Development of Solvent Inclusion Free 4H-SiC Off-Axis Wafer Grown by the Top-Seeded Solution Growth Technique

Abstract

This study reports our newly developed technology for SiC solution growth. In particular, we succeed in completely suppressing solvent inclusions, which have been a serious technological problem peculiar to the solution growth method. Then, we fabricate two-inch-diameter 4° off-axis SiC wafers without solvent inclusions. Moreover, we performed their crystal defects evaluation. It was found that our wafers were low resistance n-type 4H-SiC and contain almost no basal plane dislocation. As a result, the superior quality of our solution-grown crystal was confirmed.

Review of solution growth techniques for 4H-SiC single crystal

“…6(d), a high-quality 2-inch 4H-SiC single crystal with a thickness of 5 mm has been produced by TSSG at 2,080 °C using Si-Cr solvent. Compared to the rough texture and several dark domains that existed at the peripheral part of the crystal without adjustment of meniscus height, the ingot with accurate control of meniscus height showed smooth and inclusion-free morphology [29] . Based on the TSSG method, Daikoku et al [69] developed solution growth on concave surface (SGCS) technique to effectively avoid step-bunching by controlling the meniscus height and orienting the solution flow in the opposite direction of step movement (anti-parallel flow, which will be discussed in Chapter 2.3).…”

“…Therefore, it is vital to reduce defects through the optimization of SiC single crystal growth techniques and corresponding key parameters. [27] ; (b) Nomarski optical microscope images of KOH etching pits TSD, TED and BPD in a 4H-SiC single crystal substrate (off axis 4°) [28] ; (c) top view of solvent inclusions [29] ; (d) OM images of polytypes on 4H substrate [30] ; (e) TEM image of an SF [31] ; (f) metallographic microscope of MP [32] (a) (b)…”

“…Doping transition metal elements or rare-earth elements not only effectively lower the growth temperature but seems to be the only way to drastically improve carbon solubility in Si melt. The addition of transition group metals, such as Ti [8, 14-16, 19, 40-52] , Cr [29,30,43,50, , Co [63,76] , Fe [77][78][79][80] , etc. or rare earth metals, such as Ce [81] , Y [82] , Sc, etc.…”

“…Fig. 6: Schematic illustration of TSSG [54] (a), calculated distribution of supersaturated carbon concentration around seed crystal, with meniscus height is 0 mm (left), 2 mm (middle) and 3 mm (right), respectively [49] (b), calculated saturated carbon concentration at growth interface, as a function of meniscus height [49] (c), 4H-SiC ingots grown by TSSG without (left) and with (right) accurate meniscus height adjustment [29] (d)…”

Contribution of Dislocations in SiC Seed Crystals on the Melt-Back Process in SiC Solution Growth

“…When a 4H-SiC epi-layer is grown by the CVD method, the damaged layer is usually removed by hydrogen etching [ 2 ]. In the growth of bulk 4H-SiC single crystals by the solution growth method [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ], which is a potential technique for growing high-quality crystals, the damaged layer is removed by dissolving it through a melt-back process. In addition, without the melt-back process, adhesions of the alloy derived from vapors are present on the surface of the 4H-SiC seed crystal before seed touching the growth solution, which contributes to the formation of various defects, including the solvent inclusions [ 12 ].…”