Projection electron beam apparatus and defect inspection system using the apparatus

Abstract

A sample is evaluated at a high throughput by reducing axial chromatic aberration and increasing the transmittance of secondary electrons. Electron beams emitted from an electron gun 1 are irradiated onto a sample 7 through a primary electro-optical system, and electrons consequently emitted from the sample are detected by a detector 12 through a secondary electro-optical system. A Wien filter 8 comprising a multi-pole lens for correcting axial chromatic aberration is disposed between a magnification lens 10 in the secondary electro-optical system and a beam separator 5 for separating a primary electron beam and a secondary electron beam, for correcting axial chromatic aberration caused by an objective lens 14 which comprises an electromagnetic lens having a magnetic gap defined on a sample side.

1 : An electron beam apparatus having a projection electro-optical system for inspecting a surface of a sample, characterized by comprising:
 an electron gun for emitting an electron beam;   a primary electro-optical system for guiding the emitted electron beam onto a sample for irradiation;   a detector for detecting electrons;   a secondary electro-optical system for guiding an electron beam bearing information on the surface of the sample, emitted from the sample irradiated with the electron beam, to said detector,   wherein at least one of said primary electro-optical system and said secondary electro-optical system includes a multi-pole lens.   
   
   
       2 . An electron beam apparatus according to  claim 1 , characterized in that said multi-pole lens is disposed between a magnification lens of said secondary electro-optical system and beam separating means for separating a primary electron beam and a secondary electron beam. 
   
   
       3 . An electron beam apparatus according to  claim 2 , characterized in that an objective lens closest to the surface of the sample comprises an electromagnetic lens having a gap defined on a sample side, and axial chromatic aberration caused by said electromagnetic lens can be corrected by a multi-pole lens disposed in said secondary electro-optical system. 
   
   
       4 . An electron beam apparatus according to  claim 1 , characterized in that said multi-pole lens is disposed between a reducing lens in said primary electro-optical system and beam separating means for separating a primary electron beam and a secondary electron beam. 
   
   
       5 . An electron beam apparatus according to  claim 4 , characterized in that:
 said primary electro-optical system includes an axially symmetric lens,   wherein said axially symmetric lens is set such that off-axis aberration at an end of a visual field is equal to or less than a previously set predetermined value, and comprises an electromagnetic lens, and said lens has a Bohr radius larger by a factor of 50 or more than a maximum diameter of the visual field.   
   
   
       6 . An electron beam apparatus according to  claim 1 , characterized in that:
 said primary electro-optical system comprises means for converting an electron beam from said electron gun into multiple electron beams; and   said detector comprises a detection unit for individually detecting multiple electron beams which make up a secondary electron beam emitted from a point on the sample irradiated with the multiple electron beams.   
   
   
       7 . An electron beam apparatus according to  claim 1 , characterized in that said multi-pole lens comprises quadrupole lenses at four stages. 
   
   
       8 . A defect inspection system for inspecting a surface of a sample for defects, characterized by comprising:
 the electron beam apparatus having a projection electro-optical system according to  claim 1 ;   image capturing means for generating an image of the surface of the sample based on information on the surface of the sample included in electrons detected by said detector of said electron beam apparatus; and   defect evaluating means for testing the presence or absence of a defect on the surface of the sample by comparing the captured image with a reference image.   
   
   
       9 . A defect inspection system according to  claim 8 , further comprising:
 a sample transfer system for transferring the sample;   a sample carrier unit for carrying the sample thereon;   an XY stage for two-dimensionally moving said sample carrier unit;   a main chamber for containing said sample carrier unit and said XY stage, and holding the same in a vacuum state; and   a load lock chamber located between said main chamber and said sample transfer system for holding the vacuum state of said main chamber when the sample is moved from said sample transfer system to said main chamber.   
   
   
       10 . A defect inspection system according to  claim 9 , characterized in that said sample transfer system comprises an electrostatic chuck having a function of preventing particles from sticking to the sample. 
   
   
       11 . A defect inspection system according to  claim 8 , characterized in that said XY stage comprises an air bearing having a differential exhaust mechanism at least in one axial direction thereof. 
   
