Patent ID: 12191111

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments (first to fourth embodiments) of the present disclosure will be described with reference to the accompanying drawings. The attached drawings show specific embodiments based on a principle of the present technical idea, but these are for the purpose of understanding the present technical idea, and the present technical idea is not used for limitative interpretation.

In the embodiments, the description is made in sufficient detail for those skilled in the art to implement the present disclosure, but changes in configurations and structures and various replacements of elements are also possible without deviation from the scope and spirit of the technical idea of the present disclosure. Therefore, the following description should not be construed as to be limited to the present disclosure.

Further, as will be described later, the embodiments of the present disclosure may be implemented by software running on a general-purpose computer, or may be implemented by dedicated hardware or a combination of software and hardware.

As a sample observation device disclosed in the present embodiment, there is a charged particle beam device that scans a surface of a sample with charged particle beams (for example, electrons) and uses electrons that are secondarily generated. Examples of the charged particle beam device include an inspection device using a scanning electron microscope (SEM), a review device, and a pattern measurement device. Hereinafter, as an example, an example in which a charging measurement technique according to the present disclosure is applied to an SEM type length measurement device will be described.

As described above, in the related art, it has not been possible to accurately ascertain a charged state of a resist pattern. Therefore, it was not possible to determine an optimum scanning method, static elimination method, and static elimination timing. Furthermore, there was not known a method for automatically determining optimum conditions thereof. A time required for an operator to search for the optimum conditions is longer than an actual pattern dimensional inspection time, which causes a decrease in semiconductor production efficiency.

Therefore, in the present embodiment, there is provided a technique for automatically determining at least one of an optimum scanning method, a static elimination method, or a static elimination timing, in order to accurately ascertain a charged state of a resist pattern due to irradiation with charged particle beams and to measure a pattern without magnification fluctuation due to charging.

(1) First Embodiment

A first embodiment discloses calculation of the charging amount for each frame generated by scanning a predetermined location of the sample for a plurality of frames with an electron beam, not the charging amount generated by the basic principle (configuration) of the present technical idea, specifically by scanning the sample once with an electron beam. Further, the first embodiment also discloses that the optimum static elimination method and the static elimination timing are obtained and output based on the obtained charging amount for each frame.

<System Configuration Example>

FIG.1is a diagram showing a configuration example of an SEM type length measurement system (also referred to as a charged particle beam system, a charged particle beam inspection system, or the like) according to a first embodiment. A charged particle beam system (SEM type length measurement system)1includes an SEM type length measurement device (charged particle beam device)100including an electron beam optical system (charged particle beam optical system) for irradiating a sample105with an electron beam (also referred to as a primary electron beam)102, a detection system for detecting an electron (secondary electron)108emitted from the sample105due to irradiation with the electron beam102, and a stage mechanism system arranged in a vacuum chamber (not shown) and a computer system200including a control system that controls each component of a SEM type length measurement device100and processes various information.

The electron beam optical system includes, for example, an electron source (charged particle source)101that generates the electron beam102, an objective lens103that adjusts a focal position of the electron beam102, and a deflector104that scans the sample105with the electron beam102. The detection system includes, for example, an energy filter (also referred to as a detection charged particle sorter (discrimination device)109and a detector111. In addition, the electron beam optical system may include other lenses and electrodes, and the detection system may include other detectors. In addition, the configurations of the electron beam optical system and the detection system may be partially different from the above-mentioned components and may not be limited to the above-mentioned configurations.

In the SEM type length measurement device100, the primary electron beam102generated by the electron source101is focused on the sample105by the objective lens103. When generating the image, the primary electron beam102is deflected by the deflector104(the deflector104is operated by a deflector control unit120in response to a command of an SEM control unit121), and the sample105is scanned with the primary electron beam102.

The stage mechanism system includes a movable stage106. The sample105is mounted on the movable stage106and electrically floats by a negative voltage given by a retarding control unit107. For this reason, the primary electron beam102is subject to a deceleration action on the sample105. On the other hand, a secondary electron108generated from the sample105is accelerated by a retarding voltage given by the retarding control unit107to reach the energy filter109.

The energy filter109is used as an example of an energy discriminator, and is configured with, for example, at least one or more mesh-shaped electrodes. A negative voltage is applied from a filter control unit110to at least one mesh-shaped electrode in the energy filter109, and it is possible to filter (select) the electrons detected by the detector111by the negative voltage. Then, the filtered electrons reach the detector111. These electrons become detection signals through a detection amplifier or the like in the detector111. InFIG.1, since the detection amplifier is built in the detector111, the detection amplifier is omitted.

The control of the SEM type length measurement device100is executed via the SEM control unit121and each of the control units (the retarding control unit107, the filter control unit110, an objective lens control unit118, and the deflector control unit120). That is, the SEM control unit121gives predetermined commands to the retarding control unit107, the objective lens control unit118, the filter control unit110, and the deflector control unit120, and the respective control units respond to the command and control the control objects (the objective lens103, the deflector104, the movable stage106, and the energy filter109). Specifically, the objective lens103is controlled by the objective lens control unit118, and the energy filter109is controlled by the filter control unit110. Further, the retarding voltage applied to the movable stage106is controlled by the retarding control unit107. It is noted that, inFIG.1, only the control units related to the technical idea of the present disclosure are shown, and the other control units are omitted.

The SEM control unit121further includes an image generation unit112, a contrast adjustment unit113, a display unit114, a focus evaluation value calculation unit115, a brightness calculation unit116, a Vs (filter characteristic voltage) determination unit117, and a Vf (filter voltage) calculation unit119. The brightness calculation unit116has a function of calculating a gradation value of an SEM image. In addition, in the following, the components of the control system may be collectively referred to as a control processing unit.

The detection signal from the detector111is transmitted to the image generation unit112. The image generation unit112generates an image by two-dimensionally mapping an intensity of the detection signal based on two-dimensional scanning on the sample105by the deflector104. The image generated by the image generation unit112is stored in an image storage unit122through the SEM control unit121. Further, the image generation unit112has a function of generating an image of each frame at the time of frame integration and storing the image in the image storage unit122.

The components of the control system described above can be realized by using a general-purpose computer and may be realized as a function of a program executed on the computer. For this reason,FIG.1shows an example in which the components of the control system are realized by the computer system200. The computer system200includes at least a processor such as a CPU (Central Processing Unit), a storage unit such as a memory123, and a storage device such as a hard disk (including an image storage unit122). For example, the computer system200is configured as a multiprocessor system, that is, the SEM control unit121may be configured as main processor, and the retarding control unit107, the filter control unit110, the objective lens control unit118, and the deflector control unit120may be configured as respective sub-processors.

The control system processing described below may be stored as a program code in the memory123or a storage device (not shown), and the processor may read the respective program codes, load the program codes into an internal memory (not shown) of the processor to realize the respective control units, and execute the respective processes. A portion of the control system may be configured by hardware such as a dedicated circuit board.

