JP5187810B2 - Film thickness measuring method and sample preparation method, film thickness measuring apparatus and sample preparation apparatus - Google Patents

Description

  The present invention includes a film thickness measuring method and a film thickness measuring apparatus for measuring a film thickness of a sample formed in a thin piece, a sample preparation method using the film thickness measuring method, and the film thickness measuring apparatus. The present invention relates to a sample preparation apparatus.

  Conventionally, a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM) has been used as a method for analyzing a specific portion such as a semiconductor device. Sample observation by TEM or STEM is performed by irradiating the sample with an electron beam in the thickness direction, detecting the electron beam transmitted through the sample, and imaging it. For this reason, in order to obtain a clear observation image by TEM or STEM sample observation, it is necessary to accurately process the sample into a thin piece having a constant film thickness, for example, about 100 nm by focused ion beam processing or the like. In order to process a sample into thin pieces with high accuracy, it is important to accurately measure whether the film is formed to a predetermined thickness and to control a focused ion beam used for processing based on the measurement result. .

As a method for measuring the film thickness of a sample formed in such a thin piece, there are a film thickness measuring region formed in a thin piece for measuring the film thickness and a reference region not formed in the thin piece outside the film thickness measuring region. The sample to be observed is based on the calculated value obtained by detecting the intensity of secondary electrons generated by irradiating the sample with an electron beam and dividing the intensity of secondary electrons in the film thickness measurement area by the intensity of secondary electrons in the reference area. A method of measuring the film thickness in the film thickness measurement region has been proposed (see, for example, Patent Document 1). More specifically, a large number of standard samples with different thicknesses are prepared in advance, and the intensity of secondary electrons in the thickness measurement region and the reference region is measured for each standard sample. Then, the calculated value is calculated. Then, from these measurement results, the relationship between the film thickness and the calculated value is examined. Then, for the sample to be observed next, the thickness of the secondary electron in the film thickness measurement region and the reference region is measured, and the calculated value is calculated. From this relationship, the film thickness in the film thickness measurement region of the sample to be observed can be evaluated.
International Publication No. 06/073063 Pamphlet

  However, in the method as disclosed in Patent Document 1, it is necessary to detect the intensity of secondary electrons in the reference region that is not formed on the flakes as well as the intensity of secondary electrons in the film thickness measurement region. In addition, in order to accurately evaluate the film thickness of the sample to be observed, the relationship between the film thickness and the calculated value obtained by dividing the secondary electron intensity in the film thickness measurement area by the secondary electron intensity in the reference area. Therefore, it is necessary to prepare a large number of data based on standard samples with different film thicknesses. For this reason, when measuring the film thickness of the sample to be observed, there has been a problem that a lot of data has to be collected.

  The present invention has been made in view of the above-described circumstances, and is based on a minimum detection result regarding a secondary signal obtained from a standard sample having a minimum number of samples and a sample to be observed, respectively. Film thickness measuring method and film thickness measuring apparatus capable of accurately and stably measuring the film thickness of the sample, sample preparation method using the film thickness measuring method, and film thickness measurement A sample preparation apparatus including the apparatus is provided.

In order to solve the above problems, the present invention proposes the following means.
The present invention is a film thickness measurement method for measuring the film thickness of a target sample formed on a thin piece having both surfaces exposed in the thickness direction, and is a thickness relative to at least one standard sample formed in a predetermined film thickness. When the electron beam is irradiated in the vertical direction while changing the acceleration voltage, the acceleration voltage of the irradiated electron beam and the intensity of the secondary signal emitted from only the predetermined film thickness portion of the standard sample with respect to the irradiated electron beam A standard data creation step for creating standard data that is a relationship with the ratio; a reference value extraction step for detecting a change point formed in the standard data and extracting an acceleration voltage at the change point as a reference value; and the target The specimen is irradiated with an electron beam in the thickness direction while changing the acceleration voltage to detect the intensity of the secondary signal emitted from the target specimen, and the acceleration voltage of the irradiated electron beam and the irradiated electron beam are detected. A measurement data creation step for creating measurement data that is a relationship with an intensity ratio of a secondary signal emitted only from the thin piece portion of the target sample, a change point formed in the measurement data is detected, and the change is detected A characteristic value extracting step of extracting an acceleration voltage at a point as a characteristic value, and an evaluation step of evaluating the film thickness of the target sample with respect to the film thickness of the standard sample based on a comparison between the reference value and the characteristic value It is characterized by comprising.

