Papers by Keyword: DLTS

Abstract: The impact on doping profile, surface roughness and defect production of each process step for a suggested Multiple epitaxy and implantation (MEI) process for Super-junction has been investigated through Secondary Ion Mass Spectrometer (SIMS), Atomic Force Microscope (AFM), Deep Level Transient Spectroscope (DLTS) and Molten KOH etching. Results show that the suggested process can possibly reduce the cost of the original fabrication and speed up the process.

Abstract: The extensive study of point defects in 4H-SiC over the past two decades has led to a comprehensive understanding of their influence on device performance. Specifically, the dominant defects Z_1/2 and EH_6/7 have been well-quantified and are now formally assigned to specific states of the carbon vacancy. Building upon this foundational knowledge, our study investigates the defect landscape created by the novel process of Energy-Filtered Ion Implantation (EFII). Using DLTS and MCTS measurements conducted within the temperature range of 50−650 K, we analyzed the trap levels created by 19 MeV Nitrogen implantation in as-grown 4H-SiC epitaxial wafer. The majority carrier (electrons) trap with DLTS measurements reveal the presence of prominent peaks associated with carbon complexes, labeled as ON0a (E_c - 0.586 eV) and ON0b / Z_1/2 at (E_c - 0.681 eV), along with smaller peaks in the shallow region and a broader peak identified as EH_6/7 at (E_c - 1.53 eV) as the deepest peak. Notably, the close proximity of the ON0b peak to the well-known Z_1/2 peak poses a significant challenge, preventing the definitive assignment of a defect structure to the known carbon complexes. On the contrary, minority carrier (holes) trap detection with MCTS reveal B-center at (E_V + 0.24 eV) and (E_V + 0.33 eV) and a negligible shallow peak at (E_V + 0.22 eV) assigned as X center. There was no indication of D-center formation in the EFII implanted samples.

Abstract: This paper investigates the effect of DLTS measurement parameters on characterizing deep level defects in 4H-SiC Schottky barrier diode (SBD). By adjusting parameters such as the time window (t_W), pulse time (t_P), reverse voltage (U_R), and pulse voltage (U_P), the underlying mechanisms influencing defect peak positions, signal amplitudes, and peak broadening are analyzed. Experimental results reveal three deep level defects identified in 4H-SiC SBD: majority carrier traps T1 (E_C - 0.66 eV) and T2 (E_C - 1.0 eV), along with minority carrier trap T3 (E_V + 1.1 eV). Parameter settings not only influence defect characterization sensitivity and concentration calculations but also reveal the dynamics of carrier capture and emission. Through the thorough analysis of the DLTS signal and behavior under different DLTS measurement conditions, the electronic properties and concentration profiles of deep level defects in 4H-SiC epitaxial layers are determined.

Abstract: In this work, the impact of 200 MeV proton irradiation at a fluence of 6 × 10¹² cm⁻² on the forward characteristics and the breakdown behaviour of nickel (Ni) and titanium (Ti) Schottky barrier diodes is explored. An improvement in the ideality factor, reduction in the threshold voltage, and an increase in the breakdown voltage is observed post irradiation. Point defects induced by the irradiation are likely responsible for the observed effects. Deep Level transient Spectroscopy (DLTS) measurements were performed on the irradiated Schottky diodes to analyse the defects created during the irradiation and gauge their potential role in changing the diode behavior. The defects induced by the high-energy protons were compared to those formed by low-energy proton irradiation at 1.8 MeV to a fluence of 1 × 10¹² cm⁻². Finally, consecutive DLTS measurements were performed after a series of reverse bias anneals at low temperatures from 350-700 K to explore the annealing behaviour of the defects induced by the proton irradiations.

Abstract: The carbon vacancy (V_C) is a lifetime-killer defect that hinders the correct functionality of 4H-SiC bipolar devices. Until now, different methods based on carbon interstitial injection, have been proposed, in order to reduce its concentration. However, if on one hand these methods effectively reduce the V_C concentration in the epilayer, on the other they cannot prevent the re-generation of V_C occurring during the manufacture of a p-i-n diode, e.g., p+ implantation and activation. In the following contribution, we employ PIII of B for the formation of the anode for a p-i-n diode. We show that by PIII, it is possible to simultaneously form a p⁺n junction with a low concentration of V_C in the drift layer.

