Patent Publication Number: US-11646172-B2

Title: Charged particle beam apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a charged particle beam apparatus. 
     2. Description of the Related Art 
     Charged particle beam apparatuses such as electron microscopes and ion microscopes are used in observation of various samples having a fine structure. For example, for the purpose of process control on a manufacturing process of semiconductor devices, a scanning electron microscope that is one of the charged particle beam apparatuses is used in measurement of dimensions of a semiconductor device pattern formed on a semiconductor wafer serving as a sample, defect inspection of the semiconductor device pattern, or the like. 
     A method known as one of the sample analysis methods using an electron microscope is to form a potential contrast image from secondary electrons obtained through application of an electron beam to a sample and evaluate electrical resistance of an element formed on the sample on the basis of analysis of the potential contrast image. 
     For example, JP 2003-100823 A discloses a method for identifying a defect by calculating an electrical resistance value from a potential contrast. JP 2008-130582 A discloses a method for predicting characteristics of a defect in an electric resistance value or the like by creating, as an equivalent circuit, a netlist that describes information on electrical characteristics and connectivity of circuit elements from a potential contrast. 
     SUMMARY OF THE INVENTION 
     For inspection and measurement of semiconductor devices, it is required that a defect in electrical characteristics of the devices in a manufacturing process be detected. However, with the techniques disclosed in JP 2003-100823 A and JP 2008-130582 A, it is difficult to estimate the electrical characteristics with consideration given to interactions between a plurality of the devices using design data and inspection measurement data. In addition, it takes a lot of time and effort to convert the design data, and it takes a long time to estimate the electrical characteristics. 
     Therefore, an object of the present invention is to provide a charged particle beam apparatus that estimates, in a short time, electrical characteristics with consideration given to interactions between a plurality of devices. 
     The following is a brief description of the summary of a primary aspect of the invention disclosed herein. 
     A charged particle beam apparatus according to the primary aspect of the present invention includes a database configured to store a to-be-used-in-calculation device model for use in estimation of a circuit of a sample and an optical condition under which a charged particle beam is applied to the sample, a charged particle beam optical system configured to control the charged particle beam applied to the sample under the optical condition, a detector configured to detect secondary electrons emitted from the sample excited by the application of the charged particle beam and output a detection signal based on the secondary electrons, and a computing unit configured to generate a to-be-used-in-computation netlist on the basis of the to-be-used-in-calculation device model, estimate a first application result when the charged particle beam is applied to the sample on the basis of the to-be-used-in-computation netlist and the optical condition, and compare the first application result with a second application result when the charged particle beam is applied to the sample on the basis of the optical condition. 
     The following is a brief description of an effect obtained by the primary aspect of the invention disclosed herein. 
     That is, according to the primary aspect of the present invention, it is possible to estimate, in a short time, electrical characteristics with consideration given to interactions between a plurality of devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram showing an example of a structure of a charged particle beam apparatus according to a first embodiment of the present invention; 
         FIG.  2    is a block diagram showing an example of the structure of the charged particle beam apparatus according to the first embodiment of the present invention; 
         FIG.  3    is a diagram showing a to-be-used-in-calculation device model stored in a database; 
         FIG.  4    is a diagram showing an optical condition stored in a database; 
         FIG.  5    is a flowchart showing an example of a circuit estimation method for a sample; 
         FIG.  6    is a diagram showing an example of a to-be-used-in-calculation device model selection screen; 
         FIG.  7    is a diagram showing an example of an optical condition selection screen; 
         FIG.  8    is a diagram showing an example of a result display screen after circuit estimation; and 
         FIGS.  9 A to  9 C  are diagrams showing another example of the result display screen after circuit estimation. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Each of the embodiments described below is an example for practicing the present invention and is not intended to limit the technical scope of the present invention. Note that, in the embodiments, components having the same function are denoted by the same reference numerals, and repeated description of such components will be omitted unless particularly necessary. 
     First Embodiment 
     &lt;Structure of Charged Particle Beam Apparatus&gt; 
       FIG.  1    is a schematic diagram showing an example of a structure of a charged particle beam apparatus according to a first embodiment of the present invention.  FIG.  2    is a block diagram showing an example of the structure of the charged particle beam apparatus according to the first embodiment of the present invention. As shown in  FIGS.  1  and  2   , a charged particle beam apparatus  1  includes a charged particle beam apparatus main body  10 , a computer  30 , and an input and output part  50 . 
