Particle beam device, observation method, and diffraction grating

An observation method with a charged particle beam device, the method comprising:

• holding a specimen using a specimen holder;
• generating a charged particle beam using a source;
• emitting the charged particle beam to the specimen;
• and
• imaging the charged particle beam using an objective lens system having at least one lens which images the charged particle beam transmitted through the specimen,
• wherein said imaging uses an optical system having a plurality of lenses provided on a downstream side in a traveling direction of the charged particle beam in the objective lens system, and a diffraction grating provided on an upstream side of the specimen in the traveling direction of the charged particle beam and on the downstream side in the traveling direction of the charged particle beam in the irradiation unit,
• wherein said diffraction grating is configured with a material having transparency with respect to the charged particle beam, and
• wherein an opening region disposed at a center portion of the diffraction grating is smaller than an irradiation region of the charged particle beam to the diffraction grating, and observation is performed on a status where the irradiation region of the charged particle beam, diffracted with the diffraction grating formed on the specimen, is within the irradiation region of the charged particle beam transmitted through the diffraction grating,
• wherein said opening region diffracts said particle beam, and
• wherein the irradiation region of the charged particle beam transmitted through the diffraction grating to said specimen has a first portion that includes an optical axis of the charged particle beam device, and also has a plurality of second portions each disposed apart from said first portion on a plane which includes said specimen, and
• wherein an intensity of said particle beam is lower at said first position which includes the optical axis of the charged particle beam device than an intensity of said charged particle beam at each said second portion.