Self-bias Potential Research Articles

CAPACITIVELY COUPLED HYDROGEN DISCHARGES: MODELING VS. EXPERIMENT

This paper presents a systematic characterization of hydrogen capacitively coupled very high frequency discharges, produced within a parallel plate cylindrical setup, by comparing numerical simulations to experimental measurements for various plasma parameters. A good quantitative agreement is found between calculation and experiment for the coupled electrical power and the plasma potential, at various frequencies, pressures and applied voltages. However, the model generally underestimates the electron density and the self-bias potential with respect to measured values. Model predictions for the absolute density of H(n=l) atoms are compared to first diagnostic results, obtained by two-photon absorption laser-induced fluorescence diagnostics at various pressures and frequencies.

Characterization and design considerations of a radio frequency glow discharge spectral source for solid material analysis

This paper reports on the design and fabrication of a radio frequency (rf, 13.56 MHz) powered glow discharge source and its characterization for analytical atomic spectroscopy for solid sample analysis. The most attracting feature of rf coupling is its capability to sputter atomize conductive as well as non-conducive solid materials. The glow discharge lamp described here works under obstructed abnormal discharge condition in which the sample acts as a cathode. The fundamental processes occurring in rf powered glow discharges have been described for its characterization for direct solids elemental analysis. The discharge from the cathode surface, which is in contact with a water-cooled jacket, is observed side-on. The anode orifice diameter has been kept at 6 mm. In order to optimize the lamp performance the effect of discharge power, pressure, and dc self-bias potential, etc. on the emission intensity of copper spectral line (324.7 nm) have been studied.

Effect of temperature on etch rate of iridium and platinum in CF4/O2

Iridium and platinum films were etched in the CF4/O2 plasma in an electron cyclotron resonance etch reactor. Wafers were placed on a heated chuck during etching, with the temperature maintained in the range of 70–250 °C before etching. A rf power was applied to the wafer chuck to generate a self-bias potential. At temperature below 100 °C, the iridium etch rate was low value. The iridium etch rate increased with temperature, and reached about 1500 Å/min above 200 °C. Platinum also showed a low etch rate value below 150 °C, increasing to about 1500 Å/min at 250 °C. The increase of etch rate at higher temperature was attributed to the formation of volatile compounds, IrF6 or PtF6.

Chemical and structural analysis of crystalline carbon nitride thin films prepared by electron cyclotron resonance plasma sputtering process

Carbon nitride films were prepared on Si(100) substrate, which was at self-bias potential by an electron cyclotron resonance plasma sputtering method uses a carbon target and a nitrogen atmosphere. The maximum value of the N/C ratio for the film deposited at a substrate bias potential of about -50V and ambient temperature was 1.35, which is close to the stoichiometric composition of C 3 N 4 The surface morphology observed with scanning electron microscopy of the film deposited at a substrate bias potential of -45V and 600°C showed a crystalline structure with an average grain size of about 500nm. The x-ray diffraction patterns of the films deposited at 700°C suggests that the films are composed of crystal phases that may be different from the predicted C 3 N 4 phases and an unknown new C-N phase with a lattice space of 0.473nm.

Evaluation of self-bias potential distribution on a powered electrode of supermagnetron plasma apparatus

The distribution of self-bias potential (Vdc) on a powered electrode of a supermagnetron plasma system, where both electrodes are supplied phase-shifted radio frequency (rf) currents, was measured using five electrical probes buried in the electrode. For comparison, the same was measured for a conventional magnetron plasma system. Measurements were carried out with an Ar discharge at the pressure region of 4–50 mTorr. The data obtained with the supermagnetron and the conventional magnetron plasm systems were used to map the Vdc distribution on the powered electrodes of each plasma source. When the phase difference between rf currents applied to the two parallel electrodes of supermagnetron plasma system were changed, a drastic change of the Vdc is observed. The uniformity of the Vdc distribution is greatly improved when the phase difference between rf currents is varied from 0° to about 180°. The further increase of phase difference between two rf currents causes a decrease of the uniformity of the Vdc distribution. The uniformity of the Vdc obtained on the electrode of supermagnetron plasma source with 180° phase-shifted currents is observed to be superior to that of the conventional magnetron plasma source.

