Extreme ultraviolet source temperature monitoring using confocal sensor

A characterization system comprising:

• an illumination sub-system, wherein the illumination sub-system comprises:
• a rotatable drum at least partially coated with plasma-forming target material;
• a confocal sensor assembly including a sensor head and a light source for measuring a surface of the rotatable drum;
• and
• a laser source configured to direct pulsed illumination to a material-coated portion of the rotatable drum for exciting the plasma-forming target material and emitting broadband light as the rotatable drum is rotated in an angular direction and translated in an axial direction;
• one or more collection optics configured to collect illumination emanated from a plasma generated in response to an excitation of the plasma-forming target material;
• a set of illuminator optics configured to direct the illumination from the one or more collection optics to one or more samples disposed on a stage;
• a detector;
• and
• a set of projection optics configured to receive the illumination from the surface of the one or more samples and direct the illumination from the one or more samples to the detector;
• and
• a controller comprising one or more processors configured to execute program instructions stored in memory, wherein the program instructions are configured to cause the one or more processors to:
• direct the confocal sensor assembly to transmit a confocal optical signal to the rotatable drum;
• record a calibration measurement of a distance from the confocal sensor assembly to the rotatable drum at a first temperature;
• direct a cryogenic cooling sub-system to cryogenically cool the rotatable drum;
• convert one or more distance measurements to one or more temperature values representative of a temperature of a material of the rotatable drum during the cryogenic cooling of the rotatable drum;
• and
• determine whether a target process condition temperature of the rotatable drum is achieved based on the converted one or more temperature values.

A method comprising:

• directing a confocal sensor assembly to transmit a confocal optical signal to a rotatable drum;
• recording a calibration measurement of a distance from the confocal sensor assembly to the rotatable drum at a first temperature;
• directing a cryogenic cooling sub-system to cryogenically cool the rotatable drum;
• recording one or more distance measurements from a sensor head to the rotatable drum during the cryogenic cooling of the rotatable drum;
• converting the one or more distance measurements to one or more temperature values representative of a temperature of a material of the rotatable drum during the cryogenic cooling of the rotatable drum;
• and
• determining whether a target process condition temperature of the rotatable drum is achieved based on the converted one or more temperature values.