Image preprocessing for probe mark inspection
View Patent ↗Digital image processing methods are applied to an image of a semiconductor interconnection pad to preprocess the image prior to an inspection or registration. An image of a semiconductor pads exhibiting spatial patterns from structure, texture or features are filtered without affecting features in the image not associated with structure or texture. The filtered image is inspected in a probe mark inspection operation.
1. A method of analyzing at least one object, the method comprising:
acquiring an image of at least one object, the image having an oriented structured pattern;
transforming the image into a frequency domain to provide a transformed image;
selecting a frequency having a peak magnitude in the transformed image;
providing a spatial band-reject filter, the spatial band-reject filter having a frequency parameter corresponding to the selected frequency;
using a processor to filter the transformed image using the spatial band-reject filter to provide a filtered image; and
transforming the filtered image into a spatial domain.
2. The method of claim 1 wherein the step of selecting a frequency further comprises:
filtering the transformed image using the spatial band-reject filter using the frequency parameter corresponding to the frequency having a peak magnitude in the transformed image, to provide a first score;
providing at least one comparison frequency;
filtering the transformed image using the spatial band pass filter using the frequency parameter corresponding to the at least one comparison frequency to provide a second score; and
selecting a frequency by comparing the first score and the second score to provide a selected frequency.
3. The method of claim 2 , wherein the comparison frequency is computed from the frequency parameter corresponding to the frequency having a peak magnitude in the transformed image and a step size parameter.
4. The method of claim 1 , wherein the spatial band-reject filter is a Gabor band reject filter.
5. The method of claim 2 further comprising convolving the transformed image with a spatial filter.
6. The method of claim 5 , wherein the spatial filter is a 3×3 kernel.
7. The method of claim 2 , wherein the first score and the second score further comprises:
computing an edge magnitude image from the filtered image; computing a histogram of the edge magnitude image;
and measuring the smoothness of the histogram of the edge magnitude image to provide a score.
8. An apparatus for inspecting at least one object having an oriented structured pattern, the apparatus comprising:
a camera configured to acquire image data corresponding to the at least one object:
a machine vision system coupled to the camera and configured to convert image data acquired by the camera into a digitally filtered representation of the at least one object by applying an image processing filter on the acquired image data, and performing an inspection on the digitally filtered representation of the at least one object, applying an image processing filter including, the image processing filter transforming the image into a frequency domain to provide a transformed image; filtering the transformed image with an oriented spatial band pass filter, and transforming the transformed image into a spatial domain.
9. The apparatus of claim 8 , wherein the machine vision system includes a processor that is configured to work in cooperation with a controller to control operation of the machine vision system, the controller cooperating with the processor to fetch instructions from memory and decode the instructions so that the machine vision system is configured to acquire image data corresponding to at least one object, applying the image processing filter on the acquired image data, and perform the inspection.
10. The apparatus of claim 8 , wherein the machine vision system registers at least one object in the digitally filtered representation of the at least one object.
11. A method of analyzing at least one object, the method comprising:
acquiring an image of the at least one object, the at least one object having at least one dimensional characteristic, and the interconnection pad having at least one feature not associated with the object;
and filtering the image using an image processing filter wherein the at least one dimensional characteristic of the at least one object is preserved, and the at least one feature of the at least one object not associated with the object is not preserved, to a filtered image of the probe mark, the image processing filter transforming the image into a frequency domain to provide a transformed image; filtering the transformed image with an oriented spatial band pass filter using a processor, and transforming the transformed image into a spatial domain.