Further, the film thickness measuring apparatus of the present invention includes a sample stage for fixing a sample formed on a thin piece having both surfaces exposed in the thickness direction, and an electron beam by changing an acceleration voltage to the sample fixed to the sample stage. An electron beam column capable of irradiating the sample stage, secondary signal detection means capable of detecting a secondary signal generated from the sample by irradiating the sample fixed to the sample stage with the electron beam, and the electron beam mirror A control unit that controls a cylinder and receives a detection result from the secondary signal detection unit and analyzes a film thickness of the sample. The control unit is configured to control the electron in the thickness direction with respect to the sample. An electron beam is irradiated from a beam column while changing an acceleration voltage, and the intensity of the secondary signal emitted from the sample is detected by the secondary signal detecting means, and the electron beam irradiated from the electron beam column is detected. Accelerating voltage and irradiated electron beam On the other hand, measurement data creation means for creating measurement data that is a relationship with the intensity ratio of the secondary signal emitted from only the thin piece portion of the sample and detected by the secondary signal detection means, and formed at a predetermined film thickness When the electron beam is irradiated in the thickness direction while changing the acceleration voltage, the film thickness data representing the film thickness of the standard sample and the acceleration voltage of the irradiated electron beam were irradiated. Storage means for storing standard data which is a relationship with the intensity ratio of the secondary signal emitted from only the predetermined film thickness portion of the standard sample with respect to the electron beam, and the change points formed in the measurement data and the standard data And an acceleration voltage at the change point of the standard data relating to at least one of the standard samples. Based on a comparison between a quasi-value and a characteristic value that is an acceleration voltage at the change point of the measurement data related to the target sample, the target is the thickness of the standard sample represented by the thickness data. And an evaluation means for evaluating the film thickness of the sample.

  According to the film thickness measuring method and the film thickness measuring apparatus according to the present invention, first, as the standard data creating step, standard data is created for at least one standard sample formed in a predetermined film thickness, and stored in the control unit in advance. The means stores the film thickness data and standard data of the standard sample. Then, as the reference value extracting step, the measurement data analysis unit of the control unit detects the change point in the standard data stored in the storage unit as the reference value, and extracts the acceleration voltage at the change point. Here, the magnitude of the acceleration voltage at the changing point depends on the film thickness of the standard sample.

  Next, as a measurement data creation step, a target sample to be observed is measured. That is, the measurement data creating means of the control unit irradiates the sample fixed to the sample stage with the electron beam from the electron beam column. Then, the secondary signal detection means detects the secondary signal generated from the target sample by being irradiated with the electron beam. This process of electron beam irradiation and secondary signal detection is repeated while changing the acceleration voltage of the electron beam. Then, the measurement data creation means of the control unit creates measurement data in the target sample from the intensity and acceleration voltage of the irradiated electron beam and the intensity of the secondary signal generated correspondingly. Here, in the measurement data, the intensity of the detected secondary signal is normalized by the intensity of the irradiated electron beam, and the influence of fluctuations in the intensity of the electron beam can be subtracted.

  Next, as the characteristic value extraction step, the measurement data analysis unit of the control unit detects a change point in the created measurement data as the characteristic value, and extracts an acceleration voltage at the change point. In the same manner as described above, the magnitude of the acceleration voltage at the changing point depends on the film thickness of the target sample. For this reason, as an evaluation process, the evaluation means of the control unit compares the reference value with the characteristic value, and based on this comparison, the film thickness of the target sample is accurately calculated from the film thickness of at least one standard sample. And can be evaluated stably.

  In the film thickness measurement method, the standard data creation step and the measurement data creation step are performed in an image displayed based on the intensity of reflected electrons from the standard sample and the target sample or the intensity of the reflected electrons. It is more preferable to create the standard data and the measurement data by using the luminance of the target range as the intensity of the secondary signal.

  In the film thickness measurement apparatus, the secondary signal detection unit can detect the reflected electrons from the sample as the secondary signal, and the control unit can detect the intensity of the reflected electrons or the reflected electrons. It is more preferable to analyze the film thickness of the sample by using the luminance of the target range in the image data obtained by imaging the intensity of the image as the intensity of the secondary signal.

