ILLUMINATION ANGLE CONTROL USING DICHROIC FILTERS

• US 20090310239A1
• Filed: 06/12/2008
• Published: 12/17/2009
• Est. Priority Date: 06/12/2008
• Status: Active Grant

• Current Assignee: Orbotech Limited (KLA Corporation)
• Original Assignee: Orbotech Limited (KLA Corporation)
• Inventors: ADLER, Avraham
• Granted Patent: US 8,054,553 B2
• Time in Patent Office: Days
• US Class Current: 359/891
• CPC Class Codes: G01N 21/8806 Specially adapted optical and illumination features
• CPC Class Codes: G01N 21/956 Inspecting patterns on the surface of objects contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10

Abstract

A method of controlling the illumination angle onto a target, including, illuminating onto the target with light from at least two light sources of pre-selected wavelengths; wherein each point on the target is illuminated by light from the light sources with a respective maximal illumination angle relative to a main illumination axis extending from substantially the center of the at least two light sources to the target, selecting a dichroic filter that transmits light from the at least two light sources as a function of the angle of incidence upon the filter, positioning the dichroic filter between the at least two light sources and the target to limit the transfer of light to light of the pre-selected wavelengths; and wherein the dichroic filter is selected to limit the maximal illumination angle illuminating each point on the target.

Claims

1. A method of controlling the illumination angle onto a target, comprising:

illuminating onto the target with light from at least two light sources of pre-selected wavelengths;

wherein each point on the target is illuminated by light from the light sources with a respective maximal illumination angle relative to a main illumination axis extending from substantially the center of the at least two light sources to the target;

selecting a dichroic filter that transmits light from the at least two light sources as a function of the angle of incidence upon the filter;

positioning the dichroic filter between the at least two light sources and the target to limit the transfer of light to light of the pre-selected wavelengths; and

wherein said dichroic filter is selected to limit the maximal illumination angle illuminating each point on the target.

2. A method according to claim 1, wherein said dichroic filter is positioned perpendicular to the main illumination axis.

3. A method according to claim 1, wherein said dichroic filter does not form a right angle relative to the main illumination axis.

4. A method according to claim 3, wherein the angle of the dichroic filter is user controllable.

5. A method according to claim 1, wherein multiple dichroic filters are positioned sequentially along the main illumination axis.

6. A method according to claim 5, wherein said multiple dichroic filters are positioned at an angle relative to each other.

7. A method according to claim 1, wherein said dichroic filter is a multi pass filter.

8. A method according to claim 1, further comprising placing a lens between the at least two light sources and the target to focus the light from the at least two light sources onto the target along a first direction;

and wherein the light illuminating the target along a second direction perpendicular to the first direction have substantially the same illumination angles as the first direction as a result of the positioning of the dichroic filter.

9. A method according to claim 1, wherein said at least two light sources are provided in multiple rows of light sources parallel to each other and wherein the beams from each row of light sources is focused with a lens onto the target along a first direction, such that the combined beam that illuminates the target along the first direction has the same illumination angles as along a second direction perpendicular to the first direction as a result of the positioning of the dichroic filter.

10. A method according to claim 1, wherein each of the at least two light sources selectively provides light of multiple wavelengths and the controlled illumination angles differ for each wavelength.

11. A system for controlling the illumination angle onto a target, comprising:

at least two light sources to illuminate the target;

a dichroic filter that transmits light from the at least two light sources as a function of the angle of incidence upon the filter;

wherein the dichroic filter is positioned between the at least two light sources and the target;

wherein the light of the at least two light sources have pre-selected wavelengths;

wherein each point on the target is illuminated by light from the light sources with a respective maximal illumination angle relative to a main illumination axis extending from substantially the center of the at least two light sources to the target;

wherein said filter is selected to limit the maximal illumination angle illuminating each point on the target.

12. A system according to claim 11, further comprising a lens positioned between the at least two light sources and the target to focus the light from the at least two light sources onto the target along a first direction;

and wherein the light illuminating the target along a second direction perpendicular to the first direction have substantially the same illumination angles as the first direction as a result of positioning the dichroic filter between the target and the at least two light sources.

13. An illumination device for illuminating a target, comprising:

one or more rows of light sources, wherein each light source provides light of one or more wavelengths;

a lens parallel to each row of light sources to focus the light from the rows of light sources so that the combined light beam that illuminates the target has a specific angle relative to a main illumination axis extending from substantially the center of the at least two light sources to the target;

a dichroic filter placed between the target and the lens that transmits specific light wavelengths incident on the filter at a specific range of angles, such that the resulting illumination angles for at least one wavelength, on the target along the direction perpendicular to the row of light sources is symmetrical with the illumination angles along the direction parallel to the row of light sources.

14. A system according to claim 13, further comprising multiple dichroic filters.

15. A system according to claim 13, wherein the resulting illumination angles on the target along the direction perpendicular to the row of light sources is symmetrical with the illumination angles along the direction parallel to the row of light sources for a single wavelength.

16. A system according to claim 13, wherein the resulting illumination angles on the target along the direction perpendicular to the row of light sources is symmetrical with the illumination angles along the direction parallel to the row of light sources for more than one wavelength.