Image analysis – Image enhancement or restoration – Focus measuring or adjusting
Reexamination Certificate
2000-09-07
2004-07-13
Patel, Kanji (Department: 2625)
Image analysis
Image enhancement or restoration
Focus measuring or adjusting
C382S141000, C250S201600, C356S624000
Reexamination Certificate
active
06763140
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This is the first application filed for the present invention.
TECHNICAL FIELD
The invention relates to the field of micro-imaging and, in particular, to methods and apparatus for acquiring high magnification images of a tilted and/or uneven sample using a micro-imaging system having a shallow depth-of-field.
BACKGROUND OF THE INVENTION
In the field of micro-imaging a high magnification imaging instrument is used to acquire images of a sample. Magnification powers of 100× or more are used for micro-imaging semiconductor integrated circuits (IC) to extract design and layout information for the purposes of design verification, product quality assurance and reverse engineering. At such high magnifications, a parameter of the high magnification microscope known in the art as the depth-of-field becomes very important.
According to what is know in the art as the “Thin Lens Approximation”, while imaging an object using a theoretical optical system only an infinitesimally thin object plane in front of the optical system is in focus on an infinitesimally thin image plane, behind the optical system. The depth-of-field corresponds to the thickness of the image plane and therefore, in theory, the depth-of-field approximates zero. In practice, while imaging an object, features behind and in front of the theoretical object plane are also focused on the image plane. The depth-of-field is the thickness of the slice around the object plane that can be imaged in-focus.
Imaging objects at most one to two orders of magnitude smaller than constituent optical elements of an optical imaging system operating at small powers of magnification, the depth-of-field is large enough to capture an entirety of such objects in focus. However in micro-imaging sample IC's using a 100× power magnification: the optical elements are at most a few orders of magnitude larger than traces on a sample IC (~1 mm:~1 &mgr;m). The width of traces on the sample IC is just wide enough that interference/diffraction effects are minimal when using ultraviolet light, and the pixel size of the CCD is comparable to the trace width. This results in a dept-of-field that is about the size of the width of a trace or about the thickness of a deposition layer on an IC.
Semiconductor components manufactured on a silicon substrate of an IC are several deposition layers in height. Traces interconnecting components on the silicon substrate transcend deposition layers. The components and interconnecting traces form a relief on the silicon substrate. Focusing not only becomes very important, autofocusing techniques are unsuitable because a range of focus settings of the micro-imaging system will appear to provide in-focus images, each image correctly focusing on different features distributed over a range of deposition layers.
U.S. Pat. No. 5,647,025 entitled “AUTOMATIC FOCUSING OF BIOMEDICAL SPECIMENS APPARATUS” which issued on Jul. 8, 1997 to Frost, et al. describes an apparatus for inspecting biological specimens and a method for automatically focusing on features using morphological criteria such as brightness, contrast, size, shape, texture and context. The apparatus is adapted to extract a focus measure concurrent with performing pattern recognition. The pattern recognition is optimized for biological cell detection in a particular size range and having a particular geometry. Methods for detecting biological cell nuclei are also presented. While this invention has merit, it is not suited for micro-imaging sample IC's to extract design and layout information. The methods described by Frost only provide suitable autofocusing at 4× magnification with a field of view of 1.4 mm square. At this magnification the depth-of-field has a substantial thickness enabling reliable focusing on discrete biological cells having cell nuclei. A comparable depth-of-field is not available at 100× magnifications required for micro-imaging a sample IC.
Frost's methods provide a timely inspection of a slide having approximately 700 fields of view. In micro-imaging sample IC's a surface of interest is typically divided in excess of 10,000 fields of view each corresponding to a tile-image to be acquired. Autofocusing operations performed according to Frost's teachings to acquire tile images would be time consuming and therefore unsuitable. Minimizing the time taken to acquire tile images is very important as pointed out in co-pending United States patent application entitled “METHOD AND SYSTEM FOR RECALIBRATION DURING MICRO-IMAGING TO DETERMINE THERMAL DRIFT”, which was filed on Jun. 15, 2000 and assigned Ser. No. 09/594,169, the specification of which is incorporated herein by reference.
Therefore in micro-imaging a surface of interest for a sample IC, there is a need for methods and apparatus for providing focus settings to enable the acquisition of a very large number of tile-images of the surface of interest.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an interface for selecting locations for a plurality of focus points on a surface of interest of a sample IC to be micro-imaged and to select a focus setting associated with each focus point.
It is another object of the invention to compute a virtual focus surface that substantially mimics a surface topology found by components and interconnecting traces manufactured on sample IC silicon substrate, using a plurality of focus point locations and the associated focus settings.
It is yet another object of the invention to compute a tile image focus setting at a tile image focus location based on the focus surface and the plurality of focus points.
According to one aspect of the invention, there is provided an apparatus for micro-imaging an uneven surface of interest of a sample comprising means for selecting and storing positional coordinates of focus points associated with a sample coordinate space defined by the sample, to create a focus point list, means for determining an associated focus setting for each focus point in the focus point list, and means for generating a focus surface using the focus point list, as well as means for extracting a tile image focus setting at a tile image focus location from the focus surface, and means for positioning a micro-imaging system to acquire a tile image at the tile image focus setting.
The means for selecting and storing positional coordinates of focus points associated with a sample coordinate space preferably comprises a man-machine interface for sending control messages to the micro-imaging system, and receiving image data from the micro-imaging system. The means for determining a focus setting associated with each focus point further comprises means for extracting a focus measure from image data received from the micro-imaging system. The means for extracting a focus measure is prefreably an algorithm that performs pixel operations on the image data to extract, for example, a sharpness measure. The means for generating a focus surface using the focus point list comprises means for grouping focus points from the focus point list into focus point groups, the focus point groups being stored in a focus point group list. The means for grouping focus points into focus point groups comprises a focus point grouping algorithm, the positional coordinates and the associated focus setting of each focus point in a focus point group forming a focus facet, and the focus surface comprises abutting focus facets. The focus point grouping algorithm is preferably a mesh generation algorithm, for example, a triangular mesh generation algorithm. If so, each focus point group is a focus point triad. A preferred triangular mesh generation algorithm is the Delaunay triangulation algorithm, which is well known in the art. In order to ensure accurate focusing, the means for grouping focus points into focus point groups preferably further comprises a focus point group exclusion algorithm for excluding from the focus point group list a focus point group having substantially
Chipworks
Patel Kanji
Renault Ogilvy
Wood Max R.
LandOfFree
Method and apparatus for focusing a micro-imaging system... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for focusing a micro-imaging system..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for focusing a micro-imaging system... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3247950