مدل شبیه سازی شیمیایی تقویت مقاومت در برابر CAMP 6

In this paper, a model for computer simulation of the exposure and the development of the CAMP6 chemically amplified resist (CAR) during electron beam lithography is proposed. The distribution of the absorbed electron energy in the exposed resist is determined using our Monte Carlo algorithm and computer programs. A wider resist de-protection region due to the diffusion of the exposure catalyst product (acid) during the post-exposure bake (PEB) is estimated. It lays a special emphasis upon the development process simulation. Experimentally obtained time dependent macroscopic characteristics of the development (contrast curves, the development rate vs. the exposure dose) are taken into account, aiming to avoid the need for further calibration. The proposed model demonstrates qualitative agreement with the development kinetics of the resist developed profiles for the studied CAR.

Nanometer scale device fabrication rules require tight control of the developed polymer resist profile. Process simulation is a key tool for optimization of the obtained lithography results. The approaches for computer simulation of images in positive CARs are based on the use of a set of values concerning the material properties, molecular structure, concentrations of used polymer compound, energy dissipation and acid generation models, volume shrinkage and polymer stress effects during the post-exposure bake, the reaction constants such as the acid diffusion ranges and kinetics characteristics of the decomposition (catalytic de-protection) mechanisms, the parameters of developer penetration, polymer molecules dissolution and removing processes, as well as surface and interface property changes of resist solubility, etc. For practical use, the strong academic models involving majority of the listed data are too complicated, slow and need many previously provided empirical data. Nevertheless, due to variations in control parameters and batch-to-batch variations between the resist and developer used, the process parameters require the calibration of each computer simulation set [1].

The latent image in the case of CARs is calculated using standard algorithms in existing simulation models of lithographic processes. In the present work, the radial distributions of the absorbed electron energy density in 200 nm and 1.7 μm thick CAMP6 on Si substrate are obtained at beam energy 30 keV by means of Monte Carlo simulation. These distributions stored as areas of numerical data are approximated by an analytical function, namely the combination of double Gaussian and exponential functions. The values of the parameters of the analytical function are calculated using an original Monte Carlo technique. In the case of thick CARs (more than 200 nm), the modification of the latent image due to the acid diffusion during PEB can be evaluated approximately. In the paper, a numerical modeling of the development process in the CAMP6 resist is performed taking into account the experimentally observed nonlinear development behavior and a delay time between the time of immersion in the developer and the time of the start of the resist development. For this purpose, experimentally obtained time dependent macroscopic characteristics of the development (the development rate vs. the exposure dose) are used. Profiles at various times of development of a single 500 nm line created in the CAMP6/Si are obtained. The generated central profile fragment is characterised by a rapid removal of the resist towards the bottom and then the profile is extended towards the periphery of the developing structure. The simulation results are in qualitative agreement with the presented experimental development kinetics of the resist profiles.