Method for determining a height map and interferometric system for the same

An interferometric system for determining a height map of a sample surface including an edge, wherein the interferometric system includes a light source, an optical sensor and a processor, wherein the processor is configured for:

• obtaining a phase map of the sample surface based on a measurement of the optical sensor of light having an associated wavelength reflected on the sample surface;
• obtaining a pre-height map of the sample surface based on a measurement of the optical sensor of light reflected on the sample surface;
• identifying a first area of the sample surface and a second area of the sample surface, wherein the first area and the second area are separated by the edge;
• choosing a first location adjacent to the edge in the first area and a second location adjacent to the edge in the second area, wherein the first location is opposite the second location;
• determining a pre-height difference between the first location and the second location based on the pre-height map, and calculating a phase height difference between the first location and the second location based on the phase map and the associated wavelength;
• determining a zero phase edge height of the edge by calculating the difference between the pre-height difference and the phase height difference;
• determining a height correction by determining a difference between the zero phase edge height and an integer multiple of half the associated wavelength;
• and
• determining the height map by correcting the heights in the first area and the second area in the pre-height map with the height correction.

A non-transitory computer-readable medium storing an executable set of instructions for determining a height map of a sample surface including an edge, wherein when executed by a computer processor of an interferometric system for determining the height of the sample surface including an edge, the set of instructions causes the computer processor to execute operations comprising:

• obtaining a phase map of the sample surface by determining a phase of a light reflected on the sample surface having an associated wavelength;
• obtaining a pre-height map of the sample surface;
• identifying a first area of the sample surface and a second area of the sample surface, wherein the first area and the second area are separated by the edge;
• choosing a first location adjacent to the edge in the first area and a second location adjacent to the edge in the second area, wherein the first location is opposite the second location;
• determining a pre-height difference between the first location and the second location based on the pre-height map, and calculating a phase height difference between the first location and the second location based on the phase map and the associated wavelength;
• determining a zero phase edge height of the edge by calculating the difference between the pre-height difference and the phase height difference;
• determining a height correction by determining a difference between the zero phase edge height and an integer multiple of half the associated wavelength;
• and
• determining the height map by correcting the relative heights in the first area and the second area in the pre-height map with the height correction.