Abstract:
A system of testing semiconductor devices includes a classification module configured to classify a plurality of lots into a plurality of groups; an apparatus assignment module configured to assign a plurality of testing apparatuses to each of the groups; and a test recipe creation module configured to create a test recipe to test defects in a second group other than a first group specified in the groups, the test recipe including a definition of testing positions in the second group defined by a rule different from the first group.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS AND INCORPORATION BY REFERENCE 
   This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. P2005-75410, filed on Mar. 16, 2005; the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a testing system, more specifically to a testing system for testing semiconductor devices, a testing method for testing semiconductor devices, and a method for manufacturing semiconductor devices. 
   2. Description of the Related Art 
   A semiconductor device is manufactured by a series of processes including a combination of lithography, etching, heat treatment (oxidation, annealing, or diffusion), ion implantation, thin film formation (CVD, sputtering, or vapor deposition), washing (resist removal or washing with a solution), or the like. After the treatment of each process, testing is carried out to check adequacy of the treatment, magnitude of variation, and the like. For example, in the lithography process to transfer an image of a mask pattern to a working wafer, dimensional measurement of the transferred pattern is performed. 
   In the testing process, sampling test is performed. Specifically, in a lot including a plurality of semiconductor wafers, some semiconductor wafers are sampled and then tested. Results of the testing are considered as representative values of the lot. The sampling test in the testing process is to save time and effort required for the 100-percent-testing. However, along with a recent increase in integration of semiconductor devices, each process becomes difficult to control, and the number of items to be tested is getting larger than before. For example, the dimensional measurement after the lithography requires monitoring of variation in a shot, variation between shots, variation between wafers, and the like. 
   In currently-available method of testing, areas to be tested are previously decided. Accordingly, it is difficult to cover all the test items within the limited number of tests. For example, when the number of testing points determined on a throughput of a testing apparatus or costs is limited to 30 points, the test items are determined as: five points per shot, six shots per wafer, and one wafer per lot. The variation in a shot and variation between shots, for which many tests are carried out, can be monitored. However, the variation between wafers cannot be monitored since only one wafer is measured. However, since wafers are varied, the representative values of the lot cannot be properly calculated by sampling only one wafer from the lot. 
   SUMMARY OF THE INVENTION 
   An aspect of the present invention inheres in a system of testing semiconductor devices, encompassing a classification module configured to classify a plurality of lots into a plurality of groups; an apparatus assignment module configured to assign a plurality of testing apparatuses to each of the groups; and a test recipe creation module configured to create a test recipe to test defects in a second group other than a first group specified in the groups, the test recipe including a definition of testing positions in the second group defined by a rule different from the first group. 
   Another aspect of the present invention inheres in a method of testing semiconductor devices, encompassing classifying a plurality of lots into a plurality of groups; assigning a plurality of testing apparatuses to the groups, respectively; and creating a test recipe to test defects in a second group other than a first group specified in the groups, the test recipe including a definition of testing positions defined by a rule different from the first group. 
   Still another aspect of the present invention inheres in a method of manufacturing semiconductor devices, encompassing conducting a manufacturing procedure on a plurality of working substrates implementing one of a plurality of lots; classifying the lots into a plurality of groups; assigning a plurality of testing apparatuses to the groups respectively; creating a test recipe to test defects in a second group other than a first group in the groups, the test recipe including a definition of testing positions defined by a rule different from the first group; and testing defects in the second group based on the test recipe. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a block diagram illustrating a testing system for testing semiconductor devices according to a first embodiment of the present invention; 
       FIG. 2  is a schematic diagram illustrating an example of a method of classifying lots of the testing system according to the first embodiment of the present invention; 
       FIG. 3A  is a schematic diagram illustrating a lot belong to a GROUP A in  FIG. 2 ; 
       FIG. 3B  is a schematic diagram illustrating measurement points shots) included in a wafer; 
       FIG. 3C  is a schematic diagram illustrating measurement points (sites) included in the shot as shown in  FIG. 3B ; 
       FIG. 3D  is a schematic diagram illustrating an example of a kind of a pattern included in the cite as shown in  FIG. 3C ; 
       FIG. 4A  is a schematic diagram illustrating an example of measurement subjects of wafers belong to the GROUP B in  FIG. 2 ; 
       FIG. 4B  is a schematic diagram illustrating measurement points (shots) included in a wafer; 
       FIG. 4C  is a schematic diagram illustrating measurement points (sites) included in the shot as shown in  FIG. 4B ; 
       FIG. 4D  is a schematic diagram illustrating an example of a kind of a pattern included in the cite as shown in  FIG. 4C ; 
       FIG. 5  is a flowchart illustrating a testing method of the testing system according to the embodiment of the present invention; 
       FIG. 6  is a flowchart illustrating a method of manufacturing semiconductor devices according to the embodiment of the present invention; and 
       FIG. 7  is a block diagram illustrating a testing system according to a modification of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Various embodiments of the present invention will be described with reference to the accompanying drawings. It is to be noted that the same or similar reference numerals are applied to the same or similar parts and elements throughout the drawings, and the description of the same or similar parts and elements will be omitted or simplified. In the following descriptions, numerous details are set forth such as specific signal values, etc. to provide a thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details. 
