Abstract
In a magnetized plasma column generated from an electronegative gas, negative-ions accumulate around the plasma column via radial diffusion. In this study, a dc discharge is applied in SF6 gas to produce a plasma column, and the radial density profile of negative-ions is measured by Langmuir probes using the modified Bohm criterion. The gas pressure and discharge current dependences of negative-ion density are also measured. It is found that the negative-ion density of 8.0 × 1017 m-3 is obtained around the plasma column at r = 1.0 cm when SF6 pressure is 0.13 Pa and discharge current is 0.50 A. The negative-ion density has radial gradient, and the electron density is much lower in this region.
Highlights
It is already known that negative-ions can be produced by magnetized plasmas, in which discharge of electronegative gas such as CF4 gas makes fluorine negative-ions and they accumulate around a magnetized plasma column via radial diffusion [1,2,3,4]
The negative-ion density in the SF6 plasma is evaluated from the probe measurement utilizing the modified Bohm condition [1,14]
Radial profiles of the negative-ion density, n− and electron density, ne are shown in Figure 3 under the typical conditions of B = 0.030 T, p = 0.13 Pa, and Id = 0.50 A
Summary
It is already known that negative-ions can be produced by magnetized plasmas, in which discharge of electronegative gas such as CF4 gas makes fluorine negative-ions and they accumulate around a magnetized plasma column via radial diffusion [1,2,3,4]. Higher-density and stable fluorine negative-ion sources have potential to make fine silicon etching, because the negative-ions could reduce the charging-up damage and abnormal etching on the etching surfaces in case of LSI fabrications [5,6,7,8,9,10]. In order to obtain higher density fluorine negative-ions, on the standpoint of future application to negative-ion etching, SF6 is used as a source gas of the magnetized plasma because this gas has high electron affinity, at low electron temperatures [11]. Though multiple negative-ion species (F−, SF6− , SF5− ) may have contributed to negative charges around the SF6 plasma column via nondissociative attachment and dissociative attachment reaction schemes, F− ions have the highest density [12], to the case of CF4 plasmas [13]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