<Charging Measurement and Static Elimination>

FIG.2is a diagram showing voltage dependence (S curve) obtained when the energy filter109is used. InFIG.2, a vertical axis represents the gradation value (standardized) of the SEM image, and a horizontal axis represents an energy filter voltage applied by the filter control unit110. InFIG.2, an absolute value of the negative voltage given to the energy filter109increases toward the right side of the horizontal axis.

The charging amount of the pattern can be obtained from the energy filter voltage dependence (S curve)201of the SEM image gradation value obtained by scanning for charging measurement. As the energy filter voltage (Vf) increases, the number of secondary electron108filtered by the energy filter109increases. For this reason, the number of secondary electron108reaching the detector111is reduced, and the SEM image gradation value is lowered. A reference voltage202in the S curve201is the energy filter voltage in the reference gradation value203. The reference gradation value203is, for example, set to ½ of a maximum value204(gradation value standardized for each frame, for example, standardized by setting the maximum value of the SEM image gradation value for each frame to 1 and setting the minimum value thereof to 0) of the SEM image gradation value. The charging amount of the pattern can be obtained from a deviation amount from the reference voltage (reference S curve) when the pattern is not charged. A method for determining the reference voltage202is not limited to the above method, and a shift of the S curve201may be obtained. For example, the reference voltage202may be set to ⅓ or ⅔ of the maximum value204, or a location where the absolute value of the inclination of the S curve201is maximized may be set to the reference voltage202.

The case where the S curve to be measured is shifted in the direction in which the absolute value of Vf is smaller than the reference S curve indicates that the energy of the secondary electron108generated in the pattern in the energy filter109is reduced, that is, that positive charging is performed. On the other hand, the case where the S curve to be measured is shifted in the direction in which the absolute value of Vf is larger than the reference S curve indicates that the energy of the secondary electron108generated in the pattern in the energy filter109is increased, that is, is negative charging. The scanning used to generate the reference S curve may be, for example, scanning of one frame.

FIG.3is a diagram showing charging measurement for each number of frames performed in one time of scanning. The image acquired in one time of scanning may be an image of one frame, or may be an image of a plurality of frames (when a plurality of frame images are acquired, a specific portion is continuously scanned for the number of frames. The image of an n-th frame is stored in the image storage unit122. In the scanning of the n frames, the S curves are generated for the respective frames from 1 frame to n frames. Then, the charging amount in each frame can be measured from a deviation amount303from a reference S curve301. An operator can arbitrarily (freely) set the number of frames for measuring the charging (the number of frames for scanning). For example, when measuring the charging amount for 8 frames for scanning of 16 frames, the charging amount for the 8 frames is obtained from the deviation amount between the S curve using the SEM image of an 8-th frame and the reference S curve. As an advantage of measuring the charging for each number of frames, for example, it is possible to determine how many frames are not affected by the charging, and it is possible to determine the maximum number of frames in which the magnification fluctuation does not occur. Further, since the relationship between the number of frames and the charging amount is not limited to linear increase and differs depending on the size, shape, direction, arrangement, density, or the like of the pattern, so that it is effective to measure the charging amount for each number of frames.

By executing the charging measurement for each number of frames by a plurality of scanning methods, the charging amount for each scanning method can be measured. An example of the scanning method, there is an example in which the scanning time, the scanning order, the scanning direction, and the scanning area are changed, and there is an example in which an acceleration voltage (energy) and a dose amount of the primary electron beam are changed. Even if the number of frames is the same, the scanning method is changed, and thus, the charging amount and the positive and negative signs change, so that by performing charging measurement for each scanning method, the scanning method that minimizes the charging amount and the scanning method in which the charging with an arbitrary code occurs can be explored.

Next, the static elimination method will be described. For the positive charging, for example, there is an LCN (Local Charge Neutralization) method that eliminates static electricity only in the positive charging area by setting the retarding voltage applied to the electron gun and the wafer to the same voltage (refer to JP-A-2012-155980 (PTL 3)). In the LCN method, since the energy of the electrons irradiated on the sample105is several eV, the irradiation damage is negligibly small. On the other hand, as a static elimination method for the negative charging, for example, there are a light irradiation method in which photoelectrons are emitted by ultraviolet light irradiation (refer to JP-A-2009-004114 (PTL 4)) and a predose method in which an electron beam is irradiated with a collision energy in which a secondary electron emission yield exceeds 1. However, these static elimination methods are only examples, and the static elimination methods applicable to the present embodiment are not limited thereto. Further, for example, the optimum static elimination method may be set in advance according to the scanning conditions (scanning method), and this relationship may be stored in the memory123. At this time, the SEM control unit121may acquire (select) information on the optimum static elimination method corresponding to the scanning condition (scanning method) from the memory123and display the information on the display unit114.

<Optimal Observation Condition Determination Sequence, or the Like>

A process of automatically determining at least one of a scanning method, a static elimination method, and a static elimination timing capable of measuring a pattern without magnification fluctuation due to charging will be described with reference toFIGS.4,5,6, and7.

(A) Optimal Observation Condition Determination Sequence

FIG.4is a flowchart showing an optimum observation condition determination sequence. In the first embodiment, for example, a sequence in which only a specific location of the pattern is scanned and measured will be described.

In the following, the processing of each step will be described with “each control unit” as the subject (operating main body), but the description may be made with the processor (or computer system) as the subject (operating main body), or the description may be with the “various programs” executed by the processor as the subject (operating main body). A portion or all of the programs may be implemented by dedicated hardware or may be modularized. Various programs may be installed in a computer system by a program distribution server or storage media.

(i) Step401

The SEM control unit121reads a preset initial condition (for example, set by the operator) from, for example, the memory123and starts the charging measurement. The setting of the initial conditions will be described later.

(ii) Step402

The SEM control unit121passes the scanning conditions to the deflector control unit120. Then, the deflector control unit120sets the received scanning conditions.

(iii) Step403

The SEM control unit121passes information on the energy filter voltage value to the filter control unit110. Then, the filter control unit110sets the received energy filter voltage value.

(iv) Step404

The deflector control unit120controls the deflector104based on the scanning conditions and scans the sample105with the beam.

(v) Step405

The image generation unit112generates an SEM image based on the secondary electron detected by the detector111and passes the SEM image to the SEM control unit121. The SEM control unit121stores the received SEM image in the image storage unit122. Then, the brightness calculation unit116reads out the SEM image from the image storage unit122and calculates the gradation value of each frame. The SEM control unit121may directly supply the SEM image to the brightness calculation unit116without storing the SEM image in the image storage unit122.

(vi) Step406

The SEM control unit121determines whether the measurement based on all the energy filter conditions corresponding to the scanning conditions set at the present time has been completed (whether all the SEM image gradation values corresponding to the set energy filter voltage values can be obtained under the scanning conditions). When it is determined that the measurement based on all the energy filter conditions is completed (Yes in Step406), the process proceeds to Step408. When it is determined that the measurements based on all the energy filter conditions are not completed (No in Step406), the process proceeds to Step407.

That is, the SEM control unit121repeatedly executes the processes from Step403to Step405until the energy filter voltage is changed to a predetermined voltage in order to acquire the S curve.

