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<a name="x__Toc477949989" id="LPlnk909439" class="OWAAutoLink" previewremoved="true"></a><a name="x__Toc517301747" id="LPlnk160545" class="OWAAutoLink" previewremoved="true"></a><a name="x__Toc477983819" id="LPlnk901976" class="OWAAutoLink" previewremoved="true"></a><b><span style="font-size:14.0pt; line-height:200%; color:black">PhD
DEFENSE STUDENT: </span></b><span style="font-size:14.0pt; line-height:200%; color:black">Tianyu Ma</span><span style="color:black"></span></p>
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<b><span style="font-size:14.0pt; line-height:200%; color:black">DATE: </span></b><span style="font-size:14.0pt; line-height:200%; color:black">Monday, July 9, 2018</span><span style="color:black"></span></p>
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<b><span style="font-size:14.0pt; line-height:200%; color:black">TIME: </span></b><span style="font-size:14.0pt; line-height:200%; color:black">10:00 AM</span><span style="color:black"></span></p>
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<b><span style="font-size:14.0pt; line-height:200%; color:black">PLACE:</span></b><span style="font-size:14.0pt; line-height:200%; color:black"> Chemical Engineering Conference Room</span><span style="color:black"></span></p>
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<b><span style="font-size:14.0pt; line-height:150%; color:black">DISSERTATION CHAIR:
</span></b><span style="font-size:14.0pt; line-height:150%; color:black">Dr. Vincent Donnelly
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<b><span style="font-size:14.0pt; line-height:200%; color:black">TITLE:</span></b></p>
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<b><span style="font-size:14.0pt; line-height:105%; font-family:"Times New Roman","serif"; color:black">Plasma Wall Interactions and Recombination Coefficients Measurement on Yttrium-based Coated Chamber Wall Surfaces</span></b></p>
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<span style="font-family:"Times New Roman","serif"">Plasma etching is a widely used method to pattern materials in the fabrication of microelectronic devices. As the minimum feature sizes, or so-called critical dimensions, shrink beyond 14 nm, plasma etching
processes need to be ever more tightly controlled. At low pressures, the ~cm mean free path of species ranges are comparable to reactor dimensions. Consequently, gas phase reactions (especially three-body processes) become less likely and heterogeneous reactions
on chamber walls become increasingly important. These issues are particularly important in plasma etching processes at lower pressures (typically 1 – 100 mTorr) where heterogeneous reactions of neutrals on the chamber walls are important and can often dominate
gas-phase reactions in establishing the number density of species in the plasma. The surface layers formed on the reactor walls become a source of production or loss of species. As a result, shifting plasma composition leads to process drifts, leading to
changes in etching rates, profiles, selectivity, and yields. Hence, it is of prime importance to understand the interactions of plasmas with the dynamic chamber wall surfaces.</span></p>
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<span style="font-family:"Times New Roman","serif"">Plasma-surface interactions were investigated for Y<sub>2</sub>O<sub>3</sub>, YOF and YF<sub>3</sub> chamber wall coatings. Time-dependent behavior of chlorine inductively-coupled plasmas was studied for Si
etching, following NF<sub>3</sub> plasma cleaning of different chamber coatings. Optical emission intensities were recorded throughout the processes for Cl, O, F, Si, SiCl<sub>x=1-3</sub>, SiF, and N<sub>2</sub>, as well as from added trace rare gases Xe and
Ar for determination of number densities for selected species by actinometry. Small differences were found for the three materials. Si-to-Cl emission ratios were similar for Y<sub>2</sub>O<sub>3</sub> and YOF, and somewhat larger for YF<sub>3</sub>. SiCl<sub>x=1-3</sub>
emissions were similar for the Y<sub>2</sub>O<sub>3</sub> and YOF-coated liners, but significantly less stable with time for YF<sub>3</sub>. Compared with Cl<sub>2</sub>/Ar plasmas, Cl<sub>2</sub>/O<sub>2</sub>/Ar plasmas produced nearly time-independent and
much more consistent Cl number densities during etching. This takes place despite a consistent upward drift in SiCl<sub>x=0-3</sub> emissions for all three materials. Time-dependent Langmuir probe (LP) measurements of ion and electron number densities and
electron energy distributions were also carried out. Ex-situ X-ray photoelectron spectroscopy (XPS) measurements of the surface composition of Y<sub>2</sub>O<sub>3</sub> coupon pieces after different etching and clean processes were also performed.
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<span style="font-family:"Times New Roman","serif"">Heterogeneous loss coefficient were also investigated in power-modulated chlorine inductively-coupled plasmas (ICPs) bounded by yttria-coated chamber walls. Power at 13.56 MHz applied to the plasma was modulated
between high power and no power. Time-resolved optical emissions from Cl and Xe actinometry trace gas were recorded over the 740 to 900 nm region. The intensity ratio of Cl-to-Xe emission, proportional to Cl number density,
<i>n<sub>Cl</sub></i>, was modulated with power, allowing Cl heterogeneous loss coefficients,
</span><i><span style="font-family:Symbol">g</span></i><sub><span style="font-family:"Times New Roman","serif"">Cl</span></sub><span style="font-family:"Times New Roman","serif"">, to be obtained from a simple time-resolved, 0-dimensional model that best matched
computed absolute and relative changes in <i>n<sub>Cl</sub></i> as a function of the modulation period, with
</span><i><span style="font-family:Symbol">g</span></i><sub><span style="font-family:"Times New Roman","serif"">Cl</span></sub><span style="font-family:"Times New Roman","serif""> as the only adjustable parameter. Cl<sub>2</sub> or Cl<sub>2</sub>/O<sub>2</sub>
ICPs were studied for surfaces (a) immediately after NF<sub>3</sub> plasma cleaning (</span><i><span style="font-family:Symbol">g</span></i><sub><span style="font-family:"Times New Roman","serif"">Cl</span></sub><span style="font-family:"Times New Roman","serif"">
= 0.30), (b) during long exposure to Cl<sub>2</sub> ICPs with no substrate bias (</span><i><span style="font-family:Symbol">g</span></i><sub><span style="font-family:"Times New Roman","serif"">Cl</span></sub><span style="font-family:"Times New Roman","serif"">
= 0.09), (c) during exposure to SiCl<sub>x</sub> etching products in Cl<sub>2</sub> ICPs with Si substrate bias (</span><i><span style="font-family:Symbol">g</span></i><sub><span style="font-family:"Times New Roman","serif"">Cl</span></sub><span style="font-family:"Times New Roman","serif"">
= 0.07), and during exposure to SiCl<sub>x</sub> etching products in Cl<sub>2</sub>/O<sub>2</sub> ICPs with Si subst</span><span style="font-family:"Times New Roman","serif"">r</span><span style="font-family:"Times New Roman","serif"">ate bias (</span><i><span style="font-family:Symbol">g</span></i><sub><span style="font-family:"Times New Roman","serif"">Cl</span></sub><span style="font-family:"Times New Roman","serif"">
= 0.03). These results compare favorably to qualitative behavior reported previously for continuous Cl<sub>2</sub> ICPs in this yttria-coated chamber.</span></p>
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