     &lt;Charged Particle Beam Apparatus Main Body&gt; 
     The charged particle beam apparatus main body  10  has a structure where a lens barrel  10 A is mounted on a sample chamber  10 B in which a sample  23  to be inspected is held, and a controller  11  is disposed outside the lens barrel  10 A and the sample chamber  10 B. In the lens barrel  10 A, an electron source (charged particle source)  12  that emits an electron beam (charged particle beam), a pulsed electron generator  19  that pulses the electron beam, a diaphragm  13  that regulates an application current of the electron beam thus emitted, a deflector  14  that controls an application direction of the electron beam, an objective lens  18  that causes the electron beam to converge, and the like are held. Although not shown, in the lens barrel  10 A, a condenser lens is provided. Note that, unless the electron beam is pulsed, the pulsed electron generator  19  need not be provided. 
     Further, in the lens barrel  10 A, a detector  25  that detects secondary electrons emitted from the sample  23  excited by the application of the electron beam, and outputs a detection signal based on the secondary electrons. The detection signal is used in generation of a scanning electron microscopy (SEM) image, measurement of the size of the sample  23 , measurement of electrical characteristics, and the like. 
     In the sample chamber  10 B, a stage  21 , the sample  23 , and the like are held. The sample  23  is mounted on the stage  21 . Examples of the sample  23  include a semiconductor wafer including a plurality of semiconductor devices, and an individual semiconductor device. The stage  21  is provided with a stage drive mechanism (not shown) and is movable within the sample chamber  10 B under the control of the controller  11 . 
     The controller  11  is a functional block responsible for controlling components of the charged particle beam apparatus main body  10 . The controller  11  controls the operation of each component such as the electron source  12 , the pulsed electron generator  19 , the diaphragm  13 , the deflector  14 , and the objective lens  18  under, for example, an optical condition input from the computer  30  and the like. As described above, the controller  11 , the electron source  12 , the pulsed electron generator  19 , the diaphragm  13 , the deflector  14 , the objective lens  18 , and the like constitute a charged particle beam optical system BS that controls the electron beam. 
     Further, the controller  11  moves the sample  23  to a predetermined position by controlling the stage drive mechanism under, for example, the optical condition input from the computer  30  and the like. Further, the controller  11  controls a power supply or control signal supply to the detector  25  to control a process of detecting the secondary electrons performed by the detector  25 . 
     The controller  11  is implemented with a program executed by a processor such as a CPU. Further, the controller  11  may be configured by, for example, a field-programmable gate array (FPGA) or an application specific integrated circuit (ASIC). 
     &lt;Computer&gt; 
     As shown in  FIG.  1   , the computer  30  includes a computing unit  31  and a storage device  41 . The computing unit  31  is a functional block responsible for estimating a circuit (or equivalent circuit) of the sample  23 . As shown in  FIG.  2   , for example, the computing unit  31  includes a to-be-used-in-computation netlist generator  32 , an electron beam application result estimation computing unit  33 , and a comparator  34 . The to-be-used-in-computation netlist generator  32  generates a to-be-used-in-computation netlist corresponding to the sample  23  on the basis of a to-be-used-in-calculation device model to be described later and the optical condition. Further, the to-be-used-in-computation netlist generator  32  also updates the to-be-used-in-computation netlist on the basis of a comparison result from the comparator  34 . 
     The electron beam application result estimation computing unit  33  estimates an electron beam application result on the basis of the to-be-used-in-computation netlist generated by the to-be-used-in-computation netlist generator  32 . The comparator  34  compares the electron beam application result estimated by the electron beam application result estimation computing unit  33  (first application result) with an actually measured electron beam application result (second application result). 
     In addition to these processes, the computing unit  31  performs a process of displaying the estimated electron beam application result, the measured electron beam application result, and a netlist identified for the sample  23  (hereinafter, also referred to as “estimated netlist”), a process of generating an inspection image (SEM image or the like) of the sample  23  on the basis of the detection signal, measuring the size of the sample  23 , and measuring the electrical characteristics of the sample  23 , and the like. 
     The computing unit  31  may be implemented with a program executed by a processor such as a CPU, as in the controller  11 , or alternatively, may be configured by an FPGA, an ASIC, or the like. 
     The storage device  41  includes a database  42 , an optical condition storage section  43 , a to-be-used-in-computation netlist storage section  44 , an electron beam application result storage section  45 , and an estimated application result storage section  46 . The database  42  stores to-be-used-in-calculation device models (for example, DM 1  and DM 2 ) and optical conditions (for example, LC 1  and LC 2 ) used in generation of the to-be-used-in-computation netlist. Note that the to-be-used-in-calculation device models include a model representing a defect in a device including the sample. 
