Abstract:
Various approaches can be used to interrogate a surface such as a surface of a layered semiconductor structure on a semiconductor wafer. Certain approaches employ Second Harmonic Generation and in some cases may utilize pump and probe radiation. Other approaches involve determining current flow from a sample illuminated with radiation. Decay constants can be measured to provide information regarding the sample. Additionally, electric and/or magnetic field biases can be applied to the sample to provide additional information.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 61/980,860, filed on Apr. 17, 2014, titled “WAFER METROLOGY TECHNOLOGIES,” which is incorporated by reference herein in its entirety, including but not limited to each of the Sections I, II, III, and IV, which are each incorporated herein by reference in their entirety. 
     
    
     FIELD 
       [0002]    The subject filing relates to systems for Second Harmonic Generation (SHG) based wafer inspection, semiconductor metrology, materials characterization, surface characterization and/or interface analysis. 
       BACKGROUND 
       [0003]    In nonlinear optics, light beam input(s) are output as the sum, difference or harmonic frequencies of the input(s). Second Harmonic Generation (SHG) is a non-linear effect in which light is emitted from a material at a reflected angle with twice the frequency of an incident source light beam. The process may be considered as the combining of two photons of energy E to produce a single photon of energy 2E (i.e., the production of light of twice the frequency (2ω) or half the wavelength) of the incident radiation. 
         [0004]    A survey of scientific investigations in which the SHG technique has been employed is provided by, “Optical Second-Harmonic Generation from Semiconductor Surfaces” by T. F. Heinz et al., Published in Advances in Laser Science III, edited by A. C. Tam, J. L. Cole and W. C. Stwalley (American Institute of Physics, New York, 1988) p. 452. As reviewed, the SHG process does not occur within the bulk of materials exhibiting a center of symmetry (i.e., in inversion or centrosymmetric materials). For these materials, the SHG process is appreciable only at surfaces and/or interfaces where the inversion symmetry of the bulk material is broken. As such, the SHG process offers a unique sensitivity to surface and interface properties, 
         [0005]    So-understood, the SHG effect is described in U.S. Pat. No. 5,294,289 to Heinz et al. Each of U.S. Pat. No. 5,557,409 to Downer, et al., U.S. Pat. Nos. 6,795,175; 6,781,686; 6,788,405; 6,819,844; 6,882,414 and 7,304,305 to Hunt, U.S. Pat. No. 6,856,159 to Tolk, et al. and U.S. Pat. No. 7,158,284 to Alles, et al. also describe other approaches or “tools” that may be employed. Yet, the teachings of these patents appear not to have overcome some of the main obstacles to the adoption of SHG as an established technique for use in semiconductor manufacturing and metrology. 
       SUMMARY 
       [0006]    Various field-biased (e.g., magnetic-field biases, DC bias and/or voltage bias induced by an AC field alone, with a capacitive coupling and/or a changing magnetic field) SHG-based systems and their methods of use are described. These are treated in turn. They may be used independently and/or in a combined system. Various embodiments described herein include each of the methodology associated with the approaches described above, hardware to carry out the methodology, productions systems incorporating the hardware and products (including products-by-process) thereof. 
         [0007]    Magnetic Field Bias 
         [0008]    A static or changing magnetic field applied to the sample will cause the second order optical susceptibility tensor of a material to change. Thus, a magnetic field could be used to increase SHG signal from the sample, to an optimum value. Moreover, a changing magnetic field can be used to induce bias as further discussed below. 
         [0009]    Induced Voltage Bias for Eliminating DC Contact Probes 
         [0010]    Systems and methods are described for characterizing the SHG response of a layered semiconductor material that is subjected to a discrete electric field across its interfaces without use of contact bias probes in a system that can synchronize the pulses of a probing laser and/or the gating of a detector with a predetermined amplitude of voltage of an AC, variable or pulsed bias applied to the sample to produce a corresponding or coordinated induced voltage field at the surface to be interrogated. 
         [0011]    The subject hardware comprises an SHG apparatus (e.g., further described in the portion of U.S. Provisional Application No. 61/980,860, filed on Apr. 17, 2014, titled “W AFER  M ETROLOGY  T ECHNOLOGIES ,” referred to as Section II titled, “C HARGE  D ECAY  M EASUREMENT  S YSTEMS AND  M ETHODS ,” which is incorporated herein by reference in its entirety) together with a means of inducing (e.g., a component configured to induce) a voltage at or along the “device” surface of a sample without contact. (See also co-pending U.S. patent application Ser. No. ______, filed Apr. 17, 2015 titled “CHARGE DECAY MEASUREMENT SYSTEMS AND METHODS”, published as U.S. Publication No. ______, which is incorporated herein by reference in its entirety.) Such means or component may be either via backside contact with probes or a conductive chuck, involving capacitively coupled probes connected to a power source also in communication with backside contact probes or such a chuck, or by applying a changing magnetic field to the sample, with the purpose of inducing an external voltage field across its multilayer interfaces. 
