Masaaki Kanoh

Optical Emission and Microwave Field Intensity Measurements in Surface Wave-Excited Planar Plasma

A large-planar (22 cm diam.) high-density ( ~2×1012 cm-3) plasma is produced in argon gas at 140 Pa by 2.45 GHz–1 kW discharges, using a microwave launcher of small slot antennas. The two-dimensional distributions of optical emission intensities as well as microwave field intensities are measured near the plasma surface irradiated with microwaves. Both the optical emission and the microwave field clearly show stationary patterns of azimuthal mode m=3 and radial mode n=3 at higher pressures (140 Pa), while a mode change to m=6 and n=2 is observed at lower pressures (44 Pa). These patterns are attributed to the excitation and absorption of standing surface waves near the cutoff layer.

Mode identification of surface waves excited in a planar microwave discharge

A planar high-density plasma, 22 cm in diameter and 9 cm in length, is produced by a 2.45 GHz microwave radiation of 500 W through small slot antennas in argon at 20 - 350 Pa without a magnetic field. Several types of azimuthal and radial standing wave mode pattern are observed in the optical emission from the plasma depending on the discharge conditions. The microwave field in the plasma measured by a movable antenna decreases exponentially in the axial direction from the quartz wall adjacent to the slot antennas, thus suggesting the propagation of surface waves in the r, directions. The measured azimuthal microwave field distributions and the optical emission pattern clearly show a mode transition of the standing surface wave from a mode to a mode when the pressure is decreased from 140 to 44 Pa at the constant power of 400 W. Here denotes the transverse magnetic mode of azimuthal mode number m and radial mode number n. A wave dispersion analysis based on a one-interface uniform-density model predicts these modes in a range of electron densities corresponding to those measured by a Langmuir probe in the experiment.

Inductively Coupled Plasma Source with Internal Straight Antenna

An inductively coupled plasma source with an internal straight antenna was developed. By inserting an antenna into plasma, the induction of a strong electric field in the plasma and the efficient transmissions of power to plasma is enabled. However, there was a practical problem in that antenna sputtering occurred. Suppression of antenna sputtering and methods of insulating the antenna were studied. Consequently, it was found that sputtering impurities were reduced by covering the straight antenna with a quartz pipe. Furthermore, the amount of quartz pipe etching could be reduced to as little as 1/10th the original value. As a result of fabricating and evaluating the plasma source in which four straight antennas were arranged in parallel, electron density was determined to be as high as 1011 cm-3 even at a pressure as low as 4 mTorr. When the processing performance of the plasma source was evaluated, the ashing rate of the photoresist and the etching rate of the poly-Si were, respectively, 4.8 µm/min and 450 nm/min. These values are at practically applicable levels.

End-point Detection of Reactive Ion Etching by Plasma Impedance Monitoring

For the practical application of end-point detection of etching using plasma-impedance monitoring, the factors determining the impedance were clarified using an electric circuit model of a reaction chamber. In the model, plasma is approximated by a conductor, and the floating capacitance and wafer of a powered electrode, as well as the powered-electrode sheath (the sheath formed between the plasma and powered electrode), are approximated by capacitors. Calculated values obtained using the model agree well with measured values obtained by an impedance monitor installed between the powered electrode and the matching network. Based on this result, it was inferred that the impedance depends on the powered-electrode sheath-voltage and electron density, as well as on the floating capacitance and area of the powered electrode, the dielectric constant and thickness of the wafer, and the electron temperature. Next, the end-point detection method of etching by impedance monitoring was applied to reactive ion etching of SiO2 films, and the following finding was confirmed: the change in the impedance significantly depends on the RF power and the exposed area ratio (the ratio of etched area to wafer area) on the wafer. In addition, the feasibility of detecting the point of change of the exposed area ratio on the wafer, where the area size varies during etching, by detecting microchanges in the impedance, was demonstrated. As a result, the possibility of highly accurate end-point detection of etching by impedance monitoring was confirmed.

Dry Etching Characteristics of Si-based Materials Using CF4/O2 Atmospheric-Pressure Glow Discharge Plasma

We etched materials used for semiconductor manufacturing processes, such as poly-Si films, SiN films, SiO2 films and photoresists, using atmospheric-pressure glow discharge plasmas, where CF4 gas was added to the O2 gas in the discharge and downflow regions. High etching rates of 2.3 µm/min for the poly-Si and SiN films, 1.0 µm/min for the SiO2 films and 7.0 µm/min for photoresist were obtained in the discharge region. Furthermore, a reasonably high etching rate of 0.82 µm/min for poly-Si films was also confirmed in the downflow region. The etching characteristics obtained under atmospheric-pressure glow discharge plasmas and low-pressure glow discharge plasmas in the discharge region were very similar. However, in the downflow region, the etching rates of SiN and SiO2 films were substantially reduced compared to those in the discharge region. These etching mechanisms were also modeled based on analytical data and the results of the etching evaluation.

