Abstract:
A recipe setting method and reviewing apparatus which permit even a novice to analyze the contents of existing recipe settings without trial-and-error attempts in the reviewing apparatus for reviewing a sample and to create a new recipe in a short time based on the results of the analysis. By a reviewing apparatus having a function of reviewing a sample under registered review conditions, based on a recipe in which the review conditions are registered. The reviewing apparatus is configured to display a list of the contents of the settings of plural set items regarding plural recipes and to create a new recipe based on the results of analysis of commonality by using the contents of settings having high degrees of commonality as initial settings.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a reviewing apparatus for reviewing samples under various review conditions, based on recipes in which the review conditions are registered. Especially, the invention relates to an apparatus that needs to optimize optical conditions because optimal optical conditions are different according to the characteristics of samples such as a SEM (scanning electron microscope)-based defect reviewing apparatus or SEM-based defect review tool. Furthermore, the invention relates to a reviewing apparatus that needs to optimize conditions for achieving both high capture rate and high throughput such as an automatic defect review (ADR) tool. 
         [0002]    In semiconductor fabrication, it is important that defects produced during fabrication processes be discovered at early stages and countermeasures against them be taken, in order to secure high production yield. In recent years, as semiconductor devices have diminished in size, effects of even quite small defects on the yield can no longer be neglected. Defects to be reviewed have become more versatile. 
         [0003]    A SEM-based defect reviewing apparatus is a tool for reviewing such various defects. Generally, this reviewing apparatus is used to review defects, based on defect locations detected by a host inspection tool. Where a manual review is performed, the sample stage is moved into coordinates outputted by the host inspection tool. Then, the sample is imaged at a low magnification at which the sample comes within the field of view. The position of the defect is checked visually. Then, the sample stage is moved such that the position of the defect comes to the center of the field of view. An image of the defect for review is acquired at high magnification. Automation of this sequence of process steps is ADR. 
         [0004]    In ADR, various conditions including optical conditions corresponding to a sample, ADR mode, conditions under which low-magnification images are acquired, and conditions under which high-magnification images are acquired need to be optimized to achieve both high capture rate and high throughput. Because the number of combinations of items to be set is exorbitant, the ADR is a work which is difficult to optimize even for experienced skilled persons and which needs trial-and-error attempts. Therefore, there is a need for facilitation of the work for optimizing the contents of the settings. 
         [0005]    A recipe setting method implemented in a defect inspection tool and consisting of setting a plurality of inspection conditions, effecting inspections under each condition, and adopting a condition under which the most defects can be detected as a final recipe setting is disclosed in patent reference 1 (JP-A-2005-017159). 
         [0006]    A method of enabling recipe parameters setting forth fabrication processes in semiconductor fabrication equipment to be edited in a batch is disclosed in patent reference 2 (JP-A-05-283308). 
       SUMMARY OF THE INVENTION 
       [0007]    Although the method disclosed in the above-cited patent reference 1 makes it possible to efficiently make trial-and-error attempts for recipe condition optimization, trial-and-error attempts are still made under varied conditions. Therefore, there is the problem that the processing time is long. When the conditions are varied, it is difficult for a novice to precisely judge how the conditions should be varied. Furthermore, in the case of a SEM-based defect-reviewing apparatus, the same sample is reviewed repeatedly, creating the possibility that damages to the sample are accumulated. Consequently, it is desired to avoid acquiring images repeatedly while varying review conditions. 
         [0008]    The method disclosed in the above-cited patent reference 2 enables recipe parameters used in semiconductor fabrication equipment to be edited in a batch. This is effective in improving the efficiency of the intended editing work and reducing setting errors. However, there is no mention of any detailed method of analysis permitting one to judge as to how the set conditions should be varied to produce optimum results. In addition, when a new recipe is created, there is no mention of any detailed method of effectively exploiting the results of analysis of existing recipes. 
         [0009]    It is a main object of the present invention to provide recipe analysis method, recipe setting method, and reviewing apparatus which permit even a novice to analyze the contents of existing recipe settings without trial-and-error attempts in the reviewing apparatus and to create a new recipe in a short time based on the result of the analysis. 
