This research involved an experimental investigation of the relationship between the plasma parameters and etching properties of SiO 2 over poly-Si mask in Ar/C 4 F 8 capacitively coupled plasma (CCP). In these experiments, the etching process was conducted in CCP and the external conditions such as the applied power, pressure, and gas ratio were varied. In addition, the density of radicals, which dominantly participate in surface reactions, the electron density, and the self-bias voltage were measured. As a result, deposition of the CF x polymer film on the poly-Si mask lowered the electron density and self-bias voltage and the etch rate of the target and the mask increased as the internal parameters of the plasma increased. This result indicated that the electron density and the self-bias voltage, which represent the physical etch elements of ion flux and energy, respectively, have a marked influence on the etching process. Consequently, our work led us to propose a critical value, which is the product of the electron density and self-bias voltage, n e V bias , to analyze the etching mechanism. Our results are also expected to serve as a basic processing database that enables an in-depth understanding of etching.
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.
Because radio frequency (RF) sensors typically experience interference between their capacitive detector and inductive detector, it becomes difficult for them to precisely measure voltage and current waveforms. We developed a high-precision RF sensor by using novel double walls (NDWs), which can minimize the interference. The geometrical construction variables of the NDWs are determined by analyzing the results from three-dimensional electromagnetic simulation. The phase difference between voltage and current waveforms for the designed RF sensor is approximately 1.32° at a matched load, and that for an ENI probe (VIP1004) is 24.78°, as a result of which the developed RF sensor has better performance in preventing such interferences, compared with the other commercial sensor.
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