ROMANS II A two-dimensional process simulator for modeling and simulation in the design of VLSI devices

Abstract

During the past decade considerable effort has been devoted to the development of two-dimensional (2D) device simulators while the development of two-dimensional process simulators, except for the past few years, has been almost nonexistent. To eliminate this lag in the development of 2D process simulators recent research has been directed entirely towards the development of simulators for predicting the thermal redistribution of impurities in bulk device structures; whereas, in the present paper a process simulator, ROMANS II, has been developed which is capable of simulating the redistribution of impurities in both bulk and SOS device structures. All the elements of two-dimensional process modeling which were used to assemble ROMANS II are presented. For example, Runge's approximate procedure for characterizing 2D distributions of ion implants in physical domains of actual device structures is discussed in great detail. Also discussed in great detail are the 2D empirical and phenomenological models used to specify oxide growths on silicon surfaces. A complete formulation of the governing nonlinear boundaryvalue problem for the redistribution of impurities in the physical domain of a device and the corresponding transformation of this problem to a fixed-time invariant rectangular domain by means of a translation-scaling transformation are presented. The numerical algorithm used to solve the nonlinear boundary-value problem in the fixed-time invariant rectangular domain is briefly discussed since a more detailed discussion is given elsewhere. Finally, ROMANS II is utilized to simulate the thermal redistribution of the field, channel, and source/drain implants which were used in fabricating a 1 μmn-channel enhancement mode device. The simulation was carried through the entire device fabrication schedule and the surface topography and corresponding equi-density contours for the net impurity concentration at the end of key process steps are given.