     A user may operate the input and output part  50  to register the to-be-used-in-calculation device models and the optical conditions, or alternatively, the computer  30  may be connected to an external device to receive the to-be-used-in-calculation device models from the external device. The database  42  stores the to-be-used-in-calculation device models and the optical conditions, for example, in the form of a look up table (LUT). 
       FIG.  3    is a diagram showing an example of the to-be-used-in-calculation device model stored in the database. A unique ID  42   a  (for example, DM 1  and DM 2 ) is assigned to each of to-be-used-in-calculation device models, and each of the to-be-used-in-calculation device models is identified by the ID  42   a . Each of the to-be-used-in-calculation device models includes pieces of information such as a model  42   b , a mathematical expression  42   c , a parameter type  42   d , a parameter value  42   e , and other data  42   f . Note that, in each of the to-be-used-in-calculation device models, only some of the pieces of information may be defined. 
     The model  42   b  is information that defines a circuit of the device. Information defining a circuit such as an RC parallel circuit is registered as the model  42   b . Alternatively, a waveform model of the device or the like may be registered as the model  42   b . The mathematical expression  42   c  includes information that defines electrical characteristics of the device that cannot be expressed by the circuit. The parameter type  42   d  is information that defines a type of circuit element included in the device, such as resistance (R) or capacitance (C). The parameter value  42   e  is associated with each element of the parameter type  42   d  and is information that defines a value of the circuit element associated with the parameter type  42   d . For example, when the resistance (R) and the capacitance (C) are registered as the parameter types, their respective parameter values are a resistance value and a capacitance value. The other data  42   f  includes information such as a shape of the device or physical properties of the device. 
       FIG.  4    is a diagram showing the optical condition stored in the database. A unique ID  42   g  (for example, LC 1  and LC 2 ) is assigned to each of the optical conditions, and each of the optical conditions is identified by the ID  42   g . Each of the optical conditions includes pieces of information such as application energy  42   h , an application current  42   i , a scan condition  42   j , a parameter value  42   k , and other data  421 . Note that, in each of the optical conditions, only some of the pieces of information may be defined. 
     The application energy  42   h  is information that defines energy of the charged electron beam applied to the sample. The application energy includes, for example, an electron accelerating voltage or retarding voltage. Herein, the retarding voltage refers to a voltage that decelerates the electron beam (charged particle beam) immediately before the sample by applying the voltage to the sample. The application current  42   i  is information that defines the current of the electron beam. The application current may also be referred to as a probe current. 
     The scan condition  42   j  is information that defines an electron beam application method. The scan condition  42   j  includes, for example, pieces of information such as a scan speed (scanning speed) and a scanning interval. The parameter value  42   k  is information that defines a parameter associated with the application of the electron beam. The parameter value  42   k  includes, for example, pieces of information such as a magnification, an aperture angle, and a working distance. The other data  421  includes the other pieces of information associated with a corresponding optical condition. Further, the other data  421  may include an electron beam pulse conversion condition (modulation condition). 
     The electron beam pulse conversion condition includes, for example, a pulse width, a duty cycle, a frequency, any pattern in which the pulse width and the duty cycle change with time, and the like. 
     Note that the optical condition may be referred to as an electron optical condition, for example. 
     The optical condition storage section  43  stores a selected electron beam optical condition. The to-be-used-in-computation netlist storage section  44  stores the to-be-used-in-computation netlist generated or updated by the to-be-used-in-computation netlist generator  32 . The electron beam application result storage section  45  stores the electron beam application result of the sample  23  actually measured on the basis of the detection signal output from the detector  25 . The electron beam application result stored in the electron beam application result storage section  45  may be the detection signal output from the detector  25 , the SEM image based on the detection signal, or the like. The estimated application result storage section  46  stores the electron beam application result of the sample  23  estimated by the electron beam application result estimation computing unit  33 . 
     The storage device  41  is configured by, for example, a non-volatile memory such as a flash memory. Further, some of the storage sections included in the storage device  41  may be configured by a volatile memory such as a dynamic random access memory (DRAM) or a static random access memory (SRAM). Each of the storage sections included in the storage device  41  may be provided as a separate device, or alternatively, as a separate storage area defined in one storage device. 
     &lt;Input and Output Part&gt; 
     The input and output part  50  is a functional block responsible for operations on the charged particle beam apparatus  1 , selection of the to-be-used-in-calculation device model or optical condition, display of the electron beam application result and estimated application result of the sample  23 , and the estimated netlist, and the like. The input and output part  50  includes a display  60  of, for example, a touch screen type. On the display  60 , for example, an operation panel of the charged particle beam apparatus  1 , a selection section  51  for use in selection of the to-be-used-in-calculation device model or optical condition, an estimated netlist  52 , an estimated application result  53 , an electron beam application result  54 , and the like are displayed. 
