FIRM: a new software tool for calibration of lithography simulation
In general, simulation requires a thorough understanding of the physics and/or chemistry of the processes. This should lend itself to models which can be used to establish simulation software. In addition, for a simulation to be successful, a calibration of the model is needed. A good model using bad parameters returns bad results. In lithography simulation there are settings of parameters which are well known. Others are less known and may be hard to obtain. A typical example are the development parameters, or parameters describing the reaction mechanism for chemically amplified resists. To support the user of simulation software in the process of finding proper input parameters, the new software package FIRM has been developed and will be presented in this paper, together with applications. FIRM uses models for the optical or e-beam lithography, the same as SOLID-C and SELID, and determines any set of coefficients from given experimental observations. From an initial set of coe efficients, it tries to fit calculations to observations. FIRM accepts various types of measurements, e. g. thickness tables of the resist or focus-exposure matrices. In addition, the user selects from a wide list of resist models the parameters to be refined. FIRM then tries to find correlation between the parameters and the differences between calculation and observation. In an iterative process best parameters are determined. The validity of the algorithm is verified against well known test cases. Next, applications of FIRM to several new chemically amplified resists for DUV will be presented using different types of experimental input.