Microwave-Excited Large-Area Plasma Source Using a Slot Antenna

We developed a stable and uniform large-area plasma source using surface waves generated from a slot antenna. The propagation of microwaves radiating from the slot antenna was studied and the optimal shape of the slot antenna for uniform plasma generation was determined. The characteristics of a dry etching process using the plasma were also evaluated. It was confirmed that some of the microwaves which radiated from the slot antenna propagate as surface waves in the dielectric window. By adjusting the angle of the slot antenna, the plasma was generated in the direction perpendicular to the axis of the slot antenna. An Ar plasma electron density of the order of 1011/cm3, which exceeds the electron density required for blocking the propagation of microwaves (cutoff frequency), was obtained. On the basis of these observations, it was considered that the microwaves radiating from the slot antenna propagate in the form of surface waves in the direction perpendicular to the axis of the slot antenna, and generate surface-wave plasma. The results of the measurements of the etching rate and ashing rate yielded a poly-Si etching rate of 470 nm/min or greater with a uniformity of 5% or better, and an ashing rate of 3000 nm/min or greater with a uniformity of 7% or better. The poly-Si etching rate was approximately twofold and the ashing rate was approximately fivefold the corresponding values obtained by the conventional chemical dry etching method.

A Theoretical Study on the Realistic Low Concentration Doping in Silicon Semiconductors by Accelerated Quantum Chemical Molecular Dynamics Method

We present a theoretical study of the structural and electronic properties of a realistic low concentration (<0.5%) doping model in silicon semiconductor. The density of states was calculated using our newly developed accelerated quantum chemical molecular dynamics method, based on our original tight-binding theory. Using this approach, the band structures of large-size silicon model including n-type and p-type dopants were successfully simulated. The results are in good agreement with the experimental results. Furthermore, we also performed quantum chemical molecular dynamics simulation of the dopants in silicon and observed the change of the dopant levels during the simulation. These results clearly suggest that our original quantum chemical molecular dynamics program is a very effective tool for not only the band structure of a realistically low concentration dopant model but also for the electronic states dynamics of silicon semiconductors.

Large-area plasma produced by surface waves on a metal wall with periodic grooves

Large-area (>40 cm in diam) high-density (∼1012) plasmas are produced by 2.45 GHz microwave discharge, usually under a large dielectric plate which is needed to excite surface waves propagating along the plasma–dielectric interface. However, such a dielectric plate is often unfavorable in practical applications. This article reports a technique for producing surface wave plasmas, in a metal vessel without using such a dielectric plate. When the microwave is injected from slot antennas without a dielectric plate, the plasma is locally generated around the slots with relatively low densities even at high incident powers. This problem is solved by introducing periodic grooves in a flat metal wall, which dramatically improve the plasma uniformity and increase the electron density as high as the dielectric plate case. The dispersion relation and surface impedance are compared between the dielectric wall case and the metal wall case, while the periodic groove effect is treated in an equivalent circuit model and...

Measurement of Electron Density of Reactive Plasma Using a Plasma Oscillation Method

We measured the electron density of reactive plasma using a plasma oscillation probe and analyzed the mode change of power coupling during etching. The unique behavior of plasmas containing reactive negative ions is clarified. The change in the plasma reactor mode during silicon dioxide etching, from the inductive mode to the capacitive mode with increasing pressure, is investigated.

Improvement in downflow etching rate using Au as a catalyst

We studied the improvement in the polycrystalline silicon (poly-Si) etching rate in the downflow etching process using microwave-excited CF4/O2 plasma by enhancing the dissociation reaction of the etching gas and the etching reaction on the poly-Si film surface through the use of a catalyst. A piece of platinum (Pt), gold (Au) or silver (Ag) was placed in a quartz tube as a potential catalyst for the downflow etching of poly-Si films. The results revealed that the etching rate using Au was up to 3.6 times higher than that without any catalyst. The mechanism for the improvement in the etching rate using a Au catalyst was analyzed by evaluating the plasma and etching species in transportation paths using optical emission spectral analysis and mass spectrometry, and by examining the poly-Si film with thermal desorption spectrometry, scanning electron microscopy and x-ray photoelectron spectroscopy. The Au placed between the plasma and the sample is oxidized by the active gas dissociated from CF4/O2 gas, and Au oxides and their compounds including F and CFx are transported and deposited onto the surface of the poly-Si film. Although, the precise mechanism of these reactions is not clear, it was presumed that the gold oxides and their reaction compounds acted as catalysts in the etching reaction of the poly-Si film and significantly accelerated the etching rate.We studied the improvement in the polycrystalline silicon (poly-Si) etching rate in the downflow etching process using microwave-excited CF4/O2 plasma by enhancing the dissociation reaction of the etching gas and the etching reaction on the poly-Si film surface through the use of a catalyst. A piece of platinum (Pt), gold (Au) or silver (Ag) was placed in a quartz tube as a potential catalyst for the downflow etching of poly-Si films. The results revealed that the etching rate using Au was up to 3.6 times higher than that without any catalyst. The mechanism for the improvement in the etching rate using a Au catalyst was analyzed by evaluating the plasma and etching species in transportation paths using optical emission spectral analysis and mass spectrometry, and by examining the poly-Si film with thermal desorption spectrometry, scanning electron microscopy and x-ray photoelectron spectroscopy. The Au placed between the plasma and the sample is oxidized by the active gas dissociated from CF4/O2 gas, and ...