   FIRST EMBODIMENT 
   As shown in  FIG. 1 , a system for testing semiconductor devices according to an embodiment of the present invention includes a classification module  11 , an apparatus assignment module  12 , and a test recipe creation module  14 . The classification module  11  classifies a plurality of lots into a plurality of groups. The apparatus assignment module  12  assigns an testing apparatus  6   a ,  6   b ,  6   c , . . . , to each of the groups. The test recipe creation module  14  creates a test recipe based on testing results from the testing apparatus  6   a ,  6   b ,  6   c, . . .    
   The classification module  11 , the apparatus assignment module  12 , and the test recipe creation module  14  implement as a part of a central processing unit (CPU)  1  of a computer system as shown in  FIG. 1 . The CPU  1  further includes an analysis module  13  to analyze the testing results from the testing apparatuses  6   a ,  6   b ,  6   c , . . . The classification module  11 , the apparatus assignment module  12 , the analysis module  13 , and the test recipe creation module  14  may be each established by dedicated hardware and connected to each other through LAN or the like. 
   The testing apparatuses  6   a ,  6   b ,  6   c , . . . are connected to the CPU  1 . The CPU  1  is connected to a data memory  2  storing processing results of the CPU  1  and the like, an input unit  3  accepting an input from an operator and the like, an output unit  4  outputting the processing results of the CPU  1  and the like, and a program memory  5  storing various programs necessary for arithmetic processing of the CPU  1 . 
   The classification module  11  classifies a plurality of lots including a plurality of working substrates into a plurality of groups for each lot. Herein, the working substrates may indicate semiconductor substrates (semiconductor wafers) in manufacture of semiconductor devices, liquid-crystal substrates in manufacture of liquid-crystal devices, resin substrates in manufacture of magnetic or optical recording media, magnetic substrates in manufacture of thin-film magnetic heads, piezoelectric substrates in manufacture of ultrasonic devices, or intermediate products at an intermediate phase of a manufacturing process in manufacture of superconducting devices, such as superconducting substrates. 
   The working substrates can be formed of organic materials such as various kinds of synthetic resin or various inorganic materials such as semiconductors, metal, ceramic, and glass depending on a kind of the object product (manufactured product). Many of the working substrates are plate-shaped bases, which may be referred to as “manufactured substrates”, like semiconductor wafers. However, the working substrates are unnecessarily plate-shaped and can have various shapes such as a block shape depending on the kind of the object product (manufactured product). In the case of the manufacturing with the semiconductor wafers and the like, intermediate products including a composite structure with a semiconductor wafer, as a base material, and thin films laminated on the semiconductor wafer are also referred to as the “working substrates”. 
   The classification module  11  automatically classifies lots into a plurality of groups based on identification numbers_N attached to the lots as shown in  FIG. 2 . Specifically, the classification module  11  classifies, for example, a lot with the identification number N with final number of “1” as a “first group A” and classifies a lot with the identification number N with final number other than “1” as “a second group B”. Specifically, lots with the identification numbers N of “0001”, “0011”, and “0021” belong to the first group (group A), and lots with the identification numbers N of “0002” to “0010” and “0012” to “0020” belong to the second group (group B). 
