Bulletin of the American Physical Society
62nd Annual Gaseous Electronics Conference
Volume 54, Number 12
Tuesday–Friday, October 20–23, 2009; Saratoga Springs, New York
Session SR3: Plasma-Surface Interactions |
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Chair: Song-yun Kang, Tokyo Electron Ltd Room: Saratoga Hilton Ballroom 3 |
Thursday, October 22, 2009 10:00AM - 10:30AM |
SR3.00001: Plasma surface interactions in fluorocarbon systems Invited Speaker: Fluorocarbon plasmas have been used for close to four decades in the semiconductor industry. Because such process systems are complex, many individuals subdivided the complete system into three main subsystems, gas-phase chemistry, plasma physics and surface chemistry/physics. Using this methodology, considerable knowledge has been gained in fundamental processes found in the gas-phase chemistry and plasma physics. Despite numerous high quality studies, understanding the surface subsystem has proven to be challenging. In part this is due to the interactions of the three subsystems. In this paper we will review a model of surface interactions for fluorocarbon plasmas which is based on surface-averaged quantum mechanical processes. Using the model we arrive at a general model describing both etch and deposition. We will show how energy considerations, such a local surface temperature, can play major roles in such processes. We will examine the basic links between the model and experimental data obtained from fluorocarbon plasmas. [Preview Abstract] |
Thursday, October 22, 2009 10:30AM - 10:45AM |
SR3.00002: Temperature Impact on Plasma-Surface Interactions in an FC Plasma Environment Caleb Nelson, Iqbal Saraf, Lawrence Overzet, Matthew Goeckner Many variables influence the nature of plasma-surface interactions. These include: radical and ion fluxes, ion energy and angle distributions, surface temperatures, and surface materials. A simplified model relates radical and ion fluxes to process rates through sticking and etch yield probability coefficients, where such coefficients are functions of particle energy, surface temperature and impact angle. Here we make use of an easily adjustable plasma system, the modified GEC reference cell, to examine the influence of temperature on sticking coefficients and etch yields. The mGEC provides the option of changing chamber dimensions, wall material, and wall temperature. The variable electrode gap permits depositing radical fluxes to be controlled almost independently of ion and etching radical fluxes, allowing the deconvolution of the process rate model. The independent control of wall and chuck temperature can then be used to study the effect of surface temperature on plasma chemistry (changing wall recycling) and surface morphology, respectively. Increasing surface temperature decreases radical and ion-assisted deposition and alters the F/C ratio and process rate of the film as etch yields are increased. [Preview Abstract] |
Thursday, October 22, 2009 10:45AM - 11:00AM |
SR3.00003: SiO$_{2}$ Film Etching Process Using Environment-Friendly New Gas C$_{5}$F$_{7}$H Yudai Miyawaki, Keigo Takeda, Azumi Ito, Masahiro Nakamura, Makoto Sekine, Masaru Hori With the continuous miniaturization of semiconductor memory devices, a much precise etching process for a high aspect ratio contact hole in SiO$_{2}$ film is indispensable. Furthermore, deterioration of the SiO$_{2}$ selectivity over a fragile, thin ArF photoresist would cause the sidewall roughness and poor pattern-width definition. In this study, we utilized a newly designed C$_{5}$F$_{7}$H gas. We compared the etch performances between the new gas and conventional C$_{5}$F$_{8 }$. Ar and O$_{2}$ were introduced with the each fluorocarbon gas to controll the etching rate. A dual frequency (60 MHz / 2 MHz) capacitively coupled plasma was employed. The SiO$_{2}$ etching rate and selectivity to ArF photoresist were investigated as a function of O$_{2}$ flow rate. The maximum selectivity of only 3.7 and the SiO$_{2}$ etching rate of 416 nm/min were obtained at O$_{2}$ flow rate of 20 sccm for the C$_{5}$F$_{8}$/O$_{2}$/Ar plasma. For the newly developed C$_{5}$F$_{7}$H/O$_{2}$/Ar plasma, the maximum selectivity of 13.5 with the etching rate of 356 nm/min was achieved at 25-sccm O$_{2}$ flow rate. From these results, it was confirmed that almost four times higher selectivity than that of the conventional C$_{5}$F$_{8}$ gas was obtained by using the new C$_{5}$F$_{7}$H gas. [Preview Abstract] |
Thursday, October 22, 2009 11:00AM - 11:15AM |
