Patent Publication Number: US-8538131-B2

Title: Defect inspection apparatus and method of defect inspection

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2006-094785, filed on Mar. 30, 2006, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to defect inspection apparatus and a method of defect inspection detecting and inspecting defects of an inspected piece. 
     2. Description of the Related Art 
     Defect inspection apparatus has been used for the purpose of, for example, observing surface conditions of substrate having micro-structures represented by semiconductor devices formed thereon in an integrated manner, and confirming presence or absence of any defects. 
     The defect inspection apparatus is provided with a bright-field optical system having an illumination unit irradiating the inspected piece with an illumination beam, and taking an image of regular reflection beam from the inspected piece, or a dark-field optical system having an illumination unit irradiating the inspected piece with an illumination beam, and taking an image of irregular reflection beam from the inspected piece; and inspects defects on the surface of the inspected piece using either or both of the bright-field optical system and the dark-field optical system. 
     In recent years, a proposal has been made on a defect inspection apparatus capable of executing defect inspection and defect identification in an automated manner, as described in Patent Document 1 below, because visual defect inspection using a defect inspection apparatus casts a large operation load upon an operator and takes a long time for the operation. 
     Related art is disclosed in Japanese Patent No. 3415943. 
     In automatic judgment of presence or absence of the defects, the defect inspection apparatus preliminarily sets a predetermined threshold value with respect to intensity of the reflected beam from the inspected piece, and presence or absence of the defects is judged based on a magnitude relation between the threshold value and intensity of the reflected beam. Therefore, intensity of the reflected beam close to the threshold value inevitably destabilizes the judgment of presence or absence of the defects. Even if the threshold value is set in a stable region in which the reflected beam has only a small probability of showing intensity very close to the threshold value, judgment of presence or absence of the defects may be destabilized due to fluctuation in environment of the apparatus, such as set temperature in the apparatus, so that judgment of defects causing reflected beam having an intensity close to the threshold value is still more inevitably destabilized. Another problem resides in that quasi-defects, which do not exist on the real inspected piece, may be observed due to non-uniform color of the surface, and such quasi-defects often show an unstable behavior similarly due to fluctuations in environment of the apparatus. 
     There has never been proposed a technique of quantitatively understanding the defects (unstable defects) likely to destabilize the judgment of their existence, as being discriminated from the defects (stable defects) allowing stable judgment, so that the technique remains to be expected for further research and development for the future. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a defect inspection apparatus and a method of defect inspection capable of realizing highly-reliable products, by discriminating unstable defects from stable defects, and classifying and identifying both types of defects in a quantitative and accurate manner relying upon only a relatively simple configuration, and further by understanding tendency of occurrence of the unstable defects and managing it as a standard index for routine inspection of an inspected piece. 
     A defect inspection apparatus of the present invention has a defect detection system detecting defects of an inspected piece; and a first defect classification unit classifying the defects, based on results of a plurality of times of defect inspection executed by the defect detection system using a pre-inspection test target as the inspected piece, into first defects detected constantly in each of the plurality of times of inspection, and into second defects detected only in a part of, but not in the residual part of the plurality of times of inspection. 
     A method of defect inspection of the present invention has a step of executing, while using a pre-inspection test target as an inspected piece, defect inspection of the test target a plurality number of times; and a step of executing a first classification classifying the defects, based on results of the defect inspection of the test target, into first defects detected constantly in each of the plurality of times of inspection, and into second defects detected only in a part of, but not in the residual part of the plurality of times of inspection. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a schematic configuration of a defect inspection apparatus according to one embodiment; 
         FIG. 2  is a block diagram showing a schematic configuration of a defect inspection system which is a constituent of the defect inspection apparatus according to the embodiment; 
         FIGS. 3A and 3B  are block diagrams showing schematic configurations of an identifier producing section which is a constituent of the defect inspection apparatus according to the embodiment; 
         FIG. 4  is a block diagram showing a schematic configuration of a defect identification section which is a constituent of the defect inspection apparatus according to the embodiment; 
         FIGS. 5A and 5B  are schematic plan views showing specific examples of the method of defect identification by a first defect classification section; 
         FIG. 6  is a flow chart sequentially showing process steps of a method of defect inspection according to the embodiment; and 
         FIG. 7  is a schematic drawing showing an internal configuration of a personal user terminal device. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Basic Concept of the Present Invention 
     As described in the above, the unstable defects are supposed to be ascribable mainly to setting of threshold value of the defect detection system (having a bright-field optical system, a dark-field optical system, and a defect judgment section) or to environments of the apparatus. The present inventors considered that, by preliminarily identifying unstable defects using the defect detection system prior to defect inspection (actual inspection) of an inspected piece destined for the final product, results of the identification are applicable to the actual inspection. 