     &lt;Circuit Estimation Method for Sample&gt; 
     Next, a circuit estimation method for the sample  23  will be described. According to the present embodiment, a netlist of the sample is estimated on the basis of the to-be-used-in-computation netlist generated from the to-be-used-in-calculation device model and a comparison between the electron beam application result estimated using the optical condition and the actual electron beam application result based on the optical condition.  FIG.  5    is a flowchart showing an example of the circuit estimation method for the sample. In the example shown in  FIG.  5   , the circuit estimation for the sample is made in steps S 10  to S 130 . 
     Once the circuit estimation process is initiated, the to-be-used-in-calculation device model is selected (step S 10 ).  FIG.  6    is a diagram showing an example of a to-be-used-in-calculation device model selection screen. On the to-be-used-in-calculation device model selection screen  61  shown in  FIG.  6   , for example, a list  61   a  of the to-be-used-in-calculation device models registered in the database  42  and a selection determination button  61   e  are shown. The list  61   a  includes an ID display field  61   b  of each of the registered to-be-used-in-calculation device model, a to-be-used-in-calculation device model selection field  61   c , and a details display field  61   d  of a corresponding to-be-used-in-calculation device model. 
     From the to-be-used-in-calculation device model selection screen  61  displayed on the display  60 , the user selects a to-be-used-in-calculation device model having a circuit that is the same as or similar to the sample  23  to be measured. In the present embodiment, one to-be-used-in-calculation device model is selected. Specifically, the user checks a check box corresponding to a to-be-used-in-calculation device model to be selected, and then touches the selection determination button  61   e  to finalize the selection of the to-be-used-in-calculation device model.  FIG.  6    shows a case where a to-be-used-in-calculation device model assigned the ID “DM 1 ” is selected. The to-be-used-in-calculation device model thus selected is sent to the to-be-used-in-computation netlist generator  32  shown in  FIG.  2   . 
     In step S 20 , the to-be-used-in-computation netlist generator  32  generates a to-be-used-in-computation netlist on the basis of the to-be-used-in-calculation device model selected by the user. For example, the method for generating the to-be-used-in-computation netlist is not limited to a method by which the to-be-used-in-computation netlist generator  32  combines any of the model  42   b , the parameter type  42   d , the shape of the device, or the physical properties of the device and the parameter value  42   e  included in the selected to-be-used-in-calculation device model to generate the to-be-used-in-computation netlist. 
     In step S 30 , an optical condition is selected.  FIG.  7    is a diagram showing an example of an optical condition selection screen. On an optical condition selection screen  62  shown in  FIG.  7   , for example, a list  62   a  of the optical conditions registered in the database  42  and a selection determination button  62   e  are displayed. The list  62   a  includes an ID display field  62   b  of each of the registered optical condition, an optical condition selection field  62   c , and a details display field  62   d  of a corresponding optical condition. 
     The user selects a desired optical condition from the optical condition selection screen  62  displayed on the display  60 . More specifically, the user checks a checkbox corresponding an optical condition to be selected, and then touches the selection determination button  62   e  to finalize the selection of the optical condition.  FIG.  7    shows a case where an optical condition assigned the ID “LC 2 ” is selected. The optical condition thus selected is stored in the optical condition storage section  43  shown in  FIG.  2   . 
     Note that, in step S 10 , when the selection determination button  61   e  is touched to finalize the selection of the to-be-used-in-calculation device model, the optical condition selection screen  62  may be displayed after the to-be-used-in-calculation device model selection screen  61  is deleted. Further, when the selection of the to-be-used-in-calculation device model is finalized, the optical condition selection screen  62  may be displayed superimposed on the to-be-used-in-calculation device model selection screen  61 . The optical condition selection screen  62  may be provided with a button that causes the to-be-used-in-calculation device model selection screen  61  to be displayed again. 
     Further, for the settings of the optical condition, the electron beam pulse conversion condition (modulation condition) is used as necessary. The electron beam pulse conversion condition may be used together with the optical condition, or the electron beam pulse conversion condition alone may be set as the optical condition. 
     In step S 40 , the electron beam is applied to the sample  23  under the optical condition selected in step S 30 . The optical condition stored in the optical condition storage section  43  is sent to the controller  11  of the charged particle beam apparatus main body  10 . The controller  11  controls each component of the charged particle beam optical system BS to apply the electron beam to the sample  23  under the optical condition thus received. When the electron beam is applied to the sample  23 , the secondary electrons are emitted from the sample  23 . When detecting the secondary electrons emitted from the sample  23 , the detector  25  outputs a predetermined detection signal in accordance with the number of the secondary electrons, application energy, or the like to the computer  30  (computing unit  31 ). 
