Bulletin of the American Physical Society
60th Gaseous Electronics Conference
Volume 52, Number 9
Tuesday–Friday, October 2–5, 2007; Arlington, Virginia
Session DT1: Materials Processing in Low Pressure Plasmas I: Etching, deposition, new materials |
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Chair: Shahid Rauf, Applied Materials Room: Doubletree Crystal City Crystal Ballroom A |
Tuesday, October 2, 2007 1:30PM - 2:00PM |
DT1.00001: A new generation of cryogenic processes for silicon deep etching Invited Speaker: Deep etching of silicon is intensively used in microtechnology for MEMS and power microelectronic components. At GREMI, we study and develop the cryoetching process, which is a good alternative in terms of rapidity and cleanliness compared to other processes (e.g. Bosch process). The reactor is an ICP where the wafer is cooled down to a very low temperature (about -100\r{ }C). SF6 and O2 are the basic gases involved in the process. O2 (10 {\%}) is used to form an SiOxFy passivation layer, which grows on vertical sidewalls not submitted to ion bombardment. This oxidation occurs very efficiently at very low temperature of the substrate. The perfect control of this passivation layer formation is a key issue in the cryogenic process. Mass spectrometry measurements give the evolution of the oxidation threshold (necessary oxygen proportion to form the passivation layer) as a function of temperature, RF power and bias. The role of the etch by-products (SiF4) in the formation of the SiOxFy layer was investigated using ellipsometry and mass spectrometry. With this study, we were able to develop new processes based on steps of SiF4/O2 plasmas to enhance the passivation layer deposition and efficiency. [Preview Abstract] |
Tuesday, October 2, 2007 2:00PM - 2:15PM |
DT1.00002: Student Excellence Award Finalist: Modeling of Deep Reactive Ion Etching of Si under plasma molding in 2f-CCP in SF$_6$/O$_2$ Fukutaro Hamaoka, Takashi Yagisawa, Toshiaki Makabe In large-scale etching used in MEMS fabrication, plasma molding is one of the important issues. In our previous study, the effect of plasma molding on the etch profile was numerically investigated without neutral reaction [1]. In this study, we numerically investigate the feature profile evolution of deep Si etching under plasma molding in 2f-CCP in SF$_6$/O$_2$, including RIE by ions and F radicals and passivation layer formation by O radicals. In SF$_6$(83\%)/O$_2$ at 300 mTorr, the removal of the passivation layer at the bottom corner is strengthened by the distorted SF$_5^+$ ion incidence under plasma molding. The chemical etching rate of Si layer for F radicals is much higher than that of passivation layer. Thus, when the passivation layer is removed by ion impact, the Si etching is enhanced by addition of F radicals. As a result, this indicates that anisotropy of the etching profile is not achieved especially at the bottom in this condition [2]. In addition, we will discuss the influence of the percentage of the oxygen on anisotropic etch profile. \newline [1] F. Hamaoka et al., Jpn. J. Appl. Phys., vol. 46, no. 5A, pp. 3059-3065, 2007. \newline [2] -, IEEE Trans. Plasma Sci., (accepted for publication), Oct 2007. [Preview Abstract] |
Tuesday, October 2, 2007 2:15PM - 2:30PM |
DT1.00003: Student Excellence Award Finalist: Neutral production in SF$_6$/SiCl$_4$ inductively coupled plasmas C. Duluard, R. Dussart, L.E. Pichon, E.H. Oubensaid, P. Lefaucheux, P. Ranson, M. Puech In this study we investigate the mechanisms involved during silicon etching by SF$_6$/SiCl$_4$ mixtures in an industrial inductively coupled plasma reactor. To that purpose, the plasma is analysed by mass spectrometry and optical emission spectroscopy. Relative concentrations of reactive neutrals such as F and Cl are determined using the actinometry technique. Neutral species are also monitored in the diffusion chamber by a quadrupole mass spectrometer whose ionisation energy is set to 70 eV. At this energy, the ionisation of molecules is mostly dissociative and produces several ions of lower mass. Therefore, a detected ion can stem from various molecules. Knowledge of the fragmentation spectra for different molecules is thus crucial to deduce the contribution of all the species, either being the primary gas molecules (e.g. SF$_6$, SiCl$_4$) or the resultant radicals (e.g. SF$_4$, SiCl$_2$). The study focuses on the influence of the gas flow rate on the evolution of neutral concentrations. Other parameters such as pressure and source power are fixed in the 1-10 Pa range and 800-3000 W range respectively. All these experiments are compared between the case of a bare and an oxidised silicon wafer, so as to distinguish silicon-enhanced reactions from plasma-phase and other surface reactions. [Preview Abstract] |
Tuesday, October 2, 2007 2:30PM - 2:45PM |
