Abstract:
A defect inspection apparatus includes a charged particle beam source which emits a charged particle beam to illuminate the charged particle beam onto a sample as a primary beam; an image pickup which includes an imaging element having a light receiving face receiving at least one of a secondary charged particle, a reflective charged particle, and a back-scattered charged particle generated from the sample by the illumination of the primary beam and which outputs a signal indicating a state of the surface of the sample; a mapping projection system which maps/projects at least one of the secondary charged particle, the reflective charged particle, and the back-scattered charged particle as a secondary beam and which makes the beam to form an image on the light receiving face of the imaging element; a controller which adjusts a beam diameter of the primary beam in such a manner as to apply the beam to the sample with a size smaller than that of an imaging region as a target of review to scan the imaging region and which allows the image pickup to pick up a plurality of frame images; an image processor which processes the plurality of obtained frame images to prepare a review image; and a defect judgment unit which judges a defect of the sample based on the review image.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
   This application claims benefit of priority under 35USC § 119 to Japanese Patent Application No. 2004-085545, filed on Mar. 23, 2004, the contents of which are incorporated by reference herein. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a defect inspection apparatus, a program, and a manufacturing method of a semiconductor device. 
   2. Related Background Art 
   A method has been proposed in which a rectangular electron beam is applied to a sample, a secondary electron, a reflective electron, and a back-scattered electron generated in accordance with a variation of a shape/material/potential of a sample surface are enlarged/projected to acquire a sample surface image, and the image is applied to defect inspection of a semiconductor pattern (e.g., Japanese Patent Laid-Open (kokai) Nos. 07-249393 and 11-132975). 
   A schematic procedure of a general defect inspection method using a mapping projection type electron beam defect inspection apparatus according to a conventional technique is described. First, after setting parameters such as inspection sensitivity and electron beam condition, inspection is executed, a place extracted as a defect is reviewed in order to confirm an inspection result or optimize sensitivity. At a reviewing time, a magnification is preferably set to be higher than that at an inspection time, and imaging is performed in order to judge whether a defect is true or false. Therefore, inspection sensitivity is checked. When the sensitivity is satisfactory, the inspection is ended. However, when the sensitivity is insufficient, a parameter value is set again, and the above-described procedure is repeated until sufficient sensitivity is obtained. 
   However, since the mapping projection type electron beam defect inspection apparatus is originally designed in such a manner as to be optimum for the magnification at an inspection time, the apparatus is not suitable for imaging with a high magnification and resolution. Therefore, for example, to cover both the magnifications at an inspection time and at a reviewing time by a single beam lens column, there is a problem that the apparatus becomes huge. Additionally, there is also a method of separately installing a beam lens column for reviewing, but the method is not so preferable. 
   Additionally, for example, a control electrode is disposed right above a wafer which is a sample, or a stage for supporting the wafer is set to be movable in a Z-direction, and accordingly a working distance between the wafer and an objective lens is narrowed. Consequently, it is also possible to enhance an observation magnification without setting the apparatus to be huge. 
   However, a sufficient resolution or S/N cannot be obtained in this method. 
   BRIEF SUMMARY OF THE INVENTION 
   According to a first aspect of the present invention, there is provided a defect inspection apparatus comprising: 
   a charged particle beam source which emits a charged particle beam to illuminate the charged particle beam onto a sample as a primary beam, the sample generating a secondary charged particle, a reflective charged particle, and/or a back-scattered charged particle from the surface thereof by the illumination of the primary beam; 
   an image pickup which includes an imaging element having a light receiving face receiving at least one of the secondary charged particle, the reflective charged particle, and the back-scattered charged particle generated from the sample and which outputs a signal indicating a state of the surface of the sample; 
   a mapping projection system which maps/projects at least one of the secondary charged particle, the reflective charged particle, and the back-scattered charged particle as a secondary beam and which makes the beam to form an image on the light receiving face of the imaging element; 
   a controller which adjusts a beam diameter of the primary beam in such a manner as to apply the beam to the sample with a size smaller than that of an imaging region as a target of review to scan the imaging region and which allows the image pickup to pick up a plurality of frame images; 
   an image processor which processes the plurality of obtained frame images to prepare a review image; and 
   a defect judgment unit which judges a defect of the sample based on the review image. 