     In the present invention, in order to discriminate the unstable defects from the stable defects and to quantitatively understand the both, an index for identifying the stable defects and the unstable defects is preliminarily prepared, using a pre-inspection test target as the inspected piece, prior to the actual inspection. 
     In further detail, the defect inspection of the inspected piece to be tested, is executed a plurality of times using the defect detection system. It is our first thought to use a test-dedicated inspected piece as the inspected piece to be tested, but it is also allowable to use an inspected piece arbitrarily selected from those destined for the final products later subjected to the actual inspection. 
     The defects are then classified, based on results of the defect inspection repeated a plurality of times, into first defects detected constantly in each of the plurality of times of inspection, and into second defects detected only in a part of, but not in the residual part of the plurality of times of inspection. Information of thus-classified first and second defects (coordinate information of positions of defects, for example) is used as an index for identifying the stable defects and the unstable defects. Population of the first defects is counted while masking the second defects using a predetermined software, and a total count is used as a judgment base value. 
     Next, using the above-described defect detection system, the inspected piece destined for the final product, that is, a target for the actual inspection, is subjected to defect detection. Results of the detection are then collated with information on the second defects, and the defects are classified while assuming those agreed with the second defects as unstable defects, and assuming those disagreed with the second defects as stable defects. Based on the classification, a total count of the unstable defects and a total count of the stable defects are respectively counted. The total count of the stable defects is then collated with the above-described judgment base value, and quality of the defect inspection of the inspected piece, which is a target for actual inspection, is judged based on a magnitude relation of the total count of the stable defects with the judgment base value. On the other hand, the total count of the unstable defect is fed back as expressing a tendency of occurrence of the unstable defects in the defect detection system, and subjected to management of the apparatus. 
     As has been described in the above, according to the present invention, the unstable defects can be discriminated from the stable defects relying upon only a relatively simple configuration, and both types of defects can be classified and identified in a quantitative and accurate manner. Moreover, it is also made possible to understand tendency of occurrence of the unstable defects, and to manage the tendency as a standard index for routine inspection of the inspected piece. 
     Preferred Embodiments Applied with the Present Invention 
     Paragraphs below will detail preferred embodiments applied with the present invention, referring to the attached drawings. 
       FIG. 1  is a block diagram showing a schematic configuration of a defect inspection apparatus according to one embodiment. 
     The defect inspection apparatus is configured as having a defect inspection system  1  inspecting defects on a inspected piece, which is for example a semiconductor substrate having semiconductor devices formed thereon; an identifier producing section  2  producing, using a pre-inspection test target as an inspected piece, an identifier discriminating the stable defects from the unstable defects; a defect identification section  3  quantitatively identifying the defects detected in an actual inspection as the stable defects or the unstable defects; a defect inspection judgment section  4  making various judgments based on information on thus-identified stable defects or unstable defects; and a memory section  5  storing information on results of judgment and so forth obtained by the defect inspection judgment section  4 . Individual operations of the defect inspection system  1 , the identifier producing section  2 , the defect identification section  3 , and the defect inspection judgment section  4  are generally controlled by an unillustrated control section. 
     The defect inspection system  1  is configured as having, as shown in  FIG. 2 , a bright-field optical system  11  or a dark-field optical system  12 , and a judgment section  13 . 
     The bright-field optical system  11  has a light source irradiating the inspected piece with an illumination beam, which is typically laser beam or beam from a lamp (UV lamp, halogen lamp, and so forth), aimed at taking an image of regular reflection beam of the illumination beam from the inspected piece. 
     The dark-field optical system  12  has a light source irradiating the inspected piece with an illumination beam, which is typically laser beam, aimed at taking an image of irregular reflection beam (scattered light) of the illumination beam from the inspected piece. 
