Simulation of mass interferences considering charge exchange events and dissociation of molecular ions during extraction

Contamination due to mass interferences generally leads to severe problems in ion implantation. To be able to prevent this kind of contamination, the cause of the respective mass interference has to be known. Frequently, however, the transport mechanisms of the contamination are unknown and the search for potential transport mechanisms is troublesome. Simulation of mass interferences, therefore, is an excellent means to find potential transport mechanisms. In this paper, the simulation software ENCOTION (ENergetic COntamination simulaTION) is explained. In the latest version, an enhanced model was implemented in order to calculate the apparent mass of ions. The relevance of the new model is discussed by the example of tungsten contamination in the case of BF2+ implants. A new module that allows for the simulation or mass spectra was recently added to ENCOTION as a new feature

Purity of ion beams: Analysis and simulation of mass spectra and mass interferences in ion implantation

This paper shows that charge exchange events and dissociation reactions of ions may impact the purity of the ion beam in ion implantation, leading to contamination of the implanted target. Physical relations are derived that explain why unwanted ions are transported in the ion beam despite of a magnetic mass separation. Based on those relations, the simulation tool ENCOTION (ENergetic COntamination simulaTION) has been developed. ENCOTION is a very powerful tool for the simulation of transport mechanisms of ions through a magnet analyzer and for the simulation of mass spectra, as will be demonstrated in this paper

Influence of annealing parameters on surface roughness, mobility, and contact resistance of aluminium implanted 4H SiC

The impact of implantation temperature and dose as well as the annealing process with and without a graphite capping layer on surface roughness, carrier mobility and specific contact resistance are investigated and compared. The use of the capping layer is proven to be particularly advantageous: (1) a deterioration of surface roughness can be avoided even for high dose implantations and (2) the specific contact resistance is reduced. Furthermore, it is shown that a capping layer prevents surface contamination during annealing

Enhancement of the stability of Ti and Ni ohmic contacts to 4H-SiC with a stable protective coating for harsh environment applications

We report on wafer-level measurements of the long-term stability of Ti and Ni ohmic contacts to n-4H-SiC during thermal treatments in air or air/moisture environments up to 500°C. Contact metallizations with and without a sputtered Ti (20 nm)/TaSi x (200 nm)/Pt (150 nm) diffusion barrier stack and Ti (20 nm)/TiN (10 nm)/Pt (150 nm)/Ti (20 nm) interconnects were compared. A protective coating consisting of a SiO x (250 nm)/SiN y (250 nm) stack deposited by plasma-enhanced chemical vapor deposition (PECVD) was used. The stability of the contact metallizations during long-term thermal treatments in air and air/moisture was studied. The best performance was achieved with Ti ohmic contacts without the Ti/TaSi x /Pt stack. This system successfully withstood 1000 h thermal treatment at 500°C in air followed by 1000 h at 500°C in air/10% moisture. After the aging, the contact failure ratio was below 1% and the specific contact resistivity amounted to (2.5 ± 1.1) × 10-4 cm2. Sc anning electron microscopy (SEM) cross-sectional analysis indicated no degradation in the contact metallization, demonstrating the effectiveness of the SiO x /SiN y protective coating in preventing oxidation of the contacts. These results are very promising for applications in harsh environments, where the stability of ohmic contacts is crucial

Amorphous silicon carbide thin films (a-SiC:H) deposited by plasma-enhanced chemical vapor deposition as protective coatings for harsh environment applications

We investigated amorphous silicon carbide (a-SiC:H) thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) as protective coatings for harsh environment applications. The influence of the deposition parameters on the film properties was studied. Stoichiometric films with a low tensile stress after annealing (< 50 MPa) were obtained with optimized parameters. The stability of a protective coating consisting of a PECVD amorphous silicon oxide layer (a-SiOx) and of an a-SiC:H layer was investigated through various aging experiments including annealing at high temperatures, autoclave testing and temperature cycling in air/water vapor environment. A platinum-based high-temperature metallization scheme deposited on oxidized Si substrates was used as a test vehicle. The a-SiOx/a-SiC:H stack showed the best performance when compared to standard passivation materials as amorphous silicon oxide or silicon nitride coatings

Simulation and design optimization of transparent heaters for spectroscopic micro cells

For several applications, micro cells with a uniform temperature profile and at least one optical port are required. One example for those cells is the physics package of a chip-scale-atomic-clock. It is necessary that the micro chambers are heated homogeneously to 353 K using a low energy consumption heater. In this work transparent heating structures are investigated to achieve this goal. First an analytical approach is used to describe the behavior of thermal energy dissipation of the heating structures. Then different approaches of possible heater structures are simulated to find the optimal basic configuration. Furthermore, this configuration is optimized to obtain a uniform temperature distribution in the whole cell

Solid-phase epitaxy of silicon amorphized by implantation of the alkali elements rubidium and cesium

The redistribution of implanted Rb and Cs profiles in amorphous silicon during solid-phase epitaxial recrystallization has been investigated by Rutherford backscattering spectroscopy and secondary ion mass spectroscopy. For the implantation dose used in these experiments, the alkali atoms segregate at the a-Si/c-Si interface during annealing resulting in concentration peaks near the interface. In this way, the alkali atoms are moved towards the surface. Rutherford backscattering spectroscopy in ion channeling configuration was performed to measure average recrystallization rates of the amorphous silicon layers. Preliminary studies on the influence of the alkali atoms on the solid-phase epitaxial regrowth rate reveal a strong retardation compared to the intrinsic recrystallization rate

Comparative study on metallization and passivation materials for high temperature sensor applications

We investigated the performance of different metallization/passivation systems for high temperature applications. The metallizations comprised a 150 nm sputtered Pt or a 150 nm e-beam evaporated PtRh layer on Ti/TiN underlayers, respectively. The passivation coatings consisted of amorphous PECVD SiO x, of amorphous stress-reduced PECVD SiNy, and of a SiOx/ SiNy stack. For samples with SiOx and SiOx/ SiNy passivation layers the electrical properties changed after a short high temperature anneal at 600 °C but then remained stable during further annealing. This was attributed to the formation of PtTi alloys, which stabilized the metallization stack. In samples with SiN y passivation a significant Pt out-diffusion into the passivation layer was observed. This led to a degradation of the electrical and mechanical properties. The best performance was achieved with Pt-based metallizations and SiOx or SiOx/SiNy passivations

Deep Doping Profiles in Silicon Created by MeV Hydrogen Implantation: Influence of Implantation Parameters

The impact of dose variations of protons implanted with energies in the MeV range on the concentration and depth distribution of hydrogen‐related shallow donors in float zone and Czochralski silicon after annealing at 470 °C is examined with spreading resistance probe measurements. For moderate proton doses up to 1014 cm−2, the measured effective carrier distribution in float zone silicon correlates with the calculated distribution of the primary radiation damage caused by the penetrating protons. With increasing doses above 1014 cm−2, however, the effective carrier distribution significantly deviates from the distribution of the primary defects. Furthermore, the shape of the induced profiles in float zone and Czochralski silicon differ considerably. The effective carrier concentration at the maximum of the induced donor profile exhibits a linear dependency on the implanted dose after annealing around 370 °C, whereas this dependency becomes clearly sublinear when annealing at 470 °C. A temperature dependent model using two donor species is proposed which accounts for the different dose dependencies at the different annealing temperatures