         [0012]    A transient electric field produced by a variable waveform (optionally AC) power supply (via any of the approaches above) induces an electric field across the interfaces of the multilayer semiconductor material. The relationship between the voltage and the material interface electrical field may be modeled by a transfer function or otherwise, including by accounting for various (capacitive or otherwise) external influences. The output of this function, given a particular amplitude and frequency of AC (or other) current, may be employed as a timing cue to trigger the laser shutter and/or photon counter simultaneously for SHG characterization of the testing point for constant near-instantaneous values of the electric field amplitude at the interfaces. As such, the system is able to simulate a constant (DC) voltage applied topside (i.e., at the device layer of the substrate) via contact electrical probes. 
         [0013]    With direct application of AC to the backside of the sample, the system begins with the chuck at a ‘neutral’ or ground state, and bulk and device layers at an equilibrium potential. Then, an alternating bias is applied to the chuck, which is in galvanic contact with the bulk, or substrate layer of the multilayered semiconductor material Since the device layer is separated from the bulk by the buried oxide layer, and not directly connected with a conductor, an electric potential field, or voltage will be created (i.e., induced) between the device and bulk layers. 
         [0014]    Alternatively, capacitively coupled probe(s) that reside near (within about 1 to about 2 mm) but without touching the top side of the sample may be employed. A preferred approach in this regard may be a plate sized to cover (but not touch) the entire wafer, hovering with a small hole for the incident laser to pass through on its way to the sample and for the SHG beam to pass through on its way out of the sample. 
         [0015]    In some implementations, a non-contacting electrode can be implemented using MEMS technology. For example, in an implementation, a Si wafer can be oxidized on both sides. A spiral or a grid-like electrode can then be placed by deposition on one or more locations of the wafer. The oxide material can be removed from the back-side of the wafer at those locations. An electro-magnetic field applied to the electrode can inductively bias the wafer in such implementations through near-field inductive coupling. The magnetic field produced by an external electric current can be used to generate an electric current across the wafer by inducing a current in the deposited electrode. Other methods of implementing non-contacting probes can also be used. 
         [0016]    In any case, SHG methodology is used to interrogate the sample, for example, as further described in the portions of U.S. Provisional Application No. 61/980,860, filed on Apr. 17, 2014, titled “W AFER  M ETROLOGY  T ECHNOLOGIES ,” referred to as Section I titled, “P UMP AND  P ROBE  T YPE  SHG M ETROLOGY ,” and/or Section III, titled “T EMPERATURE -C ONTROLLED  M ETROLOGY ,” both of which are incorporated herein by reference in their entirety. See also co-pending U.S. patent application Ser. No. ______, filed Apr. 17, 2015 titled “PUMP AND PROBE TYPE SECOND HARMONIC GENERATION METROLOGY”, published as U.S. Publication No. ______, which is incorporated herein by reference in its entirety. The same holds true with respect to the other embodiments discussed below. 
         [0017]    Regardless, in the subject embodiments, since it is desirable to monitor SHG as a function of the voltage across the interfaces, the SHG signal will be synchronized with the power supply. This synchronization can be accomplished by controlling the laser(s) used for SHG signal production and SHG signal processing software, the laser(s) alone, or only the SHG signal processing software, in time with voltage changes. The voltage of the chuck can also be controlled. 
         [0018]    An advantage of this synchronization is that voltage biased SHG measurements can be obtained that would be similar to DC biased SHG measurements, without using contact voltage bias probes on the front surface of the wafer. Instead of applying a DC bias, the system would use an AC bias synchronized with SHG measurement and/or generation to collect SHG data at discrete points on the voltage cycle. The AC bias could be applied using near-field inductive coupling, or via capacitive coupling of the sample. SHG data collected with these biasing techniques would yield the same material properties information as DC biased SHG. 
         [0019]    To reduce or minimize noise and obtain statistically relevant indicator(s) of SHG intensity as a function of voltage across the interfaces, multiple photon counting windows may be desirable as further described below. 
