Method for deriving feature quantities from a sample, adjustment method for adjusting a signal processing system, and measurement system.

Abstract

The present invention makes it possible to evaluate characteristics with high accuracy regardless of a temporal change in device condition, machine difference, or the like. To this end, proposed in the present disclosure is a method for deriving feature amounts of a sample on the basis of detection by means of a detector of charged particles obtained on the basis of irradiation of the sample with a beam, wherein the feature amounts corresponding to the amount of the charged particles emitted from the sample are derived by receiving a model which represents an association between output information about the detector and the feature amounts corresponding to the amount of the charged particles emitted from the sample, and by inputting the output information about the detector to the model (see FIG. 2).

Description

Technical Field

[0001] The present disclosure relates to a method for deriving a characteristic quantity of a sample, a method for adjusting an apparatus suitable for deriving a characteristic quantity of a sample, and a system. For example, the present disclosure relates to a method and a system for deriving a characteristic quantity based on detection of electrons obtained by irradiating a sample with a charged particle beam.

Background Art

[0002] An electron microscope, which is a type of charged particle beam apparatus, is an apparatus that detects secondary electrons and the like obtained by irradiating a sample with an electron beam using a detector. The electrons detected by the detector are converted into an electrical signal, and image formation and derivation of luminance information are performed based on the electrical signal. Patent Document 1 discloses calibrating a signal waveform output from a signal processing unit of a scanning electron microscope using characteristic data showing the relationship between a probe current and a gradation value prepared according to the gain and offset of the signal processing unit (see FIG. 12 of Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The output of a detector in an electron microscope, etc., is adjusted in gain and offset by an amplifier located after the detector output, and then becomes a brightness signal for an image, etc. Typically, the gain and offset are adjusted so that the overall brightness and contrast of the image are appropriate. On the other hand, there is a method for evaluating the electrical characteristics of a target element by evaluating the brightness of a specific element of a semiconductor device, or the amount of brightness fluctuation (see Patent Document 2). When evaluating the characteristics of a specific element based on brightness information in this way, if the gain and offset are adjusted to improve the overall brightness distribution and contrast of the image, the brightness of the element will change, making it difficult to properly evaluate its characteristics.

[0005] Furthermore, in order to stably measure electrical characteristics, it is desirable that when elements with the same characteristics are irradiated with a beam under the same conditions, the detector output will be the same even if the beam irradiation occurs at different timings or with different equipment. However, Patent Documents 1 and 2 do not mention how to adjust the detector output in this way or how to correct the detector output. In light of these circumstances, this disclosure proposes a technology that enables highly accurate characteristic evaluation regardless of changes in equipment conditions over time or differences between machines. [Means for solving the problem]

[0006] As one embodiment for achieving the above objective, this disclosure proposes a method for deriving feature quantities of a sample based on the detection of charged particles by a detector obtained based on beam irradiation of the sample, the method comprising receiving a model that shows the relationship between the output information of the detector and feature quantities corresponding to the amount of charged particles emitted from the sample, and inputting the output information of the detector into the model to derive feature quantities corresponding to the amount of charged particles emitted from the sample, and a system for realizing this method.

[0007] Furthermore, in another aspect for achieving the above objective, the present disclosure proposes an adjustment method for adjusting a signal processing system that processes the output signal of a detector that detects charged particles obtained by irradiating a sample with a beam, the method of receiving reference information relating beam conditions and detector output information, and adjusting the gain and offset of the signal processing system using the received reference information, and a system for realizing the method.

[0008] Further features relating to this disclosure will become apparent from the description herein and the accompanying drawings. Furthermore, aspects of this disclosure are achieved and realized by elements and various combinations of elements and the modes of the claims described herein in detail thereafter. The descriptions herein are typical examples only and do not limit in any way the claims or applications of this disclosure. [Effects of the Invention]

[0009] The technology disclosed herein makes it possible to stably acquire feature quantities that can quantitatively evaluate electrical characteristics and other properties. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows a schematic configuration example of an electron microscope 1, which is an example of a charged particle beam apparatus (charged particle beam system) common to each embodiment. [Figure 2] This flowchart illustrates the process of acquiring the secondary electron quantity of sample 1009 based on appropriate adjustment of the detector output gain and offset according to the first embodiment. [Figure 3] Figure 3 shows an example of a curve showing the change in the amount of secondary electrons with respect to the cutoff time of a pulsed electron beam irradiated onto sample 1009. [Figure 4] This is a flowchart illustrating the process for correcting machine differences between devices according to the second embodiment. [Figure 5]Figure 5 is a flowchart illustrating the relationship between electron beam quantity and output signal quantity (relationship information) described in Figure 4, as well as the details of the process for acquiring the target output signal quantity. [Figure 6] This flowchart illustrates the details of the gain and offset adjustment process for the second device shown in S0403 to S0405 of Figure 4. [Figure 7] This figure shows an example configuration of a measurement / inspection system in which multiple electron microscopes are connected to one or more computer systems 7004 via a wired or wireless network. [Figure 8] This figure shows the relationship between beam conditions and detector output. [Figure 9] This figure shows the relationship between the first relational equation 9001 for the first device and the second relational equation 9002 for the second device. [Modes for carrying out the invention]

[0011] In a charged particle beam apparatus, the amount of electron beam irradiation to a sample can be changed by setting, but variations occur due to the instability of the beam irradiation. Since the amount of charged particles emitted from the sample also changes when the beam irradiation fluctuates, it is necessary to take into account not only the detection signal amount and the state of the apparatus but also the amount of beam irradiation to the sample when deriving the amount of emitted charged particles. The following embodiment describes a method and system for deriving the accurate amount of emitted charged particles regardless of fluctuations in the beam irradiation amount, etc.