   The apparatus assignment module  12  of  FIG. 1  selects a suitable kind of the testing apparatus  6   a ,  6   b ,  6   c , . . . according to the test recipes of the first and second groups. The testing apparatuses  6   a ,  6   b ,  6   c , . . . tests of dimensions of patterns, thickness of thin films, resistance of diffusion layers, polysilicon layers, and the like on working substrates (wafers) included in lots put into a production line. The testing apparatuses  6   a ,  6   b ,  6   c , . . . can be various types of testing apparatuses and measurement apparatuses such as a microscope, an interference-type film thickness gauge, an ellipsometer, a contact-type film thickness gauge, and a resistance meter. The analysis module  13  analyzes statistical data including an average, a maximum value, a minimum value, variation, and the like of the testing results obtained by the testing apparatuses  6   a ,  6   b ,  6   c, . . .    
   The test recipe creation module  14  creates a test recipe of a subject group to be tested next to the previous group, based on the analysis information of the previous group measured by the analysis module  13 . Herein, a description is given taking measurement of line width of resist patterns after lithography as an example. 
   Lot variation in linewidth after lithography includes, for example, variation between a plurality of wafers constituting a lot  50  shown in  FIG. 3A , variation between shots when each wafer is divided into a plurality of areas (shots) shown in  FIG. 3B , variation between sites when each shot is divided into a plurality of small areas (sites) shown in  FIG. 3C , and variation between patterns (A) to (E) formed in each sites shown in  FIG. 3D . 
   In order to focus on testing of the variations between sites shown in  FIG. 3C  and variation between patterns shown in  FIG. 3D , for the first group (group A) in  FIG. 2 , for example, the test recipe creation module  14  creates a test recipe so as to increase the number of tests shown in  FIGS. 3C and 3D . On the other hand, for the second group (group B) in  FIG. 2 , the test recipe creation module  14  creates a test recipe so as to increase the number of tests shown in  FIGS. 3A and 3B , in order to focus on testing of the variation between wafers shown in  FIG. 3A  and variation between shots shown in  FIG. 3B . 
   Specifically, in a test recipe A 1  (not shown) belonging to the first group (group A), as shown in  FIG. 3A , a wafer  51  is arbitrarily extracted from the lot  50   i . Furthermore, as shown in  FIG. 3B , three shots  52   a ,  52   b , and  52   c  are extracted from the wafer  51 . As shown in  FIG. 3C , nine sites are extracted from each of the shots  52   a  to  52   c . Measurement is performed for dimensions of, for example, five pattern shapes shown in  FIG. 30  included in each of the nine sites, specifically, (A) dense lines and spaces (L/S), (B) intermediate pitch lines and spaces (L/S), (C) an isolated line, (D) dense lines and spaces of a reversed pattern, and (E) an isolated line of the reversed pattern. 
   On the other hand, in a test recipe when a lot  50   i+1  belonging to the second group (group B) is tested, as shown in  FIG. 4A , six wafers  51   a  to  51   f  are extracted from the lot  50   i+1 . As shown in FIG.  4 B, nine shots  52   a  to  52   i  set in each of the wafers  51   a  to  51   f  are extracted. As shown in  FIG. 4C , a site “ 5 ” is extracted from each of the shots  52   a  to  52   i . Measurement is then performed for linewidth of the pattern shape (E) of  FIG. 4D  existing in each site “ 5 ”. 
   The data memory  2  of  FIG. 1  includes a classification memory  21 , a test memory  22 , an analysis memory  23 , and a test recipe memory  24 . The classification memory  21  stores results of group classification of each lot performed by the classification module  11 . The test memory  22  stores information of the testing apparatuses  6   a ,  6   b ,  6   c , . . . determined by the apparatus assignment module  12 . The analysis memory  23  stores analysis information of the analysis module  13 . The test recipe memory  24  stores the test recipes created by the test recipe creation module  14 . 
   The input unit  3  shown in  FIG. 1  includes a keyboard, a mouse, a light pen, a flexible disk, or the like. The operator can perform specification of input/output data, setting of test or analysis conditions or the like, and the like through the input unit  3 . The output unit  4  can be a display, a printer, a recording apparatus saving in a computer-readable recording medium, or the like. Examples of the computer-readable recording medium include a computer external memory, a semiconductor memory, a magnetic disk, an optical disk, a cassette tape, and an open reel tape. 
   With the testing system shown in  FIG. 1 , in a series of lots put into the production line, each group is subjected to different kinds of test using different testing apparatuses with a same number of tests. Accordingly, it is possible to obtain accurate representative values of a lot even when many test items are included in the lot. Furthermore, the classification module  11  automatically classifies lots into a plurality of groups based on the identification numbers attached to the lots, so that the production line can be automated. 