         [0020]    Induced Voltage Bias for Characterizing Interfacial Leakage 
         [0021]    Systems and methods are described for characterizing interfacial leakage current and/or carrier injection energies between layers of layered (e.g., semiconductor) materials using SHG and a voltage change (such as an alternating, variable and/or pulsed voltage or current signal or a device that changes magnetic field in a manner to induce voltage change in a device layer of a sample) applied to the layered semiconductor material as per above. 
         [0022]    By measuring the SHG response from optical pulses generated by a pulsed laser directed at a layered semiconductor/dielectrics structure while or shortly after an alternating, variable or pulsed voltage is applied to the layered semiconductor material, interfacial leakage current and/or carrier injection energies between layers can be characterized. In some embodiments, the time evolution of the SHG signal from interfaces as a function of the time constant of decay of the induced voltage can be measured. This yields information about charge carrier mobility across the interfaces. 
         [0023]    Induced Voltage Bias for Characterizing Threshold Carrier Injection Energy 
         [0024]    Systems and methods are described for SHG measurement applied in connection with a varied electrical field at a sample device layer in lieu of using tunable wavelength laser excitation to determine energy thresholds for photo-induced charge carrier injection into the dielectric in a layered semiconductor material. More specifically, to measure the threshold energy necessary for photo-induced charge carrier injection into the dielectric one can expose the material to a substantially monochromatic incident photon beam for SHG production and then incrementally change voltage across an interface of the exposed layered semiconductor material, measuring SHG signal count at each incremental voltage change until the SHG response has significant inflection or discontinuity or sudden change in slope from prior measurements. This change in slope could be a maximum or minimum (e.g., local maximum or minimum) or cusp, or step function, etc. The net charge change transfer due to all these processes can be described as the integral of the contributions of the 3rd harmonic injection current, “forward” leakage current to the dielectric due to the strong electric field, and “backward” discharge leakage current. Put in equation form: Q(t)=∫(I X +I E −I L )dt Kinetic features of this curve shape (bending moment and saturation moments of time) will then provide information for determining threshold carrier injection energy. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The figures diagrammatically illustrate aspects of various embodiments of different inventive variations. 
           [0026]      FIGS. 1A and 1B  are schematic diagrams of SHG system components as may be used herein. 
           [0027]      FIGS. 2A  is a perspective view of a first chuck configuration hereof;  FIG. 2B  is a side-sectional view of the chuck configuration in  FIG. 2A . 
           [0028]      FIGS. 3A and 3B  are partial cutaway, perspective views of a second chuck configuration hereof;  FIG. 3C  is cutaway top view of the chuck in FIG.  3 A/ 3 B. 
           [0029]      FIGS. 4A and 4B  relate to AC voltage applied to and exhibited in a sample for DC bias probe elimination. 
           [0030]      FIGS. 5A and 5B  relate to AC voltage applied to and exhibited in a sample for testing leakage current. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]      FIGS. 1A and 1B  show suitable hardware for use in the subject systems and methods as further described in the portion of U.S. Provisional Application No. 61/980,860, filed on Apr. 17, 2014, titled “W AFER  M ETROLOGY  T ECHNOLOGIES ,” referred to as Section I entitled “P UMP AND  P ROBE  T YPE  SHG M ETROLOGY ,” which is incorporated by reference in its entirety. See also co-pending U.S. patent application Ser. No. ______, filed Apr. 17, 2015 titled “PUMP AND PROBE TYPE SECOND HARMONIC GENERATION METROLOGY”, published as U.S. Publication No. ______, which is incorporated herein by reference in its entirety. Other system and method options are presented in the portion of U.S. Provisional Application No. 61/980,860, filed on Apr. 17, 2014, titled “W AFER  M ETROLOGY  T ECHNOLOGIES ,” referred to as Section II entitled “C HARGE  D ECAY  M EASUREMENT  S YSTEMS AND  M ETHODS ,” for example, as to intermediate optics, the inclusion of optical delay line(s) and optional electrode features, which is incorporated herein by reference in its entirety. See also co-pending U.S. patent application Ser. No. ______, filed Apr. 17, 2015 titled “CHARGE DECAY MEASUREMENT SYSTEMS AND METHODS”, published as U.S. Publication No. ______, which is incorporated herein by reference in its entirety. 
