Sensor module for scanning electron microscopy applications

Abstract

A scanning electron microscopy (SEM) system is disclosed. The SEM system includes an electron source configured to generate an electron beam and a set of electron optics configured to scan the electron beam across the sample and focus electrons scattered by the sample onto one or more imaging planes. The SEM system includes a first detector module positioned at the one or more imaging planes, wherein the first detector module includes a multipixel solid-state sensor configured to convert scattered particles, such as electrons and/or x-rays, from the sample into a set of equivalent signal charges. The multipixel solid-state sensor is connected to two or more Application Specific Integrated Circuits (ASICs) configured to process the set of signal charges from one or more pixels of the sensor.

What is claimed: 
     
         1 . A method of inspecting a sample comprising:
 generating a scan clock signal;   generating a first electron beam;   deflecting the first electron beam to a first location on the sample;   directing a signal generated by the sample in response to the first electron beam to a pixel;   detecting the charge collected by the pixel to generate an electrical signal corresponding to the charge collected by the pixel; and   comparing the electrical signal with a first threshold and a second threshold and determining the presence of an element if the electrical signal is greater than the first threshold and the electrical signal is smaller than the second threshold.   
     
     
         2 . The method of  claim 1 , wherein the first threshold is smaller than the electrical signal corresponding to a characteristic energy of the element, and the second threshold is greater than the electrical signal corresponding to a characteristic energy of the element. 
     
     
         3 . The method of  claim 1 , wherein the element comprises at least one of silicon, aluminum, copper, tungsten, or titanium. 
     
     
         4 . The method of  claim 1 , further comprising:
 deflecting the first electron beam to a second location on the sample;   directing a second signal generated by the sample in response to the first electron beam to a pixel;   detecting a second charge collected by the pixel to generate a second electrical signal corresponding to the second charge collected by the pixel;   comparing the second electrical signal with the first threshold and the second threshold and determining the presence of the element if the second electrical signal is greater than the first threshold and the second electrical signal is smaller than the second threshold; and   creating a map of where the element is present on the sample.   
     
     
         5 . The method of  claim 4 , further comprising:
 comparing the first and second electrical signal with a third threshold and a fourth threshold and determining the presence of a second element if the second electrical signal is greater than the third threshold and the second electrical signal is smaller than the fourth threshold; and   creating a map of where at least one of the first element or second element is present on the sample.   
     
     
         6 . A method of inspecting a sample comprising:
 generating a scan clock signal;   generating a first electron beam;   deflecting the first electron beam synchronous with the scan clock signal to scan an area on the sample;   directing a signal generated by the sample in response to the electron beam to a cluster comprising two or more pixels;   detecting charge collected by the cluster in a first time interval, wherein the first time interval is synchronized to the scan clock to generate a first electrical signal corresponding to the charge collected by the cluster in the first time interval and converting the first electrical signal into a first digital signal;   detecting the charge collected by the cluster in a second time interval, wherein the second time interval is synchronized to the scan clock to generate a second electrical signal corresponding to the charge collected in the second time interval and converting the second electrical signal into a second digital signal, wherein converting the second electrical signal starts before converting the first electrical signal is completed; and   determining the presence of a defect by analyzing the first digital signal and the second digital signal.   
     
     
         7 . The method of  claim 6 , wherein detecting the charge comprises summing the charges from the two pixels. 
     
     
         8 . The method of  claim 7 , wherein the summing comprises summing one of a voltage domain and a current domain.