A thoroughly optimized wet thermal oxidation process of epitaxial 4H-SiC on both terminating faces has been presented here. The optimum flow of molecular oxygen and inertial pressure inside the quartz horizontal furnace have to be taken as the initial parameter during the whole oxidation process. Wafers are loaded in nitrogen ambient to increase the mean free path for incoming oxidizing agent. The time of oxidation varies from 0.5 hours to 6 hours with 0.5 hours step time. Rate of oxidation on C-face has been found nearly 10 times faster than on Si-face of 4H-SiC wafer. The oxide thickness has been measured by a variable angle ellipsometer and the result has been verified by a surface profiler. A number of samples have been oxidized for each experiment in order to generate the statistical data.

Silicon Carbide (SiC) is a wide band gap semiconductor gaining acceptability for electronic devices, particularly for high temperature and harsh environment applications, where conventional materials such as silicon and Gallium Arsenide (GaAs) cease to provide sustainability. About 250 polytypes of crystalline SiC have been reported in literature [1-7]. The most common polytypes for device application are 4H-SiC, 6H-SiC, 2H-SiC, 3C-SiC and 15R-SiC, where H, C, R refer to hexagonal, cubic and rhombohedral crystal structures respectively. All these polytypes are different by the repeating layer stacking order; however, the hexagonal polytypes 4H-SiC and 6H-SiC are the key materials for devices applications because in addition to their desirable physical and electrical properties, wafers up to 3" in diameter are now commercially available [8]. Among the group of wide band gap semiconductors, SiC competes owing to its unique capability of oxidation in the form of SiO₂, thus making it an obvious choice for the replacement of mighty silicon. The oxidation growth mechanism of SiC surfaces however has been at its developmental stage. A number of recent publications [8-12] indicate not well understood phenomenon of SiC oxidation.

The present work is an experimental addition to the prevailing knowledge of wet thermal oxidation of one of the commercially available device grade polytypes of SiC—4H-SiC. The faces of hexagonal polytypes of SiC are always terminated into silicon rich and carbon rich faces resulting into Si-face and C-face surfaces. The oxidation mechanisms on Si-face and C-face have been found very different. However, the SiO₂ composition is maintained on both the faces [8]. The magic of the oxidation mechanism on the two faces, therefore, becomes interesting for exploration [12]. Efforts have been made to understand the oxidation phenomenon by dry oxidation [10] and ultra thin oxide [13], etc. The polar faces of SiC have different growth rates. Results of different growth rates in Si-face and the C-face dominate the face terminated wet thermal oxidation of 4H-SiC, which are presented in this paper.

This cleaning method is also known as Stranded Cleaning (SC). Depending on the basic and acidic nature, this method has been divided in two sections: (a) SC-1, solution contains DI water: H₂O₂: NH₄OH in the ratio of 5:1:1. Samples were immersed in solution for 10 min., followed by thoroughly rinsing in DI water. To remove the native oxide after this step, samples were dipped in 2% HF for a very short time. (b) SC-2, solution contains DI water: H₂O₂: HCL in the ratio of 6:1:1. Samples were immersed in solution for 10 min., followed by thoroughly rinsing in DI water. 2% HF dip was again repeated to make surface hydrophobic.

Science and Technology Journal, Wet Thermal Oxidation, Epitaxial 4H-SiC Substrate, Device Fabrication, Stranded Cleaning, SC, Silicon Carbide, SiC, Gallium Arsenide, GaAs, Trichloroethane, TCE, Hydrofluoric, HF, C-face, Si-face, Oxidizing Agent.