Dark field inspection system with ring illumination

Patent metadata

Field	Value
Publication number	US-9176072-B2
Application number	US-91976010-A
Country	US
Kind code	B2
Filing date	Jul 16, 2010
Priority date	Jul 22, 2009
Publication date	Nov 3, 2015
Grant date	Nov 3, 2015

Abstract

A dark field inspection system that minimizes the speckle noise due to sample surface roughness can include a plurality of beam shaping paths for generating a composite, focused illumination line on a wafer. Each beam shaping path can illuminate the wafer at an oblique angle. The plurality of beam shaping paths can form a ring illumination. This ring illumination can reduce the speckle effect, thereby improving SNR. An objective lens can capture scattered light from the wafer and an imaging sensor can receive an output of the objective lens. Because the wafer illumination occurs at oblique angles, the objective lens can have a high NA, thereby improving optical resolution of the imaging sensor, and the resulting signal level.

First claim

The invention claimed is:

1. A dark field inspection system comprising:
three or more beam shaping paths for generating a composite, focused illumination line on a wafer, each beam shaping path for illuminating the wafer at an oblique angle, the beam shaping paths forming a ring illumination, wherein each of the beam shaping paths includes an independent light source positioned to result in independent, random noise at a surface of the wafer and wherein each independent light source provides incoherent light with respect to each other independent light source, wherein each of the plurality of beam shaping paths includes a cylindrical lens, each cylindrical lens being tilted and rotated with respect to a light beam from its corresponding light source, and wherein each cylindrical lens has a cylindrical axis positioned parallel to an illumination line, an optical axis, and a b-axis perpendicular to both the cylindrical axis and the optical axis, wherein the b-axis is positioned perpendicular to the light beam from its corresponding light source;
an objective lens for capturing scattered light from the wafer; and
an imaging sensor for receiving an output of the objective lens.

2. The dark field inspection system of claim 1 , wherein the oblique angle with respect to the sample surface normal is between 60-85 degrees.

3. The dark field inspection system of claim 1 , wherein a numerical aperture (NA) of the objective lens is at least 0.5.

4. The dark field inspection system of claim 1 , wherein each cylindrical lens is rotated by its cylindrical axis to minimize aberration.

5. The dark field inspection system of claim 1 , wherein at least one beam shaping path includes first, second, and third cylindrical lenses, wherein one of the first and second cylindrical lenses is in the beam shaping path at any point in time, wherein each of the first and second cylindrical lenses determines a length of the illumination line, and wherein the third cylindrical lens determines a width of the illumination line.

6. The dark field inspection system of claim 1 , wherein at least one beam shaping path includes a continuous zoom lens and a cylindrical lens, wherein the continuous zoom lens allows selection of a specific illumination line length within a predetermined range, and wherein the cylindrical lens determines a width of the illumination line.

7. The dark field inspection system of claim 1 , wherein the imaging sensor includes a digital image processing filter that matches a shape of a particle on the wafer.

8. The dark field inspection system of claim 7 , wherein the shape is a donut shape.

9. The dark field inspection system of claim 1 , wherein each light source is a laser.

10. The dark field inspection system of claim 1 , wherein the three or more beam shaping paths include:
multiple lasers;
multi-mode fibers coupled to the multiple lasers;
a modulator for modulating beams carried by the multi-mode fibers; and
mirrors for reflecting and directing the beams for generating the illumination line.

11. The dark field inspection system of claim 10 , wherein the mirrors include an aspheric ring mirror.

12. The dark field inspection system of claim 1 , wherein the three or more beam shaping paths include:
a broadband light source;
a light pipe receiving an output of the broadband light source;
a condenser lens for collimating output of the light pipe; and
mirrors for reflecting and directing beams output from the condenser lens for generating the illumination line.

13. The dark field inspection system of claim 12 , wherein the mirrors include an aspheric ring mirror.

14. The dark field inspection system of claim 1 , wherein at least one light source includes multiple lasers and dichroic beam combiners for generating a laser beam having multiple wavelengths.

15. The dark field inspection system of claim 1 , wherein each light source is a laser, and adjacent beam shaping paths have lasers with different wavelengths.

16. The dark field inspection system of claim 1 , wherein the three or more beam shaping paths include:
a laser;
a diffuser coupled to the laser; and
a fiber bundle for receiving an output of the diffuser,
wherein each fiber contributes light to form the illumination line.

17. The dark field inspection system of claim 1 , wherein each light source is a laser diode.

18. The dark field inspection system of claim 1 , further including a beam splitter positioned to receive an output of the objective lens, wherein the imaging sensor includes a first imaging sensor for detecting a first wavelength of light output by the beam splitter and a second imaging sensor for detecting a second wavelength of light output by the beam splitter.

19. The dark field inspection system of claim 1 , further including a beam splitter positioned to receive an output of the objective lens, wherein the imaging sensor includes multiple imaging sensors, each imaging sensor for detecting a specific wavelength of light output by the beam splitter.

20. The dark field inspection system of claim 19 , wherein a subset of the multiple imaging sensors is selected for image analysis.

21. A method of providing a dark field inspection system, the method comprising:
forming three or more beam shaping paths to provide ring illumination, each beam shaping path for illuminating a wafer at an oblique angle, wherein outputs of the three or more beam shaping paths form a focused illumination line on the wafer, wherein each of the plurality of beam shaping paths includes an independent light source positioned to result in independent, random noise at a surface of the wafer, wherein each independent light source provides incoherent light with respect to each other independent light source, and wherein forming the three or more beam shaping paths includes tilting and rotating at least one cylindrical lens in each beam shaping path, wherein each cylindrical lens has a cylindrical axis positioned parallel to the illumination line, an optical axis, and a b-axis perpendicular to both the cylindrical axis and the optical axis, wherein the b-axis is positioned perpendicular to the light beam from its corresponding light source.

22. The method of claim 21 , further including rotating at least one cylindrical lens by its cylindrical axis to minimize aberration.

23. The method of claim 21 , further including using a first cylindrical lens to determine a length of the illumination line and a second cylindrical lens to determine a width of the illumination line.

24. The method of claim 21 , further including using a zoom lens to determine a length of the illumination line and a cylindrical lens to determine a width of the illumination line.

25. The method of claim 21 , wherein forming the three or more beam shaping paths includes:
coupling multi-mode fibers to outputs of coherent light sources;
modulating beams carried by the multi-mode fibers; and
reflecting and directing modulated beams for generating the illumination line.

26. The method of claim 21 , wherein forming the three or more beam shaping paths includes:
coupling a light pipe to an output of an incoherent light source;
collimating outputs of the light pipe; and
reflecting and directing beams collimated outputs for generating the illumination line.

27. The method of claim 21 , wherein forming the three or more beam shaping paths includes:
in at least one beam

Assignees

• Zhao Guoheng
• Vaez-Iravani Mehdi
• Young Scott
• Bhaskar Kris
• Kla Tencor Corp

Inventors

• Zhao Guoheng
• Vaez-Iravani Mehdi
• Young Scott
• Bhaskar Kris

Classifications

• G01N21/9501 Primary

  Semiconductor wafers (manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20) · CPC title

• G01N2021/8822

  Dark field detection · CPC title

• G01N21/8806

  Specially adapted optical and illumination features · CPC title

• H10P74/203 Primary

  Structural properties, e.g. testing or measuring thicknesses, line widths, warpage, bond strengths or physical defects · CPC title