Manufacturing method and composite substrate of the composite substrate

After bonding the semiconductor substrate 1 and the supporting substrate 3, and thinning the semiconductor substrate 1, a manufacturing method of the composite substrate to obtain a composite substrate 8 having a semiconductor layer 6 on the supporting substrate 3, the supporting substrate 3 bonding of the surface to perform, to form a coating film 4a containing polysilazane, the coating film 4a 600 ° C. or higher 1200 ° C. and fired process heating to below to form a silicon-containing insulating film 4, followed by the by bonding the semiconductor substrate 1 and the supporting substrate 3 through the insulating film 4, combined to suppress the defective bonding due to surface roughness or defects of the support substrate to obtain easily the composite substrate.