(vii) Step407

The SEM control unit121instructs the deflector control unit120to move the field of view to another pattern in the pattern of the same arrangement in order to suppress the influence of the charging caused by the scanning of the charging measurement itself. According to the instruction, the deflector control unit120sets the scanning position at a location (same coordinates in the pattern) corresponding to the scanning location in the scanned pattern, which is another pattern in the same array. Then, at the newly set scanning position, the processes from Steps403to405are executed.

(viii) Step408

The brightness calculation unit116generates an S curve (refer toFIG.3) in each frame. For example, the brightness calculation unit116acquires the SEM image gradation values for a plurality of frames corresponding to the respective energy filter set voltage values. Then, the brightness calculation unit116generates the S curve corresponding to each frame by plotting how the SEM image gradation value (normalized value) changes in each frame in response to each energy filter set voltage value on the S curve plane (horizontal axis is the energy filter set voltage value and vertical axis is the standardized SEM image gradation value).

(ix) Step409

The SEM control unit121determines whether all the processes of the set scanning conditions are completed. When all the processes of the set scanning conditions are completed (Yes in Step409), the process proceeds to Step410. When all the processes of the set scanning conditions are not completed (No in Step409), the process proceeds to Step402, and the SEM control unit121instructs the deflector control unit120to change the scanning conditions. Then, the processes of Steps403to408are repeatedly executed.

(x) Step410

The Vs determination unit117acquires the S curve corresponding to the set predetermined scanning conditions and, after that, displays the charging measurement result on the display unit114. The method for displaying the charging measurement result will be described later.

(xi) Step411

The SEM control unit121sets the optimum scanning method and number of frames according to the obtained charging amount and charging code.

(xii) Step412

The SEM control unit121sets the optimum static elimination method and the static elimination timing according to the obtained charging amount and charging code.

(B) Initial Condition Setting

FIG.5is a diagram showing an example of a screen (setting screen500) for setting conditions (initial conditions) for performing the charging measurement set in Step402, which is displayed on the display unit114.

The setting screen500includes a setting unit505for performing the charging measurement including a scanning type501, a number of frames502, a reference gradation value503, an allowable charging amount504, and the like.

The scanning type501is, for example, information indicating a scanning speed. As a scanning speed, for example, a low speed, a medium speed (normal speed), or a high speed is set. The number of frames502is information indicating the number of frames scanned by one time of scanning. The reference gradation value503is information indicating a value set as a reference gradation value as a ratio with respect to the maximum gradation value. The allowable charging amount504is information indicating the charging amount that serves as a threshold value for performing the static elimination. The allowable charging amount is held as a parameter in the SEM control unit121based on the charging amount and the deflection amount of the primary electron beam102calculated from the energy of the primary electron beam102. Further, the allowable charging amount may be freely set by the operator. The relationship between the magnification fluctuation and the charging amount can be obtained in advance by measuring the pattern size and the charging amount.

In the example ofFIG.5, as the condition setting500, a condition A which is a first charging measurement condition, a condition B which is a second charging measurement condition, and a condition C which is a third charging measurement condition are set. The condition A indicates that the charging measurement is performed by scanning for 32 frames at a TV (medium speed) under the condition of a reference gradation value of 50% and an allowable charging amount of 1 V. The condition B indicates that the charging measurement is performed by scanning for 128 frames at a TV2 (high speed) under the condition of a reference gradation value of 50% and an allowable charging amount of 1 V. The condition C indicates that the charging measurement is performed by scanning for 16 frames at a Slow (low speed) under the condition of a reference gradation value of 50% and an allowable charging amount of 1 V. Only one type of condition may be set, or a plurality of types of conditions may be set. A portion of the setting unit505ofFIG.5may be deleted, or other conditions (for example, optical conditions, imaging magnification, coordinates, pixel sizes, or the like) may be added depending on the embodiment.

(C) Charging Measurement Result Display

FIG.6is a diagram showing an example of a screen displayed on the display unit114in Step410to display the charging measurement result for each number of frames corresponding to a plurality of scanning types. InFIG.6, the vertical axis represents the charging amount, and the horizontal axis represents the number of frames.FIG.6is a graph obtained by plotting the respective charging amounts of frames 1 to n on the frame number-charging amount plane for each scanning condition.

In the example ofFIG.6, the allowable charging amount504is shown, but it is shown that static elimination does not need to be performed as long as the charging amount is within the range of the upper limit601and the lower limit602of the allowable charging amount504. Further, in the example ofFIG.6, it is shown that the positive charging is used for the first scanning type603and the second scanning type604, and the negative charging is used for the third scanning type605and the fourth scanning type606. Further, it is shown that the scanning having the smallest charging amount in the positive charging is the second scanning type604, and the scanning having the smallest charging amount in the negative charging is used for the third scanning type605.

Therefore, the scanning type having the smallest charging amount can be determined from the charging measurement results for the respective frames in a plurality of scanning types. It is also possible to determine the scanning type having the smallest charging amount for each of the positive charging and the negative charge. Further, in the first scanning type603, the fluctuation in magnification does not occur until the number of frames607reaches the upper limit601of the allowable charging amount. In the fourth scanning type606, the fluctuation in magnification does not occur until the number of frames608reaches the lower limit602of the allowable charging amount.

As described above, in each scanning type, the number of frames which is less than or equal to the allowable charging amount504and the number of frames for performing static elimination can be determined. Further, it can be seen that there is a case where the extremely large number of frames may not reach the allowable charging amount depending the scanning type, the material of the pattern, the dimensions, the shape, the direction, the arrangement, the density, or the like.

(D) Determining Optimum Scanning Type, or the Like

FIG.7is a diagram showing an example of a screen displaying an optimum scanning type701and number of frames702, a charging code703, a static elimination method704, and a static elimination timing705, which are displayed on the display unit114in Steps411and412and can measure the pattern without the magnification fluctuation due to the charging.

In the example ofFIG.7, it can be seen that the condition B for scanning 128 frames in the TV2 scanning is the scanning method in which the charging amount is minimized, and the scanning method is displayed as the optimum condition that the static elimination is not required. Further, it is shown that in the scanning method for the condition A, the positive charging exceeding the allowable charging amount occurs at the time of integrating 16 frames, and thus, the static elimination for every 16 frames is required to be performed. Then, the method for eliminating the positive charging can be selected from a tab706.

Further, it can be seen that, under the condition C, the negative charging exceeding the allowable charging amount occurs at the time of integrating 4 frames, and thus, the static elimination for every 4 frames is required to be performed. The optimum condition to be displayed may be only one condition or may have a plurality of conditions. When there are a plurality of optimum conditions, the optimum conditions may be set so that they can be selected by the operator, or the optimum conditions may be set so as to be automatically determined. In the case of automatic determination, for example, the scanning condition with the minimum charging amount (as can be seen fromFIG.6) may be selected.

