Patent Publication Number: US-9846122-B2

Title: Optical metrology system for spectral imaging of a sample

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 14/936,635, filed Nov. 9, 2015, which is a continuation of U.S. application Ser. No. 14/091,199, filed Nov. 26, 2013, now U.S. Pat. No. 9,182,351, this application further claims priority under 35 USC 119 to U.S. Provisional Application No. 62/253,092, filed Nov. 9, 2015, all of which are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     Photoluminescence imaging and spectroscopy is a contactless, nondestructive method of probing the electronic structure of materials, such as silicon semiconductor wafers, solar cells, as well as other workpieces and materials. In a typical photoluminescence process, light is directed onto a wafer or other workpiece (hereinafter collectively referred to as a “sample”), where at least some of the light is absorbed. The absorbed light imparts excess energy into the material via a process of “photo-excitation.” The excess energy is dissipated by the sample through a series of pathways; one such pathway is the emission of light, or photoluminescence. The intensity and spectral content of the photoluminescence is directly related to various material properties of the sample and, thus, can be used to determine certain characteristics of the sample, including defects, as discussed in U.S. Pat. No. 7,113,276B1, which is incorporated herein by reference. 
     Reflectance or reflectivity imaging is a contactless, nondestructive method of probing the surface with a broadband illumination source and analyzing the intensity and spectral content of the signal bounced back from the surface. The surfaces typically can be classified into specular or diffuse surfaces and real objects typically exhibit a mixture of both properties. 
     It is sometimes desirable, e.g., for semiconductor wafer inspection applications, to measure intensity and spectral content of the photoluminescence and reflectance of the semiconductor wafer-size workpiece for the purpose of quality inspection in the same apparatus either concurrently or in a short sequence, with single wafer load, while achieving a high measurement throughput combined with high measurement spatial and spectral resolution. 
     Conventionally, spectral photoluminescence or combined spectral photoluminescence and reflectance are measured using a single point-by-point inspection solution. In a point-by-point solution, the sample is placed on an X-Y motion (or R-Θ) system and is illuminated and measured at a single excitation point. The sample is moved to another measurement point and again illuminated and measured. By repeating the translation of the sample in the X-Y directions, a photoluminescence and reflectance maps could be constructed from the point-by-point measurements. This solution, however, is inherently slow and therefore impractical in the full wafer inspection systems, especially at large specimen sizes, close to and above 100 mm in diameter, due to the low throughput. 
     SUMMARY 
     An optical metrology device is capable of detection of any combination of photoluminescence light, specular reflection of broadband light, and scattered light from a line across the width of a sample. The metrology device includes a first light source that produces a first illumination line on the sample. A scanning system may be used to scan an illumination spot across the sample to form the illumination line. A detector collects the photoluminescence light emitted along the illumination line. Additionally, a broadband illumination source may be used to produce a second illumination line on the sample, where the detector collects the broadband illumination reflected along the second illumination line. The detector may also image scattered light from the first illumination line. The illumination lines may be scanned across the sample so that all positions on the sample may be measured. A signal collecting optic may collect the photoluminescence light and broadband light and focus it into a line, which is received by an optical conduit. The output end of the optical conduit has a shape that matches the entrance of the detector. 
     In one embodiment, an apparatus includes a light source that produces a first illumination beam; an optical system that receives the first illumination beam and produces an illumination spot on a surface of the sample; a scanning system that scans the illumination spot to form a first illumination line across the sample, wherein the scanning system scans the first illumination beam in a plane that is at a first non-normal angle of incidence on the sample, and wherein the sample emits photoluminescence light in response to excitation caused by the illumination spot along the first illumination line; a broadband light source that produces broadband light; a lens that focuses the broadband light into a second illumination line on the surface of the sample, the second illumination line overlays and is aligned with the first illumination line and is incident on the sample at a second non-normal angle of incidence that is different than the first non-normal angle of incidence, wherein the second illumination line is reflected by the sample to produce reflected light; a stage for providing relative movement between the sample and the first and second illumination lines; a detector receives the photoluminescence light emitted along the first illumination line and further receives the reflected light from the second illumination line as the stage produces relative movement between the sample and the first and second illumination lines; and a processor coupled to the detector and configured to a characteristic of the sample for a plurality of positions on the surface of the sample using the photoluminescence light and the reflected light. 
     In one embodiment, an apparatus that includes an illumination source that produces a first light beam; a first lens system that causes the first light beam to be incident on a surface of a sample as a first illumination line orientated along a first direction, the first illumination line being incident on the sample at a first angle of incidence, wherein the sample emits photoluminescence light in response to excitation caused by the first light beam along the first illumination line; a second illumination source; a second lens system that focuses light emitted by the second illumination source onto the sample as a second illumination line orientated along the first direction and that is overlaid on the first illumination line on the surface of the sample and that is incident on the sample at a second angle of incidence that is different than the first angle of incidence; a stage for providing relative movement between the sample and first and second illumination lines in a second direction that is different than the first direction; a detector that collects reflected light from the second illumination line and receives the photoluminescence light emitted by the sample along the first illumination line; and a processor coupled to the detector and configured to determine a characteristic of the sample for a plurality of positions on the surface of the sample using the photoluminescence light and the reflected light. 
     In one embodiment, an apparatus includes a light source that produces an illumination beam; an optical system that receives the illumination beam and produces an illumination spot on a surface of a sample; a scanning system that scans the illumination spot to form an illumination line across the sample, wherein the sample emits photoluminescence light in response to excitation caused by the illumination spot along the illumination line; a stage for providing relative movement between the illumination line and the sample; a signal collecting optic extending a length of the illumination line, the signal collecting optic receives the photoluminescence light from the illumination line and focuses the photoluminescence light into a line; an optical conduit having a linear reception end that receives the photoluminescence light focused by the signal collecting optic, the optical conduit further having an output end having a different shape than the linear reception end; a detector that collects the photoluminescence light from the optical conduit, the detector having an entrance aperture that matches a shape of the output end of the optical conduit; and a processor coupled to the detector to receive the photoluminescence light to determine a characteristic of the sample. 
     In one embodiment, a method includes illuminating a surface of a sample with a light source along an illumination line having an orientation in a first direction, wherein the sample emits photoluminescence light from the illumination line in response to excitation caused by light from the light source; collecting the photoluminescence light from the illumination line with a signal collection optic along a length of the illumination line and focusing the photoluminescence light into a line with the signal collection optic; receiving the photoluminescence light along the line with an optical conduit having a linear reception end and outputting the photoluminescence light from the optical conduit at an output end having a different shape than the linear reception end; detecting the photoluminescence light received from the output end of the optical conduit with a detector having an entrance aperture that matches a shape of the output end of the optical conduit; moving the illumination line across the surface of the sample in a second direction that is different than the first direction; and determining a characteristic of the sample for a plurality of positions on the surface of the sample using the photoluminescence light detected by the detector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an optical metrology device capable of simultaneous detection of any combination of photoluminescence light, specular reflection of broadband light, and scattered light from a line across the width of a sample. 
         FIG. 2A  illustrates a top view of the surface of the sample with an illumination spot from a first light source that is scanned across the width of the sample to produce an illumination line and the illumination line is moved across the sample. 
         FIG. 2B  illustrates a top view of the sample with the illumination line from a second light source and the illumination line is moved across the sample. 
         FIGS. 3A and 3B  illustrate a perspective view and side view, respectively, of a dark channel observation of scattered light by the optical metrology device of  FIG. 1 . 
