Wafer inspecting method

1. A wafer inspecting method comprising:

scanning a pattern image of a unit inspection region of a first wafer in a normal state in a first mode with definite inspection conditions, and setting the scanned pattern image as a first reference image;

scanning a pattern image of a unit inspection region of a second wafer to be inspected in the first mode, and storing the scanned pattern image as a first detection image;

comparing the first reference image and the first detection image, and storing a difference of the images as a first difference image;

scanning a pattern image of the unit inspection region of the first wafer in the normal state in a second mode with inspection conditions different from the first mode, and setting the scanned pattern image as a second reference image;

scanning a pattern image of the unit inspection region of the second wafer to be inspected in the second mode, and storing the scanned pattern image as a second detection image;

comparing the second reference image and the second detection image, and storing a difference of the images as a second difference image;

generating a third difference image by calculating a balance between the first difference image and the second difference image; and

discriminating a defect from noise by using the third difference image.

2. The method according to claim 1 , wherein the step of discriminating a defect from noise comprises:

calculating electrical signal values of the third difference image; and

of the calculated signal values, discriminating the signal values that exceed a predetermined threshold value as a defect and the signal values that are less than the threshold value as noise.

3. The method according to claim 2 , wherein the electrical signal values are gray level signal values.

4. The method according to claim 1 , further comprising:

displaying the discriminated defect externally on a map.

5. The method according to claim 1 , wherein the step of scanning the pattern image of the unit inspection region comprises:

outputting light from a light source;

inputting the output light to the unit inspection region so that the output light is reflected from the unit inspection region; and

inputting the reflected light from the unit inspection region to an image sensor so that the reflected light is detected.

6. The method according to claim 5 , wherein the inspection conditions include a kind of light used to scan the pattern image, a shape or amount of light being input to the unit inspection region, and a shape or amount of light being reflected from the unit inspection region.

7. The method according to claim 5 , further comprising:

changing a mode from the first mode to the second mode.

8. The method according to claim 7 , wherein the changing of a mode comprises changing the kind of the light being output from the light source.

9. The method according to claim 7 , wherein the changing of a mode comprises changing the shape or amount of the light being input to the unit inspection region.

10. The method according to claim 7 , wherein the changing of a mode comprises changing the shape or amount of the light being input to the image sensor.

11. The method according to claim 1 , wherein the unit inspection region is an entire wafer being inspected.

12. The method according to claim 1 , wherein the unit inspection region is a cell or die portion on a wafer being inspected.