     The judgment section  13  judges presence or absence of any defects, based on the images taken respectively by the bright-field optical system  11  and the dark-field optical system  12 , and on the basis of a predetermined set threshold value. 
     In this embodiment, defects on a semiconductor substrate  10  are sequentially inspected by illuminating the surface of the semiconductor substrate  10  by the bright-field optical system  11  and the dark-field optical system  12 , and the defect judgment is made by the judgment section  13 . 
     The identifier producing section  2  is configured as having, as shown in  FIG. 3A , a first defect classification section  21 , memory sections  22 ,  23 , and a base value specifying section  24 . 
     The first defect classification section  21  uses a pre-inspection test target as the inspected piece, and classifies the defects based on results of the defect inspection repeated a plurality of times by the defect detection system, into first defects detected constantly in each of the plurality of times of inspection, and into second defects detected only in a part of, but not in the residual part of the plurality of times of inspection. 
     For an exemplary case shown in  FIG. 5A  where the defect inspection is repeated six times, the first defects are those detected in all of six times of defect inspection at the same places on the semiconductor substrate  10  (indicated by ▪ in the drawing), and the second defects are those detected only a part of six times of inspection at the same places (indicated by x in the drawing). 
     More specifically, the first defect classification section  21  is configured as having, as shown in  FIG. 3B , a counting section  21   a  counting the number of times of detection, out of the plurality of times, for every defect detected by the defect detection system using a test target inspected piece; and a judgment section  21   b  judging whether the number of times of detection of the defects at the same positions on the coordinate, as a result of the counting by the counting section  21   a , is less than the above-described plurality of times (for example, five times or less for a plurality of times of six) or not. If the number of times of detection is judged by the judgment section  21   b  as being equal to the above-described plurality of times, the detected defects herein are classified into the first defects. On the other hand, if the number of times of detection is less than the plurality of times, the detected defects herein are classified into the second defect. 
     The memory section  22  registers and stores information on the first defects. The memory section  23  registers and stores information on the second defects. 
     The base value specifying section  24  calculates a total count of the first defects based on information on the first defects stored in the memory section  22 , and specifies the total count of the first defects as the judgment base value. For example, as shown in  FIG. 5B , the second defects (indicated by x in the drawing) on the semiconductor substrate  10  are masked using a predetermined software, the number of the first defects is counted in this state, and the total count is specified as the judgment base value. The judgment base value in the exemplary case shown in  FIGS. 5A and 5B  appears to be three. 
     The defect identification section  3  is configured, as shown in  FIG. 4 , as having a second defect classification section  31 , an ID allocating section  32 , a counting section  33 , and a defect count calculating section. 
     The second defect classification section  31  collates defects of the inspected piece, which is a target for the actual inspection, detected by the defect detection system  1  one by one with information on the second defects recognized on the test target, and classifies the defects while assuming those agreed with the second defects as unstable defects, and assuming those disagreed with the second defects as stable defects. 
     The ID allocating section  32  allocates an ID to information of each defect classified either into the unstable defect or stable defect. 
     The counting section  33  respectively counts up, for each defect, the unstable defects and the stable defects based on the allocated IDs. 
     The defect count calculating section  34  respectively calculates a total count of the unstable defects and a total count of the stable defects. Information on the total count of the unstable defects calculated by the defect count calculating section  34  is stored in the memory section  5 . 
     The defect inspection judgment section  4  collates the total count of the stable defects with the above-described judgment base value, and judges quality of the defect inspection of the inspected piece, which is a target for the actual inspection, based on a magnitude relation between the total count of the stable defects and the judgment base value. In the exemplary case shown in  FIGS. 5A and 5B , the result of the defect inspection of the inspected piece is judged as being acceptable if the total count of the stable defects is not larger than three, which is the judgment base value. On the other hand, the result of the defect inspection of the inspected piece is judged as being unacceptable if the total count of the stable defect is 4 or larger. In case of unacceptable judgment, the result of the defect inspection is subjected to investigations for finding causes and future measures. On the other hand, the total count of the unstable defects calculated by the defect count calculating section  34  is fed back as expressing tendency of occurrence of the unstable defects in the defect detection system, and subjected to management of the apparatus. Information on the results judged by the defect inspection judgment section  4  is stored in the memory section  5 . 
