Abstract:
Semiconductor device structures include markings that are covered by visibly opaque materials. The markings include alpha-numeric characters and are recessed within the surface of a fabrication substrate. Each character may include a series of circular holes in the substrate. The recessed characters may be filled with a material that does not cover a surface of the fabrication substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation of application Ser. No. 09/542,782, filed Apr. 4, 2000, pending. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to methods and apparatus for detecting marks or indicia formed in substrates. In particular, the present invention relates to methods and apparatus for detecting marks or indicia formed in substrates and covered by one or more material layers.  
         [0004]     2. Background of Related Art  
         [0005]     Semiconductor devices and the various structures thereof are fabricated on semiconductor substrates, such as wafers and other large-scale substrates, that include a layer of semiconductive material, such as silicon, gallium arsenide, or indium phosphide. Typically, large numbers of a single type of semiconductor device are fabricated on a large-scale substrate, such as a wafer. While many types of semiconductor devices are fabricated in large quantities and on a large number of wafers to maximize the efficiency with which fabrication equipment is utilized, some types of semiconductor devices are fabricated in relatively small quantities on only one or a few wafers.  
         [0006]     In order to maximize the throughput of fabrication equipment during fabrication of semiconductor devices in small quantities, it is desirable to simultaneously perform the fabrication process steps that are not specific to a certain type of semiconductor device, such as material layer deposition processes on a plurality of wafers, regardless of the type of semiconductor devices being fabricated on each wafer. To accomplish this task, each wafer must be separated from the other wafers with which it is grouped prior to device-specific processes (e.g., patterning of material layers), then routed and transferred to a process location appropriate for the type of semiconductor device being fabricated thereon.  
         [0007]     The substrates on which semiconductor devices are produced are typically marked with characters or other indicia that identify the types of semiconductor devices being fabricated thereon. These marks are then identified following the performance of fabrication process steps that are not device-specific so that the substrates may be routed to locations where appropriate device-specific fabrication processes may be performed. Such marks are typically recessed in the substrate or in a material layer over the substrate. For example, these marks may be etched or laser ablated into the substrate or a material layer thereover. Characters (e.g., numbers) may be formed by a group of small holes in a dot-matrix type arrangement.  
         [0008]     Conventionally, the marks on substrates have been identified by directing a narrow wavelength range of light, often from a red, green, or amber light-emitting diode (LED) source, toward the substrate at a location where the marks should be located. A camera, such as a charge-coupled device (CCD) type camera, optically analyzes the illuminated marks. The optically analyzed marks are then identified by a computer executing optical character recognition (OCR) or similar software. As a backup, images of the marks may also be visually displayed for human scrutiny.  
         [0009]     While such conventional mark reading apparatus are useful for detecting substrate marks that remain substantially uncovered with material or that are covered with very thin layers or with layers of some visually transparent or translucent materials, this type of equipment cannot be used to identify marks that are covered with one or more layers of visibly opaque materials or even with some translucent materials. It is also difficult to identify marks formed in a substrate, such as silicon, when transparent or translucent materials (e.g., silicon oxides) of very similar color are disposed thereover. As a consequence, prior to routing substrates to a device-specific fabrication process location, it is often necessary to remove material layers from the portion of a substrate where marks are believed to be located. These additional material removal processes are, however, somewhat undesirable.  
         [0010]     U.S. Pat. No. 4,896,034, issued to Kiriseko on Jan. 23, 1990 (hereinafter “the &#39;034 Patent”) discloses a method whereby a bar code formed in a silicon wafer and covered by one or more material layers is identified by directing one or more infrared wavelengths of electromagnetic radiation toward the bar code through the back side of the substrate. As silicon is relatively transparent to infrared wavelengths of electromagnetic radiation, the infrared radiation readily travels therethrough without a significant degree of reflectance or absorption. An infrared radiation detector is positioned so as to detect only the infrared radiation reflected from the recesses of the bar code. The method of the &#39;034 Patent can, however, only be employed to read marks or indicia through the back side of the wafer and not from the more readily accessible active surface of the wafer. Furthermore, the &#39;034 Patent only teaches a method for reading bar codes, not for identifying other types of marks, such as characters, or other indicia recessed in a substrate or in a layer disposed over the substrate.  
