Papers by Keyword: Ion Implantation

Abstract: Achieving reliable breakdown in ultra-high-voltage (>10 kV) SiC devices is limited by edge termination design, where low epitaxial doping (~4×10¹⁴ cm⁻³) results in lateral straggle to be more prominent, therefore necessitating wider spacing between Aluminum implants in conventional floating field rings (FFRs). This study introduces a background doping modulation (BDM) scheme, incorporating a moderately doped N-type confinement region within P+ rings, enabling tighter spacing without added process complexity for high-voltage MOSFETs. Fabricated BDM-FFRs achieved >13 kV breakdown (30% higher than conventional FFRs), with leakage current <10 nA at 10 kV, while reducing termination area by 18.6%. Therefore, the BDM-FFR demonstrates a scalable, compact, and high-performance edge termination approach for next-generation ultra-high-voltage SiC devices.

Abstract: Bipolar degradation poses a significant concern for the reliability of SiC bipolar power devices. The basic cause for bipolar degradation is expansion of Shockley Stacking Faults SSFs. These glide planes can be pinned and prevented from expansion. This study involves 19 MeV Energy Filtered Ion Implantation of Nitrogen (i.e. resulting in an energy spectrum ranging from 0 MeV to nearly 19 MeV in one shot) to explore the pinning effect of Nitrogen ions that suppresses recombination glide, which minimizes SSF growth, while providing precise doping of the entire drift region by the same Nitrogen implantation. All is performed in one single step. This procedure paves the path to immobilize any nucleation sites in the entire drift layer, this way enhancing the reliability and facilitating mass production of SiC power devices. This study employs UV illumination as an optical stressing method to create e-/h+ pair, which subsequently induce 1SSF expansion. Both, UV induced 1SSF expansion and pining were observed by photoluminescence. Carrier lifetime measurements were employed for understanding the mechanism of pinning defects.

Abstract: Within this work, the effect of high dose Al ion implantation on 4H-SiC epitaxial layer is displayed. Through TEM investigation it is demonstrated that the implanted surface is suitable as seed for subsequent epitaxial regrowth generating a crystal free of extended defects. In order to assess the defects within the projected range of the ion implanted area, High Angle Annular Dark Field STEM (HAADF-STEM) analyses were performed demonstrating the atomic arrangement of the lattice in correspondence of the dislocation loop and the deviation of the crystallographic planes of 4H-SiC, driven by stress relaxation, that determine the staircase configuration of the implant pattern. Further emphasis is given to the detailed analysis of the precipitates atomic structure, whose preferential localization is ascertained. Using Energy-Dispersive X-ray spectroscopy (EDS) analysis, the precipitate is finally established as Al crystal with an FCC structure.

Abstract: Ion implantation, as a way of doping the 4H-SiC crystal, is one of the key components of modern power device fabrication. Aluminum is used to form p-type wells for the body of n-MOSFETs and low resistance p-type contacts using heavy doping. Therefore, the ion implantation process needs to be controlled over a wide range of process conditions including implant energies and doses. The fact that Al in 4H-SiC exhibits very low diffusion puts additional burden on the accuracy and predictability of any ion implantation engineering. In device design, these requirements can be addressed by applying computer simulations to predict doping profiles ahead of the actual implant step performed in a manufacturing facility. The accepted way to predict doping profiles is based on the binary-collision approximation (BCA), numerically implemented as a statistical Monte-Carlo (MC) method [1]-[3]. Nowadays, one can refer to simulation packages available from commercial vendors [4] for studying ion implantation using BCA-MC algorithms. However, while the physical accuracy of BCA models implemented in these packages has shown to be quite remarkable, predictable simulations for a complex material system as 4H-SiC requires calibration from data including secondary ion mass spectrometry (SIMS) and scanning electron microscopy (SEM).

Abstract: Free standing wafers of the cubic polytype of silicon carbide (3C-SiC) grown on micromachined silicon substrates can be a platform for new power electronic devices, provided that suitable device fabrication processes are understood and optimized. In this frame, p-type doping is still an open issue, as results on the electrical activation of ion implanted Al in 3C-SiC are limited. This work analyses high level p-type doping with post-implantation annealing carried out at temperatures in the range 1650-1850 °C with different durations. A coherent picture emerges, showing that the resulting resistivity in 3C-SiC Al-implanted layers is higher than the one obtained in 4H-SiC implanted layers, the result being ascribed to low carrier mobility and possibly presence of compensation centers, rather than to poor Al electrical activation. The reported results highlight the importance of working on material and processing optimization.