[0012] As a means of solving the above problems, in this embodiment, relationship information between the electron beam irradiation dose and the detection signal amount is obtained using a reference sample in which the amount of emitted electron particles is known in relation to the electron beam irradiation dose, and relationship information between the amount of emitted electron particles and the detection signal amount is derived. For example, if the relationship information between the amount of emitted electron particles and the detection signal amount changes due to instrument differences or changes over time, the signal processing device adjusts the gain and offset so that the changes cancel each other out. Subsequently, the amount of emitted electron particles of the sample to be inspected is derived from the relationship information between the amount of emitted electron particles and the detection signal amount and the detection signal amount of the sample to be inspected.

[0013] The effects caused by hardware changes (changes over time, changes in the device, fluctuations in the probe current) are acquired and corrected. A relational expression between the corrected amount of emitted charged particles and the detected signal amount is output, and the amount of emitted charged particles can be derived by combining the output relational expression and the data of the detected signal amount.

[0014] Hereinafter, a method for adjusting a charged particle beam apparatus and a charged particle beam apparatus will be described with reference to the accompanying drawings. In particular, a method that enables appropriate evaluation of the amount of charged particles emitted from a sample and the amount of charged particles detected by a detector regardless of mechanical differences between multiple devices or changes in the device over time, a computer-readable medium storing a program enabling the method, and a system will be described. The electron microscope described later is controlled by, for example, one or more computer systems.

[0015] (1) First Embodiment <Configuration Example of Charged Particle Beam Apparatus (Charged Particle Beam System)> The first embodiment discloses a method for acquiring the amount of secondary electrons of a test sample and evaluating the characteristics of the sample. In this embodiment, the amount of secondary electrons of the test sample is acquired, but the backscattered electrons generated by irradiating an electron beam may be acquired, or the amount of electrons in which secondary electrons and backscattered electrons are mixed may be acquired.

[0016] FIG. 1 is a diagram showing a schematic configuration example of an electron microscope 1, which is an example of a charged particle beam apparatus (charged particle beam system) common to each embodiment. The electron microscope 1 is an apparatus that generates an observation image by irradiating an electron beam onto a sample. The electron microscope 1 includes a column unit 1000, an image formation system 1100, a computer system 1200, a control system 1300, an input device 1401, and an output device 1402.

[0017] Inside the lens barrel 1000, an electron gun 1002 that generates an electron beam 1001 is disposed. The electron beam 1001 is accelerated by an acceleration voltage applied to an acceleration electrode 1003 and focused by a condenser lens 1004. The electron beam 1001 that has passed through the condenser lens 1004 is focused onto a sample 1009 by an objective lens 1008. The electron beam 1001 is scanned over the sample 1009 by a deflector 1007. The deflector 1007 is configured to scan the electron beam 1001 one-dimensionally or two-dimensionally. Also, in order to irradiate a desired semiconductor element (such as a plug) or coordinate with a pinpoint beam, beam deflection by the deflector 1007 may be performed. By irradiating the sample 1009 with the electron beam 1001, charged particles such as secondary electrons and backscattered electrons (signal electrons 1005) are emitted from the sample 1009, and the charged particles are detected by a detector 1006. The detector 1006 outputs a detection signal representing the intensity of the signal electrons 1005.

[0018] The stage 1010 holds the sample 1009 and has a role of moving an observation region in the sample 1009 under the electron beam 1001. A shutter 1011 is installed inside the lens barrel 1000, whereby the electron beam 1001 can be prevented from irradiating the sample 1009. The shutter 1011 may block the electron beam 1001 by inserting an obstacle on the path of the electron beam 1001, or may block the electron beam 1001 by deflecting the electron beam 1001 using at least one of an electric field or a magnetic field and retreating it from the sample 1009.

[0019] In addition, in order to measure the beam current (Ip) of the electron beam 1001, a Faraday cup (not shown) may be disposed near the orbit of the electron beam 1001, and the beam current can be measured by making the beam enter the Faraday cup. The Faraday cup is arranged, for example, near the crossover of the electron beam, and is configured to measure the beam current by deflecting the beam toward the Faraday cup by a deflector as needed.

[0020] The image forming system 1100 includes a signal conversion unit 1101 that converts signal electrons 1005 into electrical signals, etc., and a signal amplification unit 1102 that amplifies the converted signals. The amplification gain of the signal amplification unit 1102 is adjusted by the action of an amplification gain adjustment unit based on an instruction value specified by an amplification gain instruction unit 1103. When not forming an image, the image forming system 1100 may also be used for processes such as selectively amplifying the luminance signal of a specific element. For this reason, the image forming system 1100 may also be referred to as a signal processing system in this specification.

