Abstract:
If an indentation mark is put in the vicinity of a defect under constant conditions regardless of the film type of samples, surroundings of the mark become cracked or the mark may be too small to view, thus causing the problem of difficulty in viewing the mark or the defect. Another problem is that in a patterned wafer, an indentation mark is coincidentally put on a film not suited for marking. To solve such problems, an elemental analysis is conducted of a position to be marked and, on the basis of the analysis results, such indentation marking conditions as the pressing load, descending rate, and marking depth of an indenter are varied to perform marking suited for a film type. If the film type of the location to be marked cannot be concluded to be a registered film type, marking under wrong conditions is prevented by switching to manual setting. It is also possible to avoid putting marks on a material if the material is not suited for marking.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a defect review apparatus using a scanning electron microscope to observe a sample by emitting an electron beam to the sample, and to a marking method in the defect review apparatus. 
         [0003]    2. Background Art 
         [0004]    Along with the miniaturization and complication of semiconductor devices, the cause of defect generation has become diverse and compositive in the process of manufacturing the devices. Accordingly, failure analysis technology has become increasingly important. In addition, an increase in the number of defects has led to a growing demand for defect review aimed at not only speeding up inspections but also extracting fatal defects. 
         [0005]    Failure analysis is initiated by first detecting defect positions on a semiconductor wafer with an optical or electronic visual inspection apparatus. Defects detected by the visual inspection apparatus usually contain a large amount of noise, and insignificant defects as well. Accordingly, high-resolution images of the defect positions obtained using the visual inspection apparatus are taken using a defect review apparatus to perform defect classification by using the images thus obtained. Such defect classification work enables a discrimination to be made as to which is a critical defect to be failure-analyzed. In recent years, defect review apparatuses have come to be provided with a function of automatically classifying taken images of defects by using teaching data. This function is referred to as ADC (Automatic Defect Classification). 
         [0006]    In failure analysis, there is used, for example, elemental analysis based on energy dispersive X-ray spectrometry (EDS) or electron energy-loss spectroscopy (EELS), in addition to high-resolution observation based on scanning electron microscopy (SEM) or transmission electron microscopy (TEM). In order to conduct a failure analysis based on transmission electron microscopy, a silicon wafer used in semiconductor manufacturing has to be cleaved into chips or columnar samples due to constraints on sample size. Thus, a laser or focused ion beam (FIB) apparatus is used in this processing. 
         [0007]    At the time of sample preparation by such wafer cleaving or by the use of focused ion beams as described above, a mark of some sort is needed in order to isolate a defect of interest. That is, a mark of such size as can be visually recognized by a person is necessary in the case of wafer cleaving. On the other hand, a mark of such size as can be recognized on an SIM (Scanning Ion Microscopy) image displayed on the FIB apparatus is necessary at the time of sample preparation by the use of focused ion beams. 
         [0008]    As one example of technologies to put such marks, JP 2000-241319A discloses an FIB apparatus equipped with an optical defect detection unit. In the apparatus, a mark is put in the vicinity of a defect position optically detected with a focused ion beam. Then, a focused ion beam is emitted to a sample on the basis of the mark to make a TEM sample. In addition. JP 2002-350731A shows an example of marking by means of indentation using diamond in an optical inspection/observation apparatus. 
         [0009]    If an indentation mark is put in the vicinity of a defect under constant conditions regardless of the film type of samples, the surroundings of the mark become cracked, thus causing the problem of difficulty in viewing the mark or the defect. Alternatively, the mark may be too small to view, thus posing a problem for analysis using a subsequent-stage analyzer. In addition, if an indentation mark is put on a film not suited for marking in a patterned wafer, the mark may be difficult to view or foreign matter or dust may arise from the marked locations of the wafer. 
         [0010]    The present invention is intended to provide a method for performing indentation marking appropriately, irrespective of the material and film type of a sample. 
       SUMMARY OF THE INVENTION 
       [0011]    In the present invention, marking suited for a film type is performed by varying such indentation marking conditions as the pressing load, descending rate, and marking depth of an indenter of an indentation marking unit on the basis of elemental analysis results obtained with an elemental analysis unit, such as an EDS. To that end, materials, i.e., the elemental analysis results and conditions of marking by the indentation marking unit are previously correlated with each other. Then, information on the correlation is stored in an apparatus. 
         [0012]    In addition if the film type of a location to be marked cannot be concluded to be a registered film type as the result of elemental analysis, marking under wrong conditions is prevented by switching to manual setting. It is also possible to avoid putting marks on a material if the material is not suited for marking. 
         [0013]    According to the present invention, marks excellent in shape are available automatically. Consequently, analysis using a subsequent-stage analyzer progresses efficiently, thereby enabling early defect cause investigation and yield improvement. 
