The rate equation for the low pressure chemical vapor deposition (LPCVD) of tungsten from tungsten hexafluoride on (100) silicon was experimentally determined in a laboratory scale single wafer vacuum reactor. The reactor was designed and built as a high vacuum stainless steel system with a minimum of heat and mass transfer limitations. The tungsten film deposition is initiated by the silicon reduction of tungsten hexafluoride. In the absence of hydrogen, the silicon reduction results in a 10-40 nm self-limiting tungsten deposit, with the thickness dependent upon the native oxide layer prior to deposition. The hydrogen reduction of tungsten hexafluoride is one-half order in hydrogen, zero order in tungsten hexa-1 fluoride, and has an activation energy of 73,000 J mol-at temperatures from 561 to 683 K, and pressures from 0.067-1.3 kPa 4 1 05 8 1 0 (0.5 to 10 torr). The pre-exponential factor was found to be 6.8 • 10 nms Pa " (4.7 • 10 A rain-torr-~). A mechanism is proposed and two possible rate limiting steps yield rate expressions consistent with the observed kinetics. The rate limiting step could be either the addition of adsorbed monatomic hydrogen to adsorbed partially fluorinated tungsten or hydrogen fluoride desorption. In the absence of hydrogen the deposition was perfectly selective over all ranges of temperature and pressure. During the hydrogen reduction selectivity was lost in less than 600s at temperatures above 653 K (380~ Due to the observation that loss of selectivity is an activated process, it is concluded that deposition of tungsten on oxide is initiated by a chemical reaction rather than by random surface defects. Due to the high vacuum procedures, films were made with tungsten resistivities of 6 ~/cm, approaching the ideal 5.5 ~/cm for bulk tungsten.For very large scale integration (VLSI), a low resistance metal film is needed due to performance limitations of aluminum and polysilicon (1). As a result of these limitations, tungsten has been st,adied and successfully used for multilevel metalization by several facilities (2,3,4)