Control of d.c. bias current in radio-frequency glow discharge source and its emission characteristics

A novel technique to control r.f.-powered Grimm-style glow discharge plasmas is described. A new channel of d.c. current driven by the self-bias potential is opened by using a low-pass filter circuit and a load resistor; as the result, a large number of electrons can flow along the d.c. circuit channel including the plasma body from the grounded electrode to the sample electrode. This phenomenon is effective for improvement of the detection sensitivity in the optical emission spectrometry. Atomic emission lines having lower excitation energies are predominantly enhanced by a factor of 10–20. The conduction of the d.c. bias current could promote these excitations.

Deposition of titanium oxide and titanium carbide containing thin carbon films in a plasma activated process

Abstract The deposition of Ti containing a-C:H (amorphous hydrogenated carbon) films was achieved using a single source metal organic (MO) precursor (titanium oxide) in a plasma activated process. To obtain a constant flow of the MO precursor, it was necessary to employ H2 as a carrier gas. The films were deposited onto Si substrates mounted onto the r.f. powered cathode. The film composition was determined using X-ray induced photoelectron spectroscopy (XPS). The Ti content was in the range 17–25 at%; it strongly depends on the self-bias potential as well as on the H2 flow. For high H2 flows and high (negative) bias potential, besides incorporated TiO2, a second Ti binding state was detected due to the formation of Ti–C bonds.

Application of a Bias-Current Modulation Technique to Radio-Frequency Glow Discharge Optical Emission Spectrometry.

A 13.56-MHz Grimm-style glow discharge plasma in which pulsated bias currents are introduced was investigated concerning the analytical applications. The d.c. bias currents driven by a self-bias potential are conducted through the r.f. plasma body by using a low-pass filter circuit and a variable resistor. Excitation by a modified r.f. plasma can yield larger emission intensities. By modulating the bias current associated with phase-sensitive detection, the emission intensities can be measured at very low noise levels, enabling the detection limit to be improved more. A detection limit of 3 × 10−4 mass % was obtained for Mn determination in Fe-based binary alloy samples, whereas 1.4 × 10−2 mass % Mn was obtained in the conventional excitation of an 80-W r.f. discharge plasma.

Working characteristics of two magnetron sputtering devices based on different unbalanced magnetic systems of type II

A comparison of the working characteristics of two similar planar d.c. magnetron sputtering devices that differ only in the geometry of the build-in magnetic assemblages is made. The comparative study includes the discharge characteristics of the two magnetrons for different pressures of the sputtering gas Ar as well as some parameters characterising the magnetron plasma in the area of the substrates, namely the self-bias electrical potential of the isolated substrate, the current towards the grounded substrate and the current to negatively biased substrate. The values of the measured parameters and the character of the curves obtained show that both magnetron devices are of unbalanced type II. However, the expected strong advantages of the second magnetic system, predicted in our previous investigation on the basis of the magnetic field distributions for the two assemblages, were not confirmed. The experimental data obtained with 1-mm Cu target indicate that the magnetron sputtering source, using the first system, produces higher values of the floating potential, higher values of the current to the grounded substrate and comparable values of the current to negatively biased substrates. These results, together with other advantages shown by the first system, namely the larger working range of the sputtering gas, lower running voltages, significantly larger efficiency of the target utilization and larger homogeneity of the thickness of the deposited films determine the first system as being more appropriate for our future experiments on ion-assisted, thin-film deposition.

The determination of the current-voltage characteristics of a closed-field unbalanced magnetron sputtering system

An investigation has been carried out into the current-voltage ( I-V) characteristics of a closed-field unbalanced magnetron sputtering system (CFUBMS). CFUBMS is a versatile technique for the high-rate deposition of high quality metal, alloy and ceramic coatings. A key factor in this system is the ability to transport high ion currents to the substrate. This can enhance the formation of fully dense coatings at relatively low values of homologous temperature. A study has been made of the parameters that determine the I-V characteristics of this system, at both the target and the substrate. From this, empirical relationships have been developed to describe the substrate ion current density and the substrate self-bias potential. Measurements have been taken of the discharge voltage, the substrate self-bias voltage, and substrate current using aluminium, zirconium, tungsten, and copper targets, at target currents of up to 8 A, over the pressure range 0.5-3 mTorr, and at substrate-to-target separations of 80 mm, 110 mm and 150 mm. The discharge voltage, VT, follows the established relationship I T= β( V T− V 0) 2, where I T is the discharge current and V 0 is the minimum voltage required to strike a discharge. The variations of β and V 0 with target material and pressure are discussed. At the substrate, a linear relationship, I s= mI T, was observed between the ion current drawn at the substrate, I s, and the discharge current, I T, where the coefficient of proportionality, m, varies with chamber pressure and substrate-to-target separation. Also, self-bias voltages, in the range −17 to −30 V, were measured. The value was largely independent of target material and substrate-to-target separation, but depended strongly on chamber pressure.