         FIGS. 4A and 4B  illustrate a perspective view and side view, respectively, of the bright field reflectance observation by the optical metrology device of  FIG. 1 , with a narrow band light source and associated optics omitted for clarity. 
         FIGS. 5A and 5B  illustrate a perspective view and side view, respectively, of the excitation of the sample with the scanning illumination beam and the emitted photoluminescence light collection by the optical metrology device of  FIG. 1 . 
         FIG. 6  illustrates an incident illumination beam and the Lambertian characteristic of the emitted photoluminescence light. 
         FIGS. 7 and 8  illustrate a side view (along the Y-Z plane) and a front view (along the X-Z plane), respectively, illustrating the simultaneous collection of dark field scattered radiation, bright field reflectance radiation and photoluminescence light by the optical metrology device of  FIG. 1 . 
         FIG. 9  illustrates the signal separation of the three spectral channels (dark field scattered radiation, bright field reflectance radiation, and photoluminescence light) imaged by a 2D sensor array. 
         FIG. 10  is a flow chart illustrating a method of optical metrology data from a number of light sources. 
         FIGS. 11 and 12  illustrate side views (along the Y-Z plane) of alternative configurations of the optical metrology device from  FIG. 1 . 
         FIG. 13  illustrates a perspective view of a long elliptical cylindrical mirror that may be used to receive photoluminescence light emitted from the sample. 
         FIG. 14  illustrates a side view (along the Y-Z plane) of the elliptical mirror collecting photoluminescence or scattered radiation from the sample. 
         FIG. 15  illustrates a perspective view of a long cylindrical lens that may be used to receive photoluminescence emitted from the sample. 
         FIG. 16  illustrates a side view (along the Y-Z plane) of the cylindrical lens collecting photoluminescence or scattered radiation from the sample. 
         FIGS. 17A and 17B  illustrate the reception end and output end, respectively, of an optical conduit of numerous optical fibers. 
         FIG. 18  illustrates an optical conduit providing collected light to a detector that includes a spectrometer. 
         FIG. 19  illustrates an optical conduit providing collected light to a detector that includes a Photomultiplier Tube (PMT) or Avalanche Photo Diode (APD). 
         FIG. 20  illustrates a side view (along the Y-Z plane) of the simultaneous collection of dark field scattered radiation, photoluminescence light, and optionally, bright field reflectance radiation by an optical metrology device employing an elliptical mirror. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an optical metrology device  100  capable of simultaneous detection of any combination of photoluminescence light, specular reflection of broadband light, and scattered light from a line across the width of a sample. The sample is moved in a single direction to sweep the line across the sample so that data may be quickly collected from every position on the surface of the sample. 
     The metrology device  100  includes a first light source  110 , which may be, e.g., a narrow band illumination source, such as a laser. By way of example, the light source  110  may be a high intensity laser, such as a Continuous Wave (CW) laser with peak wavelength at 405 nm and power in 1 mW to 500 mW range, depending on the photoluminescence efficiency of the measured sample and desired signal intensity to be recorded by the detector. If desired, more than one laser may be used to produce multiple narrow band wavelengths that are combined for light source  110 . By way of example, other laser wavelengths, such as 266 nm, 355 nm, 375 nm, 532 nm, 640 nm or 830 nm, and others not listed here, may additionally or alternatively be used, either individually or selectively combined. Laser(s) used as light source  110  may operate either in Continuous Wave or Q-Switched mode of operation. If the Q-Switched (QS) laser is used for sample excitation, the instantaneous power, i.e. power during the pulse, may be much higher, e.g., in a few (2.5 kW) kilowatt range. 
     A lens system including optics  112  is used to produce an illumination spot with the illumination beam  114  on the surface of the sample  101 . The illumination spot produced by the illumination beam  114  should have a size and/or power density to excite photoluminescence in the sample  101 . By way of example, the illumination spot size may be between 50 μm to 1 mm range and/or have a power density of between approximately 0.1 W/cm 2  to 10 8  W/cm 2  range. For example, if a CW 1 mW laser is focused to about a 1 mm spot, the power density is about 0.127 W/cm 2 . The same CW 1 mW laser focused to 50 micron spot will give power of 50 W/cm 2 . If a higher power 500 mW CW laser is used, and is focused to a 1 mm spot, a power density of 63 W/cm 2  is reached and the same laser focused to 50 μm will lead to the power density of 2.5*10 4  W/cm 2 . Thus, typical power densities for CW lasers are in 0.1 W/cm 2  to 2.5*10 4  W/cm 2  range. With the use of Q-Switched lasers for sample excitation, the power densities are much different. For example, at an average power of 1 mW, and pulse duration of 10 nanoseconds (10*10 −9  s) and repetition rate of 100 kHz, the momentary power may be as high as 1 W and the corresponding power density at a 1 mm spot is 127 W/cm 2 . When the same laser is used with an average power of 500 mW, and is focused to 50 μm spot size, the momentary power may reach, e.g., 2.5*10 7  W/cm2. 
     The lens system may further include a scanning system  116 , illustrated as including a scanning mirror  118  and a fixed mirror  120 , that is used to scan the illumination spot across the width of the surface of the sample  101  as an illumination line  122 , that is illustrated as being orientated along the X direction. The scanning speed/frequency of scanning system  116  may be adjusted depending on the scan resolution and sensor read-out speed. For example, the frequency may be, e.g., between 50-100 Hz range, but may vary in a range of 1 Hz to 10 kHz or more. The scanning mirror  118  moves to scan the illumination spot across the surface of the sample  101  and may be, e.g., a (swinging) galvanometric mirror or a rotating polygonal mirror.  FIG. 2A , by way of example, illustrates a top view of the surface of the sample  101  with an illumination spot  124 , produced by illumination beam  114  ( FIG. 1 ) that is scanned across the width of the sample, as indicated by arrows  127 . As illustrated, by lines  121  in  FIG. 1 , the scanning system  116  scans the illumination beam  114  across the sample  101  within a plane, which creates a non-zero angle of incidence α 1 , with respect to surface normal N. Thus, the illumination line  122  is incident on the surface of the sample  101  at a non-normal angle of incidence. It should be understood that the illumination line  122  is additionally scanned across the surface of the sample  101  by the stage  104  ( FIG. 1 ) moving the sample  101  along the Y direction, as illustrated by arrow  123 , so that the illumination line  122  may be incident on all positions on the surface of the sample  101 . 
     It should be understood that  FIG. 1  illustrates one configuration of the narrow band illumination source  110  and associated optics, including scanning system  116 , but that other configurations may be used if desired. For example, while the use of fixed mirror  120  is advantageous to simplify system alignment, if desired, the fixed mirror  120  may be removed from scanning system  116 , with the light source  110 , lens  112 , and scanning mirror  118  repositioned so that the illumination beam  114  illuminates the sample  101  directly, without the need for the redirecting mirror  120 . Moreover, it should be understood that the optics  112  may focus the illumination beam  114  into an illumination spot  124  on a surface of the sample  101 . If the illumination beam  114  is focused at a sample plane, which is coincident with the surface of the sample  101 , the illumination spot may become slightly defocused as the illumination beam moves along the illumination line  122 , but the signal intensity variations caused by the defocusing can be compensated by signal processing within computer  150 . Alternatively, by way of example, the optics  112  may collimate the illumination beam  114 . If desired, the collimated illumination beam  114  may be focused on the surface of the sample using an optional F-theta lens  117 , shown with dotted lines in  FIG. 1 . Moreover, if desired, the collimated illumination beam  114  may be incident on the surface of the sample  101  as the illumination spot without being focused, with an associated loss of resolution and excitation conditions. 
