Control of radical and ion density in oxygen discharges using noble gas background
Abstract
Plasmas etching and deposition processes are widely used during the production of integrated circuits. The neutral radical flux and ion flux to the wafer surface are two of the main parameters that effect the etch or deposition rate. This work focuses on developing a method to control the neutral radical and ion densities independently to yield better control of the etch and deposition processes. In this research, oxygen is used the molecular gas because it has well-known dissociation kinetics that allow for modeling. To accomplish this independent control, we develop a way to control the electron density and electron temperature independently. Electron temperature and density are modeled by 0-dimensional particle and power balance equations in pure He, Ar, and Xe plasmas and binary admixtures of two noble gases. The plasma parameters are also measured by a Langmuir probe under the same conditions. The results show that the electron density is determined mainly by the RF power and fill pressure, while the electron temperature is determined by the ionization potential of the noble gas used. Thus modulation of noble gas admixture ratios and RF power allows the electron density and temperature to be controlled independently. The plasma parameters, as well as the atomic oxygen density, are also measured in pure oxygen discharges and noble gas/oxygen mixtures. The atomic oxygen density is measured by both actinometry and appearance mass spectrometry. The 0-D model is extended to include effects of molecular gases to predict the plasma parameters and atomic oxygen density in these discharges. The background noble gas determines the electron density and temperature as long as the partial pressure of oxygen remains small. The dissociated atomic neutral oxygen density is highest in O2/Xe mixtures and lowest in O 2/He mixtures, increases with electron density, and decreases with electron temperature. The use of noble gas/oxygen mixtures allows for a larger range of atomic oxygen density and ion density than in pure oxygen plasmas, and also allows for independent control of the ion density and the atomic oxygen density.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 2005
- Bibcode:
- 2005PhDT........63T