Leland Stanford Junior University

Sensys Instruments Corporation

B T Khuri-Yakub

Fred E Stanke

F Levent Degertekin

Fahrettin Levent Degertekin

Krishna Chandra Saraswat

Abdullah Atalar

Talat Fatima Hasan

Hung Pham

Sanjay Bhardwaj

Chung-Kao Hsieh

A micromachined capacitive ultrasonic transducer is used to generate and detect Rayleigh, Lamb, and bulk waves in a solid substrate. The transducer contains a substrate with a conductive back electrode, a support material on the substrate, a membrane supported above the substrate by the support material, and a conductive film on the membrane. The support material contains parallel edges defining elongated gaps over which the membrane is supported. Unsupported free regions of the membrane above the gaps are vibrated by applying an electrical signal between the conductive film and conductive back electrode, and stresses are coupled into the substrate at the attachment edges of the membrane. Acoustic modes of the substrate are excited by the stresses, and ultrasonic waves propagate in a direction perpendicular to the parallel edges. By properly choosing the membrane width, material, and thickness, the gap separation distance, and the support material height and thickness, a particular acoustic mode can be selected for a required operating frequency. The gaps may be separated by a distance equal to the wavelength or half-wavelength of the desired acoustic mode. Alternately, the gaps may be grouped, with each group separated by a wavelength or half-wavelength. The transducer can be used in many applications, including filtering and chemical sensing.

Micromachined rayleigh, lamb, and bulk wave capacitive ultrasonic transducers

An apparatus and method are disclosed for characterizing semiconductor wafers or other test objects that can support acoustic waves. Source and receiving transducers are configured in various arrangements to respectively excite and detect acoustic waves (e.g., Lamb waves) in a wafer to be characterized. Signals representing the detected waves are digitally processed and used to compute a measurement set correlated with the waves' velocity in the wafer. A characterization sensitivity is provided that describes how different wafer characteristics of interest vary with changes in the propagation of the acoustic waves. Using the characterization sensitivity and measurement sets computed at a setup time when all wafer characteristics are known and one or more process times when at least one of the characteristics is not known the perturbation in wafer characteristics between the setup and the process times can be determined. Characterization accuracy is improved by a wafer calibration procedure wherein measurement offsets from known conditions are determined for each wafer being characterized. An apparatus and technique are disclosed for correcting for anisotropy of acoustic wave velocity due to the direction of wave propagation with respect to a preferred crystallographic axis of the wafer. An apparatus and technique are also described for measuring wafer temperature using a single transducer whose temperature is related to the temperature of the wafer and, optionally, resonator structures. For characterization steps that occur when the wafer is chucked, a chuck structure is described that reduces the likelihood of the chuck interfering with the waves in the wafer.

Apparatus and method for characterizing semiconductor wafers during processing

A method is disclosed for selecting characteristics (i.e. thickness-frequency product, length and material) of leakage plates used in ultrasonic transducers that transfer ultrasonic energy via leakage to fluid media with low acoustic impedances. High leakage efficiency and wide bandwidths are achieved by exciting the low order antisymmetric Lamb wave mode (A0) at the selected frequency in the leakage plate. Various actuator configurations that can be used to excite and detect the A0 mode in the leakage plate are described. Some embodiments employ reflector structures to intercept the leaky waves and reform them into beams normal to the plane of the leakage plate.

Micromachined ultrasonic leaky wave air transducers

A system and method is disclosed for measuring thickness of at least one film on a substrate by propagating an acoustic wave through the film on a substrate such that echo waves are generated and received by a transducer. An output signal is generated and processed to give a thickness value. The thickness valve is obtained from the time lapse between the propagated wave and receipt of the echo wave; by the frequency domain of the echo wave; or the phase of the echo wave.

Thin film process monitoring techniques using acoustic waves

The present invention provides for an inspection system and method for detecting defects in test objects which includes means for generating expansion inducing energy focused upon the test object at a first location, such expansion being allowed to contract, thereby causing pressure wave within and on the surface of the test object. Such expansion inducing energy may be provided by, for example, a laser beam or ultrasonic energy. At a second location, the amplitudes and phases of the acoustic waves are detected and the resonant frequencies' quality factors are calculated and compared to predetermined quality factor data, such comparison providing information of whether the test object contains a defect. The inspection system and method also includes means for mounting the bearing ball for inspection.

Growing community of inventors

Palo Alto, CA, United States of America

B T Khuri-Yakub