         [0011]     The inventor of the subject matter disclosed herein is unaware of any teaching in the art of a method or an apparatus for identifying marks or indicia through one or more opaque or visibly opaque material layers.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention includes a method for identifying marks or indicia that are formed in a substrate or a material layer thereover and that are covered with one or more opaque or visibly opaque material layers. Apparatus for effecting the method of the present invention are also within the scope of the present invention.  
         [0013]     The method of the present invention includes scanning across a location of a substrate where one or more marks comprising recesses or cavities in the surface of the substrate or material thereon are believed to be located, electromagnetic radiation of a specific wavelength or of various wavelengths within a specific range. The recesses or cavities defining the mark or marks may be covered with one or more material layers. The intensity, or reflectance, of each wavelength of electromagnetic radiation reflected by the substrate or the material layers formed therein is measured as electromagnetic radiation is being scanned onto the substrate. A change in the reflectance of one or more reflected wavelengths of electromagnetic radiation indicates a change in thickness of one or more material layers or of a recess or cavity formed in the substrate or a material layer disposed thereover and filled with a different material, each of which indicates the presence of a mark. Data of the locations of marks are correlated to detect the marks, the identities of which may then be recognized.  
         [0014]     A system incorporating teachings of the present invention includes at least one source of electromagnetic radiation, a reflectometer, and a detector associated with the reflectometer. An actuation element moves the light source and reflectometer relative to the substrate or the substrate relative to the light source and reflectometer to facilitate scanning of the light source and reflectometer relative to the substrate. The detector may include a processor operating under instructions from a program to monitor and sense changes in a reflectance of one or more wavelengths of electromagnetic radiation reflected by the substrate or a material layer thereon and measured by the reflectometer. Preferably, the detector includes memory to store information regarding the locations on the substrate from which electromagnetic radiation of one or more wavelengths is reflected at a reflectance that varies from a baseline intensity, or reflectance, as measured at regions of the substrate where neither marks nor semiconductor device structures are located. This stored information represents locations on the substrate where at least portions of marks are present. The system may also include a component that analyzes, or correlates, the information representing the locations of portions of marks on the substrate to facilitate identification of the marks. This component may comprise a processor, in this capacity operating under instructions from a data plotting program. The identities of the marks may also be recognized by the component, which may comprise a processor operating under instructions from an optical character recognition or similar program.  
         [0015]     Other features and advantages of the present invention will become apparent to those in the art through a consideration of the following description, the accompanying drawings, and the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0016]      FIG. 1  is a schematic top representation of a substrate, in this case a semiconductor wafer, including a mark that may be identified using the method or system of the present invention;  
         [0017]      FIG. 2  is a schematic representation of a system incorporating teachings of the present invention;  
         [0018]      FIG. 3  is a cross-sectional representation of the substrate of  FIG. 1  illustrating the direction of incident radiation thereon and the radiation reflected therefrom;  
         [0019]      FIG. 4  is a cross-sectional representation of a substrate including holes recessed in the active surface thereof, a first material disposed in the holes, and a layer of a second material disposed over both the active surface and the first material;  
         [0020]      FIG. 5  is a graph illustrating the reflectance of various wavelengths of radiation reflected from a first location of the substrate depicted in  FIG. 4 ;  
         [0021]      FIG. 6  is a graph illustrating the reflectance of various wavelengths of radiation reflected from a second location of the substrate depicted in  FIG. 4 ;  
         [0022]      FIG. 7  is a cross-sectional representation of a substrate including a hole recessed in the active surface thereof and different materials disposed in the hole and in layers over the active surface of the substrate;  
         [0023]      FIG. 8  is a graph illustrating the reflectance of various wavelengths of radiation reflected from a specific location of the substrate shown in  FIG. 7 ;  
         [0024]      FIG. 9  is a cross-sectional representation of another substrate including a hole in substantially the same location as the substrate depicted in  FIG. 7 , with the same material being disposed in the hole and layers of the same materials disposed over the active surface of the substrate, each of the layers having different thicknesses than the layers of the substrate shown in  FIG. 7 ; and  
         [0025]      FIG. 10  is a graph illustrating the reflectance of various wavelengths of radiation reflected from a specific location of the substrate shown in  FIG. 9 , which corresponds to the specific location from which radiation was reflected from the substrate depicted in  FIG. 7 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]     With reference to  FIGS. 1 and 3 , a wafer  20  including marks  60  formed in the substrate material  23  thereof is illustrated. Marks  60  are located on an area A of wafer  20  near an edge  22  thereof, opposite the portion of edge  22  where an orientation notch  21  is located. As depicted, marks  60  each include a series of circular holes  61 . Each mark  60  includes a wall  62  that extends downwardly into substrate material  23 . An edge  63  is formed at the junction of each wall  62  and an active surface  24  of substrate material  23 .  
