Electron beam apparatus and an aberration correction optical apparatus
View Patent ↗An electron beam apparatus for providing an evaluation of a sample, such as a semiconductor wafer, that includes a micro-pattern with a minimum line width not greater than 0.1 μm with high throughput. A primary electron beam generated by an electron gun is irradiated onto a sample and secondary electrons emanating from the sample are formed into an image on a detector by an image projection optical system. An electron gun 61 has a cathode 1 and a drawing electrode 3 , and an electron emission surface 1 a of the cathode defines a concave surface. The drawing electrode 3 has a convex surface 3 a composed of a partial outer surface of a second sphere facing the electron emission surface 1 a of the cathode and an aperture 73 formed through the convex surface for passage of the electrons. An aberration correction optical apparatus comprises two identically sized multi-polar Wien filters arranged such that their centers are in alignment with a ¼ plane position and a ¾ plane position, respectively, along an object plane-image plane segment in the aberration correction optical apparatus, and optical elements having bidirectional focus disposed in an object plane position, an intermediate image-formation plane position and an image plane position, respectively, in the aberration correction optical apparatus.
1. An aberration correction optical apparatus for a charged particle beam optical system, comprising:
two identically sized multi-polar Wien filters arranged such that their centers are aligned with a ¼ plane position and a ¾ plane position, respectively, along an object plane-image plane segment in said aberration correction optical apparatus; and
optical elements having bidirectional focus disposed in an object plane position, an intermediate image-formation plane position and an image plane position in said aberration correction optical apparatus.
2. An aberration correction optical apparatus for a charged particle beam optical system, comprising:
two identically sized multi-polar Wien filters arranged such that their centers are aligned with a ¼ plane position and a ¾ plane position, respectively, along an object plane-image plane segment in said aberration correction optical apparatus; and
a plurality of optical elements having bidirectional focus disposed on both sides of each of said Wien filters with respect to the traveling direction of said charged particle beam in a symmetric configuration relative to the center of each of said Wien filters such that a distance between said centers of said wien filters is shorter than a distance between an object plane position or an image plane position and an intermediate image-formation position.
3. An aberration correction optical apparatus for a charged particle beam optical system according to claim 1 or 2 , wherein said optical element is a rotationally symmetric lens.
4. An aberration correction optical apparatus for a charged particle beam optical system according to claim 1 or 2 , wherein said optical element is a multi-polar lens.
5. An aberration correction optical apparatus for a charged particle beam optical system according to claim 1 or 2 , wherein said optical element is the Wien filter.
6. An aberration correction optical apparatus for a charged particle beam optical system according to claim 1 or 2 , wherein said optical element is an electromagnetic prism.
7. An image projection optical system for guiding a charged particle beam emanating from a sample surface to a final image-formation plane, wherein an aberration correction optical apparatus according to claim 1 or 2 is arranged in a first image-formation plane between an objective lens and an intermediate lens in said image projection optical system such that said first image-formation plane is in alignment with an image plane position in said aberration correction optical apparatus.
8. A scanning type optical system for guiding a charged particle beam emanating from a charged particle beam source to a sample surface, wherein an aberration correction optical apparatus according to claim 1 or 2 is disposed in an intermediate image-formation plane of a front stage of an objective lens in said scanning type optical system.