   
       12 . An electron beam apparatus for producing an enlarge view from secondary electrons or reflected electrons emitted from a sample using a projection optical lens system, and detecting the enlarged view using a TDI or a CCD detector to capture a sample image, characterized by shaping an electron beam emitted from an electron gun into a rectangular shape through an aperture, causing the electron beam to pass along a trajectory deviated from the secondary electrons or reflected electrons emitted from the sample below an objective lens, said objective lens comprising a magnetic lens, and setting the distance between the sample and a main surface of the objective lens to be larger than a Bohr radius of the objective lens. 
   
   
       13 . An electron beam apparatus according to  claim 12 , characterized in that the Bohr radius of said objective lens is larger than the diameter of a visual field by a factor of 80 or more. 
   
   
       14 . An electron beam apparatus according to  claim 12  or  13 , characterized in that, in regard to said magnetic lens, an axially symmetric cylinder electrode is provided near a magnetic gap of said magnetic lens to apply a positive high voltage, and a sufficient distance is ensured between the cylindrical electrode and the sample to avoid a discharge therebetween. 
   
   
       15 . An electron beam apparatus according to  claim 12  or  13 , characterized in that the secondary electrons or reflected electrons emitted from the sample are deflected by an ExB separator, and subsequently impinge on the projection optical lens system, wherein said lens system comprises at least one stage of an electromagnetic lens having an NA aperture near a main surface of said lens. 
   
   
       16 . An electron beam apparatus according to  claim 12  or  13 , characterized in that said projection optical lens system comprises an auxiliary electrostatic lens and a magnification electromagnetic lens, wherein said electrostatic lens comprises two or more electrodes which can be applied with a voltage, said lens system is configured to focus a sample image position created by a preceding lens on a main surface of said auxiliary lens, and the magnification is variable by selecting an electrode for driving said electrostatic lens. 
   
   
       17 . An electron beam apparatus for producing an enlarge view from secondary electrons or reflected electrons emitted from a sample using a projection optical lens system, and detecting the enlarged view using a TDI or a CCD detector to capture a sample image,
 characterized by shaping an electron beam emitted from an electron gun into a rectangular shape through an aperture, causing the electron beam to pass along a trajectory deviated from the secondary electrons or reflected electrons emitted from the sample below an objective lens, a lens at a final stage comprises an electrostatic lens having at least five electrodes, and a voltage applied to a central electrode thereof is different in sign from voltages applied to a preceding and a subsequent electrode thereof.   
   
   
       18 . An electron beam apparatus according to  claim 17 , characterized in that said objective lens comprises a magnetic lens which has a Bohr diameter on a sample side smaller than a Bohr diameter on a detection side. 
   
   
       19 . An electron beam apparatus according to  claim 17  or  18 , characterized in that said objective lens comprises a magnetic lens, and electromagnetic coils are provided at two stages before and after a main surface of said objective lens, and these deflectors are configured to substantially satisfy a MOL condition. 
   
   
       20 . An electron beam apparatus according to  claim 6  or  7 , characterized in that said electron beam apparatus is adjusted to correct field curvature aberration and anastigmatic and reduce a difference in beam resolution between a central area of the visual field and a peripheral area of the visual field. 
   
   
       21 . A method of manufacturing a semiconductor device, characterized by comprising:
 (a) preparing a wafer;   (b) preparing a mask substrate and manufacturing a mask;   (c) performing a wafer processing step for performing required machining to the wafer;   (d) evaluating the resulting wafer using said electron beam apparatus according to  claim 12 , and repeating the steps (c) and (d) a required number of times; and   (e) cutting the wafer and assembling devices.   
   
   
       22 . A projection electron beam apparatus characterized by comprising:
 an electron gun;   axial chromatic aberration correcting means having a multi-pole lens; and   an objective lens for performing a MOL operation,   wherein said electron beam apparatus irradiates a sample with an electron beam while performing a MOL operation in a divided visual field region.   
   
   
       23 . An electron beam apparatus according to  claim 22 , characterized in that said electron beam apparatus is a lithography apparatus, and said apparatus further comprises a mask or a reticle having a pattern which should be formed on the sample. 
   
   
       24 . An electron beam apparatus according to  claim 22 , characterized in that said electron beam apparatus is a sample evaluation apparatus for evaluating a pattern formed on the sample. 
   
