Dissociation Processes in Plasma Chemistry and Gaseous Dielectrics

Abstract

Plasma processing is widely used in integrated circuit manufacturing. In a typical plasma process a chemically nonreactive feed gas flows into a discharge reactor where the discharge electrons dissociate the feed gas and produce chemically reactive products. The discharge dissociation products react at the surface of the Si, GaAs or other wafer being processed and either remove material in an etching process or deposit a thin film. Some of the gases which are used in these etching and deposition processes are listed in Table 1. Our present understanding of these plasma processes is limited, in part, by the limited availability of fundamental information about the microscopic physical and chemical processes which lead to the observed macroscopic etching and deposition processes. The important processes include electron impact ionization and dissociation, gas phase chemical reactions, surface chemical reactions and physical processes at the surfaces. Electron impact dissociation can also change the chemical composition of gaseous dielectrics. Therefore, dissociation cross section data is needed to understand and model both plasma processing reactors and the behavior of gaseous dielectrics. Dissociative ionization and dissociative excitation cross sections are available for many gases. However, for gases where the dissociation channels are known, a significant fraction of the total dissociation is due to processes which produce neutral fragments in their electronic ground state. Cross sections for these neutral dissociation processes are difficult to measure because the products are difficult to detect. Computer modeling of plasma processing discharges and the available cross section and chemical kinetic data have recently been reviewed.¹