Interferometry method and system including spectral decomposition

A method, comprising:

• directing measurement light to reflect from a measurement surface, where the measurement light simultaneously illuminates multiple locations of the measurement surface;
• combining the reflected measurement light with reference light, wherein the measurement light and reference light are derived from a common source;
• spectrally dispersing the combined light onto a multi-element detector to detect a spatially-varying intensity pattern;
• performing a spatial-frequency transform of the spatially-varying intensity pattern;
• determining spatial information about the multiple locations of the measurement surface based on the spatial-frequency transform;
• and
• outputting the spatial information.

A system, comprising:

• a light source being configured to produce input light during operation of the system;
• a multi-element detector;
• a dispersive optical element;
• an interferometer configured to derive measurement light and reference light from the input light, simultaneously illuminate multiple locations of a measurement surface with the measurement light, combine the reference light with the measurement light reflected the measurement surface, and direct the combined light to the dispersive optical element which spectrally disperses the combined light onto the multi-element detector to provide a spatially-varying intensity pattern on the detector elements, wherein the input light has a finite coherence length and the interferometer introduces an optical path length difference between the measurement light and the reference light that is greater than the coherence length of the input light;
• and
• a computer in communication with the detector, the computer being programmed to determine spatial information about the multiple locations of the measurement surface based on the spatially-varying intensity pattern.

A method, comprising:

• directing measurement light to reflect from a measurement surface;
• combining the reflected measurement light with reference light, wherein the measurement light and reference light are derived from a common source, and there is a non-zero optical path length difference between the measurement light and reference light that is greater than a coherence length of the measurement light;
• spectrally dispersing the combined light onto a multi-element detector to detect a spatially-varying intensity pattern;
• determining spatial information about the measurement surface based on the spatially-varying intensity pattern;
• and
• outputting the spatial information,
• wherein the spatial information is information about a line of points on the measurement surface where measurement light reflected from the line of points is directed to a corresponding line of elements of the multi-element detector extending along a first dimension of the detector, the measurement light reflected from each point on the line of points is spectrally dispersed across a corresponding line of elements of the multi-element detector extending along a second dimension of the detector, determining the spatial information comprises performing a spatial-frequency transform for each point by transforming an intensity profile from the corresponding line of elements of the multi-element detector to produce an interference signal, the interference signal for each point including information about the optical path length difference between measurement light reflected from the point and the reference light combined with the measurement light reflected from the point, the spatial information is determined by analyzing the interference signal for each point to determine surface height variations along the line of points on the measurement surface, the measurement surface is on a measurement object comprising a thin film on a substrate, and analyzing the interference signal for each point on the line comprises selecting a subset of the interference signal corresponding to the top surface of the thin film and analyzing the subset to determine a relative surface height for each point of the top surface of the thin film along the line.

A method, comprising:

• directing measurement light to reflect from a measurement surface, wherein a path of the measurement light is characterized by chief rays which are incident on the measurement surface at a non-zero angle of incidence;
• combining the reflected measurement light with reference light, wherein the measurement light and reference light are derived from a common source, and there is a non-zero optical path length difference between the measurement light and reference light that is greater than a coherence length of the measurement light;
• spectrally dispersing the combined light onto a multi-element detector to detect a spatially-varying intensity pattern;
• determining spatial information about the measurement surface based on the spatially-varying intensity pattern;
• and
• outputting the spatial information.

A method, comprising:

• directing measurement light to reflect from a measurement surface;
• combining the reflected measurement light with reference light, wherein the measurement light and reference light are derived from a common source, and there is a non-zero optical path length difference between the measurement light and reference light that is greater than a coherence length of the measurement light;
• spectrally dispersing the combined light onto a multi-element detector to detect a spatially-varying intensity pattern;
• determining spatial information about multiple locations of the measurement surface based on the spatially-varying intensity pattern;
• and
• outputting the spatial information,
• wherein the multiple locations are a line of points on the measurement surface where measurement light reflected from the line of points is directed to a corresponding line of elements of the multi-element detector extending along a first dimension of the detector,
• the measurement light reflected from each point on the line of points is spectrally dispersed across a corresponding line of elements of the multi-element detector extending along a second dimension of the detector,
• determining the spatial information comprises performing a spatial-frequency transform for each point by transforming an intensity profile from the corresponding line of elements of the multi-element detector to produce an interference signal, the interference signal for each point including information about the optical path length difference between measurement light reflected from the point and the reference light combined with the measurement light reflected from the point and the spatial information is determined by analyzing the interference signal for each point to determine surface height variations along the line of points on the measurement surface, and
• wherein the measurement surface is on a measurement object comprising a thin film on a substrate, and analyzing the interference signal for each point on the line comprises selecting a subset of the interference signal corresponding to the top surface of the thin film and analyzing the subset to determine a relative surface height for each point of the top surface of the thin film along the line.

A system, comprising:

• a light source being configured to produce input light during operation of the system;
• a multi-element detector;
• a dispersive optical element;
• an interferometer configured to derive measurement light and reference light from the input light, illuminate a section of a measurement surface with the measurement light, combine the reference light with the measurement light reflected the measurement surface, and direct the combined light to the dispersive optical element which spectrally disperses the combined light onto the multi-element detector to provide a spatially-varying intensity pattern on the detector elements, wherein the input light has a finite coherence length and the interferometer introduces an optical path length difference between the measurement light and the reference light that is greater than the coherence length of the input light;
• a computer in communication with the detector, the computer being programmed to determine spatial information about multiple locations of the measurement surface based on the spatially-varying intensity pattern,
• wherein the interferometer is configured to direct the measurement light to the measurement surface at a non-normal angle of incidence, and
• wherein the system further comprises a photolithography apparatus arranged to image a pattern onto the measurement surface.