Jean François Barbot

Evidence for Two Charge States of the S-Center in Ion-Implanted 4H-SiC

Proton-implanted 4H-SiC samples of n-type, have been investigated using Deep Level Transient Spectroscopy (DLTS). Two levels, referred to as S 1 and S2 have been studied in detail. S 1 and S2 are located, respectively, at 0.41 eV and 0.71 eV below the conduction band edg e. Their extrapolated capture cross-sections are both ∼5x10cm. Furthermore, isochronal annealing performed between 350 and 625K have shown a close one-to-one correlation betwee n the concentration of the two levels. Our results suggest strongly that these levels represent two charge states of the S-center, and the absence of a Pool-Frenkel effect indicates a cent r of acceptor type.

Microhardness and polarity in Cd x Hg1−xTe

The Vickers microhardness of CdxHg1−xTe alloys has been measured at room temperature as a function of composition and of the nature of the {111} faces for different conduction types. The hardness-composition curve shows a maximum at aboutx = 0.75. On the {111} faces, it has been found that the metal face (A face) is harder than the metalloid face for all studied doping types and is related to the different mobilities of the A(g) and B(g) dislocations. This behaviour is compared with a model previously developed for hardness polarity in GaAs.

Defect levels of proton-irradiated silicon with doses ranging from 1 × 1012 cm−2 to 1 × 1013 cm−2

Abstract Schottky diodes of n-type silicon have been irradiated by 800 keV and 1 MeV protons at doses ranging from 1 × 10 12 cm −2 to 1 × 10 13 cm −2 . Thermally Stimulated Capacitance (TSCAP), capacitance-voltage (CV) and Deep Level Transient Spectroscopy (DLTS) have been applied for sample analysis. By TSCAP measurements a strong compensation effect has been observed for irradiation doses up to 5 × 10 12 cm −2 . At least five deep levels have been observed in the DLTS spectra, but the E(200) trap, located at E c − 0.36 eV, was only revealed by the fitting procedure. An additional new pure damage level, labelled E(110), with an energy of E c − 0.19 eV and a capture cross section of about 5 × 10 −16 cm 2 has been also observed in the highly damaged region. The variations of the DLTS signal with pulse amplitude of the E c − 0.3 eV level, called E(170), has been found to be different of what is obtained at low dose irradiations: a dip followed by a peak in concentration near the maximum of implanted ions is suggested. A possible explanation of such behavior is discussed. We also report the possibility of an overdoping effect near the proton distribution before thermal annealing.

On the Effect of Lead on Irradiation Induced Defects in Silicon

Different group IV impurities (Pb, C, and Sn) have been introduced in the melt during the growth of n-type Czochralski silicon. The samples have been irradiated with 1 MeV electrons to a fluence of 4x1015cm-2. The irradiation-induced defects have been studied by Deep Level Transient Spectroscopy (DLTS). It is shown that the formation of one of the irradiation-induced deep level is avoided by the Pb-doping. This level is located at 0.37 eV from the conduction band edge (EC) and shows an apparent capture cross-section of 7x10-15cm2. In addition, another irradiation induced deep level located at EC - 0.32 eV has been studied in more details.

Investigation of Al-Ti Ohmic Contact to N-Type 4H-SiC

Metal/semiconductor contacts have a great impact on device performances. Contact properties to wide band gap semiconductors, in particular, are more difficult to control due to the large potential barrier which arises when the metal is deposited on the semiconductor’s surface. Moreover, intrinsic interface states also lead to deviation of the Schottky-Mott limit and the barrier height is no more dependent of the work function of the metal. The contact property has also become very important with the race for miniaturisation toward the nanoscale. Contacts must also be adherent, able to resist to the temperatures for which SiC based-devices are intended, and also they should be compatible with conventional device processing techniques (die attachment). Ohmic contacts to SiC have thus been investigated for decades. The difficulties of controlling the interface properties between the metal and SiC to obtain low resistive ohmic contact have not been overcome yet; the specific contact resistance being proportional to the exponential of the barrier height for a given doping concentration. For example, nickel has been studied for the ohmic contacts on n and p-type, however the presence of voids at the interface has been reported leading to the degradation of the contact properties [1]. More recently low ohmic contact resistance has been reported of Au/Ti/Al/n-type-4H-SiC contact [2]. The formation of TiSi, TiSi2 and Ti3SiC2 has been reported according to x-ray diffraction experiments after annealing. The formation of Ti3SiC2 (or MAX phase) has also been reported in TiAl-based contacts to both n-and p-type [3-6]. This ternary carbide layer is supposed to reduce the barrier height at the contact and thus leads to low contact resistances. The addition of Ge also leads to the formation of Ti3SiC2 at lower temperature of annealing [7]. However, other compounds are frequently observed at the interface showing that the control of the interfacial structure must be optimized. The objective of our work is to obtain uniform epitaxial Ti3SiC2 thin film on n-type 4H-SiC to form ohmic contact with low resistance by studying the influence of different parameters such as the role of Aluminium on the formation mechanisms, the polarity and doping dependence. The temperature and the annealing time are also parameters to be optimized for the improvement of the ohmic contact.

