For the first time, a layer thickness sensor has been integrated into a vertical furnace for in situ sensing ofthe layer growth as well as forpostprocess control ofthe batch. Because ofits high accuracy and versatility, an in situ spectroscopic ellipsometer (SE) was selected. The adaption ofthe SE to the vertical furnace was performed with only minor modifications to the furnace geometry. The ellipsometer light beam is guided through the base plate into the furnace tube and directed onto the wafer by quartz glass prisms operated in total internal reflection (TIR) mode. This arrangement introduces an additional phase shift in the polarization state of the light which can be determined and subtracted from the measured phase shift. The ellipsometer setup is mechanically fixed to the boat loader. SE measurements therefore can be performed with the wafer boat out ofthe furnace tube as well as during the process run with the wafer boat inserted. The SE thus can be used for in situ end-point detection during layer growth and also for postprocess measurements on selected wafers ofthe batch during the unloading sequence. A realtime controller and a run-by-run coniroller integrated into the furnace controller utilize the layer thickness data measured in the in situ and in the postprocess mode, respectively, for inimediate and automated correction of the parameter settings during the actual process run and for the following process run. The advantages ofthis novel furnace control system such as a reduction intime needed for process optimization, the avoidance of monitor wafers and a better control in integrated multilayer processing can be beneficial for future thermal batchlminibatch processing.Key words: Vertical furnace; in situ ellipsometry; end-point detection
BACKGROUNDIn recent years, the prevailing attitude ofthe semiconductor industry towards the implementation of in situ measurement techniques has undergone a considerable change. Today, they are often regarded as the key not only to a better understanding ofthe process, but also to cost-effective manufacturing in the future. In spite of the increasing interest, the number of installations of in situ metrology (in situ in the sense ofmeasurements on the wafer itself) in manufacturing equipment is still very small because some prerequisits for a successful integration are not fulfilled in most cases.' Nearly no semiconductor manufacturing system provides the optical access for a ready-to-use integration of an in situ sensor and hardly any ofthe available in situ measurement tools has been sufficiently tested and qualified for use in a production environment. If, however, the manufacturing capability of the sensor cannot be demonstrated, the equipment supplier is not willing to integrate in situ sensors, because this could detrimentally affect the reliability ofthe system. A failure ofthe in situ sensor would cause a failure ofthe whole machine. In this work, an in situ spectroscopic ellipsometer was integrated into a vertical oxidation furnace. Oxidation and also CV...