[0021] The offset of the signal amplification unit 1102 is adjusted by the offset adjustment unit 1105. Typical examples of the signal conversion unit 1101 include scintillators, semiconductor detectors, silicon photomultipliers, and MCPs (microchannel plates), but It is not limited to these. The signal amplification unit 1102 is determined by the type of signal conversion unit 1101. For example, if a scintillator is used as the signal conversion unit 1101, a photomultiplier tube is used as the signal amplification unit 1102. Also, if a semiconductor detector is used as the signal conversion unit 1101, a preamplifier circuit is used as the signal amplification unit 1102. For solid-state electron multiplier tubes and MCPs, the signal conversion unit 1101 may also include the signal amplification unit 1102. The indicated value specified by the amplification gain indicator unit 1103 does not necessarily coincide with the amplification gain. For example, for a photomultiplier tube, the indicated value is the voltage value applied to the photomultiplier tube, and the amplification gain has the characteristic of increasing exponentially with respect to the applied voltage.

[0022] The computer system 1200 comprises a storage 1201, a processor 1202, and a memory 1203. The storage 1201 and the memory 1203 store data used by the processor 1202. The processor 1202 acquires the detection signal from the detector 1006 from the image forming system 1100 and uses it to generate an observation image of the sample 1009. The memory 1203 built into the computer system 1200 is a computer-readable medium, a non-temporary computer-readable medium that stores program instructions executable on the computer system 1200. The computer-readable medium may be a storage medium such as a magnetic or optical disk, magnetic tape, or any other suitable non-temporary computer-readable medium known in the art. The method implemented in the computer may include any step of any method described herein.

[0023] The control system 1300 includes an electronic optical system control unit 1301 that controls the lens barrel 1000, and a stage control unit 1302 that controls the operation of the stage 1010.

[0024] In this embodiment, an electron microscope 1 is shown as an example of a charged particle beam apparatus, but it is not limited to this, and other charged particle beam apparatuses, such as a focused ion beam apparatus, may be used as an image forming apparatus or a brightness information acquisition apparatus.

[0025] Electron microscope 1 is a device that displays a light and dark image on a display device corresponding to the amount of secondary electrons emitted from a sample 1009 by irradiation with an electron beam 1001. Normally, the gain and offset of the amplifier that amplifies the detector output are adjusted to improve the appearance (image quality) of the image. In devices used for measuring and inspecting semiconductor devices, the gain and offset are adjusted, and measurements and inspections are performed using images with clear contrast. For example, CD-SEM (Critical Dimension Scanning Electron Microscope), which measures the line width of patterns, etc., uses gain and offset adjustments. This device enables highly accurate measurements by adjusting the offset to highlight the brightness of the areas corresponding to the pattern edges and measuring the distance between brightness peaks.

[0026] As described above, in charged particle beam devices that form images, gain and offset adjustments are usually made to prioritize the appearance (quality) of the image. On the other hand, if the gain and offset are adjusted to emphasize pattern edges, the detector output will change depending on the shape of the sample within the irradiation area, even for the same element (object to be measured or inspected).

[0027] When evaluating the electrical properties, material properties, or shape of a semiconductor device by evaluating the amount of charged particles (secondary electrons) emitted from sample 1009, if the relationship between the amount of charged particles detected by detector 1006 and the detector output is unstable, the amount of charged particles obtained will differ even when the same sample is irradiated with the beam under the same conditions, making it impossible to properly evaluate its properties.

[0028] The following describes a method and system that enables highly accurate characterization by appropriately maintaining the relationship between the amount of charged particles emitted from the sample (or the amount detected by the detector) and the detector output, regardless of instrument differences or changes over time.

[0029] <Analysis of the electrical properties of the sample> Figure 2 is a flowchart illustrating the process of obtaining the secondary electron quantity of sample 1009 based on appropriate adjustment of the detector output gain and offset according to the first embodiment.

[0030] (i)S0201 The user (operator) prepares a reference sample in which the amount of secondary electrons emitted by irradiation with electron beam 1001 is known. This reference sample may be a calibration sample in which the amount of secondary electrons relative to the electron beam dose is known, as detected by detector 1006, or a calibration sample in which the ratio of electron beam irradiation dose to secondary electron dose is known.

[0031] More specifically, for example, a sample (reference sample) in which the relationship between the beam current (Ip) and the secondary electron quantity (Ise) (γ in equation (1)) is known is prepared, and this sample is introduced into the vacuum chamber, which is the sample chamber of the electron microscope 1. Such a calibration sample may also be placed in advance on the stage inside the sample chamber. Ise = γ × Ip ··· (1)

[0032] (ii) S0202 The computer system 1200 controls the electron microscope 1 in response to an instruction to acquire a detection signal (input by the user), irradiates a reference sample with the electron beam 1001, and acquires the amount of detection signal. The acquisition of the detection signal may be the brightness value or brightness histogram of an image generated using the detection signal, or it may be waveform data instead of the signal amount. If the amount of detection signal is defined as brightness (GL: Gray Level), the computer system 1200 acquires the brightness (GL1, GL2) when the beam is irradiated under at least two conditions (Ip1, Ip2), for example.

[0033] (iii) S0203 The computer system 1200 derives relationship information between beam conditions and detected signal quantity based on the information acquired by S0202 (acquired information). Specifically, the computer system 1200 derives relationship information between the obtained luminance information and beam quantity. For example, the computer system 1200 obtains coefficients such as α and β from the relationship equation (2) below by solving simultaneous equations or regression equations. Note that the beam conditions used to acquire the relationship information may be three or more conditions, and may include conditions where the beam is not irradiated (GL when Ip=0). GL = α × Ip + β ... (2)

[0034] (iv)S0204 The computer system 1200 derives the secondary electron quantity and the detected signal quantity (Ise-GL relationship information) based on the relationship information between the beam quantity and the detected signal quantity obtained as described above (e.g., Ip-GL relationship information) and the relationship information between the beam quantity and the secondary electron quantity of the reference sample (e.g., Ip-Ise relationship information). For example, the Ise-GL relationship information is expressed as shown in equation (3). Ise = γ(GL-β) / α ··· (3)

[0035] This completes the process for deriving the calibration information for the device. The process of using this calibration information to measure and inspect the actual target will be explained in sections S0205 to S0208.

