<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; color: rgb(0, 0, 0); font-size: 14px; font-family: Calibri, sans-serif; "><div><br></div><span id="OLK_SRC_BODY_SECTION"><div xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><div lang="EN-US" link="blue" vlink="purple"><div class="WordSection1"><p class="MsoNormal" align="center" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;text-align:center;line-height:150%;background:white"><a name="_Toc473187185"></a><a name="_Toc480840318"></a><b><span style="font-size: 14pt; line-height: 150%; font-family: 'Times New Roman', serif; color: black; ">PhD DEFENSE STUDENT: </span></b><span style="font-size: 14pt; line-height: 150%; font-family: 'Times New Roman', serif; color: black; ">Qiaowei
Lou</span><span style="font-size: 12pt; line-height: 150%; font-family: 'Times New Roman', serif; color: black; "><o:p></o:p></span></p><p class="MsoNormal" align="center" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;text-align:center;line-height:150%;background:white"><b><span style="font-size: 14pt; line-height: 150%; font-family: 'Times New Roman', serif; color: black; ">DATE: </span></b><span style="font-size: 14pt; line-height: 150%; font-family: 'Times New Roman', serif; color: black; ">Monday,<b></b>July 31, 2017</span><span style="font-family: 'Times New Roman', serif; color: black; "><o:p></o:p></span></p><p class="MsoNormal" align="center" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;text-align:center;line-height:150%;background:white"><b><span style="font-size: 14pt; line-height: 150%; font-family: 'Times New Roman', serif; color: black; ">TIME: </span></b><span style="font-size: 14pt; line-height: 150%; font-family: 'Times New Roman', serif; color: black; ">1:00
PM</span><span style="font-family: 'Times New Roman', serif; color: black; "><o:p></o:p></span></p><p class="MsoNormal" align="center" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;text-align:center;line-height:150%;background:white"><b><span style="font-size: 14pt; line-height: 150%; font-family: 'Times New Roman', serif; color: black; ">PLACE:</span></b><span style="font-size: 14pt; line-height: 150%; font-family: 'Times New Roman', serif; color: black; ">
Mechanical Engineering Large Conference Room</span><span style="font-family: 'Times New Roman', serif; color: black; "><o:p></o:p></span></p><p class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:150%;background:white"><b><span style="font-size: 14pt; line-height: 150%; font-family: 'Times New Roman', serif; color: black; ">DISSERTATION CHAIRs:
<o:p></o:p></span></b></p><p class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:150%;background:white"><span style="font-size: 14pt; line-height: 150%; font-family: 'Times New Roman', serif; color: black; ">Dr. Vincent Donnelly and Dr. Demetre Economou
</span><span style="font-family: 'Times New Roman', serif; color: black; "><o:p></o:p></span></p><div style="margin-bottom:8.0pt"><div class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:150%;background:white"><span style="font-size: 14pt; line-height: 150%; font-family: 'Times New Roman', serif; color: black; "><hr size="2" width="100%" align="center"></span></div></div><p class="MsoNormal" align="center" style="text-align:center;line-height:150%;background:white"><b><span style="font-size: 14pt; line-height: 150%; font-family: 'Times New Roman', serif; color: black; ">TITLE:<o:p></o:p></span></b></p><p class="MsoNormal" align="center" style="text-align:center"><b><span style="font-size: 16pt; line-height: 105%; font-family: 'Times New Roman', serif; ">Optical Spectroscopy of CH<sub>3</sub>F/O<sub>2</sub>, CH<sub>3</sub>F/CO<sub>2</sub> and c-C<sub>4</sub>F<sub>8
</sub>Inductively Coupled Plasmas<o:p></o:p></span></b></p><p class="MsoNormal" align="center" style="text-align:center"><b><span style="font-size: 16pt; line-height: 105%; font-family: 'Times New Roman', serif; "><o:p> </o:p></span></b></p><p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:justify;text-indent:.5in;line-height:150%"><span style="font-size: 12pt; line-height: 150%; font-family: 'Times New Roman', serif; ">Despite the fact that CH<sub>3</sub>F/O<sub>2</sub> and CH<sub>3</sub>F/CO<sub>2</sub> gas mixtures are widely used in the microelectronics industry for highly anisotropic
