Bulletin of the American Physical Society
61st Annual Gaseous Electronics Conference
Volume 53, Number 10
Monday–Friday, October 13–17, 2008; Dallas, Texas
Session PR1: Fluorocarbon Plasmas I |
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Chair: Truell Hyde, Baylor University Room: Salon E |
Thursday, October 16, 2008 8:00AM - 8:30AM |
PR1.00001: Study of the ion induced etching for Si and SiO2 with F+ and CFX(X=1,2,3)+ ions Invited Speaker: Dry etching with reactive plasma has been widely used in the fabrication of semiconductors. For the development of integrated semiconductor devices, more precise control of the etching process is required for further progress. It is known that reactive ion species and reactive neutral species, which are produced in plasma, play a great role in etching reactions. However, the mechanism for the etching reaction has not yet been quantitatively described because the individual reactive species cannot be controlled independently in the conventional etching apparatus. It is necessary to clarify the roles of individual reactive ion bombardments and neutral species. A beam experimental method is a very useful tool for investigating the interactions of individual species with surfaces. Thus, we developed a mass-analyzed low-energy ion beam system for investigating the interaction of reactive ion with surfaces. It irradiates analyzed single-species ions onto sample surfaces. The irradiation chamber was maintained in the ultrahigh vacuum condition throughout our experiments. The system has neutral beam sources that independently irradiate a neutral species onto the sample surface. The system can simulate an etching reaction in a plasma environment. To investigate surface reactions for etching processes, we have determined the etching yields by incident ion, detected the scattering species and desorbed products with a differentially pumped rotatable quadrupole mass spectrometer (QMS), and measured surface modification during ion irradiation by X-ray photoelectron spectroscopy. The QMS provided time-resolved measurements and could be synchronized with pulsed ion beam. In the present work, we have investigated etching yields and time of flight distribution and angular distribution of desorption products for Si or SiO2 by F+ and CF+ (x = 1-3) ion bombardments which are considered to be the main ion species in fluorocarbon plasmas. These results clearly show that the etching reaction on SiO2 differs from that on Si surface. [Preview Abstract] |
Thursday, October 16, 2008 8:30AM - 8:45AM |
PR1.00002: Initial Formation of Carbon Nanowalls Synthesized by Ar Ions and CF$_{X}$/H Radicals Shingo Kondo, Olivera Stepanovic, Makoto Sekine, Masaru Hori, Koji Yamakawa, Shoji Den, Mineo Hiramatsu Carbon nanowalls (CNWs) consist of graphene sheets standing vertically on the substrate. Due to their unique structures, they have attracted much attentions for various applications. In order to clarify the growth mechanism, in-situ observation of the initial growth stage of CNWs is extremely important. In this study, the new apparatus of CF$_{X}$ and H radical sources with C$_{2}$F$_{6}$ and H$_{2}$ gases and an Ar ion source was constructed, and in-situ observation on the substrate surface was performed employing a spectroscopic ellipsometer. When a gas flow ratio of H$_{2}$ to C$_{2}$F$_{6}$ was 1:2 with Ar ions accelerated at 200 V at 2.5 Pa, CNWs started to grow in 7 min. The refractive index and the extinction coefficient of the material were approximately 1.3 and 0.2, respectively, and it included voids of more than 80 {\%}. Hence, it was estimated that CNWs had with metallic graphite, which was also confirmed by Raman spectroscopy and SEM. On the basis of these results, the growth mechanism of CNWs is discussed. [Preview Abstract] |
Thursday, October 16, 2008 8:45AM - 9:00AM |