Summary of First Embodiment

According to the first embodiment, the charging amount of each frame is calculated by setting a plurality of types of scanning conditions (for example, scanning a specific location with a plurality of frames by TV, TV2, Slow, or the like) for the sample, calculating the SEM image gradation value while changing the energy filter voltage according to each scanning condition, and generating an S curve (change in the gradation value with respect to each energy filter voltage value) of each frame. By doing so, it is possible to accurately ascertain the charging amount for each frame generated by the electron beam scanning for a plurality of frames. That is, it is possible to accurately ascertain the charged state of the pattern accompanying the electron beam irradiation. In addition, the calculated charging amount is compared with the set allowable charging amount, and it is confirmed at what frame scanning the allowable charging amount is exceeded. Accordingly, it is possible to derive the optimum static elimination timing. Further, since the polarity of charging of each frame can be known from the S curve, it is possible to know the optimum static elimination method.

(2) Second Embodiment

In the second embodiment, a case where multi-point measurement is performed by using a sequence for automatically determining at least one of the optimum scanning conditions, the static elimination method, and the static elimination timing will be described. Even if it is not described in the present embodiment, the matters described in the first embodiment can be applied to the present embodiment unless there are special circumstances.

When performing multi-point measurement in a wafer or chip, the charging amount increases as the number of measurement points increases, so that it is necessary to perform a static elimination operation at regular measurement point intervals. However, since the charging measurement is not performed at the time of multi-point measurement and the charging amount and the positive negative charging code are unknown, there is a problem that the static elimination operation is excessively performed and the measurement time is long. If the charging amount and the charging code for each number of measurement points can be measured or predicted, the optimum static elimination method and the static elimination timing can be known, so that the multi-point measurement time can be reduced.

The second embodiment provides measures to solve such a problem.

<System Configuration>

FIG.8is a diagram showing a configuration of an SEM type length measurement system (also referred to as a charged particle beam system, a charged particle beam inspection system, or the like)8according to a second embodiment. InFIG.8, in addition to the deflector104inFIG.1, a sub-deflector801and a sub-deflector control unit802for controlling the sub-deflector801are mounted. The movement of the field of view or the measurement point may be realized by moving the sample105by using the movable stage106or may be realized by deflecting the primary electron beam102by using the sub-deflector801.

<Multi-Point Measurement Sequence, or the Like>

A sequence for automatically determining at least one of an optimum scanning method, a static elimination method, and a static elimination timing capable of measuring a pattern without magnification fluctuation due to charging will be described with reference toFIGS.9,10,11, and12. In the present embodiment, the charging measurement and the determination of the optimum measurement conditions are automatically performed by the recipe process.

(A) Multi-Point Measurement Sequence

FIG.9is a flowchart showing a process of executing multi-point measurement based on the recipe. InFIG.9, since the processes from Steps402to409are the same as those of the first embodiment (FIG.4), the description is maintained to a minimum, and the processing contents are as described above.

(i) Step901

The SEM control unit121reads a recipe for multi-point measurement processing from, for example, the memory123. The recipe contains, for example, information about multiple measurement points on a test chip.

(ii) Step902

When the sample105is loaded on the movable stage106, the SEM control unit121controls a stage control unit (not shown) according to the read recipe so that the movable stage106performs wafer alignment for rotation and calibration of initial coordinates of the sample105.

(iii) Step903

In response to a command from the SEM control unit121, the sub-deflector control unit802operates the sub-deflector801to execute the measurement point alignment for aligning the relative positions of the measurement points of the test chip registered by the operator (user) (for example, it is specified by the operator whether all the measurement points included in the recipe are to be scanned or every predetermined number of measurement points is to be scanned) and the primary electron beam102. Although the movable stage106may be moved to perform the measurement point alignment, the measurement point alignment can be completed in a shorter time by using the sub-deflector801.

(iv) Steps402to409

Under the preset initial conditions described later, the charging measurement is performed for each frame by a plurality of scanning methods for the test chip in the same manner as the operations from Step S402to Step S409inFIG.4. That is, the deflector control unit120sets the scanning conditions (Step402). Next, the filter control unit110sets the energy filter voltage value (Step403). Then, the deflector control unit120controls the deflector and scans the measurement point with the beam (Step404).

Further, the brightness calculation unit116calculates the gradation value of each frame from the obtained SEM image (Step405). Subsequently, the SEM control unit121repeatedly executes the processes from Step403to Step405in order to acquire the S curve until the energy filter voltage is changed to be a predetermined voltage (Step406). In addition, when the execution is repeated, the field of view is moved within the pattern of the same arrangement in order to suppress the influence of the charging caused by the scanning of the charging measurement itself (Step407).

Next, the brightness calculation unit116generates an S curve in each frame (Step408). Then, the SEM control unit121changes the scanning conditions and repeatedly executes the processes from Step403to Step408(Step409).

(v) Step904

The SEM control unit121determines whether the processes from Step402to Step409are completed for all the set measurement points. When the processes are completed for all the measurement points (Yes in Step904), the process proceeds to Step906. When the processes are not completed for all the measurement points (No in Step904), the process proceeds to Step905.

(vi) Step905

The SEM control unit121issues a command to the sub-deflector control unit802, the deflector control unit120, and the like so that the unprocessed measurement points (for example, the next measurement point when the processing order is specified in the recipe) among the set measurement points are set as processing targets. That is, the processes of Steps S903and Steps S402to S409are repeatedly executed for all the measurement points set in the recipe.

(vii) Step906

The Vs determination unit117acquires the S curve at each measurement point and each scanning condition and, after that, displays the charging measurement result on the display unit114. The method for displaying the charging measurement result will be described later.

(viii) Step907

The SEM control unit121sets the optimum scanning method and number of frames according to the obtained charging amount and charging code. In the present embodiment, the optimum scanning method denotes, for example, a scanning method in which the charging amount is minimized, a scanning method in which a desired charging code is obtained, a scanning method in which a desired static elimination method is effective, or the like. Further, the optimum number of frames may be, for example, the number of frames502for which the charging measurement is performed or may be the number of frames serving as an arbitrary charging amount.

(ix) Step908

The SEM control unit121sets the optimum static elimination method and the static elimination timing according to the obtained charging measurement result. In the present embodiment, the static elimination timing denotes, for example, a measurement point interval for executing the static elimination, a chip point interval for executing the static elimination, or the like.

(x) Step909

In response to a command from the SEM control unit121, the sub-deflector control unit802operates the sub-deflector801to perform a multi-point measurement and executes the measurement point alignment for aligning the relative position between the measurement point of the measurement chip registered by the operator (user) and the primary electron beam102.

(xi) Step910

In response to a command from the SEM control unit121, the deflector control unit120starts the multi-point measurement by using the set scanning method and the number of frames. That is, the multi-point measurement is executed for the same location as the location measured by a test pattern.

(xii) Step911

The SEM control unit121executes the static elimination for each measurement point at the static elimination method and the static elimination timing set in Step908.

(xiii) Step912

The SEM control unit121ends the multi-point measurement.