   Next, a description is given of a method of testing semiconductor devices using the system according to the embodiment with reference to a flowchart of  FIG. 5 . Herein, the description is given of an example in which a process to measure linewidth of resist patterns after lithography is applied to the testing system. 
   In step S 10  of  FIG. 5 , various types of information including test recipes, types of the testing apparatuses, group classification information to classify a plurality of lots into a plurality of groups, and test items for each group are input through the input unit  3  and stored in the data memory  2 . Herein, for example, the classification memory  21  stores information to, based on the identification numbers N of lots, classify lots having the identification numbers N with final number of “1” as the first group (group A) and classify lots having the identification numbers N with final number other than “1” as the second group (group B). As the test recipe A 1  of the first group (group A), as shown in  FIGS. 3A to 3D , the test recipe memory  24  stores information to measure five pattern shapes of nine sites of three shots in one wafer. 
   In step S 11 , the classification module  11  reads the group classification information stored in the classification memory  21 . The classification module  11  automatically classifies a lot put into the production line based on the identification number N attached to the lot as the first group (group A) or the second group (group B). For example, when the lot  50   i  with the identification number N of “0001” is put into the production line, the classification module  11  classifies the lot  50   i  into the first group (group A) based on the group classification information. The result of group classification of the lot  50   i  is stored in the classification memory  21 . 
   In step S 12 , the apparatus assignment module  12  reads the result of group classification of the lot  50   i  from the classification memory  21 . The apparatus assignment module  12  reads the test recipe A 1  from the test recipe memory  24  and assigns a suitable kind of the testing apparatus  6   a ,  6   b ,  6   c , . . . according to the test recipe A 1  and the result of group classification of the lot  50   i . For example, the lot  50   i  belongs to the first group (group A). The test recipe of the group A is targeted for dimensional measurement of minute regions of various areas in one wafer. Accordingly, as the testing apparatus  6   a , a scanning electron microscope suitable for the dimensional measurement of minute regions is selected. The result of selection of the testing apparatus  6   a  is stored in the test memory  22 . 
   In step S 13 , the testing apparatus  6   a  reads the test recipe A 1  stored in the data memory  2 . Based on the test recipe A 1 , the testing apparatus  6   a  extracts the wafer  51  from the lot  50   i , extracts the three shots  52   a  to  52   c  from the wafer  51 , and tests dimensions of linewidth of the five pattern shapes (A) to (E) of each of the nine sites existing in each shot. The results of testing of the testing apparatus  6   a  are transmitted to the analysis module  13 . 
   In step S 14 , based on the result of test of the lot  50   i  transmitted from the testing apparatus  6   a , the analysis module  13  analyzes the statistical data including a maximum value, a minimum value, an average, variation, and the like of each measured minute dimension. In the sites  1  to  9  shown in  FIG. 3C , the analysis module  13  analyzes a position of a site providing a dimension averaged over pattern shapes ((A) to (E)) closest to a predetermined target dimension. The analysis module  13  analyzes a pattern shape providing a dimension closest to the target dimension in the pattern shapes (A) to (E) shown in  FIG. 3D . The analysis information by the analysis module  13  is stored in the analysis memory  23 . 
   In step S 15 , the test recipe creation module  14  reads the analysis information stored in the analysis memory  23 . Based on the read analysis information, the test recipe creation module  14  creates a test recipe B 1  of a group to be tested next. For example, in the test of the lot  50   i  belonging to the first group (group A), suppose that the test recipe creation module  14  obtains the analysis information that the dimension average of the site  5  shown in  FIG. 3C  is closest to the target dimension and the dimension of the pattern shape (E) shown in  FIG. 3D  is closest to the target dimension. In order to focus on test of the variation between the plurality of wafers and variation in a wafer, the test recipe creation module  14  creates the test recipe B 1  so that the number of tests in each shot is fixed to one point (the pattern shape (E) in the site  5  is tested) and the number of tests for the variation between wafers and variation in a wafer is increased. The created test recipe B 1  is stored in the test recipe memory  24 . 
