Apparatus and method for characterizing semiconductor wafers during processing
First Claim
1. An improved apparatus for characterizing a substrate, comprising:
- a plurality of pin transducers, each having a probe end configured to couple acoustic energy between the pin transducer and the substrate and a transducer end configured to convert the acoustic energy in the pin transducer to external electrical signals and vice-versa;
a first set of the pin transducers including a transmitting pin configured so that the transducer end of the transmitting pin when coupled to a signal pulse of a predetermined character, excites pin acoustic waves in the pin that the probe end of the transmitting pin couples into the substrate as substrate acoustic waves;
a second set of the pin transducers including one or more receiving pins configured so that the transducer end of a respective receiving pin produces a transmitted electrical signal representing the acoustic energy in a transmitted wave coupled from the substrate to the respective pin by that pin'"'"'s probe end in response to arrival at that probe end of the substrate acoustic waves; and
acquisition and processing modules configured to perform a characterization measurement wherein;
the acquisition module is configured to (1) receive the transmitted electrical signal during a measuring period following the signal pulse; and
(2) digitize the received transmitted signals; and
the processing module is configured to (3) digitally compute from the digitized, received transmitted signals a respective measurement set correlated to spectral frequency components of the substrate acoustic waves.
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Abstract
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.
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Citations
22 Claims
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1. An improved apparatus for characterizing a substrate, comprising:
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a plurality of pin transducers, each having a probe end configured to couple acoustic energy between the pin transducer and the substrate and a transducer end configured to convert the acoustic energy in the pin transducer to external electrical signals and vice-versa; a first set of the pin transducers including a transmitting pin configured so that the transducer end of the transmitting pin when coupled to a signal pulse of a predetermined character, excites pin acoustic waves in the pin that the probe end of the transmitting pin couples into the substrate as substrate acoustic waves; a second set of the pin transducers including one or more receiving pins configured so that the transducer end of a respective receiving pin produces a transmitted electrical signal representing the acoustic energy in a transmitted wave coupled from the substrate to the respective pin by that pin'"'"'s probe end in response to arrival at that probe end of the substrate acoustic waves; and acquisition and processing modules configured to perform a characterization measurement wherein; the acquisition module is configured to (1) receive the transmitted electrical signal during a measuring period following the signal pulse; and
(2) digitize the received transmitted signals; andthe processing module is configured to (3) digitally compute from the digitized, received transmitted signals a respective measurement set correlated to spectral frequency components of the substrate acoustic waves. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An improved apparatus for characterizing a substrate, comprising:
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a first set of one or more source transducers configured to excite acoustic waves in the substrate at corresponding excitation points; a second set of at least two receiving transducers, each being configured to detect acoustic waves in the substrate and to produce a transmitted electrical signal representing acoustic energy in the substrate at a probe point due to the excited acoustic waves; acquisition and processing modules configured to perform a characterization measurement, wherein the acquisition module is configured to receive the transmitted electrical signals during at least one measuring period following the excitation of the acoustic waves, and the processing module is configured to compute from the transmitted electrical signals a measurement set correlated to spectral frequency components of the acoustic waves between at least a subset of the probe points; and the acquisition and processing modules are configured to compute at least one unknown substrate characteristic associated with at least the orientation of the substrate existing at a process time based on the measurement set computed at the process time for the at least one source transducer and the at least two receiving transducers. - View Dependent Claims (12, 13, 14, 15)
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16. An improved apparatus for characterizing a substrate, comprising:
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a first set of one or more source pin transducers configured to excite acoustic waves in the substrate at corresponding excitation points; a second set of one or more receiving pin transducers, each being configured to detect acoustic waves in the substrate and to produce a transmitted electrical signal representing acoustic energy in the substrate at a probe point due to the excited acoustic waves; at least one of the receiving pin transducers being further configured to produce an echo electrical signal; and acquisition and processing modules configured to perform a characterization measurement, wherein the acquisition module is configured to receive the transmitted and echo electrical signals during a measuring period following the excitation of the acoustic waves, and the processing module is configured to compute from the transmitted and echo electrical signals a measurement set correlated to spectral frequency components of the acoustic waves between at least a subset of the points. - View Dependent Claims (17, 18, 19, 20, 21, 22)
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Specification