         [0014]    It is also possible to prevent indentations from being stamped so strongly that the surroundings of the indentations are destroyed to become a source of foreign matter or dust. 
         [0015]    Objects, configurations and advantages of the present invention other than those described above will be apparent from the following description of an embodiment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a schematic view illustrating an overall configuration example of a defect detection system and a defect review apparatus. 
           [0017]      FIG. 2A  is a schematic view illustrating the inside of a sample chamber at the time of defect review. 
           [0018]      FIG. 2B  is a schematic view illustrating the inside of a sample chamber at the time of indentation marking. 
           [0019]      FIG. 3  is a flowchart illustrating one example of the operation of the defect review apparatus according to the present invention. 
           [0020]      FIG. 4A  is a schematic view illustrating an example of a marking method. 
           [0021]      FIG. 4B  is a schematic view illustrating a first example of improper indentation marking. 
           [0022]      FIG. 4C  is a schematic view illustrating a second example of improper indentation marking. 
           [0023]      FIG. 4D  is a schematic view illustrating a third example of improper indentation marking. 
           [0024]      FIG. 4E  is a schematic view illustrating a first example of countermeasure against the third example of improper indentation marking. 
           [0025]      FIG. 4F  is a schematic view illustrating a second example of countermeasure against the third example of improper indentation marking. 
           [0026]      FIG. 5A  is a graphical view illustrating a first example of EDS analysis results. 
           [0027]      FIG. 5B  is a graphical view illustrating a second example of EDS analysis results. 
           [0028]      FIG. 5C  is a graphical view illustrating a third example of EDS analysis results. 
           [0029]      FIG. 6A  is a table showing an example of indentation marking conditions. 
           [0030]      FIG. 6B  is a table showing another example of indentation marking conditions. 
           [0031]      FIG. 7  is a schematic view illustrating an example of a marking conditions setting screen. 
           [0032]      FIG. 8A  is a schematic view illustrating another example of the marking method. 
           [0033]      FIG. 8B  is a schematic view illustrating yet another example of the marking method. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0034]    Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. 
         [0035]      FIG. 1  illustrates an overall configuration example of a defect review apparatus according to the present invention and a configuration example of a defect detection system in which the defect review apparatus is arranged. A defect review apparatus  105  includes a scanning electron microscope column (electron optical column)  107 ; a sample chamber  108 ; an indentation marking unit  109 ; an optical microscope  113 ; a control section  110 ; an ADR (Automatic Defect Review) section  111 ; an ADC (automatic defect classification) section  112 ; and a communication computer  106 , and is connected to a YMS (Yield Management System)  101  through a network. The YMS  101  is also connected to a bright-field optical visual inspection apparatus  102 , a dark-field optical visual inspection apparatus  103 , and an electron-beam visual inspection apparatus  104  through a network. 
         [0036]    Inspection data is sent from these inspection apparatuses to the YMS  101 , and further to the defect review apparatus  105 , after the completion of inspection. The defect review apparatus  105  performs ADR and ADC by using this inspection data and returns ADR and ADC results to the YMS  101  through the communication computer  106 . 
         [0037]    Next, details on the defect review apparatus will be described. The scanning electron microscope column  107  has the function of emitting a primary electron beam to the object being inspected housed in the sample chamber to detect secondary electrons or reflection electrons thus obtained, and outputting a detection signal. An unillustrated sample stage is housed in the sample chamber  108 . The sample stage moves a target position of irradiation with a primary electron beam or a target position of indentation by the indentation marking unit  109  on the object being inspected to below the scanning electron microscope column  107  or the indentation marking unit  109 , according to a control signal from the control section  110 . A scanning electron microscope image obtained by the scanning electron microscope column  107  is used to identify defect positions and set marking positions. 
         [0038]    The optical microscope  113  is located on an upper portion of the sample chamber  108  and can take an optical microscope image of a defect. The scrolling of the optical microscope  113  is performed by the sample stage as in the case of the scanning electron microscope column  107 . An optical microscope image thus obtained is used to locate defects not visible with a scanning electron microscope, and to set marking positions. An EDS detection section  114  can conduct an elemental analysis based on energy dispersive X-ray spectrometry through an EDS processing section  115 . Results of the analysis can be used as material information. 