   In step S 16 , it is judged whether a next lot is put into the production line. When the next lot is put into the production line, the procedure proceeds to the step S 11 . In the step S 11 , the classification module  11  reads the group classification information stored in the data memory  2  and, based on the identification number N “0002” of the new lot  50   i+1 , classifies the lot  50   i+1  as the group B. The result of group classification of the lot  50   i+1  is stored in the classification memory  21 . 
   In the step S 12 , the apparatus assignment module  12  reads the group type of the lot  50   i+1  from the classification memory  21 . The lot  50   i+1  belongs to the second group (group B), and the apparatus assignment module  12  reads the test recipe B 1  from the test recipe memory  24  and assigns a suitable kind of the testing apparatus  6   a ,  6   b ,  6   c , . . . according to the test recipe B 1 . Herein, an object of the test recipe B 1  is to test a large number of wafers with the testing position fixed. Accordingly, as the testing apparatus  6   b , an optical dimension gauge such as a scatterometry is selected. The result of selection of the testing apparatus  6   b  is stored in the test memory  22 . 
   In the step S 13 , the testing apparatus  6   b  reads the test recipe B 1  stored in the data memory  2 . Based on the test recipe B 1 , the testing apparatus  6   b  samples the six wafers  51   a  to  51   f  shown in  FIG. 4A  out of the lot  50   i+1  and selects the nine shots  52   a  to  52   i  from each of the wafers  51   a  to  51   f . The testing apparatus  6   b  then tests the dimension of the pattern shape (E) in one site existing in each shot. The result of tests by the testing apparatus  6   b  is transmitted to the analysis module  13 . 
   In the step S 14 , the analysis module  13  analyzes the results of tests by the testing apparatus  6   b  transmitted from the testing apparatus  6   b . In the step S 15 , based on the analysis information by the analysis module  13 , the test recipe creation module  14  creates a new test recipe to test a next group and causes the test recipe memory  24  to store the new test recipe. For all the lots put into the production line, testing shown in the steps S 11  to S 15  are repeated for each group classified based on the identification numbers N. 
   The measurement of linewidth in the testing process after lithography includes two objects of: (1) obtaining exposure conditions of the next lot from the measurement results; and (2) not transmitting a defective lot to the subsequent process. 
   In the testing method using the testing system according to the embodiment, first, in the testing of the lot  50   i  (identification number N: “0001”) classified as the group A, the wafer  51  is sampled from the lot  50   i , and measurements are performed for the dimensions of the sites existing in the shots  52   a  to  52   c  and the dimensions of the pattern shapes. By the measurement, the variation in a shot and the variation between patterns of the lot  50   i  are obtained. However, in the test items of the first group (group A), only the wafer  51  is tested, and the variation between wafers is not known. 
   Accordingly, in the testing of the lots (identification number N: “0002”-“0010”) classified as the second group (group B) to be tested next, based on the test recipe B 1  created at the test of the group A, the numbers of wafers and shots sampled are increased. As shown in  FIGS. 4A to 4D , the wafers  51   a  to  51   f  are sampled from the lot  50   i+1 , and the shots  52   a  to  52   i  are sampled from each wafer. This makes it possible to analyze which of the wafers  51   a  to  51   f  is subject to defects or which location in the wafers  51   a  to  51   f  is subject to defects. 
   When the analysis results of the group B reveal that the linewidth of the first wafer  51   a  shown in  FIG. 4A  tends to be narrowed and the linewidth around the center of the wafer  51   a  tends to be narrowed, the analysis results of the group B is reflected on a test recipe A 2  of a group to be tested next. Accordingly, in the test of a lot (identification number N; “0011”) classified as the group A next tested as shown in  FIG. 2 , it is possible to extract and test many linewidth around the center of the first wafer, which tend to be narrowed, thus providing accurate lot averages. 
   As described above, by reflecting the test recipe based on the analysis information obtained for each group on testing of the next group, the two aforementioned objects of the dimensional measurement after lithography can be satisfied. It is therefore possible to provide the testing system effective on controlling wafer linewidth. 
   Next, a description is given of a method of manufacturing a semiconductor device according to the embodiment with reference to a flowchart shown in  FIG. 6 . The flowchart of  FIG. 6  shows a part of a vast and complicated semiconductor device manufacturing process, specifically, a CVD process in S 21 , a film thickness testing process S 22 , a photoresist film formation process in step S 23 , and a resist pattern testing process in step S 24 . There are certainly a series of processes corresponding before the step S 21  and a series of processes corresponding after step S 28 . The flowchart shown in  FIG. 6  is just an example, and the embodiment can be applied to various testing processes including a modification of this example. 
