A New Negative Ion Plasma Source for Material Processing

Abstract

Summary form only given. Negative ions in plasmas are much attractive species in material processing, such as ion implantation, CVD and etching in ULSI fabrications. This is because the negative ion has a great potential of charge-up free and low damage fabrication processes which become more important as the cell size is shrinking in ULSI. However, no effective negative ion plasma source has been reported as of yet. The objective of this work is to study a negative ion plasma source. In particular, an innovative method to produce a negative ion rich plasmas is proposed by employing RF surface-wave plasma with a extremely high dielectric constant discharge tube. As well-known, the surface-wave can only be existed above the resonance density, which depends on the permittivity of the discharge tube. In this work, a negative ion plasma is produced by employing the after-glow appeared in the resonance density which is enhanced by a extremely high dielectric constant discharge tube. The surface-wave plasmas of O2 and SF6 were produced in a discharge tube of 15 mm in inner diameter and the length of 330 mm, by supplying 13.56 MHz power. The two discharge tube materials were employed; the one is a ceramic of TiCa-TiMg composite, K-140, which is commercially available from KYOCERA Co. and another is quartz. Their permittivities are, respectively, 140 and 3.8. The optical emission line measurements were carried out from the both lateral and axial view. The axial decay rate of the intensities of the optical emission lines FI in SF6 plasma were very fast in the K-140 discharge tube and its rate was 5 times larger than in the quartz. In particular, a sudden precipitation of the line intensity at the axial distance Z=13 cm could be observed, and this is due to the surface-wave ending at the resonance density, providing a high density after-glow. In O2 plasma, in this after-glow region, the OI emission lines of 777 and 845 nm, which are originated from the mutual neutralization of O- and O+, were observed to be very much enhanced after the sudden precipitation, indicating the rich negative ions populated in this region. While in the quartz discharge tube the line intensity decayed just simply and monotonically. Thus it was concluded that the surface-wave plasma with a extremely high dielectric constant discharge tube was an innovative method of negative ion rich plasma