Investigation of atomic oxygen density in a capacitively coupled O₂/SF₆discharge using two-photon absorption laser-induced fluorescence spectroscopy and a Langmuir probe

Abstract

Two-photon absorption laser-induced fluorescence (TALIF) spectroscopy was used for detection of absolute atomic oxygen density in a low-pressure capacitively coupled plasma source. We investigated the variation of atomic oxygen density for various mixtures of O 2 /SF 6 and report a significant five-fold increase of [O] when oxygen plasma was diluted with SF 6 by only 5%. We attribute this increase in [O] to a combination of a change in surface conditions caused by constituents of SF 6 plasma reacting with the reactor walls and also due to an increase in the electron temperature. Atomic oxygen production rates were determined using electron-energy distribution functions obtained with a cylindrical Langmuir probe. It was found that the effective electron temperature dramatically increased from approximately 1-8 eV as the SF 6 content varied from 0% to 60% which consequently resulted in a three-fold increase in the atomic oxygen production rate. TALIF was also used to investigate the variation of [O] due to fluorination of the reactor walls and also after etching resist-coated wafers. It was found that [O] increased by over a factor of three after fluorinating the walls with SF 6 plasma; on the other hand a coating formed on the reactor walls after a resist etch process resulted in a reduction of [O] by only 20%.

On electron heating in a low pressure capacitively coupled oxygen discharge

“…particle weight threshold wall quenching partial pressure [meV] or recombination [%] coefficients O2(X 3 Σ − g ) 5 × 10 9 500 1.0 90.648 O2(a 1 ∆g) 5 × 10 9 100 0.007 [30] 4.4039 [35,36] measured the atomic oxygen density, by TALIF and actinometry in a slightly asymmetric capacitively coupled discharge at 100 mTorr and 100 W, to be 1.4 × 10 20 m −3 , which is higher than 1.9 × 10 19 m −3 if based on oxygen partial pressure of 0.519 %. Thus this atomic oxygen partial pressure can both be over and under estimate.…”

“…et al [35,36] measured the atomic oxygen density, by TALIF and actinometry in a slightly asymmetric capacitively coupled discharge at 100 mTorr and 100 W, to be 1.4 × 10 20 m −3 , which is higher than 1.9 × 10 19 m −3 if based on oxygen partial pressure of 0.519 %. Thus this atomic oxygen partial pressure can both be over and under estimate.…”

Optimization of dry etching parameters for fabrication of polysilicon waveguides with smooth sidewall using a capacitively coupled plasma reactor

“…The maximum rates are observed for SF 6 concentrations between 80% and 90%. The low etch rates for lower concentrations of SF 6 can be attributed to the lower effective temperature of electrons in the plasma, while at higher concentrations it can be due to the lowering of electron density [24,25], both of which influence the degree of ionization in the plasma chamber and the etching of polysilicon. At the same time, the presence of oxygen can also be important for the improvement of the etching efficiency by removing the polymer products formed during etching.…”

“…Recently, fabrication processes using capacitively coupled plasma reactors have been studied [25][26][27][28][29][30], and the main parameters used in optimization were pressure, power, and their combination. The experimental design of optimization based on these two parameters is presented in Table 1.…”

Remote sensing of a low pressure plasma in the radio near field

“…by extracting the geometric resonance frequency shown in figure 4 and employing an estimate of the total sheath width. A calculation of the high voltage sheath size is carried out by employment of the Child sheath law 22) coupled with a combination of Langmuir probe measurements 13,14) for electron density and temperature and I-V measurements for estimation of the sheath voltage. 27) The 'high voltage' sheath width is estimated here as 0.…”