Design, process, and performance of all‐epitaxial normally‐off SiC JFETs

Abstract

This paper reviews the normally‐off (N‐ off) and normally‐on (N‐ on) SiC junction field effect transistor (JFET) concepts and presents an innovative all‐epitaxial double‐gate trench JFET (DGTJFET) structure. The DGTJFET design combines the advantages of lateral and buried gate JFET concepts. The lateral JFET advantage is the epitaxial definition of the channel width and the buried gate JFET advantage is the small cell size. In the DGTJFET process the epitaxial embedded growth in trenches facilitates the small cell pitch and the vertical direction of the channel. A detailed numerical simulation analysis compares the potential of the DGTJFET design with reported lateral channel and buried gate JFET structures. Migration enhanced embedded epitaxy (ME3) and planarization processes were developed to realize narrow cell pitch DGTJFETs for high‐density power integration. The highly doped vertical channel of the DGTJFET defined by the ME3 growth process makes it possible to accurately control the sub‐micron channel dimensions in order to realize a low specific on‐state resistance (RON) and a high saturation current capability. The anisotropic nature of SiC is taken into account for the channel design considerations. The successful application of the new process technologies for the development of the all‐epitaxial DGTJFETs is discussed. Fabricated 5.5 μm cell pitch 4H‐SiC DGTJFETs demonstrate the saturation current density capability of more than 1000 A/cm2. N‐ off and N‐ on DGTJFETs with 2.25 mm squared chip size and 9.5 μm cell pitch output 15 A and 20 A at gate voltage of 2.5 V and drain voltage of 5.0 V. The specific RON of the N‐ off and N‐ on DGTJFETs is at room temperature 8.1 m Ω cm2 and 6.3 mΩ cm2, respectively, indicating that N‐ off devices can be realized at the expense of a slight increase in specific RON of approximately 25%. DGTJFETs with a 13 μm drift layer doped to 5.0 × 1015 cm–3 are demonstrated with a breakdown voltage in the range of 1200 V to 1550 V at the wafer level with a leakage current below 10 μA. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Numerical analysis of the Gibbs–Thomson effect on trench-filling epitaxial growth of 4H-SiC

“…5 show that, in the case of a narrow pitch (≤ 6.0 µm), the dependence of the growth rate on the trench pitch can be explained by the GT effect on the vapor-phase diffusion of growing species. This conclusion is consistent with those in the previous studies 2,4,5) based on the surface diffusion of growing species.…”

“…everal SiC power devices have already been produced and now next-generation all-epitaxial devices, such as embedded p-n diodes, 1) double-gate trench junction field-effect transistors, 2) and super-junction devices, 3) are under development. In these devices, trenches are etched into the first epitaxial layer and are subsequently filled with the second epitaxial layer grown by vapor phase epitaxy.…”

“…The growth rate at the trench bottom (R tb ) was explained as the sum of the rate associated with the surface diffusion of growing species and the rate associated with the vapor-phase diffusion of growing species; i.e., R tb was considered to be dominated by the surface diffusion in the case of narrow trenches and the vapor-phase diffusion in the case of wide trenches. 2,4,5) Epitaxial growth on a nonplanar surface is known to be affected by the Gibbs-Thomson (GT) effect, 6) i.e., the effect of the radius of curvature (r) of a growing surface on equilibrium vapor pressure. In this study, the GT effect was first taken into account in the analysis based on the conventional boundary-layer model 7,8) as a mechanism of trench-filling epitaxy.…”

Modeling of Al Doping During 4H-SiC Chemical-Vapor-Deposition Trench Filling

“…As shown schematically in Fig. 3, on the other hand, Malhan et al reported that the low N A regions (B1 and B2) are sandwiched between the high N A regions (A/C1 and A/C2, respectively) and that the boundaries between the low and high N A regions are inclined from the vertical direction [28]. Since faces with θ of about 45 • [i.e., {110n} (n∼4)] are known as facets [29], the low N A regions (B1 and B2) in Fig.…”

Κυκλώματα Και Λογισμικό Για Μετατροπείς Σρ/Σρ Με Ημιαγωγούς Καρβιδίου Του Πυριτίου Για Χρήση Σε Φωτοβολταϊκά Συστήματα

“…Χαμηλή τιμή για την τάση κατωφλίου στην πύλη μπορεί να επιτευχθεί έχοντας ένα στενό κανάλι και πολύ ισχυρά νοθεμένη περιοχή τύπου p. Επίσης, για να επιτευχθεί χαμηλή αντίσταση αγωγής, το κανάλι πρέπει να αποτελείται από υλικό πολύ ισχυρά νοθευμένο [74]. Οι ανοχές της συγκέντρωσης των προσμίξεων και το βάθος της διάχυσης της ισχυρά νοθευμένης περιοχής τύπου p έχουν σημαντική επίδραση στην ανοχή των χαρακτηριστικών αγωγής, στην τάση κατωφλίου και στην τάση κατάρρευσης της πύλης [75].…”