     By scanning the illumination spot  124  across the sample  101  to produce the illumination line  122 , a high power density of the incident light may be maintained. Consequently, the illumination beam from light source  110  imparts energy into the material of the sample via “photo-excitation” thereby producing photoluminescence light emitted from the sample along the illumination line  122 . Additionally, surface defects on the sample  101 , such as scratches, particles, epitaxial growth defects, e.g., stacking faults or mounds, may scatter the illumination beam  114  as it is scanned along the illumination line  122 . 
     As illustrated, by lines  121  in  FIG. 1 , the scanning system  116  scans the illumination beam  114  across the sample  101  within a plane, which creates a non-zero angle of incidence α 1 , with respect to surface normal N. Thus, the illumination line  122  is incident on the surface of the sample  101  at a non-normal angle of incidence. 
     The optical metrology device  100  includes a detector  130  that receives light from the surface of the sample  101  along a detector path  131  that has a non-zero angle α 3  with respect to surface normal N. Thus, as illustrated in  FIG. 1 , the detector  130  has viewing angle α 3  that is different than the angle of incidence α 1  of the illumination line  122 . As a result, the specular reflection of the illumination beam  114  from the surface of the sample  101  does not enter the detector path  131 . Typically, the photoluminescence signal is a few orders weaker than the reflected radiation signal. With the use of the angle of incidence α 1  and the viewing angle α 3 , the optical metrology device  100  permits the illumination beam  114  to reflect from the specular surface of the sample  101  without interfering with the photoluminescence signal received by the detector  130 , thereby avoiding the need for filtering the reflection of the illumination beam  114 . Moreover, because the illumination beam  114  is not filtered, the detector  130  may receive light scattered by surface defects without receiving illumination beam  114 , i.e., enabling dark field observations. It should be understood that the photoluminescence light produced by the sample  101  in response to excitation by the illumination beam  114  will have a different wavelength(s) than the illumination beam  114  itself. Accordingly, the wavelengths from the photoluminescence light and the scattered light can be dispersed into different spectral channels. Consequently, the optical metrology device  100  may be used for simultaneous detection of surface topographical defects and photoluminescence. Additionally, with the use of the scanning system  116 , the light source  110  may function as a line illumination source without loss of power density or illumination uniformity along the line if a cylindrical lens or cylindrical mirror were used. 
     The detector  130  includes optics  132 , a spectrometer  134 , and a sensor  136  that includes a two-dimensional CCD or CMOS sensor array. The light collected along the detector path  131 , e.g., photoluminescence light or scattered light, is collected by the fore optics  132 , then passes through a narrow entrance slit aperture in the spectrometer  134 . The field of view of the spectrometer  134  is limited by the entrance slit, which matches the orientation of the illumination line  122 . Thus, the entrance slit of the detector  130 , or to be more exact, the spectrometer  134 , is aligned with the illumination line  122  and overlaying broadband illumination line  142  (discussed below), i.e. the entrance slit and illumination lines  122  and  142  all belong to the same plane, while illumination line  122  and  142  are overlaid on top of each other and the entrance slit to the detector  130  is parallel to the illumination lines  122  and  142 . The spectrometer  134  disperses the spectrum of the received light and the sensor  136  at the exit of the spectrometer  134  records with a two dimensional (2D) sensor array and produces a resulting image frame, with a first dimension of the sensor array representing the spatial position along the illumination line  122  and the second dimension of the sensor array representing spectral information. The spectrometer  134  separates the wavelengths of emitted photoluminescence light and separates the scattered light along one dimension of the 2D sensor array, while the position along the illumination line  122  is recorded by the second dimension of the 2D sensor array. For example, one point along the illumination line  122  may emit a maximum photoluminescence at 460.3 nm, while another point on the illumination line  122  may emit a maximum photoluminescence at 460.8 nm. Thus, the spectrometer  134  separates the wavelengths of the emitted photoluminescence light to perform spectral photoluminescence imaging. 
     The metrology device  100  further includes a second light source  140 , which may be, e.g., a broadband illumination source, such as a halogen light source, that includes wavelengths of light that differ from the wavelengths used by the first light source  110  or the wavelengths of photoluminescence light emitted by the sample  101  in response to excitation by the illumination beam  114 . The broadband radiation source (sometimes referred to as a “white” light source) is formed into the illumination line  142  which is aligned with and overlays the illumination line  122  on the surface of the sample  101 . As illustrated, the illumination line  142  may be produced, e.g., using a series of optical fibers  144  (only one of which is illustrated as coupled to the light source  140 ). By way of example, the second light source  140  with the series of optical fibers  144  may be a Lightline product manufactured by Schott North America, Inc. The light from the multiple optical fibers  144  is formed into a nearly collimated line-like beam with a cylindrical lens  146 .  FIG. 2B  illustrates a top view of the sample  101  with the illumination line  142  from the second light source  140 . 
     As illustrated in  FIG. 1 , the broadband light from light source  140  illuminates the surface of the sample  101  along a plain, illustrated by lines  141  that is at a non-zero angle of incidence α 2 , with respect to surface normal N. Thus, the illumination line  142  is incident on the surface of the sample  101  at a non-normal angle of incidence α 2 . It should be understood that the illumination line  142  is additionally scanned across the surface of the sample  101  (along with overlaid illumination line  122 ) by stage  104  ( FIG. 1 ), as illustrated by arrow  145  in  FIG. 2B , so that the illumination line  142  may be incident on all positions on the surface of the sample  101 . The angle of incidence α 2  is different from the angle of incidence α 1  and has a sign that is different from the sign of angle α 1 , i.e., the illumination line  142  is incident on the surface of the sample from an opposite direction as the illumination line  122 , and has a different angle of incidence. The angle of incidence α 2  of the illumination line  142 , however, is equal, but opposite in value, as the viewing angle α 3  of the detector path  131 , i.e., viewing angle α 2 =−α 3 . Thus, the detector  130  viewing angle is tuned to the incident angle of the illumination line  142  and as a result, the specular reflection of the broadband light along illumination line  142  is also aligned with the field-of-view of the spectrometer  134 . Thus, both the illumination line  122  produced by light source  110  and the illumination line  142  produced by the light source  140  are received by the detector. The spectrometer  134  separates the wavelengths of the specular reflection of the broadband illumination along the illumination line  142  into one dimension of the 2D sensor array, while the position along the illumination line  142  (and the illumination line  122 ) is represented by the second dimension of the 2D sensor array. 
     The broadband light source  140  may use wavelengths of light that are different than the wavelength(s) used by the first light source  110  and wavelength(s) of the photoluminescence light emitted by the sample  101  so that the spectrometer  134  may separate the wavelengths from the reflected broadband light from the wavelengths of the scattered light and the wavelengths of the photoluminescence lights. Accordingly, the first light source  110  and second light source  140  may be used with the detector  130  to simultaneously detect the spectral information with respect to position along with illumination lines  122  and  142  for the photoluminescence light caused by the excitation of illumination beam  114 , the dark field scattering of the illumination beam  114 , as well as the bright field reflectance from the light source  140 . By way of example, the optical metrology device  100  may use a range of wavelengths between 400-1,000 nm (i.e. 600 nm range), based on the wavelengths of the narrow band light source  110 , the broadband light source  140 , and the emitted photoluminescence light. The detector  130  may separate the received light into, e.g., 1200 wavelengths, i.e., number of pixels in the spectral dimension of the sensor array, and thus, the detector  130  may have a spectral resolution of 0.5 nm. Of course, if desired, other spectral resolutions may be used, as well as wavelengths of light or ranges of wavelengths of light, as well as the number of wavelengths detected by detector  130 . 
