Toshiki Nakano

Estimation of dissociation degree of N2 in an inductively coupled plasma by vacuum ultraviolet emission spectroscopy

A simple procedure for estimation of the N2 dissociation degrees in low-pressure, high-density plasmas is proposed. This procedure is applied to the estimation of the N2 dissociation in an N2 inductively coupled plasma and confirmed to give N2 dissociation degrees similar to those reported previously. The rf power and N2 pressure dependence of the N2 dissociation degree is also presented. The contribution of stepwise excitation out of N2 A3Σu+ [N2(A)] metastables to the N2 second positive emission is found to be negligible from the net excitation rate computed using an assumed cross section of the electron-impact excitation from N2(A) to the N2C3Πu state and the N2(A) number density deduced from a simple kinetic model. The recombination of N atoms on the inner surfaces of the plasma reactor used in this study is discussed briefly. Finally, the advantages of the N2 dissociation estimation by vacuum ultraviolet optical emission spectroscopy are mentioned.

EFFECTS OF AR DILUTION ON THE OPTICAL EMISSION SPECTRA OF FLUOROCARBON ULTRAHIGH-FREQUENCY PLASMAS : C4F8 VS CF4

The Ar dilution effects on the ultrahigh-frequency (UHF) plasmas through C4F8 and CF4 are studied by optical emission spectroscopy and Langmuir probe measurement. For the C4F8 plasma, the Ar dilution is found to extend the electron energy distribution function (eedf) toward the higher energy and increase the electron density, ne. The ne-normalized CF2 emission intensity is decreased proportionally with the partial pressure of the C4F8 feedstock gas. Thus, the Ar dilution increases the ratio of the ion density to the CF2 density, which changes the balance between the etching and the polymer deposition and affects the SiO2 etching characteristics significantly. The polymer deposited on the reactor wall is found to affect the emission spectra of the C4F8 plasma. For the CF4 plasma, the Ar dilution does not change the eedf probably because of approximately the same threshold energy for the ionization processes between Ar and CF4. However, the Ar dilution increases the ne in the CF4/Ar plasma. Since CF2 radica...

New ultrahigh‐frequency plasma discharge for overcoming the limitations of etching processes

Electron, ion, and neutral temperatures are measured in an ultrahigh‐frequency (UHF) plasma by Langmuir probe and Doppler‐shifted laser‐induced fluorescence. The electron, ion, and neutral temperatures are found to be 1.5–2.0 eV (Ar plasma), 0.066 eV for Ar+, and 0.036 eV for Ne, respectively, and are lower than those reported for electron cyclotron resonance and helicon wave plasmas. The low temperatures cause lower dissociations of CHF3 gas even in the plasma production region of the UHF plasma source. The plasma is expected to dramatically improve the selectivity of SiO2 to the underlying Si. Additionally, the plasma can be used to accomplish a notch‐free poly‐Si etching profile and microloading‐free Si trench etching with a high etching rate and high anisotropy with a narrow space pattern of less than 0.3 μm. It is suggested that the charge accumulation with the narrow space pattern is eliminated because of the low electron temperature in the UHF plasma.

Electrical properties of nitrogen-containing plasma polymer films

The electrical conductivity of plasma copolymerised films from allylamine and ethylene increases with an increase in the flow-rate of allylamine during the polymerisation, while the optical gap evaluated from optical absorption decreases. Deconvolution of infrared spectra showed that the ratio of sp2 to sp3 carbons is not related to the nitrogen content of the film. This fact shows that the conductivity increase is not due to the development of conjugated carbon double bonds. It is deduced that the increase in conductivity is mainly caused by two different effects of the introduced nitrogen, i.e. the reduction in optical gap and the increase in unpaired electrons, both arising from the interaction between nitrogen atoms and conjugated carbon double bonds.

Effects of rare gas dilution for control of dissociation, ionization, and radical density in fluorocarbon ultrahigh-frequency plasmas

The effects of diluting ultrahigh-frequency CxFy plasmas with Xe, Ar, and He are studied by optical emission spectroscopy and Langmuir probe measurement. The Ar and He dilutions are found to shift the electron energy distribution function toward higher energies. Ar and Xe also drastically increase the electron density, whereas He does not change the electron density. As a result, Ar dilution increases the ratio of ion density to CF2 density. It is expected that the Ar dilution changes the balance between the etching and the polymer deposition and significantly affects the SiO2 etching characteristics. He dilution causes a high degree of dissociation and a large increase in the density of F atoms for CxFy gases, in addition to the dilution of CF2 radical density, because of its high threshold energy for ionization. The Xe dilution drastically increases the ne while it maintains a lower electron temperature.

