Patent Number: 
Section: claims

1. A sample cross section observation method, where a gas ion beam emitted from an ion source capable of generating at least two or more kinds of gas ions with different mass numbers is irradiated onto a sample, comprising the steps of:irradiating a gas ion having a relatively large mass number among at least the two or more kinds of gas ions, so as to form a roughly vertical cross section to the surface of a sample; andirradiating a gas ion having a relatively small mass number onto the cross section to be observed. 2. The method of claim 1, wherein, for cross sectional observation, the ion with a relatively small mass number is irradiated at a lower current than a maximum current used for irradiating the ion with a relatively large mass number. 3. The method of claim 1, further comprising the steps of:simultaneously generating at least two kinds of gas ions by the ion source;mass-separating at least the two kinds of gas ions with different mass number from each other and irradiating a gas ion beam having a relatively large mass number onto a sample to process a roughly vertical cross section to the sample surface; andchanging mass-separating conditions to irradiate a gas ion beam having a relatively small mass number onto the cross section to be observed. 4. The method of claim 1, wherein the ion having a relatively large mass number is a gas ion containing at least any one of argon, xenon, krypton, neon, oxygen, and nitrogen, while the ion having a relatively small mass number is either a hydrogen gas ion or a helium gas ion, or a mixed gas ion. 5. An ion beam machining and observation method, where a gas ion beam emitted from a gas field ion source having a vacuum chamber and a gas supply mechanism to introduce gas into the vacuum chamber and generating gas ions in the vacuum chamber is irradiated onto a sample, and where the gas supply mechanism includes at least two gas introduction systems, each system having a gas cylinder, a gas volume control valve, and a stop valve, and a gas switching control unit, comprising:switching, by the gas switching control unit, a kind of gas introduced into the vacuum chamber by the stop valve of each system and setting gas pressure conditions for the vacuum chamber by the gas volume control valve of each system; andforming a pyramid structure of atoms at an apex of an emitter tip of the gas field ion source when the gas switching control unit switches a kind of gas being introduced into the vacuum chamber by the stop valve of each system. 6. The ion beam machining and observation method according to claim 5,wherein the gas switching control unit can switch between a gas ion beam used for machining the sample and a gas ion beam used for observing the sample, and the gas ion beam of neon, argon, krypton or xenon is used for machining the sample. 7. The ion beam machining and observation method according to claim 5,wherein the gas switching control unit can switch between the kind of a gas ion beam used for machining the sample and the kind of a gas ion beam used for observing the sample, and the gas ion beam of neon, argon, krypton or xenon is used for machining the sample. 8. The ion beam machining and observation method according to claim 7,wherein the gas switching control unit switches to a hydrogen or helium ion beam on observing the sample. 9. The ion beam machining and observation method according to claim 5, further comprising:setting conditions of the amount of gas volume introduced into the vacuum chamber by a needle valve of each system; andregulating, by a needle valve of the gas introduction system, an amount of gas volume flowing into the vacuum chamber. 10. The ion beam machining and observation method according to claim 9, wherein the gas supply mechanism includes a first gas introduction system which has a first gas tube connected between the vacuum chamber and a first needle valve and which introduces the kind of gas ion beam used for machining the sample, and a second gas introduction system which has a second gas tube connected between the vacuum chamber and a second needle valve and which introduces the kind of gas ion beam used for observing the sample. 11. An ion beam machining and observation method, where a gas ion beam emitted from a gas field ion source having a vacuum chamber and a gas supply mechanism to introduce gas into the vacuum chamber and generate gas ions in the vacuum chamber is irradiated onto a sample, and where the gas supply mechanism includes at least two gas introduction systems, each system having a gas cylinder, a gas volume control valve, and a stop valve, and a gas switching control unit, comprising:forming a pyramid structure of atoms at an apex of an emitter tip of the gas field ion source; andevaporating the pyramid structure at the apex of the emitter tip of the gas field ion source when the gas switching control unit switches the kind of gas being introduced into the vacuum chamber by the stop valve of each system.