         [0010]    To achieve the above-described object, an embodiment of the present invention provides a reviewing apparatus having a function of reviewing a sample under registered review conditions, based on a recipe in which the review conditions are registered. A main feature is to enable the contents of settings of plural set items for plural recipes to be displayed in the form of a list. Another main feature is to create a new recipe based on the results of analysis of common features, using the contents of settings having high degrees of commonality as initial settings. 
         [0011]    According to the present invention, even a novice can analyze the contents of existing recipe settings. Especially, he can easily judge the commonality. Therefore, it is only required to examine the contents of settings regarding only items having low degrees of commonality. Hence, a novel recipe can be created in a short time. Furthermore, the throughput of the created recipe can be forecasted. Therefore, the validity of the set items can be confirmed. Where the contents of the settings are modified, the recipe settings can be optimized while checking the effects of the modification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a cross-sectional view showing the fundamental structure of a SEM-based semiconductor defect-reviewing apparatus. 
           [0013]      FIG. 2  is a table showing one example of a shown list of the results of a recipe analysis. 
           [0014]      FIG. 3  is a diagram showing one example of GUI (graphical user interface) for setting items subjected to a recipe analysis. 
           [0015]      FIGS. 4A and 4B  are diagrams showing one example of GUI for implementing a recipe analysis. 
           [0016]      FIG. 5  is a diagram showing one example in which calculated throughput values and actually measured values are added to shown results of a recipe analysis. 
           [0017]      FIG. 6  is a diagram showing one example of GUI in which the results of a recipe analysis and an acquired image are made to correspond to each other and displayed. 
           [0018]      FIGS. 7A-7C  are diagrams showing examples of a reviewing system in which plural reviewing apparatus holding recipes are connected via a network. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0019]    Embodiments of the present invention are described.  FIG. 1  is a cross-sectional view showing the configuration of a SEM-based defect-reviewing apparatus that is one embodiment of the present invention. The SEM-based defect-reviewing apparatus shown in  FIG. 1  is used to review a sample  105  and composed of an electron gun  101 , a lens  102 , a deflector  103 , an objective lens  104 , a stage  106 , a secondary particle detector  109 , an electron optics controller  110 , an A/D converter (ADC)  111 , a stage controller  112 , an overall controller  113 , an image-processing portion  114 , a display device  115 , a keyboard  116 , a storage device  117 , a computer mouse  118 . An electron beam  107  emitted from the electron gun  101  is focused by the lens  102  and deflected by the deflector  103 . Then, the beam is focused by the objective lens  104  and made to hit the sample  105 . The sample  105  irradiated with the electron beam  107  produces secondary particles  108  such as secondary electrons and backscattered electrons according to the shape and material of the sample. The produced secondary particles  108  are detected by the secondary particle detector  109  and converted into a digital signal by the A/D converter  111 . Thus, a SEM image is created. Image processing such as detection of defects is performed by the image-processing portion  114 , using the created SEM image. The lens  102 , deflector  103 , and objective lens  104  are controlled by the electron optics controller  110 . The position of the sample is controlled by the stage  106  that is under control of the stage controller  112 . The overall controller  113  interprets inputs from the keyboard  116 , mouse  118 , and storage device  117  and controls various portions including the electron optics controller  110 , stage controller  112 , and image-processing portion  114 . If necessary, the overall controller outputs the contents of processing to the display device  115  and storage device  117 . 
         [0020]      FIG. 2  shows one example of the results of a recipe analysis. In this example, contents of recipe settings are shown as items of a list  201 . That is, the shown items are process name (Process), optical conditions (SEM Cond), ADR mode (ADR Mode), magnification of low-magnification images (Low Mag), autofocus conditions of low-magnification images (Low AF), the number of added frames of low-magnification images (Low Frame), magnification of high-magnification images (High Mag), autofocus conditions of high-magnification images (High AF), and the number of added frames of high-magnification images (High Frame). In  FIG. 2 , the optical conditions are indicated by numerals. For example, where the optical conditions are defined by combinations of plural conditions including accelerating voltage (Vac) and probe current (Ip), each condition may be treated as an independent analysis item. Furthermore, comment registered by the user, capture rate used when there is an ADR function, recipe creator, date of creation, recipe updater, date of updating, and recipe version can be registered as analysis items. In the ADR mode, the ADR algorithm is switched according to the sample. Three modes are shown in  FIG. 2 : (1) die comparison mode (Die) in which the throughput is low because it is necessary to acquire a reference image but it is possible to cope with any arbitrary background pattern; (2) cell comparison mode (Cell) in which the throughput is high because no reference image is required but the recipe can be used only when there is a background pattern having periodicity; and (3) bare mode (Bare) in which the recipe is effective only for samples having no background pattern. 