(xiv) Step913

The SEM control unit121determines whether the measurement of all the measurement chips set in the recipe is completed. When the measurement of all the measurement chips set in the recipe is completed (Yes in Step913), the process proceeds to Step914. When the measurement of all the measurement chips set in the recipe is not completed (No in Step913), the process proceeds to Step909. That is, the processes from Step909to Step912are repeatedly executed until the measurement of all the chips is completed.

(xv) Step914

The SEM control unit121ends the recipe process.

(B) Configuration Example of Charging Measurement Condition Setting Screen

FIG.10is a diagram showing a configuration example of a screen displayed on the display unit114for setting conditions for performing the charging measurement set in Step402.

A charging measurement condition setting screen1000has the setting unit505for performing the charging measurement of the scanning type501, the number of frames502, the reference gradation value503, the allowable charging amount504, or the like and a measurement point setting unit1003for setting measurement points1001for performing the charging measurement, a measurement point interval1002or the like when performing charging measurement for each periodic point.

The setting unit505has the function described in the first embodiment. That is, the allowable charging amount504indicates a charging amount that serves as a threshold value for performing static elimination. The allowable charging amount is held as a parameter in the SEM control unit121based on the charging amount and the deflection amount of the primary electron beam102calculated from the energy of the primary electron beam102. Further, the operator can set arbitrarily (freely) the allowable charging amount. The relationship between the magnification fluctuation and the charging amount can be obtained in advance by measuring the pattern size and the charging amount.

In the example ofFIG.10, a condition A which is the first charging measurement condition, a condition B which is the second charging measurement condition, and a condition C which is the third charging measurement condition are set. The condition A indicates that the charging measurement is performed by scanning for 32 frames at a TV under the condition of a reference gradation value of 50% and an allowable charging amount of 1 V. The condition B indicates that the charging measurement is performed by scanning for 128 frames at the TV2 under the condition of a reference gradation value of 50% and an allowable charging amount of 1 V. The condition C indicates that the charging measurement is performed by scanning for 16 frames at the Slow under the condition of a reference gradation value of 50% and an allowable charging amount of 1 V. The condition may be one type of condition or may be a plurality of types of conditions. A portion of the setting unit505ofFIG.10may be deleted, or other conditions (for example, optical conditions, imaging magnification, coordinates, pixel sizes, or the like) may be added depending on the embodiment.

In the measurement point setting unit1003, the operator can set the number of measurement points1001for performing the charging measurement. In the example ofFIG.10, performing the charging measurement at all measurement points is selected. In order to shorten the time required for the charging measurement, the charging measurement may be performed at each periodic point at an arbitrary measurement point interval1002.

(C) Configuration Example of Charging Measurement Result Display Screen

FIG.11is a diagram showing a configuration example of a screen displayed on the display unit114in Step906, displaying the charging measurement result for each of measurement points corresponding to a plurality of scanning types. InFIG.11, the vertical axis represents the charging amount, and the horizontal axis represents the number of measurement points. The charging amount at each measurement point on the horizontal axis may be set to the charging amount at the number of frames502in which the charging measurement is performed or may be set to the charging amount at any other arbitrary number of frames.

When the allowable charging amount504is within the range of the upper limit601and the lower limit602, the static elimination may not be performed. In the example ofFIG.11, it is shown that the positive charging is used for the first scanning type1101and the second scanning type1102, and the negative charging is used for the third scanning type1103and the fourth scanning type1104. Further, it is shown that the scanning having the smallest charging amount in the positive charging is the second scanning type1102, and the scanning having the smallest charging amount in the negative charging is used for the third scanning type1103. Therefore, the scanning type having the smallest charging amount can be determined from the charging measurement results for the respective measurement points in the plurality of scanning types.

It is also possible to determine the scanning type having the smallest charging amount for each of the positive charging and the negative charge. It can also be seen that, in the first scanning type1101, the magnification fluctuation does not occur until the number of measurement points1105reaches the upper limit601of the allowable charging amount. It can also be seen that, in the fourth scanning type1104, the magnification fluctuation does not occur until the number of measurement points1106reaches the lower limit602of the allowable charging amount. Therefore, for each scanning type, it is possible to determine at which the number of measurement points is less than or equal to the allowable charging amount504or the number of measurement points for performing the static elimination.

As described above, it can be seen that there is a case where even the extremely large number of measurement points may not reach the allowable charging amount depending on the scanning type, the material of the pattern, the dimensions, the shape, the direction, the arrangement, the density, or the like. The charging amount for each number of frames can be displayed on the display unit114in S906, for example, by using the total number of frames of all the measurement points as the horizontal axis, as in the example shown inFIG.6.

(D) Determining Optimum Scanning Type, or the Like

FIG.12is a diagram showing an example of a screen configuration displayed on the display unit114in Steps907and S908ofFIG.9for displaying an optimum scanning type701and number of frames702capable of measuring a pattern without magnification fluctuation due to charging, a charging code703, a static elimination method704, and a static elimination timing1201.

In the example ofFIG.12, the condition B for the scanning for 128 frames by TV2 (high-speed) scanning is the scanning method that minimizes charging amount, and the scanning method is displayed as the optimum condition with the longest interval between the measurement points that require static elimination. In the scanning method for the condition B, it is shown that the positive charging exceeding the allowable charging amount occurs at the time of measuring 40 points, and thus, the static elimination for every 40 measurement points is required to be performed.

Further, the tab706is configured so that a method for eliminating positive charging can be selected. Then, it is shown that in the scanning method for the condition A, the positive charging exceeding the allowable charging amount occurs at the time of measuring 10 points, and thus, the static elimination for every 10 measurement points is required to be performed. Further, it is shown that, in the scanning method for the condition C, the negative charging exceeding the allowable charging amount occurs at the time of measuring 5 points, and thus, the static elimination for every 5 measurement points is required to be performed.

The optimum conditions displayed may be only one condition or may be a plurality of conditions. When there are a plurality of optimum conditions, that the optimum conditions may be set so as to be selected by the operator, or the optimum conditions may be set so as to be automatically determined.

Summary of Second Embodiment

According to the second embodiment, the charging amount at the plurality of points (multi-points) on the test chip is calculated according to the plurality of types of scanning conditions by generating the S curve of each frame as in the first embodiment and the change in the charging amount with respect to the measurement point (refer toFIG.11) is obtained, and the static elimination timing, the optimum scanning conditions (the best conditions among the plurality of types of the scanning conditions), and the optimum static elimination method are output (are present to the operator). By doing so, it is possible to reduce the execution of unnecessary static elimination operations and optimize the measurement time.

(3) Third Embodiment

In the third embodiment, in addition to the charging measurement on the test chip in the second embodiment, a case where the charging measurement (multi-point measurement) is performed on the measurement chip used for the actual measurement will be described. Although not described in the present embodiment, the matters described in the first and second embodiments can be applied to the present embodiment unless there are special circumstances.