   According to a second aspect of the present invention, there is provided a program which allows a computer connectable to a defect inspection apparatus to execute a defect inspection method, the defect inspection apparatus comprising: a charged particle beam source which emits a charged particle beam to illuminate the charged particle beam as a primary beam onto a sample, the sample generating a secondary charged particle, a reflective charged particle, and/or a back-scattered charged particle from the surface thereof by the illumination of the primary beam; an image pickup which includes an imaging element with a light receiving face to receive at least one of the secondary charged particle, the reflective charged particle, and the back-scattered charged particle generated from the sample and which outputs a signal indicating a state of the surface of the sample; and a mapping projection system which maps/projects at least one of the secondary charged particle, the reflective charged particle, and the back-scattered charged particle as a secondary beam and which makes the beam to form an image on the light receiving face of the imaging element, the defect inspection method comprising: 
   scanning a sample with the primary beam to acquire a surface image of the sample, and extracting a defect portion from the surface image; 
   defining a surface region of the sample including the extracted defect portion as an imaging region of a review object, dividing the imaging region into a plurality of frame regions, adjusting a beam diameter of the primary beam in accordance with a size of each frame, and scanning the imaging region with the primary beam having the adjusted beam diameter to acquire a plurality of frame images; 
   processing the plurality of obtained frame images to prepare a review image; and 
   judging a defect of the sample based on the review image. 
   According to a third aspect of the present invention, there is provided a manufacturing method of a semiconductor device comprising a defect inspection method using a defect inspection apparatus comprising: a charged particle beam source which emits a charged particle beam to illuminate the charged particle beam as a primary beam onto a sample, the sample generating a secondary charged particle, a reflective charged particle, and/or a back-scattered charged particle from the surface thereof by the illumination of the primary beam; an image pickup which includes an imaging element with a light receiving face to receive at least one of the secondary charged particle, the reflective charged particle, and the back-scattered charged particle generated from the sample and which outputs a signal indicating a state of the surface of the sample; and a mapping projection system which maps/projects at least one of the secondary charged particle, the reflective charged particle, and the back-scattered charged particle as a secondary beam and which makes the beam to form an image on the light receiving face of the imaging element, the defect inspection method comprising: 
   scanning a sample with the primary beam to acquire a surface image of the sample, and extracting a defect portion from the surface image; 
   defining a surface region of the sample including the extracted defect portion as an imaging region of a review object, dividing the imaging region into a plurality of frame regions, adjusting a beam diameter of the primary beam in accordance with a size of each frame, and scanning the imaging region with the primary beam having the adjusted beam diameter to acquire a plurality of frame images; 
   processing the plurality of obtained frame images to prepare a review image; and 
   judging a defect of the sample based on the review image. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram showing a schematic constitution of one embodiment of a defect inspection apparatus according to the present invention; 
       FIG. 2  is a flowchart showing a schematic procedure of one example of a defect inspection method using a defect inspection apparatus shown in  FIG. 1 ; 
       FIGS. 3A to 3C  are explanatory views of a defect inspection method shown in  FIG. 2 ; 
       FIGS. 4A and 4B  are explanatory views of the defect inspection method shown in  FIG. 2 ; 
       FIG. 5  is an explanatory view of the defect inspection method shown in  FIG. 2 ; 
       FIGS. 6A and 6B  are schematic diagrams showing an influence of a noise electron in a case where a review image is obtained by an addition process; 
       FIG. 7  is a flowchart showing a schematic procedure of another example of the defect inspection method using the defect inspection apparatus shown in  FIG. 1 ; 
       FIGS. 8A and 8B  are explanatory views of the defect inspection method shown in  FIG. 7 ; 
       FIGS. 9A to 9C  are explanatory views of the defect inspection method shown in  FIG. 7 ; and 
       FIGS. 10A to 10C  are explanatory views of the defect inspection method shown in  FIG. 7 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiments of the present invention will be described hereinafter with reference to the drawings. It is to be noted that in the drawings, the same parts are denoted with the same reference numerals, and redundant description will be performed only when necessary. 
   FIRST EMBODIMENT 
     FIG. 1  is a block diagram showing a schematic constitution of one embodiment of a defect inspection apparatus according to the present invention. The defect inspection apparatus shown in  FIG. 1  comprises a primary column  2 , a stage chamber  4 , a secondary column  6 , a time delay integrator (TDI) sensor  76 , a controller  64 , a host computer  80 , and vacuum pumps P 1  to P 3 . 
