In this study, 4H-SiC stripe-shaped trenches preformed on an n + substrate were filled by adding HCl to the chemical vapor deposition process at relatively high pressures. HCl was found capable of counterbalancing the deposition on the mesa top by strong etching, and it thus enabled quasiselective epitaxial growth across the whole extents of the trenches, where the epilayer preferentially grows from the trench bottom. Using the established technique, the 1-µm-wide 4H-SiC trenches, with an aspect ratio of 5, which is the highest aspect ratio to date, were completely filled at a growth rate above 0.5 µm/h and acquired a flat end surface.

To construct a superjunction structure consisting of p/n columns, narrow stripe-shaped trenches (∼1.5 µm wide and ∼4.7 µm deep) preformed on an n+ 4H-SiC substrate were filled by the hot-wall CVD method using a conventional gas reaction system, SiH4:C3H8:H2. The influences of growth pressure on the coverage distribution of epilayers and the corresponding filling efficiency (the thickness ratio of epilayers on trench bottom and mesa top) were investigated. Two benefits of increasing the growth pressure from 10 to 38 kPa were found: one is the reduced growth around the mesa surface, which lessens the risk of void formation; the other is a high filling rate as well as an improved filling efficiency up to ∼7. By supplying source gases at high flow rates, a void-free trench filling with a filling rate of ∼1.3 µm/h was successfully achieved at 38 kPa.

Silicon wafer direct bonding was accomplished between two surfaces which had no hydrophilic native oxide layers. Prior to bonding, two wafers were dipped in conc-HF solution ( ∼49% aq.) to remove the native oxide layers and then immersed in deionized water. The level of bonding was evaluated by X-ray topography, high resolution transmission electron microscopy (HRTEM) and tensile strength measurement. It was found that the bonded wafer pairs were void-free and had good bonding strength. HRTEM observation showed that the crystal lattice was continuous and had only small distortions and precipitates. Spreading resistance (SR) measurement across the interface showed that the electric resistance did not increase at the bonding interface. It is suggested that the OH groups which substitute the F atoms terminated on the small portion of the surface play an important role in this conc-HF-treated bonding.

Threshold voltage (VTH) instability, channel mobility and oxide reliability have been investigated for meta-oxide-semiconductor (MOS) structures on 4H-SiC (11-20) face using various gate oxidation procedures. Channel mobility of n-channel MOSFET with a gate oxide by pyrogenic oxidation is higher than that by dilute-DRY oxidation followed by a nitrous oxide (N2O) post-oxidation annealing (POA). On the other hand, oxide reliability for the pyrogenic oxides is poor compared with the dilute-DRY/N2O oxides. A Hydrogen POA is effective in an improvement of channel mobility for both oxides, but causes a harmful effect on VTH stability. Temperature dependence of VTH instability indicates that MOS structure grown by dilute-DRY followed by N2O POA is suitable for a practical use of SiC MOS power devices.

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