Abstract: An apparatus for monitoring and detecting material deposited onto a substrate during a deposition process in a processing chamber includes a storage structure having a primary axis extending between respective first and second ends and an exterior lateral surface between the first and second ends extending about the primary axis. A plurality of monitor crystals are supported by the storage structure at spaced positions along said exterior lateral surface and in which a drive mechanism advances the storage structure rotatably and axially relative to the primary axis such that at least one monitor crystal is advanced or retracted relative to at least one measuring position. A retained crystal that is advanced to the measuring position can be electrically connected, using a brush contact or other mechanism, in order to excite the crystal using a resonance circuit.

Abstract: A sound velocity sensor is defined by a hermetic multi-chambered enclosure for containing flowing gases and mixtures of gases. The contained flowing gases are acoustically excited and the acoustic energy is measured over a fixed distance between a first sending end of the enclosure and a receiving end. The speed of sound of the gases are determined by comparing the energy transmitted through the flowing gases at various frequencies so as to precisely determine the resonant frequency of the gases flowing through the enclosure. In accordance with the present design, the chambers of the enclosure include internal transition shapes therebetween for optimizing the transmission of acoustic energy through the flowing gases and also enhancing one or more additional resonant modes at higher useful frequencies. The transition shapes used in connection with the sensor can be at least one of parabolic, hyperbolic, linear and exponential in nature.