Floating Substrate Potential Research Articles

Variation of local chemical compositions of (Ti, Al)N films on inner wall of small hole deposited by high-power impulse magnetron sputtering

The local chemical composition of (Ti, Al)N thin films grown on the inner-walls of holes by high-power impulse magnetron sputtering (HiPIMS) was analyzed in detail to investigate the transport behavior of ionized and neutral species into small holes. HiPIMS deposition was performed at the floating substrate potential and at −50 and −150V with a fixed pulse length of 100μs and a frequency of 333Hz. The deposition rate on the inner-walls decreased with increasing substrate bias at all hole depth. From the obtained local chemical compositions of (Ti, Al)N films on inner-walls, it was found that the content of the metal elements, Ti and Al, decreases with increasing depth. In addition, the rate of decrease of the Ti content with increasing depth on the inner-walls is greater than that of the Al content. This tendency becomes increasingly significant with increasing substrate bias voltage. These bias dependencies are discussed by considering the degree of thermalization for ionized species from the viewpoint of the difference in the mass number between Ti, Al, and the gas species.

Graphene Films Prepared Using Energetic Physical Vapor Deposition

ABSTRACT Carbon films were energetically deposited onto copper foil using the physical vapor deposition technique filtered cathodic vacuum arc. Raman spectroscopy and x-ray absorption spectroscopy showed that high quality graphene films of uniform thickness can be deposited onto copper foil at temperatures of 850 °C. The films can be prepared at high deposition rates (∼1 nm/min) and were comparable to graphene films grown at 1050 °C using chemical vapor deposition. This lower growth temperature was made possible by the energetic carbon flux which assisted the arrangement of carbon atoms into graphene layers on the Cu growth surface. Floating substrate potential was found to produce the highest quality graphene and the addition of hydrogen gas during film growth resulted in more defective films.

The Si3N4/TiN Interface: 5. TiN/Si3N4 Grown and Analyzed In situ using Angle-resolved X-ray Photoelectron Spectroscopy

Angle-resolved x-ray photoelectron spectroscopy (AR-XPS) was used to analyze TiN/Si3N4 bilayers grown by ultrahigh vacuum reactive magnetron sputter deposition onto Si(001), with an electrically floating substrate potential of 7 V, in mixed 1:1 Ar/N2 discharges maintained at a total pressure of 0.5 Pa (3.75 × 10−3 Torr). The Si3N4 layers were deposited at room temperature and the 4-ML thick TiN overlayers were grown at 600 °C. AR-XPS spectra were obtained using incident monochromatic Al Kα x-radiation at 0.83401 nm. TiN/Si3N4 Ti 2p spectra reveal an unscreened final-state satellite intensity that lies between that of clean TiN(001) and Si3N4/TiN(001).

The Si3N4/TiN Interface: 6. Si/TiN(001) Grown and Analyzed In situ using Angle-resolved X-ray Photoelectron Spectroscopy

Angle-resolved x-ray photoelectron spectroscopy (AR-XPS) was used to analyze Si/TiN(001) bilayers grown by ultrahigh vacuum reactive magnetron sputter deposition on MgO(001), with an electrically floating substrate potential of 7 V, in mixed 1:1 Ar/N2 discharges maintained at a total pressure of 0.5 Pa (3.75 × 10−3 Torr). The TiN(001) films were grown at 600 °C and the 4-ML-thick Si overlayers at room temperature. AR-XPS spectra were obtained using incident monochromatic Al Kα x-radiation at 0.83401 nm. Si/TiN(001) Ti 2p spectra reveal reduced unscreened final-state satellite peaks compared to Ti 2p spectra obtained from uncapped TiN(001) due to increased electronic screening.

The Si3N4/TiN Interface: 7. Ti/TiN(001) Grown and Analyzed In situ using X-ray Photoelectron Spectroscopy

X-ray photoelectron spectroscopy (XPS) was used to analyze Ti/TiN(001) bilayers grown by ultrahigh vacuum reactive magnetron sputter deposition on MgO(001), with an electrically floating substrate potential of 7 V, in mixed 1:1 Ar/N2 discharges maintained at a total pressure of 0.5 Pa (3.75 × 10−3 Torr). The TiN(001) films were grown at 600 °C and the 4-ML-thick Ti overlayers at room temperature. XPS spectra were obtained using incident monochromatic Al Kα x-radiation at 0.83401 nm. Ti/TiN(001) Ti 2p spectra reveal reduced unscreened final-state satellite peaks compared to Ti 2p spectra obtained from uncapped TiN(001) due to increased electronic screening.