  According to the film thickness measuring method and the film thickness measuring apparatus according to the present invention, the brightness of the target range in the image displayed based on the intensity of the reflected electrons or the intensity of the reflected electrons is used as the intensity of the secondary signal. The change points in each of the data and measurement data are more clearly formed. For this reason, it is possible to more accurately extract the reference value and the characteristic value, which are acceleration voltages at the change point, and thereby to evaluate the film thickness of the target sample more accurately and more stably. .

  In the film thickness measuring method, the standard data creating step creates the standard data for at least two standard samples having different film thicknesses, and the reference value extracting step is performed on each standard data. The reference value is extracted, and the evaluation step calculates the relationship between the film thickness and the acceleration voltage representing the reference value from the standard data, and the relationship between the obtained film thickness and the acceleration voltage is calculated. It is more preferable to calculate the film thickness of the target sample by inputting an acceleration voltage representing a characteristic value.

  In the film thickness measuring apparatus, the storage means of the control unit stores the film thickness data and the standard data of at least two standard samples having different film thicknesses, and the control unit The evaluation means calculates the relationship between the film thickness and the acceleration voltage representing the reference value from the film thickness data and the standard data of the plurality of standard samples, and the relationship between the obtained film thickness and the acceleration voltage is calculated. It is more preferable to calculate the film thickness of the target sample by inputting an acceleration voltage representing the characteristic value.

  According to the film thickness measuring method and the film thickness measuring apparatus according to the present invention, in the standard data creating step, the memory means of the control unit stores the film thickness data and standard data of at least two standard samples having different film thicknesses. ing. For this reason, in the evaluation process, the evaluation means of the control unit can quantitatively evaluate the relationship between the film thickness and the acceleration voltage from the two different film thicknesses and the acceleration voltage representing the reference value. Therefore, the evaluation means of the control unit determines the film thickness of the corresponding target sample from the acceleration voltage representing the characteristic value extracted by the measurement data analysis means in the measurement data analysis process from the relationship between the film thickness and the acceleration voltage. It can be calculated accurately.

  The sample preparation method of the present invention determines the etching amount of the target sample based on the film thickness of the target sample measured by the film thickness measuring method, and irradiates the target sample with a charged particle beam. Etching is performed by the etching amount.

  The sample preparation apparatus of the present invention further includes a charged particle beam column that can irradiate the sample fixed to the sample stage with a charged particle beam, and the control unit is an object evaluated by the evaluation unit. The etching amount of the sample is determined based on the film thickness of the sample, and the charged particle beam is irradiated onto the sample by the charged particle beam column according to the etching amount.

  According to the sample preparation method and the sample preparation apparatus according to the present invention, since the film thickness of the target sample can be accurately evaluated by the film thickness measurement method and the film thickness measurement apparatus, it is based on the film thickness of the target sample. Therefore, it is possible to accurately determine the etching amount required for the target sample. Therefore, the target sample is irradiated with the charged particle beam from the charged particle beam column and the target sample is accurately processed to a desired film thickness. can do.

According to the film thickness measuring method and film thickness measuring apparatus of the present invention, the film thickness of the target sample is determined from the relationship between the acceleration voltage of the irradiating electron beam and the intensity ratio of the secondary signal emitted to the irradiating electron beam. By evaluating, the film thickness of the target sample can be measured accurately and stably from the minimum detection results for the secondary signal obtained from the standard sample and the target sample with the minimum number of samples. It is.
Moreover, according to the sample preparation method and the sample preparation apparatus of the present invention, the target sample can be accurately processed into a desired film thickness by including the sample preparation method and the sample preparation apparatus.

  1 to 5 show an embodiment according to the present invention. As shown in FIG. 1, a sample preparation apparatus 1 includes a sample stage 2 for fixing a sample P, a focused ion beam column 3 that is a charged particle beam column capable of irradiating a focused ion beam A as a charged particle beam, An electron beam column 4 capable of irradiating the specimen P with the electron beam B in the thickness direction X, and a reflected electron detector (BSE detector) which is a secondary signal detecting means capable of detecting the reflected electrons C as a secondary signal. ) 5, an operation unit 6 capable of various manual inputs, a monitor 7 for displaying an image, a control unit 10, and a film thickness measuring device 20. The focused ion beam column 3 sets the acceleration voltage and the beam intensity to desired values under the operation of the operation unit 6 and the control of the control unit 10, and the desired position of the sample P by the scanning means (not shown). Further, the focused ion beam A can be irradiated. The electron beam column 4 sets the acceleration voltage and the beam intensity to desired values under the operation of the operation unit 6 and the control of the control unit 10, and the electron beam barrel 4 is set to a desired position by scanning means (not shown). The beam B can be irradiated. Further, the intensity of the reflected electrons C detected by the reflected electron detector 5 is input to the control unit 10. The reflected electron detector 5 is a detector that can detect electrons having energy larger than that of secondary electrons, such as a scintillator or a semiconductor detector.

