Patent Publication Number: US-2021191382-A1

Title: Method and system for controlling lot risk score based dynamic lot measurement on basis of equipment reliability index

Description:
TECHNICAL FIELD 
     The present disclosure relates to semiconductor measurement-related technology, and more particularly, to a method and a system for controlling lot measurement during semiconductor manufacturing. 
     BACKGROUND ART 
     In semiconductor manufacturing, measurement may be performed to monitor whether there is a quality problem in a process or equipment. However, all products are not measured and some of the products are selected according to a measurement period and are measured. 
     In some cases, engineers may decide to measure according to manuals. For example, when there is a change in manufacturing/technology, such as a change in equipment, materials, or processes, when a process or equipment does not meet specifications and thus an alarm is raised, or when manufacturing is interrupted, engineers may decide to measure. 
     Measurement performed at fixed periods is not efficient since there is no consideration for quality of a process or equipment, and measurement by engineers according manuals is restrictively performed only under special circumstances. 
     DISCLOSURE 
     Technical Problem 
     The present disclosure has been developed in order to address the above-discussed deficiencies of the prior art, and an object of the present disclosure is to provide a method and a system for dynamically controlling lot risk score-based lot measurement on the basis of an equipment reliability index of specific equipment for a specific process in semiconductor manufacturing. 
     Technical Solution 
     According to an embodiment of the present disclosure to achieve the above-described object, a measurement control method includes: calculating an equipment reliability index of specific equipment for a specific process in semiconductor manufacturing; calculating a risk score of the specific equipment for the specific process, on the basis of the equipment reliability index; and determining whether to measure a semiconductor product which is processed in the specific equipment for the specific process, on the basis of the risk score. 
     In addition, the calculating the equipment reliability index may include: calculating a process stability for the specific process; calculating an equipment stability for the specific equipment; and calculating the equipment reliability index by an arithmetic operation using the process stability and the equipment stability. 
     In addition, the equipment reliability index may be calculated by using the following equation: 
       Equipment reliability index=Process stability×Equipment stability
 
     In addition, the calculating the process stability may include calculating the process stability (S op ) by using the following equation: 
         S   op =Min( Cpk,  1) 
         Cpk =Min{(USL− m )/3σ, ( m −LSL)/3σ}
 
     Min: Minimum value of listed values 
     M: Target value on process specifications 
     USL: Upper specification limit 
     LSL: Lower specification limit 
     σ: Standard deviation 
     In addition, the calculating the equipment stability may include calculating the equipment stability on the basis of a frequency of occurrence of fault detection and classification (FDC) interlock during a specific period. 
     In addition, the measurement control method according to an embodiment of the present disclosure may further include calculating an excursion of the risk score, and the calculating the risk score may include calculating the risk score on the basis of the equipment reliability index and the excursion. 
     In addition, the excursion may have a value changed according to a number of semiconductor products processed after measurement. 
     In addition, the calculating the excursion may include calculating the excursion by an arithmetic operation using the number of semiconductor products processed after measurement and a reference measurement period. 
     In addition, the reference measurement period may be an average measurement period which is calculated by using a number of semiconductor products processed during a specific period, and a number of measured semiconductor products. 
     The calculating the risk score may include calculating the risk score by using the following equation: 
       Risk score=1−Equipment reliability index×Excursion
 
     In addition, the determining may include determining to measure when the risk score reaches a reference value. 
     In addition, the calculating the equipment reliability index may include calculating the equipment reliability periodically, and the calculating the risk score and the determining may include calculating and determining in real time whenever a semiconductor product is processed in the specific equipment. 
     According to another embodiment of the present disclosure, a measurement control system includes: an obtaining unit configured to obtain data regarding specific equipment for a specific process in semiconductor manufacturing; and a processor configured to calculate an equipment reliability index of the specific equipment for the specific process by using the obtained data, to calculate a risk score of the specific equipment for the specific process, on the basis of the equipment reliability index, and to determine whether to measure a semiconductor product which is processed in the specific equipment for the specific process, on the basis of the risk score. 
     Advantageous Effects 
     According to embodiments of the present disclosure as described above, it is possible to dynamically control lot measurement based on a lot risk score on the basis of an equipment reliability index of specific equipment for a specific process in semiconductor manufacturing. Therefore, lot measurement is frequently performed when the equipment reliability index is low, and lot measurement is intermittently performed when the equipment reliability index is high, such that differential quality monitoring/management according to the equipment reliability index is possible. 
     Accordingly, according to embodiments of the present disclosure, a measurement device can be effectively used, quality/yield can be improved through timely measurement, and management convenience can be increased through automatic/dynamic lot measurement control. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a flowchart provided to explain a method for dynamically controlling lot measurement according to an embodiment of the present disclosure; 
         FIG. 2  is a view illustrating a curve of S op ×S eq ×L ex ; 
         FIG. 3  is a view illustrating a lot risk score curve; and 
         FIG. 4  is a block diagram of a measurement control system according to another embodiment of the present disclosure. 
     
