The selective deposition of tungsten on silicon is used in the technology of integrated circuits for, for example, filling up via holes. Tungsten is thereby designationally deposited onto silicon surfaces that have been etched free. Structures of silicon oxide that surround the silicon surface should remain free of the deposition.
The problem arises in the selective deposition of tungsten that, in addition to the desired tungsten deposition on the silicon surface, a few undesired tungsten nuclei also grow on the masking structures of silicon oxide. The reason for this is the production of intermediary reaction products that arise in a low concentration during tungsten deposition onto silicon. Due to their high reactivity, these intermediary reaction products lead to the deposition of tungsten on SiO.sub.2, as well as, on the silicon surface.
It is known from C. M. McConica et al., Journal of the Electrochemical Society 133, pages 2542 through 2548 (1986) to avoid the deposition of tungsten nuclei on SiO.sub.2 surfaces in that the temperature or the pressure are reduced during the deposition. The production rate of the undesired reaction products and, thus, the number of tungsten nuclei on the masking structures of SiO.sub.2 are thus reduced. At the same time, however, the deposition rate of tungsten onto the silicon surface is also reduced. Significantly longer process times must therefore be accepted.
The process parameters of pressure, temperature as well as through-flow rates of the process gases, over and above this, are dependent on the specific geometry of the reactor wherein the deposition is undertaken from the vapor phase. These process parameters must be optimized on the basis of tedious trials such that the selectivity of the tungsten deposition is adequate and that, at the same time, the tungsten deposition rate on the silicon surface is not too low.
USPTO Backgrounds
USPTO Backgrounds