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<meta http-equiv="Content-Type" content="text/html; charset=Windows-1252"></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"><o:p> </o:p></p><p class="MsoNormal" align="center" style="text-align:center"><b><span style="font-size: 14pt; line-height: 115%; font-family: 'Times New Roman', serif; ">Student:</span></b><span style="font-size: 14pt; line-height: 115%; font-family: 'Times New Roman', serif; ">
Ashutosh K. Srivastava<o:p></o:p></span></p><p class="MsoNormal" align="center" style="text-align:center"><b><span style="font-size: 14pt; line-height: 115%; font-family: 'Times New Roman', serif; ">Defense Date:</span></b><span style="font-size: 14pt; line-height: 115%; font-family: 'Times New Roman', serif; ">
Monday, April 27<sup>th</sup> 2015<o:p></o:p></span></p><p class="MsoNormal" align="center" style="text-align:center"><b><span style="font-size: 14pt; line-height: 115%; font-family: 'Times New Roman', serif; ">Time:</span></b><span style="font-size: 14pt; line-height: 115%; font-family: 'Times New Roman', serif; ">
10 am<o:p></o:p></span></p><p class="MsoNormal" align="center" style="text-align:center"><b><span style="font-size: 14pt; line-height: 115%; font-family: 'Times New Roman', serif; ">Location:</span></b><span style="font-size: 14pt; line-height: 115%; font-family: 'Times New Roman', serif; ">
S-234 (Chemical Engineering conference room)<o:p></o:p></span></p><p class="MsoNormal" align="center" style="text-align:center"><b><span style="font-size: 14pt; line-height: 115%; font-family: 'Times New Roman', serif; ">Committee Chair:</span></b><span style="font-size: 14pt; line-height: 115%; font-family: 'Times New Roman', serif; ">
Dr. Vincent M. Donnelly</span><span style="font-size: 12pt; line-height: 115%; font-family: 'Times New Roman', serif; "><o:p></o:p></span></p><div style="margin-bottom:10.0pt"><div class="MsoNormal" align="center" style="margin-bottom:0in;margin-bottom:.0001pt;text-align:center"><b><span style="font-size: 16pt; line-height: 115%; font-family: 'Times New Roman', serif; "><hr size="2" width="100%" align="center"></span></b></div></div><p class="MsoNormal" align="center" style="text-align:center"><b><span style="font-size: 16pt; line-height: 115%; font-family: 'Times New Roman', serif; ">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: 115%; font-family: 'Times New Roman', serif; color: black; ">Chamber Wall Interactions with HBr/Cl<sub>2</sub>/O<sub>2</sub> 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: 115%; font-family: 'Times New Roman', serif; ">Studied by “Spinning Wall” Method<span style="color:black"><o:p></o:p></span></span></b></p><p class="MsoNormal" align="center" style="text-align:center"><u><span style="font-size:14.0pt;line-height:115%;font-family:"Times New Roman","serif";color:black"><o:p><span style="text-decoration:none"> </span></o:p></span></u></p><p class="MsoNormal" align="center" style="text-align:center"><b><u><span style="font-size: 14pt; line-height: 115%; font-family: 'Times New Roman', serif; color: black; ">Abstract<o:p></o:p></span></u></b></p><p class="MsoNormal" style="text-align:justify;text-indent:.5in;line-height:200%"><span style="font-size: 12pt; line-height: 200%; font-family: 'Times New Roman', serif; ">HBr plasmas are used to etch Si, as well as GaN, PZT, InP, indium zinc oxide and other materials. In Si etching, HBr plasmas create better anisotropic profiles than Cl<sub>2</sub>
plasmas, with better selectivity toward SiO<sub>2</sub>. Selectivity can be further improved by adding oxygen to the plasma. The feed gas composition of HBr/Cl<sub>2</sub>/O<sub>2</sub> plasmas is optimized to best meet the needs of the particular application.
Keeping such a complex process stable over time requires tight control over all plasma parameters, including reactor wall conditions. Here,
<span style="color:black">we have studied the interaction of HBr/Cl<sub>2</sub>/O<sub>2</sub> inductively-coupled plasmas with reactor chamber wall deposits, with and without Si etching, using the “spinning wall” technique.
<o:p></o:p></span></span></p><p class="MsoNormal" style="text-align:justify;text-indent:.5in;line-height:200%"><span style="font-size: 12pt; line-height: 200%; font-family: 'Times New Roman', serif; color: black; ">The spinning wall is part of the reactor chamber walls, allowing near-real time analysis of the composition of surface layers via Auger electron spectroscopy,
and determination of species desorbing off the walls by mass spectrometry. </span><span style="font-size: 12pt; line-height: 200%; font-family: 'Times New Roman', serif; ">In HBr plasmas with no bias voltage on the Si substrate, and hence no Si etching, HBr is ~30% dissociated and H<sub>2</sub> and Br<sub>2</sub> form in the plasma. Layers
deposited on the reactor chamber contained little if any Br under these conditions. Adding O<sub>2</sub> to an HBr plasma leads to formation of Br<sub>2</sub> and H<sub>2</sub>O products that desorb from the spinning wall. H<sub>2</sub>O has a very long residence
time on the surface. With bias voltage applied to the Si substrate in an HBr plasma, SiBr and SiBr<sub>3</sub> are prominent mass spectrometer signals, SiBr<sub>2</sub> and SiBr<sub>4</sub> appear to be the major gas phase components, and a SiO<sub>x</sub>Br<sub>y</sub>
layer deposits on the spinning wall. Adding 20% O<sub>2</sub> to HBr stops etching and eliminates Br from the surface layer, indicating that Br on the reactor walls is a result of SiBr<sub>x</sub> impingement, and not from bromination by impinging Br.
<o:p></o:p></span></p><p class="MsoNormal" style="text-align:justify;text-indent:.5in;line-height:200%"><span style="font-size: 12pt; line-height: 200%; font-family: 'Times New Roman', serif; ">With HBr/Cl<sub>2</sub> plasmas and no bias on the stage, a SiO<sub>x</sub>Cl<sub>y</sub> layer deposits; no Br is detected. In addition, the mass spectrum of HBr and
Cl<sub>2</sub> gas mixture without plasma revealed HCl, Br<sub>2</sub> and BrCl species. Further experiments revealed that these products were the result of reactions between HBr and Cl<sub>2</sub> on the plasma reactor walls. With plasma and bias on the Si
substrate, both Br and Cl incorporate in a depositing layer. Adding 20% O<sub>2</sub> to a HBr/Cl<sub>2</sub> plasma with substrate bias suppresses Br adsorption, but Cl still adsorbs. In 40% O<sub>2</sub>/HBr/Cl<sub>2</sub> plasmas with stage bias, Cl adsorption
also ceases.<o:p></o:p></span></p></div></div></div></span><style><!--
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