Patent ID: 7315642

Claim:
A method for measuring thin film thickness variations of an inspected wafer that includes an upper non-opaque thin film, comprising: a) scanning the wafer and obtaining a wafer image that includes die images, each of which is composed of pixels; b) identifying at least one region in a first block of a first die image and obtaining at least one first intensity measurement of the respective region; c) identifying a corresponding at least one region in a second block of a second die image and obtaining at least one second intensity measurement of the respective region; d) processing the at least one first intensity measurement and the at least one second intensity measurement to obtain at least one signal variation between said at least one second intensity measurement and said at least one first intensity measurement, whereby each signal variation, from among said at least one signal variations, is indicative of a thickness variation between a region in the second die and a corresponding region in the first die; and further comprising determining a first GL region image (i) being gray level (GL) values of all pixels that constitute a region (i) from among n regions 1 . . . n of said first block; the GL values of all said pixels being equal to i; said first GL region image (i) being said first intensity measurement of a region recited in (b) above; determining a second GL region image (i) being gray level (GL) values of all pixels that constitute a corresponding region (i) from among n corresponding regions 1 . . . n of said second block; said second GL region image (i) being said second intensity measurement of a region recited in (c) above; calculating a first average value (i) being an average of difference region images for region (i), where difference region images for region (i) are a result of subtracting said first GL region image (i) from said second GL region image (i); and calculating a first standard deviation value (i) being a standard deviation of said difference region images for region (i); said first average value (i) and first standard deviation value (i) being said detected signal variation measurement between said second intensity measurement and said first intensity measurement of said region (i) recited in (d) above.