Mechanical and Corrosion Properties of VT6 Titanium Alloy after Irradiation with Helium and Aluminum Lons

The effect of high-dose aluminum implantation on the structural-phase state of the surface layer of titanium alloy VT6 with a fine structure (average grain size 2.3 μm) on the mechanical and corrosion properties has been investigated. It is shown that, as a result of ion irradiation, polyphase implanted layers based on α-titanium grains are formed, containing an intermetallic Ti3Al phase along the grain boundaries of α-titanium. The modified surface layers are characterized by improved mechanical properties and corrosion resistance. The noted effect is enhanced by the use of preliminary helium implantation with a dose of 1.3 × 1017 ion / cm2.

Influence of a thin amorphous surface layer on de-channeling during aluminum implantation at different temperatures into 4H-SiC

Ion implantation is an important technique in semiconductor processing and has become a key technology for 4H-SiC devices. Today, aluminum (Al) implantations are routinely used for p-type contacts, p+-emitters, terminations and many other applications. However, in all crystalline materials, quite a few ions find a path along a crystal channel, so-called channeling, and these ions travel deep into the crystal. This paper reports on the channeling phenomenon during Al implantation into 4H-SiC, and in particular, the influence of a thin native oxide will be discussed in detail. The effects of thermal lattice vibrations for implantations performed at elevated temperatures will also be elucidated. 100 keV Al ions have been implanted along the [000-1] direction employing samples with 4° miscut. Before implantation, the samples have been aligned using the blocking pattern of backscattered protons. Secondary ion mass spectrometry has been used to record the Al depth distribution. To predict implantation profiles and improve understanding of the role of crystal structure, simulations were performed using the Monte-Carlo binary collision approximation code SIIMPL. Our results show that a thin surface layer of native oxide, less than 1 nm, has a decisive role for de-channeling of aligned implantations. Further, as expected, for implantations at elevated temperatures, a larger degree of de-channeling from major axes is present due to increased thermal vibrations and the penetration depth of channeled aluminum ions is reduced. The values for the mean-square atomic displacements at elevated temperatures have been extracted from experimental depth profiles in combination with simulations.

Decoration of Al Implantation Profiles in 4H-SiC by Bevel Grinding and Dry Oxidation

The possibility to analyze micrometer scaled 2D implantation profiles is essential for improving SiC power devices. Due to the fact that the oxidation rate depends on the doping concentration a rather simple method was developed in order to decorate highly doped (aluminum) implantation profiles. For this purpose, different samples were grinded with a shallow bevel angle and subsequently oxidized. It could be shown that this method allows analyzing the implantation depth of different box-shape implanted samples. Furthermore the ability to distinguish micrometer scaled 2D profiles for a state-of-the-art SiC power device could be shown.

Surface Erosion of Ion-Implanted 4H-SiC during Annealing with Carbon Cap

The stability/ erosion of the interface between a C-cap and 4H-SiC have been studied by secondary ion mass spectrometry (SIMS). Aluminum implantation has been used to monitor the position of the moving interface as well as to investigate the influence on the interface stability by the crystal quality of the 4H-SiC. After Al implantation a C-cap has been deposited by pyrolysis of photoresist. Subsequent annealing has been performed at 1900 and 2000 °C with durations between 15 minutes and 1 hour. SIMS measurements have been performed without removal of the C-cap. The surface remains smooth after the heat treatment, but a large amount of SiC material from the uppermost part of the wafer is lost. The amount of lost material is related to for instance annealing temperature, ambient conditions and ion induced crystal damage. This contribution gives a brief account of the processes governing the SiC surface decomposition during C-cap post implant annealing.

Observation and Analysis of a Non-Uniform Avalanche Phenomenon in 4H-SiC 4°-Off (0001) p-n Diodes Terminated with a Floating-Field Ring

4H-SiC (0001) p-n diodes terminated with a floating-field ring were found to emit light at breakdown in the opposite direction to that of substrate misorientation when the diodes were fabricated by aluminum implantation and dry-oxidation passivation. Two-dimensional simulation revealed that such non-uniform breakdown was mainly attributable to the asymmetric lateral straggling of implanted aluminum acceptors, rather than the anisotropic nature of the impact ionization coefficient.

Aluminum Implantation in 4H-SiC: Physical and Electrical Properties

For this study, 4H SiC samples were implanted with aluminum at room temperature, 200°C and 600°C with different energies, ranging from 30 to 380 keV, for a total dose of 4x1015 cm 2, to create a “box-like” profile. To activate dopants, samples were then isochronally annealed from 1650°C to 1850°C during 30min. The lowest specific contact resistance achieved, evaluated to 1.3x10-5 Ω.cm2, has been obtained for the 200°C implanted sample annealed at 1850°C. For this condition, Scanning Capacitance Microscopy study has proved that the dopant activity is quite homogeneous in opposition with the samples implanted at RT and 600°C.