Homework7

# Homework7 - C How does this difference in the rate of...

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ECE 6450 Homework #7 1.) Explain why plasma etching trends have been moving toward lower pressures while deposition trends have been moving toward higher pressures. 2.) When dilute amounts of oxygen are introduced into a CF 4 plasma process, a scavenged byproduct gas like CO (carbon monoxide) is produced. A.) If the gases are introduced to a large chamber (infinite conductance) with an exit tube with a conductance of 100 liters/(sec-torr) to a roots blower pump at 50 millitorr (50e-3 torr), what is the maximum possible throughput (in sccm) of CF 4 and CO respectively? (Assume the vapor pressure of CF 4 is 1 torr and the vapor pressure of CO is 1000 torr at the process temperature). B.) If the chamber has a volume of 10 liters and is maintained at 1 torr pressure, what (approximate) average time is required to purge the two gases (this is effectively the speed for which a process change can be made and is why minimization of the volume of process chambers is important)?
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Unformatted text preview: C.) How does this difference in the rate of removal of CO and CF 4 effect the average carbon content in the chamber for the cases where oxygen is not present verses when it is present? D.) What effect does the change in carbon content have on the sidewall polymerization and why (Assume RIE conditions)? E.) What effect does the oxygen have on the anisotropy? 3.) What percentage of gas molecules (assume 3 angstrom molecular diameter) traveling a distance of 50 cm has underwent a randomizing scattering event at 0.5 Pa (sputtering chamber) and at 10-4 Pa (evaporator chamber)? You may use the expression for scattering probability, where n is the number of molecules having been scattered, n o is the total n n e o d = − − 1 λ number of molecules, d is the distance traveled and λ is the mean free path between collisions. 4.) Look over example 12.1 in your book (no need to turn it in)....
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