         [0021]    As the magnification of a low-magnification image becomes higher, defects are detected more easily. However, the probability that defects do not come within the field of view is increased. Consequently, optimization must be done taking account of the tradeoff between the size of the defect to be detected and the coordinate accuracy. In a first set of autofocus conditions for low-magnification images, a standard algorithm is used (Standard). In a second set of autofocus conditions, the processing speed is high but the accuracy is lower than that provided by the standard algorithm (Fast). In a third set of autofocus conditions, the processing speed is low but the accuracy is higher than that provided by the standard algorithm (Slow). As the number of added frames of low-magnification images is increased, noise is reduced. Therefore, where emphasis is placed on the capture rate rather than the throughput, the number of added frames of low-magnification images is set to a large value. The magnification of high-magnification images is determined according to the size of the defect to be reviewed. The magnification of high-magnification images, autofocus conditions for high-magnification images, and the number of added frames are similar in meaning to the magnification of low-magnification images, autofocus conditions, and the number of added frames, respectively, but are used for final check of the defect image. Therefore, settings are often made while placing emphasis on the image quality rather than the throughput in comparison with low-magnification images. Contents of settings including device name and automatic device classification (ADC) (not shown in  FIG. 2 ) are items to be analyzed. 
         [0022]      FIG. 3  shows one example of GUI for selecting an item to be analyzed. Items registered in a display list  301  are displayed as results of an analysis as shown in  FIG. 2 . Items registered in a non-display list  302  are not displayed as results of an analysis. Movement from the list  301  to the list  302  is effected by depressing a right-arrow button  303 . Movement from the list  302  to the list  301  is effected by depressing a left-arrow button  304 . When an order of registration should be modified within each list, an item to be moved is selected as indicated by  305 . Where the user wants to replace the selected item by an item located at the immediately above location, an Up button  306  is depressed. Where the user wants to replace the selected item by an item located at the immediately below location, a Down button  307  is depressed. 
         [0023]    A procedure for analyzing the commonality among the set items is described taking the example of  FIGS. 4A and 4B . A list of contents of recipe settings as shown in  FIG. 4B  is displayed in a list display area  401  of  FIG. 4A .  FIG. 4B  is a part extracted from  FIG. 2 . 
         [0024]    With respect to the commonality among the set items, when the items of various contents of settings set for individual recipes contain items (herein referred to as common items) common to different recipes and the number of the common items is large in number, it is determined that the level of commonality is high. On the other hand, when the common items are few in number, it is determined that the level of commonality is low. 
         [0025]    First, “Item”  402  to be analyzed for its commonality is selected using a pointing device such as a computer mouse. In this example, “Process” is selected. After “Item” has been selected, a keyword is entered using the input device such as a keyboard. A Search button  404  is depressed. In the illustrated example, a character string starting with A is specified as the keyword. Therefore, a recipe  405  having a Process name starting with A is displayed in the list display area  401 . In this example, recipes displayed in the list are restricted using a Search function. Where recipes are few in number, it is not always necessary to limit recipes displayed. Furthermore, the list can be sorted by the Item to be analyzed. 
