Using cumulative heat amount data to qualify hot plate used for post-exposure baking

A method, comprising:

• placing a plurality of heat sensors on a test wafer;
• heating up the test wafer that is placed over a heating plate from an initial temperature to a predetermined temperature, wherein the predetermined temperature is measured when a temperature of the test wafer reaches a static level during the heating up, wherein the heating plate comprises a plurality of zones, and heat of each zone of the plurality of zones is configured to be independently applied, and one of the plurality of heat sensors is placed at interface between two adjacent zones of the plurality of zones;
• for each of the plurality of heat sensors, after the test wafer is heated up to have a predefined threshold temperature Tth, starting measuring a plurality of temperatures at a plurality of predefined intervals for a predefined period of time and summing the measured plurality of temperatures as a respective cumulative amount of heat delivered to the test wafer as the test wafer is being heated up, wherein the predefined threshold temperature Tth is a function of the predetermined temperature and is greater than the initial temperature;
• for each zone of the plurality of zones, averaging cumulative amounts associated with corresponding heat sensors;
• and
• determining, based on averaged cumulative amounts associated with the plurality of zones, whether the heating plate should be qualified for being used in actual semiconductor fabrication.

A method, comprising:

• placing a plurality of heat sensors on a test wafer;
• placing the test wafer over a hot plate configured to generate heat, wherein the hot plate comprises a plurality of zones, and heat of each zone of the plurality of zones is configured to be independently applied, wherein at least one of the plurality of heat sensors is placed directly over an interface between two adjacent zones of the plurality of zones;
• measuring, using the plurality of heat sensors, first plurality of cumulative amounts of heat, wherein each heat sensor of the plurality of heat sensors is configured to measure a corresponding first cumulative amount of heat experienced by a corresponding spot of the test wafer during a thermal process performed by the hot plate;
• calculating a corresponding second cumulative amount of heat experienced by each of the plurality of zones, wherein the corresponding second cumulative amount of heat experienced is a function of the corresponding first cumulative amounts of heat associated with heat sensors of the plurality of heat sensors placed directly over that zone;
• determining whether a range variation of a plurality of the second cumulative amount of heat experienced by the plurality of zones is less than a predefined threshold;
• and
• in response to a determination that the range variation is less than the predefined threshold, deeming the hot plate as being qualified to perform a post-exposure baking (PEB) process in semiconductor lithography.