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 GT3: Low Pressure Plasma Diagnostics |
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Chair: John Boffard, University of Wisconsin Room: Saratoga Hilton Ballroom 3 |
Tuesday, October 20, 2009 10:00AM - 10:30AM |
GT3.00001: Plasma diagnostics using floating harmonics method and recent results in processing plasmas Invited Speaker: Recently, a floating harmonics method for processing plasma has been developed [1]. When a sinusoidal voltage is applied on a probe at a floating potential, the current flowing through the probe has many harmonics due to the nonlinearity of sheath. From the harmonic current components, plasma densities and electron temperatures can be found. There are many advantages of this method such as relative low voltages (a few V), good time resolution ($\sim $msec), no perturbation (no net current), immune to rf interference, strong to contamination on probes. In this presentation, some improvement of this method and some measurements in various processing plasma reactors (SF6, CF4, N2, Ar, etc) as well as relevant physics will be given. Electron energy distribution function (EEDF) measurement based on the harmonic method and refinement technique for the EEDF will be given. A 2D wafer type probe array for 2D plasma density profile was developed and 2D plasma density profiles in an ICP at various conditions will be presented. \\[4pt] [1] MH Lee, SH Jang and CW Chung, J. Appl. Phys, \textbf{101}, 033305 (2007) [Preview Abstract] |
Tuesday, October 20, 2009 10:30AM - 10:45AM |
GT3.00002: Evaluation of Advanced Algorithms to improve EEDF extraction from Langmuir Probe data Using Tikhonov Regularization Methods A. El Saghir, C. Kennedy, S. Shannon, B. Pathak, J. Alexander, K. Nordheden EEDF extraction from Langmuir probe data is ill-posed due to the integral relationship between the EEDF and probe current. Curve fitting of data and reconstruction of the integral problem using regularization address this to some extent, with regularized solutions offering an advantage in EEDF accuracy over curve fitting. However, both methodologies have limitations in their ability to extract accurate EEDF's over a wide energy range for moderate signal noise. The limitations confronting regularization can be summarized in over and under regularization. Over regularization captures the high energy portion of the distribution at the expense of the low energy; and vice versa with under regularization. Advanced reconstruction algorithms using weighting and iteration are studied in order to overcome such limitations. Weighting factors scale the regularized conditioning with respect to energy to decouple the regions of interest. Iterative techniques modify the regularizer and conditioning matrix to converge on an optimal solution. To illustrate this point, the reconstruction of EEDF's from probe data taken in an electronegative RF discharge is studied. The non-Maxwellian EEDF generated by this system shows many of the challenges in EEDF reconstruction for low temperature plasmas. [Preview Abstract] |
Tuesday, October 20, 2009 10:45AM - 11:00AM |
GT3.00003: Impedance Characteristics of the Plasma Absorption Probe Yohei Yamazawa The plasma absorption probe (PAP) is a diagnostics for determination of spatially resolved electron density.\footnote{H. Kokura, et al., Jpn. J. Appl. Phys. \textbf{38} 5262 (1999).} PAP has attracted considerable interest because of its applicability in a reactive plasma. The simple structure of the probe allows us a robust measurement while the mechanism of the absorption is complicated and there are still some uncertainty.\footnote{M. Lapke, et al., Appl. Phys. Lett. {\bf 90}, 121502 (2007)} In this study, we focus on the frequency characteristics of the impedance instead of the absorption spectrum. An electromagnetic field simulation reveals that there is only one parallel resonance in the impedance characteristics even in a case there are many peaks in absorption spectrum. Thus, the impedance characteristics provide a clue to understanding the mechanism. [Preview Abstract] |
Tuesday, October 20, 2009 11:00AM - 11:15AM |
GT3.00004: Diagnostics of RF magnetron sputtering plasma for synthesizing transparent conductive Indium-Zinc-Oxide film Takayuki Ohta, Mari Inoue, Naoki Takota, Masafumi Ito, Yasuhiro Higashijima, Hiroyuki Kano, Shoji Den, Koji Yamakawa, Masaru Hori Transparent conductive Oxide film has been used as transparent conducting electrodes of optoelectronic devices such as flat panel display, solar cells, and so on. Indium-Zinc-Oxide (IZO) has been investigated as one of promising alternatives Indium Tin Oxide film, due to amorphous, no nodule and so on. In order to control a sputtering process with highly precise, RF magnetron sputtering plasma using IZO composite target was diagnosed by absorption and emission spectroscopy. We have developed a multi-micro hollow cathode lamp which can emit simultaneous multi-atomic lines for monitoring Zn and In densities simultaneously. Zn and In densities were measured to be 10$^{9}$ from 10$^{10}$ cm$^{-3}$ at RF power from 40 to 100 W, pressure of 5Pa, and Ar flow rate of 300 sccm. The emission intensities of Zn, In, InO, and Ar were also observed. [Preview Abstract] |