   The host computer  80  corresponds, for example, to a defect judgment unit, controls the whole apparatus including the controller  64 , and judges whether a defect obtained by tentative inspection is a true defect or a false defect based on a review image obtained by a defect inspection method described later. The controller  64  corresponds to, for example, a controller, and generates various control signals. The controller supplies the signals to an image processor  78 , additionally an electron gun, a quadrupole lens  18 , a primary beam deflector  22 , an objective lens  54 , a Wien filter  30 , first and second projection lenses  56 ,  58 , and a secondary beam deflector  62 , and controls these components. 
   The stage chamber  4  contains a stage  40  for supporting a wafer W on which a pattern that is an inspection object is formed on the upper surface. The stage  40  is constituted to be movable in three X-Y-Z directions by the control signal from the controller  64 . A vacuum pump P 2  is connected to the stage chamber  4 , and the inside of the pump is brought into a high vacuum state. The stage  40  is connected to a power supply (not shown), and has a structure in which voltage is applicable to the wafer W. 
   The primary column  2  includes the electron gun, quadrupole lens  18 , and primary beam deflector  22 . The electron gun, quadrupole lens  18 , and primary beam deflector  22  correspond to, for example, a charged particle beam source. The electron gun has a cathode  12  which emits electrons, a Weh-nelt cylinder  14  having a rectangular opening, and a deflector  16  for adjusting a beam axis. An acceleration voltage, emission current and optical axis of the electron gun are controlled while a primary beam PB is emitted. The primary column  2  is inclined/disposed with respect to a vertical direction of a wafer W surface. By this constitution, the primary beam PB enters the Wien filter  30  from an oblique direction with respect to the surface of the wafer W. The Wien filter  30  is one of electromagnetic field superimposition type deflectors. The filter-deflects the primary beam PB which obliquely enters the filter through the primary column  2  in a vertical direction with respect to a sample face of the wafer W so that the beam enters the wafer W. 
   The secondary column  6  contains a secondary beam mapping projection system, a micro channel plate (MCP) detector  72 , and a fluorescence face  74 . The secondary beam mapping projection system corresponds to, for example, a mapping projection system, and includes the objective lens  54 , an aperture AP, the Wien filter  30 , the first and second projection lenses  56 ,  58  constituted by, for example, rotationally symmetric electrostatic lenses, and the secondary beam deflector  62 . The secondary beam mapping projection system receives the primary beam PB, and guides the secondary electron, reflective electron, and back-scattered electron generated from the surface of the wafer W into the secondary column  6  from the stage chamber  4  by a magnetic field, an electric field, or a combination of the fields. While the electrons are accelerated, they are enlarged/projected and applied as secondary beams into the MCP detector  72 . It is to be noted that the Wien filter  30  is controlled with respect to a secondary beam SB applied from a wafer W side on a condition that the beam travels straight. The secondary beam SB travels straight through the Wien filter  30 , and is enlarged/projected by the first and second projection lenses  56 ,  58 . The secondary beam deflector  72  deflects the secondary beam SB in such a manner that an incidence face of the MCP detector  72  is scanned by the secondary beam SB in synchronization with the TDI sensor  76 . 
   An electron beam detector corresponds to, for example, an imaging unit, and includes the MCP detector  72 , fluorescence face  74 , and TDI sensor  76 . The secondary beam SB which has entered the MCP detector  72  is amplified into fourth to fifth power times an electron amount on the incidence face by the MCP detector  72  and then applied to the fluorescence face  74 . Accordingly, a fluorescence image generated by the fluorescence face  74  is detected by the TDI sensor  76 , and supplied to the image processor  78 . In the present embodiment, the TDI sensor  76  has a STILL mode. The STILL mode refers to a mode in which a timing signal of the TDI sensor is controlled, and accordingly an image is picked up by a general CCD sensor. The imaging by a frame unit is possible using the STILL mode. 
   The image processor  78  corresponds to, for example, an image processor which processes a detected signal of a fluorescence image, and supplies the signal as an image signal of an SEM image indicating a state of the surface of the wafer W to the host computer  80  via the controller  64 . The image processor  78  is capable of synthesizing an image picked up by a frame unit by an addition process as described later. 
   Next, several defect inspection methods using the defect inspection apparatus shown in  FIG. 1  will be described with reference to  FIGS. 2 to 5 . 
