[en] The application of silicon-on-insulator (SOI) substrates to high-power integrated circuits is hampered by the self-heating effect due to the poor thermal conductivity of the buried SiO₂ layer. We introduce aluminum nitride (AlN) thin films formed by ultra-high vacuum electron-beam evaporation with ammonia as an alternative. The chemical composition, surface morphology, and electrical properties of these films were investigated. The film synthesized at 800 deg. C shows a high AlN content, low surface roughness with a root-mean-square value of 0.46 nm, and high electrical resistivity. Based on thermodynamic analysis and our experimental results, the mechanism of AlN formation is proposed

[en] We have investigated the electrostatic charging effects of dielectric substrate materials during plasma immersion ion implantation. The results demonstrate that the time-dependent surface potential (negative) may be reduced in magnitude due to the charging effect of the dielectric surface, leading in turn to a reduction in the energy of the incident ions and a broadening of the implanted ion energy spectrum. The charging effect is greater during the plasma immersion bias pulse rise-time, and the electrostatic potential charging may be as large as 75% of the total applied (pulse) potential. This is due to abundant charge movement both of ions and secondary electrons, and has been confirmed by computer simulation. The plasma sheath capacitance has a small influence on the surface potential, via the bias pulse rise-time. Processing parameters, for example voltage, pulse duration, plasma density, and pulse rise-time, have a critical influence on the charging effects. Short pulse duration, high pulse frequency and low plasma density are beneficial from the viewpoint of maximizing the implantation ion energy

[en] Aluminum nitride (AlN) is of interest in the industry because of its excellent electronic, optical, acoustic, thermal, and mechanical properties. In this work, aluminum nitride films are deposited on silicon wafers (100) by metal plasma immersion ion implantation and deposition (PIIID) using a modified hybrid gas-metal cathodic arc plasma source and with no intentional heating to the substrate. The mixed metal and gaseous plasma is generated by feeding the gas into the arc discharge region. The deposition rate is found to mainly depend on the Al ion flux from the cathodic arc source and is only slightly affected by the N₂ flow rate. The AlN films fabricated by this method exhibit a cubic crystalline microstructure with stable and low internal stress. The surface of the AlN films is quite smooth with the surface roughness on the order of 1/2 nm as determined by atomic force microscopy, homogeneous, and continuous, and the dense granular microstructures give rise to good adhesion with the substrate. The N to Al ratio increases with the bias voltage applied to the substrates. A fairly large amount of O originating from the residual vacuum is found in the samples with low N:Al ratios, but a high bias reduces the oxygen concentration. The compositions, microstructures and crystal states of the deposited films are quite stable and remain unchanged after annealing at 800 deg. C for 1 h. Our hybrid gas-metal source cathodic arc source delivers better AlN thin films than conventional PIIID employing dual plasmas

[en] Hydrogen is implanted into single-crystal silicon wafers using plasma ion immersion implantation to improve the surface bioactivity and the mechanism of apatite formation is investigated. Our micro-Raman and transmission electron microscopy results reveal the presence of a disordered silicon surface containing Si-H bonds after hydrogen implantation. When the sample is immersed in a simulated body fluid, the Si-H bonds on the silicon wafer initially react with water to produce a negatively charged surface containing the functional group (≡Si-O^-) that subsequently induces the formation of apatite. A good understanding of the formation mechanism of apatite on hydrogen implanted silicon is not only important from the viewpoint of biophysics but also vital to the actual use of silicon-based microchips and MEMS inside a human body

[en] Rectifying undoped and nitrogen-doped ZnO/p-Si heterojunctions were fabricated by plasma immersion ion implantation and deposition. The undoped and nitrogen-doped ZnO films were n type (n∼10¹⁹ cm^-3) and highly resistive (resistivity ∼10⁵ Ω cm), respectively. While forward biasing the undoped-ZnO/p-Si, the current follows Ohmic behavior if the applied bias V_forward is larger than ∼0.4 V. However, for the nitrogen-doped-ZnO/p-Si sample, the current is Ohmic for V_forward<1.0 V and then transits to J∼V² for V_forward>2.5 V. The transport properties of the undoped-ZnO/p-Si and the N-doped-ZnO/p-Si diodes were explained in terms of the Anderson model and the space charge limited current model, respectively