     The defect inspection apparatus of this embodiment has been explained as being configured as incorporating the defect detection system, whereas it is also allowable to configure the defect detection system as an independent defect inspection apparatus or as the one available elsewhere, and a system composed of the other constituents (identifier producing section  2 , defect identification section  3 , and defect inspection judgment section  4 ) is configured as an external defect identification apparatus attached to the defect inspection apparatus, so as to configure a defect inspection system using the defect inspection apparatus and the defect identification apparatus. 
     Paragraphs below will explain a method of defect inspection using the above-described defect inspection apparatus. 
       FIG. 6  is a flow chart sequentially showing process steps in a method of defect inspection according to the embodiment. 
     First, the defect inspection is executed by the bright-field optical system  11  or the dark-field optical system  12  of the defect inspection system  1 , using a pre-inspection test target as the inspected piece (step S 1 ). It is our first thought to use a test-dedicated inspected piece, which is typically a test-dedicated semiconductor substrate, as the inspected piece to be tested, but it is also allowable to use an inspected piece arbitrarily selected from those destined for the final products later subjected to the actual inspection. 
     Next, positions on the coordinate of the individual defects recognized by the defect inspection are acquired by the judgment section  13  of the defect inspection system  1  (step S 2 ). 
     In this embodiment, steps S 1 , S 2  are executed a plurality of times (6 times in the illustrated example, and throughout the paragraphs below) using the same test-dedicated inspected piece. 
     Next, the number of times of detection out of six times of inspection is counted by the counting section  21   a  of the first defect classification section  21 , for every defect detected by the defect detection system using the inspected piece (step S 3 ). 
     Next, whether the number of times the defect was detected at the same position on the coordinate, counted by the counting section  21   b , is not larger than five or not is judged by the judgment section  21   b  of the first defect classification section  21  (step S 4 ). 
     If the number of times the defect was detected is judged as being six in step  4 , the defect is classified into the first defect, and information on the result is registered and stored in the memory section  22  (step S 5 ). A total count of the first defect is then calculated by the base value specifying section  24 , based on the information on the first defects stored in the memory section  22  (step S 6 ). The total count of the first defects is specified as the judgment base value (step S 7 ). 
     On the other hand, if the number of times the defect was detected at the same position on the coordinate, counted by the counting section  21   a , is judged as being five or less, the defect is classified into the second defect, typically registered as a second defect group “X”, and stored in the memory section  23  (step S 8 ). 
     Next, the inspected piece, which is a target for the actual inspection and is typically a semiconductor substrate, is subjected to defect inspection by the bright-field optical system or the dark-field optical system  12  of the defect inspection system (step S 9 ). 
     Next, for each of the defects recognized as a result of the defect inspection (10 defects in the illustrated example, and throughout the paragraphs below), a position on the coordinate is acquired by the judgment section  13  of the defect inspection system  1  (step S 10 ). 
     Next, one defect out of the defects of the inspected piece, which is a target for actual inspection, detected by the defect detection system  1  is extracted (step S 11 ). The extracted defect is collated with information on the second defect stored as a second defect group “X” in the memory section  23  (step S 12 ). Those defects agreed with the second defect as a result of the collation are assumed as the unstable defects, and classified thereinto (step S 13 ). Information on the defects classified into the unstable defects is allocated with an ID “B” by the ID allocating section  32  (step S 14 ). On the other hand, the defects disagreed with the second defect are assumed as the stable defects, and classified thereinto (step S 15 ). Information on the defects classified into the stable defects is allocated with an ID “A” by the ID allocating section  32  (step S 16 ). 
     Next, based on thus-allocated IDs “B” and “A”, the unstable defects and the stable defect are respectively counted up (step S 17 ). 
     In this embodiment, steps S 11  to S 17  are executed for each of ten defects recognized by the defect inspection system  1  (that is, repeated 10 times), and a total count of the unstable defects and a total count of the stable defects are respectively calculated by the defect count calculating section  34  (steps S 18 , S 19 ). 
