Printed fourier filtering in optical inspection tools

• US 20070247668A1
• Filed: 04/24/2006
• Published: 10/25/2007
• Est. Priority Date: 04/24/2006
• Status: Active Grant

• Current Assignee: Applied Materials South East Asia Pte Limited (Applied Materials Incorporated)
• Original Assignee: Negevtech Co.
• Inventors: Silberstein, Shai, Fuchs, Dan
• Granted Patent: US 8,031,931 B2
• Time in Patent Office: Days
• US Class Current: 358/3.30
• CPC Class Codes: G01N 21/95623 using a spatial filtering method per se G02B
• CPC Class Codes: G06V 10/89 using frequency domain filters, e.g. Fourier masks implemented on spatial light modulators
• CPC Class Codes: G06V 2201/06 Recognition of objects for industrial automation

Abstract

A spatial mask printer may be used in conjunction with an optical inspection tool. The tool can be used to obtain a Fourier image of an inspected object, and a filter mask image can be designed to block certain aspects of the object'"'"'s image in the Fourier plane corresponding to repetitive aspects of the imaged object. The filter mask image can then be printed and used in the tool during the inspection process. The mask image may be designed by hand or by computer and may be stored for later use. Filters may be automatically placed into the optical path of the inspection tool by a filter wheel, or may be housed in other filter banks. The printer may be configured to operate in a clean room environment, and may be integrated into the optical inspection tool.

Claims

1. A method of producing a spatial filter mask, comprising:

a) producing a Fourier image representation of an object;

b) defining a filter mask image, including the step of specifying at least one blocking area, wherein the blocking area corresponds to the Fourier image representation of at least one repetitive aspect of the object; and

c) printing a pattern corresponding to the filter mask image on a filter substrate.

2. The method of claim 1, wherein printing comprises inkjet printing.

3. The method of claim 2, wherein the pattern is printed in UV-curable ink.

4. The method of claim 1, wherein the filter mask image comprises a digital image.

5. The method of claim 1, further comprising simulating the effect of utilizing the defined filter mask image while imaging the object.

6. The method of claim 1, wherein specifying includes drawing the at least one blocking area in a bitmap, and the step of printing includes inkjet-printing the drawn area.

7. An optical inspection system, comprising:

a) an imager operative to image an object;

b) an object illumination source;

c) a filter mask printer; and

d) positioning apparatus configured to move a filter mask into the imager, such that the filter mask is disposed at the Fourier plane.

8. The system of claim 7, wherein the filter mask printer comprises:

a) a loading stage configured to hold at least one filter mask substrate;

b) a printing stage comprising at least one inkjet printing head; and

c) a substantially sealed case housing the printer components, including pressure control apparatus comprising ventilation outputs configured to interface with a fab exhaust system.

9. The system of claim 7, further comprising a filter bank configured to receive a plurality of filter masks.

10. The system of claim 9, wherein the filter bank comprises a motorized wheel configured to receive a plurality of filters such that at least one filter can be selected and disposed at the Fourier plane by rotating the wheel.

11. The system of claim 9, wherein the positioning apparatus includes at least one robotic arm or conveyor configured to receive and transport a mask output from the printer.

12. A spatial filter mask assembly for use in an optical inspection system, comprising:

a) a filter substrate; and

b) blocking areas comprising ink printed on the filter substrate in a pattern corresponding to the Fourier image produced by at least one repetitive aspect of a semiconductor device.

13. The spatial filter mask assembly of claim 12, further comprising a frame.

14. The spatial filter mask assembly of claim 13, wherein the frame further includes least one spring clip such that the filter substrate is removably attached to the filter substrate holder.

15. The spatial filter mask assembly of claim 12, wherein the ink comprises UV-cured polymer ink.

16. The spatial filter mask assembly of claim 12, further comprising identification indicia.

17. The spatial filter mask assembly of claim 16, wherein the identification indicia is selected from group of:

barcode, alphanumeric characters, RFID tag.

18. A method of Fourier filtering, comprising:

a) using an optical inspection system to create a Fourier image of an object;

b) defining a filter mask image based upon the Fourier image;

c) creating a spatial filter mask by printing the filter mask image on a filter substrate; and

d) placing the spatial filter mask in the Fourier plane such that the mask blocks a portion of the object'"'"'s image.

19. The method of claim 18, wherein placing is performed by automated machinery.

20. The method of claim 18, wherein printing comprises applying UV-curable ink to the filter substrate using at least one inkjet print head.

21. The method of claim 18, wherein placing includes selecting the filter mask from a plurality of filter masks and automatically moving the selected filter mask into the Fourier plane.

22. The method of claim 21, wherein selecting and automatically moving a filter mask includes rotating a motorized wheel configured to hold a plurality of filter masks such that a selected filter mask is placed in the Fourier plane.