Hyun-Joon Roh

How to determine the relative ion concentrations of multiple-ion-species plasmas generated in the multi-dipole filament source

This paper introduces how to determine concentrations of ion species in a mixed gas plasma that are not linearly proportional to their neutral partial pressures. A particle balance model was developed to predict the relative ion concentrations in multiple-ion-species plasmas, considering their ionization rates and loss fluxes to the wall. Analysis is carried out especially with Ar/Xe and Ar/He multi-dipole plasmas in which the neutral gases are directly ionized by the mono-energetic primary electrons. The experimental data of ion concentrations were obtained using the ion acoustic wave measurement method of the concentration of two ion species. The comparison reveals that the ion concentration ratio is linearly proportional to the ratio of the ionization cross sections and the ion loss velocity between two gas species. Especially, the model prediction is improved with using the two-ion-species sheath model (recently reported by Baalrud and Hegna) for obtaining the ion loss velocity at the sheath boundary.

Enhancement of the Virtual Metrology Performance for Plasma-Assisted Oxide Etching Processes by Using Plasma Information (PI) Parameters

Virtual metrology (VM) model based on plasma information (PI) parameter for C4F8 plasma-assisted oxide etching processes is developed to predict and monitor the process results such as an etching rate with improved performance. To apply fault detection and classification or advanced process control models on to the real-mass production lines efficiently, high-performance VM model is certainly required and principal component regression (PCR) is preferred technique for VM modeling despite this method requires many number of data set to obtain statistically guaranteed accuracy. In this paper, as an effective method to include the “good information” representing parameter into the VM model, PI parameters are introduced and applied for the etch rate prediction. By the adoption of PI parameters of b- and q-factor and surface passivation parameters as PCs into the PCR-based VM model, information about the reactions in the plasma volume, surface, and sheath regions can be efficiently included into the VM model; thus, the performance of VM is secured even for insufficient dataset provided cases. For mass production data of 350 wafers, developed PI-based VM model was satisfied required prediction accuracy of industry in C4F8 plasma-assisted oxide etching process.

Determination of electron energy distribution function shape for non-Maxwellian plasmas using floating harmonics method

A new floating harmonics method is developed to determine the electron energy distribution shape in the non-Maxwellian plasmas. The slope and curvature of the electron energy probability function (EEPF) at the floating potential can be obtained by measuring amplitude ratios among the first three sideband harmonics of the probe electron current. Together with the generalized EEPF formula, the EEPF shapes of the non-Maxwellian plasmas are able to be determined from the slope and curvature. Here, the new method is experimentally verified and its results are compared with EEPF measurements using the Langmuir probe (LP) method. The effective electron temperature and the EEPF shape parameter obtained by the method give good agreements with those of the LP measurements.

Laser-Assisted Hμ Spectroscopy for Measurement of Negative Ion Density in a Hydrogen Plasma

Abstract A novel laser-assisted Hμ spectroscopy is proposed to measure negative ion density in a hydrogen plasma. The laser-induced photodetachment of negative ions leads to a decrease in Hμ intensity due to blocking of the mutual neutralization channel associated with generation of H (n=3) atoms. The relationship between the reduced Hμ intensity and the negative ion density is investigated experimentally and analytically. It is observed that the reduced Hμ intensity follows the trend in the negative ion density as a function of pressure, indicating that this spectroscopy holds promise for determining the negative ion density. In addition, a departure from linearity between the reduced Hμ intensity and the negative ion density is also analyzed because it can affect the quantitative determination of the negative ion density in the laser-assisted Hμ spectroscopy. The departure is found to be attributed to the change in the mutual neutralization reaction rates depending on plasma conditions.