Surface chemistry of the WF6-based chemical vapor deposition of tungsten
Abstract
This paper is an overview of work at the IBM Thomas J. Watson Research Center on chemical aspects of the WF6-based chemical vapor deposition of tungsten. The focus is on two deposition processes. In the first process, tungsten deposition occurs through the chemical reduction of WF6 by a silicon substrate. The thickness of the tungsten film thus grown is limited by the transport of silicon through the deposited film. In the second process, deposition occurs in a WF6-silane mixture by the following reactions: reduction of adsorbed WF6 by a surface layer of silicon to form tungsten, and the concurrent dehydrogenation of the adsorbed silane to replenish the silicon. This process permits the deposition of tungsten on any substrate, provided the initial reaction of the substrate with the WF6-silane mixture can provide a tungsten or silicon 'seed' layer to initiate the reaction cycle. Furthermore, the process is not limited by tungsten film thickness and hence permits the deposition of relatively thick films. Although surface selectivity is possible with regard to materials such as high-quality SiO2, on which such a seed layer cannot be formed, the selectivity is adversely affected by the presence of particulates.