Image analysis – Applications – Manufacturing or product inspection
Reexamination Certificate
1998-07-08
2001-04-03
Mehta, Bhavesh (Department: 2721)
Image analysis
Applications
Manufacturing or product inspection
C250S306000, C257S080000, C257S449000, C356S237200
Reexamination Certificate
active
06212292
ABSTRACT:
BACKGROUND
The invention relates to observing sub-microscopic objects.
Optical microscopes are used to observe, e.g., microscopic variations on the surfaces of objects, including the surfaces of semiconductor materials onto which conductive or dielectric materials have been deposited. One type of optical microscope, a near-field scanning optical microscope (NSOM), uses an optical fiber with a fine tip to illuminate an object in the near-field, i.e., with the tip and the object separated by a distance less than the diameter of the tip. A photosensor then detects spatial variations in light transmitted through or reflected from the object, producing an output current in proportion to the intensity of the detected light. A rastering device, e.g., a scanning stage, is used to move the tip along the object and thus to generate an image illustrating the intensity of light across the surface area of the object.
The resolution of an image generated with an NSOM depends largely on the dimensions, geometry, and position of the tip. Resolution also depends on the size of the object and the distance between the tip and the object. Complex tip conditioning techniques have been developed to produce fibers with tips as small as tens of nanometers in diameter. However, such tips often must be processed or otherwise reconditioned before each scan of an object. Standard NSOMs also employ complex dithering techniques to ensure appropriate spacing between the fiber tip and the sensor surface.
SUMMARY OF THE INVENTION
Recognition of the above led the inventor to present an optical imaging technique that involves relatively simple tip preparation and positioning and relatively simple object image generation.
In one aspect, the invention relates to an optical microscope for use in creating an image of an object. The optical microscope includes a light source operable to produce a beam of light, an actuator coupled to the light source to scan the beam of light over a surface on which the object is to be placed, and processing circuitry. The processing circuitry receives a background scan signal when the beam of light strikes the surface during a background scan conducted without the object placed on the surface, creates a background scan dataset indicating a value of the background scan signal at each of multiple positions on the surface, receives an object scan signal when the beam of light strikes the surface during an object scan conducted with the object placed on the surface, creates an object scan dataset indicating a value of the object scan signal at each of the multiple positions on the surface, and derives image data from the background scan dataset and the object scan dataset for use in creating the image of the object.
In some implementations, the processing circuitry may subtract the object scan dataset from the background scan dataset to derive the image data. The beam of light may have a known beam profile and the processing circuitry may process the background scan dataset and the object scan dataset to account for the beam profile, e.g., by deconvolving the beam profile from the background scan dataset and the object scan dataset.
In other implementations the processing circuitry may receive an additional background scan signal during the background scan and an additional object scan signal during the object scan. The background scan signals may indicate motion of the light beam in two different directions over the surface during the background scan, and the object scan signals may indicate motion of the light beam in two different directions over the surface during the object scan. The processing circuitry may add the background scan signals before creating the background scan dataset and may add the object scan signals before creating the object scan dataset.
In other implementations, the optical microscope may include a fiber connected to the light source to deliver the beam of light to the surface on which the object is to be placed. The fiber may be positioned so that the surface lies in the near-field of the light emitted by the fiber. The optical microscope also may include a photosensor having a semiconductor surface that serves as the surface on which the object is to be placed. The photosensor may include one or more MSM diodes. The optical microscope may include a display device capable of displaying the image.
In another aspect, the invention relates to a method for use in creating an image of an object in an optical microscope. A beam of light is scanned over a surface on which the object is to be placed, and a background scan signal is received. After the object has been placed on the surface, the beam of light again is scanned over the surface, and an object scan signal is received. A background scan dataset and an object scan dataset are created. The background scan dataset indicates a value of the background scan signal at each of multiple positions on the surface, and the object scan dataset indicates a value of the object scan signal at each of the multiple positions on the surface. Image data then is derived from the background scan dataset and the object scan dataset for use in creating the image of the object.
In still another aspect, the invention relates to a computer program product embodied on a tangible storage medium and capable for use in creating an image of an object in an optical microscope. The program includes executable instructions that enable a computer to receive a background scan signal when a beam of light strikes a surface on which the object is to be placed during a background scan conducted without the object placed on the surface, create a background scan dataset indicating a value of the background scan signal at each of multiple positions on the surface, receive an object scan signal when the beam of light strikes the surface during an object scan conducted with the object placed on the surface, create an object scan dataset indicating a value of the object scan signal at each of the multiple positions on the surface, and derive image data from the background scan dataset and the object scan dataset for use in creating the image of the object.
Each implementation of the invention may provide any one or more of several advantages. Microscopic objects may be observed through a “tipless” optical microscope, i.e., a microscope for which relatively little or no tip preparation is necessary. The “tipless” nature of the optical imaging technique simplifies the observation process and reduces the cost of keeping and using the microscope. The optical microscope may be used to observe objects at a resolution of several microns or less even when the microscope's tip is much larger. The resolution of the microscope relies primarily on the resolution of the photo-sensor, which is relatively easy and inexpensive to manufacture.
The invention also allows for the use of photosensors that detect the tip's z-position, i.e., the distance between the tip and the photosensor. A relatively simple digital signal and image processing technique may be used to create images of objects.
Other embodiments and advantages will become apparent from the following description and from the claims.
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California Institute of Technology
Fish & Richardson P.C.
Mehta Bhavesh
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