     FIG. 2  is a flowchart showing a schematic procedure of a defect inspection method according to the present embodiment, and  FIGS. 3A to 5  are explanatory views of the defect inspection method shown in  FIG. 2 . 
   First, as shown in  FIG. 3A , while a whole surface of an imaging area AR 0  is illuminated with an illuminative beam CS 0 , a whole inspection area is imaged by stage-scanning by the stage  40  ( FIG. 2 , step S 1 ), and a defect portion is extracted (step S 2 ). Next, the extracted defect portion is equally divided into N regions (hereinafter referred to as frame regions) (step S 3 ), and a beam diameter is limited to a size for one frame. As shown in  FIG. 3B , an imaging area AR 1  which is a defect portion is scanned/illuminated with a focused illuminative beam CS 1  (step S 4 ). To reduce the beam diameter by the defect inspection apparatus shown in  FIG. 1 , the control signal may be supplied from the controller  64  to adjust the quadrupole lens  18 . The defect portion of the illuminative beam is scanned/illuminated by the primary beam deflector  22 . At a time when inspection is executed by collective illumination, while the stage  40  is continuously moved, the image is picked up by the TDI sensor. At a review time, while the stage  40  is allowed to stand still, the imaging is performed using the STILL mode of the TDI sensor. Accordingly, the image can be acquired by the frame unit. 
     FIGS. 4A and 4B  schematically show a state in which a frame image is continuously picked up in the STILL mode of the TDI sensor by scan illumination. When an imaging target pattern PT shown in  FIG. 4A  is continuously scanned/illuminated with the beam, frame images FR 1  to FRN shown in  FIG. 4B  can be obtained. It is to be noted that the scan illumination is repeated many times, not once, in the same manner as in a general SEM apparatus, and thereafter an integration process is performed. Consequently, an S/N of the reviewed image can be enhanced. 
   Next, the process returns to  FIG. 2 , and the obtained images of the imaging frames FR 1  to FRN are synthesized by image processing (step S 6 ). Accordingly, as shown in a schematic diagram of  FIG. 5 , a synthesized image (review image) Imrv can be obtained in accordance with the imaging target pattern PT. The image processing is executed, when the image processor  78  adds image data of the imaging frames FR 1  to FRN in the defect inspection apparatus shown in  FIG. 1 . 
   Finally, it is judged using the obtained review image Imrv whether a defect extracted by the collective illumination is true/false (step S 7 ). This judgment is executed by the host computer  80  of the defect inspection apparatus shown in  FIG. 1 . 
   Even at a review time, a whole imaging area AR 2  of the extracted defect portion can be imaged by the collective illumination in the same manner as in an inspection time, for example, as in an illuminative beam CS 2  shown in  FIG. 3C . However, the scan illumination is superior to the collective illumination in that an influence of a space charge effect can be suppressed, and therefore a high-resolution image can be obtained. In general, the scan illumination has a demerit that an imaging time is required as compared with the collective illumination, but a high speed is not required at the review time unlike the inspection time, and therefore this demerit does not raise any problem. 
   Thus, according to the present embodiment, a high-resolution review image can be obtained. 
   SECOND EMBODIMENT 
   Next, a second embodiment of the present invention will be described with reference to  FIGS. 6A to 10C . A defect inspection method according to the present embodiment can be executed using the defect inspection apparatus shown in  FIG. 1 . 
   In the first embodiment, frame images obtained by scan illumination are simply added to acquire a review image. However, as in a region denoted with symbol Imn in an imaging frame FRim of  FIG. 6B  obtained by the scan illumination with respect to an imaging target pattern PT of  FIG. 6A , the frame image sometimes include a noise image by an noise electron which does not contribute to image formation. In this case, when the respective frame images are added as such, a review image inferior in S/N is obtained. In the present embodiment, there is provided a method in which a mask image is prepared, a masking process is executed prior to an addition process, and accordingly the S/N of the review image is enhanced. 
     FIG. 7  is a flowchart showing a schematic procedure of a defect inspection method of the present embodiment. 
   First, in the same manner as in an inspection method according to a conventional art, while a whole surface of an imaging area AR 0  is illuminated with an illuminative beam CS 0 , a whole inspection area is imaged by stage-scanning by a stage  40  (step S 11 ), and a defect portion is extracted (step S 12 ). Next, the extracted defect portion is divided into N frame regions FR 1  to FRN, and a mask image is prepared in which a window is opened in an illumination region in accordance with each frame region (step S 13 ). Subsequently, the corresponding frame image and the mask image are subjected to a masking process, that is, a logical product is taken. Accordingly, an image from which any influence of noise has been removed is prepared (step S 15 ). Thereafter, in the same manner as in the first embodiment, N images subjected to the masking process are synthesized to acquire a review image (step S 16 ), and it is judged using the obtained review image whether the defect extracted by collective illumination is true/false using an obtained review image (step S 17 ). 