         [0039]    The respective components of a scanning electron microscope associated with the defect review apparatus are controlled by the control section  110 . The ADR section  111 , the ADC section  112 , and the communication computer  106  are connected to a subsequent stage of the scanning electron microscope. The ADR section  111  controls the control sequence of automatic defect review, and the ADC section  112  performs the automatic classification processing of defect images obtained by ADR. The control section  110  is equipped with various control units, including an electron optical column control unit  1101 , an indentation marking unit control unit  1102 , an optical microscope control unit  1103 , a marking object defect extraction unit  1104  and a stage control unit  1105 , in order to control the operation of the respective components of the scanning electron microscope. The communication computer  106  also serves as a management console of the defect review apparatus, and is equipped with a monitor on which a GUI (Graphical User&#39;s Interface) used to set operating conditions for defect review or an inspection recipe is displayed. 
         [0040]    The respective control units described above are materialized by means of either software implementation or hardware implementation within the control section  110 . Accordingly, the control section  110  is equipped therein a memory in which programs for realizing the functions of each control unit are stored and a processor for executing the programs. Alternatively, the control section  110  is equipped with a plurality of microcomputers corresponding to the functions of the individual control units. 
         [0041]    Next, details on the indentation marking unit of the present embodiment will be described using  FIGS. 2A and 2B .  FIG. 2A  is a schematic view illustrating the inside of the sample chamber at the time of defect review. In the sample chamber  108 , an electron beam  201  is focused by an objective lens  202  and emitted to a wafer  203  serving as a sample. The wafer  203  is mounted on a stage  204  and moved to an arbitrary position by the stage control unit  1105 . The primary electron beam may be decelerated immediately before the sample  203 , depending on the conditions of acquiring a scanning electron microscope image, to take an image of the sample  203 . In that case, a retarding voltage is applied to the sample  203  by a retarding unit  205 . 
         [0042]    At the time of review, the stage  204  moves successively from one defect position to another, and an electron beam  201  focused by the objective lens  202  is emitted to respective defect positions to take SEM images thereof. Using these SEM images, defects are detected by the defect detection unit  111  and classified by a defect classification section. In addition to the original SEM images, results of defect detection and defect classification are uploaded to the YMS  101  through a network by using the communication computer  106 . 
         [0043]      FIG. 2B  illustrates the inside of the sample chamber at the time of indentation marking. At the time of indentation marking, the stage control unit  1105  controls the stage  204  by using the position of each defect to be marked determined by the marking object defect extraction unit  1104  to move a target position of marking on the wafer  203  to below the indentation marking unit  109 . 
         [0044]    When movement is completed, the indentation marking unit  109  lowers and presses an indenter  209  attached to the leading end of a shaft  208  against the wafer  203  by a vertical drive mechanism  207  including a vacuum bellows  206 , thereby forming an indentation mark on the sample. These actions of the indentation marking unit are controlled by the indentation marking unit control unit  1102 . 
         [0045]    Next, the operation of the defect review apparatus of the present embodiment will be described using  FIG. 3 . 
         [0046]    First, inspection data is read from the YMS in step  301 . In step  302 , sampling is performed to extract defects subject to ADR from defects included in the inspection data. The purpose of sampling is to narrow down target defects, so as to be able to conduct an effective ADR in a limited time in cases where defects are large in number. For this purpose, there are used such methods as extraction and removal of cluster defects and random extraction from defects other than the cluster defects. In step  303 , wafer alignment is performed to coarsely align the wafer. In step  304 , a focus map is plotted to correct a distribution of focuses for each region within a wafer plane, so that the wafer comes into an automatic focus in a short period of time. In step  305 , the fine alignment of the scanning electron microscope is performed. The fine alignment is performed using unique patterns for respective mask shots in a photoprocess in the case of a patterned wafer. In the case of an unpatterned wafer, the fine alignment is performed by illuminating defects with an optical microscope, a dark-field microscope using a laser-light or the like in particular, to precisely detect defect positions. In step  306 , the precise position of each defect is detected by ADR to obtain an SEM image centered around the defect. In step  307 , a decision is made on classification results by ADC on the basis of the SEM image. 
         [0047]    After ADC in step  307 , the classification results are transferred from the ADC section  112  to the marking object defect extraction unit  1104  within the control section  110 . The marking object defect extraction unit  1104  determines whether or not the classified defects are those to be marked, thereby extracting defects subject to marking (step  308 ). If any defects to be marked are not included in the classification results. ADR/ADC results are uploaded to the YMS  101  through the communication computer  106  to finish the operation (step  309 ). 
         [0048]    If a defect is determined as one to be marked in step  308 , an EDS analysis is made of a location to be marked (step  310 ). A determination is made from results of the EDS analysis as to whether or not the material of the location to be marked agrees with a pre-registered material. Materials may be registered as information generated by combining the peak positions of X-ray spectrums (energy or wavelengths) corresponding to the material with peak intensity (number of counts), or under specific material names. 
         [0000]    (1) Material A (step  311 A)
 