         [0032]    As shown, system  3000  includes a primary or probe laser  3010  for directing an interrogation beam  3012  of electro-magnetic radiation at a sample wafer  3020 , which is held by a vacuum chuck  3030 . As illustrated in  FIG. 1B , the chuck  3030  includes or is set on x- and y-stages and optionally also a rotational stage for positioning a sample site  3022  across the wafer relative to where the laser(s) are aimed. The x-y stage enables scanning multiple wafer surface sites or locations  3022  without movement of other hardware. A rotational stage optionally enables assessing crystal structure effects on SHG. Further optional features, aspects and/or uses of chuck  3030  are presented elsewhere in this application entitled. The sample site  3022  can include one or more layers. The sample site  3022  can comprise a composite substrate including at least two layers. The sample site  3022  can include an interface between two dissimilar materials (e.g., between two different semiconductor materials, between two differently doped semiconductor materials, between a semiconductor and an oxide, between a semiconductor and a dielectric material, between a semiconductor and a metal or an oxide and a metal). 
         [0033]    When system  3000  is in use, a beam  3014  of reflected radiation directed at a detector  3040  will include an SHG signal. The detector  3040  may be any of a photomultiplier tube, a CCD camera, a avalanche detector, a photodiode detector, a streak camera and a silicon detector. System  3000  may also include one or more shutter-type devices  3050 . The type of shutter hardware used will depend on the timeframe over which the laser radiation is to be blocked, dumped or otherwise directed away from the sample site  3022 . An electro-optic blocking device such as a Pockel&#39;s Cell or Kerr Cell can be used to obtain very short blocking periods (i.e., with actuation times on the order of 10 −9  to 10 −12  seconds). 
         [0034]    For longer blocking time intervals (e.g., from about 10 −5  seconds and upwards) mechanical shutters or flywheel chopper type devices may be employed. However, electro-optic blocking devices will allow a wider range of materials to be tested in accordance with the methods below. A photon counting system  3044  capable of discretely gating very small time intervals, typically, on the order of picoseconds to microseconds can be employed to resolve the time-dependent signal counts. For faster-yet time frames optical delay line(s) may be incorporated as noted above. 
         [0035]    System  3000  can include an additional electromagnetic radiation source  3060  also referred to as a pump source. In various implementations, the radiation source  3060  can be a laser illustrated as emitting a directed beam  3062  or a UV flash lamp emitting a diverging or optically collimated pulse  3064 . In the case of a laser source, its beam  3062  may be collinear with beam  3012  (e.g., as directed by additional mirrors or prisms, etc.) Source  3060  output wavelengths of light may be anywhere from about 80 nm and about 1000 nm. Using shorter wavelengths in this range (e.g. less than about 450 nm), is possible to drive charge excitation using fewer photons and/or with lower peak intensities than at longer wavelengths. 
         [0036]    For a flash lamp, energy per flash or power level during flash may be substrate material dependent. A flashlamp producing a total energy of 1 J to 10 kJ per flash would be appropriate for fully depleted silicon-on-insulator (FD-SOI). However a pulsed or constant UV source would be viable as well. The important factor in the pump characteristics and use is that charge carriers are injected into the dielectric of the material to be interrogated. Manufacturers of suitable flash lamps include Hellma USA, Inc. and Hamamatsu Photonics K.K. 
         [0037]    When a laser is employed as source  3060 , it may be any of a nanosecond, picosecond or femtosecond or faster pulse laser source. It may even be a continuous solid-state laser. In various embodiments, the pump source is tunable in wavelength. Commercially available options regarding lasers which are tunable include Spectra Physics&#39; Velocity and Vortex Tunable Lasers. Additional tunable solid state solutions are available from LOTIS Ltd.&#39;s LT-22xx series of solid state lasers. 
         [0038]    Whether provided as a laser or a flash lamp, pump source  3060  can be selected for relatively high average power. This could be from about 10 mW to about 10 W, but more typically from about 100 mW to about 4 W, depending on material to be interrogated (as, again, the consideration is ensuring that charge carrier mobility is induced in a way such that charge carriers are injected into the interface of the material (e.g., the dielectric interface), which can be material specific. The average power of the pump source  3060  is selected to be below the optical damage threshold of the material. For example, pump source  3060  can be selected to have an average optical power between 1-2 W when the interrogating material comprises silicon so as to not exceed the optical damage threshold for silicon. 