In the second embodiment, it has been described that the charging measurement is performed for each frame by a plurality of scanning methods using the test chip and the multi-point measurement is started after obtaining the optimum static elimination method and the static elimination timing. However, for example, in the case where the charging amount generated is distributed in the wafer surface, there is a possibility that a discrepancy may occur between the charging amount of the test chip and the charging amount of the measurement chip. Therefore, there is a possibility that it is difficult to accurately determine (or predict) the static elimination timing for only the test chip. In this case, there is a concern that, when the static elimination is insufficient, the magnification fluctuates due to charging, and when the static elimination is excessive, the measurement time becomes long.

Therefore, in the present embodiment, as an example, a case where it is predicted that the charging tendency is different only in the outer peripheral portion of the wafer will be described. The same system configuration as inFIG.8can be applied. As a measurement chip for performing the charging measurement, at least one chip on the outer peripheral portion of the wafer is designated and used. The optimum scanning method, the static elimination method, and the static elimination timing determined by the charging measurement are applied to at least one chip on the outer periphery of the wafer. The designated area is not limited to the outer peripheral portion of the wafer, and any area can be designated. For example, a chip included in the intermediate area or the inner peripheral (center) area of the wafer may be designated as a measurement point in addition to or instead of the outer peripheral portion of the wafer.

<Multi-Point Measurement Sequence or the Like>

FIG.13is a flowchart showing a process of performing charging measurement (multi-point measurement) on the measurement chip used for the actual measurement in addition to the charging measurement on the test chip according to the recipe. The charging measurement is performed on the measurement chip at the timing immediately after the measurement point alignment process (Step909) of the measurement chip inFIG.9, and the other sequences are almost the same as those inFIG.9. Therefore, the description ofFIG.13may be simplified, but the details are as described above.

(i) Step901and Step902

For example, the SEM control unit121reads the recipe from the memory123(Step901), and controls the stage control unit (not shown) so as to rotate the sample105loaded on the movable stage106and perform wafer alignment to calibrate the initial coordinates of the movable stage106(Step902).

(ii) Step1301

The sub-deflector control unit802executes measurement point alignment for aligning the relative positions of the primary electron beams102of the measurement point of the test chip registered by the operator and the measurement chips used for actual measurement.

(iii) Steps402to409

Under the preset initial conditions described later, the charging measurement is performed for each frame by a plurality of scanning methods with the test chip in the same manner as the operations from Step S402to Step S409inFIG.4. That is, the deflector control unit120sets the scanning conditions (Step402). The charging measurement on the measurement chip used for the actual measurement is executed in Steps1303and1304described later.

Next, the filter control unit110sets the energy filter voltage (Step403). Then, the deflector control unit120controls the deflector and scans the measurement point with the beam (Step404).

Further, the brightness calculation unit116calculates the gradation value of each frame from the obtained SEM image (Step405). Subsequently, the SEM control unit121repeatedly executes the processes from Step403to Step405in order to acquire the S curve until the energy filter voltage is changed to be a predetermined voltage (Step406). In addition, when the execution is repeated, the field of view is moved within the pattern of the same arrangement in order to suppress the influence of the charging caused by the scanning of the charging measurement itself (Step407).

Next, the brightness calculation unit116generates an S curve in each frame (Step408). Then, the SEM control unit121changes the scanning conditions and repeatedly executes the processes from Step403to Step408(Step409).

(iv) Step1302

The SEM control unit121determines whether the measurement at all the measurement points (all the measurement points specified by the operator) on the test chip is completed. When the measurement at all the measurement points is completed (Yes in Step1302), the process proceeds to Step906. When the measurement at all the measurement points is not completed (No in Step1302), the process proceeds to Step905.

(v) Step905

The SEM control unit121issues a command to the sub-deflector control unit802, the deflector control unit120, and the like so that the unprocessed measurement points (for example, the next measurement point when the processing order is specified in the recipe) among the set measurement points are set as processing targets. That is, the processes of Steps S1301and S402to S409are repeatedly executed for all the measurement points set in the recipe.

(vi) Step906

The Vs determination unit117obtains an S curve at each measurement point and each scanning condition in response to a command from the SEM control unit121and, after that, displays the charging measurement result on the display unit114. The method for displaying the charging measurement result will be described later.

(vii) Step907

The SEM control unit121sets the optimum scanning method and number of frames according to the obtained charging amount and charging code. In the present embodiment, the optimum scanning method denotes, for example, a scanning method in which the charging amount is minimized, a scanning method in which a desired charging code is obtained, a scanning method in which a desired static elimination method is effective, or the like. Further, the optimum number of frames may be, for example, set as the number of frames502for which charging measurement has been performed or may be set as the number of frames having an arbitrary charging amount.

(viii) Step908

The SEM control unit121sets the optimum static elimination method and the static elimination timing according to the obtained charging measurement result. In the present embodiment, the static elimination timing denotes, for example, a measurement point interval for executing the static elimination, a chip point interval for executing the static elimination, or the like.

(ix) Step909

In response to a command from the SEM control unit121, the sub-deflector control unit802operates the sub-deflector801to perform a multi-point measurement and executes the measurement point alignment for aligning the relative positions of the measurement point of the measurement chip registered by the operator (user) and the primary electron beam102.

(x) Step1303

In the above recipe, the SEM control unit121determines whether the actual measurement chip is set as the chip that executes the charging measurement in addition to the test chip. This setting will be described later.

When the actual measurement chip is set as the chip that executes the charging measurement (Yes in Step1303), the process proceeds to Step1304. When the actual measurement chip is not set as the chip that executes charging measurement (No in Step1303), the process proceeds to Step910.

(xi) Step1304

The SEM control unit121controls the sub-deflector control unit802, the deflector control unit120, the filter control unit110, the brightness calculation unit116, the Vs determination unit117, and the like with respect to the set actual measurement chip, and the charging measurement is executed in the order of Step1301, Step402to Step409, Step1302, and Step906to Step908to set the optimum measurement conditions.

The setting value of the optimum measurement condition obtained in Step1304may be different from the set value (static elimination method and static elimination timing) obtained in Step908. In that case, for example, the set value obtained by using the actual measurement chip is used for the case of measuring the location corresponding to the measurement point of the measurement chip, and the set value obtained from the test chip can be used for the case of measuring the other location.

(xii) Step910

In response to a command from the SEM control unit121, the deflector control unit120starts the multi-point measurement by using the scanning method and the number of frames set in Step907or Step1304. That is, the multi-point measurement is executed for the same location as the test chip or the location where the charging measurement is performed by the test chip and the actual measurement chip.

(xiii) Step911

The SEM control unit121executes the static elimination at predetermined measurement points at the static elimination method and static elimination timing set in Step908or Step908and Step1304.

(xiv) Step912

The SEM control unit121ends the multi-point measurement.

(xv) Step913

The SEM control unit121determines whether the measurement of all the measurement chips set in the recipe is completed. When the measurement of all the measurement chips set in the recipe is completed (Yes in Step913), the process proceeds to Step914. When the measurement of all the measurement chips set in the recipe is not (No in Step913), the process proceeds to Step909. That is, the processes of Step909, Step1303, Step1304, and Steps910to912are repeatedly executed until the measurement of all the measurement chips is completed.

(xv) Step914

The SEM control unit121ends the recipe process.

