Interferometer for determining characteristics of an object surface, including processing and calibration

An apparatus comprising:

• an interferometer configured to direct test light to a test surface and subsequently combine it with reference light to form an interference pattern, the test and reference light being derived from a common source;
• an electronic detector;
• one or more optics configured to direct at least a portion of the combined light to the detector so that different regions of the detector correspond to different illumination angles of the test surface by the test light;
• and
• an electronic processor coupled to the detector, wherein the electronic processor is configured to process information measured by the detector to determine information about a test object having the test surface;
• wherein the test object comprises one or more layers on a substrate and the information about the test object comprises information about the layers.

An interferometry method, comprising:

• directing test light to a test surface over a range of illumination angles;
• subsequently combining the test light with reference light to form an interference pattern, wherein the test and reference light are derived from a common source;
• directing at least a portion of the combined light to a multi-element detector so that different elements of the detector correspond to different illumination angles of the test surface by the test light;
• and
• determining calibration information based on interference signals measured by the detector elements.

An interferometry method comprising;

• directing test light to a surface of a test object over a range of illumination angles, wherein the test object comprises the test object comprises one or more layers;
• subsequently combining the test light with reference light to form an interference pattern, wherein the test and reference light are derived from a common source;
• directing at least a portion of the combined light to a multi-element detector so that different elements of the detector correspond to different illumination angles of the test surface by the test light;
• and
• determining information based on interference signals measured by the detector elements, wherein the information about the test object comprises information about the layers.