Lithography process controllers and photoresist monitoring by signal response metrology (SRM)

摘要

For advanced lithography metrology, SCD (Scatterometry Critical Dimension) is a common metrology technique applied to control processes. SCD has the capability to report accurate data information such as CD (Critical Dimensions), photoresist SWA (Side Wall Angle) and photoresist HT (Height). The shape of photoresist correlates with inline process controllers, namely scanner focus and dose. However, SCD is a model-based metrology method. In order to decode the process controllers, it requires computation from a geometric model. Once the model extracts the resist shape information from the spectra, one needs further correlation of those geometric parameters with the process controllers for monitoring. Thus, information loss through multiple modeling is a major concern. Indeed, during data transformation, noise and model approximation can distort the signals, in other words, the critical parameters, focus and dose, may not be measured accurately. This study therefore seeks a methodology to monitor focus and dose with the least amount of information transformation. Signal Response Metrology is a new measurement technique that obviates the need for geometric modeling by directly correlating focus, dose or CD to the spectral response of a SCD-based metrology tool.