Systems and methods for quality control of a periodic structure

A method of quality control of a periodic structure comprising a stack of layers, the method comprising:

• illuminating the periodic structure through a first layer in the stack of layers with at least one excitation light beam, the at least one excitation light beam exciting an acoustic wave in the periodic structure;
• illuminating the periodic structure with at least one probe light beam;
• detecting the at least one probe light beam, using a photodetector, after interaction with the periodic structure, the photodetector being configured to generate a signal representing a damping rate of the acoustic wave;
• estimating, with a processor, non-uniformity of the periodic structure based at least in part on the damping rate of the acoustic wave in the periodic structure,
• wherein estimating the non-uniformity of the periodic structure comprises estimating a flatness of interfaces between adjacent layers in the stack of layers, and
• wherein estimating the flatness of the interfaces comprises detecting a deviation from an expected flatness substantially equal to or less than 5 nm.

A method of quality control of a periodic structure comprising a stack of layers, the method comprising:

• illuminating the periodic structure through a first layer in the stack of layers with at least one excitation light beam, the at least one excitation light beam exciting an acoustic wave in the periodic structure;
• illuminating the periodic structure with at least one probe light beam;
• detecting the at least one probe light beam, using a photodetector, after interaction with the periodic structure, the photodetector being configured to generate a signal representing a damping rate of the acoustic wave;
• estimating, with a processor, non-uniformity of the periodic structure based at least in part on the damping rate of the acoustic wave in the periodic structure, wherein estimating the non-uniformity of the periodic structure comprises comparing the damping rate of the acoustic signal with a reference damping rate of a reference acoustic signal in a reference periodic structure;
• measuring a dimension of the reference periodic structure;
• and
• measuring the reference damping rate of the reference acoustic signal in the reference periodic structure.

A method of quality control of a periodic structure comprising a stack of layers, the method comprising:

• illuminating the periodic structure through a first layer in the stack of layers with at least one excitation light beam, the at least one excitation light beam exciting an acoustic wave in the periodic structure;
• illuminating the periodic structure with at least one probe light beam;
• detecting the at least one probe light beam, using a photodetector, after interaction with the periodic structure, the photodetector being configured to generate a signal representing a damping rate of the acoustic wave;
• and
• estimating, with a processor, non-uniformity of the periodic structure based at least in part on the damping rate of the acoustic wave in the periodic structure,
• wherein estimating the non-uniformity of the periodic structure comprises comparing the damping rate with a threshold damping rate, and the method further comprises:
• in response to determining that the damping rate is greater than the threshold damping rate, generating a message indicating that the periodic structure is defective.

An apparatus for evaluating non-uniformity of a periodic structure comprising a stack of layers, the apparatus comprising:

• at least one light source configured to illuminate the periodic structure through a first layer in the stack of layers with an excitation light beam, the excitation light beam exciting an acoustic wave in the periodic structure, the at least one light source further configured to illuminate the periodic structure with a probe light beam;
• a detection system, in optical communication with the periodic structure, configured to detect the probe light beam after interaction with the periodic structure, the detection system further configured to generate a signal representing a damping rate of the acoustic wave in the periodic structure, the damping rate of the acoustic wave representing the non-uniformity of the periodic structure;
• and
• a processor, operably coupled to the detection system, to estimate the non-uniformity of the periodic structure based on the damping rate of the acoustic wave, wherein the processor is configured to estimate the non-uniformity of the periodic structure by estimating a period variation of the periodic structure and configured to estimate the period variation of the periodic structure by detecting a deviation in a period of the periodic structure substantially equal to or less than 5 nm from an expected period of the periodic structure.