     Moreover, the broadband light that is specularly reflected from the surface of the sample  101  is directed to the detector  130  without any need for mechanical repositioning of the detector  130 , therefore the detector  130  can collect the surface reflectance, scattering and photoluminescence signals concurrently or in a quick succession without any delay for mechanical repositioning of any apparatus optics subcomponents. Of course, if desired, the first light source  110  and second light source  140  may be used in quick succession so that the detector  130  does not simultaneously receive light from both illumination lines  122  and  142 . 
     The sample  101  is held on a linear stage  104  that can translate the sample  101  in a direction that is different than the orientation of the illumination lines  122  and  142 . For example, the orientation of the illumination lines  122  and  142  may be in a direction (e.g., the X-direction) that is orthogonal to the direction of travel of the linear stage  104  (e.g., the Y-direction). The stage  104  translates the sample  101  to place the illumination lines  122  and  142  at multiple positions across the sample  101  (as illustrated by arrows  123  and  145  in  FIGS. 2A and 2B ) and the spectral imaging of the illumination lines  122  and  142  is repeated at each new position. The process of imaging and moving the sample  101  is repeated to scan the illumination lines  122  and  142  across the sample  101  thereby producing a series of 2D image frames. If desired, the stage  104  may move the sample  101  in steps or move the sample  101  continuously so that data acquisition is performed continuously (e.g., with a high frequency scan of the illumination spot  124 ), without the Y-axis motion stopping at each line. For example, when a high frequency scan (e.g., 500 Hz) of the illumination spot  124  is used with a relatively low speed stage motion along the Y-axis and low speed collection of image frames (e.g., 100 Hz), the illumination beam  114  is scanned over the illumination line  122  several times for each given image frame, e.g., five times in the given example, which provides for improved signal averaging. The speed of the stage motion along Y axis may be expressed in millimeters per second and depends on the desired resolution along the Y direction. For example, when the Y speed is 20 mm/s and the frame rate is 100 frames per second, the Y resolution is 20 mm/s divided by 100/s equals 0.2 mm. 
     Thus, in one data capture operation, the optical metrology device  100  is able to collect concurrently the spectral photoluminescence and spectral scattered radiation and spectral reflected radiation signals from the line-illuminated portion of the sample  101 , and may move in a single axis and repeatedly perform the data capture operation to acquire data for the entire sample surface. In one embodiment the data for the entire sample surface is obtained by moving the sample  101  underneath of the illumination lines  122  and  142  with a linear stage in the Y-direction. In another embodiment, however, the data can be collected by rotating the sample  101  underneath of the illumination lines  122  and  142  with a rotary stage in Θ (angle) direction, illustrated in  FIG. 1  with a dotted arrow. In both embodiments, the sample  101  is moved in one axis only, either Y or Θ (both are not required), resulting with a high speed measurement. In comparison, conventional systems acquire data from a single illumination spot and must move the sample in two axes to acquire data for the entire sample surface. Thus, the optical metrology device  100  uses a single unidirectional stage, as opposed to the conventional two linear or linear and rotary stage systems. Moreover, data acquisition is accelerated because of the elimination of required stage motion along the X-axis. 
     It should be understood the motion between the illumination lines  122  and  142  and sample  101  is relative, and thus, if desired, the stage  104  may be held stationary and the illumination lines  122  and  142  may be moved (laterally in the Y direction or rotated in the Θ direction using a stage to move, e.g., the light sources and associated optics with respect to the sample  101 , or other appropriate means. 
     The plurality of image frames produced by the detector  130  as the sample  101  is moved and spectral information from the line-illuminated portions of the sample  101  is acquired may be received by a computer  150 , which may store the plurality of image frames as three dimensional (3D) data cube. The 3D data cube includes two dimensions that are spatial (e.g., one dimension is the position along the illumination lines  122  and  142  (X axis) and the other dimension is the position of the line scanned across the sample (Y axis)) and a third dimension represents the spectral information. The detector  130  is coupled to provide the image data to the computer  150 , which includes a processor  152  with memory  154 , as well as a user interface including e.g., a display  158  and input devices  160 . A non-transitory computer-usable medium  162  having computer-readable program code embodied may be used by the computer  150  for causing the processor to control the metrology device  100  and to perform the functions including the analysis described herein. The data structures and software code for automatically implementing one or more acts described in this detailed description can be implemented by one of ordinary skill in the art in light of the present disclosure and stored, e.g., on a computer readable storage medium  162 , which may be any device or medium that can store code and/or data for use by a computer system such as processor  152 . The computer-usable medium  162  may be, but is not limited to, magnetic and optical storage devices such as disk drives, magnetic tape, compact discs, and DVDs (digital versatile discs or digital video discs). A communication port  164  may also be used to receive instructions that are used to program the computer  150  to perform any one or more of the functions described herein and may represent any type of communication connection, such as to the internet or any other computer network. Additionally, the functions described herein may be embodied in whole or in part within the circuitry of an application specific integrated circuit (ASIC) or a programmable logic device (PLD), and the functions may be embodied in a computer understandable descriptor language which may be used to create an ASIC or PLD that operates as herein described. 
     By way of example, the computer  150  may use the photoluminescence signals received from the detector  130  for each position on the surface of the sample  101  as stored in the 3D data cube and generate a photoluminescence image (or map) of the sample  101 . The photoluminescence image may be, e.g., a map of signal intensity of the photoluminescence signal. Inspection of the photoluminescence intensity image may be used for process control to assure that all portions of the sample  101  meet desired specifications. For example, where the sample  101  contains manufactured light emitting diodes (LEDs) chips, inspection of the photoluminescence data, e.g., in the form of a photoluminescence intensity image, can be used to assure each LED will have appropriate brightness. Similarly, the photoluminescence intensity image may be used for defect segmentation and predicting yield losses based on presence of localized low photoluminescence signals, which can lead to out-of-specification device at the Back-End of Line. If desired, the photoluminescence signal may be processed to produce other images or maps. For example, a Peak Lambda image may be produced to show the distribution of Peak Lambda over the sample surface, where Peak Lambda is the wavelength at which any given point in the image or map has maximum photoluminescence. Thus, for example, one point on the sample surface may emit maximum photoluminescence at 460.3 nm, while another point on the surface of the same sample may emit a maximum photoluminescence at 460.8 nm, which can be clearly seen with a Peak Lambda image. With the use of the spectral photoluminescence imaging, the different wavelengths of photoluminescence light emitted by the sample may be identified. Accordingly, the optical metrology device  100  may be used for process control to assure that all points on the sample surface emit photoluminescence within a predefined wavelength range. Additionally or alternatively, the photoluminescence signal can be transformed into a Full-Width-Half Maximum (FWHM) image, which shows the FWHM value for each Peak Lambda at any given point on the sample. The FWHM image, by way of example, may be used to assure that light emitting diodes (LEDs) that are manufactured with the sample emit light within predefined-width (band) spectral range. The photoluminescence signal may be processed to produce images of the sample  101  other than the photoluminescence intensity, Peak Lambda and FWHM images. For example, the photoluminescence signals may be processed or analyzed to produce different qualities, such as, e.g., a map of photoluminescence intensity at a given fixed wavelength, which is different than the maximum photoluminescence intensity map. Moreover, images or maps of interest may be produced by combining sets of images, such as those discussed, e.g., by pixel-by-pixel multiplication. Thus, the photoluminescence signal may be processed to produce other desired images of the sample  101  based on the recorded photoluminescence signals or analyzed in other ways for process control during manufacture of the sample. 
