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

Paper MS-WeM10
Reaction Sensing in Multicomponent CVD Processes using an Acoustic Sensor

Wednesday, October 27, 1999, 11:20 am, Room 611

Session: Metrology I
Presenter: L. Henn-Lecordier, University of Maryland
Authors: L. Henn-Lecordier, University of Maryland
G.W. Rubloff, University of Maryland
J.N. Kidder, Jr., University of Maryland
C. Gogol, Leybold Inficon Inc.
A. Wajid, Leybold Inficon Inc.
Correspondent: Click to Email
Downstream or in-reactor chemical sensing provides information about the extent of reaction in a chemical vapor deposition process. Prior approaches have employed mass spectrometry or optical techniques. Here we utilize for this purpose an acoustic sensor which measures the sound velocity in bicomponent or multicomponent gas mixtures in the viscous flow regime. This sensor, the recently introduced Leybold Inficon Composer@super TM@, has been employed primarily to measure and confirm bicomponent inlet mixtures from MOCVD bubbler sources for process reproducibility. Here we have explored its use in downstream locations, either after or at the reactor, where the influence of the CVD reaction can be monitored in the form of gas composition changes resulting from reactant depletion and/or product generation. For W CVD processes, the heavy WF@sub 6@ reactant mixed with H@sub 2@ or SiH@sub 4@ provides substantial molecular weight contrast, so that depletion of WF@sub 6@ is readily observed. To achieve sufficiently high pressures ( ~50-100 torr) for acoustic wave propagation in a viscous medium, sensing is carried out downstream of a mechanical pump. For H@sub 2@/WF@sub 6@ mixtures, depletion levels as small as 1% or less are detectable. This is sufficient for wafer state thickness metrology and monitoring of reactant utilization efficiency, suggesting a promising approach to reaction metrology. However, the corrosive nature of the reactant gasees normally necessitates a N@sub 2@ purge of the pump. With the molecular weight of typical H@sub 2@/WF@sub 6@ mixtures close to that of N@sub 2@, this degrades sensitivity to of order several %. A variety of other implementation issues will be discussed, along with an assessment of a variety of process applications.