The gas phase reaction products during tungsten (W) atomic layer deposition (ALD) using WF6 and Si2H6 were studied using quadrupole mass spectrometry. The gas phase reactions products were different for the WF6 and Si2H6 reactions. No surface reactions were observed for WF6 exposures at room temperature. The WF6 reaction produced H-2, HF and SiF4 at a reaction temperature of 473 K. Mass spectrometer cracking patterns established that SiF4 is the silicon reaction product instead of SiHF3. Auger electron spectroscopy (AES) measurements confirmed that the H-2, HF and SiF4 gas phase reaction products during WF6 exposure coincided with the loss of silicon surface species. The Si2H6 reaction showed two separate reaction channels depending on reaction temperature. At room temperature, a temperature insensitive reaction produced SiHF3 and H-2 reaction products. A second reaction produced H-2 as the reaction product at 473 K. AES measurements confirmed that the SiHF3 and H-2 reaction products during Si2H6 exposure were concurrent with the gain of silicon surface species. Together with previous FTIR spectroscopy and AES studies, these mass spectrometer results help to identify the stoichiometry of the surface reactions during the sequential WF6 and Si2H6 exposures that define W ALD. (C) 2004 American Vacuum Society.