     In step S 50 , an actual electron beam application result of the sample  23  is stored. The computing unit  31  may store, for example, the detection signal (signal waveform) output from the detector  25  in the electron beam application result storage section  45  as the electron beam application result. Further, the computing unit  31  may generate an inspection image (SEM image or the like) on the basis of the detection signal and store the inspection image in the electron beam application result storage section  45  as the electron beam application result. Further, the computing unit  31  may measure an electrical charge carried by the sample  23  on the basis of the detection signal and store the electrical charge thus measured in the electron beam application result storage section  45 . Further, the computing unit  31  may detect brightness of the inspection image or brightness of each pixel of the inspection image and store the brightness thus detected in the electron beam application result storage section  45 . 
     In step S 60 , the to-be-used-in-computation netlist generated in step S 20  is stored in the to-be-used-in-computation netlist storage section  44 . Note that step S 20  and step S 60  are separately shown in  FIG.  5   , but the process of step S 60  may be executed in step S 20 . 
     In step S 70 , the electron beam application result is estimated. The electron beam application result estimation computing unit  33  estimates the electron beam application result of the sample  23  on the basis of the to-be-used-in-computation netlist stored in the to-be-used-in-computation netlist storage section  44  and the optical condition stored in the optical condition storage section  43 . Items of the electron beam application result to be estimated here are the same as measurement items in step S 50 , and include, for example, the detection signal (signal waveform) output from the detector  25 , the electrical charge, the inspection image, the brightness of the inspection image, the brightness of each pixel of the inspection image, and the like. 
     In step S 80 , the electron beam application result estimated in step S 70  is stored in the estimated application result storage section  46 . 
     In step S 90 , the actual electron beam application result and the estimated electron beam application result are compared. The comparator  34  compares the actual electron beam application result and the estimated electron beam application result for each item of the electron beam application result. The comparator  34  compares the detection signals for each electron beam application region or each pixel of the inspection image, for example. The comparator  34  also compares, for example, the electrical charge, the inspection image, the brightness of the inspection image, the brightness of each pixel of the inspection image, and the like. The comparator  34 , for example, digitizes these application results and calculates a difference between the actual electron beam application result and the estimated electron beam application result for each item to generate a comparison result. Note that the comparator  34  may compare all of these items, or may compare only some of the items. 
     In step S 100 , a determination is made as to whether the actual electron beam application result and the estimated electron beam application result coincide with each other on the basis of the comparison result calculated in step S 90 . For example, when a value of the comparison result is “0”, the comparator  34  determines that these application results coincide with each other. On the other hand, when the value of the comparison result is not “0”, the comparator  34  determines that these comparison results differs from each other. Note that, in practice, these application results rarely coincide with each other; therefore, it is necessary to take a measurement error within a predetermined range into account. 
     This allows the comparator  34  to determine that the application results coincide with each other when the value of the comparison result is equal to or less than a predetermined threshold. The predetermined threshold is defined for each item. Note that when the comparison is made for a plurality of items, the comparator  34  may determine that these application results coincide with each other only when the comparison results for all the items are equal to or less than the respective thresholds, or alternatively, may determine that these application results coincide with each other when the comparison results for at least a predetermined number of items are equal to or less than the respective thresholds. 
     When the comparator  34  determines in step S 100  that these electron beam application results differ from each other (No), the process of step S 110  is executed. 
     In step S 110 , the to-be-used-in-computation netlist is updated. The comparator  34  sends the comparison result to the to-be-used-in-computation netlist generator  32 , and the to-be-used-in-computation netlist generator  32  updates the to-be-used-in-computation netlist, for example. The to-be-used-in-computation netlist generator  32  changes, on the basis of the comparison result, a parameter value used in generation of the last to-be-used-in-computation netlist, and generates a to-be-used-in-computation netlist using the parameter value thus changed, for example. As described above, the to-be-used-in-computation netlist generator  32  updates the to-be-used-in-computation netlist. At this time, the to-be-used-in-computation netlist generator  32  may change the parameter value on the basis of the comparison results for a plurality of items. Further, the to-be-used-in-computation netlist generator  32  may preset a parameter whose parameter value is variable and update the to-be-used-in-computation netlist while changing the parameter value of only such a variable parameter. 
     The updated to-be-used-in-computation netlist is stored in the to-be-used-in-computation netlist storage section  44  (step S 60 ). The electron beam application result is estimated again using the updated to-be-used-in-computation netlist and the optical condition (step S 70 ), and the estimated electron beam application result is stored in the estimated application result storage section  46  (step S 80 ). Then, the electron beam application result estimated using the updated to-be-used-in-computation netlist and the actual electron beam application result are compared again (step S 90 ). 