[0036] (v)S0205 The computer system 1200 controls the electron microscope 1 and irradiates a predetermined target (e.g., region or area) on the sample 1009 introduced into the sample chamber with a beam. The electron beam conditions at this time can be any amount of current and irradiation time.

[0037] (vi)S0206 The computer system 1200 acquires the detection signal amount (GL_inspection) under the electron beam conditions in S0205. By setting the amplification gain of the amplification gain adjustment unit 1104 and the offset amount of the offset adjustment unit 1105 to be the same as in S0203 (the same as the process for deriving calibration information), calibration based on the above calibration information becomes possible.

[0038] (vii)S0207 Computer system 1200 obtained GL_inspection in S0206 Ise is derived by substituting this into, for example, GL in equation (3). The computer system 1200 stores the above Ise-GL relationship information for each device condition, such as the acceleration voltage of the electron beam, and reads the relationship information corresponding to the device condition from memory 1203 to derive Ise.

[0039] (viii)S0208 The computer system 1200 derives the target characteristics from the derived Ise. For example, by irradiating the sample 1009 with a pulsed beam and gradually increasing the non-irradiation time (cutoff time), the charged state of the sample 1009 can be changed, and the electrical characteristics of the target can be evaluated by obtaining the curve of change in the signal amount obtained at that time.

[0040] Figure 3 shows an example of a curve illustrating the change in the amount of secondary electrons with respect to the cutoff time of a pulsed electron beam irradiating sample 1009. The pulsed electron beam is a pulsed version of the electron beam 1001 emitted from the electron gun 1002. The cutoff time refers to the time between pulsed electron beam irradiations. By fitting the amount of secondary electrons, which changes with the cutoff time, to the simulation results, the physical quantities of the electrical properties can be derived. Regarding the characterization of the sample, it is possible to measure and derive not only electrical properties, but also material, structure, and shape.

[0041] Alternatively, it is conceivable to store information relating Ise to sample shape (such as hole depth) in advance and estimate the sample shape by substituting Ise into this information. Another approach is to create a database showing the relationship between Ise and material information, and output material information by inputting Ise into this database.

[0042] In the first embodiment, characterization is performed based on the amount of secondary electrons that directly indicates the characteristics of the sample, rather than on information processed within the image forming system 1100, such as brightness information. Therefore, stable measurement and inspection results can be obtained regardless of differences between devices or changes in device conditions over time.

[0043] In the first embodiment, a reference sample was used to derive information on the relationship between the beam quantity and the detected signal quantity. However, this is not the only way to do so. For example, instead of using a reference sample, a voltage (Vr) higher than the beam acceleration voltage (Vacc) is applied to the sample or stage (|Vr|>|Vacc|), and the relationship between the beam quantity and the detected signal quantity is derived based on the amount of mirror electrons reflected without reaching the sample.

[0044] The relationship information between Ise and GL derived through the process illustrated in Figure 2 is stored in the memory 1203 of the computer system 1200 and used for subsequent inspection or measurement. The computer system 1200 derives relationship information between the secondary electron quantity (Ise) and the detected signal quantity (GL) using a reference sample, and derives at least one of the following from this relationship information and the detected signal quantity obtained from the sample to be measured or inspected: secondary electron signal quantity, electrical properties, material information, and shape information in the depth direction (Z direction (beam irradiation direction)).

[0045] Here, electrical characteristics refer to, for example, the resistance and capacitance of elements contained in a semiconductor device. By pre-storing information relating Ise to resistance and capacitance in memory 1203, the processor 1202 can derive information relating resistance and capacitance based on the input (received) of this related information and the derived Ise. Alternatively, information relating material type to Ise may be pre-storing in memory 1203, and the processor 1202 may derive information relating to material type based on the input of this related information and the derived Ise.

[0046] Furthermore, some secondary electrons emitted from the bottom of deep holes and grooves collide with the side walls of these holes and grooves. The amount of these colliding secondary electrons increases as the depth of the hole or groove increases. Therefore, by pre-storing information on the relationship between the depth of the hole or groove and the amount of secondary electrons emitted in memory 1203, etc., and substituting Ise into this relationship information, the dimensions of the deep hole or groove in the Z direction can be derived.

[0047] In the first embodiment, the Ise-GL related information is described as a mathematical model, for example, as defined in equation (3). However, it may also be a trained model that has been trained by machine learning. This model may take, for example, the output information of the detector 1006 (such as the signal intensity or brightness of a specific pixel) as input and output feature quantities corresponding to the amount of charged particles emitted, such as the amount of electrons emitted from the sample 1009, or the amount of electrons emitted from the sample 1009 and detected by the detector 1006. Alternatively, it may be a model that outputs feature quantities of the sample, such as electrical characteristics, that have been appropriately corrected based on the Ise-GL related information.

