MATERIAL PROPERTIES OF LOW-PRESSURE CHEMICAL-VAPOR-DEPOSITED SILICON-NITRIDE FOR MODELING AND CALIBRATING THE SIMULATION OF ADVANCED ISOLATION STRUCTURES

The increasing cost and complexity of semiconductor process developmen t has lead to the widespread use of multidimensional semiconductor pro cess simulators. The success of a program like SUPREM-IV is primarily due to the fact that it is based on physical models, rather than empir ical equations. This is in contrast to the first generation of process simulators, which calculated impurity profiles and oxide thickness, i n one dimension based on semiempirical approaches. SUPREM-IV incorpora tes two-dimensional coupled stress-dependent oxidation and impurity di ffusion, which allows the accurate simulations of state-of-the-art int egrated processes, provided that accurate model parameter sets are ava ilable. In this article we present an improved calibration methodology for simulation of advanced isolation technologies using SUPREM-IV, ba sed on the experimental determination of the material properties of si licon nitride. The proposed strategy is applicable not only to SUPREM- IV but to any numerical simulator that uses the stress-dependent oxida tion models to calculate oxide growth. In order to simulate experiment al isolation boundary shapes, the oxidation models in SUPREM-IV must b e calibrated. This requires a set of five fitting parameters, i.e., th e material viscosities and activation volumes for stress-dependent dif fusion, reaction rate, and critical stress. These parameters form a qu intuplet but are not unique. Multiplying the viscosity values and divi ding the activation volumes by a constant will yield exactly the same isolation structure boundary shape. The calculated stresses in the sub strate however do not remain constant when different quintuplets are u sed. This has serious implications since isolation structures require the stress levels in the silicon substrate to remain well below the yi eld stress of silicon. If a nonoptimal parameter set is used, incorrec t designs will result. Based on the experimental extraction of the sil icon nitride viscosity by measuring the relative film thickness shrink age rate as a function of temperature, a scaled parameter set has been derived. SUPREM-IV simulations predict identical boundary shapes but the simulated stress levels are different from the values obtained usi ng the default parameter set. In order to validate the stress simulati ons, a comparison with experimental stress values measured by micro-Ra man spectroscopy has been carried out. It has been found that the quin tuplet based on the experimental nitride viscosity values yields the b est agreement with the experimental stress data, supporting the accura cy of the new model parameter set. (C) 1995 American Institute of Phys ics.