     The processes of steps S 60  to S 110  are repeatedly executed until the estimated electron beam application result and the actual electron beam application result coincide with each other. Note that the to-be-used-in-computation netlist may be updated in the to-be-used-in-computation netlist storage section  44 . In this case, the processes of steps S 70  to S 110  are repeatedly executed until the estimated electron beam application result and the actual electron beam application result coincide with each other. 
     On the other hand, in step S 100 , when the comparator  34  determines that these electron beam application results coincide with each other (Yes), the process of step S 120  is executed. In step S 120 , the computing unit  31  (comparator  34 ) determines that the to-be-used-in-computation netlist stored in the to-be-used-in-computation netlist storage section  44  can be identified as a netlist describing the circuit of the sample  23 , and stores this to-be-used-in-computation netlist in the estimated netlist storage section  47  as an estimated netlist. Further, in addition to the estimated netlist, a correspondence table that associates a position of a plug electrode in the inspection image with each node in the estimated netlist may be stored in the estimated netlist storage section  47 . 
     In step S 130 , the estimation result and measurement result are output to the input and output part  50 . For example, the estimated netlist stored in the estimated netlist storage section  47 , the estimated electron beam application result stored in the estimated application result storage section  46 , the actual electron beam application result stored in the electron beam application result storage section  45  are output to the input and output part  50  and displayed on the display  60 . 
       FIG.  8    is a diagram showing an example of a result display screen after circuit estimation. As shown in  FIG.  8   , a to-be-used-in-calculation device model designation section  71 , an estimated result display section  72 , an estimated electron beam application result display section  73 , and an electron beam application result display section  74  are each displayed as a result display screen  70 . 
     In the to-be-used-in-calculation device model designation section  71 , details of the selected to-be-used-in-calculation device model, the selected optical condition, and the like are displayed. For example, the user can confirm the details of the selected to-be-used-in-calculation device model and optical condition by touching the to-be-used-in-calculation device model designation section  71 . In the estimated result display section  72 , each parameter value used in generation of the estimated netlist is displayed. Further, in the estimated result display section  72 , information on whether the parameter is variable may be displayed together with the parameter value. 
     In the estimated electron beam application result display section  73 , the estimated electron beam application result is displayed. In the estimated electron beam application result display section  73 , a graph in which the horizontal axis represents the electron beam application condition (optical condition), and the vertical axis represents the brightness (brightness) is displayed. Specifically, in the estimated electron beam application result display section  73 , electron beam application results estimated for a plurality of nodes (plug electrodes) are displayed. Note that, in the estimated electron beam application result display section  73 , not only the estimated result using the estimated netlist but also the estimated result using the to-be-used-in-computation netlist before being identified may be displayed. 
     In the electron beam application result display section  74 , the actually measured electron beam application result is displayed. In the electron beam application result display section  74 , a graph in which the horizontal axis represents the electron beam application condition and the vertical axis represents the brightness (brightness) is displayed in the same manner. In the electron beam application result display section  74 , electron beam application results for a plurality of nodes are displayed. 
     Note that the graphs displayed in the estimated electron beam application result display section  73  and the electron beam application result display section  74  can be configured as desired. For example, a graph in which the vertical axis represents the amount of detected secondary electrons may be displayed. Further, in each of the estimated electron beam application result display section  73  and the electron beam application result display section  74 , the waveform of the detection signal, the inspection image, and the like may be displayed. 
     Further, the estimated electron beam application result display section  73  and the electron beam application result display section  74  may be combined such that the estimated result and the measured result are displayed together. 
       FIGS.  9 A to  9 C  are diagrams showing another example of the result display screen after circuit estimation. In the result display screen  70 , not only the sections shown in  FIG.  8   , but also images shown in  FIGS.  9 A to  9 C  may be displayed, for example.  FIG.  9 A  is an image representing an inspection image in which coordinates of plug electrodes are additionally illustrated.  FIG.  9 B  is an estimated netlist.  FIG.  9 C  is a correspondence table that associates each of the positions of the plug electrode in the inspection image with a corresponding node in the estimated netlist. Further, a circuit diagram based on the estimated netlist may be displayed in the result display screen  70 . 
     Note that processes such as the generation of the to-be-used-in-computation netlist, the measurement through application of the electron beam, and the estimation of the electron beam application result have been described in order with reference to  FIG.  5   , but these processes may be executed in parallel. For example, the measurement through application of the electron beam may be executed at the same time as the generation of the to-be-used-in-computation netlist and the estimation of the electron beam application result. 