[en] Plasma immersion ion implantation of insulators is an interesting topic both theoretically and industrially. The net energy of the incident ions is dictated by the surface potential and for conductors is equal to the voltage applied to the backside or sample stage. However, the poor electrical conductivity of insulating materials can lead not only to charging during ion bombardment but also reduced surface potential due to the capacitance effect. In the work described in this paper, we theoretically and experimentally investigate the influence of the thickness and dielectric properties of insulating materials on the implantation efficacy. The use of mesh-assisted PIII by covering the insulating materials with an electrically conducting cage to enhance the implantation efficacy is also compared experimentally. Our theoretical results suggest that a low plasma density induces less surface charges and higher surface potential. Our experimental data show good agreement with the theoretical results and mesh-assisted PIII does yield net improvement

[en] High-voltage pulsed glow discharge is applied to plasma immersion ion implantation (PIII). In the glow discharge, the target constitutes the cathode and the gas tube forms the anode under a relatively high working gas pressure of 0.15-0.2 Pa. The characteristics of the glow discharge and ion density are measured experimentally. Our results show resemblance to hollow-anode glow discharge and the anode fall is faster than that of general glow discharge. Because of electron focusing in the anode tube orifice, ions are ionized efficiently and most of them impact the negatively biased samples. The resulting ion current density is higher than that in other PIII modes and possible mechanisms of the glow discharge PIII are proposed and discussed

[en] Multiple plasma immersion ion implantation-deposition offers better flexibility compared to other thin film deposition techniques with regard to process optimization. The plasmas may be based on either cathodic arc plasmas (metal ions) or gas plasmas (gas ions) or both of them. Processing parameters such as pulsing frequency, pulse duration, bias voltage amplitude, and so on, that critically affect the film structure, internal stress, surface morphology, and other surface properties can be adjusted relatively easily to optimize the process. The plasma density can be readily controlled via the input power to obtain the desirable gas-to-metal ion ratios in the films. The high-voltage pulses can be applied to the samples within (in-duration mode), before (before-duration mode), or after (after-duration mode) the firing of the cathodic arcs. Consequently, dynamic ion beam assisted deposition processes incorporating various mixes of gas and metal ions can be achieved to yield thin films with the desirable properties. The immersion configuration provides to a certain degree the ability to treat components that are large and possess irregular geometries without resorting to complex sample manipulation or beam scanning. In this article we describe the hardware functions of such a system, voltage-current behavior to satisfy the needs of different processes, as well as typical experimental results

[en] The diffusion of indium in both the top silicon and the buried oxide (BOX) layers in separation by implantation of oxygen (SIMOX) is investigated. For all indium-implanted samples, there is a significant redistribution of indium atoms from the top Si-BOX interface toward the bottom BOX-Si interface, thereby affecting the indium concentrations in the two silicon-BOX interfaces. In the case of relatively high-dose and high-energy indium implantation (1x10¹⁴ cm^-2 at 200 keV), an anomalous segregation of indium is observed in both the bulk Si and the SIMOX substrates. However, there is a notable transportation of indium atoms from the top Si layer toward the bottom BOX-Si interface in the SIMOX, thereby affecting not only the indium concentrations in the two silicon-BOX interfaces but also the indium distribution in the top silicon layer. The unique indium-diffusion behavior in the SIMOX is believed to be a composite effect of indium trapping by the two Si-BOX interfaces, indium atoms being drawn away from the top silicon layer by the buried oxide, as well as implant damages in the top silicon. The asymmetrical structure of the BOX layer with Si islands accumulating at the bottom BOX-Si interface and the abundance of oxygen-related defects in the BOX layer are also believed to be responsible for the indium-diffusion behavior in the BOX layer

[en] Multilayer inorganic silica/alumina films with excellent mechanical, optical and anti-atomic-oxygen erosion characteristics were fabricated by the hybrid implanting and depositing processes of Al/Si plasmas on polyimide. The multilayer films exhibited an excellent mechanical stability, demonstrating that balanced internal stresses and alternating bonding structures were crucial for enhancing mechanical stability. The multilayer inorganic films exhibited higher optical transmittance. The slight change surface morphology and high mechanical stability of polyimide covered with multilayer silica/alumina films suggest that the techgnique used is an effective method to protect polymer materials which are applied to thermal control system of spacecrafts in low Earth orbit.