Sample preparation method

1. A sample preparation method, comprising:

processing a sample piece by an ion beam to form a thin film portion having a thickness that allows an electron beam to transmit therethrough;

supplying deposition gas to the thin film portion; and

irradiating the thin film portion with an electron beam to simultaneously form a first deposition film on a first surface of the thin film portion which is an incident side of the electron beam and a second deposition film on a second surface of the thin film portion through which the electron beam has transmitted the thin film portion.

2. The sample preparation method according to claim 1 , further comprising: subjecting the first deposition film to etching processing by the ion beam, thereby reducing a thickness of the first deposition film.

3. The sample preparation method according to claim 2 , wherein the reducing a thickness of the first deposition film comprises subjecting the first deposition film to the etching processing by the ion beam such that the thickness of the first deposition film becomes equal to a thickness of the second deposition film.

4. The sample preparation method according to claim 3 , wherein the thin film portion is irradiated with the ion beam from a direction perpendicular to an irradiation direction of the electron beam.

5. The sample preparation method according to claim 2 , wherein the thin film portion is irradiated with the ion beam from a direction perpendicular to an irradiation direction of the electron beam.

6. The sample preparation method according to claim 1 , wherein the supplying deposition gas to the thin film portion comprises supplying the deposition gas to both of the front surface and the rear surface of the thin film portion.

7. The sample preparation method according to claim 1 , wherein the irradiating the thin film portion with the electron beam comprises irradiating a substantially entire surface excluding an observation region of the first surface.

8. A sample preparation method, comprising:

processing a sample by an ion beam to form a thin film portion having opposed surfaces and a thickness that allows an electron beam to transmit therethrough;

spraying, at the same time, the opposed surfaces of the thin film portion with a deposition gas; and

simultaneously forming a deposition film on each of the opposed surfaces by irradiating the thin film portion with an electron beam that transmits through the thin film portion and generates secondary electrons from both opposed surfaces that decompose the sprayed deposition gas to form the deposition films.

9. The sample preparation method according to claim 8 ; further comprising using the ion beam to etch the deposition film formed on one of the opposed surfaces to reduce the thickness thereof.

10. The sample preparation method according to claim 9 ; wherein the etching of the deposition film formed on one of the opposed surfaces is carried out until the thickness thereof is equal to the thickness of the deposition film formed on the other of the opposed surfaces.

11. The sample preparation method according to claim 10 , wherein the thin film portion is irradiated with the ion beam from a direction perpendicular to an irradiation direction of the electron beam.

12. The sample preparation method according to claim 8 , wherein the thin film portion is irradiated with the ion beam from a direction perpendicular to an irradiation direction of the electron beam.

13. The sample preparation method according to claim 8 , wherein the electron beam is irradiated in a direction substantially perpendicular to the thin film portion.