         [0039]    Probe laser  3010  may be any of a nanosecond, picosecond or femtosecond or faster pulse laser source. Two options are currently commercially available regarding lasers have the peak power, wavelength and reliability needed are doped fiber and Ti:Sapphire units. Coherent&#39;s VITESSE and Spectra Physics&#39; MM TM lasers are examples of suitable Ti: Sapphire devices. Femtolasers Gmbh and others manufacture also manufacture other relevant Ti: Sapphire devices. Suitable doped fiber lasers are produced by IMRA. OneFive, and Toptica Photonics. Pico- and/or nano-second lasers from many manufacturers, such as Hamamatsu, may be options as well depending on the substrate material and pump type. Laser  3010  may operate in a wavelength range between about 100 nm to about 2000 nm with a peak power between about 10 kW and 1 GW, but delivering power at an average below about 150 mW. 
         [0040]    Various other optional so-called “intermediate” optical components may be employed in system  3000 . For example, the system  3000  may include a dichroic reflective or refractive filter  3070  for selectively passing the SHG signal coaxial with reflected radiation directly from laser  3010  and/or source  3060 . Alternatively, a prism may be employed to differentiate the weaker SHG signal from the many-orders-of-magnitude-stronger reflected primary beam. However, as the prism approach has proved to be very sensitive to misalignment, a dichroic system as referenced above may be preferred. Other options include the use of diffraction grating or a Pellicle beam splitter. An optical bundle  3080  for focusing and collimating/columniation optics may be provided. Alternatively, a filter wheel  3090 , polarizer(s)  3092  and/or zoom len(s)  3094  units or assemblies may be employed in the system. Also, an angular (or arc-type) rotational adjustment (with corresponding adjustment for the detector) and in-line optical components may be desirable. 
         [0041]    The output from the detector  3040  and/or the photon counting system  3044  can be input to an electronic device  3048 . The electronic device  3048  can be a computing device, a computer, a tablet, a microcontroller or a FPGA. The electronic device  3048  includes a processor that may be configured to execute one or more software modules. In addition to executing an operating system, the processor may be configured to execute one or more software applications, including a web browser, a telephone application, an email program, or any other software application. The electronic device  3048  can implement the methods discussed herein by executing instructions included in a machine-readable non-transitory storage medium, such as a RAM, ROM, EEPROM, etc. The electronic device  3048  can include a display device and/or a graphic user interface to interact with a user. The electronic device  3048  can communicate with one or more devices over a network interface. The network interface can include transmitters, receivers and/or transceivers that can communicate such as, for example, wired Ethernet, Bluetooth®, or wireless connections. 
         [0042]    Regarding other options, since an SHG signal is weak compared to the reflected beam that produces it, it is desirable to improve the signal-to-noise ratio of SHG counts. As photon counting gate times for the photon counting system  3044  decrease for the blocking and/or delay processes described herein, improvement becomes even more important. One method of reducing noise that may be employed is to actively cool the photon counter. This can be done using cryogenic fluids such as liquid nitrogen or helium or solid state cooling through use of a Peltier device. Others areas of improvement may include use of a Marx Bank Circuit (MBC) as relevant to shutter speed. Moreover, system  3000  may be incorporated in-line within a production line environment. Production line elements preceding or following system  100  may include any of epitaxial growth system, lithography and/or deposition (CVD, PVD, sputtering, etc.) systems. 
         [0043]    In any case,  FIGS. 2A and 2B  provide views of a first set of purpose-specific chuck hardware that may be employed in the subject SHG system. The chuck  3030  holds a wafer  3020  by vacuum thereto or other means. The chuck  3030  is conductive and connected to a power supply. Optionally, a capacitive coupling probe  3100  is also connected to the power supply  3120 . The power supply may be computer controlled, or at least its output is coordinated by computer for timing reasons as summarized above. The probe  3100  may likewise be controlled and/or monitored. It will be controlled in the sense that it will be part of a capacitive circuit attached to the power supply  3120 . It may be monitored along with the chuck  3030  by a voltmeter to ensure that voltage is being induced as intended. 
         [0044]    The probe  3100  includes a hole  3102  or port (e.g., 0.2 mm in diameter) in its ring  3104  to allow the optical beams  3012 ,  3014  (interrogation beam(s) and reflected SHG beam) to pass unblocked, and is fixed relative to the optics so that it moves or stays with the optical elements to remain centered on the (re)positioned sample site  3022  as the device surface is scanned. The coupling (indicated as having a positive “+” charge) is positioned close to the sample device surface (e.g., within about 1 mm to about 2 mm) but does not touch. It is supported by a cantilever arm or otherwise. The probe  3100  may be provided as a ring  3104  as shown in  FIG. 2B , or it may comprise a larger disc or plate. 