(2) Material B (step  311 B)
 
. . .
 
(N) Material N (step  311 N)
 
         [0049]    In this way, a determination is made as to which of the pre-registered materials A to N the material of the location to be marked corresponds to. 
         [0000]    If the material is item (1), pre-registered conditions A are determined as marking conditions (step  314 A).
 
If the material is item (2), pre-registered conditions B are determined as marking conditions (step  314 B).
 
. . .
 
If the material is item (N), pre-registered conditions N are determined as marking conditions (step  314 N).
 
         [0050]    If the material of the location to be marked does not agree with any of the pre-registered materials and is determined as being not registered (step  312 ), a query is made as to whether conditions for the material are set manually (step  313 ). If a decision is made in step  313  to manually set the conditions, a later-described manual setting screen appears to prompt inputting marking conditions. In this case, conditions Z thus input are determined as the marking conditions (step  314 Z). 
         [0051]    Once the marking conditions are determined, the indentation marking unit control unit  1102  controls the indentation marking unit  109  to actually perform marking under the marking conditions thus decided. 
         [0052]    If a decision is made in step  313  not to manually set the conditions, marking is skipped. 
         [0053]    In this process. EDS is used in elemental analysis, but the elemental analysis is not limited to this method. Alternatively, another elemental analysis method, such as WDS (Wavelength Dispersive X-ray Spectrometry) or AES (Auger Electron Spectrometry), may be used. 
         [0054]    Next, a method for determining marking conditions in the present embodiment will be described using  FIGS. 4A ,  4 B and  4 C and  FIGS. 5A ,  5 B and  5 C.  FIG. 4A  is a schematic view illustrating marking positions in the present embodiment. A marking center  402  is set in substantially the middle of a defect  401 , and a first indentation mark  403 A is stamped in a position a distance of D 1  away in an XY direction from the marking center. The distance D 1  is determined in consideration of the coordinate accuracy of indentation marking and effects on the surroundings of the mark. 
         [0055]      FIGS. 5A ,  5 B and  5 C illustrate examples of EDS analysis results (spectrums). The axis of abscissas of  FIGS. 5A ,  5 B and  5 C represents energy and the axis of ordinates represents X-ray intensity (number of counts).  FIGS. 5A ,  5 B and  5 C correspond respectively to  FIGS. 4A ,  4 B and  4 C.  FIG. 5A  shows an example in which a spectrum is composed only of silicon of a substrate,  FIG. 5B  shows an example in which a silicon oxide film is deposited on silicon, and  FIG. 5C  shows an example in which a carbon-based film, such as a resist film, is attached to silicon. 
         [0056]      FIG. 4A  shows marks stamped on a silicon substrate  404 A under correct marking conditions and formed so as to be free from cracks and the like, relatively large in size, and easy to view. If the pressing load or marking depth is inadequate for reasons of, for example, the material being too hard as in the case of a silicon oxide film  404 B, a mark  403 B is small, and therefore, difficult to view, as illustrated in  FIG. 4B . In addition, if the pressing load of marking is too heavy for reasons of, for example, the material being too brittle as in the case of a resist film  404 C, a mark  403 C is large but may be cracked, or broken to come off, thus causing the defect to be difficult to view or to become a source of dust, as illustrated in  FIG. 4C . 
         [0057]    In the case of a patterned wafer, one or two of four marks may be coincidentally located on another film, as illustrated in  FIG. 4D . In this case, an EDS analysis may be conducted for each marking position, so as to be able to vary marking conditions accordingly. 
         [0058]    If a position on another film made of a different material coincides with a position to be marked, as illustrated in  FIG. 4D , a mark may be stamped below that position, for example, as illustrated in  FIG. 4E , while avoiding the position different in material, thereby changing the marking position. Alternatively, only the position different in material may be excluded from mark stamping, as illustrated in  FIG. 4F . 
         [0059]    If a patterned wafer is used and the pattern is too small, it is advantageous to use AES higher in spatial resolution than EDS at the time of elemental analysis. 
         [0060]      FIGS. 6A and 6B  show examples of indentation marking conditions.  FIG. 6A  shows an example of setting the pressing load of the indenter as a marking condition according to the type of material.  FIG. 6B  shows an example of setting the pressing load, descending rate, maximum marking depth (distance) of the indenter as marking conditions on a material-by-material basis. As a matter of course, marking conditions are not limited to these examples. The indentation marking unit control unit  1102  stores, as information, such conditions as shown in this table. Marking conditions corresponding to the material in question are read out according to elemental analysis results. The indentation marking unit  109  is driven and controlled in accordance with the conditions thus read out to perform marking. 