Magnetically enhanced inductively coupled plasma CVD for a-Si:H fabrication

Radio-frequency (13.56 MHz) excited SiH 4 plasma is produced with an electrode of a ladder-shaped antenna with rotating magnetic fields. The negative self-bias potential on the electrode, the SiH emission intensity and the deposition rate of a-Si:H films prepared on glass substrates are examined as a function of RF power for different rotating magnetic fields. It is found that when the rotating magnetic fields are applied to the SiH 4 plasma, the negative self-bias potential becomes low, while the SiH emission intensity and the deposition rate increase. It is also found that the higher the RF power, the better the uniformity of the a-Si:H film, which is desirable for the fabrication of solar cells and thin film transistors. Furthermore, the effect of rotating magnetic fields are discussed. It is found that drift motion plays an important role in determining increases in the deposition rate of a-Si:H films.

Studies of gas-jet assisted RF-glow discharge atomic absorption spectrometry

The gas jet assisted glow discharge source has been employed for the RF-glow discharge atomic absorption spectrometry (RF-GDAAS). Data are described to illustrate the role of discharge power, pressure as well as gas flow rate on the sample loss rate, absorbance and self-bias potential. Results show that the optimum discharge conditions depend not only on the pressure and discharge power but also on the gas flow rate. The absorbance increases as much as 1 order of magnitude as the gas flow rate increases from 50 mL/min to 500 mL/min at a pressure of 3 mbar. The use of a gas-jet source allows the direct analysis of solids by RF-GDAAS.

Radio frequency synchronized triode reactor with a multihole cathode for etching of Si

A magnetically enhanced radio frequency (13.56 MHz) synchronized triode reactor with a multihole cathode used for etching of Si by a plasma is described. The ion energy is controlled independently of the plasma creation function by adjusting the phase difference between the two rf signals. The cathode shape allows a decreasing of the self-bias potential and an increasing of the ion current density when the plasma is created in the holes. We have studied the effects of ion energy and incident power on etch rate, contaminations and morphology of Si samples. The effects of the magnetic confinement and the electrode shape on the etch rate are also presented. Relative to a standard plate electrode, the etch rate is enhanced by a factor of about three at a pressure of 10 mTorr and a power of 500 W.

The dust direct current self-bias potential in a time varying plasma sheath

We introduce an important physical effect, namely, the response of the dust particle charge to an oscillating electric field in a plasma sheath. The ac field may lower the average dust potential well below the corresponding floating potential Uf in a dc sheath. The resulting dust potential will be called the dust dc self-bias potential Udc and is generally a sensitive function of the ac potential amplitude and of the ratio ωch/ω between the so-called dust charging frequency ωch and the ac frequency ω. The difference between Udc and Uf maximizes for ωch≪ω and approaches 0 for ωch≫ω. We propose that the dust dc self-bias effect is important in all plasmas having a rapid potential variation and always has to be taken into account when calculating the charge and the force on dust particles in such plasmas. Since levitation of dust particles above surfaces normally requires negative dust particles, the dust dc self-bias effect may explain why some experiments indicate that levitation of dust particles is easier in rf discharges than in dc discharges.

