Opportunities for materials modeling in microelectronics: Programmed rate chemical vapor deposition

Two case studies are presented in order to highlight the status of materials modeling in semiconductor materials processing, as well as some opportunities in the area. Both case studies involve programmed rate chemical vapor deposition (PRCVD), which is a CVD process in which conditions are systematically changed during deposition in order to enhance either processing properties or resulting film properties. In the tungsten study, quantitative simulations, based on fundamental transport and reaction modeling and a continuum film representation, are used to guide experiments that demonstrate how PRCVD can provide significantly greater throughput than conventional, constant rate CVD (CRCVD). We start the deposition process at a much higher temperature, compared to a CRCVD process, then decrease the temperature during deposition. We achieve throughput increases of about a factor of three, with more improvement clearly obtainable. In addition to the increase in throughput, the properties of the PRCVD films are equal to, or superior to, CRCVD films. The aluminum PRCVD case study demonstrates some opportunities for materials modeling. The protocols used are based upon qualitative models of nucleation and film growth, as there are no simulators that predict microstructure and film properties. Nevertheless, we demonstrate that the PRCVD processes, designed using qualitative models, can yield films with better properties than CRCVD processes. PRCVD films can have higher nuclei densities, higher fractions of(lll) orientated Al, lower surface roughnesses, higher reflectivities, and resistivities closer to that of bulk aluminum. In general, PRCVD protocols provide degrees of freedom that can be used to improve processing or film properties. PRCVD may become much more important as films get thinner and interfaces become more important.