Scanning system for inspecting anamolies on surfaces

Abstract

An optical scanning system and method for detecting anomalies, including pattern defects and particulate contaminants, on both patterned and unpatterned surfaces, using a light beam, scanning at a grazing angle with respect to the surfaces, a plurality of detectors and an interchannel communication scheme to compare data from each detector, which facilitates characterizing anomalies. The light beam illuminates a spot on the surface which is scanned over a short scan-line. The surface is moved in a manner so that the spot is scanned over its entire area in a serpentine fashion along adjacent striped regions. The plurality of detectors include groups of collector channels disposed circumferentially around the surface, a bright field reflectivity/autoposition channel, an alignment/registration channel and an imaging channel. The collector channels in each group are symmetrically disposed, in the azimuth, on opposite sides of the center of the scan line. The position of the collector channels, as well as the polarization of the beam, facilitates distinguishing pattern defects from particulate contaminants. The bright field reflectivity/autoposition channel is positioned to receive specularly reflected light that carries information concerning local variation in reflectivity, which is used to classify detected anomalies, as well as determine variations in the height of the surface. The alignment/registration channel is positioned to detect a maximum of the light scattered from the pattern on the surface to ensure that the streets of die present on the surface are oriented so as not to be oblique with respect to the scan line. The imaging channel combines the advantages of a scanning system and an imaging system while improving signal/background ratio of the present system.

1 - 52 . (canceled)  
   
   
       53 . An optical scanning system for detection of anomalies, such as particles, on a surface comprising: 
 means for producing a beam of light,    means for directing the beam onto a sample surface of the type having locations with periodic and non-periodic features, producing an illuminated spot thereon with the beam having a grazing angle of incidence,    means for scanning the spot,    means for detecting light scattered from the surface, including a plurality of detectors symmetrically positioned about the surface, to collect laterally scattered light, defining a first group of detectors, with each of the plurality of detectors producing a first electrical signal representing scattered light; and    means, in electrical communication with the opposed detectors, for processing each first electrical signal independently of the other to determine the presence or absence of anomalies, the processing means including a means for producing a map from each first electrical signal, defining a first map set, the first map set representing the entire scan path over the surface, the processing means including a means for comparing maps of the first map set to identify anomalies.    
   
   
       54 . The optical scanning system as recited in  claim 53  wherein the scanning means scans the spot in a serpentine fashion over the sample surface.  
   
   
       55 . The optical scanning system as recited in  claim 53  wherein the detecting means includes a second group of a plurality of detectors symmetrically positioned about the surface, to collect forwardly scattered light, with each of the plurality of detectors in the second group producing a second electrical signal representing scattered light.  
   
   
       56 . The optical scanning system as recited in  claim 55  wherein the producing means forms a second map set from the second electrical signals, representing the entire scan path, with the comparing means comparing maps of the second map set to identify anomalies.  
   
   
       57 . The optical scanning system as recited in  claim 56  wherein the classifying means produces a third signal representing the presence of pattern defects and a fourth signal representing particulate contaminants, based upon scattered light information carried by the first and second map set.  
   
   
       58 . The optical scanning system as recited in  claim 55  wherein each collection channel includes a variable aperture to optimize the collection angle for detecting scattered light.  
   
   
       59 . The optical scanning system as recited in  claim 55  wherein each collection channel includes a variable polarization filter to allow light having desired predetermined states of polarization to pass therethrough, while attenuating light that does not have the desired state of polarization, and a polarizing element placed in the path of the beam, between the scanning means and the surface, to polarize the beam to a predetermined state of polarization, wherein each collection channel detects an anomaly selected from the group consisting of particulate contaminant or pattern defect.  
   
   
       60 . The scanning system as recited in  claim 59  wherein the polarizing element is of the type to provide an S polarization state of the beam passing therethrough.  
   
   
       61 . The scanning system as recited in  claim 59  wherein the polarizing element is of the type to provide a P polarization state of the beam passing therethrough.  
   
   
       62 . The scanning system as recited in  claim 59  wherein the polarizing element is of the type to provide a left handed circular polarization state of the beam passing therethrough.  
   
   
       63 . The scanning system as recited in  claim 59  wherein the polarizing element is of the type to provide a right handed circular polarization state of the beam passing therethrough.  
   
   
       64 . The scanning system as recited in  claim 60  wherein the variable filters associated with the first group of detectors attenuates polarized scattered light with the variable filters associated with the second group of detectors attenuating scattered light which is not in a P state of polarization.  
   
   
       65 . The scanning system as recited in  claim 61  wherein the variable filters associated with the first group of detectors attenuates polarized scattered light with the variable filters associated with the second group of detectors attenuating scattered light which is not in an S state of polarization.  
   