         [0026]      FIG. 4B  shows the results of sorting executed based on “Process”  407 . In this way, as the need arises, preparations are made to select a recipe to be analyzed by employing a sorting or Search function. Then, the recipe to be analyzed is selected. As an example, it is assumed that a recipe  405  having a “Process” name starting at A has been selected. After the selection, an Analyze button  408  is depressed to perform the analysis. An item ( 409 ) judged to have a low degree of commonality as a result of the analysis is highlighted. In the illustrated example, only those which have low degrees of commonality are highlighted, indicating their degrees of commonality. Alternatively, those having high degrees of commonality may be distinguished from others and highlighted. Still alternatively, plural different levels of range of frequencies of occurrence may be previously set. Frequencies of occurrence may be distinguished using the levels of range. It can be seen that in the example of  409 , only the recipe having a “Process” name of A 3  is set to a low value of “Low Mag”. If this setting is made higher in conformity with other process names A 1 , A 2 , and A 4 , the low-magnification image derived by detecting a defect is enlarged. Consequently, there is the possibility that defect-detecting performance, i.e., the capture rate, can be improved. 
         [0027]    Similarly, analysis of common terms of recipes  410 , each having a “Process” name starting with B, reveals that the degree of commonality between High AF ( 411 ) of B 3  and “High Frame” ( 412 ) of B 2  is low. The result of the analysis shows that if the autofocus settings of the high-magnification image of B 3  are set to a high-speed mode in the same way as B 1  and B 2 , the throughput may be improved, and that if the number of added frames of high-magnification images of B 2  is set to the same value as that of B 1  and B 3 , an image of higher quality will be acquired. This would result in favorable results. 
         [0028]    Where the settings are modified, an element of the list that the user wants to change is selected using the pointing device such as a mouse, and then the settings can be varied using the input device such as a keyboard. Plural elements may be selected and the settings may be modified in a batch mode. 
         [0029]    A procedure of creating a recipe is now described. In this procedure, the contents of settings having high degrees of commonality are taken as initial values, based on the results of an analysis. As an example, a recipe  410  having a “Process name” starting with B is a subject to be analyzed. When the Analyze button  408  is depressed and the analysis is started, items having high degrees of commonality are displayed in the common item display area  413 . In the present example, “Process:B*”, “ADR Mode:Cell”, “Low Mag:20k”, “Low AF:Fast”, “Low Frame: 4 ”, “High Mag:60k”, “High AF:Narrow”, “High Frame: 12 ” are shown initially. Where the contents of the settings are updated according to the need and a recipe having a “Process” name of B 4 , for example, is newly created, the “Process” name of “B*” is updated to “B 4 ”. The recipe can be easily created by depressing “Save as” button  414 . 
         [0030]      FIG. 5  shows an example in which calculated values ( 501 ) of the ADR throughput and values ( 502 ) obtained by actual measurements are added to the results of the recipe analysis and displayed. Comparison of A 1 , A 2 , A 3 , and A 4 , each having a “Process” name starting with A, reveals that only A 3  is different in value ( 503 ) of “High Mag”. However, the magnification of high-magnification images does not affect the ADR throughput. Consequently, A 3  is identical with A 1 , A 2 , and A 4  in calculated value ( 504 ) of throughput. On the other hand, comparison of B 1 , B 2 , and B 3 , each having a “Process” name starting with B, shows that B 3  is lower than B 1  and B 2  in calculated value ( 506 ) of throughput, because the setting ( 505 ) of “High AF” of B 3  is in a mode in which emphasis is placed on the accuracy and thus the processing speed is low, unlike B 1  and B 2 . Furthermore, B 2  is higher than B 1  and B 3  in calculated value ( 508 ) of throughput, because the value ( 507 ) of “High Frame” of B 2  is set to a mode in which emphasis is placed on the throughput rather than the image quality and thus the processing speed is high, unlike B 1  and B 3 . The actually measured value ( 502 ) of throughput indicates the result of a measurement of the throughput in a case where ADR (automatic defect review) is carried out using the corresponding recipe in practice. At this time, the result can be either the result of the newest measurement or an average value of the results of plural measurements. Alternatively, both may be displayed. In this way, the throughput is displayed, thus making it possible to quickly check the effects of updating of the recipe. Consequently, optimization of the recipe can be carried out efficiently. 
