Yuji Kasashima

Instantaneous Generation of Many Flaked Particles by Impulsive Force of Electric Field Stress Acting on Inner Wall of Mass-Production Plasma Etching Equipment

To elucidate the mechanism of instantaneous generation of many flaked particles in plasma etching equipment, we investigate the relationship between the generation of flaked particles from deposited films (consisting of etching reaction products on the ground electrode) and the plasma stability under mass-production conditions. Many particles are observed with our particle monitoring system when plasma instability occurs. The generation of such flaked particles correlates well with the occurrence of a large, rapid change in floating potential on the chamber wall. Our results indicate that many flaked particles from films deposited on a ground electrode are generated by electric field stress acting instantaneously and working as an impulsive force.

Generation of supersonic plasma flows using an applied-field MPD arcjet and ICRF heating

A quasi-steady, supersonic plasma flow was produced by using a magneto-plasma-dynamic arcjet (MPDA) in a divergent magnetic nozzle. The ion acoustic Mach number, Mi, evaluated by spectroscopy and Mach probe measurement, was unity in the uniform field near the MPDA and reached almost 3 in the divergent magnetic nozzle. In the case of a subsonic flow near the exit of the MPDA, a magnetic Laval nozzle was effective in converting it to a supersonic flow with Mi = 1 at the throat. We heated ions of the fast-flowing plasma by ICRF (ion-cyclotron-range of frequency) in a magnetic beach field. The increased thermal energy was converted to flow energy as it passed through the divergent magnetic nozzle in accordance with the constant magnetic moment. We were able to successfully control the plasma flow with a wide range of densities for basic magnetohydrodynamic (MHD) studies and space thruster applications.

Many flaked particles caused by impulsive force of electric field stress and effect of electrostriction stress in mass-production plasma etching equipment

To investigate the mechanism of instantaneous generation of many flaked particles in plasma etching chambers, we study the relationship between particle generation from deposited films and electric field stress acting on the films under mass-production conditions. The particles are formed by stress working as an impulsive force due to rapid changes in floating potential on the chamber walls. The results indicate that Maxwell’s stress and electrostriction stress both affect particle generation in terms of the impulsive force of electric field stress. Although Maxwell’s stress mainly influences the outbreak of particles, the electrostriction stress also acts with considerable intensity.

Monitoring of inner wall condition in mass-production plasma etching process using a load impedance monitoring system

This work describes the detection of changes in the inner wall condition of mass-production plasma etching equipment using a load impedance monitoring system. The system detects the change in the imaginary part of the load impedance from a 50-Ω transmission line when the inner wall condition changes following exposure to the atmosphere. The results demonstrate that the system can be used as a practical method for real-time and noninvasive monitoring of the wall condition of etching chambers. This method will contribute to improvements in production yield and overall equipment effectiveness, and the development of predictive maintenance in semiconductor manufacturing.

Real-time characteristic impedance monitoring for end-point and anomaly detection in the plasma etching process

We propose a practical and highly sensitive characteristic impedance monitoring (CIM) system for detecting the etching end point and anomalies during the plasma etching process. The CIM system employs a directional coupler and a newly developed vector processing system. The etching end point was successfully detected when a SiO2/Si wafer was etched with CF4 plasma; the system also detected wafer fluttering occurring during SF6–N2 plasma etching. The reactance component of the characteristic impedance primarily changed with the transient response of the electric potential on the inner glass surface during SF6–N2 plasma etching.

Impulsive force phenomenon of electric field stress causing serious particle contamination in plasma etching equipment

To demonstrate electric field stress acting as an impulsive force, the action of the stress is investigated using a standard particle. Particles floated from a substrate owing to electric field stress are observed using an in situ particle monitoring system. The results indicate that the more rapidly an electric field changes, the more the stress increases, which demonstrates the impulsive force effect of electric field stress. From the results of this study, we can conclude that the cause of the instantaneous generation of many flaked particles in plasma etching chambers is electric field stress working as an impulsive force.

Detection of microarc discharge using a high-speed load impedance monitoring system

A high-speed and practical load impedance monitoring system is developed for the detection of microarc discharge. The detection system measures forward and reflected rf powers, including phase information, simultaneously with capacitances of variable capacitors, which allows real-time monitoring of load impedance. The results demonstrate that the system can detect microarc discharges at high speed and high sensitivity from a 50 Ω transmission line, and reveal that a significant change in load impedance is caused by arcing. This method is expected to contribute to improvements in plasma processing, production yield, and overall equipment effectiveness in semiconductor manufacturing.

ICRF Heating and Plasma Acceleration with an Open Magnetic Field for the Advanced Space Thruster

The ion cyclotron resonance heating and acceleration in a magnetic nozzle are performed in a fast-flowing plasma in the HITOP linear device in order to investigate an advanced space propulsion system. When radio-frequency (RF) waves are excited by a helically-wound antenna, plasma thermal energy W[perpendicular] and ion temperature drastically increase during the RF pulse. Thermal energy of the heated ion is converted its flow energy when the ions pass through a diverging magnetic nozzle. The plasma thermal energy changes so as to keep the magnetic moment constant. The exhaust plasma flow energy can be controlled by changing an input RF power only.

Numerous flaked particles instantaneously generated by micro-arc discharge in mass-production plasma etching equipment

The relationship between the instantaneous generation of flaked particles and micro-arc discharge is investigated in mass-production plasma etching equipment. To investigate the mechanism of such particle generation, we simultaneously detect particle generation from deposited films on a ground electrode and occurrence of micro-arc discharge under mass-production conditions. The results indicate that the deposited films are severely damaged and flake off as numerous particles when micro-arc discharge occurs. The rapid changes in floating potential on the films due to micro-arc discharge cause electric field stress, which works as an impulsive force. The particles are generated not from the melting of chamber parts by micro-arc discharge but from the flaking of deposited films by electric field stress acting as an impulsive force.

Transport of a helicon plasma by a convergent magnetic field for high speed and compact plasma etching

A high density argon plasma produced in a compact helicon source is transported by a convergent magnetic field to the central region of a substrate located downstream of the source. The magnetic field converging near the source exit is applied by a solenoid and further converged by installing a permanent magnet (PM) behind the substrate, which is located downstream of the source exit. Then a higher plasma density above 5 × 1012 cm−3 can be obtained in 0.2 Pa argon near the substrate, compared with the case without the PM. As no noticeable changes in the radially integrated density near the substrate and the power transfer efficiency are detected when testing the source with and without the PM, it can be deduced that the convergent field provided by the PM plays a role in constricting the plasma rather than in improving the plasma production. Furthermore it is applied to physical ion etching of silicon and aluminum substrates; then high etching rates of 6.5 µm min−1 and 8 µm min−1 are obtained, respectively.