     Additionally, the computer  150  may process the received reflected broadband signal to determine a characteristic of the sample  101  at multiple positions and produce a map of that characteristic. For example, layer thickness may be calculated based on the spectral response associated with reflection of the broadband light, and thus, the received reflected broadband signal may be used to determine thickness for points on the sample surface and an epilayer thickness image (or map) may be produced. Thus, the optical metrology device  100  may be used to monitor the epitaxial layer thickness at any given point on the surface of the sample, which may be used to assure that the measured thickness is within predefined range for a given epitaxial growth process. Additionally, using the received scattered light, the computer  150  may produce a darkfield image of the surface of the sample  101 , thereby exposing surface defects, which may be related scratches, particles, epitaxial growth defects, e.g., stacking faults or mounds, etc. 
       FIGS. 3A and 3B  illustrate a perspective view and side view, respectively, of the dark channel observation of scattered light by optical metrology device  100 . As illustrated, the light source  110  produces illumination line  122  on the surface of the sample  101  using the optics  112  and scanning system  116 , including scanning mirror  118  and fixed mirror  120 . If the sample were defect free, light would be specularly reflected by the surface of the sample  101 , as illustrated by lines  125 , and would not be detected by the camera sensor  136 . When a surface defect  126  is present on the sample  101 , a portion of the illumination beam  114  is scattered when the illumination beam  114  is scanned over the defect  126 . The scattered light along the detector path  131  received by the detector  130  and enters the spectrometer  134  through the slit aperture. The field of view of the spectrometer  134  is limited by a slit aperture, and therefore, the sensor  136  only images the illumination line  122 . The specular reflection of the illumination beam  114  is not received by the spectrometer  134 . The spectrometer  134  normally separates light into wavelength bins in the spectral dimension of the 2D sensor array. The scattered light, however, originates from the narrow band light source  110  and, thus, the scattered received by detector  130  is deflected by the spectrometer  134  into the bin(s) corresponding to the wavelength(s) of the light source  110 , which is recorded by the sensor  136 . The performance of the scattered light channel may be further altered by adding light polarizer and analyzer into the optical path of the narrow band illumination beam  114 . By way of example, a beam polarizer  119  may optionally be placed downstream of the light source  110 , e.g., between the lens  112  and mirror  118 , and the analyzer  133  may be combined with the fore optics  132 . 
       FIGS. 4A and 4B  illustrate a perspective view and side view, respectively, of the bright field reflectance observation by optical metrology device  100 , omitting the light source  110  and associated optics for clarity. The broadband light source  140  illuminates the sample  101  along the illumination line  142  line extending across the width of the sample  101  along an orientation that matches the orientation of the entrance slit of the spectrometer  134 . As a result, the light from the light source  140  that is specularly reflected from the surface of the sample  101  enters the spectrometer  134  through the slit aperture. Within the spectrometer  134 , the broadband light is separated (binned) into a series of wavelengths, which are recorded by 2D sensor array in the sensor  136 , with one dimension of the 2D sensor array representing the spectral information and the other dimension representing the spatial information along the illumination line  142 . The arrangement of the broadband light source  140 , thus, is a bright field mode of operation in which an illumination line  142 , which may be the width of the sample  101 , is spectrally imaged. The use of a non-normal angle of incidence for the bright field observation advantageous simplifies uniform illumination and spectroscopic imaging of the sample  101  along illumination line  142 . 
       FIGS. 5A and 5B  illustrate a perspective view and side view, respectively, of the excitation of the sample  101  with the scanning illumination beam  114  and the emitted photoluminescence light collection by optical metrology device  100 . Similar to  FIGS. 3A and 3B  above, the light source  110  produces illumination line  122  on the surface of the sample  101  using the optics  112  and scanning system  116 , which may include scanning mirror  118  and fixed mirror  120 . As discussed above, fixed mirror  120  may be removed or replaced and/or a F-Theta lens may be used. The light from illumination beam  114  that is specularly reflected is illustrated by lines  125 . Another portion of the light from illumination beam  114 , however, enters the sample  101  and is absorbed. The absorbed energy generates electron-hole pairs, which upon recombination emit photoluminescence light along the excitation line, i.e., illumination line  122 . The generated photoluminescence light emitted from the excitation line exits the sample  101  at multiple directions with near Lambertian characteristics.  FIG. 6 , by way of example, illustrates the incident illumination beam  114  and the Lambertian characteristic of the emitted photoluminescence light (the specularly reflected light is not illustrated in  FIG. 6 ). In addition, because the illumination beam  114  is scanned across the width of the sample  101  along illumination line  122 , the photoluminescence light is emitted along the excitation direction, as illustrated in  FIG. 5A . The emitted photoluminescence light along the detector path  131  is received through the slit aperture of the spectrometer  134 , where the light is deflected by the spectrometer  134  into the bin(s) corresponding to the wavelength(s) of the photoluminescence light, which is recorded by the sensor  136 . 
       FIGS. 7 and 8  illustrate a side view (along the Y-Z plane) and a front view (along the X-Z plane), respectively, illustrating the simultaneous collection of dark field scattered radiation, bright field reflectance radiation and photoluminescence light by the optical metrology device  100 . As illustrated, the illumination beam  114  generates scattered light  115 , and excites photoluminescence light  117 , that are received by the spectrometer  134 , along with the reflected broadband light  143 . 
       FIG. 9 , by way of example, illustrates the signal separation of the three spectral channels (dark field scattered radiation, bright field reflectance radiation, and photoluminescence light) imaged by the 2D sensor array of sensor detector  136 . As illustrated, the 2D sensor array includes a first dimension (the X axis in  FIG. 9 ) representing the spatial information along the illumination lines  122  and  142 , with the other dimension representing the spectral information, i.e., wavelength λ, with respect to the signal intensity. In  FIG. 9 , the scattered laser beam signal is illustrated by peaks  202 , the photoluminescence signal is illustrated by peaks  204 , and the reflected broadband beam signal is illustrated by peaks  206 . 
     Thus, as illustrated in  FIGS. 7, 8, and 9 , the detector  130  can simultaneously record the photoluminescence light generated in the sample  101  in response to excitation by the illumination beam  114  and a bright field reflection of the broadband light  143 . If desired, the detector  130  may further record a dark field scattering of the illumination beam  114  by defects on the sample so that, if desired, three separate signals are simultaneously imaged. The three signals may be recorded simultaneously along the entire width of the sample  101  in a macroscopic mode, as opposed to being recorded point-by point or within a narrow field of view in a microscopic as is conventionally performed. Moreover, one detector  130  is used to collect all three signals, so that there is no spatial or time shifts between the three signals. A spectrometer  134  separates the signals into three different spectral information channels, i.e., signals are spectrally separated that are recorded in different wavelength bins (sensor pixels) with the 2D sensor array sensor of the detector  130 . It should be understood that the image frame illustrated in  FIG. 9  is for one position of the illumination lines  122  and  142  along the Y axis in  FIG. 1  and that as the stage  104  moves the sample  101  in the Y direction to scan the illumination lines  122  and  142  across the sample, the sensor  136  will produce a plurality of image frames for each position of the illumination lines  122  and  142  along the Y axis in  FIG. 1 . 