  Further, the control unit 10 can analyze the film thickness of the sample P based on the detection result by the backscattered electron detector 5, and includes an image analysis unit 11, a measurement data creation unit 12, a storage unit 13, and a measurement data analysis. Means 14 and evaluation means 15 are provided. The image analysis means 11 can create image data obtained by imaging the intensity distribution of the reflected electrons C detected by the reflected electron detector 5 as a luminance distribution, and can be displayed as an image on the monitor 7. . Further, the image analysis unit 11 obtains an average luminance value Ip (hereinafter, referred to as luminance of the target range) for a predetermined range of the image, and can input this to the measurement data generation unit 12 as the intensity of the secondary signal. is there. The measurement data creating means 12 calculates an intensity ratio Ri that represents the intensity Ib of the irradiated electron beam B as a ratio of the luminance Ip of the target range when the electron beam B is irradiated with the intensity Ib. It is possible to create measurement data M that is a relationship between the acceleration voltage Eb of the emitted electron beam B and the corresponding intensity ratio Ri. The storage means 13 can store the film thickness data L representing the film thickness of a standard sample with a known film thickness and the standard data N that is the measurement data M for the standard sample in association with each other. It is. In the present embodiment, the film thickness data L is input by the operation unit 6, and the standard data N is created by the measurement data creating means 12 to create measurement data M related to the standard sample as will be described later. Are stored in the storage means 13. Further, the measurement data analyzing means 14 can analyze the measurement data M, detect a change point formed in the measurement data M, and extract a characteristic value Em that is an acceleration voltage corresponding to the change point. . Similarly, the measurement data analyzing means 14 can analyze the standard data N, detect a change point formed in the standard data N, and extract a reference value En that is a corresponding acceleration voltage at the change point. It is. Further, the evaluation means 15 compares the reference value En of the standard data N with the characteristic value Em of the measurement data M, and based on this comparison, the standard sample represented by the film thickness data L stored in the storage means 13 is compared. It is possible to evaluate the film thickness of the target sample P with respect to the film thickness. And the film thickness measuring apparatus 20 which measures the film thickness of the sample P fixed to the sample stand 2 by the control part 10 comprised by these, the sample stand 2, the electron beam column 4, and the backscattered electron detector 5. Is configured. The details of the film thickness measuring method by each configuration of the control unit 10, the operation as the film thickness measuring device 20, the sample manufacturing method using the film thickness measuring method, and the operation of the sample manufacturing device 1 are described below. Will be described based on the flowchart shown in FIG. 2 and the explanatory diagrams shown in FIGS.

