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<b style="font-family: Calibri, sans-serif; font-size: 11pt; color: inherit; font-style: inherit; font-variant-ligatures: inherit; font-variant-caps: inherit; background-color: ;"><span style="font-size:12.0pt; font-family:"Times New Roman",serif">NAME:</span></b><span style="font-size: 12pt; font-family: "Times New Roman", serif;">
Emilia Hirsch</span><br>
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<b><span style="font-size:12.0pt; font-family:"Times New Roman",serif">ADVISORS: </span>
</b><span style="font-size:12.0pt; font-family:"Times New Roman",serif">Dr. Vincent Donnelly and Dr. Demetre Economou</span></p>
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<b><span style="font-size:12.0pt; font-family:"Times New Roman",serif">DATE:</span></b><span style="font-size:12.0pt; font-family:"Times New Roman",serif"> Monday, April 20, 2020</span></p>
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<b><span style="font-size:12.0pt; font-family:"Times New Roman",serif">TIME</span></b><span style="font-size:12.0pt; font-family:"Times New Roman",serif">: 10:00 AM</span></p>
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<b><span style="font-size:12.0pt; font-family:"Times New Roman",serif">LOCATION:</span></b><span style="font-size:12.0pt; font-family:"Times New Roman",serif"> Zoom</span></p>
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<b><span style="font-size:14.0pt; font-family:"Times New Roman",serif">TITLE:</span></b><b><span style="font-size:12.0pt; font-family:"Times New Roman",serif"> In-Plasma Photo-Assisted Etching of Silicon in a High-Density Chlorine Discharge</span></b></p>
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<b><span style="font-size:14.0pt; font-family:"Times New Roman",serif">ABSTRACT:</span></b></p>
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<span style="font-size:12.0pt; font-family:"Times New Roman",serif">Etching of p-Si in 60 mTorr 10%Cl<sub>2</sub>/90%Ar Faraday-shielded inductively coupled high density plasmas was investigated under both ion-assisted etching (IAE) and photo-assisted etching
(PAE) conditions. Real-time etching rates and after-etching Si surface chemical compositions were obtained by laser interferometry and vacuum-transfer X-ray photoelectron spectroscopy (XPS), respectively. Precisely controlled ion energy distributions (IED)
were generated by applying pulsed negative DC bias on the conductive sample stage. Above a 36 eV threshold at a total flow rate of 250 sccm, the IAE rate increased with the square root of the ion energy. In contrast to DC bias, etching under RF bias did not
exhibit a threshold ion energy because of the wide IED. XPS spectra revealed that the surface layer under PAE conditions had a significantly lower chlorine content, composed of only SiCl. Under IAE conditions, however, silicon dangling bonds (Si●), SiCl<sub>2</sub>,
and SiCl<sub>3</sub> were found on the surface, in addition to SiCl, with relative abundance of SiCl>SiCl<sub>2</sub>>SiCl<sub>3</sub>. The absence of higher chlorides and Si● under PAE conditions suggested that VUV photons and above threshold-energy ions
interact with the surface very differently. By varying the duty cycle of the pulsed DC bias, it was found that the IAE rate scaled with the energetic ion dose, but only for low duty cycles. For higher duty cycles, the apparent IAE yield fell off with an
<i>increasing</i> Cl coverage on the surface, as duty cycle went up, which pointed to a negative synergy (anti-synergism) between PAE and IAE as the explanation. This anti-synergism was further supported by the observed decrease of the total etching rate with
increasing period of the pulsed DC bias. A plausible mechanism is that increasing the pulsing period causes more near-surface damage, creating more recombination centers that lead to higher loss rate of electron-hole pairs through recombination, thereby reducing
the PAE rate.</span></p>
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