[0048] (2) Second embodiment In the first embodiment, the relationship between the secondary electron quantity (e.g., Ise) and the detection signal quantity (e.g., GL) when inspecting a test sample was explained, and the secondary electron quantity was obtained from the detection signal quantity of the test sample. However, when analyzing the characteristics of a sample with multiple devices, the relationship between the secondary electron quantity (Ise) and the detection signal quantity (GL) differs for each device, so the detection signal quantity may saturate under specific electron beam conditions, and the desired secondary electron quantity may not be obtained. In the second embodiment, a method for aligning the relationship between the secondary electron quantity, which is the input to the detector, and the detection signal quantity, which is the output to the detector, across multiple devices is explained.

[0049] <Example of inspection system configuration> Figure 7 shows an example configuration of a measurement / inspection system in which multiple electron microscopes are connected to one or more computer systems 7004 via a wired or wireless network. A non-temporary computer-readable medium 7002 contains program instructions 7003 that can be executed on the computer system 7004. The computer system 7004 processes the output information from electron microscopes 1 and 7001 according to the program instructions 7003 and transmits the necessary information to electron microscopes 1 and 7001 according to the program instructions 7003. The method performed by the computer may include any step(s) of any(s) of any(s) methods described herein.

[0050] <Correction process for differences between devices> Figure 4 is a flowchart illustrating the process for correcting differences between devices according to the second embodiment. In this embodiment, the process of adjusting the gain and offset so that the change in the detected signal amount matches the change in beam conditions is described. When characterizing a sample using luminance information, it is desirable that the detected signal amount is the same when the beam is irradiated onto the target under the same beam conditions, and that the change in the detected signal amount in response to changes in characteristics is also the same. By performing the adjustments illustrated in Figure 4, it becomes possible to adjust the device to be suitable for characterization based on luminance measurement.

[0051] (i)S0401 The computer system 7004 acquires characteristic information of electron microscope 1 (first device). Alternatively, the processing described later may be performed by a computer system (not shown) installed in electron microscope 7001 (second device) instead of computer system 7004.

[0052] To acquire characteristic information, the user (operator) first introduces a reference sample into the electron microscope 1. Then, the reference sample is irradiated with an electron beam 1001. Signal electrons 1005 emitted from the reference sample by the beam irradiation are detected by the detector 1006, amplified by the signal amplification unit 1102 via the signal conversion unit 1101, and added by the offset adjustment unit 1105 to obtain the output signal quantity.

[0053] Characteristic information is, for example, a function that shows the change in detector output (GL) when the beam conditions (e.g., beam current) are changed. In this case, characteristic information of the output signal amount can be obtained by acquiring the output signal amount (GL) while changing the electron beam amount (Ip) and the instruction value (gain value) specified by the amplification gain instruction unit 1103. In this case, the computer system 7004, etc., may derive the characteristic information by, for example, finding a regression line from the three-dimensional space of Ip, gain value, and GL.

[0054] In this embodiment, characteristic information of the output signal amount was obtained when the electron beam amount and the amplification gain indicator unit 1103 were changed. However, characteristic information may also be derived based on the output signal amount (GL) when other parameters are changed, such as the set acceleration voltage by the electron optical system control unit 1301, the offset amount of the offset adjustment unit 1105, and other adjustment values ​​(adjustment amounts) by the control system 1300.

[0055] (ii) S0402 The computer system 7004 obtains a first relational expression between the electron beam quantity (Ip) and the output signal (GL) from the first device (for example, a function (Ip-GL characteristic) with IP as the independent variable and GL as the dependent variable), and a first target output signal quantity (GL_goal).

[0056] The Ip-GL characteristics represent the relationship between beam conditions and detector output information. The first relation is expressed, for example, as shown in Figure 8. The first target output signal quantity is the detector output information for the first device at a certain time and under certain beam conditions (Ip_goal). Note that the first relation and the first target The method for obtaining the output signal level will be described later.

[0057] (iii) S0403 The computer system 7004 receives characteristic information (Ip) of the second device (electron microscope 7001). -GL characteristics are acquired. The method for acquiring the characteristic information of the second device is the same as the method for acquiring the characteristic information of the first device. It appears that... Here, Figure 9 shows the relationship between the first relational equation 9001 for the first device and the second relational equation 9002 for the second device. From Figure 9, it can be seen that even if the beam condition, which is one of the device conditions, is set to Ip_goal in the second device, the output signal amount does not become GL_goal. In other words, even if the beam condition is the same, the output signal amount may differ depending on the device.

[0058] Therefore, in the second embodiment, the image forming system of the second device is adjusted so that the output signal amount is the same across multiple devices under certain device conditions, and so that the change in the output signal amount due to a change in device conditions is the same.

[0059] (iv)S0404 The computer system 7004 enables the image forming system of the electron microscope 7001 to acquire the first target output signal amount (GL_goal) in the second device (electron microscope 7001). Then adjust the gain and offset. The method for adjusting the gain and offset will be described later.

[0060] (v)S0405 The computer system 7004 acquires a second relational expression (Ip-GL characteristic) between the electron beam amount and the output signal amount based on the adjusted gain and offset, and stores this information as equipment conditions in the computer-readable medium 7002. The method for acquiring the second relational expression may be to calculate it by adding an offset amount corrected for the difference between the electron beam amount when the first relational expression is acquired and the electron beam amount when the second relational expression is acquired, or it may be calculated from the output signal amount when the electron beam is interrupted.