         [0027]      FIG. 1  illustrates wafer  20  with two material layers  25 ,  26  located over active surface  24  of substrate material  23  and at least partially filling holes  61  that form marks  60 . As the one or more material layers  25 ,  26  disposed over active surface  24  of substrate material  23  may comprise materials that are opaque or nearly opaque to visible wavelengths of electromagnetic radiation (i.e., visible light), such as polyimide, polysilicon, metal silicides, metal oxides, silicon nitrides, metal nitrides, resist coatings, or thin metal layers, or materials that have a similar appearance (e.g., color, translucence, etc.) to substrate material  23 , one or both of layers  25 ,  26  may impede or prevent the detection of holes  61  and, thus, the identification of marks  60  by conventional methods that include directing light toward active surface  24 .  
         [0028]      FIG. 2  illustrates an identification system  10  that is configured to detect holes  61  and to identify marks  60  formed in a wafer  20 , such as that illustrated in  FIG. 1 , or another large-scale substrate and covered by one or more material layers  25 ,  26 . Identification system  10  is part of a larger system for routing wafers  20  or other large-scale substrates with different types of semiconductor devices being fabricated thereon to different fabrication process locations.  
         [0029]     Identification system  10  includes a support structure  36  to which a wafer  20  or other substrate may be secured, a radiation source  30  oriented to direct electromagnetic incident radiation  34  of one or more wavelengths toward support structure  36 , a reflectometer  32  positioned to receive electromagnetic radiation of one or more wavelengths reflected from support structure  36  or a wafer disposed thereon, which is also referred to herein as reflected radiation  35 , and a processor  42  associated with reflectometer  32 .  
         [0030]     Radiation source  30  may include one or more sources of incident radiation  34 . While radiation source  30  may emit electromagnetic incident radiation  34  of any wavelength that will be reflected by substrate material  23  (see  FIG. 1 ) of wafer  20  or another substrate, it is preferred that identification system  10  include a radiation source  30  that emits incident radiation  34  of a plurality of wavelengths in the range of about 100 nm to about 1,000 nm. As an example, a radiation source  30  including a deuterium lamp and a tungsten-xenon (W—Xe) lamp would emit wavelengths over the broad range of about 140 nm to more than about 800 nm. Radiation sources  30  that emit incident radiation  34  including a plurality of wavelengths in other ranges (e.g., about 300 nm to about 780 nm, about 220 nm to about 800 nm, etc.) may also be used in identification system  10 . Alternatively, identification system  10  may include a radiation source  30  that emits incident radiation  34  of a very narrow range of wavelengths (e.g., about 500 nm to about 550 nm) or of only a single wavelength (e.g., 550 nm).  
         [0031]     Incident radiation  34  is preferably emitted from radiation source  30  in the form of a beam having a rectangular or circular cross-section. The width of the beam (i.e., the distance across a cross-section of the beam, such as the diameter of a beam of a circular cross-section) is preferably about the same as the distance across a recessed feature of a mark formed in wafer  20 , another substrate, or a layer of material disposed over wafer  20  or another substrate. The beam of incident radiation may, however, have any spot size (e.g., about 10 μm across, about 1 μm across, or smaller).  
         [0032]     A particular radiation source  30  may be selected based on the ability of one or more wavelengths of incident radiation  34  emitted therefrom to at least occasionally penetrate one or more material layers formed over wafer  20  or another substrate and to be reflected by a material, such as silicon, gallium arsenide, or indium phosphide, of wafer  20  or of another large-scale substrate.  
         [0033]     Radiation source  30  is preferably positioned to emit incident radiation  34  toward wafer  20  or another substrate at an angle that facilitates optimal reception of reflected radiation  35  by reflectometer  32 . For example, if radiation source  30  and reflectometer  32  are positioned close to one another, radiation source  30  may be positioned so as to direct incident radiation  34  toward wafer  20  or other substrate at a nearly perpendicular angle thereto. Alternatively, if radiation source  30  and reflectometer  32  are spaced a greater distance apart from one another, radiation source  30  may be positioned so as to direct incident radiation  34  toward wafer  20  or another substrate at a more oblique angle thereto.  