<Configuration Example of Charging Measurement Condition Setting Screen>

FIG.14is a diagram showing a configuration example of a screen displayed on the display unit114for setting a condition for performing the charging measurement set in Step402(FIG.13).

The charging measurement condition setting screen1400includes, as constituent items, for example, the setting unit505for performing the charging measurement such as the scanning type501, the number of frames502, the reference gradation value503, and the allowable charging amount504, a measurement points1001for performing the charging measurement, a setting unit1003for setting the measurement point interval1002and like when performing the charging measurement for each periodic point, and a setting unit1403for setting a chip type1401for which the charging measurement is performed, and the chip number1402for the case or the like where the charging measurement with the measurement chip is performed.

The setting unit505has the function described in the first embodiment. That is, the allowable charging amount504indicates a charging amount that serves as a threshold value for performing static elimination. The allowable charging amount is held as a parameter in the SEM control unit121based on the charging amount and the deflection amount of the primary electron beam102calculated from the energy of the primary electron beam102. Further, the operator can arbitrarily (freely) set the allowable charging amount. The relationship between the magnification fluctuation and the charging amount can be obtained in advance by measuring the pattern size and the charging amount.

In the configuration example ofFIG.14, the condition A which is the first charging measurement condition, the condition B which is the second charging measurement condition, or the condition C which is the third charging measurement condition is set on the charging measurement condition setting screen1400. The condition A indicates that the charging measurement is performed by scanning for 32 frames at a TV (medium speed (normal speed)) under the condition of the reference gradation value of 50% and the allowable charging amount of 1 V. The condition B indicates that charging measurement is performed by scanning for 128 frames at the TV2 (high speed) under the condition of a reference gradation value of 50% and an allowable charging amount of 1 V. The condition C indicates that the charging measurement is performed by scanning for 16 frames at the Slow (low speed) under the condition of a reference gradation value of 50% and an allowable charging amount of 1 V.

A portion of the setting unit505ofFIG.14may be deleted, or other conditions (for example, optical conditions, imaging magnification, coordinates, pixel sizes, or the like) may be added depending on the embodiment.

The measurement point setting unit1003has the function described in the second embodiment. That is, the operator can set the number of measurement points1001for performing the charging measurement. In the example ofFIG.14, performing the charging measurement at all measurement points is selected. In order to shorten the time required for the charging measurement, the charging measurement may be performed at each periodic point at an arbitrary measurement point interval1002.

The chip type setting unit1403is configured so that the chip type1401for performing the charging measurement can be set. In the example ofFIG.14, performing the charging measurement with the test chip and the charging measurement with the two chips of the actual measurement chips (1,1) and (1,9) is selected (refer to the item1402).

The screen (charging measurement result display screen) displayed on the display unit114in Step906ofFIG.13for displaying the charging measurement results for each measurement point in a plurality of scanning types can be configured in the same manner as the configuration example of the screen ofFIG.11. Further, the screen displaying the optimum scanning type701and number of frames702, the charging code703, the static elimination method704, and the static elimination timing1201displayed on the display unit114in Steps907and908ofFIG.9for measuring the pattern without the magnification fluctuation due to charging can be configured in the same manner as the configuration example ofFIG.12.

Summary of the Third Embodiment

According to the third embodiment, the charging amount at the plurality of points (multi-points) on the actual measurement chip as well as the test chip is calculated according to the plurality of types of scanning conditions by generating the S curve of the frame as in the first embodiment, and the change in the charging amount with respect to the measurement point (serving as the same characteristics as inFIG.11) is obtained, and the static elimination timing, the optimum scanning conditions (the best conditions among the plurality of types of the scanning conditions), and the optimum static elimination method are output (are present to the operator). By doing so, even when the charging is not uniformly generated in the wafer surface (for example, the charging distribution is different in the outer peripheral area, the intermediate area, and the inner peripheral (center) area of the wafer), the static elimination operation can be executed without excess or deficiency, and, thus, the measurement time can be optimized.

(3) Fourth Embodiment

A fourth embodiment discloses a modified example of the first embodiment (another configuration example of the SEM type length measurement system).

FIG.15is a diagram showing a configuration example of the SEM type length measurement system15according to the fourth embodiment. Instead of the energy filter109, the filter control unit110, and the Vf (filter voltage) calculation unit119in the SEM type length measurement system1shown inFIG.1, a spectrometer1501, a spectrometer control unit1502, and a spectrometer voltage calculation unit1503are mounted.

The spectrometer1501is an energy discriminator of a different type from the energy filter109, and is configured with two cylindrical electrodes. A voltage is applied between the outer electrode and the inner electrode from the spectrometer1501and the spectrometer control unit1502. The magnitude of the voltage applied to the inner/outer electrodes is calculated by the spectrometer voltage calculation unit1503. Herein, when it is assumed that the outer electrode has a negative voltage of −Vsp and the inner electrode has a positive voltage of +Vsp, the secondary electron108having specific energy passes through the spectrometer1501and is detected by the detector111. In this embodiment, a spectrometer using a cylindrical electrode will be described, but the effect of the present disclosure is not limited to the case of a cylindrical electrode. For example, the same effect can be obtained with a spherical type spectrometer or a spectrometer using a magnetic field. Further, the spectrometer1501may be floated by a voltage Voffset, a voltage of Voffset−Vsp may be applied to the outer electrode, and a voltage of Voffset+Vsp may be applied to the inner electrode.

FIG.16is a flowchart showing a charging amount measurement process by using the spectrometer1501. The charging measurement by using the spectrometer1501is almost the same as the sequence shown inFIG.4.

(i) Step1601

The SEM control unit121reads a preset initial condition (for example, set by the operator) from, for example, the memory123and starts the charging measurement.

(ii) Step1602

The SEM control unit121passes the scanning conditions to the deflector control unit120. Then, the deflector control unit120sets the received scanning conditions.

(iii) Step1603

The SEM control unit121passes the information on the spectrometer voltage value to the spectrometer control unit1502. Then, the spectrometer control unit1502sets the received spectrometer voltage value.

(iv) Step1604

The deflector control unit120controls the deflector104based on the scanning conditions and scans the sample105with the beam.

(v) Step1605

The image generation unit112generates an SEM image based on the secondary electron detected by the detector111and passes the SEM image to the SEM control unit121. The SEM control unit121stores the received SEM image in the image storage unit122. Then, the brightness calculation unit116reads out the SEM image from the image storage unit122and calculates the gradation value of each frame. The SEM control unit121may directly supply the SEM image to the brightness calculation unit116without storing the SEM image in the image storage unit122.

(vi) Step1606

The SEM control unit121determines where the measurement based on all the spectrometer conditions corresponding to the scanning conditions set at the present time has been completed (whether all the SEM image gradation values corresponding to the set spectrometer voltage values can be obtained under the scanning conditions). When it is determined that the measurement based on all the spectrometer conditions is completed (Yes in Step1606), the process proceeds to Step1608. When it is determined that the measurements based on all the spectrometer conditions are not completed (No in Step1606), the process proceeds to Step1607.