       FIG. 10  is a flow chart illustrating a method of optical metrology data from a number of light sources. As illustrated, a surface of a sample is illuminated at a first angle of incidence with a first light source along a first illumination line having an orientation in a first direction ( 302 ). The sample emits photoluminescence light from the first illumination line in response to excitation caused by light from the first light source. By way of example, as discussed above, the sample may be illuminated with an illumination beam produced, e.g., using a narrow band light source  110 , and that is scanned across the sample to produce the first illumination line. The surface of the sample is illuminated at a second angle of incidence with a second light source along a second illumination line having an orientation in the first direction and that overlays the first illumination line ( 304 ). The second angle of incidence is different than the first angle of incidence, and the second light source is a broadband light source. The broadband light is reflected from the surface of the sample. The photoluminescence light emitted by the sample along the first illumination line and specular reflection of broadband light from the second illumination line is detected with a two-dimensional array having a first dimension representing spatial information corresponding to position along the first illumination line and the second illumination line and a second dimension representing spectral information ( 306 ). The specular reflection of light from the first light source along the first illumination line may not be detected. The first illumination line and the second illumination line, which are overlaid, are moved across the surface of the sample in a second direction that is different than the first direction ( 308 ). For example, the first direction and second direction may be orthogonal. Movement of the first illumination line and the second illumination line may be caused by a linear stage or a rotary stage moving the sample  101  with respect to the illumination lines. If desired, movement of the first illumination line and the second illumination line may be caused by a stage moving the first illumination line and the second illumination line with respect to the sample  101 , e.g., by moving the light sources and associated optics with respect to the sample  101  which may be held stationary. A three dimensional data cube with two dimensions representing spatial information of the surface of the sample and a third dimension representing spectral information is produced using detected photoluminescence light and detected specular reflection of broadband light as the first illumination line and the second illumination line are moved across the surface of the sample ( 310 ). 
     Additionally, as discussed above, a portion of the light from the first light source may be scattered off surface defects on the sample as scattered light and the scattered light may be detected with the two-dimensional array, where the three dimensional data cube additionally includes the detected scattered light. Using the scattered light in the three dimensional data cube, a surface defect image of the surface of the sample may be produced. Additionally, a photoluminescence image of the surface of the sample may be produced using the detected photoluminescence light in the three dimensional data cube. For example, the photoluminescence image of the surface of the sample may be, e.g., a photoluminescence intensity image, photoluminescence Peak Lambda image, or a photoluminescence Full-Width-Half Maximum (FWHM) image. Additionally, a characteristic of the sample may be determined for a plurality of positions on the surface of the sample using the detected specular reflection of broadband light in the three dimensional data cube, and an image of the surface of the sample may be generated using the characteristic of the sample for the plurality of positions. For example, the epilayer thickness of the sample  101  may be determined at a plurality of locations on the surface of the sample  101  and an epilayer thickness image (or map) may be produced. As discussed above, the data from the three dimensional data cube may be analyzed for process control during manufacture of the sample. 
       FIG. 11 , by way of example, illustrates a side view of an optical metrology device  100 ′, that is similar to the optical metrology device  100  illustrated in  FIG. 7 , except that the narrow band illumination beam  114 ′ is illustrated as being incident from the same side of normal N as the broadband illumination  141 ′. Thus, while the narrow band illumination beam  114 ′ and broadband illumination  141 ′ are incident on the surface of the sample  101  from the same side of normal N, they use different angles of incidence, so that the specular reflection  125 ′ of the narrow band illumination  114 ′ is not along the detector path  131 , thereby enabling dark field mode measurement. As can be seen in  FIG. 11 , the angle of incidence of the illumination beam  114 ′ is greater than the angle of incidence of the broadband illumination  141 ′, with respect to normal N, but this is not strictly required.  FIG. 12 , by way of example, is similar to  FIG. 11 , and illustrates an optical metrology device  100 ″ that is configured so that the narrow band illumination beam  114 ″ has a smaller angle of incidence compared to the broadband illumination  141 ′, with respect to normal N, while the specular reflection  125 ″ of the narrow band illumination  114 ″ is still not along the detector path  131 , thereby enabling dark field mode measurement. 
     A significant challenge for wafer inspection equipment designers is the full wafer imaging of photoluminescence or reflected or scattered light at high resolution (on the order of hundred microns per pixel) at high speed (several dozens of wafers per hour) and with high signal collection efficiency. In order to achieve high measurement speed, low numerical aperture (NA) objective lenses and large field-of-view (FOV) arrangements are sometimes used to enable signal collection from the entire sample size in one signal capture. Per common definition, numerical aperture equals NA=n*sin(θ) where n is the index of refraction of the medium where the lens is used (1.00 for air) and θ is the maximal half-angle of light which can enter the lens through its aperture. Therefore, for typical large FOV imaging system, with a 20 mm diameter lens and typical object to lens distance of about 400 mm, the numerical aperture can be calculated as NA=0.025. Low NA objective lenses and large FOV arrangements leads to low signal collection efficiency and low instrument sensitivity, because in such an arrangement, the optics-to-sample distance must be large. A large optics-to-sample distance leads to a substantial loss of photoluminescence or scattered light radiation. Higher numerical aperture objective lenses allow for shorter optics-to-sample distances, better signal collection and higher instrument sensitivity, however, at expense of reducing the FOV of the optics. As a result, the measurement speed is low because several measurements and image stitching must be applied for reconstructing information at the full sample scale. 
     The above-described embodiments provide a high measurement resolution and high speed by exciting the sample with a laser beam by scanning the illumination spot across the surface, e.g., using a galvanometric mirror or a rotating polygonal mirror, while probing the photoluminescence or reflected or scattered radiation response with a lens-based objective combined with hyperspectral spectrometer and camera system. In order to achieve a desired high measurement speed, low numerical aperture optics, with field-of-view large enough for the entire sample (up to 300 mm) may be used. Such an arrangement allows for high measurement speed, e.g., dozens of wafers per hour, and high resolution, e.g., around hundred microns per pixel. The low numerical aperture of the objective, however, may lead to a large distance between the signal-collecting optics and sample. The optical signal collection efficiency therefore may be approved upon. 
     One way to improve the optical signal collection efficiency, for example, is by using higher numerical aperture optics, thereby enabling a decrease in the optics-to-sample distance thereby increasing the signal collection efficiency, however, at the expense of a reduced optics field-of-view. With the use of higher numerical aperture optics, only a portion of sample is scanned or viewed in one imaging cycle. Consequently, a series of measurements and image stitching are necessary for reconstructing an image of the entire sample. Such a solution inherently leads to low measurement speed and, ultimately, low measurement throughput. 
     Accordingly, in another embodiment, high NA optics having a length that e.g., is equal to or exceeds the desired image size, may be used to deliver a high collection efficiency of the optical signal. With the use of a signal collecting optic that extends over a length, e.g., a third, a half or the entire length of the illumination lines, the signal collecting optic may be placed close to the sample surface. It should be understood that if the signal collection optics extends a third of the length of the illumination line, then three scans will be necessary to capture data for the entire image, and likewise, if the signal collection optics extends a half of the length of the illumination line, then two scans will be necessary to capture data for the entire image, thereby reducing throughput relative to a signal collection optics that extends over the entire length of the illumination line. For example, the distance from the signal collection optic to the sample and the width of the signal collection optic may be configured to produce signal collection half-angle θ that is sufficient to produce an NA of 0.4 or higher. The high NA signal collection optics may be reflective or refractive based. Additionally, an optical conduit may be used with the optics to provide the received light to the detector. The implementation enables high resolution and high sensitivity signal collection at full sample size FOV, which allows overcoming the existing trade-offs between the high resolution, sensitivity, and speed. 