         [0034]     Reflectometer  32  is positioned so as to optimally receive reflected radiation  35  from wafer  20  or another substrate. Reflectometer  32  may be any known device capable of receiving reflected radiation  35  of wavelengths emitted by radiation source  30  and of measuring the intensity, or reflectance, of each wavelength of reflected radiation  35  relative to the intensity of incident radiation  34  of the same wavelength. As illustrated in greater detail in  FIG. 3 , the reflectance of reflected radiation  35  is typically different than the intensity of incident radiation  34 , and depends upon the wavelength range of incident radiation  34  and reflected radiation  35 , the absorption coefficients substrate material  23  of wafer  20  and of each of the material layers (e.g., layers  25 ,  26 ,  27 ,  28 ) formed thereon, and the distance incident radiation  34  and reflected radiation  35  travel through each material layer formed on substrate material  23 . Reflectometer  32  may include a sensing element (not shown), as known in the art, such as a charge-coupled device (CCD) array, that separately measures the reflectance of each of the different wavelengths of reflected radiation  35 .  
         [0035]     With continued reference to  FIG. 2 , identification system  10  is configured so that incident radiation  34  from radiation source  30  may be scanned, preferably in a raster fashion, across a wafer  20  or other substrate disposed on support structure  36 . In addition, reflectometer  32  of identification system  10  may be maintained at a fixed distance from radiation source  30  to facilitate reception of reflected radiation  35  during scanning of incident radiation  34  onto wafer  20 . Such scanning may be effected with a support structure  36  capable of at least two-dimensional movement (i.e., along x and y axes) in a plane substantially parallel to the plane of the active surface of a wafer  20  or other substrate held by support structure  36 , while radiation source  30  and reflectometer  32  remain in horizontally fixed positions. Support structure  36  may also be capable of movement along a third axis (i.e., the z-axis) relative to radiation source  30  and reflectometer  32  to facilitate focusing of incident radiation  34  on wafer  20  or another substrate. Actuation apparatus  38  for moving support structure  36  in two or more dimensions are known in the art and include, but are not limited to, DC-motors, stepper motors, and rotary hydraulic motors. Alternatively, radiation source  30  and reflectometer  32  may be moved along two or more axes relative to a fixed support structure  36  and a wafer  20  or other substrate supported thereby. As another alternative, each of support structure  36 , radiation source  30 , and reflectometer  32  may be moved along at least one axis to facilitate scanning or focusing of incident radiation  34  on a wafer  20  or other substrate.  
         [0036]     Identification system  10  may also include a processor  42 , such as a known computer microprocessor that includes known types of logic circuits. Processor  42 , including the logic circuits thereof, may, under control of one or more programs, perform a variety of tasks, including analyzing the reflectance of each wavelength of reflected radiation  35 , determining the locations on wafer  20  or another substrate which caused the reflectance of at least one wavelength of reflected radiation  35  to change, correlating data of the locations on wafer  20  or another substrate that caused a change in the reflectance of at least one wavelength of reflected radiation  35 , and identifying a mark from the correlated data.  
         [0037]     As a first example of the operation of processor  42 , processor  42  may be associated with reflectometer  32  so as to receive information about the measured intensity, or reflectance, of each wavelength of reflected radiation  35  from a specific location on wafer  20  or another substrate. A program directs processor  42  to convert the measured reflectance to data that may be analyzed by processor  42 , utilized by processor  42  under control of a program, or output to a user. The reflectance of each wavelength of radiation  35  reflected from locations of wafer  20  or another substrate where neither marks nor semiconductor device structures are present will be identified by processor  42  as a baseline reflectance for that wavelength of reflected radiation  35 . Processor  42  compares the measured reflectance of each wavelength of reflected radiation  35  to the corresponding baseline for that wavelength to determine whether the reflectances of any of the wavelengths of reflected radiation vary from their corresponding baselines for each scanned location.  
         [0038]     In a second example, processor  42  may be associated with support structure  36  or actuation apparatus  38  therefor so as to receive data corresponding to a location on wafer  20  or another substrate from which radiation  35  was reflected. Processor  42  may, under control of a program, associate this locational data with data of the reflectance of radiation  35  reflected from each identified location of wafer  20  or another substrate. When correlated with the corresponding reflectance data generated in accordance with the preceding example, the program instructing processor  42  may identify the locations on wafer  20  or another substrate at which the reflectances of one or more wavelengths of reflected radiation varied from the corresponding baselines.  