         [0045]    With the example shown in cross section in  FIG. 2B , a wafer  3020  or device surface (comprising silicon) is separated from a silicon bulk layer by SiO 2  insulator. Thus, as explained above, the need for inductive bias to the device surface because it is otherwise (at least substantially) electrically insulated or isolated from the underlying silicon in contact with the conductive chuck  3030 . 
         [0046]      FIGS. 3A-3C  detail an electromagnetic chuck  3030  that includes electrical coil(s)  3130  connected to a power supply  3120 . In use, the wafer  3020  sits and is secured on top of the chuck  3030 . When an alternating current (AC) is applied to the coil(s)  3130 , this generates an alternating magnetic field through the wafer  3020 . The magnetic field induces an electric potential across the wafer  3020  including its device surface. This electric field then enables the various modes of SHG interrogation noted above, some of which are detailed below. Alternatively, DC current may be applied to the coils  3130  which are oriented parallel to the chuck  3030 , creating a constant magnetic field across the chuck for other effects as described above. 
         [0047]      FIG. 4A  shows an example AC voltage (V) profile (sinusoidal wave) applied to the substrate bulk layer over time.  FIG. 4B  shows a hypothetical response for induced voltage between the device and bulk layers (V i ) of the substrate on which the device is fabricated. In various embodiments, the substrate can comprise the silicon wafer or a portion of a semiconductor material.  FIG. 5A  shows an example AC voltage (V o ) profile (square wave) applied to the substrate bulk layer over time.  FIG. 5B  shows a hypothetical response for induced voltage between the device and bulk layers (V i ). Notably, the voltage input in either of  FIG. 4A  or  5 A may differ from that shown, and could potentially be applied in steps, ramps, sine waves, or other forms. 
         [0048]    More specifically regarding  FIGS. 4A and 4B , as alluded to above, in order to minimize noise and obtain statistically relevant indicator(s) of SHG intensity as a function of voltage across the interfaces, multiple photon counting windows may be desirable. For such purposes, example points A 1  and A 2  are timed so that the voltage between the bulk and device layers, voltage A, is the same for both points. This is true for example points B 1  and B 2  at voltage B, and example points C 1  and C 2  at voltage C. Using voltage A as an example, SHG is recorded, and counts at points A 1  can be summed with counts at point A 2  and further at A 3 , A 4 , A n  . . . in an arbitrarily long series depending on the desired measurement time. The total number of counts measured in this period is then divided by the time over which this “gate” spans as a way of finding the average number of counts per second, so that SHG intensity can be plotted as a function of bulk-device voltage A. The same method can be used to obtain measurements for voltage B at points B 1  and B 2  as well as at B 3 , B 4 , B n  . . . in an arbitrarily long series depending on the desired measurement time. The total number of counts measured in this period is then divided by the time over which this “gate” spans as a way of finding the average number of counts per second, so that SHG intensity can be plotted as a function of bulk-device voltage B. Likewise, this method can be used to obtain measurements for voltage C at points C 1  and C 2  as well as at C 3 , C 4 , C n  . . . in an arbitrarily long series depending on the desired measurement time. The total number of counts measured in this period is then divided by the time over which this “gate” spans as a way of finding the average number of counts per second, so that SHG intensity can be plotted as a function of bulk-device voltage C. Further details regarding the utility of SHG intensity as a function of bias voltage can be found in the DC biasing literature, an example of which is, “Charge Trapping in Irradiated SOI Wafers Measured by Second Harmonic Generation,” IEEE Transactions on Nuclear Science, Vol. 51, No. 6. December 2004 and “Optical probing of a silicon integrated circuit using electric-field-induced second-harmonic generation,” Applied Physics Letters 88, 114107, (2006), each of which publication is incorporated herein by reference in its entirety. 
         [0049]    More specifically regarding  FIGS. 5A and 5B , these figures illustrate an example for interrogating a Silicon-On-Insulator (SOI) device. In this example, a conductive chuck begins at a ‘neutral’ ground state, and bulk and device layers being at an equilibrium potential. At moment ‘A’, voltage applied to the chuck is changed rapidly, applying that voltage to the sample&#39;s conductive bulk layer. Since the sample&#39;s device layer is separated from the bulk by a thin buried oxide layer and not directly connected with a conductor, an electric potential field, or voltage will be induced between the device and bulk layers. Between times ‘A’ and ‘B’, the voltage applied to the chuck is not changed. Since the dielectric between the bulk and device layers is not perfect, the induced potential will drive a leakage current between the layers, causing the potential between the bulk and device layers to return to its natural state. This spike and decay in electric field is then monitored via SHG to provide insight to the leakage current. At time ‘B’ the voltage applied to the chuck is returned to ground, causing the voltage across the interface to reverse. 
