Polarization imaging

1. A method of monitoring critical dimensions in a semiconductor fabrication process comprising:

a. capturing at least one image of a first structure having a geometry which has an effect on the polarization state of light reflected therefrom;

b. generating a differential image for each captured image;

c. averaging pixel intensity differences of the respective differential images over the entire differential image to obtain an average image intensity value for each differential image;

d. obtaining a critical dimension of the first structure;

e. correlating a critical dimension of the first structure with the average image intensity value;

f. capturing at least one image of a subsequent structure; and,

g. determining, based at least in part on the average image intensity value, a critical dimension of the subsequent structure.

2. The method of claim 1 further comprising:

a. capturing at least one image of a second structure having a geometry which has an effect on the polarization state of light reflected therefrom;

b. calculating, for each of the at least one images of the second structure a value that is indicative of an intensity of the light reflected from the second structure;

c. obtaining a critical dimension of the second structure;

d. correlating a critical dimension of the second structure with the calculated value;

e. capturing at least one image of a subsequent structure; and,

f. determining, based at least in part on the calculated values of the first and second structures, a critical dimension of the subsequent structure.

3. The method of claim 2 further comprising:

a. capturing at least one image of at least one additional structure having a geometry which has an effect on the polarization state of light reflected therefrom;

b. calculating, for each of the at least one images of the at least one additional structure a value that is indicative of an intensity of the light reflected from the at least one additional structure;

c. obtaining a critical dimension of the at least one additional structure;

d. correlating a critical dimension of the at least one additional structure with the calculated value;

e. capturing at least one image of a subsequent structure; and,

f. determining, based at least in part on the calculated values of the first, second and at least one additional structures, a critical dimension of the subsequent structure.

4. The method of claim 3 wherein the first, second and additional structures are entire IC devices.

5. The method of claim 3 wherein at least one of the first, second and additional structures is a selected portion of an active circuit of an IC device.

6. The method of claim 1 wherein the first structure is a part of an active portion of an integrated circuit device.

7. The method of claim 1 wherein the critical dimension of the subsequent structure is an absolute value.

8. The method of claim 1 wherein the critical dimension of the subsequent structure is a differential value.

9. The method of claim 1 , wherein determining the critical dimension of the subsequent structure is further based on correlating the critical dimension of the first structure with the average image intensity value.

10. A substrate inspection system comprising:

an optical sensor positioned to capture an image of a first structure having a geometry which has an effect on the polarization state reflected therefrom and an image of a subsequent structure;

a computer coupled with the optical sensor to receive the image of the first structure in the image of the subsequent structure, the computer having instructions that, when implemented, generate a differential image for the image of the first structure, average pixel intensity differences of the differential image over the entire differential image to obtain an average image intensity value, obtain a critical dimension of the first structure, correlate a critical dimension of the first structure with the average image intensity value and determine, based at least in part on the average image intensity value, a critical dimension of the subsequent structure.

11. The system of claim 10 wherein the first structure is part of an active portion of an integrated circuit device.

12. The system of claim 10 , wherein the critical dimension of subsequent structure is an absolute value.

13. The system of claim 10 wherein the critical dimension of the subsequent structure is a differential value.