    
    
     BEST MODE 
     Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a flowchart provided to explain a method for dynamically controlling lot measurement according to an embodiment of the present disclosure. 
     The method for dynamically controlling the lot measurement according to an embodiment of the present disclosure is a method for calculating a lot risk score on the basis of an equipment reliability index, and dynamically determining whether to measure a lot on the basis of the lot risk score. 
     Accordingly, it is dynamically determined whether a lot which is moved out of equipment is measured, and this determination is made with reference to a lot risk score based on an equipment reliability index. 
     The lot risk score is an index indicating a risk that a quality problem which may arise when a lot moved out of equipment is not measured is not recognized. 
     The method for dynamically controlling the lot measurement according to an embodiment of the present disclosure sets a lot risk score to be calculated high when the equipment reliability index is low, such that lot measurement is frequently performed. On the other hand, the method sets the lot risk score to be calculated low when the equipment reliability index is high, such that lot measurement is intermittently performed. Accordingly, it is possible to monitor/manage quality differently according to the equipment reliability index. 
     The method for dynamically controlling the lot measurement according to an embodiment of the present disclosure is separately performed according to a process and equipment. That is, the algorithm shown in  FIG. 1  is performed separately for every specific equipment (for example, the third equipment from among 20 pieces of equipment for an etching process) (hereinafter, referred to as “process_equipment”) for a specific process (for example, the etching process corresponding to the 11 th  process from among 100 processes). 
     In an embodiment of the present disclosure, it is assumed that a semiconductor product is measured on a lot basis, but this is merely an example, and embodiments in which the semiconductor product is measured in other units belong to the scope of the present disclosure. 
     The method shown in  FIG. 1  is performed by a dynamic lot measurement control system (hereinafter, referred to as a “measurement control system”), which is a kind of a computing system. 
     As shown in  FIG. 1 , the measurement control system obtains process_equipment data necessary for calculating an equipment reliability index (S 110 ). The data obtained in step S 110  includes the following data regarding the process_equipment: 
     1) m: Target value on process specifications 
     2) USL (Upper Specification Limit) 
     3) LSL (Lower Specification Limit) 
     4) σ: Standard deviation 
     5) L cnt : The number of lots which have been processed for the past two weeks 
     6) L fdc : The number of times that fault detection and classification (FDC) interlock has occurred for the past two weeks 
     7) L mes : The number of lots which have been measured for the past two weeks 
     Next, the measurement control system calculates a process stability by using the data obtained in step S 110  (S 120 ). The process stability S op  may be calculated according to the following Equation 1: 
         S   op =Min( Cpk,  1) 
         Cpk =Min{(USL− m )/3σ, ( m −LSL)/3σ}  [Equation 1]
 
     where Min is a minimum value from among listed values. Accordingly, the process stability S op  has the maximum value of 1. 
     In addition, the measurement control system calculates an equipment stability by using the data obtained in step S 110  (S 130 ). The equipment stability S eq  may be calculated by using the following Equation 2: 
         S   eq =exp(−3 ×L   fdc   /L   cnt )   [Equation 2]
 
     According to Equation 2 above, it can be seen that the equipment stability S eq  is determined according to the frequency of occurrence of the FDC interlock for the past two weeks. 
     Next, the measurement control system calculates an equipment reliability index by using the process stability S op  calculated in step  120  and the equipment stability S eq  calculated in step S 130  (S 140 ). The equipment reliability index may be calculated by using the following Equation 3: 
       Equipment reliability index= S   op   ×S   eq    [Equation 3]
 
     Thereafter, the measurement control system calculates a lot risk excursion (S 150 ). The lot risk excursion L ex  may be calculated by using the following Equation 4: 
         L   ex =exp(−30 ×L   m/o   /L   avg )   [Equation 4]
 
     where L m/o  is the number of lots which is processed after measurement in the process equipment and is moved out. For example, when the 10 th  lot which is processed in the process_equipment and is moved out is measured and then the 11 th  lot, the 12 th  lot, and the 13 th  lot are processed in the process_equipment and are moved out, and then measurement is not performed, “L m/o =3.” 
     In addition, L avg  is an average measurement period of the process_equipment for the past two weeks, and may be calculated according to the following Equation 5 by using the data obtained in step S 110 : 
         L   avg   =L   mes   /L   cnt    [Equation 5]
 
     L avg  may not be calculated according to Equation 5, and may be determined by a manager by considering equipment characteristics and a manufacturing environment. The equipment characteristics considered may include a degree of deterioration of equipment, and a past defect rate/accident history, and the manufacturing environment may include a quantity of products/manufacturing speed. 
     Next, the measurement control system calculates a lot risk score on the basis of the equipment reliability index calculated in step S 140 , and the lot risk excursion L ex  calculated in step S 150  (S 160 ). 
     As described above, the lot risk score refers to an index indicating a risk that a quality problem which may arise when a lot moved out of equipment is not measured is not recognized. The lot risk score L risk  may be calculated by using the following Equation 6: 
         L   risk =1−Equipment reliability index× L   ex =1 −S   op   ×S   eq   ×L   ex    [Equation 6]
 