Characteristics of Diamond-like Carbon Thin Films Prepared by a RF Plasma Pulse Deposition Method

Diamond-like carbon (DLC) thin film deposition was examined by applying 13.56 MHz of r.f. power to the substrate electrode. We tried to control deposition temperature by the plasma pulse deposition technique: repeated cycles of alternating 5 s of deposition with 180 s of cooling, then we investigated the influence of the deposition temperature on the thin film characteristics and structure in details.It is found that the deposition temperature plays a more significant role than the self-bias potential which is up to now considered as an important parameter. Our results suggest that the surface structure of the film after ion impacted rather than ion impact energies dominates the characteristics and structure determination. Definitely, the deposition temperature is closely related to the mobility of the fragments generated by the ion bombardments and the migration of radical and neutral species adsorbed on the film surface. Moreover, the deposition temperature is concerned in the promotion of the dehydrogenation of the film.As the model for DLC film structure, we suppose that the three dimensional random network structure is developed mainly, and the condensed aromatic ring structures as precursors of the carbon cluster and the small graphite-like carbon clusters are slightly mixed into the random network structure.

Plasma CVD using rotating E × B drift motion

Radio-frequency excited SiH 4 plasma is produced with a multi-strip-powered electrode with rotating magnetic fields. The negative self-bias potential on the multi-strip-powered electrode, the SiH emission intensity and the deposition rate of a-Si:H films prepared on glass substrates are examined as a function of r.f. power for different rotating magnetic fields. It is found that when the rotating magnetic fields are applied to the SiH 4 plasma, the negative self-bias potential becomes low, while the SiH emission intensity and the deposition rate increase. It is also found that the higher the r.f. power, the better is the uniformity of a-Si:H films, which is desirable for fabrication of solar cells and thin film transistors. Furthermore, the effect of rotating E × B drift motion is discussed, where E and B are the electric and magnetic fields. It is found that this drift motion plays an important role in determining increases in the deposition rate of a-Si:H films.

R.F. bias effect on ECR plasma

An electron cyclotron resonance plasma is produced with a multislot antenna, where r.f. powers (13.56 MHz) are applied to a substrate. Plasma parameters measured with a probe are examined as a function of r.f. power and pressure. It is found that when the r.f. powers are applied, negative self-bias potential appears and the plasma density tends to decrease and the plasma potential increases. Furthermore, the effect of the negative self-bias potential on the radial profile of plasma parameters is discussed.

Sputter-induced formation of an electron accumulation layer in In0.52Al0.48As

Ar-sputtering of In0.52Al0.48As was investigated with room-temperature Raman and photoluminescence spectroscopy. A clear increase of carrier density in the near-surface region was observed in the Raman spectra. The PL intensity was found to depend in a complex way on plasma self-bias potential, incident laser irradiance, and InAlAs doping level, indicating that the recombination mechanisms dominating the PL response differ with changing experimental conditions. The observed trends can be explained by sputter-induced formation of an electron accumulation layer in the near-surface region.

高周波放電電極上の自己バイアス電位分布の研究

Self-bias potential and its distribution of a radio-frequency (RF) electrode have been measured in argon and helium plasma using probes penetrating the electrode. In the absence of the magnetic field the self-bias potential distribution is almost homogeneous at-150 V (RF power = 26 W) in Ar plasma. When the magnetic field (B =0.04 T) parallel to the electrode is applied, the mean value of the potential is reduced to-40 V and the gradient in the potential distribution occurs along the E× B direction. Rotation of the magnetic field at a frequency below 50 Hz is unable to reduce potential inhomogeneity, but this technique enables us to measure the potential distribution as a continuous function of the azimuthal angle. In helium plasma, another type of inhomogeneity parallel to the magnetic field occurs; this inhomogeneity can be reduced effectively by pulsed Ar gas injection. These data are discussed to show physical meaning and industrial applications.

Measurements of distribution of self-bias potential on an RF-plane electrode in plasma etching devices

The self-bias potential ( V dc) induced on an RF-powdered electrode (153 mm Ø) in a plasma is measured using electrical probes which are buried in, de-insulated from, and RF-connected to the electrode. The configuration of the probes allows to study the distribution of V dc discretely on the electrode. The potential is homogeneous in the absence of external magnetic field. In the presence of a homogeneous magnetic field parallel to the electrode, it is reduced and a monotonous gradient takes place in its distribution due to the plasma shift induced by E × B drift. When the magnetic field is rotated along the axis of the RF-electrode at a frequency less than 50 Hz, the distribution, which is almost identical to the one in a static field, rotates with the magnetic field. On the coordinate system rotating with the magnetic field, the probes are regarded to be rotating. The potential distribution is obtained as a continuous function of the azimuthal angle. Thus the rotation of the field provides information for the experimental interpolation.