     For example, in one embodiment, in order to collect the photoluminescence or scattered radiation across the excitation line  122  shown in  FIG. 1 , reflective optics may be used, such as a long elliptical cylindrical mirror, e.g., a mirror having a right-elliptic-cylinder surface. By way of example,  FIG. 13  illustrates a perspective view of a long elliptical cylindrical mirror  402  that may be used to receive photoluminescence emitted from the sample  101  or light scattered the sample  101 . In the length direction, along the X axis, the mirror  402  is flat, while in the width direction, along the Y axis, the mirror  402  is elliptically curved with high NA, i.e. short focal distance. For example, the distance from the mirror to the sample may be 10 mm, and the contour size of the mirror may also be 10 mm, and thus, the signal collection half-angle θ is about 26 degrees, leading to an NA=0.45. The length of mirror  402 , for example, may exceed the desired image size, e.g., 300 mm sample size for the current wafer technology. The mirror  402 , along with collection optics, and spectrometer, discussed below, may be used in place of the detector  130 , e.g., illustrated in  FIGS. 1, 3A, 4A, 7, 11, and 12 . 
       FIG. 14  illustrates a side view (along the Y-Z plane) of the elliptical mirror  402  collecting photoluminescence or scattered radiation from a sample  101 . The mirror  402  may be placed in close proximity (several to a few dozen millimeters) to the sample  404  leading to a high collection efficiency of the optical photoluminescence or scattered radiation signal generated by the excitation laser beam  406 . The mirror  402  may include a slit  403  or multiple slits, through which the excitation laser beam  406  may pass through. Alternatively, the excitation laser beam  406  may pass under the mirror  402 , however, the use of a slit  403  permits the usage of a wider mirror, thus offering higher NA and better signal sensitivity. The laser beam  406  is scanned in the X direction across the wafer, e.g., with scanning system  116 , shown in  FIG. 1 , or the like. At each desired spatial position (along the X direction) along line  142  (illustrated in  FIG. 13  as positions X 1 , X 2 , X 3 , X 4 , and X 5 ), the mirror  402  collects the optical signal  407  from the sample  404  at a wide angle, which leads to a high instrument sensitivity. It should be understood that while discrete positions X 1 , X 2 , X 3 , X 4 , and X 5  are illustrated in  FIG. 13 , the beam  406  scans continuously across the sample  404 , and an optical signal  407  from all positions along the line  142  is received by the mirror  402 . Due to the linear configuration of the mirror  402  along the X direction, as illustrated in  FIG. 13 , with the excitation region being in a form of a line  142  across the entire sample in the X direction of the sample  404 , the resulting optical signal  407 , e.g., the photoluminescence radiation emitted from the sample  404  or radiation scattered by sample  404 , is focused by the elliptical cylindrical mirror  402  into a line  410  of the same length as the excitation line  142 . The excitation line  142  and line  410  may have the same length as the mirror  402 , i.e., a length that exceeds the desired image size, e.g., on the order of 300 mm. 
     The sample  404  is excited in a form of a line generated by moving the excitation beam  406  along the sample with the scanning system  116 . In one arrangement, in order to excite the sample  404 , the excitation beam  406  may pass outside the mirror  402  as the excitation beam  406  is scanned along the X direction. In one arrangement, the excitation beam  406  may pass under or over the mirror  402 . In another arrangement, the elliptical cylindrical mirror  402  may be include a narrow slit along the mirror length, such that the beam  406  may pass through the slit in the mirror  402  and may excite the sample  404  at any desirable angle, including normal angle. 
     The resulting optical signal  407  focused along the line  410 , as shown in  FIG. 13 , is obtained via focusing photoluminescence or scattered radiation with the elliptical cylindrical mirror  402 . The resulting optical signal  407 , which is focused along the line  410  needs to be delivered to a detector  130  for the purpose of recording the optical signal. Detectors, however, typically do not have input apertures in the shape of a 300 mm long line. Accordingly, the resulting optical signal  407 , which is focused along line  410  should be matched to the aperture of the detector  130 , with a minimal loss of light. In one embodiment, the resulting optical signal  407  focused by mirror  402  may be received by an optical conduit  412 , which has a linear signal reception end  414  (aligned with the line  410  in  FIG. 13 ), and a signal output end  416  having a shape that is compatible with the aperture of detector  130 . As illustrated, the specularly reflected light  409  is not received by the mirror  402  or the optical conduit  412 . If desired, the mirror  402  may include a slit (not shown) through which the specularly reflected light  409  passes through. 
     In another embodiment, in order to collect the photoluminescence or scattered radiation across the excitation line  122  shown in  FIG. 1 , refractive optics may be used, such as a long cylindrical focusing lens, e.g., a lens having a right-circular-cylinder shape. By way of example,  FIG. 15  illustrates a perspective view of a long cylindrical lens  502  that may be used to receive photoluminescence emitted from the sample  101  or light scattered the sample  101 . The cylindrical lens  502  may have a high NA, i.e. short focal distance. For example, if the diameter of the cylindrical lens is about 20 mm, and the lens center is also at distance of 20 mm from the sample, i.e. the air gap between the sample and the lens is 10 mm, leading to an NA=0.45. The length of lens  502 , for example, may exceed the desired image size, e.g., 300 mm sample size for the current wafer technology. The lens  502 , along with collection optics, and spectrometer, discussed below, may be used in place of the detector  130 , e.g., illustrated in  FIGS. 1, 3A, 4A, 7, 11, and 12 . 
       FIG. 16  illustrates a side view (along the Y-Z plane) of the cylindrical lens  502  collecting photoluminescence or scattered radiation from a sample  101 . The cylindrical lens  502  may be placed in close proximity (several to a few dozen millimeters) to the sample  101  leading to a high collection efficiency of the optical photoluminescence or scattered radiation signal generated by the excitation laser beam  406 . The laser beam  406  is scanned in the X direction across the wafer, e.g., with scanning system  116 , shown in  FIG. 1 , or the like. The cylindrical lens  502  collects the optical signals  407  from the sample  101  along the length of the line  142  (shown in  FIG. 15 ) on the sample  101  at a wide angle, which leads to a high instrument sensitivity. Due to the linear configuration of the cylindrical lens  502  along the X direction, as illustrated in  FIG. 15 , with the excitation region being in a form of a line  142  across the entire sample in the X direction of the sample  404 , the resulting optical signal  407 , e.g., the photoluminescence radiation emitted from the sample  404  or radiation scattered by sample  404 , is focused by the cylindrical lens  502  into a line  510  of the same length as the excitation line  142 . The excitation line  142  and line  510  may have the same length as the cylindrical lens  502 , i.e., a length that exceeds the desired image size, e.g., on the order of 300 mm. 