     The process stability S op  has the maximum value of 1, and the equipment stability S eq  which is an exp function and the lot risk excursion L ex  have the maximum value of 1. Accordingly, variables forming the lot risk score L risk  are expressed by normalized probability values (0-1), and the lot risk score L risk  in Equation 6 above is calculated as a probability value (0-1). 
     Thereafter, the measurement control system determines whether to measure the lot which is processed in the process_equipment and is moved out, on the basis of the lot risk score calculated in step S 160  (S 170 ). 
     Specifically, when the lot risk score exceeds 0.95, the lot is measured, but, when the lot risk score is less than or equal to 0.95, the lot is not measured and measurement is skipped. 
     To explain in detail,  FIG. 2  illustrates a curve of “S op ×S eq ×L ex ” and  FIG. 3  illustrates a lot risk score curve. 
     As shown in  FIG. 2 , the height (maximum value) of S op ×S eq ×L ex =P(x) is determined by process stability (S op )×equipment stability (S eq ), and the slope is determined by multiplication by the lot risk excursion (L ex ). 
     In addition, as shown in  FIG. 3 , the lot risk score curve P(y) is symmetrical to the curve P(x)[=S op ×S eq ×L ex ] with reference to a point if y=0.5. 
     In addition, as shown in  FIGS. 2 and 3 , when the lot risk score P(y)=0.95, that is, when P(x)[=S op ×S eq ×L ex ]=0.05, the measurement is performed and L m/o  becomes “0.” Accordingly, P(y) becomes a minimum value and P(x) becomes a maximum value. 
     Up to now, the lot risk score-based dynamic lot measurement method on the basis of the equipment reliability index has been described with reference to preferred embodiments. 
     The dynamic lot measurement method according to an embodiment of the present disclosure includes the process of calculating the equipment reliability index (steps S 110  to S 140 ), and the process of calculating the lot risk score and dynamically measuring according thereto (steps S 150  to S 170 ). 
     The process of calculating the lot risk score and dynamically measuring on the basis thereof (steps S 150  to S 170 ) should be performed in real time whenever the lot is processed and is moved out of the process_equipment. However, the process of calculating the equipment reliability index (steps S 110  to S 140 ) may be performed at specific periods (for example, every 8 hours). 
     The measurement control system which performs the dynamic lot measurement control method according to an embodiment of the present disclosure will be described in detail with reference to  FIG. 4 .  FIG. 4  is a block diagram of the measurement control system according to another embodiment of the present disclosure. 
     As shown in  FIG. 4 , the measurement control system according to an embodiment of the present disclosure includes a communication unit  210 , a display  220 , a processor  230 , an input unit  240 , and a storage  250 . 
     The communication unit  210  is a means for connecting communication with an external device or an external network and communicating data, and obtains/extracts process_equipment data which is used for calculating an equipment reliability index and a lot risk excursion. 
     The display  220  is a means for displaying information, and displays a lot risk score, information regarding whether measurement is performed. The input unit  240  is a means for inputting information, and may be used to input process_equipment data and/or manager&#39;s settings. 
     The display  220  and the input unit  240  may be integrated into a touch screen, and this is more useful when the measurement control system is a mobile type. 
     Since the above-described process_equipment data may be received from process_equipment or a network through the communication unit  210 , or may be inputted and collected through the input unit  240 , the communication unit  210  and the input unit  240  may function as a data obtaining means. 
     The processor  230  may perform the dynamic lot measurement control algorithm shown in  FIG. 1  by using the obtained process_equipment data, and may display a result of performing on the display  220  or may transmit the result to an external device/network through the communication unit  210 . 
     The storage  250  provides a storage space which is necessary for the processor  230  to perform the dynamic lot measurement control algorithm. 
     The technical idea of the present disclosure may be applied to a computer-readable recording medium which records a computer program for performing functions of the apparatus and the method according to the present embodiment. In addition, the technical idea according to various embodiments of the present disclosure may be implemented in the form of a computer-readable code recorded on the computer-readable recording medium. The computer-readable recording medium may be any data storage device that can be read by a computer and can store data. For example, the computer-readable recording medium may be a read only memory (ROM), a random access memory (RAM), a CD-ROM, a magnetic tape, a floppy disk, an optical disk, a hard disk drive, or the like. A computer-readable code or program that is stored in the computer readable recording medium may be transmitted via a network connected between computers. 
     In addition, while preferred embodiments of the present disclosure have been illustrated and described, the present disclosure is not limited to the above-described specific embodiments. Various changes can be made by a person skilled in the art without departing from the scope of the present disclosure claimed in claims, and also, changed embodiments should not be understood as being separate from the technical idea or prospect of the present disclosure.