   
       66 . The scanning system as recited in  claim 60  wherein the plurality of variable filters attenuates scattered light not having an S state of polarization.  
   
   
       67 . The scanning system as recited in  claim 60  wherein the plurality of variable filters attenuates scattered light not having a P state of polarization.  
   
   
       68 . The scanning system as recited in  claim 61  wherein the plurality of variable filters attenuates scattered light not having an S state of polarization.  
   
   
       69 . The scanning system as recited in  claim 61  wherein the plurality of variable filters attenuates scattered light not having a P state of polarization.  
   
   
       70 . The optical scanning system as recited in  claim 53  wherein the first group of detectors are a pair of opposed detectors oriented to receive light scattered in a direction less than 30 degrees above the surface and symmetrically disposed on opposite sides of the scanning beam at an azimuthal angle of 75 to 95 degrees, with respect to the scanning beam.  
   
   
       71 . The optical scanning system as recited in  claim 54  wherein the second group of detectors are a pair of spaced-apart detectors oriented to receive light scattered in a direction less than 30 degrees above the surface arid symmetrically disposed on opposite sides of the scanning beam at an azimuthal angle of 30 to 60 degrees, with respect to the scanning system.  
   
   
       72 . The optical scanning system as recited in  claim 53  further including an autoposition detector for collecting specularly reflected light from the spot, the autoposition detector having a means for measuring a change in height of the surface.  
   
   
       73 . The optical scanning system as recited in  claim 72  wherein the autoposition detector includes a reflectivity channel producing a normalization signal representing a threshold voltage based upon the intensity of reflecting light, wherein those anomalies represented by a signal having a voltage level less than the threshold voltage are discarded.  
   
   
       74 . The optical scanning system as recited in  claim 53  including a normal detector positioned normal to said surface to collect upwardly scattered light from the spot.  
   
   
       75 . The optical scanning system as recited in  claim 74  wherein the normal detector includes an array of sensors for forming pixels consisting of a plurality of electronic bit signals corresponding to the image viewed by the sensors, and means for transferring a charge from each said pixel in synchronism with the scanning spot so that each pixel receives light scattered from a unique area illuminated by the spot along the scan line.  
   
   
       76 . The optical scanning system as recited in  claim 53  wherein the features include a plurality of dies each having streets forming a grid and further including an alignment detector positioned above said surface to maximize collection of light scattered from the features on the surface, the alignment detector being connected to a means for aligning the surface so that the scan line is not oblique to the streets of the die.  
   
   
       77 . The optical scanning system as recited in  claim 56  further including an autoposition detector, collecting specularly reflected light, and a normal detector positioned normal to the surface, collecting upwardly scattered light, the autoposition detector producing a normalization signal representing selected light and the normal detector producing a third electrical signal representing upwardly scattered light, with the producing means forming a third map from the normalization signal and a fourth map from the third electrical signal, whereby the producing means performs logical operations, comparing the maps to detect and characterize anomalies, on the surface.  
   
   
       78 . The optical scanning system as recited in  claim 77  wherein the logical operations are digital operations from the group consisting of AND, OR and XOR.  
   
   
       79 . An optical scanning system for detection of anomalies on a surface comprising: 
 means for producing a beam of light,    means for directing the beam onto a sample surface of the type having locations with periodic and non-periodic features, producing an illuminated spot thereon with the beam having a grazing angle of incidence,    means for scanning said spot, in a serpentine fashion, over the sample surface, each scan defining a short scan line,    means for detecting light scattered from the surface, including a pair of opposed collection channels symmetrically positioned about the surface, on opposite sides of the beam to collect laterally scattered light and a pair of spaced apart collection channels symmetrically positioned about the surface, on opposite sides of the beam to collect forwardly scattered light with the opposed collection channels producing a first and a second electrical signal and the spaced apart collection channels producing a third and a fourth electrical signals, each electrical signal representing scattered light impinging on a collection channel, and    means, in electrical communication with each collection channel, for processing each of the signals therefrom independently of the remaining signals to determine the presence or absence of anomalies.    
   
   
       80 . The optical scanning system as recited in  claim 79  wherein the opposed collection channels are positioned on opposite sides of the beam of an azimuthal angle in the range of 75-95 degrees, and the spaced apart channels are positioned on opposite sides of the beam at an azimuthal angle in the range of 30-60 degrees.  
   