   A specific example of the masking process will be described with reference to schematic diagrams of  FIGS. 8A and 8B .  FIG. 8A  shows a state in which a logical product is taken between a frame image FR 1  obtained by first beam illumination in continuous scanning from a corner of an imaging target pattern PT, the corner being a start point, and a mask MK 1  prepared beforehand corresponding to the frame image FR 1  to remove a noise image Imn, and an image FRm 1  subjected to the masking process is obtained.  FIG. 8B  shows a state in which a logical product is taken between a frame image FR 2  obtained by second beam illumination following the frame image FR 1 , and a mask MK 2  prepared beforehand corresponding to the frame image FR 2  to obtain an image FRm 2  subjected to the masking process. 
     FIGS. 9A to 9C  are explanatory views showing a relation among a deflection voltage for a primary beam deflector, a frame signal of a TDI sensor, and a mask image.  FIG. 9A  shows a relation between a deflection voltage (X-direction and Y-direction) applied to a primary beam deflector  22  of the defect inspection apparatus shown in  FIG. 1 , and frame signals T 1  to T 16  applied to a TDI sensor  76 .  FIG. 9B  shows a relation between a position of a continuously scanned illumination area AR 1 , and the frame signals T 1  to T 16 . Furthermore,  FIG. 9C  shows a mask image MK 1  at a time when a frame signal T 1  is applied. As shown in  FIG. 9A , the deflection voltage is generated in a step manner in synchronization with the frame signals T 1  to T 16  to the TDI sensor  76 . As apparent from comparison of  FIG. 9A  with  FIG. 9B , in the present embodiment, an unmask region (window portion) of a mask image has a size obtained by dividing the imaging area into 4×4 regions, but the size of the illumination area AR 1  is set in such a manner as to be slightly larger than that of the unmask region. Consequently, uniformity of the image can be prevented from being influenced in a boundary of beam application. In an example shown in  FIGS. 9A to 9C , a deflection voltage is generated in such a manner that the illumination area continuously moves in order from a left upper corner of the imaging area, but the present invention is not limited to this example. As in an example shown in  FIGS. 10A to 10C , the deflection voltage may be generated in such a manner that the illumination area AR 1  moves in an irregular order by random scanning. 
   As described above, according to the present embodiment, a review image further superior in resolution and S/N can be obtained. 
   (3) Program 
   A series of procedure of the above-described defect inspection method may be incorporated in a program, and read and executed as a recipe file in a computer of an SEM apparatus. Accordingly, the above-described defect inspection method can be realized using a general-purpose SEM apparatus including the computer capable of processing the image. A series of procedure of the above-described defect inspection method may be stored as a program to be executed by the computer of the SEM apparatus in recording mediums such as a flexible disk and CD-ROM, and read and executed in the computer of the SEM apparatus. 
   The recording mediums are not limited to portable mediums such as a magnetic disk and an optical disk, and may be fixed recording mediums such as a hard disk drive and a memory. A program in which a series of procedure of the defect inspection method is incorporated may be distributed via a communication circuit (including radio communication) such as internet. Furthermore, the series of procedure of the defect inspection method may be encrypted, modulated, or compressed. In this state, the method may be distributed via a wire circuit such as internet or a radio circuit. The method may be stored in the recording medium, and distributed. 
   (4) Manufacturing Method of Semiconductor Device 
   A semiconductor device is manufactured using the above-described defect inspection method, and it is accordingly possible to manufacture a semiconductor device with a high throughput and yield. 
   As described above, several modes for carrying out the present invention have been described, but the present invention is not limited to the above-described modes, and can be variously modified and applied within the scope thereof. For example, in the above-described embodiments, the imaging area has been divided into 4×4 regions, but the number of divisions is not limited to this, and an arbitrary number can be set in accordance with precision. In the above-described embodiment, a case where an electron beam is used as a charged particle beam has been described, but the present invention is not limited to this case, and is applicable even to a defect inspection apparatus, for example, using ion beams.