No abstract

RF dischsrge is widely used in v&ous technologid processes, therefore studies of properties of such a discharge are of considerable interest. If one knows the dprrtial distribution of the de (time-averaged) plasma potential pfi then one can CL+ the mechanisms of many phenomena occarring in RF discharge. As is known (Lwibkii S.M., Zhnm.T~n.Fic.1967,~.27,p.1001; SsbadiI E. et d., Plasma Chem.Ph?mb P~lcess.1986,v.8,p.425) ("pl incr-steadily when one movea from the electrode to the b o u n d q of the electrode layer and ita value remains constant in the quasineutral plasma. Thk paper shows experiment& tbst one o h e s the " i m of the de plasma potential in the central part of the RF discharge at gae pressures p 1 0.1 Torr. Experiments have been performed in air and argon at gss pressures between 0.006 and 2 Torr Kith RF voltage d u e s U < loo0 VI BF frequency f = 13.56 MHr and spacings between plane electrodss L = 10 + 64 mm. DC plasma potential hss been mebenred with single cylindrical probes. At low gaa prea-SPIW (p < 0.1 TOR) and moderate spacings (L c 1.5 cm) it remains constant or decreases slowly when one moves from the discharge center nhereaa it experiences fast decreastt up to sero in electrode layem (F'ig.1). At p r e s " p > 0.1 Torr and sufficiently large L one observes a minimum in the axial distribution of the de plasma potential in the central part of the discharge (Fig. 2). This minimum appears when RF discharge in going from the we& current form of burning to the ntrong current one. Probably, the appearance of this minimum in due to the fact that fast electrons formed in electrode layera h e thek energy via inekrstic collisions with molecules and bnild up the region of the negative volume charge at the diecbsrge center.Fig. 1. Axial distribution of dc plasma potential p# in RF discharge in argon at L = 22 mm: a) p = 0.1 Torr. 1 -U = 100 V, 2 -200, 3 -300,4 -400,s -500 V; b)p = 1 Torr, 1 -U = 100 V, 2 -210.3-260, 4 -325. 5 -365 V.Uniformity measurements in a helicon plasma etcher.Recent research efforts on the UW helicon etcher have focused on the plasma density profile variation along the axis of the etching chamber. The goal of this research is to find ways to maintain a high plasma density while creating a radially uniform plasma. This study is unique because high magnetic fields(425-625G) are used in the source region. The UW helicon etcher consists of 21 magnetic field coils surrounding a 1 meter long, 10 cm diameter quartz tube. At one end of the tube is a Negoya Type I11 RF antenna which is run at 13.56 MHz. At the opposite end is the etching chamber containing a 20 cm diameter magnetic multidipole bucket. The purpose of the bucket is to both maintain a high plasma density and improve the radial uniformity in the etching chamber. This experiment was conducted using 20 sccm of argon at a pressure of 5 mT with an FtF power of 900 W. The magnetic field was varied between 425 and 625 Gauss. The density was measured using a Langmuir probe fitted with 3 filters to filter out the RF perturbations at...