Abstract: The diffusion welding (DW), known as direct bonding technique could be more used as an alternative approach to develop silicon carbide (SiC) Schottky rectifiers to existing mainstream metallization contact technologies. Measured results for p-type 4H-SiC Schottky barrier diodes (SBD) arepresented. And comprehensive numerical study to characterize the device has been performed. The simulations are carried out with ATLAS software (Silvaco). The measured and numerically simulated forward current-voltage (I–V) and capacitance-voltage (C–V) characteristics in a large temperaturerange are analyzed. Some of the measured p-type 4H-SiC Schottky diodes show deviation in specific ranges of their electrical characteristics. This deviation, especially due to excess current, dominates at low voltages (less than 1 V) and temperatures (less than room temperature). To verify the existence of electrically active defects under the Schottky contact, which influences the Schottky barrier height (SBH) and its inhomogeneity, the deep level transient spectroscopy (DLTS) technology was applied. DLTS measurements show the presence of a deep-level defect with activation energy corresponding typically for multilevel trap clusters.

Abstract: Stress tests were conducted for the cascode switch using the SiC buried gate static induction transistor (SiC-BGSIT). The stress of the reverse overshoot voltage was periodically applied to the pn junction between the gate terminal and source one in the BGSIT in the cascode with pulses of 40kHz for 202 hours. This simulates the stress which can be occurred in the channel region of the BGSIT during the turn-off and turn-on operation with a parasitic inductance in the interconnection of the cascode package. The result of the stress tests has revealed that there is no significant difference between the electrical characteristics of the BGSIT cascode sample before the stress and those after the stress. Thus, the BGSIT cascode can guarantee high reliability against the stress. The result from the drain current DLTS suggests that no deferent kind of defect is created in the channel region of the BGSIT by the stress.

Abstract: In this work, we examined the oxidation growth rates of the (0001) Si-face and (11−20) a-faces of 4H-SiC by carrying out oxidation in the 850°C-950 °C temperature range in a plasma afterglow furnace for application to trench MOSFETs. At 900 °C, this method results in almost equal oxide thickness on the Si-face and a-face which would nominally correspond to trench bottom and sidewalls in trench devices. Our results indicate that after NO annealing, the electronic properties of the plasma oxidized SiO₂/SiC interface is comparable to control samples with gate oxides formed by dry oxidation at 1150 °C followed by NO annealing. Next, the effect of reactive ion etching (RIE) of 4H-SiC surfaces prior to gate oxidation was investigated using planar 4H-SiC MOS capacitors. Our experiments show that oxidation followed by NO annealing of surfaces with smooth morphology following the RIE step, results in similar interface charge and trap densities as MOS capacitors which did not undergo the RIE etching.

Abstract: The diffusion of the carbon vacancy (V_C) in n-type 4H-SiC has been studied using Deep Level Transient Spectroscopy (DLTS). Samples grown along two different crystallographic planes, (0001) or c-cut and (11-20) or a-cut, have been utilized. The samples were implanted with 4.0 MeV C ions to generate V_C’s and subsequently annealed at temperatures between 200 and 1500 °C. Following each annealing stage, concentration versus depth profiles of the V_C were obtained. The V_C is essentially immobile in both the c-cut and a-cut samples up to at least 1200 °C. The 1400 °C annealing stage, however, resulted in considerable migration, predominantly along the a-direction. Using half the difference in the Full Width at Half Maximum (FWHM) of the initial and diffused concentration profiles as a measure of the diffusion length, we deduced the diffusivity of the V_C at 1400 °C to be approximately (3.8±1.1)×10^-14 cm²/s along the c-axis and (4.1±1.2)×10^-13 cm²/s along the a-axis, indicating a substantial anisotropy for the V_C diffusion in 4H-SiC.

Abstract: We present a study of electrically active radiation-induced defects formed in 4H-SiC epitaxial layers following irradiation with fast neutrons, as well as 600 keV H⁺ and 2 MeV He⁺⁺ ion implantations. We also look at electron emission energies and mechanisms of the carbon vacancy in 4H-SiC by means of first-principles modelling. Combining the relative stability of carbon vacancies at different sites with the relative amplitude of the observed Laplace-DLTS peaks, we were able to connect Z₁ and Z₂ to emissions from double negatively charged carbon vacancies located at the h- and k-sites, respectively.