Optical stress generator and detector

A method for characterizing a three dimensional sample comprised of a substrate and possibly one or more films deposited on said substrate together with at least one structure that is disposed upon or embedded within the substrate or one or more of the films, comprising the steps of:

• simulating a mechanical response of the sample, at a plurality of discrete time steps, to the application of pulses of first electromagnetic radiation;
• applying pulses of the first electromagnetic radiation to the sample for creating propagating stress pulses within the sample;
• applying second electromagnetic radiation to the sample so as to intercept the propagating stress pulses;
• sensing from a reflection of the second electromagnetic radiation from the sample at least one of a time-varying change in intensity, position, direction, polarization state, and optical phase of the second electromagnetic radiation;
• and
• associating the sensed time-varying change with a property of interest of the sample in accordance with the simulated response of the sample.

A method for characterizing a structure, comprising the steps of:

• simulating at predetermined time step increments, in accordance with one or more characteristics of the structure, a mechanical response of a simulated structure over an interval of time to an application of a first pulse of optical radiation by at least the steps of,
• determining an initial stress distribution within the simulated structure,
• determining a change over the interval of time in the stress and strain distribution in the simulated structure following an application of the first pulse of optical radiation, and
• determining the transient optical response of the simulated structure by application of a second pulse of optical radiation within the interval of time;
• applying the first pulse of optical radiation to the structure;
• applying, during the interval of time, the second pulse of optical radiation to the structure;
• comparing a measured transient response of the structure to the determined transient response for the simulated structure;
• adjusting a value of the one or more characteristics of the simulated structure so as to bring the determined transient response into agreement with the measured transient response;
• and
• associating the adjusted value of the one or more characteristics with a value of one or more actual characteristics of the structure.

A non-destructive system for characterizing a sample, comprising:

• means for generating an optical pump pulse and for focussing the pump pulse relative to a surface of the sample;
• means for generating an optical probe pulse and for focussing the probe pulse relative to the surface of the sample;
• means for measuring at least one transient response of the structure to the pump pulse by detecting a change in a reflected or transmitted portion of the probe pulse;
• means for simulating an effect of an application of pump and probe pulses to an area on the surface of the sample;
• and
• detector means for automatically adjusting the focus of at least one of the pump and probe pulses in response to reflected portions of at least one of the pump and probe pulses in order to stabilize an effective area of overlap of the pump and the probe pulses on the surface of the sample so as to be in agreement with the simulation.

A non-destructive system for characterizing a sample, comprising:

• means for a generating a sequence of optical pump pulses and for directing the sequence of pump pulses to an area of the surface of the sample;
• means for generating a sequence of optical probe pulses, wherein a delay between individual ones of the probe pulses, with respect to an individual one of the pump pulses, is varied at a frequency f and for directing the sequence of delay varying probe pulses to a same or different area of the surface of the sample;
• and
• means for synchronizing, as a function of f, the measurement of at least one transient response of the structure to the sequence of pump pulses by detecting a change in a characteristic of a reflected or transmitted portion of the sequence of delay varying probe pulses.

A non-destructive system for characterizing a sample, comprising:

• means for generating an optical pump pulse having a first wavelength and for directing the pump pulse to an area of the surface of the sample;
• means for generating an optical probe pulse from the optical pump pulse and for directing the probe pulse to a same or different area of the surface of the sample so as to arrive after the pump pulse, the optical probe pulse being generated to have a second wavelength that is a harmonic of the first wavelength;
• and
• means for measuring at least one transient response of the structure to the pump pulse by detecting a change in a characteristic of the reflected or transmitted portion of the probe pulse.

A non-destructive system for characterizing a sample, comprising:

• means for generating an optical pump pulse and an optical probe pulse from an input pulse having a first wavelength, wherein the pump pulse has a wavelength that is a harmonic of the first wavelength and the probe pulse has a wavelength that is equal to the first wavelength;
• means for directing the pump pulse to an area of the surface of the sample and for directing the probe pulse to a same or different area of the surface of the sample so as to arrive after the pump pulse;
• and
• means for measuring at least one transient response of the structure to the pump pulse by detecting a change in a characteristic of the reflected or transmitted portion of the probe pulse.

A method for operating a non-destructive system for characterizing a sample, comprising the steps of:

• generating an optical pump pulse and directing the pump pulse to an area of the surface of the sample;
• for each generated optical pump pulse, generating an optical probe pulse and directing the probe pulse to the surface of the sample so as to arrive after the pump pulse, wherein some of the probe pulses are directed to the surface at a first angle relative to the surface, and others of the probe pulses are directed to the surface at a second angle relative to the surface;
• and
• measuring at least one transient response of the structure to the pump pulses by detecting a change in a reflected portion of the probe pulses at each of the first and second angles.

A method for characterizing a structure comprised of a substrate and at least one layer that is an intentionally or a non-intentionally formed layer that is disposed over the substrate, comprising the steps of:

• generating a reference data set of a transient optical response of the structure to an optical pump pulse, the reference data set being generated from at least one of (a) at least one reference sample or (b) a simulation of a mechanical motion of a simulated structure at predetermined time step increments selected to have a duration of less than one half of a time required for an acoustic pulse to propagate through a thinnest layer of the structure;
• applying a sequence of optical pump pulses and optical probe pulses to the structure;
• comparing a measured transient response of the structure to the reference data set;
• adjusting a value of the one or more characteristics of the structure so as to bring the reference data set into agreement with the measured transient response;
• and
• associating the adjusted value of the one or more characteristics with a value of one or more actual characteristics of the structure.

A method for characterizing a structure comprised of a substrate and at least one layer disposed on the substrate, comprising the steps of:

• simulating a response of a model of the structure to an application of a first pulse of optical radiation followed by a transient response of the structure to an application of a second pulse of optical radiation within an interval of time;
• applying the first pulse of optical radiation to the structure;
• applying, during the interval of time, the second pulse of optical radiation to the structure;
• comparing a measured transient response of the structure to the determined transient response;
• adjusting one or more characteristics of the model of the structure so as to bring the determined transient response into agreement with the measured transient response;
• and
• associating the adjusted one or more characteristics with one or more actual characteristics of the structure, wherein the step of adjusting adjusts at least one of a crystal orientation within the at least one layer, an interface roughness between the at least one layer and another layer or the substrate, a thermal diffusivity within the at least one layer;
• an electronic diffusivity within the at least one layer, optical constants within the at least one layer, derivatives of optical constants with respect to stress or strain within the at least one layer, and a surface roughness of the sample.

A method for characterizing a structure comprised of a substrate and at least one layer disposed on the substrate, comprising the steps of:

• simulating a mechanical response of a model of the structure to an application of a first pulse of optical radiation by the steps of determining an initial stress distribution within the structure in response to the first pulse of optical radiation, calculating acoustical normal modes of the structure, decomposing the determined initial stress distribution into a sum over the calculated normal modes, and determining a change in a transient optical response of the structure, at a time of interest, to a second pulse of optical radiation by summing, for each calculated normal mode, a change in the transient optical response due to a spatial stress pattern associated with each normal mode;
• applying the first pulse of optical radiation to the structure;
• applying, at the time of interest, the second pulse of optical radiation to the structure;
• comparing a measured transient optical response of the structure to the determined transient optical response;
• adjusting one or more characteristics of the structure so as to bring the determined transient optical response into agreement with the measured transient optical response;
• and
• associating the adjusted one or more characteristics with one or more actual characteristics of the structure.