A Study on the Structure Collapse Mechanisms for High Aspect Ratio Structures with Application to Clean Processing

Introduction The fabrication of state of the art semiconductor devices includes the generation of high aspect ratio structures, i.e. the vertical dimension exceeds the lateral dimension multiple times. Such geometries are found e.g. in Shallow Trench Insulation (STI), Capacitor over Bitline (CoB) and gate stacks. In the final device, the gaps between the structures are filled with e.g. dielectric materials for insulation and the filler acts also as a mechanical support. During production, however, there are several process steps where such support has not been established yet. Consequently, these structures may be damaged if the lateral mechanical stability is exceeded during processing. A typical example is the wet cleaning step which can produce such forces when ill adjusted. The most extreme forces during a wet process are introduced by physical force assisted cleaning (Megasonic, Aerosol and Shock wave systems) and capillary force in the subsequent drying step. A good understanding of the mechanical stability of nanostructures is therefore essential to tune force balance between particle removal and damage during the cleaning process or improve the stability of the structures. Mechanical fracture tests were performed with an AFM on polysilicon line structures to gain experimental data about the stability of such nanostructures. In this paper a comparison between the simulation of a lateral load on a beam and an experimental force on a gate stack is presented. Therefore the lateral forces on three line widths (nominally 25 nm, 40 nm and 65 nm) have been studied.