Eiji Shidoji

Two-Dimensional Self-Consistent Simulation of a DC Magnetron Discharge

A two-dimensional simulation of dc magnetron discharge is performed by a hybrid of fluid and particle models. In this hybrid model, ions and bulk electrons are treated by the fluid model and fast electrons are treated by the particle model. The numerical results indicate that the number density of the fast electrons has little effect on the electric field distribution in dc magnetron discharge at 30 mTorr since the ratio of fast electrons to bulk electrons is quite low. The transport of fast electrons is, however, quite important for dc discharge because the spatial distribution of the net ionization rate is subject to the spatial behavior of the fast electrons.

Three-Dimensional Simulation of Target Erosion in DC Magnetron Sputtering.

We simulate the erosion profiles of a rectangular planar target in the DC magnetron sputtering system. The simulation model assumes time-independent magnetic and electric fields that are not disturbed by the magnetron plasma. The electron trajectories are obtained by integrating partial orbits. The Monte Carlo technique, taking account of the differential cross section, is used to discriminate the ionization collision from the excitation and elastic collisions. Thus we determine the coordinates where an argon ion and an electron appear to indicate the erosion profiles. The calculated 3D erosion profiles are in very good agreement with those of the target actually used. This simulation technique for the sputtering process will be valuable in designing the magnet arrangement of a magnetron sputter target.

Influence of gas pressure and magnetic field upon dc magnetron discharge

We have proposed a hybrid model for dc magnetron discharge. Simulations of the discharges under different applied voltages are performed using the hybrid model. We confirm that this hybrid model is able to predict a magnetron discharge under conditions of less than 1 Pa by comparing the results from the simulation with that from the experiment. We also perform simulations of dc magnetron discharges under conditions of different gas pressures and different magnitudes of magnetic field. In so doing, we clarify the influence of gas pressure and magnetic field upon dc magnetron discharge.

Prediction of the evolution of the erosion profile in a direct current magnetron discharge

We have performed a simulation of ion and fast neutral transport in the sheath region of a direct current magnetron discharge under different pressures by using the Boltzmann equation and the database from the two-dimensional (2D) results of a plasma structure, which was given by a hybrid model. Evolution of the erosion profile on the target surface has been predicted by using the 2D energy distributions of ions and fast neutrals incident on the target (cathode) surface. We confirmed that an accurate prediction of the erosion profile can be obtained by assuming that the constant sputtering yield corresponds to the cathode voltage under conditions of low pressures that make use of the film deposition processes.

Numerical simulation of the discharge in d.c. magnetron sputtering

Numerical simulation of d.c. magnetron discharge for sputtering in Ar is performed using a hybrid model consisting of a particle model and a fluid model. The various discharges with different anodes size are simulated to investigate the effect of film conductivity on the anode and the substrate. In the case of a large area anode formed by the deposition of conductive material, the plasma potential becomes higher, suppressing the excess electron flux to the large anode. In the case of a small anode formed by an non-conductive film deposition, the plasma potential becomes lower, dragging a large number of electrons into the small anode. The low plasma potential lowers the potential difference between the cathode and plasma, and the production rate of an electron-ion pair decreases in the cathode sheath region under a constantly applied voltage mode, therefore decreasing the plasma density. It is shown that the plasma potential and the density changes with film conductivity or anode size under a constantly applied voltage. High energy ion injection to the central part of the glass substrate is estimated at the beginning of the film deposition. This implies that the film property at the central part of the non-conductive substrate will differ from the one at the other position due to the difference of the ion impact to the substrate.

A comparative study of an unbalanced magnetron with dielectric substrate with a conventional magnetron through the use of hybrid modelling

The influence of the differing magnetic field arrangements in both an unbalanced magnetron (UBM) and balanced magnetron (BM), both of which employ a dielectric substrate, on plasma characteristics has been numerically investigated under identical pressures and voltages. The UBM exhibits some interesting intrinsic characteristics with regard to the bulk plasma and the incident flux on the dielectric substrate. A property unique to the UBM is the appearance of negative plasma potential owing to the slightly excess amount of electrons when a magnetic field is arranged parallel to the axis of the bulk plasma in a cylindrical reactor and an electric field is arranged transversely to this axis. The dielectric substrate is negatively deep-biased, as compared with that in the BM, and is exposed to positive ion impact with a higher energy and flux, which will be controlled by changing the magnitude and direction of the external magnetic field.

Magnetron plasma structure with strong magnetic field

We perform simulations of the magnetron plasma under a strong magnetic field as well as the conventional magnetic field in the cylindrical geometry in order to examine the typical plasma structure of the magnetron with a strong magnetic field. In the case of the strong magnetic field, an electric field is formed even in the outside region of the sheath. Because the electron diffusion is strongly suppressed by the strong magnetic field, the electron diffusion to the anode is enforced by the electric field in the outside region of the sheath in order to sustain the plasma. Due to the additional electric field, the distributions of the net generation rate and the number density of the plasma are broadened to the anode direction.

Improving Mobility of F-Doped SnO2 Thin Films by Introducing Temperature Gradient during Low-Pressure Chemical Vapor Deposition

High mobility is required to suppress free-carrier absorption in the near-infrared (NIR) region. Toward this end, we investigated the properties of a F-doped SnO2 (FTO) film deposited using low-pressure chemical vapor deposition (LPCVD) and found that the optimum deposition temperature varied with film thickness. On the basis of this result, we introduced a temperature gradient into LPCVD, which resulted in an improvement in the mobility of F-doped SnO2 on glass to 77.5 cm2 V-1 s-1.

Relation of TCO surface texture shape to a-Si/μc-Si tandem cell performance on W-texture SnO 2 :F TCO substrates

Double-texture (W-texture) TCO, which was named “HU-TCO”, has a combination of 300–500nm height and over 1μm width hills which are covered with submicron-size pyramidal texture that leads to high haze value in a wide wavelength range. We studied the relation between the bottom current of the a-Si:H/μc-Si:H tandem solar cells and the TCO texture indexes, such as the haze ratio at 800nm, and light scattering angle distribution. There is a positive correlation between bottom current and haze ratio at 800nm; however it was observed that the bottom current hit a peak at very high haze value. We modified amorphous p-layer of top cell and confirmed that the player configuration strongly affected Voc. Appropriate player configuration not only affected the Voc but also further increased the bottom current on the HU-TCO with high hills.

Numerical simulation of plasma confinement in DC magnetron sputtering under different magnetic fields and anode structures

The plasma confinement between the electrodes in direct current magnetron sputtering has been investigated by using the two-dimensional hybrid model. We have quantitatively clarified plasma behavior for different magnetic fields and anode structures. The results show that plasma can be confined in the space near the sputtering target by applying a center-dominant magnetic array even in the absence of an anode facing the target (cathode). This knowledge is expected to be useful for film deposition on insulating materials such as glasses.