  As shown in FIG. 2, first, as standard data creation step S1, standard data N of a standard sample made of the same material as the observation target sample P3 and having a known thickness is created. In this embodiment, a standard sample P1 having a film thickness Q1, a standard sample P2 having a film thickness Q2 larger than the film thickness Q1 of the standard sample P1, and two standard samples having different film thicknesses are used. First, the standard sample P1 is fixed to the sample stage 2. Then, the film thickness Q1 corresponding to the standard sample P1 is input by the operation unit 6. The input film thickness Q1 is stored by the storage means 13 of the control unit 10 as the film thickness data L1. Next, the measurement data creation means 12 of the control unit 10 scans the electron beam B within the predetermined range of the standard sample P1 with the predetermined acceleration voltage Eb and the intensity Ib by the electron beam column 4. The backscattered electron detector 5 detects backscattered electrons C from the standard sample P1 as the electron beam B is irradiated. The detected intensity of the reflected electrons C is converted into luminance by the image analysis unit 11 of the control unit 10, and image data is created in association with position information for scanning the electron beam B. FIG. 4 is an example of an image of the sample P displayed on the monitor 7 based on this image data. The intensity of the reflected electrons decreases according to the thickness in the range where the thickness of the sample is thinner than the penetration length of the incident electrons. For this reason, when the portion Pb sufficiently thicker than the penetration length of the incident electrons and the portion Pa formed on the thin film of the penetration depth or less are compared on the reflected electron image, the portion Pa is expressed darker than the portion Pb. Further, the image analysis means 11 of the control unit 10 includes the brightness of the target range, which is an average value of the brightness in a preset range (for example, the range F shown in FIG. 4) of the film thickness measurement. Ip is calculated. The calculated luminance Ip of the target range is input to the measurement data creating means 12, and the intensity ratio Ri (= Ip / Ib) is calculated from the intensity Ib of the corresponding electron beam B. This is repeated while changing the acceleration voltage Eb of the electron beam B to irradiate, and the measurement data M, which is the relationship between the acceleration voltage Eb of the electron beam B and the corresponding intensity ratio Ri, is created. The standard data N1 is stored in the storage means 13 in association with the film thickness data L1. Then, the same process as described above is performed for the standard sample P2, the film thickness Q2 is input by the operation unit 6, the corresponding film thickness data L2 is stored in the storage means 13, and the standard data P2 is measured by the measurement data creation means 12. Corresponding standard data N2 is created and stored in the storage means 13 in association with the film thickness data L2.

  In FIG. 4, the alternate long and short dash line indicates standard data N1, and the alternate long and two short dashes line indicates standard data N2. Here, as shown in FIG. 4, there are a region where the intensity ratio Ri hardly changes with an increase in the acceleration voltage Eb, and a region where the intensity ratio Ri gradually decreases with an increase in the acceleration voltage Eb. Change points N1a and N2a are formed. In the actual measurement data, the change points N1a and N2a are not recognized as slopes on a clear graph. For example, a straight line is formed in a region where the intensity ratio Ri hardly changes and a region where the intensity ratio Ri gradually decreases. The change points N1a and N2a can be recognized by a method of fitting and obtaining the intersection. Since the change points N1a and N2a at which the intensity ratio Ri starts to change in this way are considered to be cases where the penetration depth becomes substantially equal to the sample thickness as the electron beam energy increases, the acceleration voltage at this change point Eb can be used as a value corresponding to the sample thickness.

  When the standard data N1 and N2 are created as described above, the measurement data analyzing means 14 of the control unit 10 then changes the standard data N1 and N2 from the change points formed in the standard data extraction step S2. N1a and N2a are detected (step S2a), and acceleration voltages at the respective change points N1a and N2a are extracted as reference values En1 and En2 (step S2b). Then, these reference values En1 and En2 are stored in the storage means 13 in association with the corresponding film thickness data L1 and L2. Here, in order to transmit the electron beam B through the sample P, it is necessary to increase the energy, that is, to increase the acceleration voltage Eb as the film thickness of the sample P increases. That is, in the standard data N1 and N2, the reference values En1 and En2 that are acceleration voltages at the change points N1a and N2a depend on the film thicknesses Q1 and Q2 of the corresponding standard samples P1 and P2. For this reason, the acceleration voltage En2 of the change point N2a of the standard sample P2 having the film thickness Q2 is larger than the acceleration voltage En1 of the standard sample P1 having the film thickness Q1 smaller than the film thickness Q2. In the standard data creation step S1 and the reference value extraction step S2, the storage unit 13 of the control unit 13 previously stores film thickness data L1, L2, standard data N1, N2, and reference values En1, En2. You don't have to do it when you are.