Effect of polar groups on the electrical breakdown strength of plasma-polymerized films

The electrical breakdown of plasma polymer films was studied by applying rectangular voltage pulses. Experimental evidence indicates that the breakdown field increases after incorporation of fluorine atoms into the film when the pulse width is >

Plasma-Polymerized Films as Orientating Layers for Liquid Crystals

Many experimental studies on plasma-polymerized films have been carried out recently. If plasma-polymerized films can be used as an orientating layer for a liquid crystal, they will enlarge application of the liquid crystal. Although there have been some papers concerning a plasma-polymerized orientatig layer for a liquid crystal,(1) there are still many problems left to be solved. The effects of the surface properties of a plasma-polymerized film on liquid crystal alignment are discussed in this paper.

Influence of driving frequency on oxygen atom density in O2 radio frequency capacitively coupled plasma

The influence of the driving frequency on the absolute oxygen atom density in an O2 radio frequency (RF) capacitively coupled plasma (CCP) was investigated using vacuum ultraviolet absorption spectroscopy with pulse modulation of the main plasma. A low-power operation of a compact inductively coupled plasma light source was enabled to avoid the significant measurement errors caused by self-absorption in the light source. The pulse modulation of the main plasma enabled accurate absorption measurement for high plasma density conditions by eliminating background signals due to light emission from the main plasma. As for the effects of the driving frequency, the effect of VHF (100 MHz) drive on oxygen atom production was small because of the modest increase in plasma density of electronegative O2 in contrast to the significant increase in electron density previously observed for electropositive Ar. The recombination coefficient of oxygen atoms on the electrode surface was obtained from a decay rate in the afterglow by comparison with a diffusion model, and it showed agreement with previously reported values for several electrode materials.

Diagnostics of N2 dissociation in RF plasmas by vacuum ultraviolet emission and absorption spectroscopy

The N2 dissociation degrees in a 50 MHz inductively coupled plasma (ICP) are evaluated by a procedure using vacuum ultraviolet optical emission spectroscopy (VUVOES). The number density of N 4S° atoms (nN) is evaluated from the N2 dissociation degree by determining the N2 rotational temperature that is in equilibrium with the gas temperature. The nN evaluated by VUVOES is crosschecked by the nN measured by vacuum ultraviolet absorption spectroscopy (VUVAS). The comparison reveals a fair proportionality between the nNs evaluated by VUVOES and those measured by VUVAS, suggesting that VUVOES is applicable to the monitoring of N2 dissociation in low-pressure, high-density N2 plasmas. The number density of N 2D° metastables is also measured by VUVAS and found to be comparable to the number density of the ground-level N atoms (4S°). The dissociative recombination of with electrons is suggested as a possible mechanism of N 2D° metastable generation that makes the N 2D° density comparable to the N 4S° density in the pulsed N2 ICP during power-off periods.

Radial distributions of ion velocity, temperature, and density in ultrahigh-frequency, inductively coupled, and electron cyclotron resonance plasmas

Spatially resolved velocity distribution functions of metastable chlorine ions are measured in ultrahigh-frequency (UHF) plasma and compared with those in electron cyclotron resonance (ECR) plasma and inductively coupled plasma (ICP). In UHF plasma, ion velocity distribution function (IVDF) perpendicular to the surface normal of a wafer exhibits approximately no acceleration of ions to the side wall of a plasma reactor as the measuring point becomes radially far from the center of the reactor, even at 14 cm from the center where IVDF’s are shifted evidently in ECR plasma and ICP. This indicates that an almost flat profile of plasma potential is realized along the radius of the reactor in UHF plasma. As a consequence, metastable chlorine ion temperature remains low and almost constant over a radius of 14 cm in UHF plasma. Relative density of metastable chlorine ions in UHF plasma increases toward the side wall of the reactor. In contrast to this, the density exhibits a maximum in the center of the reactor ...