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<div dir="ltr"><b style="font-family: "Times New Roman", serif; font-size: 12pt;">NAME:</b><span style="font-family: "Times New Roman", serif; font-size: 12pt;"> Ya-Ming Chen</span><br>
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<p style="background:white"><span style="color:#201F1E"> </span><span style="font-size:11.0pt; font-family:"Calibri",sans-serif; color:#201F1E"></span></p>
<p style="background:white"><b><span style="color:#201F1E">ADVISORS: </span></b><span style="color:#201F1E">Dr. Vincent Donnelly and Dr. Demetre Economou</span><span style="font-size:11.0pt; font-family:"Calibri",sans-serif; color:#201F1E"></span></p>
<p style="background:white"><span style="color:#201F1E"> </span><span style="font-size:11.0pt; font-family:"Calibri",sans-serif; color:#201F1E"></span></p>
<p style="background:white"><b><span style="color:#201F1E">DATE:</span></b><span style="color:#201F1E"> Thursday, May 14, 2020</span><span style="font-size:11.0pt; font-family:"Calibri",sans-serif; color:#201F1E"></span></p>
<p style="background:white"><span style="color:#201F1E"> </span><span style="font-size:11.0pt; font-family:"Calibri",sans-serif; color:#201F1E"></span></p>
<p style="background:white"><b><span style="color:#201F1E">TIME</span></b><span style="color:#201F1E">: 01:00 PM</span><span style="font-size:11.0pt; font-family:"Calibri",sans-serif; color:#201F1E"></span></p>
<p style="background:white"><span style="color:#201F1E"> </span><span style="font-size:11.0pt; font-family:"Calibri",sans-serif; color:#201F1E"></span></p>
<p style="background:white"><b><span style="color:#201F1E">LOCATION:</span></b><span style="color:#201F1E"> Zoom</span><span style="font-size:11.0pt; font-family:"Calibri",sans-serif; color:#201F1E"></span></p>
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<p style="background:white"><b><span style="font-size:14.0pt; color:#201F1E">TITLE:</span><span style="color:#201F1E">
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<p class="MsoNormal" style="background:white"><b><span style="color:#201F1E">Nearly Monoenergetic Positive Ion Beam with Self-Neutralized Space Charge Extracted From a Pulsed Plasma and Its Application</span></b><b><span style="font-size:11.5pt; font-family:"Segoe UI",sans-serif; color:#201F1E">
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<p style="background:white"><b><span style="font-size:14.0pt; color:#201F1E">ABSTRACT:</span></b><span style="font-size:11.0pt; font-family:"Calibri",sans-serif; color:#201F1E"></span></p>
<p style="background:white"><b><span style="color:#201F1E"> </span></b><span style="font-size:11.0pt; font-family:"Calibri",sans-serif; color:#201F1E"></span></p>
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<span style="color:#201F1E">Space charge neutralization of an ion beam extracted from a plasma is crucial for advanced plasma processes which require precise control of the ion flux and the width of the ion energy distribution (IED). In previous studies, filaments
thermionically emitting electrons were used for neutralizing the space charge, which would otherwise cause the ion beam to diverge owing to Coulomb explosion. However, the performance of the neutralizing filaments is restricted by their limited lifetime and
required extra power supplies.</span></p>
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<span style="color:#201F1E">This study reports that a positive ion beam with a self-neutralized space charge can be extracted from a pulsed plasma. In particular, a nearly monoenergetic ion beam was realized by applying a synchronous DC bias to a “boundary
electrode” in the afterglow (power-off) of the plasma. A retarding field energy analyzer (RFEA) and a movable Faraday cup were used to measure the IED and the time resolved ion and electron current densities, as a function of position along the beam axis,
to unravel the mechanism of self-neutralization of the space charge of the ion beam. When a +100 V DC bias was applied to the boundary electrode during the afterglow, a ~100 eV beam (ion density ~109 cm-3) emerged that was space-charge neutralized by periodic
injection of electrons, mainly during the early afterglow, into the region downstream of the extraction grid. A background plasma (electron density ~1010 cm-3) was formed by these electrons, in conjunction with relatively low-energy (1-10 eV) ions that exited
the inductively coupled plasma (ICP) source when the DC bias was off, as well as formed by resonant charge exchange of the 100 eV beam ions with the background Ar atoms, in the downstream region near the extraction grid. The behavior of the beam IED as a function
of pressure and power of the ICP as well as the timing of application of the DC bias voltage was also studied. </span></p>
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<span style="color:#201F1E">Highly anisotropic reactive ion beam etching of polysilicon masked with SiO2, has been demonstrated using a monoenergetic Ar+ ion beam (generated by a pulsed ICP) in the presence of Cl2 gas. Vertical sidewall profiles and smooth
flat bottom surfaces were achieved. Specifically, the sample was placed 2 cm downstream of the ion extraction grid and electrons effusing from the pulsed plasma (mainly during the early afterglow) neutralized not only the positive ion space charge, but also
the surface of the silicon dioxide mask. Thus, etching artifacts that have been reported in the literature due to insulator surface charging did not appear in the present system.</span></p>
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