Methods, systems, and apparatus for measuring a gap between a support surface for a substrate and an opposing upper surface of a processing chamber

A method for calibrating a robot blade in a processing chamber having a support surface for a substrate, the method comprising:

• supporting a sensor substrate with the robot blade at a handoff position spaced from the support surface, the sensor substrate having an image capture device at a center of the sensor substrate;
• capturing an image that includes a portion of the support surface having an alignment feature, and a calibration feature of the image capture device;
• determining from the captured image whether there is a misalignment between the alignment feature and the calibration feature;
• and
• if there is a misalignment, calibrating the handoff position of the robot blade based on an amount of the misalignment.

A sensor substrate, comprising:

• a body having a first side and a second side opposite the first side;
• a first sensor on the first side and configured for measuring distance;
• and
• a second sensor on the second side and configured for measuring distance;
• and
• an image capture device located at a center of the sensor substrate.