Impact of Oxidation Conditions and Surface Defects on the Reliability of Large-Area Gate Oxide on the C-Face of 4H-SiC

Abstract

This paper discusses the issues regarding reliability of large-area (up to 25mm2) gate oxide on the C-face of 4H-SiC. We have shown that the TDDB characteristics of large-area gate oxide improved by separating gate oxidation processes into oxide growth by dry-oxidation and successive interface control by anneal in N2O ambient or that by wet-oxidation followed by anneal in H2 ambient. In particular, dry-oxidation followed by anneal in N2O ambient for interface treatment (dry+N2O process) is effective for the suppression of the random failure in TDDB characteristics. The estimated lifetime of gate oxide of less than 9mm2 by the dry+N2O process is six-digits larger than 30 years. In the case of the TDDB characteristics of 25mm2 gate oxide grown by the dry+N2O process, the initial and random failure in TDDB characteristics is dominant. However, even in this case, we have confirmed that the evaluated lifetime of 25mm2 gate oxide is more than 30 years. In order to clarify the mechanism of the degradation of the TDDB characteristics of large-area gate oxide, we examined the effect of the surface defect on the TDDB characteristics by observing the surface of each broken MOS capacitor after the TDDB test. We have found following results. (1) The initial failures in TDDB characteristics are mainly due to surface defects such as “down fall”, “comet”, and “triangular defect”. (2) The footprints of random failure do not correspond to the positions of smaller surface defects such as “bump”. Finally, we have found that the quality of the epitaxial layer affects random failure rate in the TDDB characteristics of large area gate oxide; the random failure in the TDDB characteristics of 25mm2 gate oxide on epitaxial layer grown by a certain epitaxial vendor is almost suppressed. However, the cause of the difference in TDDB characteristics is not identified.

Characterization of comet-shaped defects on C-face 4H-SiC epitaxial wafers by electron microscopy

“…Our observations indicate that triangular-shaped defects have been one of the dominant defects introduced during epitaxial film growth on the C-face, similar to the case of the Si-face [8]; however, comet-shaped defects are very frequently observed in current 41 offaxis C-face epitaxial films using optical microscopy. In contrast, comet-shaped defects are not frequently observed in current epitaxial films grown on the Si-face of 41 off-axis wafers.…”

Simulation Study of 4H-SiC Trench Insulated Gate Bipolar Transistor with Low Turn-Off Loss

“…The P + shield, P + source region, and N + source regions are formed by ion implantation [23,24], as shown in Figure 2c. The gate oxide layer is thermally grown in dry O 2 [25][26][27] and the trench regions are filled with polysilicon [28], as shown in Figure 2d. The substrate is removed and backside p-polySi and p-SiC epitaxial layers are dry-etched, as shown in Figure 2e.…”

Dependence of 4H-SiC Epitaxial Layer Quality on Growth Conditions with Wafer Size Corresponding to 150 mm

“…We selected shallow pits and triangular defects as important defects, because such defects are important issues for device yield and reliability [7,8]. Figure 4 shows the image of shallow pits and triangular defect obtained by the confocal microscope.…”

“…In addition, reducing epitaxial defects such as triangular defects, shallow pits, and step bunching is an important issue to increase device yield and reliability [7,8]. A.…”