DT1.00004: Atomic-scale model analysis of the feature profile evolution during Si etching in chlorine- and bromine-containing plasmas Shoki Irie, Yugo Osano, Masahito Mori, Koji Eriguchi, Kouichi Ono Profile simulations are indispensable for understanding the influences of complex reaction processes in plasma etching, to achieve the nanometer-scale control of etched profiles and critical dimensions. This paper presents an atomic-scale model for the feature profile evolution during Si etching in chlorine- and bromine-containing plasmas. The model incorporated an atomic-scale cellular model of surface reaction layers and the Monte Carlo calculation for the trajectory of ions on feature surfaces, including their reflection on and penetration into surfaces, where the potential function for Cl-Si and Br-Si systems was determined from quantum chemical calculations. The model also took into account the formation of surface reaction layers caused by adsorption of neutrals and penetration of ions, chemical etching, ion-enhanced etching, deposition of etch products and by-products, and surface oxidation. The simulation was performed to reproduce experimental observations in Si etching with Cl$_{2}$/O$_{2}$ and HBr/O$_{2}$ chemistries: profile anomalies near the feature bottom such as footing and microtrenching, sidewall tapering and etched depth depending on feature width, and surface roughness or residues. The mechanisms concerned are discussed in terms of competition between etching and passivation, along with ion reflection on feature surfaces. [Preview Abstract] |
Tuesday, October 2, 2007 2:45PM - 3:00PM |
DT1.00005: Effect of VUV Radiation on Fluorination of Polypropylene in Low Pressure Plasmas Yang Yang, Mark Strobel, Seth Kirk, Mark J. Kushner Affixing fluorine to the surface of polypropylene (PP) lowers surface energy and increases hydrophobicity. One such fluorination process is the immersion of PP sheets in a low pressure, F$_{2}$ containing plasma wherein F atoms both abstract H atoms from and adhere to the surface. The vacuum ultraviolet (VUV) radiation these plasmas produce affect surface properties by reactions such as cross-linking, bond scission and removal of molecular group (e.g., CH$_{3})$. In this talk, the consequences of VUV radiation during low-pressure plasma fluorination of PP will be discussed with results from a computational investigation. The capacitively coupled discharge is sustained in He/F$_{2}$ mixtures. The reactor is patterned after industrial plasma sources for polymer fluorination. Plasma and surface processes on the moving web were simulated using a 2-dimensional plasma hydrodynamics and surface chemistry model. To properly address radiation trapping, a Monte Carlo radiation transport module is used to generate the photon fluxes incident on the PP film. Assessment of the roles of various photon activated processes in the fluorination process will be made. [Preview Abstract] |
Tuesday, October 2, 2007 3:00PM - 3:15PM |
DT1.00006: Effect of gas mixture ratio on atomic oxygen density in an inductively coupled plasma in O$_{2}$/Ar mixture Toshikazu Sato, Toshiaki Makabe Oxygen plasmas are extensively used in material processing such as ashing of photoresist, surface modification and oxidation. It is well known that dilution of oxygen by rare gas increases the plasma density and enhances the processing speed. Kitajima et al experimentally investigated argon diluted oxygen plasma and showed that the metastable argon efficiently produces metastable atomic oxygen in capacitively coupled discharge [1]. In this work, we perform a two-dimensional modeling of an inductively coupled plasma (ICP) in O$_{2}$/Ar mixture and investigate the effect of Ar dilution on the mechanism of the atomic oxygen production. A steady state plasma structure and the spatial distribution of neutral species are calculated by using the relaxation continuum model. Atomic oxygen is produced mainly through the dissociation of oxygen molecule by electron impact and the recombination on the reactor surface is the most dominant loss mechanism of atomic oxygen in highly diluted O$_{2}$/Ar ICP at 100 mTorr. Ground state atomic oxygen increases monotonically with increasing O$_{2}$ fraction (less than 10{\%}), on the other hand, metastable atomic oxygen steeply increases under the O$_{2}$ fraction less than 3{\%}. \newline [1] T. Kitajima, T. Nakano, and T. Makabe, Appl. Phys. Lett. 88, 091501 (2006). [Preview Abstract] |
Tuesday, October 2, 2007 3:15PM - 3:30PM |
DT1.00007: Student Excellence Award Finalist: Ion Flux and Energy Measurement at a Pulsed Biased Electrode in a C$_{2}$H$_{2}$:Argon Inductively Coupled Plasma During DLC Growth. A. Baby, C.M.O. Mahony, P.D. Maguire Diamond-like carbon is an important material for biomedical and mechanical applications. Knowledge of growth mechanisms is severely limited by lack of basic hydrocarbon plasma data since measurement is extremely challenging due mainly to probe deposits. Plasma models suffer from a lack of basic information e.g. T$_{e}$, n$_{e}$. We measured ion energy distributions and neutral fluxes for six dominant species directly at the growing substrate in a C$_{2}$H$_{2}$:Argon ICP ($\le $10mTorr) for the first time. By RF pulse biasing the substrate electrode we have also determined the absolute values of positive ion flux$^{[1]}$. From analysis of bimodal IEDs and 1D modelling of multi-species ion transport across the sheath, we intend to extract plasma density. This requires internal probe measurement to confirm model estimates of n$_{e}$ and T$_{e}$. Pulsed bias generates a central peaked trimodal IED from which we can better isolate the impact of ion energy during our DLC growth. We estimate dissociation kinetics from infrared TDLAS and neutral flux measurement. Correlation of film properties with growing substrate fluxes will be a first for this important material and will be an critical input to current rudimentary growth models. [1] Braithwaite et.al. Plasma Source Sci Technol. \textbf{5 }(1996) 6 [Preview Abstract] |
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