         [0039]     A third example of the use of processor  42  includes correlating data of the locations on wafer  20  or another substrate that caused a change in the reflectance of at least one wavelength of reflected radiation  35 . Each of the locations where the measured reflectance of at least one wavelength of reflected radiation  35  varied from the baseline reflectance may be mapped to provide data about the character of one or more marks.  
         [0040]     A fourth example of the use of processor  42  includes employing an optical character recognition (OCR) program to identify a characterized mark. Known optical character recognition systems, such as the plug-in marketed as ACUREADER/OCR II™ by Cognex Corporation of Natick, Mass., may be used to instruct processor  42 .  
         [0041]     Processor  42 , under control of programming of a known type, may also direct the movement of support structure  36  or of radiation source  30  and reflectometer  32  to facilitate scanning of incident radiation  34  on wafer  20  or another substrate, as well as the measurement by reflectometer  32  of the reflectance of reflected radiation  35 . Such scanning may be completely automated or controlled by way of a user interface  46 , such as a computer keyboard, mouse, or touch pad, associated with processor  42 .  
         [0042]     Processor  42  may similarly control the wavelengths and intensity of incident radiation  34  directed onto wafer  20  or another substrate. These types of variations in incident radiation  34  may be caused, for example, by controlling the amount of power supplied to radiation source  30 , by the use of filters to prevent certain wavelengths of radiation from source  30  from reaching wafer  20  or other substrates, and by selectively activating radiation sources  30  that emit radiation of different wavelengths or wavelength ranges.  
         [0043]     A display  44 , such as a printer, a video monitor, or another known data output device, may also be associated with processor  42  to provide a user of identification system  10  with information about the reflectances of radiation measured by reflectometer  32 , the character of one or more marks  60  or a portion thereof determined by processor  42 , or the identities of one or more marks  60  that have been determined by processor  42 . Of course, processor  42  may also output other data to a display  44 , including, without limitation, data regarding the wavelengths of incident radiation  34  directed onto wafer  20 , the timing of the identification process, the type of semiconductor devices being fabricating on wafer  20 , or the preceding and/or next fabrication stages for wafer  20 .  
         [0044]     Each of the foregoing uses of processor  42  may be effected by a single processor  42  or by separate, associated processors  42 . Programming of processor  42  for each of these functions may be in the form of software or hardware programs.  
         [0045]      FIG. 3  illustrates an example of the effects of directing incident radiation  34  onto a wafer  20  or other substrate with one or more layers  25 ,  26  over a mark  60  formed therein. Depending upon the type of material from which a layer or layers (e.g., layers  25 ,  26  shown in  FIG. 1 ) overlying substrate material  23  is formed, some wavelengths of electromagnetic radiation will be reflected by the layer or layers, while all or portions of other wavelengths of incident radiation  34  may penetrate the layer or layers and be reflected by substrate material  23 . A change in the intensity, or reflectance, of one or more of the wavelengths of reflected radiation  35  from baseline reflectance values for those wavelengths of radiation  35  reflected from the same substrate (e.g., wafer  20 ) with one or more layers of the same material or materials formed thereover may be caused by a variation in the thickness of one or more of the material layers or the presence of a recess, such as a hole  61 , in active surface  24  of substrate material  23 . Variations in the thickness of one or more material layers typically occur when the material layers are formed over a recess, such as hole  61 , formed in active surface  24 . Thus, when incident radiation is scanned over an area of wafer  20  where one or more marks  60  are believed to be located, such as area A, opposite notch  21  ( FIG. 1 ), a change in the reflectance of one or more of the wavelengths of reflected radiation  35  from a baseline value may indicate the presence of a hole  61  in active surface  24 .  
         [0046]     The mark identification method of the present invention works best when at least the outermost layer  26  formed over a mark  60  in a wafer  20  or other substrate is at least partially transparent to at least one wavelength of incident radiation  34 . Even thin metallization layers (e.g., layers of titanium, tungsten, copper, aluminum, and platinum having thicknesses of about 500 Å or less) may be at least partially transparent to one or more wavelengths of incident radiation  34 .  
