Mask blanks inspection tool

• US 20060138338A1
• Filed: 12/09/2005
• Published: 06/29/2006
• Est. Priority Date: 09/13/2004
• Status: Active Grant

• Current Assignee: Misaki Ito, Yoshihiro Tezuka
• Original Assignee: Misaki Ito, Yoshihiro Tezuka
• Inventors: Ito, Masaaki, Tezuka, Yoshihiro
• Granted Patent: US 7,220,969 B2
• Time in Patent Office: Days
• US Class Current: 250/372
• CPC Class Codes: G01N 2021/8822 Dark field detection
• CPC Class Codes: G01N 2021/95676 Masks, reticles, shadow masks
• CPC Class Codes: G01N 21/47 Scattering, i.e. diffuse reflection G01N21/25, G01N21/41 take precedence G01N21/55 takes precedence
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G01N 21/9505 Wafer internal defects, e.g. microcracks

Abstract

Embodiments include determining whether defects exist in an extreme ultraviolet (EUV) light mask blank. Incident EUV light scattered or diffused by abnormalities in the layers of the mask blank may be measured, normalized, and compared to threshold values to determine if and where a defect exists. Normalizing may be performed by dividing a light intensity value for a pixel by the average of light intensity values for one or more rings of surrounding pixels. A defect may be determined by considering whether the normalized intensity value for a pixel is greater than a pixel threshold to identify the pixel is a candidate for a location with a defect; and by determining whether the sum of normalized light intensity values for a block of pixels including the pixel satisfies a pixel block threshold to determine whether the block scatters or diffuses a critical amount of light to identify a defect.

Claims

1. A system comprising:

a source of extreme ultraviolet (EUV) light to illuminate a multilayered patterning mask blank;

a first spherical mirror having a first perimeter and an opening, the first mirror designed to reflect scattered light to be received from a multilayered patterning mask blank illuminated by the source;

a second spherical mirror having a second perimeter smaller than the first perimeter, the second mirror designed to reflect the scattered light received from the first spherical mirror through the opening and to a detector; and

a first comparator coupled to the detector to compare a first threshold value to a pixel reflective light intensity value received by the detector for a first pixel of a multilayered patterning mask blank;

a second comparator coupled to the detector to compare a second threshold value to a pixel reflective light intensity value received by the detector for a plurality of pixel block reflective light intensity values for a pixel block of the multilayered patterning mask blank, wherein the pixel block includes the pixel.

2. The system of claim 1, further comprising a mask blank moving apparatus to move a multilayered patterning mask blank to be illuminated in two dimensions with respect to an axis of the first spherical mirror.

3. The system of claim 2, wherein the detector includes a charge-coupled device (CCD) camera, and further comprising a mirror disposed along the axis to reflect the EUV light from the source to the mask blank.

4. The system of claim 3, wherein an axis of the first spherical mirror is perpendicular to a surface of the multilayered patterning mask blank.

5. The system of claim 1, wherein the source of EUV light is to illuminate a plurality of layers of the multilayered patterning mask blank, and the first spherical mirror is to receive diffused light reflections from the plurality of layers.

6. The system of claim 1, wherein the source of extreme ultraviolet (EUV) light is to illuminate the multilayered patterning mask blank with EUV light having a centroid wavelength of between 1.005 and 1.010 times a centroid wavelength of a patterning light to expose portions of a light sensitive material on a wafer during a photo-lithographic process, wherein the portions correspond to a pattern to be formed on the mask blank.

7. The system of claim 6, wherein the patterning light is to be incident upon a surface of the pattern at an angle of between six degrees and 8 degrees from perpendicular to the surface, and the first mirror is disposed such that an axis of the first spherical mirror is perpendicular to the surface.

8. The system of claim 1, further comprising logic circuitry coupled to the detector to divide the pixel reflective light intensity value received by the detector for a pixel by an average of the pixel block reflective light intensity value received by the detector for a plurality of pixels.

9. The system of claim 1, wherein the plurality of pixels of the mask blank form a shape of one of a trapezoid, a rectangle, a square, and a ring.

10. The system of claim 1, wherein the pixel of the multi-layered patterning mask blank is within a perimeter of the plurality of pixels.

11. The system of claim 1, wherein the first and second comparator are to compare one of scattered extreme ultraviolet (EUV) light reflection measurements and EUV dark-field image detections from a multi-layered mask blank.

12. The system of claim 1, wherein the mask comprises reflective portions of a multi-layered material and transparent portions.

13. The system of claim 1, wherein a criteria indicating a defect in the mask blank at the first pixel is satisfied if one of:

the pixel reflective light intensity value received by the detector for the first pixel satisfies the first threshold;

the pixel reflective light intensity value received by the detector for the plurality of pixel block reflective light intensity values for the pixel block satisfies the second threshold.

14. The system of claim 1, wherein the pixel block is a first pixel block;

and further comprising a third comparator coupled to the detector to compare a third threshold value to a pixel reflective light intensity value received by the detector for a plurality of pixel block reflective light intensity values of a second pixel block of the multi-layered patterning mask blank, wherein the second pixel block includes the first pixel block and has more pixels than the first pixel block.

15. They system of claim 14, wherein a criteria indicating a defect in the mask blank is satisfied if one of:

the pixel reflective light intensity value received by the detector for the first pixel of the mask blank satisfies the first threshold value; and

the pixel reflective light intensity value received by the detector for the plurality of pixel block reflective light intensity values for the first pixel block of the mask blank satisfies the second threshold; and

the pixel reflective light intensity value received by the detector for a plurality of pixel block light reflective intensity values for the second pixel block of the mask blank satisfies the third threshold value.

16. The system of claim 15, wherein satisfaction of the criteria indicates a defect in the mask blank at one of the first pixel block and the second pixel block.

17. The system of claim 15, wherein the first pixel block comprises at least two pixels, and the second pixel block comprises at least nine pixels.

18. The system of claim 15, wherein the first pixel block is a 2×

2 pixel block, and the second pixel block is a 5×

5 pixel block.