   
       81 . The optical scanning system as recited in  claim 79  wherein the processing means includes a means for producing a map from each electrical signal representing the entire scan path over the surface with a first map generated from the first signal, the second map generated from the second signal, the third map generated from the third signal and the fourth map generated from the fourth signal, the processing means including a means for comparing the first map with the second map, with the differences between them being anomalies recorded as a first composite map, and comparing the third map with the fourth map, with the differences between them being anomalies recorded as a second composite map.  
   
   
       82 . The optical scanning system as recited in  claim 81  wherein the processing means further includes a classifying means for comparing the first composite map with the second composite map, thereby classifying the anomalies present as a material selected from the group consisting of particulate contaminant or pattern defect.  
   
   
       83 . The optical scanning system as recited in  claim 82  including a normal detector positioned normal to said surface to collect upwardly scattered light from the spot.  
   
   
       84 . The optical scanning system as recited in  claim 83  wherein the normal detector includes an array of sensors for forming pixels consisting of a plurality of electronic bit signals corresponding to the image viewed by the sensors, and means for transferring a charge from each of the pixels in synchronism with the scanning spot so that each pixel receives light scattered from a unique area illuminated by the spot along the scan line.  
   
   
       85 . The optical scanning system as recited in  claim 84  wherein each collection channel includes a variable aperture to optimize the collection angle for detecting scattered light.  
   
   
       86 . The optical scanning system as recited in  claim 85  wherein each collection channel includes a variable polarization filter, each of the variable filters being adjusted to permit detection of light having a state of predetermined polarization, and a polarizing element placed in the path of the beam, between the producing means and the surface to place the beam in a predetermined state of polarization, wherein each collection channel detects an anomaly selected from the group consisting of particulate contaminant and pattern defect.  
   
   
       87 . An optical scanning system for detection of anomalies on a surface comprising: 
 means for producing a beam of light,    means for directing the beam onto a sample surface, producing an illuminated spot thereon,    means in the path of the light beam for scanning said spot along a scan line,    a detector having an array of sensors for forming pixels consisting of a plurality of electronic bit signals corresponding to the image viewed by the array of sensors, and means for transferring a charge from each of the pixels in synchronism with the scanning spot so that each pixel receives light scattered by the spot along the scan line, producing an electrical signal representing scattered light, and    means, in electrical communication with the detector, for processing the electrical signals received from the sensors, producing an image.    
   
   
       88 . The optical scanning system as recited in  claim 87  wherein the array of sensors are positioned normal to the sample surface for collecting upwardly scattered light therefrom.  
   
   
       89 . The optical scanning system as recited in  claim 87  wherein each pixel is positioned so as to receive light scattered from a unique area of the sample surface, illuminated by the spot along the scan line.  
   
   
       90 . A method of detecting anomalies on a surface comprising: 
 scanning an illuminated spot over a substantially flat surface of the type having locations with periodic and non-periodic features,    simultaneously detecting laterally scattered light on opposite sides of the scanning spot at an azimuthal angle in the range 75-95 degrees, with respect to the scanning spot, producing a first and a second electrical signal representing scattered light,    producing a first map from the first signal, representing light detected along the entire scan path and a second map from the second signal, representing light detected along the entire scan path, and    comparing the first map with the second map, differences between them representing anomalies on the surface, defining a first composite map.    
   
   
       91 . The method as recited in  claim 90  further including the steps of simultaneously detecting forwardly scattered light on opposite sides of the scanning spot at an azimuthal angle in the range of 30-60 degrees, producing third and fourth electrical signal, 
 producing a third map from the third signal, representing light detected along the entire scan path and a fourth map from the fourth signal, representing light detected along the entire scan path, and    comparing the third map with the fourth map, differences between them representing anomalies on the surface, defining a second composite map.    
   
   
       92 . The method as recited in  claim 91  further including the step of classifying the anomalies by comparing the first composite map with the second composite map, wherein each anomaly detected is classified as a material selected from the group consisting of particulate contaminant or pattern defect.  
   
   
       93 . The method as recited in  claim 90  further including the steps of, detecting specularly reflected light and producing a normalization signal having a threshold voltage level based upon the intensity of detected reflected light, and 
 normalizing the differences found by comparing the voltage level of the first, second, third and fourth signals with the threshold level, wherein anomalies represented by a signal having a voltage level less than the threshold level are discarded.    
   
   
       94 . The method as recited in  claim 87  further including the step of moving the surface so that it is scanned in a serpentine fashion over the entire surface.  
   
   
       95 . The method as recited in  claim 91  wherein both laterally and forwardly scattered light is detected at an angle of elevation of less than 30 degrees, with respect to the surface.  
   