Co-Germanide Schottky Contacts on Ge

In this study, Co germanide Schottky barrier diodes on n-Ge (100) substrate were fabricated by sputtering metal Co on Ge, followed by annealing in vacuum at 700°C. The influence of annealing time was investigated on both the electrical properties of Co germanide Schottky barrier diodes and on the phase formation on n-Ge (100) substrate. With increasing annealing times growing or transformation of germanide entities occurs leading to reduction of the trap concentration and therefore the leakage current.

A Study on the Chemistry of Epitaxial Ti3SiC2 Formation on 4H-SiC Using Al-Ti Annealing

In order to form Ti3SiC2 on 4H-SiC(0001) 8°-off, 200 nm of Ti30Al70 was deposited onto SiC substrates by magnetron sputtering from pure Ti30Al70 targets. The samples were then annealed at 1000°C for 10 min under Ar atmosphere in a Rapid Thermal Annealing (RTA) furnace. Structural analyses reveal the formation of epitaxial hexagonal Ti3SiC2 (0001) oriented. Elemental analyses show that high amount of Al and O elements are present inside the deposit. Obviously, the formation of Ti3SiC2 is accompanied by parasitic Al oxide, probably due to some unwanted oxygen residual in the RTA chamber. By using proper backing steps before the annealing, the deposit is not anymore composed of only Ti3SiC2 but accompanied with other compounds (Al3Ti, and Al). On the oxide-free sample, the specific contact resistance ρc of the Ti3SiC2 based contact on p-type 4H-SiC (having Na= 2×1019 cm-3) was measured to be as low as 6×10-5 Ω.cm2.

Investigation of Die Attach for SiC Power Device for 300°C Applications

The mechanical properties of die attach system SiC/Au-Ge/Au-Ni-Cu-Si3N4 using the eutectic Au-Ge solder (Teut = 356°C) were investigated in a temperature range up to 300°C. The as-resulting structure of the solder is observed to be lamellar with pockets of high concentration of Au close to the interfaces. The shear strength of joint decreases with temperature but, even at 300°C, its value is well higher than the IEC standard. The creep behavior of Au-Ge solder alloy was also investigated at 300°C for different strain levels. The creep curves show a high creep resistance even for high stress level.

Depth Resolved Defect Analysis by Micro-Raman Investigations of Plasma Hydrogenated Czochralski Silicon Wafers

Depth resolved μ-Raman measurements were carried out on plasma hydrogenated and annealed silicon samples. The plasma exposure was done at 260 270 °C, and subsequent annealing at 450 °C or 550 °C. A thin structured plasma damage layer up to 100 150 nm depth and a subsurface layer up to a depth of ∼ 1 μm were observed by cross-sectional transmission electron and atomic force microscopy. In the subsurface region (111)and (100)-oriented platelets are located. Si-H Raman modes attributed to the plasma damage at the wafer surface exhibit a significant higher intensity than those attributed to platelets in the subsurface region. H2 molecules are located in the platelets, as was clearly seen by the fact that the H2 Raman signal exhibits a maximum in the intermediate subsurface region, where the platelets are located. After annealing hydrogen is released from the surface damage layer, while at the platelets it is still trapped.

Strain Build-Up, Swelling and Stacking Fault Formation in Implanted 4H-SiC

Ion implantation into 4H-SiC induces a local gradient of strain which increases with the nuclear energy losses. With the increase of temperature the strain tends to become uniform in the whole implanted area requiring the migration of particles. In case of helium implantation, defects are more stabilized and their evolutions observed post thermal annealing are concomitant with the surface swelling. The local modifications imputed to the ion process lead to the formation and the pile-up of stacking faults in the highly damaged region.