Tuesday, October 20, 2009 11:15AM - 11:30AM |
GT3.00005: Origin of electrical changes occurring at plasma etching endpoint Mark Sobolewski, David Lahr When a plasma etch consumes one layer and exposes an underlying layer, changes are detected in measured electrical parameters, such as impedance magnitude, phase, and dc self-bias voltage. Consequently, these electrical signals are useful for endpoint detection. However, the mechanisms responsible for the observed electrical changes are not well understood. To investigate these mechanisms, we performed experiments and numerical modeling of CF4/Ar plasma etches of thermal silicon dioxide films on silicon substrates, in an rf-biased, inductively coupled plasma reactor. A wave cutoff probe was used to measure the plasma electron density as a function of time during etching. As the etch breaks through the oxide and exposes the underlying silicon, changes in the gas-phase densities of etch products and reactants cause the electron density to increase. This increase (and an accompanying increase in ion current) has a large effect on the measured electrical signals. Using a numerical model and measurements made at varying bias frequencies, the effect of changes in electron density can be distinguished from smaller effects caused by other parameters that vary at endpoint, including the electron temperature, average ion mass, and the ion-induced emission of electrons from the wafer surface. In addition to explaining the experimental results, the model provides predictions, over a wide range of conditions, for the sensitivity and reliability of the electrical endpoint signals. [Preview Abstract] |
Tuesday, October 20, 2009 11:30AM - 11:45AM |
GT3.00006: Behavior of hydrogen atoms in plasma enhanced chemical vapor deposition of microcrystalline silicon film Yusuke Abe, Sho Kawashima, Keigo Takeda, Makoto Sekin, Masaru Hori Microcrystalline silicon ($\mu $c-Si) thin film grown by low temperature plasma enhanced chemical vapor deposition (PECVD) is an attractive material for applications in large area electronics and optoelectronics especially on flexible plastic substrates. In the PECVD processes for the ${\rm g}\mu $c-Si film formation, conditions with high pressure (1 Torr $\sim )$ and high H$_{2}$-dilution of SiH$_{4}$ are widely appropriated. Hence, the role of H atoms is very important to fabricate highly crystallized $\mu $c-Si film, however their behavior in the gas phase has not been clarified yet. In this study, we measured the absolute density and translational temperature of H atoms in a very high frequency capacitilvely coupled plasma (VHF-CCP) source at high pressure by using vacuum ultraviolet laser absorption spectroscopy (VUVLAS). The VHF power and the flow rate of SiH$_{4}$/H$_{2}$ gas were fixed at 500 W and 5/495 sccm, respectively. The pressure was varied from 0.5 Torr to 7 Torr. The absolute density increased 4.1 $\times$ 10$^{12}$ cm$^{-3}$ to 9.0 $\times$ 10$^{12}$ cm$^{-3}$ and translational temperature increased from 500 to 1600 K with increasing pressure. [Preview Abstract] |
Tuesday, October 20, 2009 11:45AM - 12:00PM |
GT3.00007: Tomographic diagnostics of nonthermal plasmas Natalia Denisova In the previous work [1], we discussed a ``technology'' of tomographic method and relations between the tomographic diagnostics in thermal (equilibrium) and nonthermal (nonequilibrium) plasma sources. The conclusion has been made that tomographic reconstruction in thermal plasma sources is the standard procedure at present, which can provide much useful information on the plasma structure and its evolution in time, while the tomographic reconstruction of nonthermal plasma has a great potential at making a contribution to understanding the fundamental problem of substance behavior in strongly nonequilibrium conditions. Using medical terminology, one could say, that tomographic diagnostics of the equilibrium plasma sources studies their ``anatomic'' structure, while reconstruction of the nonequilibrium plasma is similar to the ``physiological'' examination: it is directed to study the physical mechanisms and processes. The present work is focused on nonthermal plasma research. The tomographic diagnostics is directed to study spatial structures formed in the gas discharge plasmas under the influence of electrical and gravitational fields. The ways of plasma ``self-organization'' in changing and extreme conditions are analyzed. The analysis has been made using some examples from our practical tomographic diagnostics of nonthermal plasma sources, such as low-pressure capacitive and inductive discharges. \\[0pt] [1] Denisova N. Plasma diagnostics using computed tomography method // IEEE Trans. Plasma Sci. 2009 37 4~502. [Preview Abstract] |
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