Characterization studies of pulse magnetron sputtered hard ceramic titanium diboride coatings alloyed with silicon

The composition, structure and mechanical properties of pulsed-DC unbalanced magnetron sputtered Ti–Si–B thin films—hard coatings with the potential for excellent thermal stability and oxidation resistance—are investigated and reported in this paper. Fully dense, hard (19–37 GPa) Ti–Si–B coatings were deposited at substrate bias voltages ( V s) ranging from floating potential to −150 V which resulted in substrate temperatures of ∼90–135 °C. We found that variation of substrate biasing conditions critically affected film composition, structure and resultant mechanical properties. For instance, concentration of Si in films decreased from 18.4 at.% to 3.8 at.% as V s was increased from floating potential to −150 V; composition profile analysis of the near-surface region of films (0–10 nm) revealed them to be rich in Si with significant differences among specimens produced at different substrate bias conditions. Variation of substrate biasing conditions provided coating structures that ranged from completely amorphous at floating substrate potential to nanocrystalline at V s = −50 to −100 V and crystalline nanocolumnar at V s = −150 V. We found that each of the structures obtained exhibited different specific values of hardness and elastic modulus, which is also in a good agreement with results reported for other coatings possessing similar micro- and nano-structures. Film structure was analyzed in detail by conventional and analytical transmission electron microscopy. Coatings that exhibited the highest values of hardness (37 GPa) were found to possess features such as crystalline nanocolumnar grains a few nanometres in diameter and disordered intergranular regions of different chemical composition, thus qualifying as nanocomposite films. Results of this work allowed relationships to be drawn between deposition parameters and Ti–Si–B coating composition, structure and mechanical properties. Qualitatively similar relationships are also expected for other biased plasma-assisted physical vapour deposited transition-metal-based ceramic coatings alloyed with Si (e.g. Ti–Si–N, Cr–Si–N, Cr–Al–Si–N).

Dependence of interface layer thickness in FeCo–Si multilayers on sputtering parameters

The thickness dependence of interface layers in FeCo–Si multilayers on sputtering voltage, argon pressure and substrate bias potential was examined. The multilayers were characterised by in situ kinetic ellipsometry, X-ray reflection, X-ray diffraction, polarized neutron reflection and atomic force microscopy. A minimum thickness for the sum of both interface layers per period between 23 Å and 24 Å was found for different combinations of production parameter values. For an argon pressure of 1.3×10 −3 mbar the minimum interface thickness was found at a sputtering voltage of 708 V, and for an argon pressure of 2.3×10 −3 mbar at 880 V. These values were determined for a floating substrate potential of approximately +60 V relative to ground. Applying a substrate bias potential of −70 V the minimum interface thickness occurred for a sputtering voltage of 880 V at an argon pressure of 1.3×10 −3 mbar. This study confirmed the results of the former empirical optimisation. By revealing the existence of several sets of optimum parameters it opens up a further parameter to adjust other properties like stress. The interface layer on top of the FeCo layer is 16% thicker than the one on top of the Si layer due to the larger roughness of the FeCo layers.

誘導結合高周波プラズマ支援マグネトロンスパッタ放電におけるイオンエネルギー分布

The energy distribution of ions during magnetron sputtering enhanced with an inductively coupled rf plasma at 10-110-2 Pa was measured using a quadrupole mass spectrometer combined with an ion energy filter. The cathode in this sputtering system has an rf coil attached to the planar magnetron sputtering target. Other discharge properties of this plasma, including V-I characteristics and floating substrate potential, were also evaluated. The ion current of both the sputtered metal and the Ar gas increased significantly with increasing rf coil input power at a constant DC inut power to the target. Simultaneously, the energies of both ion species increased moderately. It was possible to increase the ratio of the ion current of the sputtered metal to that of the Ar gas by adjusting the rf coil input power in relation to the DC power. It was concluded that this sputtering method was very effective in ionizing sputtered particles in comparison with conventional magnetron sputtering.

電子サイクロトロン共鳴スパッタリング法による窒化炭素薄膜の合成

Carbon nitride films were prepared by electron cyclotron resonance (ECR) sputtering deposition method using a carbon target and a nitrogen atmosphere. The deposited films were evaluated with the x-ray photoelectron spectroscopy, Raman spectroscopy, atomic force microscopy (AFM) and x-ray diffraction. The nitrogen concentration, chemical bonding, surface morphology and structure were clearly dependent on the floating substrate potential, corresponding to the ion irradiation energy onto substrates. The maximum of nitrogen to carbon atomic ratio (N/C) for the film deposited at a floating substrate potential of - 50 V reached to 1.35, which was stoichiometry of C3N4. The XPS N 1 s and Raman spectra indicated that the change of bonding structure occurred with increasing nitrogen concentration in the deposited film. Furthermore micro-crystals were observed with AFM. The x-ray diffraction measurement of the film deposited at 600°C suggests that the lattice parameters of the micro-crystal are similar to the predicted beta and/or alpha C3N4.