     The sample  101  is excited in a form of a line generated by moving the excitation beam  406  along the sample with the scanning system  116 . As illustrated, to excite the sample  101 , the excitation beam  406  passes below the cylindrical lens  502  as the excitation beam  406  is scanned along the X direction. The resulting optical signal  407  focused along the line  510 , as shown in  FIG. 15 , is obtained via focusing photoluminescence or scattered radiation with the cylindrical lens  502 . The resulting optical signal  407 , which is focused along the line  510  needs to be delivered to a detector  130  for the purpose of recording the optical signal. As discussed above, the resulting optical signal  407 , which is focused along line  510  should be matched to the aperture of the detector  130 , with a minimal loss of light. In one embodiment, the resulting optical signal  407  focused by cylindrical lens  502  may be received by an optical conduit  412 , which has a linear signal reception end  414  (aligned with the line  510  in  FIG. 15 ), and a signal output end  416  having a shape that is compatible with the aperture of detector  130 . As illustrated, the specularly reflected light  409  is not received by the cylindrical lens  502  or the optical conduit  412 . 
       FIG. 17A  illustrates the linear signal reception end  414  of the optical conduit  412  to receive the optical signal  407  from the optics  402  or  502  and  FIG. 17B  illustrates a rectangular signal output end  416  to provide the optical signal  407  to the detector  130 . The optical conduit  412  includes numerous optical fibers  418  between the linear signal reception end  414  and a rectangular signal output end  416 . As illustrated, the fibers  418  may be arranged at the linear signal reception end  414  in a single row that matches the length of the optical signal  407  or to match the length of the optics, e.g., elliptical cylindrical mirror  402  or cylindrical lens  502 . By way of example, 1298 fibers can be used, each of 0.245 mm in diameter to form a line which is approximately 318 mm long, slightly larger than the 300 mm sample in order to collect most of signals from the sample edges. If desired, a different number of fibers or different fiber diameters may be used, or a different number of fiber rows may be used at the linear signal reception end  414 . Moreover, if the sample size is different, e.g., 200 mm, a different number of fibers may be used, e.g., 891 fibers can be used to form a line which is approximately 218 mm long. Of course, if the length of the optical conduit  412  is shorter than the length of the optics  402  or  502 , a portion of the optical signal  407  may not be received by the optical conduit  412 , and thus, the detector  130 , and multiple passes may be required to acquire data for the entire sample. The fibers  418  are mechanically re-arranged from the linear signal reception end  414  to the rectangular signal output end  416 . For example, as illustrated in  FIG. 17B , the fibers may be arranged in a number of layers. For example, 1298 fibers on the linear signal reception end  414  may be re-arranged into 118 layers by 11 layers giving the same number of fibers on the spectrometer side (118×11=1298 fibers). For a different sized sample, e.g., a 200 mm sample, where 891 fibers are on the linear signal reception end  414 , the 891 fibers may be re-arranged into 81 layers by 11 layers giving the same number of fibers on the spectrometer side (81×11=891 fibers). The re-arrangement into the rectangular shape of 81 by 11 layers, per the example, resizes the optical conduit  412  from 218 mm long (by 0.245 mm) at the linear signal reception end  414  to approximately 20 mm by 2.5 mm at the rectangular signal output end  416 , which is accepted by the detector  130 . Thus, the optical signal  407  is focused by the optics  402  or  502  into the linear signal reception end  414  and the optical fibers  418  are used to provide the optical signal to the rectangular signal output end  416 , which is coupled to the detector  130 . Such arrangement facilitates delivery of the optical signal  407  into the signal detector  130 , which ultimately converts the optical radiation into electrical signal. Different shapes on the signal output end  416  of the optical conduit  412  can be used such as, for example, rectangular, square or circular. Additionally, further focusing optics may be applied between the rectangular signal output end  416  and the detector  130  to achieve even better matching, if desirable. 
     The optical signal  407  upon exiting from the optical conduit  412  may by further formed by the exit optics to match the signal to the detector input. A variety of the detection scenarios can be used depending on the desired end result. For example, the detector  130  may use a spectrometer. As illustrated in  FIG. 18 , the optical signal  407  after exiting the optical conduit  412  may be filtered by an optical filter  452  and provided to the slit of a spectrometer  454 , where the light is dispersed by a grating or prism into different wavelengths, and finally delivered into the array of CCD or CMOS camera sensors  456  and recorded by a data acquisition device  458 , which provides the data to the processor  152  for analysis. Thus, the detector  130  may capture multiple output signals while the excitation beam  406  is scanned across the wafer in the X direction in order to obtain spectral and spatial information. 
     In another embodiment, the detector  130  may use a Photo Multiplier Tube (PMT) or avalanche photodiode (APD). As illustrated in  FIG. 19 , the optical signal  407  after exiting the optical conduit  412  may be filtered by an optical filter  452  and provided to the Photomultiplier Tube (PMT) or Avalanche Photo Diode (APD)  462 . The optical signal  407  is converted into electrical signal and is recorded by the data acquisition device  458 , which provides the data to the processor  152  for analysis. In this embodiment, no spectral information is acquired, but rather all wavelengths are integrated into one electrical signal. Thus, it may be desirable to synchronize the first light source  110  and the second light source  140  ( FIG. 1 ) so that the resulting signals are not received at the same time by the detector  130 . 
       FIG. 20  illustrates a side view (along the Y-Z plane) illustrating, by way of example, the simultaneous collection of dark field scattered radiation, photoluminescence light, and optionally, bright field reflectance radiation, by the optical metrology device using the elliptical mirror  402  with the optical conduit  412 . As illustrated, the illumination beam  114  generates scattered light  115 , and excites photoluminescence light  117 , that are received by the spectrometer  134 , along with the reflected broadband light  143 . 
     The detector  130 , which may include including optics  132 , spectrometer  134 , and sensor  136  can simultaneously record the photoluminescence light generated in the sample  101  in response to excitation by the illumination beam  114  and scattered light from the illumination beam  114 , and optionally a bright field reflection of the broadband light  143 , e.g., if the optical conduit  412  has a signal output end in the form of a line to provide spatial information. If desired, the detector  130  may further record a dark field scattering of the illumination beam  114  by defects on the sample so that, if desired, three separate signals are simultaneously imaged. The detector  130  is used to collect all three signals, so that there is no spatial or time shifts between the three signals. A spectrometer  134  separates the signals into three different spectral information channels, i.e., signals are spectrally separated that are recorded in different wavelength bins (sensor pixels) with the 2D sensor array sensor of the detector  130 . 
     With the use of the elliptical mirror  402 , the optical signal emitted from the surface of the sample  101  is collected by high NA mirror-based optics, which delivers high collection efficiency of the optical signal and high instrument sensitivity. In the X direction, the sample is excited in a form of a line generated by scanning system  116 , which enables high measurement speed. The measurement arrangement is complemented by application of an optical conduit  412 , which enables collection of the optical signal from a sample-size-long line and transformation of the optical signal into a desired shape without any mechanical movement, such as a small circular area or in a line. Application of the multi-fiber conduit with several thousand individual fibers enables high measurement resolutions on the order of tens of microns per pixel. As a result, the apparatus delivers high sensitivity, high resolution and high speed (measurement throughput). 
     Although specific embodiments are provided herein for instructional purposes, the described embodiments are not limiting. Various adaptations and modifications may be made without departing from the scope of the present discloser. For example, a rotary stage may be used in place of a linear stage for scanning the illumination lines  122  and  142  across the surface of the sample  101 . Moreover, the scanning system  116  may be modified to eliminate, e.g., the fixed mirror, or an F-theta lens may be used for focusing the illumination beam  114  on the surface of the sample  101 . Other modifications and variations are possible, and therefore, the spirit and scope of the appended claims should not be limited to the foregoing description.