     Further, artificial intelligence (AI) based on a method such as machine learning or deep learning may be applied to processes such as the estimation of the electron beam application result in step S 70 , the update of the to-be-used-in-computation netlist in step S 110 , and the like. 
     Main Effects of the Present Embodiment 
     According to the present embodiment, the to-be-used-in-computation netlist is generated on the basis of the to-be-used-in-calculation device model, and the electron beam application result when the electron beam is applied to the sample is estimated on the basis of the to-be-used-in-computation netlist and the optical condition. Further, the estimated electron beam application result is compared with the electron beam application result when the electron beam is applied to the sample  23  on the basis of the optical condition. 
     This configuration eliminates the need of converting an external netlist input from the outside into the to-be-used-in-computation netlist, and thereby allows the electrical characteristics of the sample  23  to be estimated in a short time, increasing the throughput. The configuration further allows the electrical characteristics and circuit of the sample  23  to be freely estimated without being affected by the configuration of the external netlist, and thereby allows the electrical characteristics to be estimated with consideration given to interactions between a plurality of devices. 
     Further, according to the present embodiment, when the estimated electron beam application result and the actual electron beam application result differ from each other, the to-be-used-in-calculation device model is updated. Specifically, the computing unit  31  updates the to-be-used-in-computation netlist by changing the parameter value included in the to-be-used-in-calculation device model and creating the to-be-used-in-computation netlist again using the changed parameter value. This configuration makes it possible to update the to-be-used-in-computation netlist while suppressing the computation amount and to thereby suppress a load on the computing unit  31 . 
     Further, according to the present embodiment, the electron beam application result includes any one of the detection signal, the inspection image based on the detection signal, the brightness of the inspection image, or the brightness of each pixel in the inspection image. This configuration makes it is possible to collate application results with various forms based on the detection signal. 
     Further, according to the present embodiment, the to-be-used-in-calculation device model includes a model representing a defect in the sample  23 . This configuration makes it possible to easily detect a defect (manufacturing defect) in the sample  23  and to thereby increase accuracy in circuit estimation. 
     Further, according to the present embodiment, the to-be-used-in-calculation device model includes any one of a model defining a circuit of a device, a mathematical expression defining electrical characteristics of the device, a shape of the device, or physical properties of the device. This configuration makes it possible to estimate the circuit of the sample  23  from not only the circuit configuration but also the electrical characteristics, the shape, the physical properties, and the like and to thereby increase accuracy in circuit estimation. 
     Further, according to the present embodiment, the computing unit  31  generates a correspondence table that associates the position of the plug electrode in the inspection image with each node in the identified to-be-used-in-computation netlist (estimated netlist). This configuration makes the correspondence between the netlist and the inspection image clear. 
     Further, according to the present embodiment, the electron beam application result is estimated on the basis of the optical condition and the electron beam pulse conversion condition. This configuration makes it is possible to increase accuracy in estimation of the electrical characteristics of the sample  23  with the electron beam that changes in a complicated manner. 
     Second Embodiment 
     Next, a second embodiment will be described. According to the present embodiment, a plurality of to-be-used-in-calculation device models and one optical condition are used, and application results are compared for each of the to-be-used-in-calculation device models. An apparatus structure according to the present embodiment is the same as the structure shown in  FIGS.  1  to  4   . 
     &lt;Circuit Estimation Method for Sample&gt; 
     Next, a circuit estimation method according to the present embodiment will be described. According to the present embodiment, the circuit estimation is also performed according to the flow shown in  FIG.  5   . The following mainly describes processes different from the processes according to the first embodiment. 
     In step S 10 , a plurality of to-be-used-in-calculation device models are selected. For example, the user selects the plurality of to-be-used-in-calculation device models by checking the check boxes of the plurality of to-be-used-in-calculation device models on the to-be-used-in-calculation device model selection screen  61  shown in  FIG.  6    and touching the selection determination button  61   e.    
     In step S 20 , the to-be-used-in-computation netlist for each of the selected plurality of to-be-used-in-calculation device models is generated. Then, in step S 60 , the to-be-used-in-computation netlists generated in step S 20  are stored in the to-be-used-in-computation netlist generator  32 . 
     In step S 70 , the electron beam application result is estimated using each of the to-be-used-in-computation netlists stored in the to-be-used-in-computation netlist generator  32 . In step S 80 , a plurality of electron beam application results estimated in step S 70  are stored in the estimated application result storage section  46 . 
     In step S 90 , the actual electron beam application result and the estimated plurality of electron beam application results are compared. The comparator  34  generates a comparison result for each of the estimated electron beam application results. In step S 100 , a determination is made as to whether the actual electron beam application result and each of the estimated electron beam application results coincide with each other. 