  Next, as measurement data creation step S3, measurement data M3 of the target sample P3 to be observed is created. First, the target sample P3 is fixed to the sample stage 2. Next, the measurement data creating means 12 of the control unit 10 causes the electron beam barrel 4 to irradiate the target sample P3 with the electron beam B at a predetermined acceleration voltage Eb and intensity Ib. Then, scanning is performed within a predetermined range of the target sample P3 while keeping the acceleration voltage Eb and the intensity Ib constant. The backscattered electron detector 5 detects backscattered electrons C from the target sample P3 as the electron beam B is irradiated. Then, the detected intensity of the reflected electrons C is converted into luminance by the image analysis unit 11 of the control unit 10, and image data is created in association with position information for scanning the electron beam B. Further, the image analysis means 11 of the control unit 10 calculates the luminance Ip in the range F that is a target of film thickness measurement set in advance among the image data. The calculated luminance Ip of the target range is input to the measurement data creating means 12, and the intensity ratio Ri (= Ip / Ib) is calculated from the intensity Ib of the corresponding electron beam B. This is repeatedly performed while changing the acceleration voltage Eb of the electron beam B to irradiate, and for the target sample P3, as shown in FIG. 4, the measurement is a relationship between the acceleration voltage Eb of the electron beam B and the corresponding intensity ratio Ri. Data M3 is created. Next, as the characteristic value extraction step S4, the measurement data analysis unit 14 of the control unit 10 detects the change point M3a from the measurement data M3 of the target sample P3 (step S4a), and determines the acceleration voltage at the change point M3a as the characteristic value. Extracted as Em3 (step S4b).

  Then, as the evaluation step S5, the evaluation unit 15 of the control unit 10 compares the reference values En1 and En2 extracted in the reference value extraction step S2 with the characteristic value Em3 extracted in the characteristic value extraction step S4. Based on this comparison, the film thickness Q3 of the target sample P3 is calculated from the film thicknesses Q1 and Q2 of the standard samples P1 and P2, respectively. That is, the evaluation means 15 of the control unit 10 represents the relationship between the film thickness Q and the acceleration voltage Eb of the electron beam B from the film thicknesses Q1 and Q2 and the corresponding reference values En1 and En3 regarding the two standard samples P1 and P2. Find a linear approximation. And the evaluation means 15 of the control part 10 can obtain | require the film thickness Q3 of the target sample P3 corresponding to the characteristic value Em3 by inputting the characteristic value Em3 as the acceleration voltage Eb in the obtained linear approximation formula.

  Here, in the standard data N1 and N2 of the standard samples P1 and P2 and the measurement data M3 of the target sample P3, the intensity ratio Ri obtained by normalizing the luminance Ip of the target range with the intensity Ib of the electron beam B is used. Thus, the influence of the fluctuation of the intensity Ib when the acceleration voltage Eb is changed is prevented.

  Next, as the sample processing step S6, the target sample P3 is etched and processed to have a desired film thickness. That is, the control unit 10 calculates the etching amount by comparing the film thickness Q3 of the target sample P3 calculated in the evaluation step S5 with the target film thickness after processing (step S6a). Then, the control unit 10 etches the target sample P3 by irradiating the target sample P3 with the focused ion beam A based on the calculated etching amount (step S6b). Thereby, the target sample P3 can be accurately processed into a desired film thickness. Note that the measurement data creation step S3 may be repeated again to confirm whether the target sample P3 has a desired film thickness. If it is determined that further processing is necessary, the sample processing step S6 may be repeatedly performed.

  As described above, in the sample preparation device 1, the film thickness measurement device 20 has a relationship between the acceleration voltage Eb of the irradiated electron beam B and the intensity ratio Ri of the luminance Ip of the target range to be detected with respect to the irradiated electron beam B. By calculating the film thickness Q3 of the target sample P3 from the standard sample, the film thickness of the target sample is accurately and stably determined from the standard sample with the minimum number of samples and the minimum detection result obtained from each target sample. It is possible to measure. Moreover, in the sample preparation apparatus 1, by providing such a film thickness measuring apparatus 20, the target sample P3 can be accurately processed into a desired film thickness.

  In the present embodiment, the film thickness of the target sample is measured based on the standard samples P1 and P2 and the two standard samples. However, the present invention is not limited to this. Even if only one standard sample is used, whether the target sample film thickness is larger than the standard sample film thickness is accurate by comparing whether the target sample characteristic value is higher than the standard sample reference value. Can be evaluated. In addition, if there are three or more standard samples, when calculating the relationship between the film thickness and the acceleration voltage using a linear approximation equation, the calculation is made with higher accuracy, and the film thickness of the target sample can be calculated more accurately based on this relationship equation. Can be calculated. Furthermore, the relational expression between the film thickness Q and the acceleration voltage Eb of the electron beam B is not limited to the linear approximation expression, but may be obtained by a curve approximation expression. In the present embodiment, as the standard data creation step, standard data is created by irradiating a standard sample with a known film thickness with an electron beam. However, the present invention is not limited to this, and a known simulation method such as a Monte Carlo method is used. The standard data for the target film thickness and the corresponding reference value may be calculated. Alternatively, the measurement data creation process and the characteristic value extraction process are performed in advance, and the standard value creation process and the reference value extraction process are performed by calculating back the standard value and standard film thickness that match the characteristic value extracted for the target sample. It is good to do.

