Materials Science Forum Vols. 483-485

Abstract: Oxidized Ta2Si layers have been used as high-k dielectric layer for 4H-SiC MOSFETs. The gate insulator was grown by dry oxidation of 40nm deposited Ta2Si during 1h at 1050oC. The dielectric constant obtained from 4H-SiC MIS capacitors is ~20 with an insulator thickness of 150nm. These devices exhibit adequate subthreshold, saturation and drive characteristics. For the MOSFETs fabricated on a p-implanted and annealed region, a peak mobility up to 45cm2/Vs has been extracted. The specific on-resistance of this device is 29mW·cm2 at room temperature with VDS=0.2V and VGS=14V.

Abstract: Silicon carbide (SiC) is a wide bandgap semiconductor suitable for high-voltage, highpower and high-temperature applications [1]. However, and among other issues, the production of advanced SiC power devices still remains limited due to some shortcomings of the dielectric properties of the passivation layer [2]. Due to their supposed high operating temperature and dielectric strength [3], spin coated polyimide materials appear as a possible candidates for SiC device passivation and insulation purposes. As a matter of fact, they are already used in current commercial SiC devices allowing a maximum junction temperature of 175 °C. The aim of this paper is to study the ability of polyimide (PI) coatings to be used for a Tjmax up to 300 °C. Therefore, the main electrical properties (dielectric permittivity, leakage current and breakdown field) at different temperatures of a high temperature commercially available polyimide material (from HD Microsystems) in both Metal-Insulator-Semiconductor (MIS) and Metal-Insulator-Metal (MIM) structures are presented and discussed.

Abstract: We investigated the effect of high temperature annealing on the Schottky barrier height (Fb) and the ideality factor (n-factor) of a Mo contact. In a Mo contact, the Fb increased and the leakage current decreased by annealing at 600oC, while no increase in n-factor and forward excess current owing to the high temperature annealing was observed. The Schottky barrier diode with Mo contact annealed at 600oC showed a blocking-voltage (Vb) of 4.15 kV and a specific on resistance (Ron) of 9.07 mWcm2, achieving a high Vb 2/Ron value of 1898 MW/cm2.

Abstract: An effect of electron beam annealing (EBA) on both surface morphology and characteristics of test Ti/n-6H-SiC contacts was investigated. It was found that the mean roughness of the n-6H-SiC surface decreased from 3.43 nm to 1.35 nm and the surface sheet resistance increased from 3.1 to 4.0 Ω/sq after EBA. The Ti/n-6H-SiC contacts formed on substrates after EBA exhibited ohmic properties, while the same contacts formed on the un-annealed samples were Schottky contacts with the barrier height of 0.63 eV and ideality factor of 1.92.

Abstract: The effects of ion irradiation on the Ti/4H-SiC Schottky barrier are discussed. The Ti/SiC interfacial region of test Schottky diodes was irradiated with 8 MeV Si+4 ions at fluences between 1×109 and 1×1012 ions/cm2. By increasing ion fluence, an increase of the Schottky barrier FB was observed, from FB=1.05 eV in the non-irradiated sample to FB =1.21 eV after irradiation at the highest fluence, accompanied by a decrease of the leakage current. Using different experimental analytical techniques enabled us to correlate the modification of the interfacial region with the contacts electrical behaviour. In particular, the structural and electrical modifications in the nearinterface region (different orientation of the Ti film, defects in the epilayer, dopant deactivation) were responsible for the change of the Ti barrier after irradiation.

Abstract: In this work we report an analysis on Ni/4H-SiC interfaces aimed at optimizing the ohmic contacts. Several thermal cycles have been performed by rapid thermal annealing checking the possible chemical reactions at the metal semiconductor interfaces. Micro x-ray diffraction and micro Raman techniques have been performed in order to study the interface micro structural evolution. Inter diffusion of each element at the Ni - SiC interface was examined using Auger spectroscopy. Electrical measurements have been performed in order to check the ohmic behavior of the contacts. Finally, a correlation between microstructures evolution and electrical behaviors is reported.

Abstract: Recently Ni/SiC contacts have been studied in order to achieve very low contact resistivity (rc) values on n-type SiC. In this work contact resistivity values of Ni-silicide contacts to n-type ion implanted 6H-SiC are analyzed aiming at extracting the Schottky Barrier Height (SBH). The n-type ion implanted 6H-SiC specimens were annealed at 1300, 1500, 1650°C for 20 min in a high purity Ar ambient. The rc values have been extracted from Transmission Line Method (TLM) measurements in the range of temperatures 25-290°C. The rc values are in the range 1-5×10-5 Wcm2 depending on the annealing temperature. The SBH fBn has been extracted by exploiting the dependence of the contact resistivity on the temperature. By using the field emission model, the value obtained for fBn on our samples is in the range 1.1-1.3 eV depending on the annealing temperature. The SBH on p-type 6H-SiC has been evaluated on Schottky diodes by means of both IV and C-V measurements. A value of qfBp= (1.75±0.05) eV has been obtained on p-type SiC through the C-V method. The average SBH extracted from I-V data collected at room temperature is (1.19±0.03) eV and this value increases as a function of the temperature until (1.50±0.01) eV at 290°C. Differences between values of SBH extracted from I−V and from C−V measurements are explained in terms of inhomogeneous barrier height

Abstract: Low-energy electron diffraction (LEED), scanning tunneling microscopy (STM) and spectroscopy (STS), and Auger electron spectroscopy (AES) were used for a study of silver interaction with the (3×3) and ° × 30 ) 3 3 ( R surface phases of clean 4H-SiC(0001). The development of the surface structure and morphology after room temperature (RT) deposition and annealing was investigated. On the (3×3) phase silver forms small clusters leaving the initial reconstruction intact. At high coverages three-dimensional (3D) growth (Vollmer-Weber mode) was found. For the ° × 30 ) 3 3 ( R phase the initial structure seems more disturbed upon Ag deposition and thermally induced diffusion. Yet, no new surface phase develops. In both cases Ag can be removed from the surface by annealing, but Ag appears to be more stable on the ° × 30 ) 3 3 ( R phase according to AES.

Abstract: We report on the investigation of electrical properties of polycrystalline 3C-SiC thin films deposited on oxidized Si by low pressure chemical vapor deposition (LPCVD) to obtain bi-layer structures [Si(100)/SiO2/poly 3C-SiC] for pressure sensors and micro-electromechanical system (MEMS) applications. Polycrystalline 3C-SiC films have been preliminary characterized in their compositional, structural, morphological and electrical properties. Moreover, metal contact definition has been carefully optimized by transmission line method (TLM) analyses performed at different temperatures. We focuses the attention on the evaluation of the bulk resistivity (ρ), the specific contact resistivity (ρc) and their behavior dependence on the temperature because these are the characteristics of major importance for the fabrication of pressure sensors or MEMS.

Abstract: X-ray photoelectron spectroscopy is used to study the effect of the metal composition on the electrical and thermal properties of Au/Pd/Ti/Pd contacts to SiC. No reactions and interdiffusion between the contact components and SiC are found for the as-deposited contact layer. The steep metal/SiC interface corresponds to the Schottky behaviour observed before the annealing. Annealing at 900 oC causes Pd2Si formation at the SiC interface and ohmic properties appearance. Due to the addition of Ti to the contact composition the carbon resulting from the SiC dissociation during annealing is completely consumed, which leads to improvement of the thermal stability.