In-line photoluminescence imaging of semiconductor devices

Abstract

Methods and systems are presented for acquiring photoluminescence images ( 2 ) of silicon solar cells and wafers ( 4 ) as they progress along a manufacturing line ( 36 ). In preferred embodiments the images are acquired while maintaining motion of the samples. In certain embodiments photoluminescence is generated with short pulse, high intensity excitation, ( 8 ) for instance by a flash lamp ( 50 ) while in other embodiments images are acquired in line scanning fashion. The photoluminescence images can be analysed to obtain information on average or spatially resolved values of one or more sample properties such as minority carrier diffusion length, minority carrier lifetime, dislocation defects, impurities and shunts, or information on the incidence or growth of cracks in a sample.

1 . A method for analysing a sample of a semiconductor material, said method comprising the steps of:
 passing said sample to a measurement zone;   applying an illumination to said sample to produce a photoluminescence response from said semiconductor material; and   conducting at least a photoluminescence analysis of said sample in said measurement zone while maintaining motion of said sample,   
       wherein said photoluminescence analysis comprises providing a multi-pixel image capture device for acquiring an image of the photoluminescence emitted from said sample. 
     
     
         2 . A method according to  claim 1 , wherein said method is performed with a system that meets Class 1 accessible emission limits (AELs) without said measurement zone being enclosed. 
     
     
         3 . A method according to  claim 1 , wherein the illumination source, the image capture device or an optical element associated with the illumination source or the image capture device moves or pivots to follow the motion of said sample. 
     
     
         4 . A method according to  claim 1 , wherein said analysis is performed in less than 1 second. 
     
     
         5 . A method according to  claim 1 , wherein said illumination is applied to an area of said sample and said image is acquired with an area image capture device in an acquisition time t,
 wherein said sample is moving at a speed v relative to said area image capture device, and wherein the product of the acquisition time t (s) and the speed v (m·s −1 ) is less than a distance on said sample corresponding to one row of pixels in said area image capture device.   
     
     
         6 . A method according to  claim 5 , wherein said method is applied to a sample of a semiconductor material comprising silicon, and said photoluminescence is generated with an illumination intensity between about 10 and 100 W·cm −2 . 
     
     
         7 . A method according to  claim 5 , wherein said illumination is applied to the entire area of a surface of said sample, and said area image capture device acquires an image of the photoluminescence emitted from said entire area. 
     
     
         8 . A method according to  claim 1 , wherein said illumination is provided by a source positioned so as to illuminate a first portion of said sample and said image capture device is positioned so as to detect photoluminescence emitted from a second portion of said sample, wherein said first portion and said second portion are at least partially overlapping, and wherein said method further comprises the steps of:
 moving said sample relative to said source and to said image capture device such that said second portion is scanned across a substantial area of said sample; and   interrogating said image capture device repeatedly to acquire an image of the photoluminescence emitted from said area.   
     
     
         9 . A method according to  claim 8 , wherein said image of the photoluminescence is acquired with a line camera or a time-delay integration camera. 
     
     
         10 . A method according to  claim 8 , wherein said first portion is wholly within said second portion. 
     
     
         11 . A method according to  claim 8 , wherein said source provides broad area illumination of said sample. 
     
     
         12 . A method according to  claim 8 , wherein said first and second portions extend across a substantial fraction of a dimension of said sample, said dimension being substantially perpendicular to the direction of movement of said sample. 
     
     
         13 . A system for conducting an analysis of a sample of a semiconductor material, said apparatus comprising:
 a transport mechanism for transporting said sample to a measurement zone;   analysis equipment for conducting at least a photoluminescence analysis of said sample within said measurement zone, said analysis equipment comprising a source of predetermined illumination suitable for generating photoluminescence from said semiconductor material, and a multi-pixel image capture device for acquiring an image of the photoluminescence emitted from said sample; and   motion apparatus to maintain motion of said sample within said measurement zone during said analysis.   
     
     
         14 . A system according to  claim 13 , wherein said system is adapted such that, in use, said system meets Class 1 accessible emission limits (AELs) without said measurement zone being enclosed. 
     
     
         15 . A system according to  claim 13 , wherein said source, said image capture device or an optical element associated with said source or said image capture device is capable of moving or pivoting to follow the motion of said sample. 
     
     
         16 . A system according to  claim 13 , wherein said source of predetermined illumination is adapted to illuminate an area of said sample, and said image capture device is an area image capture device adapted to capture an image of said photoluminescence in an image acquisition time t, wherein said motion apparatus moves said sample at a speed v relative to said area image capture device such that the product of the image acquisition time t (s) and the speed v (m·s −1 ) is less than a distance on said sample corresponding to one row of pixels in said area image capture device. 
     
     
         17 . A system according to  claim 16 , wherein said system is configured to conduct an analysis of a sample of a semiconductor material comprising silicon, and said source is configured to generate photoluminescence with an illumination intensity between about 10 and 100 W·cm −2 . 
     
     
         18 . A system according to  claim 16 , wherein said source is adapted to illuminate the entire area of a surface of said sample, and said area image capture device is adapted to acquire an image of the photoluminescence emitted from said entire area. 
     
     
         19 . A system according to  claim 13 , wherein said source is adapted to illuminate a first portion of said sample, and said image capture device is adapted to detect photoluminescence emitted from a second portion of said sample, wherein said first portion and said second portion are at least partially overlapping, and wherein said analysis equipment further comprises an interrogation module for interrogating said image capture device repeatedly while said motion apparatus moves said sample such that said second portion is scanned across a substantial area of said sample, to acquire an image of the photoluminescence emitted from said substantial area. 
     
     
         20 . A system according to  claim 19 , wherein said image capture device comprises a line camera or a time-delay integration camera. 
     
     
         21 . A system according to  claim 19 , wherein said first portion is wholly within said second portion. 
     
     
         22 . A system according to  claim 19 , wherein said source is adapted to provide broad area illumination of said sample. 
     
     
         23 . A system according to  claim 19 , wherein said first and second portions extend across a substantial fraction of a dimension of said sample, said dimension being substantially perpendicular to the direction of movement of said sample.