         [0047]      FIGS. 4-10  further illustrate the use of incident radiation  34  of one or more wavelengths and of the measurement of reflected radiation  35  and the analysis of deviation in the intensity, or reflectance, patterns of one or more wavelengths of reflected radiation  35  to detect a mark  60  (see  FIG. 1 ) or portion thereof (e.g., a hole  61 ) through one or more material layers formed over mark  60 .  
         [0048]     Turning to  FIG. 4 , a wafer  20  including a substrate material  23  of silicon with two material layers  25 ,  26  thereon is depicted. While layer  25  fills holes  61  formed in active surface  24  of substrate material without substantially covering active surface  24 , layer  26  covers layer  25  and active surface  24 . As illustrated, layer  25  is a silicon oxide layer having a thickness of about 1,000 Å, while layer  26  is formed from tungsten silicide (WSi x ) and has a thickness of about 1,250 Å. As incident radiation  34  of a wavelength range of about 250 nm to about 750 nm is directed toward locations  70  and  72  of wafer  20 , different intensities, or reflectances, are measured by reflectometer  32  (see  FIG. 2 ) for some of the wavelengths of reflected radiation  35 .  
         [0049]      FIG. 5  graphically depicts the measured reflectance for various wavelengths of radiation  34 ,  35  directed toward and reflected from location  70  of wafer  20 , which is a location at which layer  26  directly contacts active surface  24  of substrate material  23 .  FIG. 6  shows the measured reflectance for various wavelengths of radiation  34 ,  35  directed toward and reflected from location  72  of wafer  20 , which is a location where layer  26  overlies material  25 -filled holes  61  formed in active surface  24  of substrate material  23 . As can be seen by comparing the reflectance patterns illustrated in  FIGS. 5 and 6 , as incident radiation  34  (see, e.g.,  FIG. 3 ) is scanned in a direction parallel to a plane of wafer  20  from location  70  to location  72  (see  FIG. 4 ), the intensity, or reflectance, of reflected radiation  35  of various wavelengths changes (particularly at wavelengths of about 550 nm and greater), indicating the presence of a hole  61  or other recess in active surface  24 .  
         [0050]     By way of further example,  FIG. 7  shows a wafer  20  with a silicon substrate material  23 , a hole  61  formed in active surface  24  of substrate material  23 , a first material layer  25  substantially filling hole  61  without covering active surface  24 , a second material layer  27  covering first material layer  25  and active surface  24 , and a third material layer  28  disposed over second material layer  27 . Layer  25  may comprise silicon oxide and have a thickness of about 90 Å. Layer  27  may comprise polysilicon and have a thickness of about 850 Å. Layer  28  may comprise tungsten silicide (WSi x ) and have a thickness of about 1,250 Å.  
         [0051]      FIG. 9  illustrates a wafer  20 ′ with layers  25 ′,  27 ′, and  28 ′ formed from the same materials as layers  25 ,  27 , and  28 , respectively, depicted in  FIG. 7 . The thicknesses of layers  25 ′,  27 ′, and  28 ′ differ from the thicknesses of layers  25 ,  27 , and  28 , however, with layer  25  having a thickness of about 1,000 Å, layer  27  having a thickness of about 4,000 Å, and layer  28  having a thickness of about 1,250 Å.  
         [0052]      FIG. 8  graphically depicts the measured reflectances for various wavelengths of radiation  34 ,  35 , respectively, directed toward and reflected from location  76  of wafer  20 , where layers  27  and  28  overlie material  25 -filled holes  61  formed in active surface  24  of substrate material  23 .  FIG. 10  graphically depicts the measured reflectances for various wavelengths of radiation  34 ,  35  directed toward and reflected from location  76 ′ of wafer  20 ′, where layers  27 ′ and  28 ′ overlie material  25 ′-filled holes  61 ′ formed in active surface  24 ′ of the substrate material  23 ′ thereof. A comparison of  FIGS. 8 and 10  shows that the measured intensities, or reflectances, of a number of wavelengths of radiation  35  reflected from corresponding locations  76 ,  76 ′ of wafers  20 ,  20 ′, respectively, vary significantly. These variations are caused primarily by differences in the thicknesses of one or more of the material layers formed over wafers  20  and  20 ′.  