   In the step S 21 , insulating films such as thermal oxidized films are grown on wafers by CVD. In the step S 22 , film thickness of the insulating films formed on the wafers is tested. Specifically, in step S 221 , the classification module  11  of  FIG. 1  classifies lots put into the production line into a plurality of groups based on the identification numbers N attached to the respective lots. 
   In step S 222 , the apparatus assignment module  12  selects a kind of the testing apparatus  6   a ,  6   b ,  6   c , . . . suitable for the film thickness testing based on the test recipe stored in the data memory and group classification information. 
   In step S 223 , the testing apparatus  6   a ,  6   b ,  6   c , . . . reads the test recipe stored in the data memory  2  and measures the film thickness on the wafer. The results of the film thickness testing is transmitted to the analysis module  13 , and the analysis module  13  analyzes the statistical data including an average, a maximum value, a minimum value, variation, and the like of the film thickness. 
   In step S 224 , the test recipe creation module  14  creates a film thickness test recipe of a group to be tested next based on statistical data obtained from the analysis information of the analysis module  13 , such as film thickness defects. In step S 225 , the process shown in the aforementioned steps S 221  and  224  is repeated again based on the identification number N attached to the next lot. 
   In step S 226 , when the test of all the lots is finished, it is determined whether the CVD process of the step S 21  is properly performed. When the CVD process is determined not to be properly performed, the operation is stopped in step  5227 . When the CVD process is determined to be properly performed, the procedure proceeds to the step S 23 . 
   In the step s 23 , photoresist films are applied on the surfaces of the insulating films on the wafers by a photolithographic technique. Thereafter, in the step S 24 , patterns of the formed photoresist films are tested. Specifically, in step S 241 , the classification module  11  classifies the lots put into the production line into a plurality of groups based on the identification numbers N attached to the lots. 
   In step S 242 , the apparatus assignment module  12  selects a kind of the testing apparatus  6   a ,  6   b ,  6   c , . . . suitable for the dimensional measurement based on the test recipe stored in the data memory and group classification results. 
   In step S 243 , the testing apparatus  6   a ,  6   b ,  6   c , . . . reads information of the test recipe for resist patterns stored in the data memory  2  and measures dimensions of the resist patterns formed on the wafers. The results of the dimensional measurement is transmitted to the analysis module  13 , and the analysis module  13  analyzes statistical data including an average, a maximum value, a minimum value, and a variation of dimensions of the patterns for each testing area. 
   In step S 244 , the test recipe creation module  14  creates a test recipe for resist patterns of a group to be tested next, based on information of dimensional defects of the resist patterns obtained from the analysis information of the analysis module  13 . 
   In step S 245 , according to the conditions of the group decided based on the identification number N attached to the next lot, the dimensional measurement of the resist patterns shown in the steps S 241  to S 244  is repeated. After the testing for all the lots is finished, in step S 246 , it is determined whether the formation of the resist patterns is properly performed. When the formation is determined not to be properly performed, the procedure proceeds to step S 247 , and the operation is stopped. When the formation is determined to be properly performed, the procedure proceeds to the step S 25 , and an etching (RIE) process is performed. 
   With the semiconductor device manufacturing method as shown in  FIG. 6 , the plurality of lots are automatically classified according to the identification numbers N, and a predetermined test based on the test recipe is performed for each classified group. In the test recipe, the testing object is determined based on the defect information obtained from the testing results of each group. As the testing proceeds, more accurate test recipes can be created. It is therefore possible to detect defects of the semiconductor devices with higher accuracy. 
   (Modification) 
   As shown in  FIG. 7 , a system of testing semiconductor devices according to a modification of the embodiment is different from the testing system shown in  FIG. 1  in that the analysis module  13  includes a measurement point calculation unit  131 . The classification module  11 , the apparatus assignment module  12 , the analysis module  13 , and the test recipe creation module  14  may be constituted as a part of the CPU  1  of a computer system or may be separately composed of dedicated hardware to be connected through LAN or the like. 