  Further, in the present embodiment, the film thickness measurement as described above is automatically performed based on control and analysis by each configuration of the control unit 10, but the present invention is not limited to this. The operator may manually measure the film thickness of the target sample along the above-described process by an input from the operation unit 6. In the present embodiment, the intensity of the reflected signal detected when the electron beam B is emitted and detected from the sample is detected as the intensity Ip of the target range when the intensity of the detected reflected electrons is imaged. However, the present invention is not limited to this, and the standard data and measurement data may be configured based on the intensity of the reflected electrons detected. Furthermore, secondary signals emitted from the sample upon irradiation with the electron beam B are not limited to reflected electrons, but include secondary electrons, absorption currents, secondary X-rays, etc. Standard data and measurement data may be configured. For example, in the case of secondary electrons, when the accelerating voltage of the irradiated electron beam is low, secondary electrons are generated only from the irradiated surface, so that the intensity of the secondary electrons shows a substantially constant value. On the other hand, when the acceleration voltage of the electron beam increases, secondary electrons are generated from the surface opposite to the irradiation surface, and the intensity of the detected secondary electrons increases rapidly. For this reason, similarly, a change point can be formed with the acceleration voltage corresponding to a film thickness, and the film thickness of a target sample can be measured based on this. As described above, the intensity of the reflected electrons or the brightness of the target range in the image displayed based on the intensity of the reflected electrons is set as the intensity of the secondary signal that is a parameter of the standard data and the measurement data. And the change point in the measurement data is more clearly formed and suitable.

  As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the concrete structure is not restricted to this embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included.

It is a block diagram of the film thickness measuring apparatus and sample preparation apparatus of embodiment of this invention. It is a flowchart of the film thickness measuring method and sample preparation method of embodiment of this invention. It is explanatory drawing of the image obtained by detecting the reflective electron discharge | released from a sample in the film thickness measuring apparatus of embodiment of this invention. It is explanatory drawing of the created standard data and measurement data in the film thickness measuring apparatus of embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sample preparation apparatus 2 Sample stand 3 Focused ion beam column (charged particle beam column)
4 Electron beam column 5 Backscattered electron detector (secondary signal detection means)
DESCRIPTION OF SYMBOLS 10 Control part 12 Measurement data preparation means 13 Storage means 14 Measurement data analysis means 15 Evaluation means 20 Film thickness measurement apparatus A Focused ion beam (charged particle beam)
B Electron beam C Reflected electron (secondary signal)
Eb Acceleration voltage Em3 Characteristic value En1, En2 Reference value Ib Intensity of electron beam Ip Image brightness M, M3 Measurement data M3a Change point N, N1, N2 Standard data N1a, N2a Change point P Sample P1, P2 Standard sample P3 Target sample Ri intensity ratio S1 Standard data creation process S2 Reference value extraction process S3 Measurement data creation process S4 Characteristic value extraction process S5 Evaluation process X Thickness direction

Claims (8)