Abstract: In the 4H-SiC device fabrication process, ion implantation of aluminium to form p-regions results in spreading (lateral straggling) from the mask design width by a few 100 nm. This has a significant impact on device performance, so device design must take lateral straggling into account. In this study, the impact of lateral straggling is estimated by applying a Gaussian distribution to one dimensional depth profiles obtained from Monte Carlo simulations. In our studies, this approach reduced the computation time by a factor of 300 compared to two-dimensional Monte Carlo simulations. The parameters describing the Gauss function are determined with the aid of fabricated JFET test structures. The pinch-off behaviour of JFET devices with vertical and horizontal channels was analysed in electrical TCAD simulations and calibrated to the characteristics of the fabricated devices. Ultimately, the electrical characteristics of simulations and measurements were found to be in good agreement.

Abstract: A large amount of chemicals and ultrapure water (UPW) have been used for wet cleaning process in the semiconductor manufacturing processes. One of the most commonly used cleaning solutions is Sulfuric acid (H₂SO₄) and Hydrogen Peroxide (H₂O₂) Mixture (SPM). It is used for resist stripping, etc. on a silicon wafer. As the cleaning process increases, so does the amount of chemicals used with the recent miniaturization. As a result, wastewater will also increase, and there are concerns about the impact on the environmental aspects. The technologies to reduce H₂SO₄ [1, 2] have been developed, but its consumption still persists. Therefore, in this paper, we developed high concentrated O₃-water without using H₂SO₄, and conducted a resist stripping test verify its effectiveness as an alternative to SPM.

Abstract: We have investigated the p-dopant potential of 14 different impurities (Be, B, F, Mg, Al,Ca, Sc, Cu, Zn, Ga, In, Ba, Pt, and Tl) within 4H-SiC via Density Functional Theory (DFT) calcu-lations using a hybrid density functional. We analyse the incorporation energies of impurity atomson Si and C sites as well as the character of lattice distortion induced by impurities. The calculatedthermal ionization energies confirm that Al and Ga on the Si site are the best candidates for p-dopingof 4H-SiC. Although we find some correlation of incorporation energies with atomic radii of impuri-ties, the difference in chemical interaction with neighbouring atoms and strong lattice distortions playimportant roles in determining the impurity incorporation energies and charge transition levels. Wefind Al to still be the best and most industrially viable p-dopant for 4H-SiC.

Abstract: A novel high energy implantation system has been successfully developed to fabricate 4H-SiC superjunction devices for medium and high voltages via implantation of dopant atoms with multi-energy ranging from 13 to 66 MeV to depths up to 12um. Since the level of energies used is significantly higher than those employed for conventional implantation, lattice damage caused by such implantation must be characterized in detail to enhance the understanding of the nature of the damage. In regard to this, by employing the novel high energy system, 4H-SiC wafers with 12μm thick epilayers were blanket implanted by Al atoms at energies ranging from 13.8MeV to 65.7MeV and N atoms at energies ranging up to 42.99MeV. The lattice damages induced by the implantation were primarily characterized by Synchrotron X-ray Plane Wave Topography (SXPWT). 0008 topographs recorded from the samples are characterized by an intensity profile consisting of multiple asymmetric diffraction peaks with an angular separation of only 2” (arcseconds). Using Rocking-curve Analysis by Dynamical Simulation (RADS) program, diffracted intensity profile was used to extract the corresponding strain profile indicating an inhomogeneous strain distribution across the depth of the implanted layer.

Abstract: Multiple PIN diodes with junction termination extension (JTE) were fabricated on 4H-SiC wafers with 10 μm thick epilayers by ion implantation with various dosages of Al ions at room temperature (RT) and high temperature (600 °C). The subsequent annealing process was conducted at 1650 °C for 10 minutes to activate the dopant atoms and recover the lattice damages introduced by the implantation. Synchrotron X-ray topography was used to characterize the defects in the devices, and it is observed that basal plane dislocations (BPDs) were generated during the annealing process from the boundaries between the high (P+) and low (P-) doping concentration in devices implanted with relatively high doses at RT. Further, topographs also manifest motion of BPDs due to implantation-induced stresses, where BPDs with opposite sign Burgers vectors move in directions accommodative of nature of stress (tensile/compressive). On the other hand, generation of BPDs due to implantation was not observed in devices implanted either at relatively low dosages at both temperatures or relatively high dosages at high temperature. Measurements of blocking behaviors of devices illustrate that devices with higher densities of process-induced BPDs yield higher leakage currents.