Monitoring witness structures for temperature control in RTP systems
View Patent ↗Temperature control in an RTP system can be improved by consideration of one or more witness structures different from the wafer (or other semiconductor object) being processed. For example, power coupling between the RTP heating system and witness structure can be used to adjust one or more control parameters, such as model definitions, that are used by the RTP system to control wafer heating. As another example, a stored trajectory of a desired witness structure temperature or other property can be used as a basis for control during a processing cycle. Thus, the witness structure may be controlled “closed-loop” while the wafer is heated “open-loop.” As a further example, a heat flux between the RTP heating system and witness structure can be used to determine radiant energy from the heating system that is incident on the witness structure. One or more control actions can be taken based on this incident energy.
1. A method for thermally processing an object in a thermal processing chamber, the method comprising:
placing an object to be processed in a thermal processing chamber containing a witness structure, the thermal processing chamber being in association with a measurement device, wherein the measurement device has previously monitored a property of the witness structure over a time interval to produce stored data, and wherein the measurement device comprises either a light pipe embedded in the body of the witness structure or a pyrometer;
performing a processing cycle, including directing radiant energy into the chamber via a heating system, wherein the heating system is controllable so as to direct energy to a plurality of zones of the object to be processed; and
during the process cycle:
observing a property of the witness structure using the measurement device,
comparing the property of the witness structure observed to the stored data produced by the measurement device over the time interval;
deducing the thermal response of the witness structure based on the comparison of the property of the witness structure observed to the stored data produced by the measurement device over the time interval,
determining the amount of radiant energy incident on the witness structure based on the thermal response of the witness structure,
making a control decision based on the amount of radiant energy determined to be incident on the witness structure, and
changing the amount of radiant energy directed into the chamber and applied to a zone of the object relative to another zone of the object to thereby adjust a temperature distribution across the object if warranted by the control decision.
2. The method set forth in claim 1 , wherein changing the radiant energy comprises changing the total amount of radiant energy directed into the chamber by the heating system.
3. The method set forth in claim 1 , wherein the control decision is made without regard to determining the amount of radiant energy determined to be incident on the object to be processed.