[0061] Furthermore, if the relationship between the beam conditions (such as Ip) of the reference sample and the amount of secondary electrons emitted is known, the computer system 7004 can derive the relationship between the amount of secondary electrons and the output signal, as shown in equation (3) above.

[0062] <Details of the process for acquiring related information and target output signal amount> Figure 5 is a flowchart illustrating the details of the process for acquiring the relationship between electron beam quantity and output signal quantity (relationship information) and the target output signal quantity, as explained in Figure 4. The following describes each step in Figure 5. Here, we will mainly explain the specific processing details of S0401 and S0402, as exemplified in Figure 4.

[0063] (i)S0501 When the user (operator) loads the first inspection sample into the first device (electron microscope 1) and instructs the system to start processing, the computer system 7004 activates the control system 1300 and other components to prepare for the start of processing. Here, the first inspection sample is, for example, the sample to be actually measured or inspected.

[0064] (ii) S0502 The computer system 7004 sets the optical conditions for acquiring an image of the first sample.

[0065] (iii) S0503 The computer system 7004 acquires characteristic information (Ip-GL characteristic information) of the first device. The Ip-GL characteristic information is obtained by deriving at least the slope (α1) and intercept (β1) based on two or more Ips (Ip_1 and Ip_2 in the example of Figure 8) and corresponding GLs (GL_1 and GL_2), as illustrated in Figure 8. Here, the slope is the rate of change between the beam conditions and the detector output information.

[0066] (iv)S0504 The computer system 7004 acquires the measured value of the electron beam amount irradiated onto the sample. The electron beam amount can be measured by actually measuring the beam current using, for example, the Faraday cup described above. Furthermore, the computer system 7004 derives the difference ΔIp between the set value Ip_s and the measured value Ip_a of the beam current, and this can be used as a correction value when acquiring characteristic information, which will be described later.

[0067] (v)S0505 The computer system 7004 moves the electron beam irradiation position to the region of interest of the first sample (e.g., a plug that conducts to an element whose electrical properties are to be evaluated) and determines the first gain and first offset. The gain and offset are adjusted, for example, by adjusting the gain so that the contrast of the plug is clear and adjusting the offset so that the brightness of the plug is appropriate. The gain and offset may be set by the user or may be those that are automatically set on the computer system 7004.

[0068] (vi)S0506 The computer system 7004 derives the first target output signal amount (GL_goal) from the characteristic information of the first device (Ip-GL characteristic information) and the first probe current amount (Ip_goal).

[0069] (vii)S0507 The computer system 7004, for example, acquires (calculates) relational information (relational expression) shown in the following equation (4) and stores it in the computer-readable medium 7002. GL = α1 × Ip + β1 ... (4)

[0070] Equation (4) is a relational expression that includes a coefficient (α1) corresponding to the gain when the beam is irradiated onto the first test sample, and a constant (β1) corresponding to the offset. The relational expression shown in equation (4) is obtained by deriving the slope (α1) and intercept (β1) from at least two beam current values ​​(Ip_1, Ip_2) and their corresponding brightness information (GL_1, GL_2), as illustrated in Figure 8. It is also possible to include a state where the beam current is zero (Ip_0). The computer system 7004 can obtain the first relation 8001 by solving simultaneous equations or regression equations.

[0071] (viii)S0508 The computer system 7004 decides whether or not to update the characteristic information acquired before executing the flowchart process shown in Figure 5 with newly acquired characteristic information (including characteristic lines or characteristic curves). The decision to update or not may be based on user selection using a GUI (not shown), for example. More specifically, a GUI that allows selection of update cycle, update time, etc., may be provided, and the computer system may perform the update process when the time set by the selection is reached. Updates may also be performed in conjunction with updates to the recipe, which is the operating program for running the electron microscope, or when switching the sample to be measured. Furthermore, the system may monitor the trend of output results such as electrical characteristics and perform updates when there are sudden fluctuations.

[0072] <Details of the process for adjusting the gain and offset of the second device> Figure 6 is a flowchart illustrating the details of the gain and offset adjustment process for the second device (electron microscope 7001) shown in S0403 to S0405 of Figure 4.

[0073] (i)S0601 When the user (operator) loads the second test sample into the second device (electron microscope 7001) and instructs the system to start processing, the computer system 7004 activates the control system 1300 and other components to prepare for processing. Here, the second test sample can be the same as, or of the same quality as, the first test sample introduced into the first device.

[0074] (ii) S0602 The computer system 7004 sets the optical conditions for acquiring an image of the second inspection sample with the second device (electron microscope 7001).

[0075] (iii) S0603 The computer system 7004 acquires characteristic information (Ip-GL characteristic information) of the second device (electron microscope 7001). The reference sample used when acquiring the characteristic information of the second device may be the first reference sample, or another sample equivalent to (same material as) the first reference sample may be used. For example, in order to derive relational information of the second device (electron microscope 7001), the computer system 7004 receives at least two beam current values ​​(Ip_1, Ip_2) and corresponding brightness information (GL_1', GL_2') from the second device (electron microscope 7001), as illustrated in Figure 9, and determines its slope (α2) and intercept (β2). The second relational information can be defined, for example, as shown in equation (5), and can be expressed as the second relational equation 9002, as illustrated in Figure 9. GL = α² × Ip + β² ... (5)

[0076] (iv)S0604 The computer system 7004 acquires measured data of the electron beam quantity in the second device (electron microscope 7001). For example, the electron beam quantity can be measured using a Faraday cup installed inside the electron microscope 7001.

