PURPOSE: To relieve a wafer, which is conventionally excluded as a defective, and to improve the yield of the wafer by cleaning the wafer in heated nitric acid and adjusting the film thickness of a monocrystal film or the dissipation magnetic field of a magnetic bubble so that it can be a reference value when either the film thickness of the monocrystal film or the dissipation magnetic field of the magnetic bubble is thicker or larger than the reference value.

CONSTITUTION: A monocrystal film 3 composed of magnetic garnet is formed on the surface of a substrate 2, and when the film thickness or the dissipation magnetic field of the magnetic bubble of the monocrystal film 3 formed on the surface of the substrate 2 is thicker or larger than a previously set reference value in the process of forming a wafer 1 for a magnetic bubble memory element, by soaking and ultrasonic-cleaning the wafer 1 in the heated nitric acid of 20wt.% and 80°C for 60min, the film thickness of the monocrystal film is decreased approximately for 0.02μm, and the dissipation magnetic field of the magnetic bubble is decreased approximately for 2.5Oe. Thus, by cleaning the wafer in the heated nitric acid and adjusting the wafer so that it can be the reference value, the wafer is relieved, which is conventionally excluded as the defective, and further, the etching quantity of this degree never generates a rough surface on the surface of the monocrystal film.