E. Morvan

Montecarlo simulation of ion implantation into SiC-6H single crystal including channeling effect

Abstract An ion implantation simulator for single crystal 6H-SiC is presented. This simulator uses a Montecarlo method together with either physically based or semiempirical models to calculate the slowing down of the incoming ions in the crystal. Channeling effect, which appears not to be negligible in SiC single crystal for standard ion implantation conditions, arises naturally as a consequence of the crystal structure and valence electrons distribution. The effect of a native oxide, dynamical amorphization and thermal vibration of the lattice atoms, which affect the channeling behavior of the ions, are also included in the simulation. Recent models for electronic stopping are also used. After calibration, the simulation profiles show good agreement with published SIMS profiles.

Channeling implantations of Al+ into 6H silicon carbide

A strong channeling effect of Al+ ions implanted into crystalline SiC has been observed by Monte Carlo simulations and experiments especially designed to demonstrate this phenomenon have been performed. Depth distributions of implanted Al were measured for on- and controlled off-axis Al implantations using secondary ion mass spectrometry (SIMS). Much deeper and wider profiles are obtained for the on-axis implantations as compared to off-axis implants. For higher doses, the experiment also reveals the growth of an intermediate peak slightly deeper than the random peak. The origin of the intermediate peak can be understood by combining SIMS results with Monte Carlo simulations, which motivates the development of advanced simulation tools for the ion implantation process in SiC.

Lateral spread of implanted ion distributions in 6HSiC: simulation

In this paper, Monte Carlo simulation, using improved models for electronic stopping and 3D damage accumulation has been carried out to calculate the lateral distribution of ions implanted into 6Hue5f8SiC crystal. Two dimensional concentration contour plots are used to show the lateral spread of implanted Al+ ions at mask edges. It appears that channeling strongly influences the shape of lateral distributions due to the capture of random implanted ions by axial channels lying parallel to the (0001) surface of 6Hue5f8SiC which appears alternatively every 30° around the 〈0001〉 axis, according to the symmetry of the 6Hue5f8SiC crystal. This phenomenon, if confirmed by SIMS 2D profiling, could have important consequences on the behavior of ion implanted lateral junctions of SiC devices.

Aluminum multiple implantations in 6H–SiC at 300 K

Abstract A complete study was driven in order to elaborate a p + –n junction in 6H–SiC. The chosen techniques were aluminum multiple implantations, followed with high-temperature furnace annealings. First, we had to configure the furnace geometry aiming at optimizing the annealed material characteristics. We evidenced the beneficial effects of a SiC plate inside the furnace reactor on the surface stoichiometry of the annealed sample, and also on its crystal reordering velocity. Then, the fivefold aluminum implantation necessary for the 0.5 μm depth p + -region creation has been studied, especially the energy order influence on the junction steepness. It was found that the increasing energy order implantations lead to a channeling effect less important, a deeper amorphized zone, and a defect interface at volume more abrupt. After an annealing performed with the optimized furnace, the best electrical activation obtained equated the degree of ionization even though the as-implanted material was totally amorphized up to 0.25 μm. Moreover, the three different multiple implantations investigated during this study induced different amorphized layer depths, despite they all have the same total aluminum dose with the same highest energy value. All along the paper, we propose to explain this fact. This is probably due to distinct mechanisms involved in the amorphization phenomena, which were tentatively estimated with a specific Monte Carlo simulator recently developed.

Confocal micro-Raman characterization of lattice damage in high energy aluminum implanted 6H-SiC

High energy (MeV) and low dose aluminum implants were performed in p-type 6H-SiC at room temperature. The material was characterized by means of Rutherford backscattering in channeling configuration and confocal micro-Raman scattering. The damage induced changes in the optical absorption coefficient of the implanted layer can be extracted from the depth profiling of the first order Raman intensity of the undamaged portion of the sample, using a confocal microprobe setup. Optical modeling indicates the formation of two layers: an outermost and low absorbing layer with thickness proportional to the energy of the bombarding ions, and a more highly damaged and absorbing layer. Since the damage level is low, the disorder can be essentially removed by annealing at relatively low temperatures.

Electronic stopping power for Monte Carlo simulation of ion implantation into SiC

Abstract A new electronic stopping power model for Monte Carlo simulation of ion implantation into 6H–SiC is presented. This model is based on the nonlinear density functional approach of Echenique et al. for the energy loss of slow ions moving through an electron gas and the ab initio pseudopotential calculations of Park et al. for the map of valence electrons of 6H–SiC crystal. A modified linear response theory has been used to treat the core electrons stopping. This model does not need fitting parameters and allows to fit the experimental distributions of implanted dopants in SiC both the peak region and the channeling tail of the SIMS profiles.

Mapping of 6H-SiC for implantation control

Abstract In this paper, the problem of ion implantation control for SiC technology with respect to the channeling phenomenon is addressed. To obtain a good reproducibility of the implantation process, it is necessary to control the orientation of the ion beam with respect to the crystal axis, which for SiC, is different from the wafer axis, due to the off-axis of the crystals. Ion implantation simulation has been used, together with a mapping procedure, to investigate the beam angle effects on implant profiles and to find some optimum conditions for control and reproducibility of the process.

Silicon carbide power devices

The more and more demanding requirements of the power device users bring the silicon technology very close to its own physical limits. Silicon carbide (SiC) appears today as the only semiconductor having the capability for significantly improving the ratings of major power components (such as high voltage Schottky rectifiers), indeed for creating novel devices for new applications. The choice of SiC comes from superior physical properties, an existing substrate commercialization, and an experimental confirmation of several potentialities (at high voltage, temperature, or frequency) via demonstrative prototypes. However, such a young technology still suffers from a too poor quality of the available basic materials, and from the fabrication step immaturity, delaying the SiC power electronics emergence.

SiC power DIMOS with double implanted Al/B P-well

Abstract Power 6H- and 4H-SiC DIMOS test structures have been fabricated using a new technology. P-well formation was optimised from simulation study and previous experiments on high-energy Al implantation. Reduction of Al presence at interface and reduced defect formation during implantation were the main objectives of this optimisation. Complementary surface implantation of boron was performed to adjust the interface (channel) doping. Power DIMOS were characterised at ambient temperature and up to 320°C. 4H-SiC DIMOS exhibits very poor characteristics while 6H-SiC device functionality is maintained at 300°C. Power DIMOS without complementary boron implantation also exhibits good performances up to 300°C.

Confocal micro-Raman scattering and Rutherford backscattering characterization of lattice damage in aluminum implanted 6H–SiC

Abstract High energy (MeV) and low dose aluminum implants were performed in p-type 6H–SiC at room temperature. The material was characterized by means of Rutherford backscattering in channeling configuration and confocal micro-Raman scattering. Information on the damage-induced changes in the absorption coefficient of the implanted layer can be extracted from the depth profiling of the first-order Raman intensity of the undamaged portion of the sample, using a confocal microprobe set-up. Optical modeling indicates the formation of two layers: an outermost, low absorbing, layer with thickness proportional to the energy of the bombarding ions; and a deeper, more damaged, and absorbing layer.