   
       25 . An electron beam apparatus according to  claim 22 , characterized by further comprising an objective lens, and a deflector contained in said objective lens for generating a deflection magnetic field which is proportional to a differentiated value with respect to an optical axis direction of an axial magnetic field distribution of said objective lens. 
   
   
       26 . An electron beam apparatus for irradiating a sample with a rectangular primary beam and enlarging and projecting secondary electrons emitted from the sample by an electro-optical system to detect the secondary electrons, characterized in that:
 said electro-optical system comprises an aperture plate having apertures arranged in a ring shape for transforming the secondary electrons into hollow beams.   
   
   
       27 . An electron beam apparatus according to  claim 26 , characterized in that said ring-shaped apertures have a width small enough to neglect spherical aberration. 
   
   
       28 . An electron beam apparatus according to  claim 26  or  27 , characterized in that said electro-optical system further comprises a correction lens for correcting the electron beam for axial chromatic aberration. 
   
   
       29 . An electron beam apparatus for irradiating a sample with a primary beam emitted from an electron gun through an objective optical system to detect secondary electrons emitted from the sample, characterized by comprising:
 an evaluation apparatus for transforming the primary beam into hollow beams when the primary beam passes through said objective optical system to irradiate the sample with the hollow beams, and detecting the secondary electrons to evaluate the sample; and   a correction lens for correcting the primary beam or the secondary electrons for axial chromatic aberration.   
   
   
       30 . An electron beam apparatus according to  claim 29 , characterized in that said electron gun comprises a cathode which has a ring-shaped edge. 
   
   
       31 . An electron beam apparatus according to  claim 30 , characterized by further comprising a multi-aperture plate for transforming the primary beam into multiple beams which are irradiated to the sample, wherein the secondary electrons are detected by a plurality of detectors. 
   
   
       32 . A method of manufacturing a device, characterized by comprising the steps of:
 a. preparing a wafer;   b. performing a wafer process;   c. evaluating the wafer after undergoing the step b;   d. repeating the steps a-c a required number of times; and   e. cutting the wafer after the step d and assembling devices.   
   
   
       33 . An electron beam apparatus for scanning a sample using a plurality of primary beams arranged in m rows and n columns, and detecting secondary beams emitted from the sample to evaluate the sample, characterized by:
 simultaneously scanning m*n beams in a direction inclined by an angle equivalent to sin −1 (1/m) in a row direction, wherein the raster pitch of the scanning is an integer multiple of a pixel dimension.   
   
   
       34 . An electron beam apparatus for irradiating a surface of a sample with an electron beam having a rectangular cross-section, enlarging secondary electron beams emitted from the sample using a projection optical system including an NA aperture plate, and capturing an image of the sample, characterized by:
 disposing said NA aperture plate or forming an optical conjugate plane of said NA aperture plate at a position at which aberration is minimized.   
   
   
       35 . An electron beam apparatus according to  claim 34 , characterized in that said enlarged image has a square shape. 
   
   
       36 . An electron beam apparatus for irradiating a sample with a plurality of primary beams, separating a plurality of secondary beams emitted from the sample from the primary beams by a beam separator, extending the distances between the plurality of secondary electron beams by a magnification optical system, and directing the secondary electron beams into a detector, characterized by comprising:
 a correction lens for correcting the plurality of primary beam for axial chromatic aberration, wherein said beam separator is disposed between said correction lens and the sample.   
   
   
       37 . An electron beam apparatus for forming a primary beam into a beam having a rectangular cross-section, conversing the primary beam by an objective lens, irradiating a sample with the primary beam, accelerating and converging secondary electron beams emitted from the sample by the objective lens, enlarging the secondary electron beams by a magnification optical system including an NA aperture plate, and detecting the secondary electron beams by a sensor, characterized in that:
 said objective lens is an electromagnetic lens; and   an optical conjugate plane of said NA aperture plate is located at a position which is passed by the secondary electron beams emitted about a specified direction with respect to a normal direction of the sample.   
   
   
       38 . A method of manufacturing a device, characterized by comprising the steps of:
 a. preparing a wafer;   b. performing a wafer process;   c. evaluating the wafer after undergoing the step b;   d. repeating the steps a-c a required number of times; and   e. cutting the wafer after the step d and assembling devices.