Geometrically symmetric capacitively coupled oxygen plasmas are studied experimentally by optical emission spectroscopy and probe measurements as well as via numerical simulations using the kinetic Particle-in-Cell/Monte Carlo collision (PIC/MCC) approach. The experiments reveal that at a fixed pressure of 20 mTorr and a driving frequency of 13.56 MHz, the central electron density increases with an increased electrode gap, while the time averaged optical emission of atomic oxygen lines decreases. These results are reproduced and understood by the PIC/MCC simulations performed under identical conditions. The simulations show that the electron density increases due to a mode transition from the Drift-Ambipolar-mode to the a-mode induced by increasing the electrode gap. This mode transition is due to a drastic change of the electronegativity and the mean electron energy, which leads to the observed reduction of the emission intensity of an atomic oxygen line. The observed mode transition is also found to cause a complex non-monotonic dependence of the O þ 2 ion flux to the electrodes as a function of the electrode gap. These fundamental results are correlated with measurements of the etch rate of amorphous carbon layers at different gap distances.Published under license by AIP Publishing. https://doi.

Atomic layer etching (ALE), a cyclic process of surface modification and removal of the modified layer, is an emerging damage-less etching technology for semiconductor fabrication with a feature size of less than 10 nm. Among the plasma sources, inductively coupled plasma (ICP) can be a candidate for ALE, but there is a lack of research linking discharge physics to the ALE process. In this study, we comprehensively investigated the discharge physics of ICPs with a radio frequency (RF) bias and Ar/C4F6 mixture to be considered for the ALE process. Detailed studies on the discharge physics were conducted in each step of ALE (i.e., modification step, removal step) as well as the whole cycle as follows: (1) In the general ALE cycle, plasma properties dependent on the chamber geometry and the discharge mode of the ICP were analyzed; (2) in the modification step, a plasma instability with molecular gas was observed. The timescale for molecular gas removal was also investigated; (3) in the removal step, changes in plasma characteristics with the RF bias power were studied. Based on measurements of these plasma physical parameters, the discharge condition for ALE was optimized. ALE was performed on various thin films, including a-Si, poly c-Si, SiO2, and Si3N4. For each thin film, thicknesses of 0.5–2.0 nm were etched per cycle, as in quasi-ALE. Finally, ALE was performed on a patterned wafer, and the etch thickness of 0.6 nm per cycle and fine etch profile were obtained.

The microwave cutoff probe (CP) is an accurate diagnostic technique to measure absolute electron density even in processing gas plasmas. Because this technique needs the installation of two probe tips and a probe body in the plasma chamber, it may cause plasma perturbation in semiconductor plasma processing; this may increase the uncertainty of the measured value. In this work, a flat CP, which is embedded in the substrate chuck or chamber wall, is proposed to measure electron density without plasma perturbation and to monitor processing plasma in real-time. We first evaluated the performance of various types of flat CPs, such as the point CP, ring CP, and bar cutoff probe (BCP), through electromagnetic (EM) field simulation. The BCP showed better performance with clearer cut-off signal characteristics and minimization of noise signals compared with the other probe types. Therefore, we focused on the characteristics of the BCP through experiments and/or EM simulations and concluded the followings: (i) the measured electron densities of the BCP agree well with those of the conventional CP; (ii) the BCP measures the plasma density near the plasma-sheath boundary layer, which is very closely adjacent to the chamber wall or wafer; (iii) it was demonstrated for the first time that the plasma density can be measured, even though the processing wafers such as un-doped silicon, P type silicon, amorphous carbon, or amorphous carbon/SiO2 patterned wafers were placed on the flat CP; and (iv) we performed real-time measurements of the electron density using the BCP covered with the wafers in plasmas with various process gases, such as Ar, NF3, and O2. These results indicate that the chuck-embed-type or wall-type flat CP can be used as a real-time electron density measurement (monitoring) tool during industrial plasma processing, such as during etching, deposition, sputtering or implantation, and the chuck-embed-type flat CP can measure the plasma density impinging on the wafer in real-time without stopping the processing.

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The microwave planar cutoff probe, recently proposed by Kim et al. is designed to measure the cutoff frequency in a transmission (S21) spectrum. For real-time electron density measurement in plasma processing, three different types have been demonstrated: point-type, ring-type (RCP), and bar-type (BCP) planar cutoff probes. While Yeom et al. has shown that the RCP and BCP are more suitable than the point-type probe for process monitoring, the basic characteristics of the ring- and bar-type probes have yet to be investigated. The current work includes a computational characterization of a RCP and BCP with various geometrical parameters, as well as a plasma parameter, through a commercial three-dimensional electromagnetic simulation. The parameters of interest include antenna size, antenna distance, dielectric thickness of the transmission line, and input electron density. Simulation results showed that the RCP has several resonance frequencies originating from standing-wave resonance in the S21 spectrum that the BCP does not. Moreover, the S21 signal level increased with antenna size and dielectric thickness but decreased with antenna distance. Among the investigated parameters, antenna distance was found to be the most important parameter to improve the accuracy of both RCP and BCP.

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Fine tuning of plasma parameters is essential in semiconductor plasma processing because of the demand for smaller, low-power, and high-integration nanoelectronic devices in the semiconductor industry. Existing method monitors process abnormality based on the real-time measurement of some in situ processing sensors, such as optical emission spectroscopy and voltage-current sensor, owing to the absence of a direct plasma measurement sensor applicable to in situ plasma processing monitoring. In this paper, we propose a microwave flat cutoff probe and its circuit modeling, in which the plasma and sheath are considered as coplanar capacitance. The circuit model was verified through both electromagnetic simulation and experiment, and the results were found to be in good agreement. Through this circuit model with the coplanar capacitance, the effect on the distance between the microwave radiating antenna and detecting antennawas analyzed in detail.

Copper sulfide (CuS) nanoparticle films with different nanoparticle sizes were fabricated using an inductively coupled plasma (ICP) and a vapor-phase sulfurization method. First, the ICP is applied to a thin copper film to obtain a copper nanoparticle film, based on the plasma-surface interactions through the ion bombardment on the film. The fabrication of the Cu nanoparticles revealed that their size and spatial distribution depend on the discharge mode of the ICP and plasma irradiation time. From the measurements of the plasma density, optical emission spectrum, and ion flux energy distribution function, it was found that the inductive mode of the ICP, compared to the capacitive mode of the ICP, is efficient at fabricating the uniform nanoparticle film due to the optimal plasma potential and high ion flux with narrow ion energy distribution. The Cu nanoparticles are then transformed to CuS nanoparticles through vaporphase sulfurization. For the hydrophobicity application of the CuS nanoparticle film, the contact angles of the CuS nanoparticle films were measured and compared with those of other thin films, such as SiO 2 and bulk CuS. The contact angle of the CuS nanoparticle film, fabricated through the plasma-surface interactions and sulfurization, was significantly higher than that of other thin films owing to the hydrophobic surface of the CuS with the nanoparticle structure.