Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
2001-07-06
2003-11-25
Tran, Huan (Department: 2861)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S306000, C250S307000
Reexamination Certificate
active
06653631
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and a method for defect detection using a charged particle beam, and more particularly to a charged particle beam defect detection apparatus and a method of using such an apparatus in which a charged particle beam such as an electron beam or an ion beam is used for observing and detecting defects on the surface of an object such as a semiconductor substrate or a liquid crystal substrate.
2. Description of the Background Art
Semiconductor elements are formed by using planar techniques to generate a fine pattern on the surface of a semiconductor substrate. Demands for smaller semiconductor elements have lead to these patterns becoming finer and more highly integrated. Charged particle beam microscopes which utilize the charged particles from electron beams and the like are used for conducting observations and defect inspections of the surface condition of such semiconductor elements. Currently, the most widely known and widely used charged particle microscope is the scanning electron microscope (SEM). In recent years, imaging electron microscopes have been proposed as an alternative to scanning electron microscopes, and the development of charged particle beam imaging projection optical systems for this type of mapping electron microscopes is being actively pursued. As follows is a brief description of the construction of a charged particle beam imaging projection optical system.
A primary electron beam is emitted as an illuminating electron beam from an electron gun which functions as a charged particle source, and this beam passes through a primary optical system which functions as an illumination optical system, and enters an electromagnetic prism known as an E cross B (E×B). Passage through the E×B converts the cross-sectional shape of the primary electron beam to a linear shape, a rectangular shape, a circular shape or an oval shape, and the shaped beam then passes through a cathode lens which functions as an object optical system, and is illuminated onto the surface of a sample object. When the primary electron beam is irradiated onto the surface of an object, a reflected electron beam having a comparatively high energy is produced by reflection of the primary electron beam off the object surface, and furthermore, a secondary electron beam having a low energy is emitted from the object surface.
Of these two electron beams emitted from the object surface, the secondary electron beam is typically used for image generation. This secondary electron beam, which functions as an observation electron beam, passes through the cathode lens and enters the E×B. Following passage through the E×B, the secondary electron beam passes through a secondary optical system, which functions as an imaging optical system, and enters an electron beam detector. Observation and defect inspection of the object surface is then performed based on information obtained from injection of the secondary electron beam into the electron beam detector.
By the way, in devices such as the scanning electron microscope and the imaging electron microscope described above, where the observation and defect inspection of an object is carried out by the irradiation of charged particles such as an electron beam onto the object, because charged particles are irradiated onto the surface of the sample, the sample itself is charged up. Even if a charged particle beam with a uniform distribution relative to the sample surface is used, the amount of this charge-up will differ depending on the sample material. Therefore, in the case of a semiconductor element for example, the amount of charge-up in those areas where wiring is formed will differ from the amount of charge-up in those areas where an oxidation inhibiting film is formed, and so a charge-up distribution (a surface voltage distribution corresponding with the amount of accumulated charge on the object) generates.
Furthermore, the initial energy of a secondary electron beam generated in a section where charge-up has occurred will differ from the initial energy of a secondary electron beam generated in a section where absolutely no charge-up has occurred. Therefore, even if the focal position of the secondary optical system is adjusted so that the secondary electron beam from an area of no charge-up undergoes imaging onto the electron beam detector, the same focal position will not match the secondary electron beam emitted from an area where charge-up occurs. As a result, in order to ensure a more accurate observation of those areas where this charge-up phenomenon has occurred, the secondary optical system needs to be controlled and a correction made for this deviation in focal position. However, in order to correct this type of deviation in focal position, an operator must perform a manual correction for each sample, which is an extremely complex operation.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a charged particle beam defect detection apparatus and a charged particle beam defect detection method, in which, even if charge-up occurs on the sample being observed, the focal position deviation resulting from this charge-up can be corrected without causing inconvenience to the operator, and a clear, in-focus observation and a highly accurate defect inspection can be performed.
In order to achieve the above object, a charged particle beam defect detection apparatus according to a first aspect of the present invention comprises an irradiation device which irradiates a beam from a charged particle beam source as a primary beam onto an object, an electron detection device which detects electrons emitted from the object as a result of the primary beam irradiation as a secondary beam and captures an image of the object, and a detection device which detects a surface voltage distribution for the object which corresponds with the amount of accumulated charge generated on the object upon irradiation with the primary beam.
According to this aspect of the invention, the surface voltage distribution for the object, corresponding with the amount of accumulated charge generated on the object upon irradiation with the primary beam, is detected with the detection device, and so information can be obtained which resolves the problems (such as focal position deviation and image distortion) due to accumulated charge on the object.
A charged particle beam defect detection apparatus according to a second aspect of the present invention comprises an irradiation device which irradiates a beam from a charged particle beam source as a primary beam onto an object, an electron detection device which detects electrons emitted from the object as a result of the primary beam irradiation as a secondary beam and captures an image of the object, a focus deviation detection device which detects in advance the degree of focus deviation of the secondary beam at the detection surface of the electron detection device, which corresponds with the amount of accumulated charge generated on the object upon irradiation with the primary beam, and a focus control device which controls the focal position of the secondary beam in accordance with the degree of focus deviation detected by the focus deviation detection device.
According to this aspect of the invention, the degree of focus deviation of the secondary beam at the detection surface corresponding with the amount of accumulated charge generated on the object upon irradiation with the primary beam, is detected in advance by the focus deviation detection device, and the focus control device then corrects the focal position of the secondary beam in accordance with this detected degree of focus deviation. Therefore, even in those cases where accumulated charge is generated on the object, the image of the object can be displayed in a focused state, and a clear and in-focus observation and a highly accurate defect inspection can be performed.
A charged particle beam defect detection apparatus according to a thir
Nikon Corporation
Oliff & Berridg,e PLC
Tran Huan
LandOfFree
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