AVS 46th International Symposium
    Manufacturing Science and Technology Group Wednesday Sessions
       Session MS-WeA

Paper MS-WeA3
Chemical Process Sensing using Mass Spectrometry in Multicomponent Reaction Systems

Wednesday, October 27, 1999, 2:40 pm, Room 611

Session: Metrology II
Presenter: Y. Xu, University of Maryland
Authors: Y. Xu, University of Maryland
T. Gougousi, University of Maryland
N. Gupta, University of Maryland
J.N. Kidder, Jr., University of Maryland
G.W. Rubloff, University of Maryland
Correspondent: Click to Email
A significant number of CVD applications in VLSI manufacturing, such as CVD of W, TiN, SiO@sub 2@, Cu, and more complex high K materials, involve multicomponent reactant mixtures. We have investigated experimentally W CVD processes from H@sub 2@/WF@sub 6@ mixtures in attempts to develop mass spectrometry based thickness and rate metrology approaches. This direction poses a variety of challenges, both fundamental and practical. First, the choice of reactant stoichiometry is dictated by the mechanistics of the application, and typically an overabundance of one reactant is required, so that transport of the other is at least in part rate-limiting. This determines which species is suitable for measurement of reactant depletion for deposition metrology. For example, in SiO@sub 2@ CVD from SiH@sub 4@/N@sub 2@O, the N@sub 2@O must be in large excess to assure fully oxidized, high quality material, while in W CVD, low H@sub 2@ to WF@sub 6@ ratio (usually 4) is required to achieve good conformality in via filling. Second, gaseous species may undergo substantial wall reactions, which in turn depend on previous process history (e.g., in W CVD, HF and WF@sub 6@ condense on walls and subsequently desorb slowly). Third, the mass spectrometer ionizer provides a second reaction region (in addition to the wafer), contributing to the depletion of the reactants and occasionally generating the same products as the CVD reaction itself (HF in W CVD from H@sub 2@/WF@sub 6@ precursors). Fourth, the combination of wall adsorption/desorption and sensor reactions can lead to another extraneous source of products. In the H@sub 2@/WF@sub 6@ system sustained H@sub 2@ flow after the WF@sub 6@ flow is terminated leads to sensor generated HF utilizing the WF@sub 6@ desorbing from the walls. We illustrate these phenomena through both experimental and modeling results, and we assess key aspects of the general approach for multicomponent CVD systems.