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)

A mathematical model has been developed for predicting radius profiles in cylindrical pores during tungsten deposition from silane, tungsten hexafluoride, and hydrogen. The model is based on an unsteady-state mass balance over a differential element of the pore, from which a system of partial differential equations has been derived. The conformality of deposition is measured by the parameter step coverage.Step coverage is found to be highly sensitive to deposition rate, decreasing with increasing temperature, silane and hydrogen reactant concentration, and aspect ratio of the pores. However, it is found to increase with increasing tungsten hexafluoride concentration even though the deposition rate is zero order in this variable. Experimentally derived step coverage measurements were also compared to simulations run under comparable reactor conditions. The agreement between the experimental and simulated results is good.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.192.114.19 Downloaded on 2015-06-28 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.192.114.19 Downloaded on 2015-06-28 to IP

The rate of tungsten nucleation and island growth is characterized on thermal silicon dioxide in the absence of exposed silicon surfaces in a stainless steel cold wall high vacuum differential reactor. Tungsten hexafluoride (0.05–2.50 torr) was found to react with undoped thermal silicon dioxide in the presence of adjacent tungsten areas for temperatures ranging from 240° to 380°C and reaction times from 1.10 to 2h. The silicon dioxide film did not change thickness, but electron spectroscopy for chemical analysis (ESCA) revealed a surface covering of tungsten, oxygen, fluorine, and silicon. Tungsten nucleates rapidly on silicon dioxide in the presence of reactive surfaces and the hydrogen reduction reaction of tungsten hexafluoride. The observed nucleation is autocatalytic and initiated by an intermediate diffusing from areas of tungsten deposition. For a gas flow rate of 160 sccm, tungsten hexafluoride pressure of 0.05 torr, a hydrogen pressure of 0.70 torr, and temperatures ranging from 268° to 348°C, the activation energy for initiation of nucleation is 23–25 kcal mol−1.

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Tungsten hexafluoride adsorbs on tungsten surfaces and reacts to form WFs, which desorbs at about 250 K. At higher temperatures, WEe desorbs. Tungsten fluoride desorption was not affected by co-adsorption of Hz or H20, so production of WF~ appears to be an unavoidable feature of tungsten chemical vapor deposition processes based on WF~. The initial sticking coefficient for WF 6 on tungsten at 240 K is about 10 -~.