and selective etching of Si<sub>3</sub>N<sub>4</sub> over Si or SiO<sub>2</sub>, only a limited number of fundamental plasma studies of these gases have been reported. Recently, an inductively coupled plasma (ICP) beam system was used in this laboratory to
study fundamental aspects of this etching process. The topic of this thesis was to characterize that plasma beam, operated with CH<sub>3</sub>F/CO<sub>2</sub> feed gases, as a function of power (5-400 W) and gas composition at 10 mTorr, using optical emission
spectroscopy and rare gas actinometry. Number densities of H, F, and O increased rapidly between 74-80% CO<sub>2</sub>, ascribed to the transition from polymer-covered to polymer-free reactor walls, similar to that in CH<sub>3</sub>F/O<sub>2</sub> ICPs at
48% O<sub>2</sub>. The plasma composition of the two gas mixtures were almost identical below 40% O<sub>2</sub> or CO<sub>2</sub>, except for higher OH/Xe over the full range of CH<sub>3</sub>F/CO<sub>2</sub> composition. CO number densities were obtained
by self-actinometry. CO<sub>2</sub> was little dissociated below 40 W while the dissociation increased with power to ~83% at 400 W.</span><span style="font-size: 12pt; line-height: 150%; font-family: 'Times New Roman', serif; "> A model
from previous work was used to predict F/Ar number density ratios and estimate the probability ($B&C(B) of hydrogen abstraction from the wall by F atoms.</span><span style="font-size: 12pt; line-height: 150%; font-family: 'Times New Roman', serif; "><o:p></o:p></span></p><p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:justify;text-indent:.5in;line-height:150%"><span style="font-size: 12pt; line-height: 150%; font-family: 'Times New Roman', serif; ">The species concentrations measurements performed in this study are used to explain the faster deposition rates and other properties, observed in other studies, of fluorocarbon
(FC) films on p-Si exposed to CH<sub>3</sub>F/CO<sub>2</sub> compared to CH<sub>3</sub>F/O<sub>2</sub> plasma beams emanating from an ICP source, used in separate etching studies.
<span style="color:red"> </span><o:p></o:p></span></p><p class="MsoNormal" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:justify;text-indent:.5in;line-height:150%"><span style="font-size: 12pt; line-height: 150%; font-family: 'Times New Roman', serif; color: black; ">A C<sub>4</sub>F<sub>8</sub> inductively coupled plasma in pulse mode was investigated as a function of peak power (25-400 W), pulse repetition frequency (5-100
kHz), and duty cycle (10-90%) to support a study of atomic layer etching of SiO<sub>2</sub>. Relative
</span><span style="font-size: 12pt; line-height: 150%; font-family: 'Times New Roman', serif; ">emission intensity ratios of C/Xe, CF/Xe, CF<sub>2</sub>/Xe, C<sub>2</sub>/Xe and F/Ar were obtained and analyzed. All ratios were underestimated at high powers and
duty cycles, except for F/Ar, due to the energy mismatch. The CF<sub>2</sub> emission from electron impact dissociative excitation was dominant below 50 W, but became much less important at high powers. A decrease of the emission intensity ratios of all species
was observed with increasing frequency. CF<sub>2</sub> number density measured by UV absorption spectroscopy was found to be nearly constant at ~2.5x10<sup>14</sup> cm<sup>-3</sup> between 150~450 W. The highest CF<sub>2</sub>/F density ratio, required in
atomic layer etching for self-limiting deposition of a thin FC film growth, was achieved at a peak power of 50 W, for pulse repetition frequency of 10<b><span style="color:red"></span></b>kHz, duty cycle of 50%, and pressure of 6.5 mTorr. This near self-limiting deposition of a ~2 monolayer thick FC film also required producing a plasma beam with a CF<sub>2</sub> flux that was much higher than that of the sum of CF and C fluxes. Thus,
the reported large sticking coefficient of CF<sub>2</sub> on bare SiO<sub>2</sub>, combined with the much lower sticking coefficient on Teflon-like films produced from the CF<sub>2</sub> precursor, will result in a near-self-limiting FC film deposition.<b><o:p></o:p></b></span></p></div></div></div></span><style><!--
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