Bulletin of the American Physical Society
2006 59th Annual Gaseous Electronics Conference
Tuesday–Friday, October 10–13, 2006; Columbus, Ohio
Session MW1: Diagnostics II: Optical |
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Chair: Ed Barnat, Sandia National Laboratories Room: Holiday Inn Salon CD |
Wednesday, October 11, 2006 4:00PM - 4:15PM |
MW1.00001: Gaussian expansion and annular analysis of ultracold Sr plasma Sampad Laha, Clayton Simien, Priya Gupta, Thomas Killian Expansion of plasma in vacuum is an important problem in astrophysics and when intense lasers ablate solid targets. In an ultracold neutral plasma, the details of a self-similar expansion of Gaussian density distribution can be seen by absorption images. The image of the plasma is divided into concentric annuli, which gives us the ability to probe the plasma properties spatially. This gives direct verification of the fact that the density maintains its Doppler profile over time. Thus, we can use existing theories of a self-similar gaussian expansion to calculate the initial electron temperature (Te), which plays a critical role in the evolution of the plasma. For example, calculating Te will tell us how many ions are we losing due to three-body recombination (TBR). The annular analysis of the plasma also allows us to probe other phenomena such as the dependence of ion temperature with position (which gives us the correlation energy) and ion density singularities at some points (shock waves). [Preview Abstract] |
Wednesday, October 11, 2006 4:15PM - 4:30PM |
MW1.00002: Electric Field Measurement by Fluorescence-Dip Spectroscopy in Krypton Tobias Kampschulte, Dirk Luggenhoelscher, Julian Schulze, Uwe Czarnetzki, Marc Bowden The electric field in the boundary sheath of discharges is a key parameter for understanding the structure and dynamics of both electrons and ions. Knowledge of the field allows the determination of e.g. voltages, charge densities and currents. Electric fields can be measured directly by Fluorescence-Dip Spectroscopy (FDS). This technique is a combination of two-photon laser induced fluorescence and absorption spectroscopy using the Stark effect of Rydberg-states. It is non-invasive and provides high field sensitivity combined with excellent temporal and spatial resolution. Here the technique is applied for the first time to krypton as a probe gas. Rydberg-states up to n~=~50 can be excited. Calibration measurements with known electric fields are performed and fields as low as 50 V/cm can be measured. In addition, the Stark-splitting has been calculated ab initio. Experimental and theoretical results agree very well. First measurements in the sheath of a capacitively coupled discharge in pure krypton are presented. [Preview Abstract] |
Wednesday, October 11, 2006 4:30PM - 4:45PM |
MW1.00003: A Laser-based Measurement System for Atmospheric Pressure Plasmas Mark Bowden, Ronan Faulkner, Mike Hopkins Plasmas operated at atmospheric pressure are the subject of an increasing amount of basic and application-based research. Due to the small size of the discharge regions, in-situ measurement of plasma properties is difficult, and research often is based on simulation studies or on relatively simple measurements such as emission spectroscopy. Laser-based methods have the potential to provide time- and space-resolved measurement of plasma properties but until now have rarely been applied. To increase the ease of laser-based measurements in atmospheric conditions, we have developed an instrument that significantly enhances the amount of signal that is detected during a laser scattering or a laser fluorescence measurement. An external cavity is used with the measurement laser so that the measurement volume is repeatedly probed with the same laser beam. In this paper, the instrument will be described together with data from test measurements. [Preview Abstract] |
Wednesday, October 11, 2006 4:45PM - 5:00PM |
MW1.00004: Gas temperature and the degree of dissociation for different operating regimes of a nitrogen helicon plasma source Costel Biloiu, Earl Scime, Xuan Sun, Ioana A. Biloiu, Robert Hardin, Zane Harvey We report on the gas temperature and the degree of dissociation in E, H, and W operating regimes of nitrogen helicon plasma. The gas temperature was inferred from the fit of synthetically generated spectra to the recorded emission spectra of the 2-0, 1-0, and 0-0 bands of the first positive system of nitrogen. The dissociation degree was inferred from the relative population ratios of atomic to molecular nitrogen states determined experimentally from integrated emission intensities of atomic triplet lines (3s $^{4}$P -- 3p $^{4}$S$^{0}$ at 742.36 nm, 744.23 nm, 746.83 nm) and the molecular band ($B{ }^3\Pi _g $, v$'$=4 $\to \quad A{ }^3\Sigma _u^+ $, v$''$=2 at 750.39 nm). The computation took into account available published values of the transition probabilities and electron impact excitation rate coefficients. Electron energy distribution functions were obtained experimentally from the second derivative of Langmuir probe I-V characteristics. It was found that both the gas temperature and the dissociation degree increase as the discharge transitions from capacitevely coupled (E) to inductively coupled (H) and then to helicon mode (W) operational regimes. [Preview Abstract] |
Wednesday, October 11, 2006 5:00PM - 5:15PM |
MW1.00005: Estimation of N atom density in a nitrogen radical source for GaN growth by optical emission spectroscopy--comparison with appearance mass spectrometry K. Sasaki, J. Osaka, H. Kanai, T. Ishijima, H. Toyoda, H. Sugai, N. Sadeghi We adopted optical emission spectroscopy (OES) for estimating N atom density in a nitrogen radical source, which was used for the growth of GaN film by molecular beam epitaxy. In addition, we compared the N atom density evaluated by OES with that evaluated by appearance mass spectrometry (AMS). We measured the intensities of optical emissions from N (747 nm) and N$_2$ (337 nm, the 2nd positive band) using a monochromator combined with an ICCD camera. The ratio of the N to N$_2$ densities ($[{\rm N}]/[{\rm N}_2]$) was obtained from the emission intensity ratio, by considering the rate coefficients for electron impact excitations. The absolute N atom density was estimated from the density ratio with the help of a thermodynamic equation of state $p=([{\rm N}] + [{\rm N}_2])k_{\rm B}T_{\rm g}$, where the pressure $p$ was measured using a capacitance manometer and the gas temperature $T_{\rm g}$ was evaluated from the rotational temperature of N$_2$ 2nd positive band. We found an excellent agreement between the N atom densities evaluated by OES and AMS, when we assumed an electron temperature of 10 eV and an N$_2$ vibrational temperature of 5000 K. This work was supported by 21st Century COE (Center of Excellence) Program ```Information Nano-Devices Based on Advanced Plasma Science" of Nagoya University. [Preview Abstract] |
Wednesday, October 11, 2006 5:15PM - 5:30PM |
MW1.00006: Characteristics of in-situ chamber cleaning for DPS+ metal etcher by using optical emission spectroscopy Yonghwan Ryu, Woojin Cho, Yongwoo Lee, Minchul Chae, Sungun Kwon, Jaeseung Hwang Plasma enhanced in-situ chamber cleaning (ICC) is generally used for plasma processes such as plasma etching system and plasma enhanced chemical vapor deposition (PECVD) system. It is generally believed that ICC makes a chamber condition to be constant and be able to extend wet cleaning period. We have studied ICC characteristics for DPS+ metal etcher by using the optical emission spectroscopy (OES) as a function of the source power, the chamber pressure and the composition and total flow rate of the gases used. We observe that the higher source power and the lower pressure are more efficient for the ICC and also investigate the effects of the additional gases. We have applied our ICC condition to the patterned wafers and concluded that the chamber condition is maintained in a stable way. However, ICC treatment to the chamber result in some process changes such as the profile of the metal line and the oxide recess and the etch selectivity of the metal line to the oxide hard mask. [Preview Abstract] |
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