     Next, the total count of the stable defects calculated by the defect count calculating section  34  is collated with the above-described judgment base value (step S 20 ). If the total count of the stable defects was found, by the collation, to be not larger than the judgment base value, the result of the defect inspection of the inspected piece is judged as acceptable (step S 21 ). On the other hand, if the total count of the stable defects was found to be larger than the judgment base value, (judgment base value +1 or more), the result of the defect inspection of the inspected piece is judged as unacceptable (step S 22 ). In case of the unacceptable judgment, the result of the defect inspection is subjected to investigations for finding causes and future measures (step S 23 ). On the other hand, the total count of the unstable defects calculated by the defect count calculating section  34  is subjected to management of the apparatus, as expressing tendency of occurrence of the unstable defects in the defect detection system (step S 24 ). 
     As has been described in the above, according to the present invention, the unstable defects can be discriminated from the stable defects relying upon only a relatively simple configuration, and both types of defects can be classified and identified in a quantitative and accurate manner. Moreover, it is also made possible to understand tendency of occurrence of the unstable defects, and to manage the tendency as a standard index for routine inspection of the inspected piece. 
     Functions of the individual constituents composing the defect inspection apparatus of this embodiment (the judgment section  13  of the defect inspection system  1 ; the first defect classification section  21  and the base value specifying section  24  of the identifier producing section  2 ; individual constituents of the defect identification section  3 ; the defect inspection judgment section  4 ; and so forth) can be realized by execution of a program stored in a RAM or a ROM of a computer. Similarly, the individual steps (steps S 1  to S 24  in  FIG. 6 , and so forth) of the method of defect inspection can be realized by execution of the program stored in the RAM or the ROM of the computer. Also the program and a computer-readable storage media having the program stored therein are within the scope of the present invention. 
     More specifically, the program is supplied to the computer, in a form of being recorded in one of recording media such as CD-ROM, or through various transmission media. The recording media to which the program is recordable, other than CD-ROM, include flexible disc, hard disc, magnetic tape, magneto-optical disc, non-volatile memory card and so forth. On the other hand, as the transmission media of the program  1 , available is a communication medium in a computer network system capable of supplying program information by carrier-wave-assisted transmission. The computer network herein includes LAN, WAN such as the Internet, radio communication network and so forth, and the communication media include and wired circuit such as optical fiber circuit, wireless circuit and so forth. 
     The program included in the present invention is not only the one such as realizing the functions described in the above embodiment, by being executed by the computer. For example, the program is included in the present invention also for the case where the program can realize the functions described in the above embodiment in cooperation with an OS (operating system) or any other application software running on the computer. The program is included in the present invention still also for the case where the all of, or a part of processing by the supplied program is executed on a function-expansion board or a function-expansion unit of the computer. 
       FIG. 7  is a schematic drawing showing an exemplary internal configuration of a personal user terminal device. In  FIG. 7 , reference numeral  1200  represents a personal computer (PC) equipped with a CPU  1201 . The PC  1200  executes a device control software stored in a ROM  1202  or a hard disc (HD)  1211 , or supplied from a flexible disc drive (FD)  1212 . The PC  1200  generally controls the individual devices connected to a system bus  1204 . 
     The procedures of steps S 1  to S 24  shown in  FIG. 6 , for example, are realized by the program stored in the CPU  1201 , the ROM  1202  or the hard disc (HD)  1211  of the PC  1200 . 
     Reference numeral  1203  represents a RAM which functions as a main memory, a work area and so forth of the CPU  1201 . Reference numeral  1205  represents a keyboard controller (KBC) controlling command input through a keyboard (KB)  1209  or any other unillustrated devices. 
     Reference numeral  1206  represents a CRT controller (CRTC) controlling display on a CRT display (CRT)  1210 . Reference numeral  1207  represents a disc controller (DKC). The DKC  1207  controls access to the hard disc (HD)  1211  and the flexible disc (FD)  1212  storing a boot program, a plurality of applications, editor, user file, network management program and so forth. The boot program herein means a start program initiating execution (operation) of hardware and software of the personal computer. 
     Reference numeral  1208  represents a network interface card (NIC), assisting bidirectional data transmission through a LAN  1220  with a network printer, other network devices, or other PCs. 
     The present invention is successful in realizing highly-reliable products by discriminating unstable defects from stable defects relying upon only a relatively simple configuration, and by classifying and identifying both types of defects in a quantitative and accurate manner, and further by understanding tendency of occurrence of the unstable defects and managing it as a standard index for routine inspection of an inspected piece.