Abstract: The application discloses a method for forming a hybrid substrate of a SOI wafer. Buried oxide and silicon-on-insulator in some areas are removed, a layer of SiOCN is deposited on a SOI sidewall to protect the silicon-on-insulator sidewall, and then the growth of epitaxial silicon is performed to cause the silicon substrate area to grow to be flush with the silicon-on-insulator area. The SiOCN on the SOI sidewall acts as a protective layer to prevent the growth of epitaxial silicon on the SOI sidewall, thereby preventing the generation of a bulge at a boundary between the SOI area and the silicon substrate area and improving the product yield. Moreover, a SiOCN film may be deposited with high conformality, and the SiOCN deposited on the SOI sidewall has good uniformity, so that the growth of epitaxial Si from the SOI does not occur during subsequent growth of the epitaxial silicon.