That is, in order to acquire the S curve, the SEM control unit121repeatedly executes the processes from Step1603to Step1605until the spectrometer voltage is changed to a predetermined voltage.

(vii) Step1607

The SEM control unit121instructs the deflector control unit120to move the field of view to another pattern in the pattern of the same arrangement in order to suppress the influence of the charging caused by the scanning of the charging measurement itself. According to the instruction, the deflector control unit120sets the scanning position at a location (same coordinates in the pattern) corresponding to the scanning location in the scanned pattern, which is another pattern in the same array. Then, at the newly set scanning position, the processes from Steps1603to1605are executed.

(viii) Step1608

The brightness calculation unit116generates a spectrum (S curve) (refer toFIG.17) in each frame. For example, the brightness calculation unit116acquires the detection signal amounts for a plurality of frames corresponding to the respective spectrometer set voltage values. Then, the brightness calculation unit116generates the S curve corresponding to each frame by plotting how the detection signal amount (normalized value) changes in each frame in response to each spectrometer set voltage value in the S-curve plane (horizontal axis is the spectrometer set voltage and vertical axis is the normalized detection signal amount).

(ix) Step1609

The SEM control unit121determines whether all the processes of the set scanning conditions are completed. When all the processes of the set scanning conditions are completed (Yes in Step1609), the process proceeds to Step1610. When all the processes of the set scanning conditions are not completed (No in Step1609), the process proceeds to Step1602, and the SEM control unit121instructs the deflector control unit120to change the scanning conditions. Then, the processes of Steps1603to1608are repeatedly executed.

(x) Step1610

The Vs determination unit117displays the charging measurement result on the display unit114after acquiring the S curve corresponding to the set predetermined scanning conditions. The method for displaying the charging measurement result will be described later.

(xi) Step1611

The SEM control unit121sets the optimum scanning method and number of frames according to the obtained charging amount and charging code.

(xii) Step1612

The SEM control unit121sets the optimum static elimination method and the static elimination timing according to the obtained charging amount and charging code. The display contents of Steps1611and1612are as shown inFIG.7.

<Calculation of Charging Amount>

FIG.17is a diagram showing a method for calculating the charging amount from the spectrum (S curve).FIG.17shows the spectrum (example) generated in Step1608. InFIG.17, the horizontal axis represents the voltage value applied to the spectrometer1501by the spectrometer control unit1502, and the vertical axis represents the detection signal amount of the detector111.

When the sample105is positively charged, the energy of the secondary electron108in the spectrometer1501decreases, so that the spectrum shifts to the left. On the other hand, when the sample105is negatively charged, the energy of the secondary electron108in the spectrometer1501increases, so that the spectrum shifts to the right.

The charging amount1703can be calculated by the difference between the reference spectrum1701and the spectrum1702at the n-th frame. In the present embodiment, the difference between the spectrum1701and the spectrum1702is shown so as to be the difference in the spectrometer voltage that is maximized as the detection signal amount, but the difference between the reference spectrum1701and the spectrum1702of the nth frame may be calculated by another method. For example, the shift amount may be calculated by using the result of differentiating the spectrum.

The charging amount obtained in the present embodiment can also be applied to the charging amount measurement according to the second and third embodiments.

Summary of Fourth Embodiment

According to the fourth embodiment, instead of the energy filter (high-pass filter) used in the first embodiment, a spectrometer (band pass filter) that allows only secondary electron having a specific energy different from that of the energy filter to pass through is used. By doing so, it is possible to detect secondary electrons that cannot be detected by the energy filter depending on the type of sample, and even in such a case, it is possible to accurately ascertain the charged state of the pattern resulting from irradiation of the electron beam. In addition, the calculated charging amount is compared with the set allowable charging amount, and it is confirmed at what frame scanning the allowable charging amount is exceeded. Accordingly, it is possible to derive the optimum static elimination timing. Further, since the polarity of charging of each frame can be known from the S curve, it is possible to know the optimum static elimination method.

(5) Other Embodiments

The function of each embodiment can also be realized by a program code of the software. In this case, a storage medium in which the program code is recorded is provided to the system or device, and the computer (or CPU or MPU) of the system or device reads out the program code stored in the storage medium. In this case, the program code itself read out from the storage medium realizes the function of the above-described embodiment, and thus, the program code itself and the storage medium storing the program code itself constitute the present disclosure. As examples of the storage medium for supplying such a program code, used are a flexible disk, a CD-ROM, a DVD-ROM, a hard disk, an optical disk, a magneto-optical disk, a CD-R, a magnetic tape, a non-volatile memory card, a ROM, and the like.

Further, the OS (operating system) or the like running on the computer may perform a portion or all of the actual processes based on the instruction of the program code, and the functions of the above-described embodiment may be realized by the processes. Further, after the program code read from the storage medium is written in the memory on the computer, the CPU of the computer or the like performs a portion or all of the actual processes based on the instruction of the program code, so that the functions of the above-described embodiment may be realized by the processes.

Further, by distributing the program code of the software that realizes the functions of the embodiment via the network, the program is stored in a storage means such as a hard disk or a memory of a system or a device or a storage medium such as a CD-RW or a CD-R and the computer (or CPU or MPU) of the system or device may read and execute the program code stored in the storage means or the storage medium at the time of use.

Finally, it should be understood that the processes and techniques described here are not essentially associated with any particular device and can be implemented with any suitable combination of components. In addition, various types of devices for general purpose can be used according to the teachings described herein. It may be found out it is useful to build a dedicated device to carry out the steps of the method described here. In addition, various inventions can be formed by appropriately combining the plurality of components disclosed in the embodiments. For example, some components may be removed from all the components shown in the embodiments. In addition, components across different embodiments may be combined as appropriate. The present disclosure has been described in connection with specific examples, but these are for illustration purposes only, not for limitation in all respects. Those skilled in the art will find that there are numerous combinations of hardware, software, and firmware suitable for implementing the present disclosure. For example, the described software can be implemented in a wide range of programs or scripting languages such as assembler, C/C++, perl, Shell, PHP, and Java (registered trade mark).

Further, in the above-described embodiment, the control lines and information lines are shown as necessary for explanation, and the product does not necessarily show all the control lines and information lines. All configurations may be interconnected.

REFERENCE SIGNS LIST

1,8,15: SEM type length measurement system (charged particle beam system)100,810,1510: SEM type length measurement device (charged particle beam device)200,820,1520: computer system101: electron source102: primary electron beam103: objective lens104: deflector105: sample (wafer)106: movable stage107: retarding control unit108: secondary electron109: energy filter110: filter control unit111: detector112: image generation unit113: contrast adjustment unit114: display unit115: focus evaluation value calculation unit116: brightness calculation unit117: filter characteristic voltage (Vs) determination unit118: objective lens control unit119: Vf (filter voltage) calculation unit120: deflector control unit121: SEM control unit122: image storage unit801: sub-deflector802: sub-deflector control unit1501: spectrometer1502: spectrometer control unit1503: spectrometer voltage calculation unit