Emi Kawamura

A benchmark study of a capacitively coupled oxygen discharge of the oopd1 particle-in-cell Monte Carlo code

The oopd1 particle-in-cell Monte Carlo collision (PIC-MCC) code is used to simulate a capacitively coupled discharge in oxygen. oopd1 is a one-dimensional object-oriented PIC-MC code in which the model system has one spatial dimension and three velocity components. It contains a model for planar geometry and will contain models for cylindrical and spherical geometries, and replaces the xpdx1 series, which is not object-oriented. The oopd1 also allows for different weights of simulation particles and relativistic treatment of electrons. The revised oxygen model includes, in addition to electrons, the oxygen molecule in the ground state, the oxygen atom in the ground state, the negative ion O− and the positive ions O+ and . The cross sections for the collisions among the oxygen species have been significantly revised from earlier work using the xpdp1 code and the electron kinematics have been enhanced. Here we make a benchmark study and compare the oopd1 code to the well-established planar xpdp1 code and discuss the differences using a limited cross section set with ions, O− ions and electrons as the charged particles. We compare the electron energy distribution function, the electron temperature profile, the density profiles of charged particles and electron heating rates for a capacitively coupled oxygen discharge at 50xa0mTorr with electrode separation of 4.5xa0cm. Then we explore the effect of adding O atoms and O+ ions on the overall discharge.

Effect of a dielectric layer on plasma uniformity in high frequency electronegative capacitive discharges

The authors use a fast 2D axisymmetric fluid-analytical code to study the effect of adding a dielectric layer over the wafer electrode of a high frequency capacitively coupled plasma (CCP) reactor. At higher frequencies and larger areas, the wavelengths of the radially propagating surface waves in the plasma can become significantly shorter than the reactor dimensions, leading to center-high plasma nonuniformities. These wavelengths increase with increasing sheath widths, suggesting that a method to suppress wave effects in a high frequency CCP is to increase the effective sheath width by adding a dielectric layer over the wafer electrode. The authors conducted simulations with and without a dielectric layer and found that the dielectric layer improved plasma uniformity. The authors also studied the effect of adding a thin conducting or resistive silicon wafer above the dielectric layer and found that a conducting silicon wafer shorts out the fields and shields the discharge from the dielectric layer, while the resistive silicon wafer allows the fields to pass through to the dielectric layer.The authors use a fast 2D axisymmetric fluid-analytical code to study the effect of adding a dielectric layer over the wafer electrode of a high frequency capacitively coupled plasma (CCP) reactor. At higher frequencies and larger areas, the wavelengths of the radially propagating surface waves in the plasma can become significantly shorter than the reactor dimensions, leading to center-high plasma nonuniformities. These wavelengths increase with increasing sheath widths, suggesting that a method to suppress wave effects in a high frequency CCP is to increase the effective sheath width by adding a dielectric layer over the wafer electrode. The authors conducted simulations with and without a dielectric layer and found that the dielectric layer improved plasma uniformity. The authors also studied the effect of adding a thin conducting or resistive silicon wafer above the dielectric layer and found that a conducting silicon wafer shorts out the fields and shields the discharge from the dielectric layer, whi...

Nonlinear resonance effects on electron heating in capacitive discharges

In capacitive radio frequency discharges operated at gas pressures below 20 mTorr two mechanisms of electron heating play a major role: i) ohmic heating due to collisions of electrons with neutrals of the background gas and ii) stochastic heating - often referred to as Fermi heating - due to momentum transfer from the oscillating boundary sheath. In this contribution we show that the plasma series resonance due to interaction of the plasma bulk and the nonlinear sheath significantly effects the electron heating. The series resonance can enhance both the ohmic and stochastic heating by factors of 2-5. We conclude that the nonlinear plasma dynamics has to be taken into account in order to describe quantitatively correct electron heating in low-pressure capacitive radio frequency discharges.