Reaction Steps and Mechanism for Chemical Vapor Deposition of Tungsten

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The PIs propose a comprehensive research program to study the chemical vapor deposition (CVD) reaction between tungsten hexafluoride (WF6) and silicon/silicon dioxide surfaces. Understanding of this reaction could help semiconductor processing companies in the manufacture of very large scale integration (VLSI), ultra large scale integration (ULSI), and wafer scale integration (WSI) chips. Tungsten has potential usage because of (1) its resilience to electromagnetism, (2) low resistivity, (3) high melting point, and (4) a thermal coefficient of expansion that is close to silicon. The selective nature of tungsten along with its electrical and physical properties makes it suitable for many VLSI large circuit applications because selectively-deposited tungsten films provide highly reliable, low resistance, and low cost contact barriers for shallow junctions. As the scale of devices decreases, tungsten's potential use will increase as an interconnect for multilevel metallization. This will be essential for advances in ULSI and WSI technology. CVD of tungsten has the advantages of low temperature processing, selectivity, radiation-damage-free deposition and conformal coverage. To obtain a better understanding of the gas-solid reaction between silicon and WF6, the PIs plan to use a Auger electron spectroscopy (AES), temperature- programmed reaction (TPR), and high resolution electron energy loss spectroscopy (HREELS) in ultrahigh vacuum. AES permits analysis of a surface to determine its elemental composition. TPR gives the rate that each gaseous product forms during reaction. HREELS determines chemical bonds present in adsorbed species. This combination of measurements of gaseous products, adsorbed species, and elemental surface composition should provide a complete picture of the reaction process.