Method and system for inspecting surfaces with improved light efficiency

Abstract

The radiation beam of discrete light source such as LEDs is shaped by a cylindrical lens and a spherical lens to form two perpendicular narrow lines to illuminate a surface. The first line is projected onto a sample surface to improve illumination efficiency, and the second line is projected onto a pupil plane of an imaging lens to improve illumination uniformity. The layout of the LED chip is optimized to match the aspect ratio of the imaging detector. Multiple LEDs at different wavelengths are combined to improve sensitivity. The full surface of the sample is inspected through the relative motion between the sample and the optics.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:

FIG. 1A is a schematic diagram of a prior art system using a fiber line light or a LED line array for illumination;

FIG. 1B is a detailed diagram of illumination field and imaging field of FIG. 1A;

FIG. 2A is a schematic diagram of a top view of a new illumination technique using a discrete LED light source;

FIG. 2B is a schematic diagram showing a front view of FIG. 2A;

FIG. 3 is a schematic diagram of combining multiple LED light sources of different wavelengths, according to one embodiment of the present invention;

FIG. 4A is a schematic diagram of an exemplary layout of a commercial LED chip dimension;

FIG. 4B shows an optimized orientation of a LED chip for illuminating the optical field of view of a line scan CCD or TDI;

FIG. 5A to FIG. 5D are respective examples of the layout of the light emitting area of LED chips optimized for use in the illumination and imaging optics configuration in FIG. 2;

FIG. 6 is a diagram of an embodiment using the LED illumination for high speed inspection of large surfaces;

FIG. 7 is a sectional view of the system of FIG. 6; and

FIG. 8 is a diagram of combining multiple optics modules with different inspection and metrology functions.

Claims

1. A system for inspecting a surface of a substrate, the system comprising: a line scan sensor;an imaging lens; andan illumination source, including a number of light sources, provided via at least two lenses to illuminate a surface of a substrate being inspected, wherein the two lenses include: a cylindrical lens and a spherical lens to produce first and second lines from the illumination source, the first line projected on the surface and the second line projected in a perpendicular direction at a pupil plane of the imaging lens to achieve both intensity uniformity and angular uniformity across a field of view of the line scan sensor, and an image of the surface is focused onto the line scan sensor by the imaging lens.

2. The system as recited in claim 1, wherein the line scan sensor is a CCD or a TDI sensor.

3. The system as recited in claim 1, further comprising: an air bearing conveyor transporting the substrate; anda moving mechanism to cause a relative movement of the substrate with respect to the system.

4. The system as recited in claim 3, further comprising a vacuum preload air bearing chuck to support and stabilize the substrate under the field of view of the line scan sensor.

5. The system as recited in claim 1, wherein the light sources include at least a first LED to generate a light at wavelength λ1 and a second LED to generate a light at wavelength λ2, the light from the first or second LED is collimated and combined by a dichroic beam splitter.

6. The system as recited in claim 5, wherein the dichroic beam splitter reflects the light at wavelength λ2 and transmits the light at wavelength λ1.

7. The system as recited in claim 6, further including a control unit configured to independently control a corresponding intensity of the light at wavelength λ1 or λ2.

8. The system as recited in claim 6, wherein the intensity of the light at wavelength λ1 or λ2 is adjustable to optimize for defect detection sensitivity based on characteristics of the surface of the substrate.

9. The system as recited in claim 1, wherein the light sources are arranged substantially in a squared array that is rotated by 45 degrees such that a diagonal direction of the squared array is aligned with a longer axis of the cylindrical lens, as a result, light distribution on the surface of the substrate includes one strong central line and two weaker side lobes.

10. The system as recited in claim 1, wherein the substrate is one of liquid crystal displays (LCD), flat panel displays (FPD), organic light emitting diode (OLED) substrates, masks and semiconductor wafers.

11. The system as recited in claim 1, further comprising a dark field illumination positioned at an angle from a normal to the surface.

12. A system for inspecting a surface of a substrate, the system comprising: a line scan sensor;an imaging lens;a front illumination source provided via at least two lenses to illuminate a surface of a substrate being inspected, wherein the two lenses include: a cylindrical lens and a spherical lens to produce first and second lines from the illumination source, the first line projected on the surface and the second line projected in a perpendicular direction at a pupil plane of the imaging lens to achieve both intensity uniformity and angular uniformity across a field of view of the line scan sensor, and an image of the surface is focused onto the line scan sensor by the imaging lens;a back illumination source to enhance detection of defects that are otherwise difficult to detect with only the front illumination source; andat least one vacuum preload air bearing chuck to provide a down force to stabilize the substrate during a high-speed motion of the substrate over air bearings.

13. The system as recited in claim 12, further comprising a moving mechanism to cause a relative movement of the substrate with respect to an inspection module that includes the line scan sensor; the imaging lens; the front and back illumination sources, and a control unit to control intensity of light sources in the front and back illumination sources.

14. The system as recited in claim 13, wherein the light sources include at least a first LED to generate a light at wavelength λ1 and a second LED to generate a light at wavelength λ2, the light from the first or second LED is collimated and combined by a dichroic beam splitter.

15. The system as recited in claim 14, wherein the dichroic beam splitter reflects the light at wavelength λ2 and transmits the light at wavelength λ1.

16. The system as recited in claim 12, wherein an intensity of the light at wavelength λ1 or λ2 is adjustable to optimize for defect detection sensitivity based on characteristics of the surface of the substrate.

17. The system as recited in claim 12, wherein the light sources in the front illumination source are arranged substantially in a squared array that is rotated by 45 degrees such that a diagonal direction of the squared array is aligned with a longer axis of the cylindrical lens, as a result, light distribution on the surface of the substrate includes one strong central line and two weaker side lobes.

18. The system as recited in claim 12, wherein the substrate is one of liquid crystal displays (LCD), flat panel displays (FPD), organic light emitting diode (OLED) substrates, masks and semiconductor wafers.

19. The system as recited in claim 12, further comprising a dark field illumination positioned at an angle from a normal to the surface.