Method for defocus detection

A non-transitory computer readable medium storing a program configured to instruct a processor to:

• apply a segment mask on a die thereby forming a segment on the die;
• calculate a mean intensity of the segment with data including red, green, and blue colors using a bright field mode and with data including red, green, and blue colors using a dark field mode;
• compare defocus value against the mean intensities;
• determine a color combination that optimizes defocus sensitivity;
• determine sensitivity to defocus for each pixel in the segment;
• apply a threshold to the sensitivity for each pixel;
• and
• generate a second segment mask on the die based on pixels that are above the threshold to the sensitivity.

A system comprising:

• a chuck configured to hold a wafer;
• a measurement system configured to measure a surface of the wafer, wherein the measurement system provides an image of the wafer using a bright field mode and a dark field mode;
• and
• a controller in electronic communication with the measurement system, wherein the controller includes a processor, an electronic data storage unit in electronic communication with the processor, and a communication port in electronic communication with the processor, and wherein the controller is configured to:
• apply a segment mask on a die of the wafer thereby forming a segment on the die;
• calculate a mean intensity of the segment with data including red, green, and blue colors using the bright field mode and with data including red, green, and blue colors using the dark field mode;
• compare defocus value against the mean intensities;
• determine a color combination that optimizes defocus sensitivity;
• determine sensitivity to defocus for each pixel in the segment;
• apply a threshold to the sensitivity for each pixel;
• and
• generate a second segment mask on the die based on pixels that are above the threshold to the sensitivity.