[0077] (v)S0605 The computer system 7004 calculates the variation (ΔIp) in electron beam dose. This variation can be calculated, for example, by determining the difference between the set value and the measured value, or by determining the difference in beam dose between multiple devices when the same set value is applied.

[0078] (vi)S0606 The computer system 7004, for example, reads the first relational expression (Ip-GL characteristics) from the computer-readable medium 7002 and compares it with the second relational expression (relationship between electron beam amount and output signal amount due to adjusted gain and offset: Ip-GL characteristics) to derive the target output signal amount. The target output signal amount is, for example, the GL corresponding to Ip_goal + ΔIp. (If the variation is zero, it is GL_goal in Figure 9.)

[0079] (vii)S0607 The computer system 7004 derives the gain adjustment amount based on the target output signal amount (or difference), the first relation, and the second relation.

[0080] Specifically, the computer system 7004, or the computer system mounted on the electron microscope 7001, derives the gain amount, for example, by matching the slope (α) of the Ip-GL characteristic in the second relational equation 9002 with that of the first relational equation 8001. The computer system 7004 can also determine the difference in slope (gain adjustment amount) by solving simultaneous equations or regression equations, as described in the first embodiment.

[0081] (viii)S0608 The computer system 7004, or the computer system mounted on the electron microscope 7001, uses the first relation and the second relation Ip_goal+ΔIp (specific beam conditions) to calculate The difference in the corresponding GL (ΔG in Figure 9 if the variation is zero) is derived. Then, the computer system 7004, etc., derives an offset (bias) amount so that ΔG is zero or approaches zero.

[0082] (ix)S0609 The computer system mounted on the electron microscope 7001 reads the derived gain and offset amounts and adjusts the gain and offset of the detector output amplifier.

[0083] (3) Third Embodiment In the second embodiment, adjustment of gain and offset was described to obtain the same detection signal between different devices. Similar adjustments may be used to adjust for variations in the detection signal at different time points in the same device. In the second embodiment, the first device can be read as the first time point of the same device, and the second device as the second time point of the same device.

[0084] Furthermore, the timing at which the computer system 1200 acquires characteristic information may be automatically acquired at typical time intervals in which the characteristic information changes over time, or it may be acquired at any time chosen by the user.

[0085] (4) Fourth Embodiment In the first to third embodiments, examples were described in which the apparatus was calibrated using a reference sample (or standard sample) in which the beam current Ip and the amount of secondary electrons emitted from the sample when irradiated with the beam of said beam current are known.

[0086] On the other hand, the amount of secondary electrons emitted changes not only with the beam current Ip, but also with other beam conditions, such as the energy of electron beam 1001 reaching sample 1009. Therefore, it is desirable to use a sample for which the relationship between beam conditions, including conditions other than beam current, and the amount of secondary electrons is known as the reference sample.

[0087] If the relationship between certain beam conditions and the secondary electron quantity is known, it is also possible to extract information about the relationship between beam conditions and secondary electron quantity by plotting the change in detector output (GL) when certain beam conditions are changed and deriving the relationship equation.

[0088] Furthermore, the signal electrons (secondary electrons) 1005 emitted from sample 1009 include some that do not reach the detector 1006 after being emitted, such as by colliding with structures within the electron microscope 1. The amount of these undetected electrons varies depending on the arrangement conditions of the structures within the electron microscope 1. For this reason, a reference sample may be used in which the relationship between beam conditions and the amount of secondary electrons (the number of electrons incident on the detector) is known for each structure and type of apparatus.

[0089] Furthermore, when irradiated with electron beam 1001, the ratio of secondary electrons emitted from the irradiated area to the amount of incident electrons (secondary electron emission efficiency δ) depends on the type of material. Therefore, a sample with a known secondary electron emission efficiency δ may be used as a reference sample. The reference sample can be any type of sample, as long as the parameters related to beam conditions and emitted electron quantity are known.

[0090] (5) Others The functions disclosed in each of the embodiments described above can also be realized by software program code. In this case, a storage medium containing the program code is provided to a system or device, and the computer (or CPU or MPU) of that system or device reads the program code stored in the storage medium. In this case, the program code read from the storage medium itself realizes the functions of the embodiments described above, and the program code itself and the storage medium that stores it constitute the present disclosure. Examples of storage media used to supply such program code include flexible disks, CD-ROMs, DVD-ROMs, hard disks, optical disks, magneto-optical disks, CD-Rs, magnetic tapes, non-volatile memory cards, ROMs, and the like.

[0091] Furthermore, based on the instructions in the program code, the operating system (OS) running on the computer may perform some or all of the actual processing, thereby realizing the functions of the embodiment described above. In addition, after the program code read from the storage medium is written to the computer's memory, the computer's CPU may perform some or all of the actual processing based on the instructions in the program code, thereby realizing the functions of the embodiment described above.

[0092] Furthermore, the program code for the software that realizes the functions of each embodiment may be distributed via a network and stored in a storage means such as a hard disk or memory of the system or device, or in a storage medium such as a CD-RW or CD-R, so that when in use the system or device's computer (or CPU or MPU) reads and executes the program code stored in the storage means or storage medium.

[0093] The processes and techniques described herein are not inherently related to any specific device and can be implemented by combining the components. Various types of general-purpose devices can also be added. Dedicated devices may be constructed to perform the functions of each embodiment. Furthermore, various functions can be formed by appropriately combining the multiple components disclosed in each embodiment. For example, some components may be removed from all the components shown in each embodiment, or components from different embodiments may be appropriately combined.