         [0061]      FIG. 7  illustrates an example of a marking conditions setting screen. This setting screen is displayed when Yes is selected for the query “Setting manually?” in step  313  of  FIG. 3 . An operator numerically inputs parameters denoted by reference numeral  701  on the screen. At that time, the operator can input parameters, while scrolling through pre-registered conditions  702  up and down with a scroll bar  703  for reference. 
         [0062]    Referring back to  FIG. 3 , marking is finished after being performed on all of defects to be marked, and the sample  203  is moved out of the defect review apparatus. 
         [0063]    The above-described process of indentation marking may be carried out manually by an equipment operator or may be executed automatically by the apparatus. 
         [0064]    After the sample  203  is moved out, a decision is made on analysis objects. Examples of methods for selecting analysis objects include selecting main defects high in occurrence ratio among all defects, selecting rare defects unique to the wafer in question, and selecting several defects each from various types of defects to roughly observe the overall state thereof. 
         [0065]    In addition, the wafer is cleaved into chips so as to fit into an holder of the analysis apparatus (step  316 ). In step  317 , each chip is housed in the FIB apparatus to search out defect positions therein, and the front surface of each chip is protected, as necessary, by means of deposition or the like. Thereafter, a cross section of the chip desired to be observed is FIB-processed and the chip is thin-filmed to be taken out as a sample. In step  318 , a cross-sectional observation is made of the thin sample thus obtained, using a TEM, a high-resolution SEM or the like. 
         [0066]    In a conventional method, a sample is often loaded into an FIB apparatus without being provided with defect searching marks even for defects to be failure-analyzed. Thus, time is taken in the step of searching for defects in the FIB apparatus. In the case of an unpatterned bare wafer, a film-formed wafer or the like in particular, time is taken in searching for minute defects. According to the present embodiment, indentation marks can be directly attached to a significant defect in the defect review apparatus. Consequently, search for processing positions on the analyzer side becomes more efficient than before. 
         [0067]    As has been described heretofore, the present embodiment allows significant defects to be selected as analysis objects in a subsequent stage in accordance with a predetermined strategy, thereby enabling early defect cause investigation and yield improvement. In addition, defects unobservable with an SEM can also be analyzed to enable yield improvement. 
         [0068]    Yet additionally, although the way indentations are stamped has been described by citing a method for squarely stamping four marks around each defect, methods of marking are not limited to this method. As illustrated by way example in  FIGS. 8A and 8B , the number of indentations may be increased to improve visibility. 
         [0069]    It should be noted that the present invention is not limited to the foregoing embodiment but encompasses various modified examples. For example, the foregoing embodiment has been described in detail for the purpose of easier understanding of the present invention and is, therefore, not necessarily limited to apparatuses including all of the configurations mentioned above. 
       DESCRIPTION OF SYMBOLS 
       [0000]    
       
           101  YMS 
           102  Bright-field optical visual inspection apparatus 
           103  Dark-field optical visual inspection apparatus 
           104  Electron-beam visual inspection apparatus 
           105  Defect review apparatus 
           106  Communication computer 
           107  Scanning electron microscope column 
           108  Sample chamber 
           109  Indentation marking unit 
           110  Control section 
           111  ADR section 
           112  ADC section 
           113  Optical microscope 
           114  EDS detector 
           115  EDS processing section 
           201  Electron beam 
           202  Objective lens 
           203  Sample (wafer) 
           204  Stage 
           205  Retarding unit 
           206  Vacuum bellows 
           207  Vertical drive mechanism 
           208  Shaft 
           209  Indenter 
           401  Defect 
           402  Center position of defect 
           403 A,  403 B,  403 C Indentation marking 
           1101  Electron optical column control unit 
           1102  Indentation marking unit control unit 
           1103  Optical microscope control unit 
           1104  Marking object defect extraction unit 
           1105  Stage control unit