   
       96 . The method as recited in  claim 91  wherein the features include a plurality of dies each of which has a plurality of streets positioned at rights angles to one another and further including the step of, 
 aligning the surface so that a scan line is not oblique with respect to the streets.    
   
   
       97 . A method of detecting anomalies on a surface comprising: 
 scanning an illuminated spot over a surface of, the type having locations with periodic and non-periodic features,    simultaneously detecting laterally scattered light, forwardly scattered light, upwardly scattered light and specularly reflected light with an optical detecting system, and producing a first plurality of electrical signals, representing laterally scattered light, a second plurality of electrical signals, representing forwardly scattered light, a third signal representing upwardly scattered light and a normalization signal representing specularly reflected light,    producing a first map from the first signal, a second map from the second signal, a third map from the third signal and a fourth map from the normalization signal with each map representing light detected along the entire scan path, and    comparing the first map, second map, third map and fourth map to determine the presence and type of anomaly.    
   
   
       98 . The method as recited in  claim 97  wherein the normalization signal defines a threshold voltage and further including the step of comparing the voltage level of the first, second, third and fourth signals with the normalization signal, wherein anomalies represented by a signal having a voltage level less than the threshold are discarded.  
   
   
       99 . The method as recited in  claim 97  wherein the comparing step includes performing logical operations on data represented by the first, second, third and fourth maps, the logical operations selected from the group consisting of AND, OR and XOR.  
   
   
       100 . The method as recited in  claim 97  wherein laterally scattered light is detected at the same azimuthal angle, simultaneously on opposite sides on the scanning spot with the azimuthal angle being in the range 75-95 degrees, with respect to the scanning spot, and the forwardly scattered light is detected at the same azimuthal angle, simultaneously on opposite sides on the scanning spot, with the azimuthal angle being in the range 30-60 degrees, with respect to the scanning spot.  
   
   
       101 . The method as recited in  claim 100  wherein laterally and forwardly, scattered light is detected at an angle of elevation of less than 30 degrees, with respect to the surface.  
   
   
       102 . The method as recited in  claim 97  wherein the upwardly scattered light is detected by an array of sensors for forming pixels consisting of a plurality of electronic bit signal corresponding the an image viewed by the sensor and further including the step 
 transferring a charge from each pixel in synchronism with the scanning of that spot so that each pixel receives light scattered from a unique area illuminated by the spot along the scan line.    
   
   
       103 . The method as recited in  claim 97  further including the step of producing a reflectivity map of the surface based upon the information carried by the normalization signal.  
   
   
       104 . A surface inspection method for distinguishing between particles on a surface and defects in the surface, comprising: 
 receiving the surface;    causing the surface to be scanned by a P-polarized beam of light at an oblique angle to the surface;    collecting light scattered from the surface at a first imaging channel, and at least at a second oblique channel, said second channel offset angularly from said first imaging channel;    converting the collected light from the two channels into respective signals representative of light scattered into the two channels;    comparing the two signals and    determining whether a defect is one of a particle or a defect in the surface based at least in part on said comparing.    
   
   
       105 . The method of  claim 104 , wherein said second channel is offset at least forwardly of said first channel.  
   
   
       106 . The method of  claim 105 , wherein said second channel receives substantially only forward scattered light.  
   
   
       107 . The method of  claim 104 , wherein said first channel includes a scattering direction substantially perpendicular to the surface.  
   
   
       108 . The method of claims  104 - 107 , wherein said signals are representative of intensities of the light scattered into said channels.  
   
   
       109 . The method of claim  104 - 107 , wherein said P-polarized light is incident upon said surface at an angle in a range of about 55 to 85 degrees of perpendicular.  
   
   
       110 . The method of claim  104 - 107 , wherein the light collected in said second channel is scattered at an angle in the range of about 3 to 30 degrees from the surface.  
   
   
       111 . The method of  claim 104 , additionally including forming a first display map identifying the locations of surface defects on the surface.  
   
   
       112 . The method of  claim 111 , including forming a second display map identifying the locations of particle defects on the surface.  
   
   
       113 . The method of  claim 104 , wherein the scanning further comprises translationally transporting the surface along a path.  
   
   
       114 . A surface inspection method for distinguishing between particles on a surface and defects in the surface, comprising: 
 receiving the surface at a surface inspection system;    scanning the surface at the inspection system with a beam of P-polarized light at an angle of incidence oblique to the surface;    collecting light scattered from the surface at the inspection system at a first central zone, and at least at a second oblique zone offset angularly from said first zone;    converting the collected light components from said zones into respective signals representative of light scattered into said zones;    comparing said signals and    determining whether a defect is one of a particle or a defect in the surface based at least in part on said comparing.