SR3.00004: Plasma-surface interactions during Si etching in Cl- and Br-based plasmas: An empirical and atomistic study Hirotaka Tsuda, Tatsuya Nagaoka, Hiroki Miyata, Yoshinori Takao, Koji Eriguchi, Kouichi Ono Nanometer-scale control of Si etching in Cl$_{2}$- and HBr-containing plasmas is indispensable in the fabrication of gate electrodes and shallow trench isolation. There are profile anomalies of sidewalls such as tapering, bowing, footing (or corner rounding), and notching, which largely affect the critical dimension. There are also anomalies of bottom surfaces such as microtrenching and roughness (or residues), which affect the bottom uniformity, and lead to recess and damage in gate fabrication. Atomic-scale cellular model (ASCeM) based on the Monte Carlo method has been developed to simulate plasma-surface interactions and the profile evolution during etching, including passivation layer formation, and also ion reflection and penetration on feature surfaces. We have also studied atomistic plasma-surface interactions by classical molecular dynamics (MD) simulation, where an improved Stillinger-Weber interatomic potential was newly developed. The numerical results were compared with etching experiments and also with surface diagnostics including \textit{in-situ} Fourier-transform-infrared reflection absorption spectroscopy (FTIR-RAS), to reveal the origin of profile anomalies on feature surfaces during etching, and then to achieve the precise control of etched profiles. [Preview Abstract] |
Thursday, October 22, 2009 11:15AM - 11:30AM |
SR3.00005: Analysis of the surface reactions of ArF photoresist during fluorocarbon plasma etching by XPS Takuya Takeuchi, Makoto Sekine, Hirotaka Toyoda, Keigo Takeda, Masaru Hori, Song-Yun Kang, Ikuo Sawada High-aspect ratio pattern etching processes with nano-scale accuracy is desired in such as a contract hole etching for the silicon dioxide that is used as a dielectric passivation layer over MOSFETs. However, photoresist used in the advanced ArF lithography is not tolerant enough for plasma etching processes, and it often causes deformations in the etched feature with bowing, distortion, twisting and so on. It is important to investigate the reaction of photoresist with fluorocarbon to overcome these problems and realize sophisticated etch processes. In this research, the modified layer of the photoresist by bombardment of CF$_{x}^{+}$ ions was analyzed. The ions, such as CF$^{+}$, CF$_{2}^{+}$, CF$_{3}^{+}$, and F$^{+}$, were produced from CF$_{4}$ gas by electron impact, and selected by quadrupole mass filter. The CF$_{x}^{+}$ ions were bombarded to ArF photoresist as ion beam with an accelerated energy from 100 to 400 eV. The equipment system is evacuated by four turbo molecular pumps. Ultimate pressure of the equipment is lower than 10$^{-9}$ Torr. The beam equipment and XPS analysis chamber are connected in vacuum, so we can use XPS analysis without atmospheric influence after the ion etch process. In this study, we investigated the modified layer of the photoresist by \textit{in-situ} XPS. [Preview Abstract] |
Thursday, October 22, 2009 11:30AM - 11:45AM |
SR3.00006: Determination of gas phase and surface reactions in plasma polymerization Dirk Hegemann Using macroscopic kinetics, the reactions within the gas phase are governed by the reaction parameter power input per gas flow $W$/$F$, which corresponds to a specific energy, while reactions by energetic particle bombardment at the growing film surface are rather related to power input $W$ alone. Assuming activation reactions, the mass deposition rate per gas flow can be described by an Arrhenius-like approach: \[ \frac{R_m }{F}=G\exp \left( {-\frac{E_a }{W \mathord{\left/ {\vphantom {W F}} \right. \kern-\nulldelimiterspace} F}} \right) \] Mixtures of hydrocarbons (C$_{2}$H$_{4})$ and reactive gases (CO$_{2}$, N$_{2}$+H$_{2})$ were examined within low pressure RF plasmas. Thus, functional a-C:H:O or a-C:H:N plasma coatings result. At increasing energy input it is found that the deposited mass shows a deviation from the above equation, commonly related to energetic particle interactions. However, using the same range of $W$/$F$ with varying power input $W$, it was found that the observed drop in deposition rate scales solely with energy input $W$/$F$ for a-C:H:O, i.e. depending on plasma chemistry. a-C:H:N films, on the other hand, show both chemical and physical influences on the film growth. Hence, gas phase reactions such as a change of film-forming species play a major role in plasma polymerization. [Preview Abstract] |
Thursday, October 22, 2009 11:45AM - 12:00PM |
SR3.00007: Role of plasma activation in the kinetics of CNT growth in PECVD process Irina Lebedeva, Alexey Gavrikov, Alexey Baranov, Maxim Belov, Andrey Knizhnik, Boris Potapkin, Timothy Sommerer The work presents kinetic modeling of the effect of acceleration for the growth kinetics of carbon nanotubes by hydrocarbon gas mixture modification with plasma discharge. The plasma activation creates active species in hydrocarbon gas mixture, which can easily adsorb and dissociate on the catalyst surface. So plasma treatment of the gas mixture in the CVD process allows to increase the carbon supply rate by a few orders of magnitude compared to that in thermal CVD process. On the other hand, plasma can also provide etching of carbon species from the catalyst surface. To correctly reproduce both of these effects of plasma, the kinetic model of growth of carbon nanotubes is developed based on first-principles analysis of heterogeneous processes on the catalyst surface and detailed kinetics of gas phase chemistry. The model is used to compare the growth rates of carbon nanotubes in thermal and plasma-enhanced CVD processes and to determine critical gas pressures, at which CNT growth kinetics switches from the adsorption limitation to the limitation by reaction and diffusion on the catalyst. [Preview Abstract] |
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