   The classification module  11  shown in  FIG. 7  classifies lots having the identification numbers N followed by “30(n+1)+1” (n is an integral number not less than 1) as a group A and the other lots as a group B. In other words, the classification module  11  classifies one lot as the group A per 30 lots. The apparatus assignment module  12  selects test items about the variation between patterns and variation between shots for the group A. The apparatus assignment module  12  selects test items about the variation between sites and variation between wafers, which are not tested in the group A. 
   The testing apparatus  6   a ,  6   b ,  6   c , . . . tests lots put into the production line based on information of the testing apparatus information transmitted from the test memory  22  and the test recipe stored in the data memory  2 . For example, when there are 25 wafers included in one lot, 80 shots per one wafer, nine sites per one shot, and 10 type of pattern shapes per one site, the total numbers of patterns included in one lot is 180000. The testing apparatus  6   a ,  6   b ,  6   c , . . . measures linewidth of total 10800 patterns of 6 wafers×20 shots×9 sites×10 patterns for the lot  50   i  with the identification number N of “0001”, which belongs to the group A. For the testing apparatus  6   a ,  6   b ,  6   c , . . . capable of measuring 10800 patterns at high speed, an optical measurement apparatus such as a scatterometry is suitable. In the case of using the scatterometry as the testing apparatus  6   a ,  6   b ,  6   c , . . . , when measurement time per one point is about 2.5 seconds, it takes 7.5 hours to measure 10800 patterns. 
   The measurement point calculation unit  131  analyzes standard deviations (σ p , σ s , σ f , σ w ) of a variation p between patterns, a variation s in a shot, a variation f in a wafer, and a variation w between wafers based on the testing results from the testing apparatus  6   a ,  6   b ,  6   c , . . . to calculate a sampling number Nw of wafers, a sampling number Nf of shots, a sampling number Ns in a shot, and a sampling number Np of patterns of lots of the group B to be next tested using the following expression.
 
 Nw ={(σ 2   w   *N )/(σ 2   f *σ 2   s *σ 2   p )} 1/4   (1)
 
 Nf ={(σ 2   f   *N )/(σ 2   w *σ 1   s *σ 2   p )} 1/4   (2)
 
 Ns ={(σ 2   ,*N )/(σ 2   w *σ 2   f *σ 2   p )} 1/4   (3)
 
 Np ={(σ 2   p   *N )/(σ 2   w *σ 2   f *σ 2   s )} 1/4   (4)
 
Herein, N is a total number of sampling points (N=Nw·Nf·Ns·Np). The analysis module  13  calculates the sampling numbers Nw, Nf, Ns, and Np when the total sampling number N of each lot of the group B to be next tested is 120. The measurement time when the total sampling number N is 120 is 300 seconds in the case of using a scatterometry or the like whose measurement time per one point is 2.5 seconds as the testing apparatus  6   a ,  6   b ,  6   c , . . . The test recipe creation module  14  of  FIG. 7  creates a test recipe  60  including testing areas, the kind of the testing apparatus, the sampling numbers Nw, Nf, Ns, and Np, and the like.
 
   When the variations (σ p , σ s , σ f , σ w ) in each lot are normally distributed, a confidence interval of a population mean in each lot belonging to the group B is proportional to a coefficient A {(Nw/σ p   2 )+(Nf/σ s   2 )+(Nf/σ f   2 )+(Nw/σ w   2 )} 1/2 . Herein, when the total sampling number N is fixed to a constant value, the confidence interval of the population mean is minimized by the coefficient A, and the estimation accuracy of lot averages of the group to be tested next is increased. Consequently, the number of tests are optimized so as to increase the estimation accuracy of the lot average of the next group, and it is therefore possible to efficiently obtain reliable lot representative values in a short time. 
   OTHER EMBODIMENTS 
   Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof. 
   In the aforementioned testing system, the testing system based on a lot composed of a plurality of wafers is shown. However, it is obvious that this testing system can be applied to a testing system based on a wafer including a number of measurement points. 
   The present invention is not limited to wafers for use in semiconductor devices but is certainly available in a manufacturing process of other manufactured products in which some samples are taken out from a population for testing, for example, such as manufacturing processes of liquid crystal devices, magnetic recording media, optical recording media, thin film magnetic heads, and super-conducting elements. For example, the manufacturing process of the thin film magnetic heads includes less steps but includes repetition of a CVD process, photolithography process, etching process, and the like similar to semiconductor integrated circuits, and it is therefore easily understood that the testing method of the present invention is applicable thereto.