Wide-area uniform plasma processing in an ECR plasma

Large-area uniform material processing is demonstrated in reactive plasmas produced by a plane antenna with permanent magnets for the electron-cyclotron resonance at 2.45 GHz. Oxygen plasmas are used for the ashing of photoresist films; sulphur hexafluoride and carbon tetrafluoride are used for the etching of polysilicon and silicon dioxide films, respectively. In both cases the plasma parameters are measured in detail. Typically, the electron density in and plasmas is about (1 - 2) and the electron temperature is about 3 eV for a microwave power of 600 W. However, in the plasma. The ashing and etching rates for photoresist and polysilicon are 40 - 50 and the etching rate of silicon dioxide is about 10 in the uniform plasma region (z = 25 - 35 cm), when the microwave power is 600 W under the condition of the floating substrate potential. A quite homogeneous material processing of those films is established over a diameter of 40 - 45 cm at the distance of 25 - 35 cm from the antenna.

An SOS MOSFET model based on calculation of the surface potential

A circuit simulation model is presented suitable for the design of analogue and digital SOS MOSFET integrated circuits. Both the drift and diffusion components of channel current are modeled, which are computed from the surface potentials at the drain and source ends of the channel. The surface potential function varies continuously from subthreshold to strong inversion allowing a smooth transition of device conductances and capacitances at the threshold voltage. Charge is conserved in the model formulation yielding reliable simulation results in transient analysis. The model has been implemented in the SPICE program, together with important extrinsic elements such as impact ionization current, pn-junction current and capacitances, and substrate resistance. The pn-junction current expression includes a physical formulation for the drain leakage current. The influence of temperature on device characteristics is included, making the model valid from /spl minus/55 to 125/spl deg/C. Simulation results are compared with measured dc device characteristics showing considerable improvement over bulk MOS models in predicting the drain conductance. In subthreshold, the model predicts the observed increase in inverse subthreshold slope with drain bias for n-channel devices. Transient simulations show that capacitive coupling from drain, gate and source nodes can strongly influence the floating substrate potential. The model has been successfully applied to the design of analogue SOS circuits. >

Low current 1-D model for SOI structures—Numerical analysis by a fixed function integration method (fixfun)

A detailed one-dimensional model for SOI structures, including the relevant device parameters is presented. The model allows for a general study of the low drain voltage characteristics of SOI/MOSFETs (including the subthreshold regime), as well as the capacitance of the two-terminal MOS/SOI structures characterized by a floating substrate potential. Specific results are presented and discussed. The numerical analysis of the potential distribution and the determination of an automatic meshpoint distribution for Poisson's equation are performed simultaneously by imposing a FIXed FUNction criterion (FIXFUN).

Influence of substrate freeze-out on the characteristics of MOS transistors at very low temperatures

The low temperatures current-voltage characteristics of N-channel MOS transistors have been analysed. An excess drain current is observed for intermediate values of drain voltage. This anomalous drain current is explained in terms of substrate freeze-out, since at very low temperatures the MOS structure has a type of floating substrate potential within the depletion region. Due to the increase of the majority carrier current, flowing through the substrate to the source at increasing drain voltage, this substrate potential increases and causes a change of threshold voltage. This change is observed in the current-drain voltage characteristics of the MOSFET. Various experiments, such as measurements of substrate current, effects of temperature, gate and substrate voltages, support this interpretation. MOS transistors with various geometries and various dopings are analysed.

Charge pumping in SOS—MOS transistors

The variation of the floating-substrate potential of SOS-MOS transistors is studied by applying frequent pulses to the gate. The minority carriers are injected into the floating substrate by charge pumping and they recombine there. The injected charges are stored because of the reverse-biased junctions at the source and drain. The threshold-voltage change by the substrate bias is also investigated. If the silicon film is fully depleted under the gate, the threshold-voltage change does not occur. This condition is used to stabilize the high-speed operations of the SOS-MOS integrated circuits. A new memory cell consisting of only one transistor without a storage capacitor is realized utilizing the change of the floating-substrate potential by the charge pumping and the avalanche multiplication. The sensitivity of the memory cell is affected by the channel length of an SOS-MOS transistor. The memory storage time is obtained as 300 µs.

Influence of the floating substrate potential on the characteristics of ESFI MOS transistors

A model is proposed to explain the anomalous current-voltage characteristics of ESFI MOS transistors. Due to the floating state the substrate potential of the ESFI transistor is increasing with increasing majority carrier current flowing through the substrate to source. In the region of multiplication by avalanche that effect will get quite pronounced. The change of substrate potential yields a change of the threshold voltage hereby increasing the drain current and resulting a bend in the I D (U D) curves. The assumptions of the model have been justified by additional experiments as with illumination of light or increased temperatures. Based on the physical model a computer program was developed to simulate the I D (U D) characteristics of ESFI MOS transistors of the enhancement type, resulting good agreement between measured and simulated characteristics.

On the substrate current noise in MOS transistors beyond pinchoff

Low-frequency current noise flowing through the substrate contact has been observed in MOS transistors beyond pinchoff by means of a special circuit preventing a floating substrate potential. The noise is of the same order of magnitude as that observed in junction-gate FETs and evidently is due to impact ionization.