PR1.00003: Critical roles of CF$_{4}$ and SiCl$_{4}$ plasma treatments on AlGaN/GaN transistor performance Anirban Basu, Ilesanmi Adesida Advancements of AlGaN/GaN transistors for high speed and high power applications are tied to realization of high quality gate/ohmic contacts. Plasma processing of semiconductor surfaces plays a crucial role in the contact formation process. Our findings indicate that plasma treatments of gate and source/drain regions by CF$_{4}$ and SiCl$_{4}$ plasmas, respectively, affect AlGaN/GaN transistor performance significantly. The CF$_{4}$ plasma incorporates fluorine ions in the AlGaN epilayer that critically affects the contact barrier height and electron transport in the electron gas at the AlGaN/GaN interface. Therefore, important metrics such as leakage current, mobility and sheet concentration can be controlled using plasma conditions. The implications of such plasma treatment in affecting the ultimate device performance will be discussed. Results related to plasma induced effects such as creation of defects and diffusion of fluorine will be presented in the context of AlGaN/GaN transistor performance. The SiCl$_{4}$ plasma treatment on AlGaN/GaN surface is a complex process that triggers multiple competing phenomena such as introduction of defects, creation of vacancies and implantation of ions. Our observation of enhanced mobility and sheet concentration in SiCl$_{4}$ plasma treated samples indicate soft ion implantation of silicon. Its implications on ohmic contact formation and other device performances will be discussed. [Preview Abstract] |
Thursday, October 16, 2008 9:00AM - 9:15AM |
PR1.00004: On the effect of additional CF$_2$ scattering data on a CF$_4$/O$_2$ plasma etch simulation James J. Munro, Natasha Doss, Jonathan Tennyson, Song-Yun Kang, Masato Kawakami, Sumie Segawa An analysis of the effect of adding a number of new CF$_2$ processes to a CF$_4$ and a CF$_4$/O$_2$ plasma chemistry model is presented. A CF$_4$ and a CF$_4$/O$_2$ capacitively coupled plasma (CCP) etch process is simulated using a zero-dimensional global plasma model. The reaction data is then extended using a new set of electron impact reaction rates for CF$_2$. Namely, \begin{eqnarray*} e + \mathrm{CF}_2 & \rightarrow & e + \mathrm{CF}_2^*(^3B_1), \\ e + \mathrm{CF}_2 & \rightarrow & e + \mathrm{CF} + \mathrm{F}, \\ e + \mathrm{CF}_2^*(^3B_1) & \rightarrow & e + \mathrm{CF}_2, \\ e + \mathrm{CF}_2^*(^3B_1) & \rightarrow & e + \mathrm{CF} + \mathrm{F}, \end{eqnarray*} the addition of which leads to a significant change in the concentration of CF$_2$. These electron-impact reaction rates are derived from cross-section calculations using Quantemol-N[1]. Measured etch-rates from an equivalent CCP tool are used to validate the model. [1] J. Tennyson et al, J. Phys.: Conf. Ser., 86, 012001 (2007) [Preview Abstract] |
Thursday, October 16, 2008 9:15AM - 9:30AM |
PR1.00005: Li$^{+}$ attachment mass spectrometric investigation of high-mass neutral species in the downstream region of Ar/CF$_{4}$, Ar/CF$_{4}$/O$_{2}$ and Ar/CF$_{4}$/H$_{2}$ plasmas Kenji Furuya, Hiroshi Okumura, Yuji Tamai, Akihiro Ide, Akira Harata Recently gaseous high-mass species have received significant attentions as important contributors to the nucleation of films and particulates in fluorocarbon plasmas. We have unambiguously identified the gaseous high-mass neutral species in the downstream region of the Ar/CF$_{4}$ plasma [1], using the Li$^{+}$ attachment ionization technique that is a fragment-free ionization method. In this report, we show the results of mass analysis of high-mass neutral species in the Ar/CF$_{4}$/O$_{2}$ and Ar/CF$_{4}$/H$_{2}$ plasmas as well as Ar/CF$_{4}$. In the Ar/CF$_{4}$ plasma, we observed C$_{n}$F$_{2n+2}$ (n = 2-7) and C$_{n}$F$_{2n}$ (n = 4-8) as neutral species. Adding O$_{2}$ to the Ar/CF$_{4}$ plasma resulted in the intensity decrease of C$_{n}$F$_{2n+2}$ and C$_{n}$F$_{2n}$, especially of those with relatively small n values. C$_{n}$F$_{2n}$O (n = 1-7) were newly observed in the Ar/CF$_{4}$/O$_{2}$ plasma. In contrast, adding H$_{2}$ to the Ar/CF$_{4}$ plasma resulted in the production of various new compounds, such as C$_{n}$F$_{2n-2}$ (n=3-8), C$_{n}$F$_{2n-4}$ (n=3-9), C$_{n}$F$_{2n+1}{\rm H}$ (n=1-7), C$_{n}$F$_{2n-1}{\rm H}$ (n=2-8), C$_{n}$F$_{2n-3}{\rm H}$ (n=4-9) and C$_{n}$F$_{2n-5}{\rm H}$ (n=5-9). These species are produced through the abstraction of F from various C$_{n}$F$_{m}$ species by the H radical and the addition of H to them. [1] K. Furuya, S. Yukita, H. Okumura, A. Harata, Chem. Lett. \textbf{34}, 224 (2005). [Preview Abstract] |
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