RESUMEN
One of the cleaning processes in semiconductor fabrication is the ashing process using oxygen plasma, which has been normally used N2 gas as additive gas to increase the ashing rate, and it is known that the ashing rate is strongly related to the concentration of oxygen radicals measured OES. However, by performing a comprehensive experiment of the O2 plasma ashing process in various N2/O2 mixing ratios and RF powers, our investigation revealed that the tendency of the density measured using only OES did not exactly match the ashing rate. This problematic issue can be solved by considering the plasma parameter, such as electron density. This study can suggest a method inferring the exact maximum condition of the ashing rate based on the plasma diagnostics such as OES, Langmuir probe, and cutoff probe, which might be useful for the next-generation plasma process.
RESUMEN
As the conventional voltage and current (VI) probes widely used in plasma diagnostics have separate voltage and current sensors, crosstalk between the sensors leads to degradation of measurement linearity, which is related to practical accuracy. Here, we propose a VI probe with a floating toroidal coil that plays both roles of a voltage and current sensor and is thus free from crosstalk. The operation principle and optimization conditions of the VI probe are demonstrated and established via three-dimensional electromagnetic wave simulation. Based on the optimization results, the proposed VI probe is fabricated and calibrated for the root-mean-square (RMS) voltage and current with a high-voltage probe and a vector network analyzer. Then, it is evaluated through a comparison with a commercial VI probe, with the results demonstrating that the fabricated VI probe achieved a slightly higher linearity than the commercial probe: R2 of 0.9967 and 0.9938 for RMS voltage and current, respectively. The proposed VI probe is believed to be applicable to plasma diagnostics as well as process monitoring with higher accuracy.
RESUMEN
As the importance of measuring electron density has become more significant in the material fabrication industry, various related plasma monitoring tools have been introduced. In this paper, the development of a microwave probe, called the measurement of lateral electron density (MOLE) probe, is reported. The basic properties of the MOLE probe are analyzed via three-dimensional electromagnetic wave simulation, with simulation results showing that the probe estimates electron density by measuring the surface wave resonance frequency from the reflection microwave frequency spectrum (S11). Furthermore, an experimental demonstration on a chamber wall measuring lateral electron density is conducted by comparing the developed probe with the cutoff probe, a precise electron density measurement tool. Based on both simulation and experiment results, the MOLE probe is shown to be a useful instrument to monitor lateral electron density.
