Thickness measurement of substrate using color metrology

A computer program product for obtaining a measurement representative of a thickness of a layer on a substrate, the computer program product tangibly embodied in a non-transitory computer readable medium, comprising instructions for causing a processor to:

• receive a first color image of the substrate and a second color image of the substrate from one or more cameras;
• store a function that provides a value representative of a thickness as a function of a position on a predetermined path in a coordinate space of at least four dimensions including a first color channel and a second color channel from the first color image and a third color channel and a fourth color channel from the second color image;
• for a pixel of the first color image and a corresponding pixel in the second color image, determine a coordinate in the coordinate space from color data in the first color image for the pixel and the color data in the second color image for the corresponding pixel;
• determine a position of a point on the predetermined path that is closest to the coordinate;
• and
• calculate a value representative of a thickness of a layer on the substrate from the function and the position of the point on the predetermined path.

A method of obtaining a measurement representative of a thickness of a layer on a substrate, comprising:

• positioning a substrate for integrated circuit fabrication in view of a color camera;
• generating a first color image of the substrate and a second color image of the substrate using one or more color cameras, the first color image generated with light impinging the substrate at a first angle of incidence and the second color image generated with light impinging the substrate at a different second angle of incidence;
• storing a function that provides a value representative of a thickness as a function of a position on a predetermined path in a coordinate space of at least four dimensions including a first color channel and a second color channel from the first color image and a third color channel and a fourth color channel from the second color image;
• for a pixel of the first color image and a corresponding pixel in the second color image, determining a coordinate in the coordinate space from color data in the first color image for the pixel and the color data in the second color image for the corresponding pixel;
• determining a position of a point on the predetermined path that is closest to the coordinate;
• and
• calculating a value representative of a thickness of a layer on the substrate from the function and the position of the point on the predetermined path.

A polishing system, comprising:

• a polishing station including a platen to support a polishing pad;
• a support to hold a substrate;
• an in-line metrology station to measure the substrate before or after polishing of a surface of the substrate in the polishing station, the in-line metrology station including
• one or more elongated white light sources each having a longitudinal axis and configured to direct light toward the substrate at a non-zero incidence angle to form an illuminated region on the substrate that extends along a first axis during scanning of the substrate,
• a first color line-scan camera having detector elements arranged to receive light reflected from the substrate that impinged the substrate at a first angle of incidence and form an image portion that extends along the first axis during scanning of the substrate,
• a second color line-scan camera having detector elements arranged to receive light reflected from the substrate that impinged the substrate at a different, second angle of incidence and form a second image portion that extends along the first axis during scanning of the substrate,
• a frame supporting the one or more light sources, the first color line-scan camera and the second color line-scan camera, and
• a motor to cause relative motion between the frame and the support along a second axis perpendicular to the first axis to cause the one or more light sources, the first color line-scan camera and the second color line-scan camera to scan across the substrate;
• and
• a controller configured to receive color data from the first color line-scan camera and the second color line-scan camera, to generate a first 2-dimensional color image from color data from the first color line-scan camera and generate a second 2-dimensional color image from color data from the second color line-scan camera, and to control polishing at the polishing station based on the first 2-dimensional color image and the second 2-dimensional color image.