         [0050]    The systems and methods described herein can be used to characterize a sample (e.g., a semiconductor wafer or a portion thereof). For example, the systems and methods described herein can be used to detect defects or contaminants in the sample as discussed above. The systems and methods described herein can be configured to characterize the sample during fabrication or production of the semiconductor wafer. Thus, the systems and methods can be used along a semiconductor fabrication line in a semiconductor fabrication facility. The systems and methods described herein can be integrated with the semiconductor fabrication/production line. The systems and methods described herein can be integrated into a semiconductor fab line with automated wafer handling capabilities. For example, the system can be equipped with an attached Equipment Front End Module (EFEM), which accepts wafer cassettes such as a Front Opening Unified Pod (FOUP). Each of these cassettes can be delivered to the machine by human operators or by automated cassette-handling robots which move cassettes from process to process along fabrication/production line. 
         [0051]    In various embodiments, the system can be configured such that once the cassettes are mounted on the EFEM, the FOUP is opened, and a robotic arm selects individual wafers from the FOUP and moves them through an automatically actuated door included in the system, into a light-tight process box, and onto a bias-capable vacuum chuck. The chuck may be designed to fit complementary with the robotic arm so that it may lay the sample on top. At some point in this process, the wafer can be held over a scanner for identification of its unique laser mark. 
         [0052]    Accordingly, a system configured to be integrated in a semiconductor fabrication/assembly line can have automated wafer handling capability from the FOUP or other type of cassette; integration with an EFEM as discussed above, a chuck designed in a way to be compatible with robotic handling, automated light-tight doors which open and close to allow movement of the robotic wand/arm and software signaling to EFEM for wafer loading/unloading and wafer identification. 
         [0053]    As described above each of Sections I, II, III, and IV of U.S. Provisional Application No. 61/980,860, filed on Apr. 17, 2014, titled “WAFER METROLOGY TECHNOLOGIES,” are incorporated herein by reference in their entirety. Similarly, co-pending patent applications (i) U.S. patent application Ser. No. ______, filed Apr. 17, 2015 titled “PUMP AND PROBE TYPE SECOND HARMONIC GENERATION METROLOGY”, published as U.S. Publication No. ______, and (ii) U.S. patent application Ser. No. ______, filed Apr. 17, 2015 titled “CHARGE DECAY MEASUREMENT SYSTEMS AND METHODS”, published as U.S. Publication No. ______, are each incorporated herein by reference in their entirety. PCT Application No. PCT/US2015/026263, filed Apr. 16, 2015 titled “WAFER METROLOGY TECHNOLOGIES” is also incorporated herein by reference in its entirety. Accordingly, features from the disclosure of any of these documents incorporated by reference may be combined with any features recited elsewhere herein. 
         [0054]    Variations 
         [0055]    Example invention embodiments, together with details regarding a selection of features have been set forth above. As for other details, these may be appreciated in connection with the above-referenced patents and publications as well as is generally known or appreciated by those with skill in the art. The same may hold true with respect to method-based aspects of the invention in terms of additional acts as commonly or logically employed. Regarding such methods, including methods of manufacture and use, these may be carried out in any order of the events which is logically possible, as well as any recited order of events. Furthermore, where a range of values is provided, it is understood that every intervening value, between the upper and lower limit of that range and any other stated or intervening value in the stated range is encompassed within the invention. Also, it is contemplated that any optional feature of the inventive variations described may be set forth and claimed independently, or in combination with any one or more of the features described herein. 
         [0056]    Though the invention embodiments have been described in reference to several examples, optionally incorporating various features, they are not to be limited to that which is described or indicated as contemplated with respect to each such variation. Changes may be made to any such invention embodiment described and equivalents (whether recited herein or not included for the sake of some brevity) may be substituted without departing from the true spirit and scope hereof. 
         [0057]    The various illustrative processes described may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor can be part of a computer system that also has a user interface port that communicates with a user interface, and which receives commands entered by a user, has at least one memory (e.g. hard drive or other comparable storage, and random access memory) that stores electronic information including a program that operates under control of the processor and with communication via the user interface port, and a video output that produces its output via any kind of video output format, e.g., VGA, DVI, HDMI, DisplayPort, or any other form. 
         [0058]    A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. These devices may also be used to select values for devices as described herein. 
