residue on the etched features and due to the high etch selectivity over W or TiN. Especially, CO/NH$_{\mathrm{3\thinspace }}$reactive ion beam was the most effective for the MTJ etching by showing the most anisotropic MTJ etch profiles. [Preview Abstract] |
Friday, October 16, 2015 12:00PM - 12:15PM |
TF2.00008: Dry Etching of Si$_{3}$N$_{4}$, SiO$_{2}$ and Si Using Remote Plasma Sources Sustained in NF$_{3}$ Mixtures Shuo Huang, Vladimir Volynets, Sangheon Lee, In-Cheol Song, Siqing Lu, James Hamilton, Jonathan Tennyson, Mark J. Kushner Remote plasma sources (RPS) are used in microelectronics fabrication to produce fluxes of radicals for etching and passivation in the absence of damage by charging and energetic ions. RPS reactors use distance and grids to reduce or eliminate charged particle fluxes from reaching the wafer. Nitrogen trifluoride (NF$_{3}$) is often used in RPS due to the efficiency of producing F atoms by dissociative attachment. RPS sustained in NF$_{3}$ gas mixtures, such as Ar/NF$_{3}$/O$_{2}$, increases the variety of reactive species, for example, N$_{\mathrm{x}}$O$_{\mathrm{y}}$ and FO, and so may enable optimization the etching rates of Si$_{3}$N$_{4}$, SiO$_{2}$ and Si. Meanwhile, by using pulsed power or pulsed gas sources, fluxes of F, O and N$_{\mathrm{x}}$O$_{\mathrm{y}}$ may be optimized to achieve various etch rates. In this paper, we report on a computational investigation of RPS sustained in different NF$_{3}$ containing gas mixtures at pressures of less than a few Torr using continuous and pulsed power for low-damage plasma etching applications. The electron impact cross sections for NF$_{3}$, NF$_{2}$, and NF were produced using ab initio computational techniques based on the molecular R-matrix method. A reaction mechanism was developed for plasmas sustained in Ar/NF$_{3}$/N$_{2}$/O$_{2}$ mixtures and a surface reaction mechanism was developed for etching of Si$_{3}$N$_{4}$, SiO$_{2}$ and Si. Plasma properties and etch rates will be discussed for different pulse-power scenarios and gas mixtures. [Preview Abstract] |
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