On the Etching Mechanism of Highly Hydrogenated SiN Films by CF4/D2 Plasma: Comparison with CF4/H2

With the increasing interest in dry etching of silicon nitride, utilization of hydrogen-contained fluorocarbon plasma has become one of the most important processes in manufacturing advanced semiconductor devices. The correlation between hydrogen-contained molecules from the plasmas and hydrogen atoms inside the SiN plays a crucial role in etching behavior. In this work, the influences of plasmas (CF4/D2 and CF4/H2) and substrate temperature (Ts, from −20 to 50 °C) on etch rates (ERs) of the PECVD SiN films were investigated. The etch rate performed by CF4/D2 plasma was higher than one obtained by CF4/H2 plasma at substrate temperature of 20 °C and higher. The optical emission spectra showed that the intensities of the fluorocarbon (FC), F, and Balmer emissions were stronger in the CF4/D2 plasma in comparison with CF4/H2. From X-ray photoelectron spectra, a thinner FC layer with a lower F/C ratio was found in the surface of the sample etched by the CF4/H2 plasma. The plasma density, gas phase concentration and FC thickness were not responsible for the higher etch rate in the CF4/D2 plasma. The abstraction of H inside the SiN films by deuterium and, in turn, hydrogen dissociation from Si or N molecules, supported by the results of in situ monitoring of surface structure using attenuated total reflectance-Fourier transform infrared spectroscopy, resulted in the enhanced ER in the CF4/D2 plasma case. The findings imply that the hydrogen dissociation plays an important role in the etching of PECVD-prepared SiN films when the hydrogen concentration of SiN is higher. For the films etched with the CF4/H2 at −20 °C, the increase in ER was attributed to a thinner FC layer and surface reactions. On the contrary, in the CF4/D2 case the dependence of ER on substrate temperature was the consequence of the factors which include the FC layer thickness (diffusion length) and the atomic mobility of the etchants (thermal activation reaction).

Spectral study of argon-methane mixture plasma jet generated by a DC plasmatron

We present the results of studying optical emission spectra of Ar:CH4 plasma produced on a DC plasmatron for graphene synthesis. We have identified the basic set of spectral lines and bands in the obtained spectra and shown that H lines and C2 bands appear due to direct excitation by an electron strike of corresponding neutral particles. C2 molecular bands were also identified in the spectra with intensity considerably lower compared to previous studies where He: C2H2 mixture was used as plasma-forming gas.

The Effect of Oxygen Admixture with Argon Discharges on the Impact Parameters of Atmospheric Pressure Plasma Jet Characteristics

Dry argon (Ar) discharge and wet oxygen/argon (O2/Ar) admixture discharge for alternating current atmospheric pressure plasma jets (APPJs) were studied for Ar discharges with flow rates ranging from 0.2 to 4 slm and for O2/Ar discharges with different O2 ratios and flow rates ranging from 2.5 to 15 mslm. The voltage–current waveform signals of APPJ discharge, gas flow rate, photo-imaging of the plasma jet length and width, discharge plasma power, axial temperature distribution, optical emission spectra, and irradiance were investigated. Different behavior for varying oxygen content in the admixture discharge was observed. The temperature recognizably decreased, axially, far away from the nozzle of the jet as the flow rate of dry argon decreased. Similar behavior was observed for wet argon but with a lower temperature than for dry argon. The optical emission spectra and the dose rate of irradiance of a plasma jet discharge were investigated as a function of plasma jet length, for dry and wet Ar discharges, to determine the data compatible with the International Commission on Non-Ionizing Radiation Protection (ICNIRP) data for irradiance exposure limits of the skin, which are suitable for the disinfection of microbes on the skin without harmful effects, equivalent to 30 μJ/mm2.

In-situ monitoring of optical emission spectra for microscopic pores in metal additive manufacturing Submitted for Publication

Quality assurance techniques are increasingly demanded in additive manufacturing. Going beyond most of the existing research that focuses on the melt pool temperature monitoring, we develop a new method that monitors the in-situ optical emission spectra signals. Optical emission spectra signals have been showing a potential capability of detecting microscopic pores. The concept is to extract features from the optical emission spectra via deep auto-encoders, and then cluster the features into two quality groups to consider both unlabelled and labelled samples in a semi-supervised manner. The method is integrated with multitask learning to make it adaptable for the samples collected from multiple processes. Both a simulation example and a case study are performed to demonstrate the effectiveness of the proposed method.

REFORMING OF ETHANOL IN PLASMA-CATALYTIC SYSTEM WITH DC AND AC ROTATING GLIDING DISCHARGE

The article presents the results of the investigation of the reforming of ethanol into synthesis gas using a plasmacatalytic system with either AC or DC wide-aperture rotating gliding discharge. Current and voltage oscillograms of the wide-aperture rotating gliding discharge were measured. The time-dependence of the instantaneous power of the discharge in the air was built. The photographs of the discharge in the airflow and discharge during the ethanol reforming were compared. The optical emission spectra of the plasmas of the torches of AC and DC wide-aperture rotating gliding discharges were studied. The rotational and vibrational temperatures of the plasma torch in the reaction chamber were determined. The results of the gas-chromatography of the synthesis gas produced during the plasm-catalytic reforming of ethanol using either AC or DC rotating gliding discharge are presented.

PLASMA-CATALYTIC SYSTEM WITH NARROW-APERTURE ROTATING GLIDING DISCHARGE

The article presents the results of the investigation of the rotating gliding discharge with the narrow aperture in the airflow. The photographs of the rotating gliding discharge with the narrow aperture were matched with its voltage oscillograms. Photographs were used to determine the maximum length of the discharge channel and its dependence on the airflow Gd into the discharge chamber. Voltage oscillograms were used to determine the difference between the maximum and minimum discharge voltage ΔU = Umax-Umin. The dependence of the electric field in the positive column on the airflow Gd into the discharge chamber was plotted. Optical emission spectra of the plasma of the rotating gliding discharge with a narrow aperture were captured and used to determine the distribution of the vibrational Tv and rotational Tr temperatures along the length of the plasma torch inside the reaction chamber.