         [0053]     An example of the use of identification system  10  is explained with reference to  FIGS. 1-3 . To begin, a wafer  20  such as that illustrated in  FIG. 1  is placed upon support structure  36 , shown in  FIG. 2 . While  FIG. 2  illustrates a single wafer being disposed upon support structure  36 , the support structure may be a wafer carrier or other apparatus by which one or more wafers  20  or other large-scale substrates are carried during conventional semiconductor device fabrication processes. Furthermore, although  FIG. 2  illustrates wafer  20  as being oriented in a substantially horizontal position, identification system  10  may be used to identify one or more marks  60  on wafers  20  that are not horizontally oriented (i.e., that are vertically or otherwise oriented).  
         [0054]     Radiation source  30  emits incident radiation  34  of one or more wavelengths toward an area of wafer  20  where a mark  60  is believed to be located, typically opposite notch  21 . The wavelengths of incident radiation  34 , as well as the intensities of these wavelengths, may be controlled by processor  42 . Incident radiation  34  may include wavelengths to which at least one of the material layers (e.g., layers  25 ,  26 ) formed over wafer  20  is at least partially transparent. Stated another way, one or more of the wavelengths of incident radiation  34  will at least occasionally pass through one or more of the material layers formed over wafer  20 .  
         [0055]     Radiation  35  reflected by substrate material  23  of wafer  20  or by a material layer, such as layers  25 ,  26  on wafer  20 , is received by reflectometer  32 , which measures the intensity, or reflectance, of reflected radiation  35 . Generally, the intensity, or reflectance, of a wavelength of radiation changes as it passes through a material. Reflectance typically varies when the thickness of the material through which the wavelength of radiation changes.  
         [0056]     Processor  42  receives intensity signals from reflectometer  32 , as well as signals that indicate the location of wafer  20  from which radiation  35  was reflected, which are also referred to herein as locational signals. The intensity signals may be used by processor  42  to generate intensity data, while the locational signals may be used by processor  42  to generate locational data. The generated intensity data may be compared to baseline intensity data for corresponding wavelengths of reflected radiation  35 . If the generated intensity data differ from the baseline intensity data, processor  42  may store locational data to indicate a location on wafer  20  where a hole  61  is located. In addition, in order to confirm the presence of a hole  61  at a location where a the measured intensity data differed from the baseline intensity data, the intensity data may be compared to known intensity data, such as intensity data for a layer of a particular material and of a particular thickness or known intensity data that corresponds to the presence of a hole  61  or other recess in the same type of substrate material  23 .  
         [0057]     The position of either support structure  36  or of radiation source  30  is moved (e.g., under control of processor  42 ) to effect scanning of incident radiation  34  onto another location of wafer  20 . The subsequent processes are then repeated to determine whether a hole  61  is present on the next location of wafer  20 . Each of these processes are repeated until area A ( FIG. 1 ), where one or more marks  60  are believed to be located has been substantially completely scanned with incident radiation  34  and reflected radiation  35  from each of the scanned locations of that area has been measured.  
         [0058]     Once area A or another area of wafer  20  has been at least partially scanned, processor  42  may correlate or map the data of each of the stored locations of the scanned portion of wafer  20  to provide data regarding the character of one or more marks  60  or a portion thereof. The character of the mark or marks  60  or portion thereof is then analyzed (e.g., by processor  42  or by another processor) by use of the OCR program to identify the mark or marks  60  formed in wafer  20 .  
         [0059]     When the mark or marks  60  of wafer  20  have been identified, wafer  20  may be sent to the next appropriate process location under control of a processor (e.g., processor  42 ) or otherwise as known in the art.  
         [0060]     Of course, data generated by one or more processors (e.g., processor  42 ) associated with identification system  10  may be output to one or more associated displays  44  at any time during the identification process.  
         [0061]     Identification system  10  ( FIG. 2 ) may be used to identify one or more marks  60  or portions thereof formed in a wafer  20  during various stages of the semiconductor device fabrication process. Identification system  10  is particularly useful for identifying marks  60  on wafers  20  following material layer deposition processes and prior to patterning one or more material layers that have been formed over wafer  20 .  
         [0062]     Although the foregoing description contains many specifics, these should not be construed as limiting the scope of the present invention, but merely as providing illustrations of some of the presently preferred embodiments. Similarly, other embodiments of the invention may be devised which do not depart from the spirit or scope of the present invention. Features from different embodiments may be employed in combination. The scope of the invention is, therefore, indicated and limited only by the appended claims and their legal equivalents, rather than by the foregoing description. All additions, deletions and modifications to the invention as disclosed herein which fall within the meaning and scope of the claims are to be embraced thereby.