Radiant energy – Inspection of solids or liquids by charged particles – Electron microscope type
Reexamination Certificate
2000-06-02
2002-10-15
Lee, John R. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron microscope type
C250S306000, C250S307000, C250S310000
Reexamination Certificate
active
06465783
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to apparatus and methods for manufacturing semiconductor devices, displays, and the like. More specifically, the invention pertains to apparatus and methods for inspecting wafers and analogous substrates at any of various times during a wafer-fabrication procedure. Even more specifically, the invention pertains to such methods and apparatus that utilize an electron beam that is scanned over at least a portion of the wafer surface in order to reveal surficial detail of the wafer, including surface features having dimensions of 0.2 &mgr;m or less.
BACKGROUND OF THE INVENTION
During the manufacture of integrated circuits, displays, and the like on a semiconductor wafer or other suitable substrate, it is necessary at various steps to inspect the wafer for defects. Inspections are also required when manufacture is complete, before the wafer is cut (“diced”) into individual chips or other units. Inspections are indispensable for improving yield and avoiding the shipping of defective goods.
Much wafer inspection is still performed using optical microscopes employing light to illuminate the wafer, wherein defects are detected from characteristics of light reflected from the wafer. I.e., the wafer surface is imaged using an optical microscope. The magnified image is compared with a reference pattern by means of video processing. In view of the resolution limits of light-based microscopy, these methods have increasingly limited applicability, especially with wafers on which the critical dimension is 0.2 &mgr;m or less.
To obtain better resolution than obtainable with optical microscopy, electron-beam scanning apparatus have been used for inspecting wafers in the manner of a scanning electron microscope. In a conventional electron-beam apparatus, a single electron beam (focused to a point) is scanned in a raster manner over a selected portion of the wafer. When irradiated in such a manner, the wafer emits secondary electrons and backscattered electrons from the point of irradiation. The secondary and/or backscattered electrons are detected, and the presence of surficial defects can be determined from the resulting pattern of detected electrons.
Although conventional scanning-electron-beam inspection apparatus are capable of resolving detail measuring 0.2 &mgr;m or less, the fact that scanning is performed using a single, narrowly focused beam results in very low inspection throughput due to the long scanning time required per wafer. Consequently, these apparatus are impractical for high-throughput wafer fabrication. Rather, they are relegated to use for supplementary defect inspection in testing situations.
This problem is circumvented somewhat simply by performing sampling inspections (in which not all wafers or only portions of wafers actually are inspected) using a scanning electron-beam apparatus. Unfortunately, this compromise results in an unacceptable amount of finished product being shipped that have major defects.
SUMMARY OF THE INVENTION
In view of the shortcomings of the prior art as summarized above, an object of this invention is to provide inspection methods and apparatus that achieve high-throughput inspection of specimens, such as semiconductor wafers and other substrates, using a charged particle beam such as an electron beam. Another object is to provide manufacturing methods, for semiconductor devices, that include such inspection methods.
To such ends, and according to a first aspect of the invention, apparatus are provided for inspecting a surface of a specimen. An embodiment of such an apparatus comprises an emitter array, first and second electromagnetic lenses, a secondary electron (SE)-detector array, and a deflector. The emitter array comprises multiple charged-particle emitters (e.g., electron-beam emitters) each configured to emit simultaneously a separate individual charged particle beam along a separate respective beam axis. The first and second electromagnetic lenses are situated downstream of the emitter array. The lenses are configured to focus simultaneously the individual charged particle beams, from the emitter array, onto respective loci on the surface of the specimen so as to cause each of the loci to emit secondary electrons. The secondary-electron (SE)-detector array comprises multiple SE-detector units each situated and configured to receive and detect secondary electrons from a respective locus on the specimen. The deflector is situated between the first and second electromagnetic lenses and is configured to deflect the charged particle beams and cause the beams to scan simultaneously respective regions on the surface corresponding to the respective loci.
In this embodiment, deflection and scanning of the individual charged particle beams can be performed by a single deflector, which imparts the same deflection and scanning to all the beams. Individual respective SE detectors detect the secondary electrons from the various loci. The SE detectors desirably are configured such that “crosstalk” between the various SE detectors is negligible.
The scanning range of each charged particle beam is determined by the deflector and other components of a charged-particle-beam (CPB) optical system used to direct and focus the individual beams on their respective loci. Respective regions about the loci are inspected by scanning the respective beams within a defined range. Areas outside the regions are inspected simply by moving the specimen to within the scanning range of the charged particle beams.
The emitter array can be in one dimension (linear array). However, such an array requires that the specimen be moved continuously to obtain a two-dimensional scanning range. A two-dimensional emitter array allows less movement of the substrate, and permits (for example) inspection using a step-and-repeat scheme.
The first and second electromagnetic lenses can be configured as a symmetric magnetic doublet (SMD), which is a type of electromagnetic lens assembly used to form an image of the emitter array on the surface of the specimen. An SMD is advantageous because it minimizes the occurrence of aberrations and improves the perpendicular incidence properties of the individual charged particle beams on the specimen surface. The SMD can be a magnifying lens or 1:1 (non-magnifying and non-reducing) lens. A 1:1 lens provides excellent control of aberrations but can pose difficulties in arranging the individual SE detector units. A magnifying lens allows the emitter array to be made smaller.
The SMD further can comprise a magnification-adjusting lens.
Such a lens allows the pitch of the CPB emitters, as projected onto the specimen to be adjusted to some extent to match the pitch of, e.g., dies on the specimen. It is also possible to have various SE-detector arrays available that match the die pitch of any of several types of specimens to be inspected, wherein the array having the correct pitch can be selected for use with a particular specimen.
The charged-particle emitters of the emitter array can be in an X-Y plane (wherein the beam axes extend in a Z-direction). Alternatively, the charged-particle emitters can be displaced individually from the X-Y plane so as to correct curvature of an image collectively formed on the specimen by the charged particle beams passing through the first and second electromagnetic lenses. The most pronounced aberration in CPB optical systems using an SMD is image curvature. By shifting the respective positions of the various charged-particle emitters in the Z-direction, effects of image curvature can be reduced greatly or eliminated.
The loci typically are arrayed on the surface of the specimen with an X-direction pitch and a Y-direction pitch. Desirably, at least one (more desirably both) of the X-direction pitch and the Y-direction pitch is adjustable. Such an adjustment allows the pitch used for inspection to be adjusted to match the pitch of, e.g., dies on the surface of the specimen.
Further desirably, each SE-detector unit in the SE-detector array comprises a respective detector electrod
Klarquist & Sparkman, LLP
Lee John R.
Nikon Corporation
Vanore David A.
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