         [0031]      FIG. 6  shows one example of GUI (graphical user interface) in which a list of results of a recipe analysis and an image acquired with a recipe specified from the list are made to correspond to each other and displayed. In this example, an image display portion  602  and image updating buttons  603  are added to the example of GUI of  FIG. 4A . An image acquired using the recipe  601  selected from the displayed list indicating the results of a recipe analysis is displayed in the image display portion  602 . The displayed image can be updated using the image updating buttons  603 . A button indicated by &gt; is used for movement to the next image. A button indicated by &lt; is used for movement to the immediately previous image. A button indicated by &gt;&gt; is used to move the cursor to an image spaced by a given amount, e.g., skipping of 10 successive images. A button indicated by &lt;&lt; is used to move the cursor to a previous image spaced by a given amount, e.g., skipping of 10 successive images. In this way, the image is updated. With respect to the form of image display, plural windows may be opened at the same time as long as a recipe selected from a list can be made to correspond to an image acquired with the selected recipe. In this way, the recipe and image can be made to correspond to each other easily. Therefore, regarding a recipe that cannot be judged as to whether it should be subjected to a similarity analysis, for example, only using a device name or a process name, a decision as to whether the recipe should be subjected to the similarity analysis can be easily made by checking the image. 
         [0032]      FIGS. 7A-7C  show reviewing systems in each of which plural reviewing apparatus are connected via a network, each reviewing apparatus holding recipes to be analyzed by a recipe-analyzing function. In  FIG. 7A , plural reviewing apparatus  701 ,  702 , and  703  are connected with a network  704 . The network  704  can be a wired network or a wireless network if data can be sent and received by the network. The reviewing apparatus  703  is not fitted with the recipe-analyzing function and so this apparatus cannot perform a recipe analysis. However, the apparatus  703  can analyze recipes held in the reviewing apparatus  703 , using the recipe-analyzing function of the reviewing apparatus  701  or  702 . 
         [0033]      FIG. 7B  shows a reviewing system in which plural reviewing apparatus not having a recipe-analyzing function are batch-managed by a recipe management server  705 . Created recipes are batch-managed by the recipe management server. If necessary, the recipes can be transferred to the reviewing apparatus and to recipe management clients  706  and  707 . Each reviewing apparatus does not have a recipe-analyzing function and, therefore, cannot perform a recipe analysis. However, the recipe analysis can be performed by the recipe management server  705  or by the recipe management client  706  or  707 . 
         [0034]      FIG. 7C  shows a reviewing system having a recipe management server capable of batch-managing recipes. In this system, each reviewing apparatus has a recipe-analyzing function. Therefore, a recipe analysis can be performed from whatever of the recipe management server, recipe management clients, and reviewing apparatus. 
         [0035]    The present invention can have the following configurations: 
         [0036]    (1) A reviewing apparatus for acquiring review images of a sample, the reviewing apparatus comprising: 
         [0037]    a storage device in which plural recipes are stored, the recipes having plural review conditions under which the review images are acquired, the review conditions being registered in the recipes; 
         [0038]    an arithmetic unit for extracting common review conditions registered in all of the plural recipes from the first-mentioned review conditions, taking the common review conditions most frequently registered out of the common review conditions as initial review conditions, storing the initial review conditions in the storage device, and creating a new recipe under the initial review conditions; and 
         [0039]    a display device for displaying information sent from the arithmetic unit; 
         [0040]    wherein the arithmetic unit displays the plural recipes on one display screen of the display device in such a way that the common review conditions are distinguished from other conditions. 
         [0041]    (2) A method of setting recipes for a reviewing apparatus for acquiring review images of a sample, said method comprising the steps of: 
         [0042]    preparing plural recipes in which plural review conditions under which the review images are acquired are registered; 
         [0043]    extracting common review conditions registered in all of the recipes from the recipes; 
         [0044]    taking common review conditions most frequently registered out of the first-mentioned common review conditions as initial review conditions; 
         [0045]    storing the initial review conditions in memory; 
         [0046]    creating a new recipe using the initial review conditions; 
         [0047]    causing the new recipe created using the initial review conditions to be displayed on a display device; and 
         [0048]    displaying the plural recipes on one display screen of the display device in such a way that the common review conditions are distinguished from other conditions. 
         [0049]    It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.