         [0059]    The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in Random Access Memory (RAM), flash memory, Read Only Memory (ROM), Electrically Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An example storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal. 
         [0060]    In one or more example embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on, transmitted over or resulting analysis/calculation data output as one or more instructions, code or other information on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. The memory storage can also be rotating magnetic hard disk drives, optical disk drives, or flash memory based storage drives or other such solid state, magnetic, or optical storage devices. 
         [0061]    Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. 
         [0062]    Operations as described herein can be carried out on or over a website. The website can be operated on a server computer, or operated locally, e.g., by being downloaded to the client computer, or operated via a server farm. The website can be accessed over a mobile phone or a PDA, or on any other client. The website can use HTML code in any form, e.g., MHTML, or XML, and via any form such as cascading style sheets (“CSS”) or other. 
         [0063]    Also, the inventors hereof intend that only those claims which use the words “means for” are to be interpreted under 35 USC 112, sixth paragraph. Moreover, no limitations from the specification are intended to be read into any claims, unless those limitations are expressly included in the claims. The computers described herein may be any kind of computer, either general purpose, or some specific purpose computer such as a workstation. The programs may be written in C, or Java, Brew or any other programming language. The programs may be resident on a storage medium, e.g., magnetic or optical, e.g. the computer hard drive, a removable disk or media such as a memory stick or SD media, or other removable medium. The programs may also be run over a network, for example, with a server or other machine sending signals to the local machine, which allows the local machine to carry out the operations described herein. 
         [0064]    It is also noted that all features, elements, components, functions, acts and steps described with respect to any embodiment provided herein are intended to be freely combinable and substitutable with those from any other embodiment. If a certain feature, element, component, function, or step is described with respect to only one embodiment, then it should be understood that that feature, element, component, function, or step can be used with every other embodiment described herein unless explicitly stated otherwise. This paragraph therefore serves as antecedent basis and written support for the introduction of claims, at any time, that combine features, elements, components, functions, and acts or steps from different embodiments, or that substitute features, elements, components, functions, and acts or steps from one embodiment with those of another, even if the following description does not explicitly state, in a particular instance, that such combinations or substitutions are possible. It is explicitly acknowledged that express recitation of every possible combination and substitution is overly burdensome, especially given that the permissibility of each and every such combination and substitution will be readily recognized by those of ordinary skill in the art. 
         [0065]    In some instances entities are described herein as being coupled to other entities. It should be understood that the terms “interfit”, “coupled” or “connected” (or any of these forms) may be used interchangeably herein and are generic to the direct coupling of two entities (without any non-negligible, e.g., parasitic, intervening entities) and the indirect coupling of two entities (with one or more non-negligible intervening entities). Where entities are shown as being directly coupled together, or described as coupled together without description of any intervening entity, it should be understood that those entities can be indirectly coupled together as well unless the context clearly dictates otherwise. 
         [0066]    Reference to a singular item includes the possibility that there are a plurality of the same items present. More specifically, as used herein and in the appended claims, the singular forms “a,” “an,” “said,” and “the” include plural referents unless specifically stated otherwise. In other words, use of the articles allow for “at least one” of the subject item in the description above as well as the claims below. 
         [0067]    It is further noted that the claims may be drafted to exclude any optional element (e.g., elements designated as such by description herein a “typical,” that “can” or “may” be used, etc.). Accordingly, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or other use of a “negative” claim limitation language. Without the use of such exclusive terminology, the term “comprising” in the claims shall allow for the inclusion of any additional element—irrespective of whether a given number of elements are enumerated in the claim, or the addition of a feature could be regarded as transforming the nature of an element set forth in the claims. Yet, it is contemplated that any such “comprising” term in the claims may be amended to exclusive-type “consisting” language. Also, except as specifically defined herein, all technical and scientific terms used herein are to be given as broad a commonly understood meaning to those skilled in the art as possible while maintaining claim validity. 
         [0068]    While the embodiments are susceptible to various modifications and alternative forms, specific examples thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that these embodiments are not to be limited to the particular form disclosed, but to the contrary, these embodiments are to cover all modifications, equivalents, and alternatives falling within the spirit of the disclosure. Furthermore, any features, functions, acts, steps, or elements of the embodiments may be recited in or added to the claims, as well as negative limitations (as referenced above, or otherwise) that define the inventive scope of the claims by features, functions, steps, or elements that are not within that scope. Thus, the breadth of the inventive variations or invention embodiments are not to be limited to the examples provided, but only by the scope of the following claim language. That being said, we claim: