Auto focus system for inspection of high-density parts
AssigneeVelocity Image Processing LLC
InventorsRobert P. Bishop, Timothy Pinkney
Life of this patent
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Abstract
A method and apparatus to maintain image focus on parts such as wafers, circuit boards, or high-density substrates as the part is being inspected. Focus performance is independent of feature and trace orientation and density. This apparatus can be easily integrated into an inspection system and can maintain focus on parts with high aspect ratio structures and or low or non-reflective insulators. It enables the inspection of high-density fine line products requiring the use of high resolution, high numerical aperture (NA) imaging optics with small depths of focus (DOF) that must be kept in focus during the inspection.
Claims11
A method of operating a focus system for use in inspection of a part such as a panel, substrate or wafer comprising:
- a) projecting two or more different patterns onto the part (FIGS. 13A, 13B),
- b) each different projected pattern being composed of multiple copies of a given geometric shape (FIG. 13A),
- c) viewing the patterns projected onto the part with a focus camera (FIG. 14),
- d) each pattern projected at a different wavelength, vector angle and vector direction relative to a perpendicular drawn to optics of the focus camera (FIG. 13B),
- e) geometric shapes in each pattern moving on a surface of the focus camera as a function of projected vector angle, projected vector direction and / or changes in vertical height between features on the part and focus optics of the focus camera (FIG. 20),
- f) dividing one or more of the geometric shapes on the surface of the focus camera into one or more slices (FIG. 13 at 13-7 and 13-8),
- g) each slice oriented parallel to the vector angle and vector direction of motion of the geometric shapes on the surface of the focus camera corresponding to a same direction of motion on the part (FIG. 20),
- h) measuring a width and signal intensity of the one or more slices on the focus camera (FIG. 15A),
- i) comparing each individual width / intensity measurement, above a minimum predetermined brightness intensity, to an expected width, and only if such measurement is within predetermined width tolerances then considering the measurement valid (FIG. 15B),
- j) the expected width corresponding to the width of a slice for a fully reflected shape (FIG. 15A),
- k) finding a location of one or more valid measurement slices on the focus camera and their corresponding positions on the part (FIG. 16),
- l) processing resulting valid measurement slice locations on the camera, corresponding to positions on the part, to calculate a distance between the part and lens optics at the measured position within an optical field of view (FIG. 16), and
- m) changing the distance between the part and focus camera optics to keep the part in focus within an optical depth of field across the optical field of view (FIG. 28 at 28-34).
A method for operating a focus system for use in inspection of panels, substrates or wafers comprising:
- a) projecting two or more different patterns onto a part being inspected for defects (FIG. 21B),
- b) each different projected pattern being composed of multiple copies of a geometric shape (FIG. 21C),
- c) viewing the patterns projected onto the part with a focus camera (FIG. 21A),
- d) each pattern projected at a different wavelength, vector angle and vector direction relative to a perpendicular drawn to optics of the focus camera FIG. 13B),
- e) the geometric shapes in each pattern moving on a surface of the focus camera as a function of projected vector angle, projected vector direction and changes in vertical height between features on the part and focus camera optics FIGS. 21A, 21B),
- f) fitting a known good reference shape to edge points or perimeter points of one or more shapes on the surface of the focus camera to create best fit positions for each fitted set of edge or perimeter points (FIG. 23A),
- g) using these best fit positions to calculate a distance between the part and focus optics at corresponding locations on the part, and to calculate a height profile of the part (FIG. 23B), and
- h) changing the vertical distance between the part and focus camera optics to keep the part in focus within an optical depth of field across the optical field of view (FIG. 29 at 29-18).
Dependencies are inferred from the claim text.