[0094] This disclosure describes specific embodiments, which are for illustrative purposes (to understand the technology of this disclosure) and not for limitation in any respect. A person with ordinary skill in the art will understand that there are many combinations of hardware, software, and firmware suitable for implementing the technology of this disclosure. For example, the described software can be implemented in a wide range of programming or scripting languages, such as assembler, C / C++, Perl, Shell, PHP, and Java®.

[0095] Furthermore, in the embodiments described above, the control lines and information lines shown are those deemed necessary for illustrative purposes, and not all control lines and information lines are necessarily shown in the actual product. All components may be interconnected.

[0096] In addition, any person with ordinary skill in the art can see from the consideration of each embodiment that other implementations of this disclosure may be apparent. The specification and examples are typical, and the scope and spirit of the art of this disclosure are shown in the subsequent claims. [Explanation of Symbols]

[0097] 1,7001 electron microscope 1000 Telescope Tube Section 1001 Electron beam 1002 Electronic Gun 1003 Accelerating electrode 1004 Condenser Lens 1005 Signal Electronics 1006 Detector 1007 Deflector 1008 Objective lens 1009 samples 1010 Stages 1011 Circuit breaker 1100 Image Forming System 1101 Signal conversion unit 1102 Signal Amplification Section 1103 Amplification Gain Indicator 1104 Amplification Gain Adjustment Section 1105 Offset adjustment section 1200, 7004 Computer Systems 1201 Storage 1202 processors 1203 memory 1300 Control System 1301 Electron Optical System Control Unit 1302 Stage Control Unit 1401 Input device 1402 Output device 7002 Computer-readable media

Claims

1. A feature derivation method for a sample, in which a computer system derives feature quantities of the sample based on the output of a detector that detects charged particles obtained by irradiating the sample with a beam, The computer system acquires a model showing the relationship between the output information of the detector and a feature quantity corresponding to the amount of charged particles emitted from the sample. The computer system derives a feature quantity corresponding to the amount of charged particles emitted from the sample by inputting the output information of the detector into the model, Includes, The model is defined by relational information representing the relationship between the detector output information and the feature quantity, based on the detector output information acquired under at least two different beam irradiation conditions. Feature derivation method.

2. A method for deriving feature quantities of a sample in a computer system based on the output of a detector that detects charged particles obtained by irradiating the sample with a beam, The computer system acquires a model showing the relationship between the output information of the detector and a feature quantity corresponding to the amount of charged particles emitted from the sample. The computer system derives a feature quantity corresponding to the amount of charged particles emitted from the sample by inputting the output information of the detector into the model, Includes, The model is a feature quantity derivation method in which relational information is derived based on the output of a detector when a beam is irradiated onto a sample, the relationship between the beam irradiation conditions for the sample and the amount of charged particles emitted from the sample when the beam is irradiated under those conditions is known.

3. A method for deriving feature quantities of a sample in a computer system based on the output of a detector that detects charged particles obtained by irradiating the sample with a beam, The computer system acquires a model showing the relationship between the output information of the detector and a feature quantity corresponding to the amount of charged particles emitted from the sample. The computer system derives a feature quantity corresponding to the amount of charged particles emitted from the sample by inputting the output information of the detector into the model, Includes, The aforementioned model is a mathematical model that shows the relationship between the output information (GL) of the detector and the amount of charged particles (Ise) emitted from the sample, and is a method for deriving feature quantities.

4. In claim 3, The computer system is a feature derivation method that generates the model based on the output information (GL) of the detector obtained when the beam is irradiated onto a reference sample in which the relationship (γ) between the beam conditions (Ip) and the amount of charged particles (Ise) emitted from the sample is known.

5. In claim 4, The computer system generates the model by deriving the unknowns included in the relationship between the charged particles emitted from the sample and the detector output information, based on the detector output obtained by irradiating the reference sample with the beam, the feature derivation method.

6. A charged particle beam apparatus equipped with a detector for detecting charged particles obtained based on the irradiation of a beam onto a sample, and one or more computer systems configured to be communicatively coupled to the charged particle beam apparatus, The aforementioned computer system, A process to obtain a model that shows the relationship between the output information of the detector and a feature corresponding to the amount of charged particles emitted from the sample, The process involves inputting the output information of the detector into the aforementioned model to derive a feature quantity corresponding to the amount of charged particles emitted from the sample, Execute, The model is defined by relational information representing the relationship between the detector output information and the feature quantity, based on the detector output information acquired under at least two different beam irradiation conditions. Measurement system.

7. A charged particle beam apparatus comprising a detector for detecting charged particles obtained based on the irradiation of a beam onto a sample, and one or more computer systems configured to be communicatively coupled to the charged particle beam apparatus, The aforementioned computer system, A process to obtain a model that shows the relationship between the output information of the detector and a feature corresponding to the amount of charged particles emitted from the sample, The process involves inputting the output information of the detector into the aforementioned model to derive a feature quantity corresponding to the amount of charged particles emitted from the sample, Execute, The aforementioned model is a measurement system in which relational information is derived based on the output of a detector when a beam is irradiated onto a sample, where the relationship between the beam conditions applied to the sample and the amount of charged particles emitted from the sample when the beam is irradiated under those beam conditions is known.

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