A film thickness measuring method for measuring a film thickness of a target sample formed on a thin piece in which both sides in the thickness direction are exposed ,
When at least one standard sample formed in a predetermined film thickness is irradiated with an electron beam in the thickness direction while changing the acceleration voltage, the acceleration voltage of the irradiated electron beam and the standard for the irradiated electron beam A standard data creation step of creating standard data that is a relationship with the intensity ratio of the secondary signal emitted from only the predetermined film thickness portion of the sample;
A reference value extracting step of detecting a change point formed in the standard data and extracting an acceleration voltage at the change point as a reference value;
The target sample is irradiated with an electron beam in the thickness direction while changing the acceleration voltage to detect the intensity of the secondary signal emitted from the target sample. The acceleration voltage of the irradiated electron beam and the irradiated electrons are detected. A measurement data creation step of creating measurement data that is a relationship with an intensity ratio of a secondary signal emitted from only the flake portion of the target sample with respect to a beam;
A characteristic value extracting step of detecting a change point formed in the measurement data and extracting an acceleration voltage at the change point as a characteristic value;
A film thickness measuring method comprising: an evaluation step of evaluating a film thickness of the target sample with respect to a film thickness of the standard sample based on a comparison between the reference value and the characteristic value. In the film thickness measuring method according to claim 1,
In the standard data creation step and the measurement data creation step, the intensity of the reflected electrons from the standard sample and the target sample or the luminance of the target range in the image displayed based on the intensity of the reflected electrons is calculated based on the secondary signal. A method for measuring a film thickness, wherein the standard data and the measurement data are created as intensity. In the film thickness measuring method according to claim 1 or 2,
The standard data creation step creates the standard data for at least two standard samples having different film thicknesses,
The reference value extraction step extracts the reference value for each of the standard data,
In the evaluation step, the relationship between the film thickness and the acceleration voltage representing the reference value is calculated from the standard data, and the acceleration voltage representing the characteristic value is input into the obtained relationship between the film thickness and the acceleration voltage. Thus, the film thickness measuring method is characterized in that the film thickness of the target sample is calculated.   An etching amount of the target sample is determined based on the film thickness of the target sample measured by the film thickness measuring method according to any one of claims 1 to 3, and the target sample is irradiated with a charged particle beam. Is etched by the etching amount. A sample stage for fixing a sample formed on a thin piece having both surfaces exposed in the thickness direction ;
An electron beam column capable of irradiating an electron beam by changing an acceleration voltage to the sample fixed to the sample stage;
Secondary signal detection means capable of detecting a secondary signal generated from the sample by irradiating the sample fixed to the sample stage with an electron beam;
A control unit that controls the electron beam column, receives a detection result of the secondary signal detection unit, and analyzes a film thickness of the sample;
The control unit irradiates the sample with the electron beam from the electron beam column in the thickness direction while changing the acceleration voltage, and outputs the intensity of the secondary signal emitted from the sample as the secondary signal detecting means. And the secondary voltage detected by the secondary signal detection means emitted from only the thin piece portion of the sample with respect to the irradiated electron beam and the acceleration voltage of the electron beam irradiated from the electron beam column Measurement data creation means for creating measurement data that is a relationship with the signal intensity ratio;
When a standard sample formed with a predetermined film thickness is irradiated with an electron beam while changing the acceleration voltage in the thickness direction, the film thickness data indicating the film thickness of the standard sample and the irradiation electron beam Storage means for storing standard data that is a relationship between an acceleration voltage and an intensity ratio of a secondary signal emitted from only the predetermined film thickness portion of the standard sample with respect to an irradiated electron beam;
A measurement data analyzing means capable of detecting a change point formed in the measurement data and the standard data and extracting an acceleration voltage at the change point;
Based on a comparison between a reference value that is an acceleration voltage at the change point of the standard data for the at least one standard sample and a characteristic value that is an acceleration voltage at the change point of the measurement data for the sample of interest, A film thickness measuring apparatus comprising: an evaluation unit that evaluates the film thickness of the target sample with respect to the film thickness of the standard sample represented by the film thickness data. In the film thickness measuring device according to claim 5,
The secondary signal detection means is capable of detecting reflected electrons from the sample as the secondary signal,
The control unit analyzes the film thickness of the sample using the intensity of the reflected electrons or the brightness of the target range in the image data obtained by imaging the intensity of the reflected electrons as the intensity of the secondary signal. Thickness measuring device. In the film thickness measuring device according to claim 5 or 6,
The storage means of the control unit stores the film thickness data and the standard data of at least two standard samples having different film thicknesses,
The evaluation unit of the control unit calculates a relationship between the film thickness and the acceleration voltage representing the reference value from the film thickness data and the standard data of the plurality of standard samples, and the obtained film thickness and acceleration A film thickness measuring apparatus for calculating a film thickness of the target sample by inputting an acceleration voltage representing the characteristic value in relation to a voltage. In the sample preparation apparatus provided with the film thickness measuring apparatus according to any one of claims 5 to 7,
A charged particle beam column capable of irradiating a charged particle beam to the sample fixed to the sample stage;
The control unit determines an etching amount of the sample based on the film thickness of the sample to be evaluated by the evaluation unit, and charges the sample by the charged particle beam column according to the etching amount. A sample preparation apparatus characterized by irradiating a particle beam.

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