Yasunori Ohtsu

CF3, CF2 and CF Radical Measurements in RF CHF3 Etching Plasma Using Infrared Diode Laser Absorption Spectroscopy

We have measured the characteristics of CF 3 , CF 2 and CF radical densities in RF CHF 3 etching plasma under the same condition using infrared diode laser absorption spectroscopy, for the first time. The CF 2 radical density measurements have been performed as a function of input RF power, CHF 3 gas pressure and distance from the RF electrode. On the basis of these systematic measurements, the generation and loss processes of CF 2 radicals in RF CHF 3 plasma were discussed

Observation of radio‐frequency discharges at various driving frequencies

Radio‐frequency discharges at various driving frequencies f in the range of 1.9–28 MHz are observed, especially from the viewpoint of the sheath structure. The results reveal that for f≥10 MHz, the sheath thickness Zs measured by an emissive probe varies directly as f−1, while for f≤10 MHz, Zs∝f−1/2. The electron density estimated from the ion saturation current of a needle probe is almost proportional to f2 in the former case. High‐energy electrons accelerated by the expanding rf sheath can contribute to sustaining rf plasmas in the high‐frequency region, whereas in the low‐frequency region, secondary electrons emitted from an electrode can contribute to it in a similar manner to dc and ac discharges.

Production of high-density capacitive plasma by the effects of multihollow cathode discharge and high-secondary-electron emission

High-density capacitively coupled plasma with electron density of 1011cm−3 was produced with the effects of the multihollow cathode discharge and the high-secondary-electron emission from radio frequency (rf)-biased electrode using Ar gas. It was found that the optimum pressure was around 3–15Pa. In the case of only multihollow cathode discharge, the plasma density increased from 1.2×1010to8×1010cm−3 with the increasing distance z from the cathode electrode for 5mm<z<15mm. Moreover, plasma density increased with increasing voltage of rf-biased electrode. The rate of deposited amorphous hydrocarbon thin films of about 200nm∕min was attained with the high-density rf plasma enhanced chemical vapor deposition using CH4 gas.

Development of a high-density radio frequency plasma source with a ring-shaped trench hollow electrode for dry processing

A high-density plasma driven by a capacitive discharge with a radio frequency of 13.56 MHz has been developed using a powered electrode with a ring-shaped trench for dry processing. It was found that a hollow cathode discharge was produced in the trench at a wide range of pressures from 10 to 400 mTorr. In order to satisfy the hollow cathode discharge, it was clarified that the trench width was twice as long as the sheath thickness formed in the trench experimentally. It became clear that a wider trench width easily produced the hollow cathode discharge under lower pressure conditions. A maximum plasma density of 1011 cm−3 was attained at Ar gas pressures of 100–350 mTorr and/or an input power density of 0.64 W cm−2. It was indicated that the radial profile of plasma density had a peak near the ring-shaped trenches and was uniform inside the ring-shaped trench.

Measurements of electron energy distribution function in an asymmetric radio‐frequency discharge plasma

Electron energy distribution functions in an asymmetric radio‐frequency (rf) discharge helium plasma were measured using an electrostatic energy analyzer looking opposite ways toward both the powered electrode and the bulk plasma. The grid and collector in the analyzer were connected to a series of parallel inductance‐capacitance (L‐C) filters to minimize rf interference. Electrons with high energies (15–30 eV) flowing from the electrode toward the bulk plasma were observed near the electrode. The energy is caused by the acceleration mechanism due to the rf sheath expansion, which should be the rf discharge sustaining mechanism. The electrons with high energies decreased in number with the distance from the electrode and became Maxwellian far from it. Electrons directed toward the electrode from the plasma were almost Maxwellian, and this situation was almost independent of the distance from the electrode.

Production of high-density capacitively coupled radio-frequency discharge plasma by high-secondary-electron-emission oxide

High-density capacitively coupled radio-frequency plasma with electron density ne>1010cm−3 was produced using MgO electrodes with a high secondary-electron-emission coefficient. It was found that in the case of MgO electrodes, both plasma density and optical emission intensity were about one order of magnitude higher than those in the case of Al electrodes.

Two-dimensional ion velocity distribution functions in electron cyclotron resonance plasma under a divergent magnetic field

Two‐dimensional ion velocity distribution functions are measured in electron cyclotron resonance (ECR) argon plasmas under a divergent magnetic field configuration using a directional analyzer. Ions produced in the ECR source grow to a beam in the downstream region inside an allowed angle, while the distribution function is almost isotropic outside the angle. The beam energy corresponds to the potential difference between the ECR source and downstream locations. The ion beam is almost parallel to an applied magnetic field, the beam being deflected along the divergent magnetic field lines. The energy spread and the temperature of the ion beam, and the temperature of the bulk ions are also shown as a function of the distance from the ECR source or of the gas pressure. The validity of the directional analyzer measurements is discussed by considering the motion of an ion in a sheath in front of the analyzer.

Influences of Gap Distance on Plasma Characteristics in Narrow Gap Capacitively Coupled Radio-Frequency Discharge

The narrow gap distance of a parallel plate was studied experimentally to investigate plasma characteristics in a capacitively coupled radio-frequency (RF) discharge. It was revealed that by increasing the gap distance from 1 cm to 4 cm, temperature and density of electrons markedly decreases and increases, respectively. It was also found that RF sheath electric field penetration into the bulk plasma increases with decreasing gap distance so as to sustain the discharge, resulting in an increase in the high-energy component of electron energy distribution.

Effects of downstream magnetic field collimation on ion behavior in electron cyclotron resonance microwave plasma

Effects of a magnetic held collimation on ion behavior in the downstream region of an electron cyclotron resonance (ECR) plasma device are clarified experimentally using a directional ion energy analyzer. The drift energy and its spread of the ion beam observed in the downstream region decrease and the beam temperature increases with the collimating magnetic flux density. Then, the ion temperature measured perpendicular to the axis of the plasma stream slightly decreases. The ion beam is found to be almost parallel to the magnetic field lines, that is, the beam tends to be collimated. >

Potential structures in asymmetrical radio frequency discharges containing negative ions

Abstract Potential structures in radio frequency (rf, 13.56 MHz) discharges containing negative ions (SF 6 in He gas) have been clarified experimentally in an asymmetrical electrode system using an emissive probe. A double layer type potential profile is picked up near an instantaneous anode unlike the almost flat profile in He plasma. A SF 6 addition provides a spatial shift of the double layer position toward the electrode, lowers the plasma potential, and decreases the sheath thickness. These results are ascribed to the negative ion production which is confirmed by an electrostatic analyzer measurement.