     When a determination is made in step S 100  that the actual electron beam application result coincides with none of the estimated electron beam application results (No), all the to-be-used-in-computation netlists are updated in step S 110 . On the other hand, when a determination is made that the actual electron beam application result coincides with any one of the estimated electron beam application results (Yes), the process of step S 120  is executed. 
     In step S 120 , the to-be-used-in-computation netlist corresponding to the estimated electron beam application result that coincides with the actual electron beam application result is identified as a netlist describing the sample  23 . The identified to-be-used-in-computation netlist is stored in the estimated netlist storage section  47  as an estimated netlist. 
     In step S 130 , the estimation results for the plurality of to-be-used-in-calculation device models may be displayed on the result display screen  70 . 
     Main Effects of the Present Embodiment 
     According to the present embodiment, the following effects can be obtained in addition to the effects of the above-described embodiment. According to the present embodiment, a plurality of to-be-used-in-calculation device models and one optical condition are used, and, for each of the to-be-used-in-calculation device models, the estimated electron beam application result and the actual electron beam application result are compared. This configuration makes it possible to estimate, in a short time, the circuit and electrical characteristics of the sample  23  having a complicated structure. 
     Third Embodiment 
     Next, a third embodiment will be described. According to the present embodiment, one to-be-used-in-calculation device model and a plurality of optical conditions are used, and application results are compared for each of the optical conditions. An apparatus structure according to the present embodiment is also the same as the structure shown in  FIGS.  1  to  4   . 
     &lt;Circuit Estimation Method for Sample&gt; 
     Next, a circuit estimation method according to the present embodiment will be described. According to the present embodiment, the circuit estimation is also performed according to the flow shown in  FIG.  5   . The following mainly describes processes different from the processes according to the first embodiment. 
     In step S 30 , a plurality of optical conditions are selected. For example, the user selects the plurality of optical conditions by checking the check boxes of the plurality of optical conditions on the optical condition selection screen  62  shown in  FIG.  7    and touching the selection determination button  62   e.    
     In step S 40 , the electron beam is applied to the sample  23  sequentially under the plurality of optical conditions thus selected. In step S 50 , the actual electron beam application result of the sample  23  is stored in the electron beam application result storage section  45  for each of the optical conditions. 
     In step S 90 , the actual electron beam application result and the estimated electron beam application result are compared for each of the optical conditions. The comparator  34  generates a comparison result for each of the optical conditions. In step S 100 , a determination is made as to whether each of the electron beam application results and a corresponding one of the estimated electron beam application results coincide with each other. 
     When a determination is made in step S 100  that none of the plurality of electron beam application results coincides with the estimated electron beam application results (No), the to-be-used-in-computation netlists are updated in step S 110 . On the other hand, when a determination is made that any one of the electron beam application results coincides with a corresponding one of the estimated electron beam application results (Yes), the process of step S 120  is executed. 
     In step S 120 , the to-be-used-in-computation netlist stored in the to-be-used-in-computation netlist storage section  44  is stored in the estimated netlist storage section  47  as an estimated netlist. At this time, the optical condition when the actual electron beam application result and the estimated electron beam application result coincide with each other may be stored together. 
     In step S 130 , measurement results for the plurality of optical conditions may be displayed on the result display screen  70 . 
     Main Effects of the Present Embodiment 
     According to the present embodiment, with one to-be-used-in-calculation device model and a plurality of optical conditions, the estimated electron beam application result and the actual electron beam application result are compared for each of the optical conditions. This configuration makes it is possible to increase accuracy in estimation of the electrical characteristics. 
     [Modification] 
     Note that the present embodiment is also applicable to a case where a comparison is made on the basis of the estimated netlist identified in the first embodiment and a plurality of optical conditions. In this case, steps such as the selection of the to-be-used-in-calculation device model, the generation/update of the to-be-used-in-computation netlist, and the identification of the to-be-used-in-computation netlist can be omitted as appropriate. 
     This facilitates the estimation of the electrical characteristics of the sample whose netlist has been identified, and makes it possible to increase accuracy in estimation. 
     Note that the present invention is not limited to the above-described embodiments and includes various modifications. Further, some of the components of one embodiment can be replaced with corresponding components of another embodiment, and a component of another embodiment can be added to the components of one embodiment. Further, it is possible to add different components to the components of each embodiment, delete some of the components of each embodiment, and replace some of the components of each embodiment with different components. Note that each member and relative size shown in the drawings have been simplified and idealized for easy understanding of the present invention, and the present invention may have a more complicated shape when being implemented.