Plasma particulate contamination control. II. Self-cleaning tool design

Abstract

Macroscopic particles are often observed in etching, sputtering, and deposition plasmas, in laboratory and manufacturing tools, in concentrations far exceeding ambient cleanroom conditions and acceptable process specifications. Controlling particle contamination is an important goal in modern fabrication lines. Controlling plasma-generated particulates is especially important as these tools and processes are a major source of wafer contamination. Plasma particles acquire negative charge by electron attachment and are influenced by electric fields and plasma inhomogeneities. Improper tool design exacerbates tool contamination problems by trapping particles near wafers or other sensitive surfaces. Conversely, proper tool and electrode design can provide greatly improved contamination results. The concept of a self-cleaning plasma tool is presented for the first time, along with evidence of the effectiveness and usefulness of this approach in laboratory and manufacturing studies. The method does not reduce the generation of particles, but limits the number deposited on the wafer. The self-cleaning plasma tool uses a topographically designed electrode to intentionally trap particles in designated regions of the plasma. Feed gas drag forces carry the trapped particles along a groove or series of grooves in the electrode away from the wafer and into the pump port. Manufacturing tools fitted with this electrode design have shown particle reductions ranging from 20% to 70%, depending on the tool condition, percentage of plasma-generated particles, and competition from other particle traps formed by the tooling or wafers. No influence on other aspects of the process quality is noted. © 1992, American Vacuum Society. All rights reserved.