Calibration of chemically amplified resist models

Abstract

Chemically amplified (CA) resists are expected to provide the majority of the lithography capability for 0.25 micron feature sizes. The sensitivity of CA resists to processing conditions makes implementation of a resist system very dependent on the tool set (stepper, track, etc.) used. Modeling of these systems can be useful in optimizing a process for a particular tool set. However, the modeling parameters are also sensitive to the target tool set. Variations in dose calibration between different steppers, the differing temperature ramps found in contact and proximity bakes, and batch to batch variations between resist materials are examples why resist model parameters require calibration to each tool set. An ideal calibration procedure would entail in-situ measurement techniques at each processing step. The techniques would analytically determine chemical, physical, and kinetic quantities relevant to the resist system and processing conditions. Methods previously used have included interferometric measurement of photobleaching, FTIR measurement of the deprotection extent, in-situ DRM measurements, etc. Unfortunately, few if any fabs are equipped with the necessary in-situ techniques for complete model calibration.