Practical One-Step Solution of Smoothly Tapered Junction Termination Extension for High Voltage SiC Gate Turn-off Thyristor

Assessment of Junction Termination Extension Structures For Ultrahigh-Voltage Silicon Carbide Pin-Diodes; A Simulation Study

“…Note, that JTE structures formed by p-type epitaxial growth (e.g., anode doping) and step etch JTE, minimize crystal defects due to lack of ion implantation processing [48]. Further simplifications are provided by negative bevel termination structures (and smoothly tapered structures [31]), which are area-efficient and facilitate low leakage currents. These structures are, however, mainly targeting p-type thyristor structures [20], [21], [32].…”

“…Y. Wen et al, [23] have recently, demonstrated a 30.4 % decrease in one-sided JTE length, lJTE, by introducing an additional etching step to the conventional field-limiting-ring termination. The JTE length efficiency (i.e., VB/lJTE) of selected JTE structures with drift region doping concentrations of 1-2×10 14 cm -3 [7], 2×10 14 cm -3 [8], [13], [30], [33], [35], [37], 2.5×10 14 cm -3 [6], 3×10 14 cm -3 [36], 4.5×10 14 cm -3 [31], and 5×10 14 cm -3 [11], [23], [24], are summarized in Fig. 1.…”

“…The majority of the JTE structures strives towards the ideal effective charge by employing various patterns of ion implanted guard rings [11], [26], JTE zones [26], [27], or combinations of the two [7], [25], [26], [33], [34]. The same applies for different beveled termination structures [20], [21], [31], [32] and etched-step (ES)-JTE structures [19], [29], [30], [37], [43]- [45], [48].…”

“…The SZ implant introduces an additional region, besides the PiN anode region (or gate layer in e.g., thyristors), where bevel etch or step etch charge shaping are possible. Here, the bevel etch requires a low angle to etch along the complete JTE length, which may be realized for short termination lengths by an ultralow bevel etch (1.9º angle [29]) or a smoothly tapered etch method (5 nm/μm ~ 0.29º angle [31]). However, this structure is unsuitable for UHV devices since the requirements of the bevel etch become unrealistic (e.g., either < 0.05º bevel angle or > 6 μm ion implant penetration depth for JTE designs targeting > 30 kV).…”

“…Thus, alternative termination structures may be required for UHV devices, especially as the length and process complexity increases with breakdown voltage capability. Additional processing steps may be required to relax/circumvent issues such as large number of guard rings [23], [24], to small bevel angle [29], [31] and large influence of SiO2/SiC surface charges [33], [46], voltage transient stability [47] and/or device degradation/reliability over time [12], [24]. The ESZ-JTE structure for UHV devices is evaluated and compared to the SM-JTE design, both simulated with the same one-sided termination length for each blocking voltage class for fair comparison.…”